ELECTRICAL AND ELECTRONICS ENGINEERING..!!

What is Buchholz Relay ?

2012-11-24T08:34:00.000-08:00

Buchholz Relay principle

The Buchholz Relay working principle of is very simple. Buchholz Relay function is based on very simple mechanical phenomenon. It is mechanically actuated. Whenever there will be a minor internal fault in the transformer such as an insulation faults between turns, break down of core of transformer, core heating, the transformer insulating oil will be decomposed in different hydrocarbon gases, CO2 and CO. The gases produced due to decomposition of transformer insulating oil will accumulate in the upper part the Buchholz Container which causes fall of oil level in it. Fall of oil level means lowering the position of float and thereby tilting the mercury switch. The contacts of this mercury switch are closed and an alarm circuit energized. Sometime due to oil leakage on the main tank air bubbles may be accumulated in the upper part the Buchholz Container which may also cause fall of oil level in it and alarm circuit will be energized. By collecting the accumulated gases from the gas release pockets on the top of the relay and by analyzing them one can predict the type of fault in the transformer.

More severe types of faults, such as short circuit between phases or to earth and faults in the tap changing equipment, are accompanied by a surge of oil which strikes the baffle plate and causes the mercury switch of the lower element to close. This switch energized the trip circuit of the Circuit Breakers associated with the transformer and immediately isolate the faulty transformer from the rest of the electrical power system by inter tripping the Circuit Breakers associated with both LV and HV sides of the transformer. This is how Buchholz Relay functions.

Construction of Buchholz Relay

Buchholz Relay in transformer is an oil container housed the connecting pipe from main tank to conservator tank. It has mainly two elements. The upper element consists of a float. The float is attached to a hinge in such a way that it can move up and down depending upon the oil level in the Buchholz Relay Container. One mercury switch is fixed on the float. The alignment of mercury switch hence depends upon the position of the float.

The lower element consists of a baffle plate and mercury switch. This plate is fitted on a hinge just in front of the inlet (main tank side ) of Buchholz Relay in transformer in such a way that when oil enters in the relay from that inlet in high pressure the alignment of the baffle plate along with the mercury switch attached to it, will change. In addition to these main elements a Buchholz Relay has gas release pockets on top. The electrical leads from both mercury switches are taken out through a molded terminal block.

Buchholz Relay Operation – Certain Precaution

The Buchholz Relay operation may be actuated without any fault in the transformer. For instance, when oil is added to a transformer, air may get in together with oil, accumulated under the relay cover and thus cause a false Buchholz Relay operation. That is why mechanical lock is provided in that relay so that one can lock the movement of mercury switches when oil is topping up in the transformer. This mechanical locking also helps to prevent unnecessary movement of breakable glass bulb of mercury switches during transportation of the Buchholz Relays.

The lower float may also falsely operate if the oil velocity in the connection pipe through, not due to internal fault, is sufficient to trip over the float. This can occurs in the event of external short circuit when over currents flowing through the winding cause overheated the copper and the oil and cause the oil to expand.

TRANSDUCERS

2012-06-28T21:46:00.001-07:00

In general terms, the transduction process involves the transformation of oneform of energy into another form. This process consists of sensing withspecificity the input energy from the measurand by means of a “sensing element” and then transforming it into another form by a “transductionelement.”

The sensor-transduction element combination shown in Fig. 5.1 will henceforth be referred to as the “transducer.” Measurand relates to the quantity, property, or state that the transducer seeks to translate into an electrical output.

As an example, consider a “walkie-talkie” intercom set where the loudspeaker also functions as a microphone. At the input end, the loudspeaker functions as an acousto electric transducer and at the output end as an electro acoustic transducer. Moreover, in the reverse direction, the functions of the loudspeakers are interchanged, and for this reason we say that the loud-speaker is a bidirectional transducer and the transduction process is reversible.

Another example of reversible transduction is seen in piezoelectric materials; when an electric voltage is applied to the faces of a piezoelectric substrate, it produces a change in its physical dimensions; and conversely, when the material is physically deformed, an electric charge is generated on these faces.

In this transducer, the sensing and transduction functions cannot be separated as easily, and it represents a good example of a practical transducer used in the field of nondestructive testing (NDT) of materials and in medical ultrasound imaging of body tissues and organs. This is a bidirectional transducer, but most practical transducers are not bidirectional.

Transducers may be classified as self-generating or externally powered.

Fig 5.1. Sensor-Transduction Element Combination

Windows 7 - The Missing Manual

2012-01-18T09:14:00.000-08:00

Windows has recently been going through a tough phase of its glorious legacy in the world of technology which it has dominated for the past few decades. Its internet Browser "internet explorer" is getting upstaged by other browsing engines like Mozilla Firefox and Google Chrome while it also went through that fiasco of Vista which really was shockingly bad.
So it was no surprise when I found myself holding onto XP and waiting for what else Microsoft would come up with. Trust the worlds richest man and he came up with the Windows 7. Though I wanted to do a head bang on it right away! the prospect of going through another technical manual which would have me scratching my head was not exactly tempting.
In computer book land, you either get lame introduction type material which leaves you with only the basics and at times actually makes you feel like a lost soul, or you get a thoroughly informative book that puts you into a short lived coma.

At this critical juncture of time enter Windows 7 - The Missing Manual.

The Missing Manual is a guide to everything that you need to know regarding Microsoft's newest adventure. One may ask how is it any different from the other manuals that continue to bore us to death. The answer lies in the fact that it does exactly the opposite of what the other manuals do i.e. it does not bore you. The language used by the author is a conversational one that everyone can comprehend making the material extremely simple to grasp.

The flow of this book allows you to move from section to section without there being a "hard" interruption in between, the index and appendix are top notch for anyone choosing to pick helpful nuggets here and there. The bad aspect of other books are that the humour in them is so false that it actually irritates you rather than lightening your mood. Although the book will not make you roll all over the floor, it will bring a lot of smiles to your face making your read enjoyable.

If you want a comprehensive manual for Windows 7 that is useful for beginners through to advanced users then get the book that Microsoft forgot to put in your box.

If you would like to read a chapter of this comprehensive guide click here

For your chance to get a free iPad or Amazon Kindle do check out http://powerfulreviews.com thanks.

My New iPad: A User's Guide Book Review

2012-01-18T09:10:00.000-08:00

Wallace Wang, best seller of My New Mac and My New iPhone for the No Starch Press publisher has written a new book detailing everything you need to know about the iPad in a book called "My New iPad: A User's Guide." No Starch Press provided a reviewer's copy of "My New iPad: A User's Guide" for this review.
"My New iPad: A User's Guide" includes seven chapters including: basic training; customizing your iPad; getting on the Internet; sharing data with your iPad; video, music, and eBooks; organizing yourself and additional tips. Each chapter is small and comes in easily consumable chunks of information that can instantly help new users complete a certain task with easy to follow step by step instructions.
The first chapter called "Basic Training" teaches you how to turn on and off the iPad, what the various buttons and slides perform and how to use and customize the virtual keyboard. Apple changed the Screen Location Lock since the book was published so information has changed since the publish date resulting in incorrect information.

"Customizing Your iPad" is the second chapter that details how to customize your home screen, set the date and time, restoring and resetting your iPad and installing and uninstalling iPad apps.

The third chapter called "Getting on the Internet" shows how to use the email client and web browser called Safari including some intermediate information such as how to use bookmarks and automatically fill out forms with Safari.

If you do not know how to transfer content to your iPad, chapter four is perfect for you. "Sharing Data with Your iPad" shows how to synchronize with iTunes to transfer media such as photos, movies, TV shows and even podcasts. The chapter further goes on to show steps to synch your eBooks, Audio Books, Contacts, Appointments, Mail, Notes, Bookmarks and even iTunes University Courses. The book is light on how to actually configure Yahoo! or Google services with your iPad however.

The next chapter focuses on content consumption on the iPad and it titled "Video, Music and eBooks". This chapter shows you how to watch your photos to listen to your music to watching YouTube videos.

Chapter six focuses on how to use the iPad to keep yourself organized using included iPad apps and is called "Organizing Yourself."

Finally, the last chapter called "Additional Tips" provides some additional miscellaneous tips including how to update the iOS or use foreign languages. This last chapter also includes a section called "Best iPad Apps" which includes some good apps but is dated. To keep up with the best iPad apps, you should watch for articles that continually are updated such as the Gizmos for Geeks Favorite iPad Apps monthly updated list.

I started and finished "My New iPad: A User's Guide" in one afternoon. The book is geared towards new users of not only the iPad device but of Apple's iOS devices including iPod Touch and iPhones and definitely not towards advanced user's of the iOS. For example, this book would be ideal for my parents since they have never used an iOS device, but I found the book way to simplistic to really become engaged.

Doug Felteau enjoys blogging about the latest gadgets and anything technology related and maintains a monthly article on Gizmos for Geeks listing the best iPad apps. An avid iPad user since the device was released, Doug has integrated the device and apps into his everyday life.

High Ohmic Series Resistance with Micro ammeter

2012-01-08T10:25:00.000-08:00

High D.C. voltages are usually measured by connecting a very high resistance (few hundreds of mega ohms) in series with a micro ammeter. Only the current flowing through the large calibrated resistance R is measured by the moving coil micro ammeter. The voltage of the source is given by

Series resistance micrometer

The voltage drop in the meter is negligible, as the impedance of the meter is only few ohms com pared to few hundred mega-ohms of the series resistance R. A protective device like a paper gap, a neon glow tube, or a zener diode with a suitable series resistance is connected across the meter as a protection against high voltages in case the series resistance R fails or flashes over. The ohmic value of the series resistance R is chosen such that a current of one to ten microamperes is allowed for full-scale deflection. The resistance is constructed from a large number of wire wound resistors in series. The voltage drop in each resistor element is chosen to avoid surface flashovers and discharges. A value of less than 5 kv /cm in air or less than 20 kV/cm in good oil is permissible. The resistor chain is provided with corona free terminations. The material for resistive elements is usually a carbon-alloy with temperature coefficient less than 1T Carbon and other metallic film resistors are also used. A resistance chain built with ±1% carbon resistors located in airtight transformer oil filled P.V.C. tube, for 100 kV operations had very good temperature stability.

The limitations in the series resistance design are:

•   Power dissipation and source loading

•   Temperature effects and long time stability

•   Voltage dependence of resistive elements, and

•   Sensitivity to mechanical stresses

Series resistance meters are built for 500kV D.C. with accuracy better than 0.2%.

Welding:

2012-01-08T08:15:00.000-08:00

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the work pieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld.

This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the work pieces to form a bond between them, without melting the work pieces

Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding can be done in many different environments, including open air, under water and in outer space. Regardless of location, however, welding remains dangerous, and precautions must be taken to avoid burns, electric shock, eye damage, poisonous fumes, and overexposure to ultraviolet light.

Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for centuries to join metals by heating and pounding them. Arc welding and oxyfuel welding were among the first processes to develop late in the century, and resistance welding followed soon after.

Welding technology advanced quickly during the early 20th century as World War I and World War II drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like shielded metal arc welding, now one of the most popular welding methods, as well as semi-automatic and automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc welding and electroslag welding. Developments continued with the invention of laser beam welding and electron beam welding in the latter half of the century. Today, the science continues to advance. Robot welding is becoming more commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality and properties.

Potentiometric Type Digital Voltmeter

2011-12-31T13:12:00.000-08:00

•    A potentiometric type of DVM employs voltage comparison technique. In this DVM the unknown voltage is compared with reference voltage whose value is fixed by the setting of the calibrated potentiometer.

•    The potentiometer setting is changed to obtain balance (i.e. null conditions).

•    When null conditions are obtained the value of the unknown voltage, is indicated by the dial setting of the potentiometer.

•    In potentiometric type DVMs, the balance is not obtained manually but is arrived at automatically.

•    Thus, this DVM is in fact a self- balancing potentiometer.

