ENGINEERING

HONING

2011-03-14T10:21:00.000-07:00

These are some operations by which a product receives the final machining stage or finishing operation before final dispatch. These processes or methods remove a very small amount of metal, and hence the surface finish obtained is specified in the ranges of micro finishes. Honing is one of these operations.

HONING

The process of finishing ground surfaces to a high degree of accuracy and smoothness with abrasive blocks applied to the surface under a light controlled pressure and with a combination of rotary and reciprocating motions.

Honing is a controlled, low-speed sizing and surface finishing process in which stock is abraded by the shearing action of a bonded abrasive honing stick. In honing, simultaneous rotating and reciprocating action of the stick results in a characteristic cross-hatch lay pattern. Because honing is a low-speed operation, metal is removed without the increased temperature that accompanies grinding and thus any surface damage caused by heat is avoided. Honing uses a special tool, called a honing stone or a hone, to achieve a precision surface. The hone is a composed of abrasive grains that are bound together with an adhesive

In addition to removing stock, honing involves the correction of errors from previous machining operations. These errors include

Geometrical errors such as out-of-roundness, waviness, bell mouth, barrel, taper, rainbow, and reamer chatter
Dimensional inaccuracies
Surface character (roughness, lay pattern, and integrity)

Honing corrects all of these errors with the least possible amount of material removal; however, it cannot correct hole location or perpendicularity errors. The most frequent application of honing is the finishing of internal cylindrical holes. However, numerous outside surfaces also can be honed. Gear teeth, valve components, and races for antifriction bearings are typical applications of external honing.

Process

The tool reciprocates through the bore, the pressure and the resulting penetration of grit is greatest at high spots and consequently the waviness crests are abraded, making the bore straight and round. After leveling high spots, each section of the bore receives equal abrading action. The hole axis is usually in the vertical position to eliminate gravity effects on the honing process; however, for long parts the axis may be horizontal

Advantages of Honing

It is characterized by rapid and economical stock removal with a minimum of heat and distortion.
It generates round and straight holes by correcting form errors caused by previous operations.
It achieves high surface quality and accuracy.

Honing Machines

For the production of few parts, honing may be performed on drill presses or engine lathes on which arrangements can be made for simultaneous rotating and reciprocating motions. The stroking can be done manually or powered depending on the equipment capabilities. On the other hand, the production honing is done with machines built for the purpose. These vertical machines are available in a wide range of sizes and designs. Some horizontal machines operate by manual stroking. In power stroking, the WP is usually held stationary in a rigid fixture, while the hone is rotated and hydraulically powered for stroking, which is considered beneficial for heavier WPs.

Machining Parameters

Parameters affecting the performance of honing process are:

Rotation speed the choice of the optimum surface speeds is influenced by:
Material being honed—higher speed can be used for metals that shear easily.
Material hardness—harder material requires lower speed.
Surface roughness—rougher surfaces that mechanically dress the abrasive stick permit higher speed.
Number and width of sticks in the hone—speed should be decreased as the area of abrasive per unit area to hone increases.
Finish requirement—higher speed usually results in finer surface finish

Tool Specifications
In addition to the variables involved in the honing process, the most important influence on the work result are the specifications of the honing stones, i.e. grain type, grain size, type of bond, hardness and treatment.

The Turbine Flow Meter and its Calibration

2011-03-14T07:22:00.000-07:00

The Turbine Flow Meter and its Calibration

Turbine Meters

A turbine meter consists of a practically friction-free rotor pivoted along the axis of the meter tube and designed in such a way that the rate of rotation of the rotor is proportional to the rate of flow of fluid through the meter. This rotational speed is sensed by means of an electric pick-off coil fitted to the outside of the meter housing.

The only moving component in the meter is the rotor, and the only component subject to wear is the rotor bearing assembly. However, with careful choice of materials (e.g., tungsten carbide for bearings) the meter should be capable of operating for up to five years without failure.

There are several characteristics of turbine flow meters that make them an excellent choice for some applications. The flow sensing element is very compact and light weight compared to various other technologies. This can be advantageous in applications where space is a premium

Primary Vs. Secondary Standards

A primary standard calibration is one that is based on measurements of natural physical parameters (i.e., mass, distance, and time). This calibration procedure assures the best possible precision error, and through traceability, minimizes bias or systematic error.

A secondary standard calibration is not based on natural, physical measurements. It often involves calibrating the user's flow meter against another flow meter, known as a "master meter," that has been calibrated itself on a primary standard.

Calibration

"To calibrate" means "to standardize (as a measuring instrument) by determining the deviation from a standard so as to determine the proper correction factors." There are two key elements to this definition: determining the deviation from a standard, and ascertaining the proper correction factors.

Flow meters need periodic calibration. This can be done by using another calibrated meter as a reference or by using a known flow rate. Accuracy can vary over the range of the instrument and with temperature and specific weight changes in the fluid, which may all have to be taken into account. Thus, the meter should be calibrated over temperature as well as range, so that the appropriate corrections can be made to the readings. A turbine meter should be calibrated at the samekinematic viscosity at which it will be operated in service. This is true for fluid states, liquid and gas.

Master Meter

A master meter is a flowmeter that has been calibrated to a very high degree of accuracy. Types of flowmeters used as master meters include turbine meters, positive displacement meters, venturi meters, and Coriolis meters. The meter to be calibrated and the master meter are connected in series and are therefore subject to the same flow regime. To ensure consistent accurate calibration, the master meter itself must be subject to periodic recalibration

Gravimetric Method

This is the weight method, where the flow of liquid through the meter being calibrated is diverted into a vessel that can be weighed either continuously or after a predetermined time. The weight is usually measured with the help of load cells. The weight of the liquid is then compared with the registered reading of the flow meter being calibrated

Volumetric Method

In this technique, flow of liquid through the meter being calibrated is diverted into a tank of known volume. The time to displace the known volume is recorded to get the volumetric flow rate eg gallons per minute. This flow rate can then be compared to the turbine flow meter readings

K-Factor.

“K” is a letter used to denote the pulses per gallon factor of a flowmeter.

Repeatability.

The maximum deviation from the corresponding data points taken from repeated tests under identical conditions.

Positive Displacement Calibrators:

Some of the most dramatic improvements in flow calibrator technology involve the evolution of Positive Displacement calibrators. PD systems are Primary Standard calibrators, which take into account the varying conditions under which flowmeters operate. These calibrators are able to compensate for temperature, density, viscosity and other variables that can shift a meter’s output.it utilizes a precision machined measurement chamber, or flow tube, that houses a piston. This piston acts as a moving barrier between the calibration fluid and the pressurizing media used to move the piston. Attached to the piston is a shaft that keeps the piston moving in a true path and provides the link between the piston and the translator. The translator converts the linear movement of the piston through the precision flow chamber into electrical pulses that are directly related to the displaced volume. Calibrators of this style can be directly traceable to the National Institute of Standards and Technology via water draw validation. Total accuracy of this type of calibrator is conservatively specified at 0.05%

Flow Transfer Standards:

Unlike primary flow standards, whose most important characteristics are their traceability to primary physical measurements (resulting in the minimization of absolute uncertainties, with less concern for usability or cost issues), the key criteria for secondary Flow Transfer Standards are portability, low cost and the ability to calibrate the flowmeter in the physical piping configuration it lives in.

Instead of removing flowmeters from service for recalibration, FTS devices allow users to “bring the calibrator to the flowmeter.” These portable, documenting field flow calibrators are intended for in-line calibration and validation of meters using the actual process conditions for gas or liquid. Advanced FTS systems incorporate hand-held electronics with built-in signal conditioners, thus eliminating bulky interface boxes and the need to carry a laptop computer into the field. High-quality Flow Transfer Standards also have the capability of measuring and correcting the influences of line pressure and temperature effects on flow.

Operation of a portable Flow Transfer Standard requires that a master meter be installed in series with the flowmeter under test. The readings from these instruments are compared at various flow rates or flow totals. A technician can install the master meter in the same system as the test meter, perform the calibration, and note any changes in performance. New calibration data might cause rescaling or new data points to be programmed into a flowmeter’s computer to align the measurement with the current flow calibration data.

Typical Calibration Techniques

Most flowmeter calibration service suppliers provide a choice of calibration techniques to accommodate different applications and flow measurement requirements. One of the most common techniques is the single-viscosity calibration, which consists of running 10 evenly spaced calibration points at a specified liquid viscosity. Single-viscosity calibrations are recommended when the viscosity of the liquid being measured is constant. If a higher degree of accuracy is needed, again, the more data points taken the better defined the meter calibration curve will be

Strouhal Number/Roshko Number

The best, and only completely correct way to present the data for a Turbine Meter is Strouhal Number as a function of Roshko Number, i.e., through the use of two dimensionless parameters. The St vs. Ro presentation takes into account all of the secondary effects to which the meter is sensitive. This presentation or correlation is correct for both liquids and gases. It is almost a must for gas calibrations since the density and kinematic viscosity are a function of both temperature and pressure

Your Calibrated Flowmeter

Once your flowmeter is calibrated, it may still read exactly the same under the same flow conditions as it did before it was calibrated. The difference is that you will know exactly how close those values are to the true values, and you will have a formula to use to calculate the true values from the actual values read by your flowmeter. You can have a correction factor obtained from calibratiob which you can apply to the flow meter readings to obtain the correct or true flowmeter readings. K-factor ignores the effects of changing temperature on the meter body since the meter will change diameter when the temperature changes. The use of Strouhal Number instead of simple K-Factor will account for this temperature effect.

INDUSTRIAL LIGHTNING SYSTEM

2011-03-08T21:18:00.001-08:00

INDUSTRIAL LIGHTNING SYSTEM

Lighting is an essential service in all the industries. The power consumption by the industrial lighting varies between 2 to 10% of the total power depending on the type of industry. Innovation and continuous improvement in the field of lighting, has given rise to tremendous energy saving opportunities in this area. Lighting is provided in industries, commercial buildings, indoor and outdoor for providing comfortable working environment. The primary objective is to provide the required lighting effect for the lowest installed load i.e highest lighting at lowest power consumption.

Lighting Principles and Terminology

Illumination
The distribution of light on a horizontal surface. The purpose of all lighting is to produce illumination.

Circuit Watts
It is the total power drawn by lamps and ballasts in a lighting circuit under assessment.

Lumen
A measurement of light emitted by a lamp. As reference, a 100-watt incandescent lamp emits about 1750 lumens.

Footcandle
A measurement of the intensity of illumination. A footcandle is the illumination produced by one lumen distributed over a 1-square-foot area. For most home and office work, 30–50 footcandles of illumination is sufficient. For detailed work, 200 footcandles of illumination or more allows more accuracy and less eyestrain. For simply finding one's way around at night, 5–20 footcandles may be sufficient.

Efficacy
The ratio of light produced to energy consumed. It's measured as the number of lumens produced divided by the rate of electricity consumption (lumens per watt).

Color temperature
It is color of the light source. By convention, yellow-red colors (like the flames of a fire) are considered warm, and blue-green colors (like light from an overcast sky) are considered cool. Color temperature is measured in Kelvin (K) temperature.

Glare
The excessive brightness from a direct light source that makes it difficult to see what one wishes to see. A bright object in front of a dark background usually will cause glare. Bright lights reflecting off a television or computer screen or even a printed page produces glare. Intense light sources—such as bright incandescent lamps—are likely to produce more direct glare than large fluorescent lamps. However, glare is primarily the result of relative placement of light sources and the objects being viewed.

Dimming:-
A procedure of varying the luminous flux from lamps in a lighting installation, by way of an electrical or electronic component.

Discharge Lamp
Lamp in which the light is produced, directly or indirectly, by an electric discharge through a gas, a metal vapour, or a mixture of several gases and vapours.

Light:-
Electromagnetic radiation with a wavelength of between 380-720nm. Ultraviolet light has a wavelength of less than 380nm whilst infrared light is greater at 720nm. i.e the cooler and warmer end of the lighting spectrum.

Lux:-
The unit of illuminance, equal to one lumen per square metre (lm/m2)

High-pressure mercury (vapour) lamp:-
Mercury vapour lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapor is of the order of 105 Pa - for example: HPL and HPL-N lamps.

High-pressure sodium (vapour) lamp:-
Sodium vapour lamp in which the partial pressure of the vapour during operation is of the order of 104 Pa - for example, SON and SON-T lamps.

Incandescent lamp:-
Lamp in which an electric current is passed through a filament thus creating heat. The light is the glow produced.

Low-pressure mercury (vapor) lamp:-
Mercury vapor lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapor does not exceed 100 Pa - for example a 'TL' lamp.

Low-pressure sodium (vapor) lamp:-
Sodium vapor lamp in which the partial pressure of the vapor during operation does not exceed 5 Pa - for example a SOX lamp.

Metal halide lamp:-
Discharge lamp in which the major portion of the light is produced by the radiation from a mixture of a metallic vapour (for example, mercury) and the products of the dissociation of halides (for example, halides of thallium, indium or sodium) - for example: HCI-T/HQI-TS lamps.

Power Factor Correction (pfc):-
Electricity supply require that the companies require that the power factor at which the supply is used shall be maintained at not less than 0.9 lagging, on average between one meter reading and the next. Low power factors increase the KVa demand from the supply, reduces the useful load that can be safely handled by the cables and distribution equipment, and in some cases can attract additional tariff penalties. Lamp circuits which incorporate a choke, leakage reactance transformer, or an electronic ballast can have low power factors, often between 0.3 and 0.6. Low power factor from these circuits can be corrected by the addition of a compensation capacitor. These can be placed at the central point of the supply, locally for each group of luminaries , or integral within each luminaire.

Starter:-
Device for starting a discharge lamp (in particular a fluorescent lamp) that provides for the necessary preheating of the electrodes and/or causes a voltage surge in combination with the series ballast.

Types of Lighting
You'll find that you have several options to consider when selecting what type of lighting you should use
Types of lighting include:
1) Fluorescent lighting
2) High-intensity discharge lighting
3) Incandescent lighting
4) Low-pressure sodium lighting
5) Outdoor solar lighting

Lamp is equipment, which produces light. The most commonly used lamps are described briefly as follows:

INCANDESCENT LIGHT BULBS
Incandescent light bulbs consist of a glass enclosure (the envelope, or bulb) which is filled with an inert gas to reduce evaporation of the filament. Inside the bulb is a filament of tungsten wire, through which an electric current is passed. The current heats the filament to an extremely high temperature (typically 2000 K to 3300 K depending on the filament type, shape, size, and amount of current passed through). The heated filament emits light that approximates a continuous spectrum. The useful part of the emitted energy is visible light, but most energy is given off in the near-infrared wavelengths.