•    The potentiometric DVM is provided with a readout which displays the voltage being measured.

•   The block diagram of basic circuit of a potentiometric DVM is shown.

•   The unknown voltage is filtered and attenuated to suitable level.

•   This input voltage is applied to a comparator (also known as error detector).

•   This error detector may be chopper.

•   The reference voltage is obtained from a fixed voltage source.

•   This voltage is applied to a potentiometer.

•   The value of the feedback voltage depends up the position of the sliding contact.

•   The feedback voltage is also applied to the comparator.

•   The unknown voltage and the feedback voltages are compared in the comparator.

•   The output voltage of the comparator is the difference of the above two voltages.

•   The difference of voltage is called the error signal.

•   The error signal is amplified and is fed to a potentiometer adjustment device, which moves the sliding contact of the potentiometer.

•   This magnitude by which the sliding contact moves depends upon the magnitude of the error signal.

•   The direction of movement of slider depends upon whether the feedback voltage is larger or the input voltage is larger.

•   The sliding contact moves to such a place where the feedback voltage equals the unknown voltage.

•   In that case, there will not be any error voltage and hence there will be no input to the device adjusting the position of the sliding contact and therefore it (sliding contact) will come to rest.

•   The position of the potentiometer adjustment device at this point is indicated in numerical form on the digital readout device associated with it.

Since the position at which no voltage appears at potentiometer adjustment device is the one where the unknown voltage equals the feedback voltage, the reading of readout device indicates the value of unknown voltage.

BIPOLAR TRANSISTORS

2011-11-04T06:33:00.000-07:00

Bipolar Transistor Basics

In the Diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material, either silicon or germanium to form a simple PN-junction and we also learnt about their properties and characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-junctions connected together in series that share a common P or N terminal. The fusion of these two diodes produces a three layer, two junction, three terminal device forming the basis of a Bipolar Junction Transistor, or BJT for short.

Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistor's ability to change between these two states enables it to have two basic functions: "switching" (digital electronics) or "amplification" (analogue electronics). Then bipolar transistors have the ability to operate within three different regions:

1. Active Region - the transistor operates as an amplifier and Ic = β.Ib
2. Saturation - the transistor is "fully-ON" operating as a switch and Ic = I(saturation)
3. Cut-off - the transistor is "fully-OFF" operating as a switch and Ic = 0

Typical Bipolar Transistor

The word Transistor is an acronym, and is a combination of the words Transfer Varistor used to describe their mode of operation way back in their early days of development. There are two basic types of bipolar transistor construction, PNP and NPN, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made.

The Bipolar Transistor basic construction consists of two PN-junctions producing three connecting terminals with each terminal being given a name to identify it from the other two. These three terminals are known and labelled as the Emitter ( E ), the Base ( B ) and the Collector ( C ) respectively.

Bipolar Transistors are current regulating devices that control the amount of current flowing through them in proportion to the amount of biasing voltage applied to their base terminal acting like a current-controlled switch. The principle of operation of the two transistor types PNP and NPN, is exactly the same the only difference being in their biasing and the polarity of the power supply for each type.

Bipolar Transistor Construction

The construction and circuit symbols for both the PNP and NPN bipolar transistor are given above with the arrow in the circuit symbol always showing the direction of "conventional current flow" between the base terminal and its emitter terminal. The direction of the arrow always points from the positive P-type region to the negative N-type region for both transistor types, exactly the same as for the standard diode symbol.

Bipolar Transistor Configurations

As the Bipolar Transistor is a three terminal device, there are basically three possible ways to connect it within an electronic circuit with one terminal being common to both the input and output. Each method of connection responding differently to its input signal within a circuit as the static characteristics of the transistor vary with each circuit arrangement.

1. Common Base Configuration - has Voltage Gain but no Current Gain.
2. Common Emitter Configuration - has both Current and Voltage Gain.
3. Common Collector Configuration - has Current Gain but no Voltage Gain.

The Common Base (CB) Configuration

As its name suggests, in the Common Base or grounded base configuration, the BASE connection is common to both the input signal AND the output signal with the input signal being applied between the base and the emitter terminals. The corresponding output signal is taken from between the base and the collector terminals as shown with the base terminal grounded or connected to a fixed reference voltage point. The input current flowing into the emitter is quite large as its the sum of both the base current and collector current respectively therefore, the collector current output is less than the emitter current input resulting in a current gain for this type of circuit of "1" (unity) or less, in other words the common base configuration "attenuates" the input signal.

The Common Base Transistor Circuit

This type of amplifier configuration is a non-inverting voltage amplifier circuit, in that the signal voltages Vin and Vout are in-phase. This type of transistor arrangement is not very common due to its unusually high voltage gain characteristics. Its output characteristics represent that of a forward biased diode while the input characteristics represent that of an illuminated photo-diode. Also this type of bipolar transistor configuration has a high ratio of output to input resistance or more importantly "load" resistance (RL) to "input" resistance (Rin) giving it a value of "Resistance Gain". Then the voltage gain (Av) for a common base configuration is therefore given as:

Common Base Voltage Gain

Where: Ic/Ie is the current gain, alpha (α) and RL/Rin is the resistance gain.

The common base circuit is generally only used in single stage amplifier circuits such as microphone pre-amplifier or radio frequency (Rf) amplifiers due to its very good high frequency response.

The Common Emitter (CE) Configuration

In the Common Emitter or grounded emitter configuration, the input signal is applied between the base, while the output is taken from between the collector and the emitter as shown. This type of configuration is the most commonly used circuit for transistor based amplifiers and which represents the "normal" method of bipolar transistor connection. The common emitter amplifier configuration produces the highest current and power gain of all the three bipolar transistor configurations. This is mainly because the input impedance is LOW as it is connected to a forward-biased PN-junction, while the output impedance is HIGH as it is taken from a reverse-biased PN-junction.

The Common Emitter Amplifier Circuit

In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as Ie = Ic + Ib. Also, as the load resistance (RL) is connected in series with the collector, the current gain of the common emitter transistor configuration is quite large as it is the ratio of Ic/Ib and is given the Greek symbol of Beta, (β). As the emitter current for a common emitter configuration is defined as Ie = Ic + Ib, the ratio of Ic/Ie is called Alpha, given the Greek symbol of α. Note: that the value of Alpha will always be less than unity.

Since the electrical relationship between these three currents, Ib, Ic and Ie is determined by the physical construction of the transistor itself, any small change in the base current (Ib), will result in a much larger change in the collector current (Ic). Then, small changes in current flowing in the base will thus control the current in the emitter-collector circuit. Typically, Beta has a value between 20 and 200 for most general purpose transistors.

By combining the expressions for both Alpha, α and Beta, β the mathematical relationship between these parameters and therefore the current gain of the transistor can be given as:

Where: "Ic" is the current flowing into the collector terminal, "Ib" is the current flowing into the base terminal and "Ie" is the current flowing out of the emitter terminal.

Then to summarise, this type of bipolar transistor configuration has a greater input impedance, current and power gain than that of the common base configuration but its voltage gain is much lower. The common emitter configuration is an inverting amplifier circuit resulting in the output signal being 180^o out-of-phase with the input voltage signal.

The Common Collector (CC) Configuration

In the Common Collector or grounded collector configuration, the collector is now common through the supply. The input signal is connected directly to the base, while the output is taken from the emitter load as shown. This type of configuration is commonly known as a Voltage Follower or Emitter Follower circuit. The emitter follower configuration is very useful for impedance matching applications because of the very high input impedance, in the region of hundreds of thousands of Ohms while having a relatively low output impedance.

The Common Collector Transistor Circuit

The common emitter configuration has a current gain approximately equal to the β value of the transistor itself. In the common collector configuration the load resistance is situated in series with the emitter so its current is equal to that of the emitter current. As the emitter current is the combination of the collector AND the base current combined, the load resistance in this type of transistor configuration also has both the collector current and the input current of the base flowing through it. Then the current gain of the circuit is given as:

The Common Collector Current Gain

This type of bipolar transistor configuration is a non-inverting circuit in that the signal voltages of Vin and Vout are in-phase. It has a voltage gain that is always less than "1" (unity). The load resistance of the common collector transistor receives both the base and collector currents giving a large current gain (as with the common emitter configuration) therefore, providing good current amplification with very little voltage gain.

Bipolar Transistor Summary

Then to summarise, the behaviour of the bipolar transistor in each one of the above circuit configurations is very different and produces different circuit characteristics with regards to input impedance, output impedance and gain whether this is voltage gain, current gain or power gain and this is summarised in the table below.

Bipolar Transistor Characteristics

The static characteristics for a Bipolar Transistor can be divided into the following three main groups.

Input Characteristics:-	Common Base -	ΔV_EB / ΔI_E
	Common Emitter -	ΔV_BE / ΔI_B

Output Characteristics:-	Common Base -	ΔV_C / ΔI_C
	Common Emitter -	ΔV_C / ΔI_C

Transfer Characteristics:-	Common Base -	ΔI_C / ΔI_E
	Common Emitter -	ΔI_C / ΔI_B

with the characteristics of the different transistor configurations given in the following table:

Characteristic	Common Base	Common Emitter	Common Collector
Input Impedance	Low	Medium	High
Output Impedance	Very High	High	Low
Phase Angle	0^o	180^o	0^o
Voltage Gain	High	Medium	Low
Current Gain	Low	Medium	High
Power Gain	Low	Very High	Medium

In the next tutorial about Bipolar Transistors, we will look at the NPN Transistor in more detail when used in the common emitter configuration as an amplifier as this is the most widely used configuration due to its flexibility and high gain. We will also plot the output characteristics curves commonly associated with amplifier circuits as a function of the collector current to the base current.

Electromagnetism

2011-11-04T06:30:00.000-07:00

Electromagnetism is produced when an electrical current flows through a simple conductor such as a piece of wire or cable. A small magnetic field is created around the conductor with the direction of this magnetic field with regards to its "North" and "South" poles being determined by the direction of the current flowing through the conductor. Magnetism plays an important role in Electrical and Electronic Engineering because without it components such as relays, solenoids, inductors, chokes, coils, loudspeakers, motors, generators, transformers, and electricity meters etc, would not work if magnetism did not exist. Then every coil of wire uses the effect of electromagnetism when an electrical current flows through it. But before we can look at Magnetism and especially Electromagnetism in more detail we need to remember back to our physics classes of how magnets and magnetism works.

The Nature of Magnetism

Magnets can be found in a natural state in the form of a magnetic ore, with the two main types being Magnetite also called "iron oxide", ( FE₃O₄ ) and Lodestone, also called "leading stone". If these two natural magnets are suspended from a piece of string, they will take up a position inline with the earths magnetic field always pointing north. A good example of this effect is the needle of a compass. For most practical applications these natural occurring magnets can be disregarded as their magnetism is very low and because nowadays, man-made artificial magnets can be produced in many different shapes, sizes and magnetic strengths.

There are basically two forms of magnetism, "Permanent Magnets" and "Temporary Magnets", with the type being used dependant upon its application. There are many different types of materials available to make magnets such as iron, nickel, nickel alloys, chromium and cobalt and in their natural state some of these elements such as nickel and cobalt show very poor magnetic quantities on their own. However, when mixed or "alloyed" together with other materials such as iron or aluminium peroxide they become very strong magnets producing unusual names such as "alcomax", "hycomax", "alni" and "alnico".

Magnetic material in the non-magnetic state has its molecular structure in the form of loose magnetic chains or individual tiny magnets loosely arranged in a random pattern. The overall effect of this type of arrangement results in zero or very weak magnetism as this haphazard arrangement of each molecular magnet tends to neutralise its neighbour. When the material is Magnetised this random arrangement of the molecules changes and the tiny unaligned and random molecular magnets become "lined-up" in such a way that they produce a series magnetic arrangement. This idea of the molecular alignment of ferromagnetic materials is known as Weber's Theory and is illustrated below.

Magnetic Molecule Alignment of a Piece of Iron and a Magnet

Weber's theory is based on the fact that all atoms have magnetic properties due to the spinning action of the atoms electrons. Groups of atoms join together so that their magnetic fields are all rotating in the same direction. Magnetic materials are composed of groups of tiny magnets at a molecular level around the atoms, and a magnetised material will have most of its tiny magnets lined up in one direction only to produce a north pole in one direction and a south pole in the other direction. Likewise, a material that has its tiny molecular magnets pointing in all directions will have its molecular magnets neutralised by its neighbouring magnet, thereby neutralising any magnetic effect. These areas of molecular magnets are called "domains".

Any magnetic material will produce a magnetic field itself which depends on the degree of alignment of magnetic domains in the material set up by orbital and spinning electrons. This degree of alignment can be specified by a quantity known as magnetisation, M. In an unmagnetised material, M = 0, but some of the domains remain aligned over small regions in the material once the magnetic field is removed. The effect of applying a magnetising force to the material is to align some of the domains to produce a non-zero magnetisation value.

Once the magnetising force has been removed, the magnetism within the material will either remain or decay away quiet quickly depending on the magnetic material being used. This ability of a material to retain its magnetism is called Retentivity and materials which are required to retain their magnetism will have a high retentivity and are used to make permanent magnets, while those materials required to loose their magnetism quickly such as soft iron cores for relays and solenoids will have a very low retentivity.

Magnetic Flux

All magnets, no matter what their shape, have two regions called magnetic poles with the magnetism both in and around a magnetic circuit producing a definite chain of organised and balanced pattern of invisible lines of flux around it. These lines of flux are collectively referred to as the "magnetic field" of the magnet. The shape of this magnetic field is more intense in some parts than others with the area of the magnet that has the greatest magnetism being called "poles". At each end of a magnet is a pole.

These lines of flux (called a vector field) can not be seen by the naked eye, but they can be seen visually by using iron fillings sprinkled onto a sheet of paper or by using a small compass to trace them out. Magnetic poles are always present in pairs, there is always a region of the magnet called the North-pole and there is always an opposite region called the South-pole. Magnetic fields are always shown visually as lines of force that give a definite pole at each end of the material where the flux lines are more dense and concentrated. The lines which go to make up a magnetic field showing the direction and intensity are called Lines of Force or more commonly "Magnetic Flux" and are given the Greek symbol, Phi ( Φ ) as shown below.

Lines of Force from a Bar Magnets Magnetic Field

As shown above, the magnetic field is strongest near to the poles of the magnet were the lines of flux are more closely spaced. The general direction for the magnetic flux flow is from the North ( N ) to the South ( S ) pole. In addition, these magnetic lines form closed loops that leave at the north pole of the magnet and enter at the south pole. Magnetic poles are always in pairs. However, magnetic flux does not actually flow from the north to the south pole or flow anywhere for that matter as magnetic flux is a static region around a magnet in which the magnetic force exists. In other words magnetic flux does not flow or move it is just there and is not influenced by gravity. Some important facts emerge when plotting lines of force:

1. - Lines of force NEVER cross.
2. - Lines of force are CONTINUOUS.
3. - Lines of force always form individual CLOSED LOOPS around the magnet.
4. - Lines of force have a definite DIRECTION from North to South.
5. - Lines of force that are close together indicate a STRONG magnetic field.
6. - Lines of force that are farther apart indicate a WEAK magnetic field.

Magnetic forces attract and repel like electric forces and when two lines of force are brought close together the interaction between the two magnetic fields causes one of two things to occur:

1. - When adjacent poles are the same, (north-north or south-south) they REPEL each other.
2. - When adjacent poles are not the same, (north-south or south-north) they ATTRACT each other.

It can be remembered by the famous expression that "opposites attract" and this interaction of magnetic fields is easily demonstrated with iron fillings. The effect upon the magnetic fields of the various combinations of poles as like poles repel and unlike poles attract can be seen below.

Magnetic Field of Like and Unlike Poles

When plotting magnetic field lines with a compass it will be seen that the lines of force are produced in such a way as to give a definite pole at each end of the magnet where the lines of force leave the North pole and re-enter at the South pole. Magnetism can be destroyed by heating or hammering the magnetic material, but cannot be destroyed or isolated by simply breaking the magnet into two pieces. If you take a bar magnet and break it into two pieces, each piece will have its own North pole and a South pole. If you take one of those pieces and break it into two again, each of the smaller pieces will have a North pole and a South pole. No matter how small the pieces of the magnet become, each piece will have a North pole and a South pole. In order to make use of magnetism in electrical or electronic calculations, it is necessary to define the various aspects of magnetism.

The Magnitude of Magnetism

We now know that the lines of force or more commonly the magnetic flux around a magnetic material is given the Greek symbol, Phi, ( Φ ) with the unit of flux being the Weber, ( Wb ) after Wilhelm Eduard Weber. But the number of lines of force within a given unit area is called the "Flux Density" and since flux ( Φ ) is measured in ( Wb ) and area ( A ) in metres squared, ( m² ), flux density is therefore measured in Webers/Metre² or ( Wb/m² ) and is given the symbol B.

However, when referring to flux density in magnetism, flux density is given the unit of the Tesla after Nikola Tesla so therefore one Wb/m² is equal to one Tesla, 1Wb/m² = 1T. Flux density is proportional to the lines of force and inversely proportional to area so we can define Flux Density as:

Magnetic Flux Density

The symbol for magnetic flux density is B and the unit of magnetic flux density is the Tesla, T.

It is important to remember that all calculations for flux density are done in the same units, e.g., flux in webers, area in m2 and flux density in Teslas.

Example No1

The amount of flux present in a round magnetic bar was measured at 0.013 webers. If the material has a diameter of 12cm, calculate the flux density.

The cross sectional area of the magnetic material in m2 is given as:

The magnetic flux is given as 0.013 webers, therefore the flux density can be calculated as:

So the flux density is calculated as 1.15 Teslas.

When dealing with magnetism in electrical circuits it must be remembered that one Tesla is the density of a magnetic field such that a conductor carrying 1 ampere at right angles to the magnetic field experiences a force of one newton-metre length on it and this will be demonstrated in the next tutorial about Electromagnetism.

RF Unit Converter

2011-11-04T06:25:00.000-07:00

RF Unit Converter Introduction

This tool is a unit converter for voltage and power. There is an input for impedance that allows the relationship between power and voltage.

Ohm

The unit for resistance or impedance. Resistance can define the relationship between voltage and current and voltage and power. Based upon ohms law the voltage and current relatinship is:

and power is

Vpeak – Peak Voltage

Peak voltage of an AC signal is the peak amplitude.

Vrms – RMS Voltage

The Root Mean Square Voltage or Vrms is:

uV – Microvolt (RMS)

This value is the RMS voltage in microvolts.

uV EMF

This value is microvolt with no termination or load.

uV PD

This value is microvolt with with a load. When a signal has a matched load then half of the voltage is droped across the load. This value is the same value as uV, The unit is just explicitly defined as having the load.

dBuV – dB Microvolts RMS

This unit is the decible of RMS microvolt.

dBuV EMF – dB Microvolts EMF

This unit is the decible of EMF microvolt.

dBuV PD – dB Microvolts PD

This unit is the decible of EMF microvolt.

W – Watts

Watts is a unit of power.

mW – Miliwatts

One thousandth of a watt.

uW – Microwatts

One millionth of a watt.

dBm

dBm is a power measurement and is the decibal of the power in mW.

dBuW

dBuW is a power measurement and is the decibal of the power in uW.

dBuW EMF

dBuW EMF is a power measurement and is the decibal of the power in uW. In a system with no termination or load.

dBuW PD

dBuW PD is a power measurement and is the decibal of the power in uW. In a system with a matched load.

dBpW

dBpW is a power measurement and is the decibal of the power in pW.

dBpW EMF

dBpW EMF is a power measurement and is the decibal of the power in pW. In a system with no termination or load.

dBpW PD

dBpW PD is a power measurement and is the decibal of the power in pW. In a system with a matched load.

Microchip PIC Microcontrollers Now with Configurable Logic

2011-11-04T06:19:00.000-07:00

Microchip Technology has introduced new PIC10F, PIC12F, and PIC16F microcontrollers that boast configurable logic cells (CLCs), enabling Engineers to have peripherals talk to each other in new and interesting ways. These new microcontrollers are available in 6- to 20-pin packages.

Microchip PIC with new Blocks
Microchip PIC with new Blocks
The PIC10F(LF)32X and PIC1XF(LF)150X microcontrollers include new peripherals such as Configurable Logic Cells (CLCs), Complementary Waveform Generators (CWGs) and Numerically Controlled Oscillators (NCOs).

The CLC peripherals on the PIC10F(LF)32X and PIC1XF(LF)150X microcontrollers provide software control of configurable logic between peripherals and I/Os.

The CWG peripheral controls peripherals to generate complementary waveforms with dead-band control and auto shutdown.

The NCO peripheral provides linear frequency control at high resolution, targeting applications such as lighting ballast, tone generation and other resonant control circuits.


Microchip Configurable Logic Cell (CLC)


Microchip PIC with new Blocks

PIC Microcontrollers with CLC Features:
Features of these new PIC10 microcontrollers include:

    * PIC10F, PIC12F, and PIC16F cores at 16MHz
    * 1.75KBytes to 14KBytes Flash
    * 64Bytes to 512Bytes RAM
    * Watchdog
    * Power-On Reset
    * Two 8-bit timers
    * One 16-bit timer
    * Four 10-bit PWM
    * Up to 12-channels 10-bit ADC
    * one 5-bit DAC on some devices
    * Up to two comparators
    * EUSART
    * SPI
    * I2C
    * Configurable Logic Cell
    * Complementary Waveform Generator
    * Numerically Controlled Oscillators

Microchip Configurable Logic Cell (CLC)
Microchip Configurable Logic Cell (CLC)
Low Power performance for these parts are spec'ed at an Active Current of 30uA/MHz and sleep current of 20nA.

A free CLC Configuration Tool is available from Microchip.

Microchip PIC Microcontroller Packaging
The PIC10F(LF)320 and PIC10F(LF)322 microcontrollers are available in a 6-pin SOT-23 package, as well as 8-pin PDIP and 2 mm x 3 mm DFN packages.

The PIC12F(LF)1501 microcontrollers will be available in 8-pin PDIP, SOIC, MSOP and 2 mm x 3 mm DFN packages.

The PIC16F(LF)1503 microcontrollers will be in 14-pin PDIP, SOIC and TSSOP packages, as well as a 3 mm x 3 mm QFN package.

The PIC16F(LF)1507 microcontroller is available in 20-pin SSOP, PDIP, SOIC, and 4 mm x 4 mm QFN packages, as will the PIC16F(LF)1508/9 MCUs, when available.

Pricing and Availability
Pricing starts at $0.37 each, in 10,000-unit quantities. Samples and volume-production quantities of the PIC10F(LF)320, PIC10F(LF)322 and PIC16F(LF)1507 microcontrollers are available today. The PIC1XF(LF)1501/3/8/9 microcontrollers are expected to be available for sampling and purchase within the next six months.

About Microchip Technology
Microchip Technology Inc. (NASDAQ: MCHP) is a leading provider of microcontroller, analog and Flash-IP solutions. The Microchip name and logo, HI-TECH C, MPLAB, and PIC are registered trademarks of Microchip Technology Inc. in the U.S.A., and other countries. mTouch, PICDEM, PICkit, and REAL ICE, are trademarks of Microchip Technology Inc. in the U.S.A., and other countries. All other trademarks mentioned herein are the property of their respective companies.

Atmel AVR XMEGA-B1 Microcontroller is Lower Power with Innovative LCD

2011-11-04T06:14:00.000-07:00

Atmel has introduced the Atmel XMEGA-B1 family of microcontrollers that is lower power, with support for LCD and high accuracy ADC.