(Incandescence : The state of glowing from intense heat, as when a metal becomes white hot from an electric current flowing through it.)

Reflector lamps:
Reflector lamps are basically incandescent, provided with a high quality internal mirror, which follows exactly the parabolic shape of the lamp. The reflector is resistant to corrosion, thus making the lamp maintenance free and output efficient.

Gas discharge lamps:
The light from a gas discharge lamp is produced by the excitation of gas contained in either a tubular or elliptical outer bulb.
The most commonly used discharge lamps are as follows:
• Fluorescent tube lamps (FTL)
• Compact Fluorescent Lamps (CFL)
• Mercury Vapour Lamps
• Sodium Vapour Lamps
• Metal Halide Lamps

HALOGEN BULBS
Halogen light bulbs produce light in a similar method to a regular incandescent bulb. A halogen bulb has a filament made of Tungsten, which glows when electricity is applied, same as a regular incandescent bulb. What makes a halogen bulb different is that it is filled with halogen gas instead of argon gas like a regular bulb is. The halogen gas removes the carbon deposits on the inside of the bulb, caused by the burning of the tungsten filament, and re deposits it back on to the filament, resulting in a light bulb which can be burned at a higher temperature therefore creating, both a whiter as well as a brighter light per watt than a regular bulb. The average rated life of halogen bulbs are typically between 2,000 and 4,000 hours.

Types of Fluorescent Lamps
Two general types of fluorescent lamps include these:
Compact fluorescent lamps (CFLs)
Fluorescent tube and circline lamps

FLOURESCENT TUBE LIGHT
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. Compared with incandescent lamps, fluorescent lamps use less power for the same amount of light, generally last longer, but are bulkier, more complex, and more expensive than a comparable incandescent lamp. Fluorescent lamps - namely CFL's - are significantly more expensive than incandescent, but they are about 3 to 4 times as efficient as incandescent and last 10 times longer or more

COMPACT FLOURESCENT LIGHTS/ENERGY SAVER
A compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb (or less commonly as a compact fluorescent tube [CFT]), is a type of fluorescent lamp. Many CFLs are designed to replace an incandescent lamp and can fit in the existing light fixtures formerly used for incandescents. Compared to general service incandescent lamps giving the same amount of visible light, CFLs use less power and have a longer rated life, but generally have a higher purchase price. Compact fluorescent lamps (CFLs) combine the energy efficiency of fluorescent lighting with the convenience and popularity of incandescent fixtures
CFLs can replace incandescents that are roughly 3–4 times their wattage, saving up to 75% of the initial lighting energy. Although CFLs cost 3–10 times more than comparable incandescent bulbs, they last 6–15 times as long (6,000–15,000 hours).

Low-Pressure Sodium Lighting
Low-pressure sodium lamps provide the most energy-efficient outdoor lighting compared to high-intensity discharge lighting, but they have very poor color rendition. Typical applications include highway and security lighting, where color isn't important.
Low-pressure sodium lamps work somewhat like fluorescent lamps. Like high-intensity discharge lighting, low-pressure sodium lamps require up to ten minutes to start and have to cool before they can restart. Therefore, they are most suitable for applications where they stay on for hours at a time. They are not suitable for use with motion detectors.

Mercury Vapor Lamps
Mercury vapor lamps—the oldest types of high-intensity discharge lighting—are used primarily for street lighting. Mercury vapor lamps provide about 50 lumens per watt. They cast a very cool blue/green white light. Most indoor mercury vapor lamps in arenas and gymnasiums have been replaced by metal halide lamps. Metal halide lamps have better color rendering> and a higher efficacy. However, like high-pressure sodium lamps, mercury vapor lamps have longer lifetimes (16,000–24,000 hours) than metal halide lamps.

Control Gear
The gears used in the lighting equipment are as follows:

Ballast:
A component that is used to stabilize the current flow through, or operation of, a circuit,stage or device. 2. An iron-core choke connected in series with one of the electrodes in a fluorescent or other gas-discharge lamp.

Ignitors:
These are used for starting high intensity Metal Halide and Sodium vapour lamps.

Recommended Illumination
Chemicals
Petroleum, Chemical and Petrochemical works Exterior walkways, platforms, stairs and ladders 30–50–100
Exterior pump and valve areas 50–100–150
Pump and compressor houses 100–150–200
Process plant with remote control 30–50–100
Process plant requiring occasional manual intervention 50–100–150
Permanently occupied work stations in process plant 150–200–300
Control rooms for process plant 200–300–500

Pharmaceuticals Manufacturer and Fine chemicals manufacturer
Pharmaceutical manufacturerGrinding, granulating, mixing, drying, tableting, s 300–500–750
terilising, washing, preparation of solutions, filling,
capping, wrapping, hardening

Fine chemical manufacturersExterior walkways, platforms, stairs and ladders 30–50–100
Process plant 50–100–150
Fine chemical finishing 300–500–750
Inspection 300–500–750
Soap manufacture
General area 200–300–500
Automatic processes 100–200–300
Control panels 200–300–500
Machines 200–300–500

Paint worksGeneral 200–300–500
Automatic processes 150–200–300
Control panels 200–300–500
Special batch mixing 500–750–1000
Colour matching 750–100–1500

USEFUL LIGHT CALCULATION FORMULAS FORMULAS
1) Demand for Power (kW) = System Input Wattage (W) ÷ 1,000
2) Energy Consumption (kWh) = System Input Wattage (kW) x Hours of Operation/Year
3) Hours of Operation/Year = Operating Hours/Day x Operating Days/Week x Operating Weeks/Year
4) Lighting System Efficacy (Lumens per Watt or LPW) = System Lumen Output ÷ Input Wattage
5) Unit Power Density (W/sq.ft.) = Total System Input Wattage (W) ÷ Total Area (Square Feet)
6) Watts (W) = Volts (V) x Current in Amperes (A) x Power Factor (PF)
7) Voltage (V) = Current in Amperes (A) x Impedance (Ohms) [Ohm's Law]

SELECTION CHART FOUND ON A TYPICAL INDUSTRIAL LUX METER
SELECTION ON A LUTRON LIGHT METER
1 for TUNGSTEN , SUN
2 for FLUORESCENT
3 for SODIUM
4 for MERCURY

Light Control
The simplest and the most widely used form of controlling a lighting installation is "On-Off" switch. The initial investment for this set up is extremely low, but the resulting operational costs may be high. This does not provide the flexibility to control the lighting, where it is not required.
Hence, a flexible lighting system has to be provided, which will offer switch-off or reduction in lighting level, when not needed. The following light control systems can be adopted at design stage:

• Grouping of lighting system, to provide greater flexibility in lighting control
Grouping of lighting system, which can be controlled manually or by timer control.

•Installation of microprocessor based controllersAnother modern method is usage of microprocessor / infrared controlled dimming or switching
circuits. The lighting control can be obtained by using logic units located in the ceiling, which
can take pre-programme commands and activate specified lighting circuits. Advanced lighting
control system uses movement detectors or lighting sensors, to feed signals to the controllers.

• Optimum usage of daylighting
Whenever the orientation of a building permits, day lighting can be used in combination with electric lighting. This should not introduce glare or a severe imbalance of brightness in visual environment. Usage of day lighting (in offices/air conditioned halls) will have to be very limited, because the air conditioning load will increase on account of the increased solar heat dissipation into the area. In many cases, a switching method, to enable reduction of electric light in the window zones during certain hours, has to be designed.

• Installation of "exclusive" transformer for lighting
In most of the industries, lighting load varies between 2 to 10%. Most of the problems faced by the lighting equipment and the "gears" is due to the "voltage" fluctuations. Hence, the lighting equipment has to be isolated from the power feeders. This provides a better voltage regulation for the lighting. This will reduce the voltage related problems, which in turn increases the efficiency of the lighting system.

• Installation of servo stabilizer for lighting feeder
Wherever, installation of exclusive transformer for lighting is not economically attractive, servo stabilizer can be installed for the lighting feeders. This will provide stabilized voltage for the lighting equipment. The performance of "gears" such as chokes, ballasts, will also improved due to the stabilized voltage. This set up also provides, the option to optimise the voltage level fed to the lighting feeder. In many plants, during the non-peaking hours, the voltage levels are on the higher side. During this period, voltage can be optimised, without any significant drop in the illumination level.

Lighting Occupancy Sensor Controls
Occupancy sensors detect activity within a certain area. They provide convenience by turning lights on automatically when someone enters a room. They reduce lighting energy use by turning lights off soon after the last occupant has left the room.
Occupancy sensors must be located where they will detect occupants or occupant activity in all parts of the room. There are two types of occupancy sensors: ultrasonic and infrared. Ultrasonic sensors detect sound, while infrared sensors detect heat and motion. In addition to controlling ambient lighting in a room, they are useful for task lighting applications, such as over kitchen counters. In such applications, task lights are turned on by the motion of a person washing dishes, for instance, and automatically turn off a few minutes after the person stops

Lighting Photosensor Controls
You can use photosensors to prevent outdoor lights from operating during daylight hours. This can help save energy because you don't have to remember to turn off your outdoor lights. Photosensors sense ambient light conditions, making them useful for all types of outdoor lighting. They offer little utility in controlling lights inside the home because lighting needs vary with occupant activity rather than ambient lighting levels.

Types of Solar Cells
The performance of a solar or photovoltaic (PV) cell is measured in terms of its efficiency at converting sunlight into electricity. There are a variety of solar cell materials available, which vary in conversion efficiency.
Semiconductor Materials
A solar cell consists of semiconductor materials. Silicon remains the most popular material for solar cells, including these types:
Monocrystalline or single crystal silicon
Multicrystalline silicon
Polycrystalline silicon
Amorphous silicon
The absorption coefficient of a material indicates how far light with a specific wavelength (or energy) can penetrate the material before being absorbed. A small absorption coefficient means that light is not readily absorbed by the material. Again, the absorption coefficient of a solar cell depends on two factors: the material making up the cell, and the wavelength or energy of the light being absorbed.

2011-03-08T21:09:00.000-08:00

COMPUTER BASICS FOR EVERYONE

What is a Computer?

An electronic device for processing information and performing calculations; follows a program to perform sequences of mathematical and logical operations

Computer Parts

A computer has various parts, and each part performs a specific function.

Part Description

Input Devices

You use input devices to provide information to a computer, such as typing a letter or giving instructions to a computer to perform a task. Some examples of input devices are described as follows

Mouse:

A device that you use to interact with items displayed on the computer screen. A standard mouse has a left and a right button. You use the left button to select items and provide instructions by clicking an active area on the screen. You use the right button to display commonly used menu items on the screen.

Keyboard:

A set of keys that resembles a typewriter keyboard. You use the keyboard to type text, such as letters or numbers into the computer.

Microphone:

A device that you can use to talk to people in different parts of the world. You can record sound into the computer by using a microphone. You can also use a microphone to record your speech and let the computer convert it into text.

Scanner:

A device that is similar to a photocopy machine. You can use this device to transfer an exact copy of a photograph or document into a computer. A scanner reads the page and translates it into a digital format, which a computer can read. For example, you can scan photographs of your family using a scanner.

Webcam:

A device that is similar to a video camera. It allows you to capture and send the live pictures to the other user. For example, a webcam allows your friends and family to see you when communicating with them.

Output Devices

You use output devices to get feedback from a computer after it performs a task. Some examples of output devices are described as follows.

Monitor:

A device that is similar to a television. It is used to display information, such as text and graphics, on the computer.

Printer:

A device that you use to transfer text and images from a computer to a paper or to another medium, such as a transparency film. You can use a printer to create a paper copy of whatever you see on your monitor.

Speaker/Headphone

Devices that allow you to hear sounds. Speakers may either be external or built into the computer.

Central Processing Unit and Memory

The central processing unit (CPU) is a device that interprets and runs the commands that you give to the computer. It is the control unit of a computer. The CPU is also referred to as the processor.

Memory is where information is stored and retrieved by the CPU. There are two main types of memory.

Random Access Memory (RAM):

It is the main memory and allows you to temporarily store commands and data. The CPU reads data and commands from RAM to perform specific tasks. RAM is volatile, which means it is available only while the computer is turned on. The contents of RAM must be copied to a storage device if you want to save the data in the RAM.

Read Only Memory (ROM):

It is the memory that retains its contents even after the computer is turned off. ROM is nonvolatile, or permanent, memory that is commonly used to store commands, such as the commands that check whether everything is working properly or not.

Motherboard

The motherboard is the main circuit board inside the computer. It has tiny electronic circuits and other components on it. A motherboard connects input, output, and processing devices together and tells the CPU how to run. Other components on the motherboard include the video card, the sound card, and the circuits that allow the computer to communicate with devices like the printer. The motherboard is sometimes called a system board.

Expansion Cards

An expansion card is a circuit board that can be attached to the motherboard to add features such as video display and audio capability to your computer. An expansion card either improves the performance of your computer or enhances its features. Expansion cards are also called expansion boards. Some types of expansion cards are described below.

Video Card:

It is connected to the computer monitor and is used to display information on the

monitor.

Network Interface Card (NIC):

It allows the computer to be connected to other computers so that information can be exchanged between them.

Sound Card:

It converts audio signals from a microphone, audio tape, or some other source to digital signals, which can be stored as a computer audio file. Sound cards also convert computer audio files to electrical signals, which you can play through a speaker or a headphone. The microphone and the speakers or the headphones connect to the sound card.

Storage Devices

You use storage devices to store computer information. Storage devices come in many forms. Some examples are hard drive or disk, CDROM, floppy disk, and DVD‐ROM. Storage devices can be divided into two types, internal storage devices and external storage devices. Some common storage devices are described below

Hard Disk:

A magnetic disk that is usually the main storage device on most computers. It can be an external or an internal device.

Floppy Disk:

A portable storage device that allows you to store a small amount of data. A disadvantage of this disk is that it can be easily damaged by heat, dust, or magnetic fields.

CD‐ROM:

A portable storage medium that allows you to store 400 times more data than on a floppy disk. It is less prone to damage than a floppy disk.

DVD‐ROM:

A portable storage medium that is similar to a CD‐ROM; however, it can store larger amounts of data than a floppy disk or a CD‐ROM. A DVD‐ROM is commonly used to store movies and videos.