Atmel XMEGA-B1 Block Diagram
Atmel XMEGA-B1 Block Diagram
The Atmel XMEGA microcontroller family has an 8-bit datapath with a 16-bit ALU. The Atmel XMEGA-B1 is manufactured in Atmel's proprietary low-leakage 0.25µ process. This microcontroller requires only one 1.6V-3.6V power supply.

The Atmel XMEGA-B1 is spec'ed at 100nA RAM retention mode, which retains RAM and can wakeup from any interrupt in 5µsec.

Features of the new Atmel XMEGA-B1 include:

    * 8/16-bit XMEGA core
    * Up to 128KBytes Flash
    * Up to 8KBytes boot Flash
    * Up to 46KBytes SRAM
    * Up to 4KBytes EEPROM
    * 4x40 Segment LCD controller with built-in ASCII character mapping
    * Watchdog
    * Real-time Clock (RTC)
    * 16-bit Timers
    * 32 PWM outputs
    * QTouch Capacitive Touch Peripheral
    * Check Sum module
    * AES/DES Crypto
    * 4-channel Direct Memory Access (DMA) Controller
    * Up to two 12-bit 2MSPS ADC
    * Up to 4-channels 12-bit 1MSPS DAC
    * USART
    * SPI
    * I2C
    * USB 2.0


Atmel XMEGA-B1 Block Diagram

The ultra-low-power LCD controller in the Atmel XMEGA-B1 microcontrollers supports up to 4x40 segments and has built-in ASCII character mapping. The LCD module draws only 3µA and includes LCD buffers and power supply. A SWAP mode allows flexible pinout configurations. Modes include programmable segment blinking scrolling text.

The Atmel AVR XMEGA-B1 family boasts high-precision analog peripherals, including two 12-bit analog-to-digital converters (ADCs) with programmable gain. The ADCs operate down to 1.6V operating voltage, and have a combined sample rate up to 4MSPS. Two 12-bit digital-to-analog converters (DACs) have high current outputs, while built-in current outputs enable embedded applications to remove external resistors or other constant current sources.

Pricing and Availability
"The new Atmel AVR XMEGA devices with USB are available now. Pricing starts at U.S. $2.00 each in 10,000-piece quantities."

About Atmel
"Atmel Corporation is a worldwide leader in the design and manufacture of microcontrollers, capacitive touch solutions, advanced logic, mixed-signal, nonvolatile memory and radio frequency (RF) components. Leveraging one of the industry's broadest intellectual property (IP) technology portfolios, Atmel is able to provide the electronics industry with complete system solutions focused on industrial, consumer, communications, computing and automotive markets."

Development of two laboratory experiments for teaching electrodynamic forces in an advanced course in electromechanical systems

2011-11-04T06:06:00.000-07:00

Abstract In this paper, two experiments on electrodynamic forces designed for students on an advanced course in electromechanical systems are proposed. Details are first given for an experiment involving a pendulum system whose damping is controlled by the electrodynamic forces that are induced in a conducting plate. The pendulum system is modelled using Maxwell's equations and experimental results obtained from the system are compared with those estimated from the model developed. A second experiment is also presented, consisting of a magnetic levitation system where electrodynamic forces are induced in a moving conducting plate by two permanent magnets, resulting in lifting and drag forces on them. These two components of the electrodynamic forces, the lifting and drag forces, are analysed based on the magnetic field distribution, also verifying their dependence on plate speed and lifting height.

Keywords continuum electromechnics; electrical education; electrodynamics teaching; electromechanical systems; magnetic levitation

(ProQuest: ... denotes formulae omitted.)

In any advanced course in electromechanical systems, students usually study the distributed parameters modeling of electromagnetic systems, including electrodynamic forces on conducting materials.1-4 In this context, we propose in this paper two experiments where the electrodynamic forces significantly affect the systems' dynamics. The first experiment takes a pendulum system made of a conducting plate, which is subjected to a uniform and constant magnetic field. Due to the electrodynamic forces induced in the conducting plate, the pendulum damping can be controlled. The system is first modelled by the use of Maxwell's equations,5 assuming a set of assumptions coming from the system's geometry and its materials. Experimental results obtained with the pendulum system are compared with results estimated from the model to show the consistency and validity of the model assumptions and thus validate the model.

In a second experiment, two permanent magnets are located above a conducting plate which moves with a speed that can be controlled. The relative motion between the magnets and plate induce electric currents in the conducting sheet, producing a repulsive force that causes the lifting of the permanent magnets. The magnetic field distribution in the system is studied first to explain the appearance of drag and lifting forces. Following this, the co-dependence of these forces with speed of the conducting plate and the lifting height is discussed taking into account the experimental results obtained.

Experiment 1

Experimental setup

Figure 1(a) shows the experimental apparatus where a rectangular conducting plate made of aluminum is suspended by a pendulum with length r, and located in a gap (see this detail in Fig. 1(b)) where a constant magnetic flux density B0 of 70.2 mT is imposed by a magnetic circuit. Magnetic drag forces appearing in the conducting plate cause damping when it swings in the perpendicular direction to B0 (see Fig. 1(a)). The potential and kinetic energies of the pendulum are dissipated in the form of power losses in the aluminium plate.

The magnetic circuit shown in Fig. 1(b) is composed of two parts with an E-form. Also, one coil with 400 turns and located in the central leg was used to energise the magnetic circuit. The pendulum position was measured using an ultrasonic sensor.

Experiment 1 - distributed parameter modelling

Figure 2 is a schematic diagram of the experimental system shown in Fig. 1 but seen from the upper side. The conducting sheet shown in Fig. 2 has the shape of a long plate with uniform thickness d and conductivity σ, moving in the positive x direction with constant speed vx. This experiment considers a uniform and constant magnetic field B = -B0ey located in a rectangular region on the conducting plate with area lz0 which is imposed by an electromagnet not represented in the figure.

With the assumptions of a symmetric system and neglecting border effects, the system is studied in two dimensions only, -x and -y directions, with the z component of B assumed to be zero. The system's magnetic flux density becomes, thus, defined by:

... (1)

with the conducting plate moving with a linear speed defined by:

... (2)

The electric field E induced in the conducting plate is given by:

... (3)

which results in an induced density current according to Ohm's law J = σE of:

... (4)

Using (4) with the following two Maxwell equations

... (5)

and

... (6)

the equation establishing field B in the conducting plate becomes defined as:

... (7)

The -x and -y components of (7) can be obtained considering the earlier assumptions used in the definition of the magnetic flux density in (1), resulting in:

... (8)

... (9)

Considering that the thickness of the conducting plate is very small when compared with the distance between the magnetic poles (d

- the -x component of B inside the plate can be ignored, B^sub x^ [congruent with] 0;

- and it can be considered that the vertical component B^sub y^ only varies with the x direction, B^sub y^(x,y) [congruent with] B^sub y^(x).

Using these approximations (9) can be rewritten as:

... (10)

The solution of (10) can assume the form given by (11). In this equation, parameter R^sub m^ = σμv^sub x^l is usually called the magnetic Reynolds number, and parameters C1 and C2 are constants to be determined from two boundary conditions.

... (11)

First boundary condition

As indicated in Fig. 3, the first boundary condition is obtained by integrating Ampere's Law over the ABCD way yielding:

... (12)

where Jz is the -z component of the eddy current density induced in the conducting plate in z direction, and linked by the contour ABCD. Due to the plate's extreme thinness, we assume that the magnetic field component Hy does not vary appreciably over its width d and, from our previous assumptions, that the magnetic field component Hx becomes zero. Therefore (12) results in:

... (13)

where J^sub z^ = σv^sub x^B^sub y^.

Second boundary condition

This condition is obtained using the magnetic flux conservation through the plate surface that is located between the magnetic poles.B^sub 0^ being the magnetic flux density, imposed by the magnetic circuit it can be written:

... (14)

Resolving (12) and (13) for the constants C1 and C2, we obtain the analytic expression for the flux density distribution inside the conducting plate given by:

... (15)

The drag force appearing in the conducting plate can thus be determined by integrating the force density (16) through plate volume, yielding the result shown in (17). This result shows that the drag force depends on the integral of B^sub y^^sup 2^, being thus proportional to the power dissipated by the eddy currents.

... (16)

... (17)

Drag force

Because the aluminium plate is very thin and the induced currents are not considered to be high enough, in order for their magnetic field to distort the applied one B0, it has been assumed that the value of the flux density in the plate is constant:

... (18)

Substituting eqn (18) for eqn (17), the drag force becomes given by:

... (19)

The pendulum linear velocity v^sub x^ can be approximated by expression (20) for small pendulum angular displacements.

... (20)

The motion equation of the pendulum given by (21) results then in the approximated (22), where θ is the angular position, m is the pendulum mass, r its radius and I is the moment of inertia of the pendulum, being equal to I = mr^sub 2^.

... (21)

... (22)

Substituting (19) and (20) in eqn (22) and rearranging the equation terms, this results in the second-order position equation (23) for the pendulum system where the parameter Kθ becomes given by (24).

... (23)

... (24)

The roots of the characteristic equation for the differential equation (23) are:

... (25)

Where, because the pendulum is a damped oscillating system, relation (26) must be satisfied.

... (26)

The main dimensions of the pendulum system are: z^sub 0^ = 4 cm, d = 1 mm, l = 4 cm and r = 10 cm. The aluminium conductivity is equal to σ = 3 × 10^sup 7^ S*m^sup -1^ resulting in a mass to the conducting plate equal to m = 24.3 g. Substituting these parameter values in (26), this becomes satisfied, presenting a value of about 6 × 10^sup -4^, which is less than 1 as required for an oscillatory damping system.

Experiences in teaching electric drives based on basic modelling simulations and industrial a.c. drive measurements

2011-11-04T06:01:00.000-07:00

Abstract The objective of this paper is to compare laboratory tests of industrial electric a.c. drives and simulation results obtained from the basic model introduced to our students in practical sessions. This basic model takes into account the electrical, electronic and control subsystems which comprise a simplifi ed electric a.c. drive. The proposed tests allow us to analyse the electric drive in four-quadrant operation, which are included in this paper. The main advantage of this approach is that students can verify the differences between real and simulated results and, in this way, they can also progress, strengthen and expand their theoretical knowledge. The proposed methodology has been implemented during the past few years in two optional subjects related to electric and electronic fi elds. Academic results and student reaction are also discussed.

Keywords drives; electric machines education; power electronics education; PWM inverters

In universities all over the world, courses in electric machines and drives are suffering from lack of student interest1 and, in some cases, are being cancelled from the curriculum. However, nowadays, industry is demanding more and more trained engineers in this fi eld. From this point of view, universities have to modernise and improve the electrical machines and drives curriculum, meeting these industry demands, since power electronics and electric machines/ drives courses have in many cases not changed in several decades.2 With the aim of attracting more students, a modernisation of both course and the supporting laboratory is thus essential. In this way, laboratory experiments must be updated to fulfi l these requirements, though continuing the conventional way of providing practical experience to electrical and electronic engineering students, through the use of extensive laboratorybased systems. Engineering students must become acquainted with the equipment and techniques used in professional environments. When selecting the practical resources to be used in an engineering course, a trade-off must be found between their industrial signifi cance and the educational requirements.3

One essential element of power engineering education must be a renewed emphasis on the laboratory.4-6. Any new laboratory should address the areas of electrical machines, power electronics and their control, maintaining the conventional way of providing practical experience to electrical and electronic engineering students. In this context, it is necessary to point out that more than 75% of all generated power is processed by power electronics. The extensive usage of switching converter circuits in electronic products and systems makes the fundamental understanding of power electronics a necessity for students and electronic engineers.7 However, these laboratories are costly to build and diffi cult to maintain, being usually designed for their use along the years. Indeed, some authors claim that virtual instruction environments overcome this problem adding safety and security,8,9 and the use of computers do much to alleviate the students' frustration and give them an early sense of satisfaction and accomplishment10. Additionally, during the past decade, Internet technologies have become the basis of computer-assisted education. Web-based systems take advantage of giving access to many resources using a standard, universal, and well-known user interface11. In this context, computer games have also been integrated in a basic automatic control course at the undergraduate university level.12

In our opinion, it would be desirable if engineering education could combine both aspects: computer simulations and laboratory experiments. From this point of view, the main contribution of this paper is focused on describing our satisfactory experience when both simulations and laboratory experiments are proposed as practical sessions in different subjects. In our case, electric drives are considered in the present work as topic of interest, since they appear as a preferred objective in different electrical and electronics undergraduate subjects.

Industrial Engineering Degree

According to the current undergraduate curriculum of the Industrial Engineering degree13, the Electrical Engineering and Electronic Technology Departments of the Technical University of Cartagena (Spain), teach the subjects shown in Table 1, where ECTS represents the European Credit Transfer System equivalent14. This undergraduate curriculum was elaborated from a generalist education point of view, with emphasis on industrial engineering fundamentals and practices.

In this curriculum there is only one compulsory subject directly related to the fi eld of electronics - Power Electronics - , in which the goals are limited and have to be focused on basic concepts. The optional subjects give us the opportunity to extend the basic concepts, but those subjects are normally assigned to different departments. For this reason, a good coordination between these departments would be desirable in order to optimise the contents, avoiding overlap and offering a more effi cient education. In our case, Extension of Electric Machines and Power Electronics optional subjects - both given during the 5th-year course - have been coordinated during the past few years. They involve different areas including electric, electronics, semiconductors, and control, and, from our experience, students do not easily assimilate these interdisciplinary concepts. Moreover, they normally do not relate them, tending to study them as separate - even isolated - disciplines. With the aim of mitigating this problem, different laboratory tests of adjustablespeed drives have been proposed from these optional subjects to relate and strengthen power electronics, electric machine control and inverter performance concepts.

On the other hand, the average ratio between the ECTS credits of subjects related to electronics and the total undergraduate ECTS credits for the Industrial Engineering curriculum approved and given in different Spanish universities is around 40% - nowadays, in Spain, this curriculum includes the equivalent Electrical, Mechanical, Power and Electronics Engineering degree. However, in our case, the percentage of credits (20%) is signifi cantly lower than the average value, which justifi es our interest and necessity to minimise this defi ciency by means of the different proposed laboratory experiments.15

Resource description

In this section, a brief description of the hardware and software is provided. In this case, all the hardware system equipment is common in the industrial environment, and thus, less costly than their educational counterparts. Specifi cally, these items are the following:

* Variable speed a.c. drive.16 Unidrive UNI1403 - 1.5kW - from Control Technniques �. In our case, two a.c. drives have been used: one works in motor mode, and the other one in regenerative braking mode.

Induction electric machine.17 This induction electric machine is a three-phase motor, 4 pole, with squirrel-cage rotor from Lucas-N�lle� laboratory technology.

Electrical measurements.18 Two-channel oscilloscopes and digital voltmeters and ammeters have been used to measure and store the real voltage and current evolution.

In reference to the software packages, an evaluation version of Orcad-PSpice Computer � has been used for the simulation stage.19 In this case, the circuits have been simplifi ed according to our educational and curriculum objectives: for example, power converters are simulated as d.c.-controlled-transformers. In the same way, this freeware distribution allows students to simulate any equivalent circuit as well as share their experiences and contributions.

Laboratory tests: results

From these equipments and software packages, different laboratory experiments have been proposed. Laboratory tests of industrial electric a.c. drives have been implemented inside the Extension of Electric Machines subject, being their equivalent circuits simulated inside the Power Electronics subject. The main aim of these simulations is to show clearly how converters work, avoiding complex control systems according to our curriculum objectives. From this point of view, the proposed real and simulated laboratory experiments include: One-leg switch-mode inverter (PWM), averaged one-leg switch-mode inverter (simplifi cation), threephase inverter (PWM), averaged three-phase inverter, averaged three-phase inverter with 3rd harmonic injection, and regenerative braking process - including energy balance.

A project-based competitive learning scheme to teach mobile communications

2011-11-04T05:55:00.000-07:00

Abstract This paper presents a project-based learning experience to teach mobile communications courses, carried out at Alcal� University, Madrid, Spain. The experience consists of a competition among teams formed by students, who act as consultant companies working for imaginary operators. The objective of the teams is to obtain the best network design and the most economical budget for an imaginary operator in the city of Alcal� de Henares. The proposed learning scheme uses existing concepts of different fields, such as the project-based or competitive games methodologies, and applies them to the teaching of telecommunications subjects. Details of the practical application of the methodology and results obtained at Alcal� University are discussed in this paper.

Keywords competitive games; electrical engineering course; mobile communications; project-based learning
Mobile communications are nowadays one of the fastest growing technologies in the communications business,1,2 representing close to 2% of GDP in the majority of developed countries.3 Following this trend, most universities and technical schools offer mobile telecommunications courses to prepare engineers in these technologies. 4,5 Specifically, in most institutions where electrical engineering is taught, basic courses about the GSM (2nd Generation Mobile Communications), and the UMTS (3rd Generation) systems are offered.
These courses, usually called Mobile Communications, Wireless Communications or Communications Networks, may vary among different universities, but generally all of them give a good overview of the technical and economical foundations of this field. Teaching the GSM and UMTS systems in technical schools is usually carried out by following two steps. First, the students receive theoretical classes comprising a description of how the system and its components work; afterwards, they take some laboratory classes where practical aspects of the GSM and UMTS6 systems implementation are revised.

In the last few years, the teaching methodology known as project-based learning has arisen as one of the most promising and used techniques in higher education. Specifically, different works have been published recently discussing several applications of project- and problem-based learning in electrical engineering.7-11 These works have shown the applicability of the project-based learning scheme in very different aspects of electrical engineering teaching, and very good results in terms of improvement of teaching quality and students' acceptance have been obtained. In spite of the large amount of works in the literature discussing project-based schemes in electrical engineering, up to now we have not found a direct application of the project-based technique to specific mobile communications courses.

The objective of this paper is to describe a specific implementation of a projectbased learning (PjBL) scheme in a Mobile Communications course taught in a Spanish university. Specifically, we discuss the implementation of the PjBL scheme in the course Mobile Communications taught in the 5th year of the Telecommunications Engineering degree at the Universidad de Alcal� (UAH), Spain. The idea is to include in the course concepts of engineering and economics related to mobile communication systems. Briefly, we have structured the PjBL implementation in the following way: after a first stage in which the basic theoretical notions of the GSM architecture are explained, a project-based learning scheme is organized by dividing the students on the course into groups of 3 to 6 people. Each group represents a Consulting Firm, with its corresponding team leader. The work consists of performing a full technical and economical study for a virtual operator in a specific city, with its specific economic and technical features. This work is planned as realistically as possible, and then it is like a competition among all teams in such a way that the best project will obtain the best qualification. The evaluation is done by considering the technical quality of the solution, the presentation (how well the team is able to show how good their study is) and the efficiency (in terms of network investment and consulting budgets).

The rest of the paper has the following structure: the next section presents the PjBL proposed, describing the organization and structure of the projects given to the students. The following section shows the results of the experience in a graduate course at the University of Alcal� (UAH), Madrid, Spain. The concluding section presents some final remarks.

Description of the proposed project-based methodology

Nowadays, most network deployments take place in GSM and UMTS systems, so a solid foundation in these technologies is a must in a telecommunications engineering degree. On the other hand, most telecommunications engineers have jobs related to techno-economical studies, consulting studies12 and/or project management, whereas only a few of them work on low level technical issues. This fact made us prepare a different type of mobile communications course, with special focus on project management. In this section the basic details of this project-based learning scheme are given.

The complete course is based on two interrelated blocks:

* A set of theoretical lectures, where the concepts and working of mobile communications are explained;

* The Work Project, which is designed as real consultancy work.

The final mark for the course is the mean of the mark obtained in the final exam of the course (over 10 points), and the mark of the consulting work project (also over 10 points). The main objectives of the project are the following:

* Learning how to work in a real case scenario inside a work team;

* Learning how to assume a specific role and responsibilities in team work;

* Learning how to manage efficiently scarce resources, specifically time and human effort;

* Learning how to apply the knowledge acquired in the lectures to a real case;

* Learning how to survive in a harsh competitive environment;

* Learning how to present the results of the work (how to sell them to the client).

The project has been structured as follows: the students are divided into several groups with 3 to 6 students, are each group is treated as a consulting company that works for an imaginary operator. The task of each group is to perform the complete mobile network deployment in a specific city of Spain, with the corresponding real equipment, and to calculate the values of the cost per minute of the different services offered by the operator.13 In the courses in 2007/2008 and 2008/2009 the city selected was our home town, Alcal� de Henares, where the University of Alcal� is located. In the next subsections we detail the complete methodology used to supervise the projects.

Composition of the teams

As has been mentioned before, each group is composed of 3 to 6 students. The selection of the members of the group is done by the students themselves. The students are previously told that smaller groups will have less complicated projects than bigger groups, because bigger groups can use economy of scale to leverage the work of the project. Each group has to select the name of the consulting firm and the corresponding corporate logo. Furthermore they have to establish a template for all the reports they have to produce, in order to provide a professional image.

A relevant issue at this point is the figure of the team leader. In the real world the team leader in a consulting project is a senior consultant who, obviously, has more responsibility than the rest of the project members. On the other hand, he/she earns more money. In this case, the team leader takes responsibility for the success of the project. If the project ends correctly, the qualification of the team leader will be higher than the rest of team members. On the other hand, if the project fails, the team leader will be consequently penalized. The students with more initiative are encouraged to be team leaders.

Work definition

As outlined above, each team is commissioned with the mobile network deployment of a virtual operator. The input data given to the team is described below.

* The technologies adopted by the operator, GSM or GSM / UMTS.

* The market share of the operator.

* The bandwidth acquired by the operator in each frequency band, GSM 900 MHz, GSM 1800 MHz, UMTS 2000 MHz.

* The total annual minutes billed by the operator.

* The service briefcase for each technology.

The level of difficulty of the work depends on the number of members in each team. We have divided the possible consulting firms to choose from into three categories.

- Small operator. Using only GSM technology with low market power, about 15-20% and with not very favourable frequency bands and limited service briefcase. The network design is simple, but the profitability is low. Therefore in the conclusions of the report they have to make many statements to the regulatory authorities. This kind of operator is adequate for small teams of 3 members.

- Medium operator. GSM and UMTS technology with market power about 30% and reasonable frequency bands and service briefcase. It is a comfortable position for the network design but the level of exigency in the profitability results will be high. Adequate for teams of 4 members.

- Large operator. This will be the case of the dominant operator with a very high market power, more than 40%, with a large briefcase and large spectrum due to its economic power. The network design is more difficult but the profitability is ensured due to economy of scale. However in the report the students have to defend against possible regulatory intrusions to favour the small operators. Adequate for teams of 5 or 6 members.

The result of the project is a final report where the following points must be described:

* An executive summary describing the network design;

* Firm, model, price and description of the commercial equipment used for each network element;

* Location in UTM coordinates of each BTS, BSC and radio link used in the network design;

* Graphical representation of the results, by means of the corresponding maps;

* Consultant economic report;

* Network design economic report;

* Profitability of the proposed solution;

* Diagram with the effort in man/months;

* Conclusions and allegations for the regulatory authorities.

Apart from the final report, each team will have to perform a short presentation to the lectures of the subject and other colleagues, some of them coming from mobile operators such as Vodafone group. The objective of this presentations to force the students to defend their solution against a semi-hostile audience, which represents the client in the real world, and which tries to find any possible error on the design.

Economic budgets

There are three topics in the final report related to economic issues: the consultancy budget, the network investment budget and the profitability study. This section will go deeper into these points.