Ports and Connections

A port is a channel through which data is transferred between input/output devices and the processor. There are several types of ports that you can use to connect the computer to external devices and networks. Some types of ports below

Universal Serial Bus (USB) Port:

You use this to connect peripheral devices such as a mouse, a modem, a keyboard, or a printer to a computer.

FireWire:

You use this to connect devices such as a digital camera. It is faster than the USB.

Network Port:

You use this to connect a computer to other computers to exchange information between the computers.

Parallel Port and Serial Port:

You use these ports to connect printers and other devices to a personal computer. However, the USB is now the preferred method for connecting peripheral devices because it is faster and easier to use.

Display Adapter:

You connect a monitor to the display adapter on your computer. The display adapter generates the video signal received from the computer, and sends it to a monitor through a cable. The display adapter may be on the motherboard, or on an expansion card.

Power:

The motherboard and other components inside a computer use direct current (DC). A power supply takes the alternating current (AC) from the wall outlet and converts it into DC power.

STRESS

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STRESS

Stress is the internal resistance of a material to the distorting effects of an external force or load.

Stress, s = f/a

When a metal is subjected to a load (force), it is distorted or deformed, no matter how strong the metal or light the load. If the load is small, the distortion will probably disappear when the load is removed. The intensity, or degree, of distortion is known as strain. If the distortion disappears and the metal returns to its original dimensions upon removal of the load, the strain is called elastic strain. If the distortion disappears and the metal remains distorted, the strain type is called plastic strain.

Stress is the internal resistance, or counterforce, of a material to the distorting effects of an external force or load. These counterforces tend to return the atoms to their normal positions. The total resistance developed is equal to the external load. This resistance is known as stress.

Although it is impossible to measure the intensity of this stress, the external load and the area to which it is applied can be measured. Stress (s) can be equated to the load per unit area or the force (f) applied per cross-sectional area (a) perpendicular to the force as shown

Stress, s = f/a

Where:

s = stress (psi or lbs of force per in.2)

F = applied force (lbs of force per in.2)

A = cross-sectional area (in.2)

Types of stress

Stresses occur in any material that is subject to a load or any applied force. There are many types of stresses, but they can all be generally classified in one of six categories

1) Residual stress

Residual stresses are due to the manufacturing processes that leave stresses in a material. Welding leaves residual stresses in the metals welded

2) Structural stress

Structural stresses are stresses produced in structural members because of the weights they support. The weights provide the loadings. These stresses are found in building foundations and frameworks, as well as in machinery parts.

3) Pressure stress

Pressure stresses are stresses induced in vessels containing pressurized materials. The loading is provided by the same force producing the pressure. In a reactor facility, the reactor vessel is a prime example of a pressure vessel.

4) Flow stress

Flow stresses occur when a mass of flowing fluid induces a dynamic pressure on a

conduit wall. The force of the fluid striking the wall acts as the load. This type of

Stress may be applied in an unsteady fashion when flow rates fluctuate. Water hammer is an example of a transient flow stress.

5) Thermal stress

Thermal stresses exist whenever temperature gradients are present in a material.

Different temperatures produce different expansions and subject materials to internal stress. This type of stress is particularly noticeable in mechanisms operating at high temperatures that are cooled by a cold fluid

6) Fatigue stress

Fatigue stresses are due to cyclic application of a stress. The stresses could be due to vibration or thermal cycling.

Types of applied stresses

These are known as tensile, compressive, and shear

As illustrated in figure, the plane of a tensile or compressive stress lies perpendicular to the axis of operation of the force from which it originates. The plane of a shear stress lies in the plane of the force system from which it originates.

a) Tensile stress

Tensile stress is that type of stress in which the two sections of material on either side of a stress plane tend to pull apart or elongate

b) Compressive stress

Compressive stress is the reverse of tensile stress. Adjacent parts of the material tend to press against each other through a typical stress plane

c) Shear stress

Shear stress exists when two parts of a material tend to slide across each other in any typical plane of shear upon application of force parallel to that plane

Assessment of mechanical properties is made by addressing the three basic stress types. Because tensile and compressive loads produce stresses that act across a plane, in a direction perpendicular (normal) to the plane, tensile and compressive stresses are called normal stresses.

Two types of stress can be present simultaneously in one plane, provided that one of the stresses is shear stress. Under certain conditions, different basic stress type combinations may be simultaneously present in the material. An example would be a reactor vessel during operation. The wall has tensile stress at various locations due to the temperature and pressure of the fluid acting on the wall. Compressive stress is applied from the outside at other locations on the wall due to outside pressure, temperature, and constriction of the supports associated with the vessel. In this situation, the tensile and compressive stresses are considered principal stresses. If present, shear stress will act at a 90° angle to the principal stress.

INTERNET: AN INTRODUCTION

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INTERNET: AN INTRODUCTION
The Internet is the largest computer network in the world. It consists of millions of computers all over the planet, all connected to each another

World Wide Web
The World Wide Web is what you probably think of when you think of the Internet, although it’s really just a part of the Internet. The Web consists of millions of documents that are stored on hundreds of thousands of computers that are always connected to the Internet. These documents are called Web pages, and you can find Web pages on every subject imaginable—from your local newspaper to online catalogs to airline schedules, and much more.

Web Servers
Web pages are stored on Web servers. A Web server is a computer, not unlike your own computer, only bigger and faster. There are hundreds of thousands of Web servers located all over the world. Web servers are always connected to the Internet so that people can view their Web pages 24 hours a day.

What Can I do on the Internet?

Send and Receive E-mail
Exchanging electronic mail (or e-mail) is the most popular feature on the Internet. Just like regular paper mail, you can send and receive e-mail with people around the world, as long as they have access to a computer and the Internet. Unlike regular paper mail, e-mail is delivered to its destination almost instantly.

Browse the World Wide Web
The World Wide Web is what most people think of when they think of the Internet—although it’s really only a part of the Internet. The World Wide Web is an enormous collection of interconnected documents stored on Web servers all over the world. The World Wide Web has information on every subject imaginable.

Join online discussions with newsgroups
Newsgroups are discussion groups on the Internet that you can join to read and post messages to and from people with similar interests. There are thousands of newsgroups on topics such as computers, education, romance, hobbies, politics, religion, and more.

Chat with other online users
Chatting lets you communicate with people on the Internet instantly—no matter how far away they are! Most chats are text-based, meaning you have to type when you converse with people on the Internet. A growing number of chats have voice and even video capabilities—all without having to pay long distance changes.

Download software
You can download pictures, demo programs, patches and drivers for your computer, and many other types of files and save them to your computer.

Listen to music and watch videos
You can listen to sound on the Web, such as radio stations, or music by your favorite artists.

Requirements for using the internet
There are three things you’ll need to connect to the Internet:

1. An Internet Service Provider (ISP):
An Internet Service Provider is a lot like a phone company, except instead of letting you make telephone calls to other people, an Internet Service Provider lets your computer connect to the Internet. Just like your telephone company, Internet Service Providers charge for their services.

2. A Web Browser:
A Web browser is a program that lets your computer view and navigate the World Wide Web. Windows comes with a built-in Web browser—Internet Explorer.

3. A Phone Line and Modem or Other Connection:
A modem is your computer’s very own telephone that lets it talk to other computers on the Internet. There are slower dial-up modems that connect to the Internet using your phone and much faster cable modems and Digital Subscriber Lines (DSL) as well. DSL is technology that provides high-speed Internet access through standard phone lines. A cable modem connects to the Internet through the cable hookup in your house. Both of these connections are much faster than a dial-up modem and are connected to the Internet 24 hours a day, so you don’t tie up any phone lines.

Web addresses
Web addresses are everywhere—on television advertisements, in magazine and newspaper articles, and even on business cards. These www.something.coms you’ve seen and heard so much about are URLs (Uniform Resource Locator). Just like there is a house, office, or building behind a postal address, there is a Web page behind every Web address. Unlike postal addresses, however, through the magic of technology you can instantly arrive at a Web page by typing its Web address, or URL, into your Web browser

Searching
The Internet’s greatest strength is also its greatest weakness: with so much information— literally millions of Web pages—it can be extremely difficult to find what you’re looking for. Fortunately, there are many search engines that catalog the millions of Web pages on the Internet so that you can find Web pages on topics that interest you, such as Google, Yahoo! and Excite.

Downloading
Another common use of the Internet is to download files from a Web server and save them onto your local hard drive. Some of the most common types of files people download from the Internet include:

Images:
You can save any picture that you see on a Web page, print it, use it as your
Windows wallpaper, or anything else you can think of.

Programs:
Many software companies have demo versions of their programs available on the Internet that you can download and evaluate. In addition, thousands of shareware programs are available for you to download for free!

Patches, Fixes, and Drivers:
One of the great things about the Internet is finding fixes for your programs, and drivers for your hardware devices, such as a driver for a discontinued foreign printer.

Music:
MP3s are revolutionizing the music industry. MP3 files are sound files that you can listen to on your computer. They have digital CD quality sound, but use compression so that they are 11 times smaller than the CD equivalent and small enough to be easily downloadable from the Internet.

Viruses:
Just kidding—the last thing you want to download from the Internet is a computer virus! Since you won’t always know where a program or file you want to download comes from, you should make sure your computer has a virus protection program installed before you download anything from the Internet.

Understanding Information Security
Information security is the practice of protecting your computer from intruders. Here are some security precautions that help protect your sensitive information. Install anti-virus software; Update anti-virus software; Update software; Use firewalls; Be smart with e-mail

Understanding Windows Firewall
This security utility keeps your computer secure by restricting the information that comes into your Computer

Different Types of Connections
The first step in going online is establishing a connection between your computer and the Internet. To do this, you have to sign up with an Internet service provider (ISP), which, as the name implies, provides your home with a connection to the Internet. Depending on what’s available in your area, you can choose from two primary types of connections—dial-up or broadband. Dial-up is slower than broadband, but it’s also lower priced. That said, dial-up connections are going the way of the dodo bird; if you do a lot of web surfing, it’s probably worth a few extra dollars a month to get the faster broadband connection.

Traditional Dial-Up
A dial-up connection provides Internet service over normal phone lines. The fastest dial-up connections transmit data at 56.6Kbps (kilobits per second), which is okay for normal web surfing but isn’t fast enough for downloading music or videos.

Broadband DSL
DSL is a phone line-based technology that operates at broadband speeds. DSL service piggybacks onto your existing phone line, turning it into a high-speed digital connection. Not only is DSL faster than dial-up (384Kbps to 10Mbps, depending on your ISP), you also don’t have to surrender your normal phone line when you want to surf; DSL connections are “always on.”

Broadband Cable
Another popular type of broadband connection is available from your local cable company. Broadband cable Internet piggybacks on your normal cable television line, providing speeds in the 500Kbps to 30Mbps range, depending on the provider.

Broadband Satellite
If you can’t get DSL or cable Internet in your area, you have another option—connecting to the Internet via satellite. Any household or business with a clear line of sight to the southern sky can receive digital data signals from a geosynchronous satellite at 700Kbps

Connecting to a Public WiFi Hotspot
If you have a notebook PC, you also have the option to connect to the Internet when you’re out and about. Many coffeehouses, restaurants, libraries, and hotels offer wireless WiFi Internet service, either free or for an hourly or daily fee. Assuming that your notebook has a built-in WiFi adapter (and it probably does), connecting to a public WiFi hotspot is a snap. When you’re near a WiFi hotspot, your PC should automatically pick up the WiFi signal. Make sure that your WiFi adapter is turned on (some notebooks have a switch for this, either on the front or on the side of the unit), and then look for a wireless connection icon in Windows’ system tray or notification area. Click this icon (or select Start, Connect To), and Windows displays a list of available wireless networks near you. Select the network you want to connect to; then click the Connect button.

TRANSFORMERS

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TRANSFORMER

Transformer is used to convert electrical energy of higher voltage (usually 11-22-33kV) to a lower voltage (250 or 433V) with frequency identical before and after the transformation. Its main application is mainly within suburban areas, public supply authorities and industrial customers. With given secondary voltage, distribution transformer is usually the last in the chain of electrical energy supply to households and industrial enterprises.

INTRODUCTION
A transformer has no internal moving parts, and it transfers energy from one circuit to another by electromagnetic induction. External cooling may include heat exchangers, radiators, fans, and oil pumps. Radiators and fans are evident in figure. The large horizontal tank at the top is a conservator. Transformers are typically used because a change in voltage is needed. Power transformers are defined as transformers rated 500 kVA and larger. Larger transformers are oil-filled for insulation and cooling. Transformers smaller than 500 kVA are generally called distribution transformers.

Radiator : Any of numerous devices, units, or surfaces that emit heat, mainly by radiation, to objects in the space in which they are installed.

All electrical devices using coils (in this case, transformers) are constant wattage devices. This means voltage multiplied by current must remain constant; therefore, when voltage is “stepped-up,” the current is “stepped-down” (and vice versa). Transformers transfer electrical energy between circuits completely insulated from each other. This makes it possible to use very high (stepped-up) voltages for transmission lines, resulting in a lower (stepped-down) current. Higher voltage and lower current reduce the required size and cost of transmission lines and reduce transmission losses as well. Transformers have made possible economic delivery of electric power over long distances. The transformer cannot change the frequency of the supply. If the supply is 60 hertz, the output will also be 60 hertz.

Basic principle

A simple transformer consists of two electrical conductors called the primary winding and secondary winding, and a steel core that magnetically links them together These two windings can be considered as a pair of mutually coupled coils. At the instant a transformer primary is energized with AC, a flow of electrons (current) begins. During the instant of switch closing, buildup of current and magnetic field occurs. As current begins the positive portion of the sine wave, lines of magnetic force (flux) develop outward from the coil and continue to expand until the current is at its positive peak. The magnetic field is also at its positive peak. The current sine wave then begins to decrease, crosses zero, and goes negative until it reaches its negative peak. The magnetic flux switches direction and also reaches its peak in the opposite direction.