In the project definition it is specified that each team must act as a consulting company performing a work for a virtual operator. Therefore the members of the team spend some effort, measured in working hours, to complete this work. In the final report they have to provide an economic report with the total amount they will bill to the operator for the work done. This bill may include not only the personal payments but also the corresponding part of the material used by the consulting firm (computers, printers and so on), and the benefit margin.

In the economic budget there will be a specific item related to the things acquired by the team for doing the project. In fact, these things are, in most cases, only information about network equipment and prices, economic issues, network planning procedures or geographical and demographical information about the city of Alcal� de Henares. Information can be obtained on the Internet, from reference books or asking the lecturers directly. However, in this work, the role of the lecturer is to be an external consultant, therefore if the team asks the lecturer something, the lecturer will bill the team for this concept. The amount of virtual money the lecturer will charge depends not only on the type and complexity of the question, but also on other factors such as the type of team asking: a larger team works for a larger operator and will have to pay more. Also, when a team asks for information, it has been imposed that the closer to the deadline of the project, the higher the price the team will have to pay. This service request has to be done to the lecturer by filling in a form using the company's template.

LAWS OF THERMODYNAMICS:

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(i). Zeroth Law of thermodynamics:

If two bodies are in thermal equilibrium and a third body is in thermal equilibrium with any one of the first two bodies, then it can be inferred that all the three bodies are in thermal equilibrium.

(ii). First Law of Thermodynamics:

If any system is carried through a cycle then the summation of the work delivered to the surroundings is proportional to the summation of the heat taken from the surroundings.

¤∫ dW α ¤ ∫ dQ

¤∫ dW = J ¤ ∫ dQ J is th proportionality constant known as the mechanical

equivalent of heat = 1 KJ / KNm

¤∫ dQ - ¤ ∫ dW / J = 0

¤∫ [ [dQ - dW / J] = 0

Path:

    If a system passes through a series of state point then it is said to describe a path.

Process:

    Whenever a state change occurs then the system is said to undergo a process

Cycle:

    If a system starts from a particular thermodyanmic coordinate point, under goes different process and once again comes back to its initial state points it is said to undergo a cycle or thermodyanmic cycle

Corollary:

(a) Internal energy is a property.

    Consider a system of two cycles 1 A 2 B 1 and 1 A 2 C 1

       Applying first law to cycle I: 1 A 2 B 1

1A∫2 [dQ-dW/J] + 2B∫1 [dQ-dW/J] = 0

1A∫2 [dQ-dW/J] = - 2B∫1 [dQ-dW/J]

1A∫2 [dQ-dW/J] = 1B∫2 [dQ-dW] ---- (a)

Applying first law to cycle I: 1 A 2 C1

1A∫2 [dQ-dW/J] + 2C∫1 [dQ-dW/J] = 0

1A∫2 [dQ-dW/J] = - 2C∫1 [dQ-dW/J]

1A∫2 [dQ-dW/J] = 1C∫2 [dQ-dW] ---- (b)

From (a) & (b) we get 1A∫2 [dQ-dW/J] = 1B∫2 [dQ-dW] =   1C∫2 [dQ-dW]

The quantity [dQ-dW/J] is independent of the path.

Any quantity, independent of the path is known as property.

     [dQ-dW/J] is a property.

But we have taken that [dQ-dW/J]= dU and U is the internal energy for the given mass m. Therefore internal energy is a property.

(b) Law of conservation of Energy.

    Energy can neither be created not destroyed if mass is conserved.

It is defined as the internal energy remains unchanged if the system is completely isolated.

    if Q=0 ;    W = 0 then ∆U =0

(c) Perpetual Motion Machine   of I kind ( PMM I) is impossible.

It is imposible to construct an engine which produces work without taking heat from the surrounding.
An engine which can produce work without taking heat from the surrounding is known as PMM I. This is not possible.

ZENER DIODE

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In a general purpose PN diode the doping is light; as a result of this thebreakdown voltage is high. If a P and N region are heavily doped then the breakdown voltage can be reduced.

When the doping is heavy even the reverse voltage is low, the electric field atbarrier will be so strong thus the electrons in the covalent bands can break away from the bonds. This effect is known as zener effect.

A diode which exhibits the zener effect is called a zener diode. Hence it isdefined as a reverse biased heavily doped PN junction diode which operates in breakdown region. The zener diodes have been designed to operate at voltages ranging from a few volts to several hundred volts.

Zener breakdown occurs in junctions which is heavily doped and have narrowdepletion layers. The breakdown voltage sets up a very strong electric field. This field is strong enough to break or rupture the covalent bonds thereby generating electron hole pairs.

Even a small reverse voltage is capable of producing large number of currentcarrier, When a zener diode is operated in the breakdown region care must be taken to see that the power dissipation across the junction is within the power rating of the diode otherwise heavy current flowing through the diode may destroy it.

Equivalent Circuit of Zener diode

The schematic symbol and its equivalent circuit are shown in figure 14. It is similar to that of normal diode except the line representing cathode is bent both ends are shown in figure 14.

V-I Characteristics of zenerdiode

The forward characteristic of a zener diode is similar to that of a P N Junction diode. The reverse characteristic of zener diode is obtained as follows.

The reverse current that is present at the origin and the knee of the curve isdue to the reverse leakage current due to the minority carriers. This current is specified by stating its value at 80% of the zener voltage Vz

As the reverse voltage is gradually increased, the breakdown occurs at theknee and the current increases rapidly. To control this current a suitable external resistance has to be used. The maximum permissible value of the current is denoted by Izmax. The minimum usable current is Izmin

The voltage across the terminals of the diode for a current Iz which is theapproximate midpoint of the linear range of the reverse characteristics in called the zener voltage Vz. At the knee point, the breakdown voltage remains constant between Izmax and Izmin. This ability of a diode is called regulating ability and is an important feature of a zenerdiode.

Application of Zener Diode

It can be used

a) As voltage regulators

b) As peak clippers

c) For reshaping waveforms

d) For meter protection against damage from accidental application of excessive voltage

PROGRAMMABLE UNIJUNCTION TRANSISTOR

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The programmable unijunction transistor (PUT) is an improved version of UJT.But PUT is a four layer PNPN device it also known as small version of thyristors as shown in figure 12.

Its operation is similar to the UJT hence it is always considered with UJT, itstrigger voltage VP can be programmed or decided by the designer via external potential divider [ but in UJT, it is fixed for the given device] thus it is known as programmable unijunction transistor.

The symbol of PUT is shown in figure 12. In this case the gate terminal isconnected to the N region [but in thyristor or SCR gate is connected with P region], thus the anode and cathode constitute the PN junction which controls the ON and OFF states of PUT.

Usually positive potential is applied to gate with respect to cathode. When theanode voltage is less than gate voltage VG the anode gate junction becomes reverse biased, the PUT is in OFF state.

When the anode voltage exceeds the gate voltage V anode cathode junctionbecomes forward biased, thus PUT is turned ON. In the ON state, the PUT behaves like other four layer PNPN devices [SCR]. The PUT is also known as complementary SCR [because the gate is connected with ‘N’ layer instead of ‘P’ layer].

Advantages of PUT over UJT

1. The switching voltage is easily yarned by changing Vg through the potential divider.

2. PUT can operate at lower voltages then IC’s. 3. Peak current is lower UJT.

PUT as relaxation oscillator

A PUT can be used as relaxation oscillator it is shown in figure 12. The gate voltage VG is maintained from the supply by the potential divider R1 and R2 and determines the peak point voltage Vp In the case of the UJT, VP is fixed for a device by the dc supply voltage. But VP of a PUT can be varied by varying the potential divider it and it Tithe anode voltage VA is less than the gate voltage V the device will remains in its off state.

ZENER DIODE

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In a general purpose PN diode the doping is light; as a result of this thebreakdown voltage is high. If a P and N region are heavily doped then the breakdown voltage can be reduced.

When the doping is heavy even the reverse voltage is low, the electric field atbarrier will be so strong thus the electrons in the covalent bands can break away from the bonds. This effect is known as zener effect.

A diode which exhibits the zener effect is called a zener diode. Hence it isdefined as a reverse biased heavily doped PN junction diode which operates in breakdown region. The zener diodes have been designed to operate at voltages ranging from a few volts to several hundred volts.

Zener breakdown occurs in junctions which is heavily doped and have narrowdepletion layers. The breakdown voltage sets up a very strong electric field. This field is strong enough to break or rupture the covalent bonds thereby generating electron hole pairs.

Even a small reverse voltage is capable of producing large number of currentcarrier, When a zener diode is operated in the breakdown region care must be taken to see that the power dissipation across the junction is within the power rating of the diode otherwise heavy current flowing through the diode may destroy it.

V-I Characteristics of zenerdiode

The forward characteristic of a zener diode is similar to that of a P N Junction diode. The reverse characteristic of zener diode is obtained as follows.

The reverse current that is present at the origin and the knee of the curve isdue to the reverse leakage current due to the minority carriers. This current is specified by stating its value at 80% of the zener voltage Vz

As the reverse voltage is gradually increased, the breakdown occurs at theknee and the current increases rapidly. To control this current a suitable external resistance has to be used. The maximum permissible value of the current is denoted by Izmax. The minimum usable current is Izmin

The voltage across the terminals of the diode for a current Iz which is theapproximate midpoint of the linear range of the reverse characteristics in called the zener voltage Vz. At the knee point, the breakdown voltage remains constant between Izmax and Izmin. This ability of a diode is called regulating ability and is an important feature of a zenerdiode.

Application of Zener Diode

It can be used

a) As voltage regulators

b) As peak clippers

c) For reshaping waveforms

d) For meter protection against damage from accidental application of excessive voltage

SILICON CONTROLLED RECTIFIER

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It is a four layered PNPN device and is a prominent member of thyristorfamily. It consists of three diodes connected back to back with gate connection or two complementary transistor connected back to back.

It is widely used as switching device in power control applications. It canswitch ON for variable length of time and delivers selected amount of power to load.

It can control loads, by switching the current OFF and ON up to manythousand times a second. Hence it possess advantage of RHEOSTAT and a switch with none of their disadvantages

Construction

As shown in figure 1 it is a four layered three terminal device, layers being
alternately P-type and N-type silicon. Junctions are marked J1, J2, J3 whereas terminals are anode (A), cathode
(C) and gate
(G). The gate terminal is connected to inner P-type layer and it controls the firing or switching of 5CR.

Biasing

The biasing of SCR is shown in figure
1(a). The junction J1 and J3 become
forward biased while J2 is reverse biased. In figure 1 polarity is reversed. It is seen that now junction J1 and J3 become reverse biased and only J2 is forward biased.

Operation of SCR

In SCR a load is connected in series with anode and is kept at positivepotential with respect to cathode when the gate is open i.e., no voltage is applied at the gate.

Under this condition, junctions J1 and J3 are for ward biased and junction J2is reverse biased. Due to this, no current flows through RL and hence the 8CR is cutoff.

However when the anode voltage is increased gradually to breakover voltage,then breakdown occurs at junction J due to this charge carriers are able to flow from cathode to anode easily, hence SCR starts conducting and is said tobe in ON state.

The SCR offers very small forward resistance so that it allows infinitely highcurrent. The current flowing through the 8CR is limited only by the anode voltage and external resistance.

If the battery connections of the applied voltage are reversed as shown infigure 2 the junction J1 and J3 are reverse biased. J2 is forward biased.

If the applied reverse voltage is small the SCR is OFF and hence no currentflows through the device.

If the reverse voltage is increased to reverse breakdown voltage, the junctionJ1 and J3 will breakdown due to avalanche effect. This causes current to flow through the SCR.

From the above discussion we conclude that the SCR can be used to conduct only in forward direction. Therefore SCR is called as “unidirectional device”.

Vl Characteristics of SCR

The “forward characteristics” of SCR may be obtained using the figure 3.

The volt-ampere characteristics of a SCR for IG = 0 is shown in figure 3.

As the applied anode to cathode voltage is increased above zero, very smallcurrent flows through the device, under this condition the 5CR is off. It will be continued until; the applied voltage reaches the forward Breakover voltage (point A).

if the anode-cathode (applied) voltage exceeds the Breakover voltage itconducts heavily the SCR turns ON and anode to cathode voltage decreases quickly to a point B because, under this condition the 5CR offers very low resistance hence it drops very low voltage across it.

At this stage the 5CR allows more current to low through it. The amplitude ofthe current is depending upon the supply voltage and load resistance connected in the circuit.

The current corresponding to the point ‘B’ is called the “holding current (IH)”It can be defined as the minimum value of anode current required to keep the SCR in ON State. If the 5CR falls below this holding current the SCR turns OFF.

If the value of the gate current I is increased above zero, (‘G > O) the SCRturns ON even at lower Breakover voltage as shown in figure 3(b).

The region lying between the points OA is called forward blocking region. Inthis region 5CR is OFF’. The region lying between the points BC is called forward conduction region. In this region SCR is ON.

Once the SCR is switched ON then the gate looses all the control. So SOBcannot be turned OFF by varying the gate voltage. It is possible only by reducing the applied voltage.

To obtain the “reverse characteristics”the following points are followed.

1.In this case the SCR is reverse biased, if the applied reverse voltage is increased above zero, hence a very small current flows through the SCR.

Under this condition the SCR is OFF, it continues till the applied reverse voltage reaches breakdown voltage.

2.As the applied reverse voltage is increased above the breakdown voltage, the avalanche breakdown occurs hence 5CR starts conducting in the reverse direction. It is shown in curve DE. Suppose the applied voltage is increased to   a very high value, the device may get damaged.

SCR rating

The SCR rating are defined as follows

1) “Forward Breakover voltage”:It   is   the   voltage   at   which   the   5CR is switched from its OFF position to ON position. Its: values are maximum for zero gate current, its values lie in the range of 50 to l200volts

2) “Holding current”: it is the minimum value of anode current required to keep the SCR in ON position.

3)   “Gate triggering current”:    It is the value of anode current necessary to switch 5CR from OFF to ON position under specified condition. It is typically   about 4OmA.

4)   “Average forward current”:   It is the maximum value of anode current at which the 5CR can handle in its ON position. Its value lies in the range of 1 to 1800Amps.

5)   “Reverse breakdown voltage”:   It is the value of reverse voltage between cathode to anode at which the avalanche breakdown occurs.

6) “Turn ON time – TON”: It can be defined as, the time required to switch it from OFF to ON state when triggering signal is applied. TON decreases if the trigger voltage is increased; TON is increases when anode current increases.

7)   “Turn OFF Time – TOFF”: It is the time required to switch it from ON to OFF state by dropping anode voltage. TOFF is small if anode voltage in reverse direction and increases with temperature and anode current.

8) “Gate Recovery time”:    It is the time required for which anode voltage is reduced to VH to turn OFF SCR.

Basic Operation of an SCR

The operation of a PNPN device can best be visualized as a specially coupled
pair of transistors as shown in Figure

The connections between the two transistors are such that regenerative action can occur when a proper gate signal is applied to the base of the NPN transistor. Normal leakage current is so low that the combined hFE of the specially coupled two- transistor feedback amplifier is less than unity, thus keeping the circuit in an off- state condition. A momentary positive pulse applied to the gate will bias the NPN transistor into conduction which, in turn, biases the PNP transistor into conduction. The effective hFE momentarily becomes greater than unity so that the specially coupled transistors saturate. Once saturated, current through the transistors is enough to keep the combined hFE greater than unity. The circuit will remain “on” until it is “turned off” by reducing the anode-to-cathode current (IT) such that the combined hFE is less than unity and regeneration ceases; this threshold anode current is the holding current of the SCR.

Electrical Characteristic Curves of Thyristors V-I Characteristics of SCR Device

Methods of Switching on Thyristors There are three general ways to switch thyristors to on-state condition:

Application of Gate Signal

Static dv/dt Turn-On

Voltage Breakover Turn-On

Listed below is a brief description of each method.

Application Of Gate Signal

For an SCR (unilateral device), this signal must be positive with respect to the cathode polarity. A triac (bilateral device) can be turned on with gate signal of either polarity; however, different polarities have different requirements of IGT and VGT which must be satisfied. Since a diac does not have a gate, this method of turn-on is     not applicable to diacs; in fact, the single major application of diacs is to switch-on   triacs.

Static dv/dt Turn-On

Comes from a fast rising voltage applied across the anode and cathode terminals of an SCR or the main terminals of a triac. Due to the nature of thyristor construction, a small junction capacitor is formed across each PN junction. Figure 14.14 shows how typical internal capacitors are linked in gated thyristors. When voltage is impressed suddenly across a PN junction, a charging current will flow which is equal to:

i = C (dv/dt)

When   c   (dv/dt)   becomes   greater   or equal to thyristor IGT, the thyristor switches on. Normally, this type of turn on does not damage or hurt the device providing the surge current is limited. Generally, thyristor application circuits are designed with static dv/dt snubber networks if fast rising voltages are
anticipated.

Voltage Breakover Turn-On

Is the method used to switch on diacs. However, exceeding voltage break over of SCRs and triacs is definitely not recommended as a turn-on method. In the case of   SCRs and triacs, the leakage current increases until it exceeds the gate current required to turn-on these gated thyristors in a small localized point. When turn-on occurs by this method, there is localized heating in a small area which may melt the    silicon or damage the device if di/dt of the increasing current is not sufficiently limited. Diacs used in typical phase control circuits are basically protected against excessive current at breakover as long as the firing capacitor is not excessively large. When diacs are used in a zener function, current limiting is necessary.

COMMON COLLECTOR CONFIGURATION OF A TRANSISTOR

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COMMON COLLECTOR CONNECTION

In this configuration the input is applied between the base and the collector and the output is taken from the collector and the emitter. Here the collector is common to both the input and the output circuits as shown in Fig.

Common Collector Transistor Circuit

In common collector configuration the input current is the base current IB and the output current is the emitter current IE. The ratio of change in emitter current to the change in the base current is called current amplification factor.

It is represented by

COMMON COLLECTOR CIRCUIT

A test circuit for determining the static characteristic of an NPN transistor is shown in Fig. In this circuit the collector is common to both the input and the output circuits. To measure the base and the emitter currents, milli ammeters are connected in series with the base and the emitter circuits. Voltmeters are connected across the input and the output circuits to measure VCE and VCB

INPUT CHARACTERISTICS

Common Collector Input Characteristic Curve

It is a curve which shows the relationship between the base current, IB and the collector base voltage VCB at constant VCE This method of determining the characteristic is as follows.

First, a suitable voltage is applied between the emitter and the collector. Nextthe input voltage VCB is increased in a number of steps and corresponding values of IE are noted.

The base current is taken on the y-axis, and the input voltage is taken on the x-axis. Fig. shows the family of the input characteristic at different collector- emitter voltages.

The following points may be noted from the family of characteristic curves. 1.Its characteristic is quite different from those of common base andcommon emitter circuits.

2.When VCB increases, IB is decreased.

Output Characteristics

It is a curve which shows the relationship between the emitter current l and collector-emitter voltage, the method of determining the output characteristic is as follows.

First, by adjusting the input a suitable current IB is maintained. Next VCB increased in a number of steps from zero and corresponding values of IE are noted.

The above whole procedure is repeated for different values of IB. The emitter current is taken on the Y-axis and the collector-emitter voltage is taken on the X-axis.

Fig shows the family of output characteristics at different base current values. The following points are noted from the family of characteristic curves.

Common Collector Output Characteristic Curves

1.This characteristic is practically identical to that of the common emitter circuit.

2.Its current gain characteristic for different values of VCE is also similar to that of a common emitter circuit.

Swinburne’s Test Method For Testing DC shunt motor

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For a d.c shunt motor change of speed from no load to full load is quite small. Therefore, mechanical loss can be assumed to remain same from no load to full load. Also if field current is held constant during loading, the core loss too can be assumed to remain same.

In this test, the motor is run at rated speed under no load condition at rated voltage. The current drawn from the supply IL0 and the field current If are recorded (figure 40.4).

     Since the motor is operating under no load condition, net mechanical output power is zero.
Hence the gross power developed by the armature must supply the core loss and friction &
windage losses of the motor. Therefore,

                                        Pcore + Pfriction = (V − I a 0 ra ) I a 0 = Eb 0 I a 0

       Since, both Pcore and Pfriction for a shunt motor remains practically constant from no load to
full load, the sum of these losses is called constant rotational loss i.e.,

                                 constant rotational loss, Prot = Pcore + Pfriction

In the Swinburne's test, the constant rotational loss comprising of core and friction loss is
estimated from the above equation.

After knowing the value of Prot from the Swinburne's test, we can fairly estimate the
efficiency of the motor at any loading condition. Let the motor be loaded such that new current
drawn from the supply is IL and the new armature current is Ia as shown in figure 40.4. To
estimate the efficiency of the loaded motor we proceed as follows:

Input power to the motor, Pin=VIL

Cu loss in the field circuit Pfl=VIf

Power input to the armature=vIa

Cu loss in the armature circuit=Ia2 Ra

Net mechanical output power, Pnet mech=Eb Ia- Prot

The estimated value of Prot obtained from Swinburne’s test can also be used to estimate the

efficiency of the shunt machine operating as a generator. In figure 40.5 is shown to deliver a

load current IL to a load resistor RL. In this case output power being known, it is easier to add

the losses to estimate the input mechanical power.

Efficiency of the generator, η= Pin,mech/VIl

The biggest advantage of Swinburne's test is that the shunt machine is to be run as motor
under no load condition requiring little power to be drawn from the supply; based on the no load
reading, efficiency can be predicted for any load current. However, this test is not sufficient if we
want to know more about its performance (effect of armature reaction, temperature rise,
commutation etc.) when it is actually loaded. Obviously the solution is to load the machine by
connecting mechanical load directly on the shaft for motor or by connecting loading rheostat
across the terminals for generator operation. This although sounds simple but difficult to
implement in the laboratory for high rating machines (say above 20 kW), Thus the laboratory
must have proper supply to deliver such a large power corresponding to the rating of the
machine. Secondly, one should have loads to absorb this power.

LPT PRINTER PARALLEL PORT part-1

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1. PREFACE

Every PC has one or more LPT printer parallel port adapter. This adapter have several I/O port. In old PC, the parallel port may be set at video adapter card or at separate I/O device card (multi I/O). In the beginning, this port only used for printer device, so the data port (8 bits) only used for sending data to the printer and can not receive data from the outside. Now, everything has changed. Many device were connected to this parallel port, so the design always change time to time, even the characteristic always the same (i.e. new card usually used a new chip design and have more capabilities, like bidirectional data transfer, can be configured to work more faster, etc., etc.). Ok, lets we explore more about it now.

2. SIGNAL NAME & PURPOSE

Because the parallel port have many location, so the port also follow this procedure and always standard. For our description, DP refer to printer Data Port, PC refer to Printer Control and PS refer to Printer Status. Tabel-1 shown each port and their function.