NOTE: Direct current (DC) is not transformed, as DC does not vary its magnetic fields. A transformer usually consists of two insulated windings on a common iron (steel) core:
With an AC power circuit, the current changes (alternates) continually 60 times per second, which is standard in the United States. Other countries may use other frequencies. In Europe, 50 cycles per second is common. Strength of a magnetic field depends on the amount of current and number of turns in the winding. When current is reduced, the magnetic field shrinks. When the current is switched off, the magnetic field collapses

Transformer Voltage and Current If the secondary coil has twice as many turns as the primary, it will be cut twice as many times by the flux, and twice the applied primary voltage will be induced in the secondary. The total induced voltage in each winding is proportional to the number of turns in that winding. If E1 is the primary voltage and I1 the primary current, E2 the secondary voltage and I2 the secondary current, N1 the primary turns and N2 the secondary turns, then:

E1/E2 = N1/N2 = I2/I1

Note that the current is inversely proportional to both voltage and number of turns. This means that if voltage is stepped up, the current must be stepped down and vice versa. The number of turns remains constant unless there is a tap changer. The power output or input of a transformer equals volts times amperes (E x I). If the small amount of transformer loss is disregarded, input equals output or:

E1 x I1 = E2 x I2
Transformers are adapted to numerous engineering applications and may be classified in many ways:

§ By power level (from fraction of a watt to many megawatts),
§ By application (power supply, impedance matching, circuit isolation),
§ By frequency range (power, audio, RF)
§ By voltage class (a few volts to about 750 kilovolts)
§ By cooling type (air cooled, oil filled, fan cooled, water cooled, etc.)
§ By purpose (rectifier, arc furnace, amplifier output, etc.).
§ By ratio of the number of turns in the coils

Step Down Transformers
If there are fewer turns in the secondary winding than inthe primary winding, the secondary voltage will be lower than the primary.

Step Up TransformersIf there are fewer turns in the primary winding than in the secondary winding, the secondary voltage will be higher than the secondary circuit. Isolating
When the primary winding and the secondary winding havethe same amount of turns there is no change voltage, the ratio is 1/1 unity. Variable
The primary and secondary have an adjustable number of turns which can be selected without reconnecting the transformer.
Note: The primary winding is the winding which receives the energy; it is not always the high-voltage winding.

CONSTRUCTION
There are 3 main parts in the distribution transformer:

1) Coils/winding
where incoming alternating current (through primary winding) generates magnetic flux, which in turn induces a voltage in the secondary coil.

2) Magnetic corematerial allowing transfer of magnetic field generated by primary winding to secondary winding by the principle of electromagnetic induction. A transformers core and windings are called its Active Parts. This is because these two are responsible for transformer s operation.

3) Tank
serving as a mechanical package to protect active parts, as a holding vessel for transformer oil used for cooling and insulation.

Transformer Accessories
Bucholz relay
Breather
Pressure relief device etc

(Breather pipe A pipe that opens into a container for ventilation, as in a crankcase or oil tank. Also known as crankcase breather.)

A Buchholz relay, also called a gas relay or a sudden pressure relay, is a safety device mounted on some oil-filled power transformers, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment

Losses
An ideal transformer would have no losses, and would therefore be 100% efficient. In practice energy is dissipated due both to the resistance of the windings (known as copper loss), and to magnetic effects primarily attributable to the core (known as iron loss). Transformers are in general highly efficient, and large power transformers (around 100 MVA and larger) may attain an efficiency as high as 99.75%. Small transformers such as a plug-in "power brick" used to power small consumer electronics may be less than 85% efficient.

The losses arise from:
1) Winding resistance
Current flowing through the windings causes resistive heating of the conductors.
2) Eddy currents
Induced currents circulate in the core and cause its resistive heating.
3) Stray losses
Not all the magnetic field produced by the primary is intercepted by the secondary. A portion of the leakage flux may induce eddy currents within nearby conductive objects such as the transformer's support structure, and be converted to heat. The familiar hum or buzzing noise heard near transformers is a result of stray fields causing components of the tank to vibrate, and is also from magnetostriction vibration of the core.
4) Hysteresis losses
Each time the magnetic field is reversed, a small amount of energy is lost to hysteresis in the magnetic core. The level of hysteresis is affected by the core material.
5) Mechanical losses
The alternating magnetic field causes fluctuating electromagnetic forces between the coils of wire, the core and any nearby metalwork, causing vibrations and noise which consume power.
6) Magnetostriction
The flux in the core causes it to physically expand and contract slightly with the alternating magnetic field, an effect known as magnetostriction. This in turn causes losses due to frictional heating in susceptible ferromagnetic cores.

The magnetic circuit and windings are the principal sources of losses and resulting temperature rise in various parts of a transformer. Core loss, copper loss in windings (I2R loss), stray loss in windings and stray loss due to leakage/high current field are mainly responsible for heat generation within the transformer.

§ Cooling system
Large power transformers may be equipped with cooling fans, oil pumps or water-cooled heat exchangers designed to remove the heat caused by copper and iron losses. The power used to operate the cooling system is typically considered part of the losses of the transformer.

Modes of Heat Transfer
The heat transfer mechanism in a transformer takes place by three modes, viz. conduction, convection and radiation. In the oil cooled transformers, convection plays the most important role and conduction the least important.

Conduction
Almost all the types of transformers are either oil or gas filled, and heat flows from the core and windings into the cooling medium. From the core, heat can flow directly, but from the winding it flows through the insulation provided on the winding conductor. In large transformers, at least one side of insulated conductors is exposed to the cooling medium, and the heat flows through a small thickness of the conductor insulation. But in small transformers the heat may have to flow through several layers of copper and insulation before reaching the cooling medium.

Radiation
Any body, at a raised temperature compared to its surroundings, radiates heat energy in the form of waves. The heat dissipation from a transformer tank occurs by means of both radiation and natural convection. The cooling of radiators also occurs by radiation, but it is far less as compared to that by convection.

Convection
The oil, being a liquid, has one important mechanical property that its volume changes with temperature and pressure .The change of volume with temperature provides the essential convective or thermosiphon cooling. The change of volume with pressure affects the amount of transferred vibrations from the core to tank.

The heat dissipation from the core and windings occurs mainly due to convection. When a heated surface is immersed in a fluid, heat flows from the surface to the cooling medium. Due to increase in the fluid temperature, its density (or specific gravity) reduces. The fluid (oil) in oil-cooled transformers, rises upwards and transfers its heat to outside ambient through tank and radiators. The rising oil is replaced by the colder oil from the bottom, and thus the continuous oil circulation occurs.

Common Cooling Arrangements ONAN/OA cooling (Oil Natural and Air Natural)
In small rating transformers, the tank surface area may be able to dissipate heat directly to the atmosphere; while the bigger rating transformers usually require much larger dissipating surface in the form of radiators/tubes mounted directly on the tank or mounted on a separate structure. If the number of radiators is small, they are preferably mounted directly on the tank so that it results in smaller overall dimensions.

Oil is kept in circulation by the gravitational buoyancy in the closed-loop cooling system as shown in figure. The heat developed in active parts is passed on to the surrounding oil through the surface transfer (convection) mechanism. The oil temperature increases and its specific gravity drops, due to which it flows upwards and then into the coolers. The oil heat gets dissipated along the colder surfaces of the coolers which increases its specific gravity, and it flows downwards and enters the transformer tank from the inlet at the bottom level.
Since the heat dissipation from the oil to atmospheric air is by natural means (the circulation mechanism for oil is the natural thermosiphon flow in the cooling
equipment and windings), the cooling is termed as ONAN (Oil Natural and Air Natural) or OA type of cooling. Since the heat dissipation from the oil to atmospheric air is by natural means (the circulation mechanism for oil is the natural thermosiphon flow in the cooling equipment and windings), the cooling is termed as ONAN (Oil Natural and Air Natural) or OA type of cooling.

ONAF/FA cooling (Oil Natural and Air Forced)
If fans are used to blow air on to the cooling surfaces of the radiators, the heat transfer coefficient is significantly increased. For a given set of ambient air temperature and oil temperature, a compact arrangement is possible since less number of radiators is required to cool the oil. This type of cooling is termed as ONAF (Oil Natural and Air Forced) or FA type of cooling.

OTHER TRANSFORMER TYPES
Current Transformer(CT)
Current transformers are used in electric metering for large load situations to reduce the current level presented to the metering circuit in order to make it more manageable and safe. A current transformer is a type of "instrument transformer" that is designed to provide a current in its secondary which is accurately proportional to the current flowing in its primary.

Potential Transformer

A Potential Transformer is a special type of transformer that allows meters to take readings from electrical service connections with higher voltage (potential) than the meter is normally capable of handling without at potential transformer. Potential transformers are used with voltmeters, wattmeters, watt-hour meters, power-factor meters, frequency meters, synchroscopes and synchronizing apparatus, protective and regulating relays, and undervoltage and overvoltage trip coils of circuit breakers. One potential transformer can be used for a number of instruments if the total current required by the instruments connected to the secondary winding does not exceed the transformer rating.

Autotransformers
It is possible to obtain transformer action by means of a single coil, provided that there is a “tap connection” somewhere along the winding. Transformers having only one winding are called autotransformers, shown schematically in figure . An autotransformer has the usual magnetic core but only one winding, which is common to both the primary and secondary circuits. The primary is always the portion of the winding connected to the AC power source. This transformer may be used to step voltage up or down. If the primary is the total winding and is connected to a supply, and the secondary circuit is connected across only a portion of the winding (as shown), the secondary voltage is “stepped-down.”

Step-up and step-down transformers
A transformer designed to increase voltage from primary to secondary is called a stepup
transformer. A transformer designed to reduce voltage from primary to secondary is
called a step-down transformer.

Power Transformer
Power transformers are selected based on the application, with the emphasis toward custom design being more apparent the larger the unit. Power transformers are available for step-up operation, primarily used at the generator and referred to as generator step-up (GSU) transformers, and for step-down operation, mainly used to feed distribution circuits. Power transformers are available as single-phase or three-phase apparatus.
The construction of a transformer depends upon the application. Transformers intended for indoor use are primarily of the dry type but can also be liquid immersed. For outdoor use, transformers are usually liquid immersed.

AccessoriesThere are many different accessories used to monitor and protect power transformers, some of which are considered standard features, and others of which are used based on miscellaneous requirements. A few of the basic accessories are briefly discussed here.

Liquid-Level Indicator
A liquid-level indicator is a standard feature on liquid-filled transformer tanks, since the liquid medium is critical for cooling and insulation. This indicator is typically a round-faced gauge on the side of the tank, with a float and float arm that moves a dial pointer as the liquid level changes.

Pressure-Relief Devices
Pressure-relief devices are mounted on transformer tanks to relieve excess internal pressures
that might build up during operating conditions. These devices are intended to avoid damage to the tank. On larger transformers, several pressure-relief devices may be required due to the large quantities of oil.

Liquid-Temperature IndicatorLiquid-temperature indicators measure the temperature of the internal liquid at a point near the top of the liquid using a probe inserted in a well and mounted through the side of the transformer tank.

Sudden-Pressure Relay
A sudden- (or rapid-) pressure relay is intended to indicate a quick increase in internal pressure that can occur when there is an internal fault. These relays can be mounted on the top or side of the transformer, or they can operate in liquid or gas space.

Desiccant (Dehydrating) Breathers
Desiccant breathers use a material such as silica gel to allow air to enter and exit the tank, removing moisture as the air passes through. Most tanks are somewhat free breathing, and such a device, if properly maintained, allows a degree of control over the quality of air entering the transformer

‘‘Buchholz’’ Relay
On power transformers using a conservator liquid-preservation system, a ‘‘Buchholz’’ relay can be installed in the piping between the main transformer tank and the conservator. The purpose of the Buchholz relay is to detect faults that may occur in the transformer. One mode of operation is based on the generation of gases in the transformer during certain minor internal faults. Gases accumulate in the relay, displacing the liquid in the relay, until a specified volume is collected, at which time a float actuates a contact or switch. Another mode of operation involves sudden increases in pressure in the main transformer tank, a sign of a major fault in the transformer. Such an increase in pressure forces the liquid to surge through the piping between the main tank and the conservator, through the ‘‘Buchholz’’ relay, which actuates another contact or switch.

Introduction to Jet Engines

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Introduction to Jet Engines

An aircraft engine, or power plant, produces thrust to propel an aircraft. Reciprocating engines and turboprop engines work in combination with a propeller to produce thrust. Turbojet and turbofan engines produce thrust by increasing the velocity of air flowing through the engine. All of these power plants also drive the various systems that support the operation of an aircraft.

Turbine Engines

An aircraft turbine engine consists of an air inlet, compressor, combustion chambers, a turbine section, and exhaust. Thrust is produced by increasing the velocity of the air flowing through the engine. Turbine engines are highly desirable aircraft power plants. They are characterized by

Smooth operation

High power-to-weight ratio

Readily available jet fuel.

Types of Turbine Engines
Turbine engines are classified according to the type of compressors they use. There are three types of compressors—centrifugal flow, axial flow, and centrifugal-axial flow. Compression of inlet air is achieved in a centrifugal flow engine by accelerating air outward perpendicular to the longitudinal axis of the machine. The axial-flow engine compresses air by a series of rotating and stationary airfoils moving the air parallel to the longitudinal axis. The centrifugal-axial flow design uses both kinds of compressors to achieve the desired compression.

The path the air takes through the engine and how power is produced determines the type of engine. There are four types of aircraft turbine engines—turbojet, turboprop, turbofan, and turboshaft.

Turbojet

The turbojet engine consists of four sections: compressor, combustion chamber, turbine section, and exhaust. The compressor section passes inlet air at a high rate of speed to the combustion chamber. The combustion chamber contains the fuel inlet and igniter for combustion. The expanding air drives a turbine, which is connected by a shaft to the compressor, sustaining engine operation. The accelerated exhaust gases from the engine provide thrust. This is a basic application of compressing air, igniting the fuel-air mixture, producing power to self-sustain the engine operation, and exhaust for propulsion.

Turboprop

A turboprop engine is a turbine engine that drives a propeller through a reduction gear. The exhaust gases drive a power turbine connected by a shaft that drives the reduction gear assembly. Reduction gearing is necessary in turboprop engines because optimum propeller performance is achieved at much slower speeds than the engine’s operating rpm. Turboprop engines are a compromise between turbojet engines and reciprocating power plants. Turboprop engines are most efficient at speeds between 250 and 400 mph and altitudes between 18,000 and 30,000 feet. They also perform well at the slow airspeeds required for takeoff and landing, and are fuel efficient.

Turbofan

Turbofans were developed to combine some of the best features of the turbojet and the turboprop. Turbofan engines are designed to create additional thrust by diverting a secondary airflow around the combustion chamber. The turbofan bypass air generates increased thrust, cools the engine, and aids in exhaust noise suppression. This provides turbojet-type cruise speed and lower fuel consumption.

The inlet air that passes through a turbofan engine is usually divided into two separate streams of air. One stream passes through the engine core, while a second stream bypasses the engine core. It is this bypass stream of air that is responsible for the term “bypass engine.” A turbofan’s bypass ratio refers to the ratio of the mass airflow that passes through the fan divided by the mass airflow that passes through the engine core.

Turboshaft

The fourth common type of jet engine is the turboshaft. It delivers power to a shaft that drives something other than a propeller. The biggest difference between a turbojet and turboshaft engine is that on a turboshaft engine, most of the energy produced by the expanding gases is used to drive a turbine rather than produce thrust. Many helicopters use a turboshaft gas turbine engine. In addition, turboshaft engines are widely used as auxiliary power units on large aircraft.

BEARINGS

2011-03-08T08:45:00.001-08:00

BEARINGS

Bearings permit smooth, low-friction movement between two or more surfaces. Conventional bearings provide support to rotating machinery by allowing relative movement. They allow rotation and provide support in either radial or axial planes of rotation. The most common types of bearings are rolling element bearings, and oil film or journal bearings. Bearings reduce friction by providing smooth metal balls or rollers. These balls or rollers "bear" the load, allowing the device to spin smoothly

Bearings typically have to deal with two kinds of loading, radial and thrust. Depending on where the bearing is being used, it may see all radial loading, all thrust loading or a combination of both e.g. electric motor bearing supports a radial load , a revolving stool bearing supports axial or thrust load

What is load?
Load is the force applied to the bearing, which the bearing has to withstand. Generally there are two types of load
1) Radial load is the load which is applied perpendicular to the shaft axis.
2) Axial load is the load applied parallel to the shaft axis
3) Combined load is radial plus axial load

Principle of operation
Rolling element bearings consist of a stationary outer race and a rotating inner race; in between them are the rolling elements, most common are spherical balls, but cylinders or tapered pins are also used. During rotation, these 3 items are in contact with each other and the weight being supported is transferred through the rolling elements between the inner race and outer race.

Oil film bearings have no rolling elements, but make use of pressurized oil to provide a film of support, and prevent galling between the shaft and the bearing journal. The oil is circulated so that fresh, cool oil is constantly entering the space between the stationary and rotating pieces. The shaft rotation shears the oil in this gap, causing it to heat up. The oil then exits the journal for cooling, filtering, and recirculation.

Types of bearings

1) Ball bearings
Ball bearings are very commonly used. They are found in everything from skate boards, to washing machines to PC hard drives. These bearings are capable of taking both radial and thrust loads, and are usually found in applications where the load is light to medium and is constant in nature (i.e. not shock loading). In a ball bearing, the load is transmitted from the outer race to the ball and from the ball to the inner race

2) Roller bearings
Roller bearings are used in heavy duty applications such as conveyor belt rollers, where they must hold heavy radial loads. In these bearings the roller is a cylinder, so the contact between the inner and outer race is not a point (like the ball bearing above) but a line. This spreads the load out over a larger area, allowing the roller bearing to handle much greater loads than a ball bearing. However, this type of bearing cannot handle thrust loads to any significant degree. A variation of this bearing design is called the needle bearing. The needle roller bearing uses cylindrical rollers but with a very small diameter. This allows the bearing to fit into tight places such as gear boxes that rotate at higher speeds.

3) Thrust ball bearings
Ball thrust bearings are mostly used for low-speed non precision applications. They cannot take much radial load.

4) Roller thrust bearing
Roller thrust bearings can support very large thrust loads. They are often found in gearsets like car transmissions between gears

5) Taper roller bearing
Tapered roller bearings are designed to support large radial and large thrust loads. These loads can take the form of constant loads or shock loads. Tapered roller bearings are used in many car hubs, where they are usually mounted in pairs facing opposite directions. This gives them the ability to take thrust loads in both directions.

6) Magnetic Bearing
Magnetic bearing systems represent a completely different approach to the support of rotating equipment. Magnetic bearings are a non-contact technology, which means negligible friction loss and no wear, and higher reliability. It also enables previously unachievable surface speeds to be attained. Lubrication is eliminated, meaning that these bearings can be incorporated into processes that are sensitive to contamination, such as the vacuum chambers in which many semiconductor manufacturing processes take place.

General Application Guidelines:
Ball bearings are the less expensive choice in the smaller sizes and under lighter loads, while roller bearings are less expensive for larger sizes and heavier loads. Roller bearings are more satisfactory under shock or impact loading than ball bearings. Ball-thrust bearings are for pure thrust loading only. At high speeds, a deep-groove or angular-contact ball bearing usually will be a better choice, even for pure thrust loads. Self-aligning ball bearings and cylindrical roller bearings have very low friction coefficients. Deep-groove ball bearings are available with seals built into the bearing so that the bearing can be pre-lubricated to operate for long periods reducing maintenance requirements.

Rolling bearing types
Numerous rolling bearing types with standardized main dimensions are available for the various requirements. Rolling bearings are differentiated according to: – (1) the direction of main load: radial bearings and thrust bearings. Radial bearings have a nominal contact angle a0 of 0° to 45°. Thrust bearings have a nominal contact angle a0 of over 45° to 90°. – (2) The type of rolling elements: ball bearings and roller bearings.

Difference between Ball & Roller bearing
The essential differences between ball bearings and roller bearings are,
– Ball bearings: lower load carrying capacity, higher speeds
– Roller bearings: higher load carrying capacity, lower speeds

Rolling bearing components
Rolling bearings generally consist of bearing rings (inner ring and outer ring), rolling elements which roll on the raceways of the rings, and a cage which surrounds the rolling elements. The lubricant also has to be regarded as a rolling bearing component as a bearing can hardly operate without a lubricant. Seals are also increasingly being integrated into the bearings.

Types of Rolling elements
Rolling elements are classified, according to their shape, into balls, cylindrical rollers, needle rollers, tapered rollers and barrel rollers. The rolling elements function is to transmit the force acting on the bearing from one ring to the other. For a high load carrying capacity it is important that as many rolling elements as possible, which are as large as possible, are accommodated between the bearing rings. Their number and size depend on the cross section of the bearing. Also it is just as important for loadability that the rolling elements within the bearing are of identical size.

INTRODUCTION TO AEROPLANE

2011-03-08T08:39:00.000-08:00

INTRODUCTION TO AEROPLANE

Airplane is defined as an engine-driven, fixed-wing aircraft that is supported in flight by the dynamic reaction of air against its wings

Lift and Basic Aerodynamics
Four forces act upon an aircraft in relation to straight-and-level, unaccelerated flight. These forces are thrust, lift, weight, and drag.

Thrust is the forward force produced by the powerplant/propeller. It opposes or overcomes the force of drag. As a general rule, it is said to act parallel to the longitudinal axis. This is not always the case. Drag is a rearward, retarding force, and is caused by disruption of airflow by the wing, fuselage, and other protruding objects. Drag opposes thrust, and acts rearward parallel to the relative wind. Weight is the combined load of the airplane itself, the crew, the fuel, and the cargo or baggage. Weight pulls the airplane downward because of the force of gravity. It opposes lift, and acts vertically downward through the airplane’s center of gravity (CG). Lift opposes the downward force of weight, is produced by the dynamic effect of the air acting on the wing, and acts perpendicular to the flightpath through the wing’s center of lift.

An aircraft moves in three dimensions and is controlled by moving it about one or more of its axes. The longitudinal or roll axis extends through the aircraft from nose to tail, with the line passing through the CG. The lateral or pitch axis extends across the aircraft on a line through the wing tips, again passing through the CG. The vertical, or yaw, axis passes through the aircraft vertically, intersecting the CG. All control movements cause the aircraft to move around one or more of these axes, and allows for the control of the airplane in flight.

One of the most significant components of aircraft design is CG. It is the specific point where the mass or weight of an aircraft may be said to center; that is, a point around which, if the aircraft could be suspended or balanced, the aircraft would remain relatively level. The position of the CG of an aircraft determines the stability of the aircraft in flight. As the CG moves rearward (towards the tail) the aircraft becomes more and more dynamically unstable. In aircraft with fuel tanks situated in front of the CG, it is important that the CG is set with the fuel tank empty. Otherwise, as the fuel is used, the aircraft becomes unstable. The CG is computed during initial design and construction, and is further affected by the installation of onboard equipment, aircraft loading, and other factors.

Major Components
Although airplanes are designed for a variety of purposes, most of them have the same major components. Most airplane structures include a fuselage, wings, an empennage, landing gear, and a powerplant.

Fuselage
The fuselage is the central body of an airplane and is designed to accommodate the crew, passengers, and cargo. It also provides the structural connection for the wings and tail assembly. Older types of aircraft design utilized an open truss structure constructed of wood, steel, or aluminum tubing. The most popular types of fuselage structures used in today’s aircraft are the monocoque (French for “single shell”) and semimonocoque.

Wings
The wings are airfoils attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight. There are numerous wing designs, sizes, and shapes used by the various manufacturers. Wings may be attached at the top, middle, or lower portion of the fuselage. These designs are referred to as high-, mid-, and low-wing, respectively. The number of wings can also vary. Airplanes with a single set of wings are referred to as monoplanes, while those with two sets are called biplanes.

The principal structural parts of the wing are spars, ribs, and stringers. These are reinforced by trusses, I-beams, tubing, or other devices, including the skin. The wing ribs determine the shape and thickness of the wing (airfoil). In most modern airplanes, the fuel tanks either are an integral part of the wing’s structure, or consist of flexible containers mounted inside of the wing.

Attached to the rear or trailing edges of the wings are two types of control surfaces referred to as ailerons and flaps. Ailerons extend from about the midpoint of each wing outward toward the tip, and move in opposite directions to create aerodynamic forces that cause the airplane to roll. Flaps extend outward from the fuselage to near the midpoint of each wing. The flaps are normally flush with the wing’s surface during cruising flight. When extended, the flaps move simultaneously downward to increase the lifting force of the wing for takeoffs and landings.

Empennage
The empennage includes the entire tail group and consists of fixed surfaces such as the vertical stabilizer and the horizontal stabilizer. The movable surfaces include the rudder, the elevator, and one or more trim tabs.

The rudder is attached to the back of the vertical stabilizer. During flight, it is used to move the airplane’s nose left and right. The elevator, which is attached to the back of the horizontal stabilizer, is used to move the nose of the airplane up and down during flight. Trim tabs are small, movable portions of the trailing edge of the control surface. These movable trim tabs, which are controlled from the flight deck, reduce control pressures. Trim tabs may be installed on the ailerons, the rudder, and/or the elevator.

Landing Gear
The landing gear is the principal support of the airplane when parked, taxiing, taking off, or landing. The most common type of landing gear consists of wheels, but airplanes can also be equipped with floats for water operations, or skis for landing on snow. The landing gear consists of three wheels—two main wheels and a third wheel positioned either at the front or rear of the airplane. Landing gear with a rear mounted wheel is called conventional landing gear

Automotive battery basics

2011-03-08T08:22:00.000-08:00

Automotive battery basics

The battery stores electricity in the form of chemical energy. Through a chemical reaction process the battery creates and releases electricity as needed by the electrical system or devices. Since the battery loses its chemical energy in this process, the battery must be recharged by the alternator. By reversing electrical current flow through the battery the chemical process is reversed, thus charging the battery. The cycle of discharging and charging is repeated continuously and is called "battery cycling".

The purpose of the battery

The battery supplies electricity when the:

Engine is off:
electricity from the battery is used to operate lighting, accessories, or other electrical systems when the engine is not running.

Engine is starting:
electricity from the battery is used to operate the starter motor and to provide current for the ignition system during engine cranking. Starting the car is the battery’s most important function.

Engine is running:
electricity from the battery may be needed to supplement the charging system when the vehicle’s electrical load requirements exceed the charging system’s ability to produce electricity. Both the battery and the alternator supply electricity when demand is high.

Batteries - primary or secondary

Batteries can either be a primary cell, such as a flashlight battery once used, throw it away, or a secondary cell, such as a car battery (when the charge is gone, it can be recharged).

Primary cell:
because the chemical reaction totally destroys one of the metals after a period of time, primary cells cannot be recharged. Small batteries such as flashlight and radio batteries are primary cells.

Secondary cell:
the metal plates and acid mixture change as the battery supplies voltage. As the battery drains the metal plates become similar and the acid strength weakens. This process is called discharging. By applying current to the battery in the reverse direction, the battery materials can be restored, thus recharging the battery. This process is called charging. Automotive lead-acid batteries are secondary cells and can be recharged.

Batteries - wet or dry charged

Batteries can be produced as wet-charged, such as current automotive batteries are today, or they can be dry-charged, such as a motorcycle battery where an electrolyte solution is added when put into service.

Wet-charged:
the lead-acid battery is filled with electrolyte and charged when it is built. During storage, a slow chemical reaction will cause self-discharge. Periodic charging is required. Most batteries sold today are wet charged.

Dry-charged:
the battery is built, charged, washed and dried, sealed, and shipped without electrolyte. It can be stored for up to 18 months. When put into use, electrolyte and charging are required. Batteries of this type have a long shelf life. Motorcycle batteries are typically dry charged batteries.

Battery construction

An automobile battery contains a diluted sulfuric acid electrolyte, positive and negative electrodes, in the form of several plates. Since the plates are made of lead or lead-derived materials, this type of battery is often called a lead acid battery. A battery is separated into several cells (usually six in the case of automobile batteries), and in each cell there are several battery elements, all bathed in the electrolyte solution.

Cell voltage

Each cell element of the battery produces approximately 2.1 volts, regardless of the quantity or size of the plates. Automobile batteries have six cells that are connected in series, which produces a total voltage of 12.6 volts.

Specific gravity of electrolyte

Specific gravity means exact weight. A "hydrometer" or a "refractometer" compares the exact weight of electrolyte with that of water. Electrolyte in a charged battery is stronger and heavier than electrolyte in a discharged battery. By weight, the electrolyte in a fully charged battery is about 36% acid and 64% water. The specific gravity of water is 1.000, and the specific gravity of sulfuric acid is 1.835, which means the acid is 1.835 times heavier than the water. The battery electrolyte mixture of water and acid has a specific gravity of 1.270 and is usually stated as "twelve and seventy."

Battery terminal identification

Battery terminals are identified as either "positive" or "negative". Battery cases are marked with a "+" for the positive terminal, and a "-" on the negative terminal. The words "pos" or "neg" are often used instead of the + or -. On top post terminal batteries, the positive post is slightly wider than the negative terminal post. This allow for easy identification.

Battery capacity

Batteries are generally rated using two parameters. The first, and most obvious, is voltage. The second, and less intuitive, is amp-hours. Amp-hours indicate the maximum current that a battery can continuously deliver for a period of 1 hour. When a battery is discharged at this rate, usually its full charge will be expended. A battery that has a 250 amp-hour rating is capable of delivering 250 amps at the batteries full voltage for 1 hour. A battery that has a 500 ma-hour rating is capable of delivering 1/2 amp for 1 hour. It should also be noted that the amp-hour rating is an indication of the capacity of battery. If our 250 amp-hour battery is discharged at a rate of 2 amps, its charge life will be 125 hours. Similarly, if we discharge the battery at 375 amps, the charge life will be 0.66 hours or 39.6 minutes.

Amp-hours/discharge rate= charge life

Another figure we see on automotive batteries is “cold cranking amps.” This figure is generally higher than the amp- hour rating. This rating refers to the maximum current that the battery can deliver at full charge for a short period of time. This is a loose standard and shouldn’t be relied on when selecting a battery for peak demand applications. It should also be noted that when a battery is pressed into this type of service, it can get fairly hot and a long cool down period is required.

Battery service

Battery services are routinely performed. These services include:

1) Testing

2) Charging

3) Cleaning

4) Jumping a dead battery.

5) Adding water

Battery testing

Battery testing has changed in recent years; although the three areas are basically the same, the equipment has improved

· Visual inspection

· State of charge

a. Specific gravity

b. Open circuit voltage

· Capacity or heavy load test

Visual inspection

Battery service should begin with a thorough visual inspection. This inspection may reveal simple, easily corrected problems.

1. Check for cracks in the battery case and broken terminals. Either may allow electrolyte leakage, which requires battery replacement.

2. Check for cracked or broken cables or connections. Replace, as needed.

3. Check for corrosion on terminals and dirt or acid on the case top. Clean the terminals and case top with a mixture of water and baking soda. A battery wire brush tool is needed for heavy corrosion on the terminals.

4. Check for a loose battery hold-down or loose cable connections. Clean and tighten, as needed.

5. Check the electrolyte fluid level. The level can be viewed through the translucent plastic case or by removing the vent caps and looking directly into each cell. The proper level is 1/2" above the separators (about 1/8" below the fill ring shown below). Add distilled water if necessary. Do not overfill.

6. Check for cloudy or discolored electrolyte caused by overcharging or vibration. This could cause high self discharge. Correct the cause and replace the battery.

State of charge

The state of charge of a battery can be easily check in one of two ways:

· Specific gravity test

·Open circuit voltage test

Specific gravity readings
By measuring the specific gravity of the electrolyte, you can tell if the battery is fully charged, requires charging, or must be replaced. It can tell you if the battery is sufficiently charged for a capacity (heavy-load) test. The battery must be at least 75% charged to perform a heavy load test. In other words, each cell must have a specific gravity of 1.230 or higher to proceed.

Cell readings percent charged
1.270 = 100 %

1.230 = 75%

1.190 = 50%

1.145 = 25%

1.100 = 0%

Open circuit voltage

A digital voltmeter must be used to check the battery’s open-circuit voltage. Analog meters are not accurate and cannot be used.

1. Turn on the headlamps’ high beam for several minutes to remove any surface charge.

2. Turn headlamps off, and connect the digital voltmeter across the battery terminals.

3. Read the voltmeter. A fully charged battery will have an open-circuit voltage of 12.6 volts.

On the other hand, a totally dead battery will have an open-circuit voltage of less than 12.0 volts.

Battery terminal cleaning
Over a period of time, sulfuric acid will corrode battery terminals, clamps, and hold-down. This corrosion adds resistance and lowers current flow to and from the battery. Corrosion can be easily cleaned with a mild solution of baking soda and water. Battery terminals and cables are routinely removed, cleaned, and reinstalled.

Battery jumping with booster cables

Jump starting a dead battery with a booster battery or battery in a car can be dangerous, so the proper sequence of connections will prevent sparks. First, connect the two positive terminals, one from the good battery and the other to the dead battery. Next connect one end of the jumper cable to the negative terminal of the booster (good) battery. Finally connect the other end to a good ground on the engine away from the dead battery. If a spark occurs, it won’t be near the battery, thus reducing the chance for explosion. If the jump starting from another vehicle, start the vehicle, running the engine at 1500 rpm for a few minutes. While the engine is running, start the dead vehicle. Never jump start a frozen battery.

Adding water

Under the rare occurrence of adding water to a battery, use only distilled water. Minerals and chemicals that are commonly found in regular drinking water will react with the plate material and shorten battery life. Under normal conditions the addition of water should not be required. However, the addition of water may be necessary when the battery has been overcharged, for overcharging results in excessive evaporation of water from the electrolyte. The water level should be no higher than 1/8 inch below the bottom of the vent well. To avoid permanent damage, make sure the electrolyte level never drops below the top of the plates. Also, avoid over filling, this may result in electrolyte overflow from the battery.

PLASMA SPRAY PROCESS

2011-03-08T07:38:00.001-08:00

PLASMA SPRAY PROCESS

An inert gas such as Argon, when excited by an electric arc, becomes partially ionized and in this state is able to carry an electric current for the generation of a hot gas stream having temperatures approaching 12,000°C. Powder material is injected into the flame at optimum conditions and projected in a semi-molten (plastic) state on to a suitably prepared work piece to form high integrity coatings of typically 0.05mm. to 3mm.thickness. The gun is manipulated by hand or by using a robot, enabling a wide range of component configurations to be coated. The Plasma Spray process is probably the most versatile of all the major Thermal Spray processes. This is predominantly due to the extremely high heat source temperatures available.The plasma generated for plasma spraying usually incorporates one or a mixture of the following gases:

• Argon
• Helium
• Nitrogen
• Hydrogen

Plasma flames for thermal spraying can produce temperatures around 7,000 to 20,000K far above the melting temperature (and vapour temperature) of any known material. The extreme temperature of the plasma is not the only reason for the effective heating properties. If for example helium gas is heated to around 13,000K without a plasma forming, it would have insufficient energy for normal plasma spraying. Nitrogen on the other hand heated to 10,000K going through dissociation and ionisation forming a plasma is an effective heating media for thermal spraying, being able to supply about six times more energy than an equal volume of helium at 13,000K. The plasma is able to supply large amounts of energy due to the energy changes associated with dissociating molecular gases to atomic gases and ionisation which occur with little change in temperature.

The Plasma Spray Process is basically the spraying of molten or heat softened material onto a surface to provide a coating. Material in the form of powder is injected into a very high temperature plasma flame, where it is rapidly heated and accelerated to a high velocity. The hot material impacts on the substrate surface and rapidly cools forming a coating. This plasma spray process carried out correctly is called a "cold process" (relative to the substrate material being coated) as the substrate temperature can be kept low during processing avoiding damage, metallurgical changes and distortion to the substrate material.

The processes gases used, in combination with the current applied to the electrode controls the amount of energy produced by the process. Since the flow of each of the gases and the applied current can be accurately regulated, repeatable and predictable coating results can be obtained. In addition, the point and angle that the material is injected into the plume, as well as the distance of the gun to the target, component can also be controlled. This provides a high degree of flexibility to develop appropriate spray parameters for materials with melting temperatures across a very large range.

The distance of the plasma gun from the target components, gun and component speeds relative to each other, and part cooling (usually with the help of air jets focused on the target substrate) keep the part at a controlled spray temperature that is usually in the range of 38 °C to 260 °C (100 °F to 500 °F).

The plasma spray gun comprises a copper anode and tungsten cathode, both of which are water cooled. Plasma gas (argon, nitrogen, hydrogen, helium) flows around the cathode and through the anode which is shaped as a constricting nozzle. The plasma is initiated by a high voltage discharge which causes localised ionisation and a conductive path for a DC arc to form between cathode and anode. The resistance heating from the arc causes the gas to reach extreme temperatures, dissociate and ionise to form a plasma. The plasma exits the anode nozzle as a free or neutral plasma flame (plasma which does not carry electric current) which is quite different to the Plasma Transferred Arc coating process where the arc extends to the surface to be coated. When the plasma is stabilised ready for spraying the electric arc extends down the nozzle, instead of shorting out to the nearest edge of the anode nozzle. This stretching of the arc is due to a thermal pinch effect. Cold gas around the surface of the water cooled anode nozzle being electrically non-conductive constricts the plasma arc, raising its temperature and velocity. Powder is fed into the plasma flame most commonly via an external powder port mounted near the anode nozzle exit. The powder is so rapidly heated and accelerated that spray distances can be in the order of 25 to 150 mm.

Plasma Spray Process advantage
Plasma spraying has the advantage that it can spray very high melting point materials such as refractory metals like tungsten and ceramics like zirconia unlike combustion processes, Plasma sprayed coatings are generally much denser, stronger and cleaner than the other thermal spray processes. Plasma spray coatings probably account for the widest range of thermal spray coatings and applications and make this process the most versatile. Disadvantages of the plasma spray process are relative high cost and complexity of process.

Features of the Atmospheric Plasma Spray Process:

Large choice of coating materials, including metals, alloys, ceramics, cermets, carbides and others.

Coating systems are possible, using layers of different materials.

Produces surfaces for a wide variety of applications, including resistance to many different types or wear and corrosion mechanisms, desirable thermal or electrical characteristics, and surface restoration and dimensional control.

Excellent control of coating thickness and surface characteristics, such as porosity and hardness .

No heat affected zone or component distortion.

High deposition rate.

High bond of the coating to the substrate.

Coating of complex geometries.

Easy masking of areas that should not be coated.

Process can be fully automated.

Coating of internal geometries possible.

WHAT IS MECHATRONICS

2011-03-08T07:31:00.001-08:00

WHAT IS MECHATRONICS

Basic Definitions

The word, mechatronics, is composed of “mecha” from mechanism and the “tronics” from electronics. In other words, technologies and developed products will be incorporating electronics more and more into mechanisms, intimately and organically, and making it impossible to tell where one ends and the other begins.

“The synergistic integration of mechanical engineering, with electronics and intelligent computer control in the design and manufacturing of industrial products and processes”.

MECHATRONICS is a methodology used for the optimal design of electromechanical products.

“A mechatronic system is not just a marriage of electrical and mechanical systems and is more than just a control system; it is a complete integration of all of them”.

All these definitions agree that mechatronics is an interdisciplinary field, in which the following disciplines act together:

• Mechanical systems (mechanical elements, machines, precision mechanics)

• Electronic systems (microelectronics, power electronics, sensor and actuator technology) and

• Information technology (systems theory, automation, software engineering, artificial intelligence)

Key Elements of Mechatronics

The study of mechatronic systems can be divided into the following areas of specialty:

1. Physical Systems Modeling

2. Sensors and Actuators

3. Signals and Systems

4. Computers and Logic Systems

5. Software and Data Acquisition

As the field of mechatronics continues to mature, the list of relevant topics associated with the area will most certainly expand and evolve.

The Development of the Automobile as a Mechatronic System

The evolution of modern mechatronics can be illustrated with the example of the automobile. Until the 1960s, the radio was the only significant electronics in an automobile. All other functions were entirely mechanical or electrical, such as the starter motor and the battery charging systems. There were no “intelligent safety systems,” except augmenting the bumper and structural members to protect occupants in case of accidents. Seat belts, introduced in the early 1960s, were aimed at improving occupant safety and were completely mechanically actuated. All engine systems were controlled by the driver and/or other mechanical control systems. For instance, before the introduction of sensors and microcontrollers, a mechanical distributor was used to select the specific spark plug to fire when the fuel–air mixture was compressed. The timing of the ignition was the control variable. The mechanically controlled combustion process was not optimal in terms of fuel efficiency. Modeling of the combustion process showed that, for increased fuel efficiency, there existed an optimal time when the fuel should be ignited. The timing depends on load, speed, and other measurable quantities.

The electronic ignition system was one of the first mechatronic systems to be introduced in the automobile in the late 1970s. The electronic ignition system consists of a crankshaft position sensor, camshaft position sensor, airflow rate, throttle position, rate of throttle position change sensors, and a dedicated microcontroller determining the timing of the spark plug firings.

The Antilock Brake System (ABS) was also introduced in the late 1970s in automobiles. The ABS works by sensing lockup of any of the wheels and then modulating the hydraulic pressure as needed to minimize or eliminate sliding.

The Traction Control System (TCS) was introduced in automobiles in the mid-1990s. The TCS works by sensing slippage during acceleration and then modulating the power to the slipping wheel. This process ensures that the vehicle is accelerating at the maximum possible rate under given road and vehicle conditions.

The Vehicle Dynamics Control (VDC) system was introduced in automobiles in the late 1990s. The VDC works similar to the TCS with the addition of a yaw rate sensor and a lateral accelerometer. The driver intention is determined by the steering wheel position and then compared with the actual direction of motion. The TCS system is then activated to control the power to the wheels and to control the vehicle velocity and minimize the difference between the steering wheel direction and the direction of the vehicle motion . In some cases, the ABS is used to slow down the vehicle to achieve desired control. In automobiles today, typically, 8, 16, or 32-bit CPUs are used for implementation of the various control systems. The microcontroller has onboard memory (EEPROM/EPROM), digital and analog inputs, A/D converters, pulse width modulation (PWM), timer functions, such as event counting and pulse width measurement, prioritized inputs, and in some cases digital signal processing. The 32-bit processor is used for engine management, transmission control, and airbags; the 16-bit processor is used for the ABS, TCS, VDC, instrument cluster, and air conditioning systems; the 8-bit processor is used for seat, mirror control, and window lift systems. Today, there are about 30–60 microcontrollers in a car.

Micro Electromechanical Systems (MEMS) is an enabling technology for the cost-effective development of sensors and actuators for mechatronics applications. Already, several MEMS devices are in use in automobiles, including sensors and actuators for airbag deployment and pressure sensors for manifold pressure measurement. Integrating MEMS devices with CMOS signal conditioning circuits on the same silicon chip is another example of development of enabling technologies that will improve mechatronic products, such as the automobile.

What do Mechatronics Engineers do?

Mechatronics combines mechanical, electrical and software engineering in the design, development and control of diverse systems used in a range of industries including manufacturing, medicine and the service industries. Examples of mechatronic systems include aircraft, dishwashers, motor vehicles, automated manufacturing plants, medical and surgical devices and systems, robots of all types, many toys, artificial organs and many others. Mechatronics engineers are therefore involved in almost every possible industry at levels from applications development to manufacturing to advanced research.

Where do Mechatronics Engineers work?

Graduates with a Mechatronics degree can take up careers in a wide spectrum of industries including robotics, aerospace, chemical, defence and automotive and manufacturing where complex software plays a major role, as well as in businesses that require extensive computer support, such as banking and commerce. Contributions can be made to these industries in a variety of roles including design engineer, software engineer, project planner, product designer and project manager.

GEARS

2011-03-08T07:16:00.000-08:00

GEARS

Gears are toothed wheels which transmit motion and power between rotating shafts by means of successively engaging teeth. They give a constant velocity ratio and different types are available to suit different relative positions of the axes of the shafts

The slipping of a belt or rope is a common phenomenon, in the transmission of motion or power between two shafts. The effect of slipping is to reduce the velocity ratio of the system. In precision machines, in which a definite velocity ratio is of importance (as in watch mechanism) , the only positive drive is by gears or toothed wheels. A gear drive is also provided, when the distance between the driver and the follower is very small.

Gears are used in tons of mechanical devices. They do several important jobs, but most important, they provide a gear reduction in motorized equipment. This is key because, often, a small motor spinning very fast can provide enough power for a device, but not enough torque. For instance, an electric screw driver has a very large gear reduction because it needs lots of torque to turn screws, but the motor only produces a small amount of torque at a high speed. With a gear reduction, the output speed can be reduced while the torque is increased.

Advantages and Disadvantages of Gear Drives
The following are the advantages and disadvantages of the gear drive as compared to other drives, i.e. belt, rope and chain drives :

Advantages
1. It transmits exact velocity ratio.
2. It may be used to transmit large power.
3. It may be used for small centre distances of shafts.
4. It has high efficiency.
5. It has reliable service.
6. It has compact layout.

Disadvantages
1. Since the manufacture of gears require special tools and equipment, therefore it is costlier than other drives.
2. The error in cutting teeth may cause vibrations and noise during operation.
3. It requires suitable lubricant and reliable method of applying it, for the proper operation of gear drives.

Classification of Gears
The gears or toothed wheels may be classified as follows :
1. According to the position of axes of the shafts. The axes of the two shafts between which he motion is to be transmitted, maybe
a) Parallel
b) Intersecting
c) Non-intersecting and non-parallel.

The two parallel and co-planar shafts connected by gears are usually spur gears and the arrangement is known as spur gearing. These gears have teeth parallel to the axis of the wheel as shown. Spur gears are one of the most used gears in the industry

Another name given to the spur gearing is helical gearing, in which the teeth are inclined to the axis. The tooth profile have an angle with rotation axis in a helical gear. Helical gears are more silent and can carry more load than spur gears. They are used in gearboxes of vehicles, gear reducers and machinery.

Another type is double helical gear.The object of the double helical gear is to balance out the end thrusts that are induced in single helical gears when transmitting load. The double helical gears are known as herringbone gears. Herringbone gears (also known as double helical gears) have two helical gears with opposite angles placed in the same body. They are generally used in rolling mills

The two non-parallel or intersecting, but coplaner shafts connected by gears is called bevel gears and the arrangement is known as bevel gearing. Bevel gears enable a change in the axes of rotation of the respective shafts, commonly 90

The bevel gears, like spur gears may also have their teeth inclined to the face of the bevel, in which case they are known as helical bevel gears. Spiral bevel gears have the same functionality with straight bevel gears. More than that, these gears are more silent and offer more load carrying capacity with higher rpm

Notes :

(i) When equal bevel gears (having equal teeth) connect two shafts whose axes are mutually perpendicular, then the bevel gears are known as mitres.

The gears may also be classified as

2. According to the peripheral velocity o fthe gears. The gears, according to the peripheral velocity of the gears, may be classified as :
(a) Low velocity, (b) Mediumvelocity, and (c) High velocity.
The gears having velocity less than 3 m/s are termed as low velocity gears and gears having velocity between 3 and 15 m/ s are known as medium velocity gears. If the velocity of gears is more than 15 m / s, then these are called high speed gears.

3. According to the type of gearing. The gears, according to the type of gearing, may be
classified as :
(a) External gearing, (b) Internal gearing, and (c) Rack and pinion.
In external gearing, the gears of the two shafts mesh externally with each other. The larger of these two wheels is called spur wheel or gear and the smaller wheel is called pinion. In an external gearing, the motion of the two wheels is always unlike .In internal gearing, the gears of the two shafts mesh internally with each other. The larger of these two wheels is called annular wheel and the smaller wheel is called pinion. In an internal gearing, the motion of the wheels is always like.

Sometimes, the gear of a shaft meshes externally and internally with the gears in a straight line, as shown in Fig. Such a type of gear is called rack and pinion. The straight line gear is called rack and the circular wheel is called pinion. A little consideration will show that with the help of a rack and pinion, we can convert linear motion into rotary motion and vice-versa. They are generally used in vinches, routers and sliding gates. A perfect example of this is the steering system on many cars. The steering wheel rotates a gear which engages the rack. As the gear turns, it slides the rack either to the right or left, depending on which way you turn the wheel.

4. According to the position of teeth on the gear surface. The teeth on the gear surface may be
(a) Straight, (b) Inclined, and (c) Curved.

We have discussed earlier that the spur gears have straight teeth where as helical gears have their teeth inclined to the wheel rim. In case of spiral gears, the teeth are curved over the rim surface.

Worm Gears

The worm gear only has one tooth but it is like a screw thread. The wormwheel is like a normal gear wheel or spur gear. The worm always drives the worm wheel round, it is never the opposite way round as the system tends to lock and jam. Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater.

Gear Ratio

The ratio of the speed of rotation of the powered gear of a gear train to that of the final or driven gear is the gear ratio. A gear ratio is a numerical value that describes the relationship between two gears (a spur and pinion gear for our discussion). A gear ratio can also describe the relationship between the FIRST gear and the LAST gear in a gear train (or a transmission). You take the number of teeth on the DRIVEN (Spur) gear and divide it by the number of teeth on the DRIVE (Pinion) gear

GEAR RATIO (VELOCITY RATIO)

The reason bicycles are easier to cycle up a hill when the gears are changed is due to what is called Gear Ratio (velocity ratio). Gear ratio can be worked out in the form of numbers and examples are shown below. Basically, the ratio is determined by the number of teeth on each gear wheel, the chain is ignored and does no enter the equation.

EXAMPLE:

Pedal gear = 60 teeth

Sprocket = 30 teeth

If the pedal gear revolves once how many times will the sprocket gear revolve?

No of teeth on pedal gear/ No of teeth on sprocket = 60/30 = 2

The example above shows that every time the pedal gear revolves once the sprocket gear on the back wheel revolves twice making it easier to cycle up hill.

Gear Ratio = 1 : 2

AC MOTOR INTRODUCTION

2011-03-08T07:12:00.001-08:00

AC MOTOR INTRODUCTION

AC motors are used worldwide in many applications to transform electrical energy into mechanical energy. There are many types of AC motors, but three phase AC induction motors, is the most common type of motor used in industrial applications. An AC motor of this type may be part of a pump or fan or connected to some other form of mechanical equipment such as a winder, conveyor, or mixer. The electric motor in its simplest terms is a converter of electrical energy to useful mechanical energy. The electric motor has played a leading role in the high productivity of modern industry, and it is therefore directly responsible for the high standard of living being enjoyed throughout the industrialized world.

AC motors provide the motive power to lift, shift, pump, drive, blow, drill, and perform a variety of other tasks in industrial, domestic, and commercial applications. The induction motor, the most versatile of the AC motors, has truly emerged as the prime mover in industry, powering machine tools, pumps, fans, compressors, and a variety of industrial equipments.

Fundamentals of three-phase AC motors
Three-phase AC motors are known as the ‘workhorses of industry’ because of their wide use and acceptance. They are popular because they are low in cost, compact in size, require less maintenance, withstand harsh industrial environments, etc. Three-phase AC motors are a class of motors that convert the three-phase electric power supplied at the input terminals, to mechanical power at the rotating shaft, through the action of a rotating magnetic field, produced by a distributed winding on the stator.

Three-phase AC motors are broadly classified as:
1. Induction motor
2. Synchronous motor
3. Wound rotor induction motor.

1. Induction motor
As the name implies, no voltage is applied to the rotor. The voltage is applied to the stator winding and when the current flows in the stator winding, a current is induced in the rotor by transformer action. The resulting rotor magnetic field will interact with the stator magnetic field, causing torque to exert on the rotor.

2. Synchronous motor
As the name suggests, rotor speed remains in synchronism with that of the stator magnetic field. The motor runs at the same speed. Unlike induction motors, synchronous motors are not self-starting. They have to be brought up to synchronous speed. Once they are locked then the rotor will continuously rotate.

3. Wound rotor induction motor
This motor has a ‘wire wound rotor’ from which three leads are brought out to the slip rings. It is possible to vary the rotor resistance. Introducing different resistances in the rotor circuit through the slip rings does this. The speed and the starting torque will now be variable.

Principle of operation of a induction motor
An electric motor’s principle of operation is based on the fact that a current-carrying conductor, when placed in a magnetic field, will have a force exerted on the conductor proportional to the current flowing in the conductor and to the strength of the magnetic field. In alternating current induction motors, the windings placed in the laminated stator core produce the magnetic field. The aluminum bars in the laminated rotor core are the current-carrying conductors upon which the force acts. The resultant action is the rotary motion of the rotor and shaft, which can then be coupled to various devices to be driven and produce the output.

FORCE & MOTION

Before discussing AC motors it is necessary to understand some of the basic terminology associated with motor operation. Force In simple terms, a force is a push or a pull. Force may be caused by electromagnetism, gravity, or a combination of physical means. Net Force Net force is the vector sum of all forces that act on an object, including friction and gravity. When forces are applied in the same direction, they are added. For example, if two 10 pound forces are applied in the same direction the net force would be 20 pounds.

TORQUE
Torque is a twisting or turning force that causes an object to rotate. For example, a force applied to the end of a lever causes a turning effect or torque at the pivot point. Torque (τ) is the product of force and radius (lever distance). τ = Force x Radius In the English system of measurements, torque is measured in pound-feet (lb-ft) or pound inches (lb-in). For example, if 10 lbs of force is applied to a lever 1 foot long, the resulting torque is 10 lb-ft.

SPEED
An object in motion takes time to travel any distance. Speed is the ratio of the distance traveled and the time it takes to travel the distance.

ANGULAR SPEED
The angular speed of a rotating object determines how long it takes for an object to rotate a specified angular distance. Angular speed is often expressed in revolutions per minute (RPM). For example, an object that makes ten complete revolutions in one minute, has a speed of 10 RPM.

INERTIA

Mechanical systems are subject to the law of inertia. The law of inertia states that an object will tend to remain in its current state of rest or motion unless acted upon by an external force. This property of resistance to acceleration/deceleration is referred to as the moment of inertia. The English system unit of measurement for inertia is pound-feet squared (lb-ft2).

FRICTION

Friction occurs when objects contact one another. As we all know, when we try to move one object across the surface of another object, friction increases the force we must apply. Friction is one of the most significant causes of energy loss in a machine.

WORK
Whenever a force causes motion, work is accomplished. Work can be calculated simply by multiplying the force that causes the motion times the distance the force is applied. Work = Force x Distance Since work is the product of force times the distance applied, work can be expressed in any compound unit of force times distance. For example, in physics, work is commonly expressed in joules. 1 joule is equal to 1 newton-meter, a force of 1 newton for a distance of 1 meter. In the English system of measurements, work is often expressed in foot-pounds (ft-lb), where 1 ft-lb equals 1 foot times 1 pound

POWER
Another often used quantity is power. Power is the rate of doing work or the amount of work done in a period of time.

HORSEPOWER
Power can be expressed in foot-pounds per second, but is often expressed in horsepower. This unit was defined in the 18 th century by James Watt. Watt sold steam engines and was asked how many horses one steam engine would replace. He had horses walk around a wheel that would lift a weight. He found that a horse would average about 550 foot-pounds of work per second. Therefore, one horsepower is equal to 550 foot-pounds per second or 33,000 foot-pounds per minute.

KILOWATTS

AC motors manufactured in the United States are generally rated in horsepower, but motors manufactured in many other countries are generally rated in kilowatts (kW). Fortunately it is easy to convert between these units
Horsepower=1.341 * kilowatts

CONSTRUCTION
Three-phase AC induction motors are commonly used in industrial applications. This type of motor has three main parts, rotor, stator, and enclosure. The stator and rotor do the work, and the enclosure protects the stator and rotor.
The stator is the stationary part of the motor’s electromagnetic circuit. The stator core is made up of many thin metal sheets, called laminations. Laminations are used to reduce energy loses that would result if a solid core were used. Stator laminations are stacked together forming a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core,

The rotor is the rotating part of the motor’s electromagnetic circuit. The most common type of rotor used in a three phase induction motor is a squirrel cage rotor. Other types of rotor construction is discussed later in the course. The squirrel cage rotor is so called because its construction is reminiscent of the rotating exercise wheels found in some pet cages

ENCLOSURE
The enclosure consists of a frame (or yoke) and two end brackets (or bearing housings). The stator is mounted inside the frame. The rotor fits inside the stator with a slight air gap separating it from the stator. There is no direct physical connection between the rotor and the stator.

BEARING
Bearings, mounted on the shaft, support the rotor and allow it to turn. Some motors also use a fan mounted on the rotor shaft, to cool the motor when the shaft is rotating.

MOTOR SPECIFICATIONS (Important Nameplate Data)
• Catalog number.
• Motor model number.
• Frame.
• Type (classification varies from manufacturer to manufacturer).
• Phase - single, three or direct current.
• HP - horsepower at rated full load speed.
• HZ - frequency in cycles per second. Usually 60 hz in United States,
50 hz overseas.
• RPM - revolutions per minute.

• Voltage.
• Amperage (F.L.A.) - full load motor current.
• Maximum ambient temperature in centigrade - usually +40°C (104°F).
• Duty - most motors are rated continuous. Some applications,
however, may use motors designed for intermittent, special, 15, 30 or
60 minute duty.
• NEMA electrical design - B, C and D are most common. Design letter
represents the torque characteristics of the motor.
• Insulation class - standard insulation classes are B, F, and H. NEMA has
established safe maximum operating temperatures for motors. This
maximum temperature is the sum of the maximum ambient and
maximum rise at maximum ambient.
• Code - indicates locked rotor kVA per horsepower.
• Service factor - a measure of continuous overload capacity.

Electrical Characteristics and Connections
Voltage, frequency and phase of power supply should be consistent with the motor nameplate rating. A motor will operate satisfactorily on voltage within 10% of nameplate value, or frequency within 5%, or combined voltage and frequency variation not to exceed 10%.

Voltage
Common 60 hz voltages for single-phase motors are 115 volt, 230 volt, and
115/230 volt. Common 60 hz voltage for three-phase motors are 230 volt, 460 volt and 230/460 volt.

Phase
Single-phase motors account for up to 80% of the motors used in the United States but are used mostly in homes and in auxiliary low-horsepower industrial applications such as fans and on farms.

Three-phase motors are generally used on larger commercial and industrial equipment.

Speeds
The approximate RPM at rated load for small and medium motors operating at 60 hz and 50 hz at rated volts are as follows:
60 hz 50 hz Synch. Speed
2 Pole 3450 2850 3600
4 Pole 1725 1425 1800
6 Pole 1140 950 1200
8 Pole 850 700 900

Synchronous speed (no-load) can be determined by this formula:
Frequency (Hertz) x 120 / Number of Poles

Insulation Class
Insulation systems are rated by standard NEMA classifications according to maximum allowable operating temperatures. They are as follows:
Class Maximum Allowed Temperature*
A 105°C (221°F)
B 130°C (266°F)
F 155°C (311°F)
H 180°C (356°F)
* Motor temperature rise plus maximum ambient

Generally, replace a motor with one having an equal or higher insulation class. Replacement with one of lower temperature rating could result in premature failure of the motor. Each 10°C rise above these ratings can reduce the motor’s service life by one half.

Service Factor
The service factor (SF) is a measure of continuous overload capacity at which a motor can operate without overload or damage, provided the other design parameters such as rated voltage, frequency and ambient temperature are within norms. Example: a 3/4 HP motor with a 1.15 SF can operate at .86 HP, (.75 HP x 1.15 = .862 HP) without overheating or otherwise damaging the motor if rated voltage and frequency are supplied at the motor’s leads.

BASIC ELECTRICAL CONCEPTS

2011-03-08T06:48:00.001-08:00

BASIC ELECTRICAL CONCEPTS

Basic electrical concepts

In each plant, the mechanical movement of different equipments is caused by an electric prime mover (motor). Electrical power is derived from either utilities or internal generators and is distributed through transformers to deliver usable voltage levels.

Electricity is found in two common forms:

• AC (alternating current)

• DC (direct current).

Electrical equipments can run on either of the AC/DC forms of electrical energies. The selection of energy source for equipment depends on its application requirements. Each energy source has its own merits and demerits.

Industrial AC voltage levels are roughly defined as LV (low voltage) and HV (high voltage) with frequency of 50–60 Hz. An electrical circuit has the following three basic components irrespective of its electrical energy form:

• Voltage (volts)

• Ampere (amps)

• Resistance (ohms).

1. Voltage is defined as the electrical potential difference that causes electrons to flow.

2. Current is defined as the flow of electrons and is measured in amperes.

3. Resistance is defined as the opposition to the flow of electrons and is measured in ohms.

All three are bound together with Ohm’s law, which gives the following relation between the three:

V = I × R

(a) Power

In DC circuits, power (watts) is simply a product of voltage and current.

P =V × I

For AC circuits, the formula holds true for purely resistive circuits; however, for the following types of AC circuits, power is not just a product of voltage and current.

Apparent power is the product of voltage and ampere, i.e., VA or kVA is known as apparent power. Apparent power is total power supplied to a circuit inclusive of the true and reactive power.

Real power or true power is the power that can be converted into work and is measured in watts

Reactive power If the circuit is of an inductive or capacitive type, then the reactive component consumes power and cannot be converted into work. This is known as reactive power and is denoted by the unit VAR.

(b) Relationship between powers

Apparent power (VA) = V × A

True power (Watts) = VA × cosφ

Reactive power (VAR) = VA × sinφ

(c) Power factor

Power factor is defined as the ratio of real power to apparent power. The maximum value it can carry is either 1 or 100(%), which would be obtained in a purely resistive circuit.

Power factor = True power / Apparent power

Types of circuits

There are only two types of electrical circuits – series and parallel.

A series circuit is defined as a circuit in which the elements in a series carry the same current, while voltage drop across each may be different.

A parallel circuit is defined as a circuit in which the elements in parallel have the same voltage, but the currents may be different.

Transformer

A transformer is a device that transforms voltage from one level to another. Transformer working is based on mutual emf induction between two coils, which are magnetically coupled. When an AC voltage is applied to one of the windings (called as the primary), it produces alternating magnetic flux in the core made of magnetic material (usually some form of steel). The flux is produced by a small magnetizing current which flows through the winding. The alternating magnetic flux induces an electromotive force (EMF) in the secondary winding magnetically linked with the same core and appears as

a voltage across the terminals of this winding. Cold rolled grain oriented (CRGO) steel is used as the core material to provide a low reluctance, low loss flux path. The steel is in the form of varnished laminations to reduce eddy current flow and losses on account of this.

There is a very simple and straight relationship between the potential across the primary coil and the potential induced in the secondary coil. The ratio of the primary potential to the secondary potential is the ratio of the number

of turns in each and is represented as follows:

N1/N2 = V1/V2

Current-induced

When the transformer is loaded, then the current is inversely proportional to the voltages and is represented as follows:

N1/N2 = V1/V2= I2/I1

NON DESTRUCTIVE TECHNIQUES

2011-03-08T06:34:00.000-08:00

NON DESTRUCTIVE TECHNIQUES

Nondestructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation, troubleshooting, and research. Common NDT methods include ultrasonic, magnetic particle, liquid penetrant, radiographic, and eddy-current testing. Penetrant is used to check discontinuities i.e cracks, pits etc open to the surface on parts made of non porous materials. This method depends on the ability of the penetrant to enter into a surface discontinuity in the material to which it is applied. It is applicable to all solid non-porous material

Types
1. Fluorescent Penetrant inspection (fpi)
2. Magnetic particle inspection (mpi)
3. Ultrasonic
4. Eddy Current
5. X-ray

1. FLUORESCENT PENETRANT INSPECTION (FPI)
This is a method which can be employed for the detection of open to surface discontinuities in any industrial product which is made from a non porous material. This method is widely used for testing of nonmagnetic materials. In this method liquid penetrant is applied to the surface of the product for a certain predetermined time, after which the excess penetrant is removed from the surface. The surface is then dried and a developer is applied to it. The penetrant which remains in the discontinuity is absorbed by the developer to indicate the presence as well as the location, size and the nature of the discontinuity. Penetrants used in liquid penetrant are either visible dye penetrant or fluorescent dye penetrant. The inspection of the presence of indications dye visible by penetrant is made under white light while inspection of presence of indications by fluorescent dye penetrant is made under ultra violet (or black) light under darken condition. The liquid penetrant processes are further subdivided according to the method of washing of the specimen. The penetrants can be:

Water washable.

Post emulsifiable, i.e. an emulsifier is added to the excess penetrant or surface of the specimen to make it water washable, and

Solvent removable, i.e. the excess penetrant is needed to be dissolved in a solvent to remove it from the Test Specimen surface.

Advantages

• Capable of examining all of the exterior surface of objects
• Capable of detecting very small surface discontinuities
• Can be used on a wide variety of materials ferrous and non-ferrous
• Can be accomplished with relatively inexpensive non sophisticated equipment

Types of penetrant
• Visible dye
• Fluorescent
• Dual mode(Visible dye & Fluorescent)

Steps involved in FPI
1. Step 1 Cleaning
Removes oil, soil, moisture inside flaw or on part surface

2. Step 2 Penetrant Application
Penetrant applied to the surface of the clean part. It is allowed to remain on the surface of the part surface for a period of time to allow it to enter and fill any openings or discontinuities open to the surface

3. Step 3 Washing
After a suitable dwell period , penetrant is removed from the part surface

4. Step 4 Drying
The part is dried

5. Step 5 Developer
A material called developer is then applied. The developer aids in drawing any trapped penetrant from discontinuities and improves visibility of indications

6. Step 6 Inspection
This step involves visual inspection under appropriate lighting conditions

Function of Developer
The basic function of developers is to improve the visibility of the entrapped penetrant indication. The improvement in visibility is achieved through a number of mechanisms that includes the following
• Assists in extracting the entrapped penetrant from discontinuities
•Spread or disperse the extracted penetrant laterally on the surface thus increasing the apparent size of the indication
• Improve the contrast between the indication & background

Visual inspection (Lighting)
When fluorescent materials are energized by ultraviolet radiations visible light is emitted. Visual inspection is one of the most common and most powerful means non-destructive testing. Visual testing requires adequate illumination of the test surface and proper eye-sight of the Inspector

2) MAGNETIC PARTICLE TESTING
A process of non-destructive testing for detecting surface and sub-surface defects in magnetic retentive materials. The process uses externally applied magnetic field or the part is magnetized using; either AC or DC current passed through the part. With the principle of magnetic flux a leakage field is created at discontinuities i.e. (cracks, voids).The presence of a surface or sub surface flaw (void or crack) in the material allows the magnetic flux to leak at the flaw. This deformation of the magnetic field is not limited to the immediate locality of the defect but extends outside the part. The distance the leakage field extends to the surface and to the outside of the part into air relates to the strength of the magnetic field induced into the part. The amount of magnetism relates to the size of the part and amount of current AC or DC or externally applied magnetic field to magnetize the part. This allows different types of magnetic particles commonly Iron Oxide to gather at the leakage field.

A discontinuity which crosses the magnetic field creates north & south poles on either side of the defect area. When magnetic particles are applied to the part, the poles attract the particles and an indication of the discontinuity is formed. Mainly uses for detecting surface & sub surface discontinuities in ferromagnetic materials.

Magnetic particle inspection is a nondestructive testing method which can be used in the evaluation of all ferrous materials. Like other forms of nondestructive testing, this method has the advantage of not damaging or compromising the materials being tested during the testing process. This method is one of the fastest and least expensive ways to test ferrous materials before certifying them as safe and ready for use.

3) ULTRASONIC INSPECTION
This method uses ultrasound to detect internal discontinuities. it can be used to measure the overall thickness of the material and the specific depth of a defect. The term ultrasonic pertains to sound waves having a frequency greater than 20000 Hz. Ultrasonic vibrations are generated by applying high frequency electrical pulses to a transducer element (piezoelectric element) contained within a search unit. Ultrasonic energy is transmitted between the search unit & the test part through a coupling medium such as oil, grease

Ultrasonic testing is often performed on steel and other metals and alloys, though it canalso be used on concrete, wood and composites, albeit with less resolution. It is a formof non-destructive testing used in many industries including aerospace, automotive and other transportation sectors.

4) EDDY-CURRENT TESTING
Eddy-Current Testing is an electrical NDT method which can be used to detect and quantify surface breaking or near surface defects in materials, components and structures. It is a non-contact method, and can successfully test through good quality paint coatings etc. it is used to detect discontinuities in parts that are conductors of electricity. Eddy currents are electrical currents inducedin a conductor by a changing magnetic field. When eddy currents encounter an obstacle, such as crack the surroundings become distorted. The change is detected on a meter or other type of display

Principle of Operation
A coil energized by an AC current is placed in close proximity to the test specimen (which must be an electrically conducting material). The current inthe coil generates a magnetic field which induces currents to flow in the specimen. These currents (the “eddy-currents”) generate their own magnetic field, which interacts with the original field.

Changes in the field, due to the presence of defects etc, cause changes to the coil’s impedance which are displayed on the screen of the eddy-current flaw detector instrument

5) RADIO-GRAPHIC TESTING (X-RAY INSPECTION)
Radiography (x-ray) is an NDI method used to inspect material and components, using the concept of differential adsorption of penetrating radiation. A material discontinuity such as void or change in configuration changes the effective thickness of a material and thus changes the degree of radiation absorption. Each specimen under evaluation will have differences in density, thickness, shapes, sizes, or absorption characteristics, thus absorbing different amounts of radiation. The unabsorbed radiation that passes through the part is recorded on film, fluorescent screens, or other radiation monitors. Indications of internal and external conditions will appear as variants of black/white/gray contrasts on exposed film, or variants of color on fluorescent screens.

The radiographic testing method is used for the detection of internal flaws in many different materials and configurations. An appropriate radiographic film is placed behind the test specimen and is exposed by passing either X-rays or gamma rays (Co-60& Ir-192 radioisotopes) through it. The intensity of the X-rays or gamma rays while passing through the product is modified according to the internal structure of the specimen and thus the exposed film, after processing, reveals the shadow picture, known as a radiograph, of the product. It is then interpreted to obtain data about the flaws present in the specimen. This method is used on wide variety of product such as forging, casting and weldments

X & gamma radiographic inspection uses the penetrating abilities of electromagnetic radiations to examine the interior of objects.

Limitations
Compared to other nondestructive methods of inspection, radiography is expensive. Relatively large costs and space allocations are required for a radiographic laboratory. Costs can be reduced considerably when portable x-ray or gamma-ray sources are used in film radiography and space is required only for film processing and interpretation. Operating costs can be high because sometimes as much as 60 percent of the total inspection time is spent in setting up for radiography. With real-time radiography, operating costs are usually much lower, because setup times are shorter and there are no extra costs for processing or interpretation of film.

*****ENGINEERING*****

HONING

The Turbine Flow Meter and its Calibration

INDUSTRIAL LIGHTNING SYSTEM

STRESS

INTERNET: AN INTRODUCTION

TRANSFORMERS

Introduction to Jet Engines

BEARINGS

INTRODUCTION TO AEROPLANE

Automotive battery basics

PLASMA SPRAY PROCESS

WHAT IS MECHATRONICS

What do Mechatronics Engineers do?

Where do Mechatronics Engineers work?

GEARS

AC MOTOR INTRODUCTION

BASIC ELECTRICAL CONCEPTS

NON DESTRUCTIVE TECHNIQUES

ENGINEERING