Tabel-1. LPT location, function and description.
LPT 0	LPT 1	LPT 2	Operation	Description
3BC Hex	378 Hex	278 Hex	(Read)/Write	Data Port (DP), 8 bits
3BD Hex	379 Hex	279 Hex	Read only	Printer Status (PS), 5(6) bits
3BE Hex	37A Hex	27A Hex	Read/Write	Printer Control (PC), 4(6) bits

a. Data Port (DP)

DP has 8 bits length. It means that it can be transfer or sending data 8 bits long at a moment time. The old PC has LPT parallel port function only for sending data. Many devices nowadays have attached to this port and can work bidirectional. For examples : scanner device, many storage device like zip drive, etc., etc. This means that this port can be used for sending or receiving data. New card can be configured to work like this (eg:bi-directional port), but old one don't. In the end of this article, you can change the ability of the old card, so that it can be used to receive data. Data bits are naming as DP-0 trought DP-7. For the relation number to the D-25 socket refer to the LPT Connector. DP port can sink 24 mA at logic 0 and can source 2.6 mA at logic 1. Notice that the external device don't try to pull these DP lines to ground for a long period. The latch IC could be burn.

b. Printer Control (PC)

PC is used for controlling the function of printer. Only 4 bits used by printer and 1 bit used for interrupt enable flag. The complete description was shown on Figure-1. The interrupt enable bit flag used for handshake operation between computer and printer, so that the device can work with a little time of CPU to interfere. The most important things must be taken if you connect your own device are : the PC-0, PC-1 and PC-3 logic are inverting at socket connector terminal. This means that, when you send logic 1 (high) to this related bit, the logic output terminal is 0 (low). The PC-2 and PC-4 are normal. The PC-5 to PC-7 are not used by the hardware circuit. Note that, PC-4 bit only for the adapter card function. This means this bit does not connect out to the connector terminal. PC port can sink 7 mA at logic 0 and can source 0.6 mA at logic 1. Besides that, in some PC/AT's LPT adapter card, bit PC-5 is used for control direction (and also in bi-directional card). It means that, if this bit is high, DP port can act as input port, the latch output is tri-state. Data from outside can be read from DP port.

c. Printer Status (PS)

PS port used for feedback signal from printer to the computer. Only 5 MSB bits are used, the 3 LSB bits not used. The complete description was shown on Figure-2. Only 1 bit is inverting input ie. PS-7 use for busy signal. PS-6 bit use for acknowledge signal This signal used when the printing goes on with interrupt handshake operation. This is a hardware interrupt. In some PC/AT's card and bi-directional card, PS-2 is used to reflex the state of IRQ, weather it is on or off state. This bit only for internal use.

3. CONNECTOR TERMINAL

LPT port adapter use a female DB-25 D-shell connector type. The complete connection can be seen in Figure-3. Only 17 terminals be used, and the rest are grounded all. This is a standard terminal connection. The connection are the same for all of the LPT's connector. Figure-4. show the connection between printer to the LPT adapter.

4. PRINTER INTERFACE DESCRIPTION

LPT printer parallel interface in PC computer type have specification like this :

Data transfer rate : 1000 cps (maximum)
Synchronization : by externally-supplied STROBE pulses.
Handshaking -ACK or +BUSY signals.
Logic level : input data and all interface control signal are compatible with the TTL level.

Generally this specification allways the same for new card design, but the data transfer may vary between one design and another. This type of interface also called CENTRONICS interface and have the data transfer sequence time as shown in Figure-5.

STROBE pulse to read data in. Pulse width must be more than 0.5 us at receiving terminal. The signal level normally high. Read in of data is performed at the low level of this signal. ACK signal is approximately 5 us pulse. Logic low indicates that data has been received and the printer is ready to accept other data. BUSY signal high indicates that the printer can not receive data. This signal becomes high in the following cases :

During data entry
During printing operation
In offline state
During printer error status

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G. DECODING

Build a prototype card implies how to decode the addresses. There are 2 types of decoding techniques, i.e.: I/O decoding and Memory decoding. If the hardware used I/O map for its port, it was called I/O mapped I/O, and if the hardware used memory map for its port, it was called memory mapped I/O.
What are the different point between this 2 types of decoding ?
If we use I/O mapped I/O port, we only can access this port by using the IN and OUT commands. If we used memory mapped I/O port, we can access this port by using all of the commands usually used for data transfer like MOVE, STORE, or any other modes of addressing transfer. In the I/O mapped I/O port, we can only used the reserved location among 1024 locations which implemented for. In the memory mapped I/O, we can used the upper location of memory above A0000 hex, and it is more wisely if we use the upper limit of FXXXX hex boundary which is still available; e.g.: start at F0000 hex, because many of the available locations can be used for UMB block or for XMS pages.

I/O Mapped I/O Decoding

Because of the I/O restriction, we only use 10 address lines (A₀ ~ A₉). Besides that we need AEN line, -IOR & -IOW, -I/O CH RDY (for some card that needs wait states). Notes that, adding wait states will make the computer to run more slowly. It is more wisely not to use this line.

How we decoding this lines ?

For example; we use address location 300 hex which is still available for prototype card. We need 8 consecutive I/O port locations. The decoding is as follows :

AEN A₉ A₈A₇A₆ A₅A₄A₃A₂A₁A₀

 0  1  1     0  0  0  0    1 X  X  X   =  300 ~ 307 hex

So the decode is :

___    _ _ _ _

AEN A₉A₈A₇A₆A₅A₄A₃A₂A₁A₀

Memory Mapped I/O Decoding

Because of DOS restriction, we only use 20 address lines (A0 ~ A19). Besides that we need -MEMR & -MEMW lines.

For example; we used 16 consecutive I/O start at the F0000 hex location. So the decoding is as follows :

A₁₉ A₁₈ A₁₇ A₁₆ A₁₅ A₁₄ A₁₃ A₁₂ A₁₁ A₁₀ A₉ A₈ A₇ A₆ A₅ A₄ A₃ A₂ A₁ A₀

 1  1   1  1    0  0   0  0    0  0  0  0   0  0 0  0   X  X X  X

= F0000 ~ F000F hex

So the decode is :

              _  _   _  _  _   _  _  _ _ _  _ _

A₁₉A₁₈A₁₇A₁₆A₁₅A₁₄A₁₃A₁₂A₁₁A₁₀A₉A₈A₇A₆A₅A₄A₃A₂A₁A₀

H. EXPANDING I/O MAP

What are you doing if you run out all of the I/O location ?
There are still more techniques to take advantage of this problem. One is to utilise the upper address line (A₁₀ to A₁₅). On the faceof it this is unacceptable, since these address lines are not decoded by either the system hardware or any expansion cards. These items of hardware will therefore respond to "echoes" of their base addresses, making addresses above 3FFH unuseable. However this problem is avoided if we only use addresses that are "echoes" of the still available address range in the upper block of 512 addresses. For example if the range in 300H to 31FH (32 consecutive I/O ports) are still available, we can expanded it to the limit of 16 x 32 consecutive I/O ports by implemented the above technique. By decoding one or more of the upper address lines as well as the lower 10 address lines, these 32 addresses can effectively be used over and over again, with one set of hardware using the base address range, and each additional piece of hardware using a different "echo" address range. This gives what should be more than enough input/output addresses to satisfy even the most prolific expansion card builder.
The second technique is by used an I/O port as an indexed port like used by video display adapter port. This technique let us to expand 8 I/O ports by used only 2 of the existing I/O port addresses, i.e.: one for the indexed port and the other for the enable port.

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C. I/O MAP

IBM PC computer mapped its I/O by used address decoder. There are 400 Hex I/O address locations preserved. Some have been used for its own purpose and some used by the external cards and some are still not been use yet. Tabel A-1. show some of these I/O address used for. In fact, I/O address locations can be as much as 2²⁰ locations. But in the previous design it is not used all the address lines. Only 10 lines were used, i.e.: 2¹⁰ = 1024 locations (400 Hex). If you run out these locations all, there is still way to get some of the locations by used the decoder techniques or by used indexed I/O map. This will be describe later.

Tabel A-1. I/O map for AT computer.
ADDRESS	DEVICE	S Y S T E M B O A R D I / O
000H ~ 01FH	DMA Controller 1, 8237A-5
020H ~ 03FH	Interrupt Controller 1, 8259A, Master
040H ~ 05FH	Timer, 8254-2
060H ~ 06FH	Keyboard Controller, 8254
070H ~ 07FH	Real Time Clock, NMI (Non Maskable Interrupt) Mask
080H ~ 09FH	DMA (Direct Memory access) page register, 74LS612
0A0H ~ 0BFH	Interrupt Controller 2, 8259A
0C0H ~ 0DFH	DMA Controller 2, 8237A-5
0F0H	Clear Math Co-Processor busy
0F1H	Reset Math Co-Processor
0F8H ~ 0FFH	Math Co-Processor
1F0H ~ 1F8H	Fixed Disk Controller	E X P A N S I O N C H A N N E L I / O
200H ~ 207H	Game I/O Controller
210H ~ 217H	Expansion Slot
220H ~ 24FH	Reserved
278H ~ 27FH	Parallel Printer Port 3 (LPT-3)
2E8H ~ 2EFH	Serial Port 4 (COM-4)
2F0H ~ 2F7H	Reserved
2F8H ~ 2FFH	Serial Port 2 (COM-2)
300H ~ 31FH	Prototype Card
320H ~ 32FH	Fixed Disk Controller
360H ~ 36FH	Reserved
378H ~ 37FH	Parallel Printer Port 2 (LPT-2)
380H ~ 38FH	SDLC, Bisynchronous 2
3A0H ~ 3AFH	Bisynchronous 1
3B0H ~ 3BBH	Monochrome Display Adapter
3BCH ~ 3BFH	Parallel Printer Port 1 (LPT-1)
3C0H ~ 3CFH	EGA/VGA Adapter Controller
3D0H ~ 3DFH	Color/Graphics Monitor Adapter (CGA Adapter)
3E8H ~ 3EFH	Serial Port 3 (COM-3)
3F0H ~ 3F7H	Floppy Disk (Diskette) Controller
3F8H ~ 3FFH	Serial Port 1 (COM-1)

As we can see from the tabel, I/O port in the PC divided in 2 section, i.e.: direct addressing mode (0 ~ FFH port) are used for system I/O purpose, and indirect mode used by another peripheral which connected to the I/O slots.

The first decision that has to be made when designing a PC prototype card is just where in the input/output map it should be placed. As explained previously, only 1024 of the 65536 possible places for input/output addresses are availabel on a PC, and the lower 512 addresses are reserved for the computer's internal hardware. Much of the upper block of 512 addresses are reserved for essential and standard expansion cards such as serial ports, and display adapters. We can only use the upper block of 512 addresses for our add-ons cards. There are still more places as mark by reserved that are not been used yet by any cards. We can use it. Even the prototype card has the location itself, it can't make a guarantee that these location are still reserved for our purpose, because many company had built their own card that used this location (include one that introduce by the IBM). Besides the standard card, there are many cards was introduced in the market this day, like video card (VCD or DVD card), TV card, radio card, etc ... etc. This also have several I/O locations that can be choose when installed in the first time. Be sure to check your configuration of I/O ports.

D. MEMORY MAP

In the first PC design of memory architecture, memories implemented to it's limit 1 MB boundary (2²⁰ as the address only 20 address lines). But not all of this location filled with memories. 2¹⁶ location (640 kB) was fillled by RAM (Random Access Memory) for the system, program and temporary data. The upper portion was filled with ROM (Read Only Memory) by parts, depends of the configuration of the system; system initialization program, POST (Power On Self Test), BIOS (Basic Input/Output System), BASIC system, display controller, hard disk controller, etc ... etc. This upper portion location also called the UMB (Upper Memory Block) area. If we used DOS version 4.00 and up, we can activated this UMB area to store some portion of the system by put the 'DOS=UMB' statement in the CONFIG.SYS file. But the EMM386.EXE file must be installed first. This ability also valid for any other program if we use the 'LOADHIGH= . . .' statement.
Then the PC design architecture was developing the ability to expanded memory. This technique was development by Lotus-Intel-Microsoft, so become the standard EMS (Expanded Memory Specification) and also called LIM-EMS standard. The alocation method used UMB to map the expanded memory. 16 kB each block and called memory page. Up to 4 pages can be accesses at a time. We can used this option (or any programs which used this standard) by installed EMM386.EXE in the CONFIG.SYS file.
When the AT architecture was introduced, the limit of memory to implemented becomes more wide; 80286 CPU could be implemented up to 16 MB location (24address lines) and 80386 CPU up to 4 GB (32 address lines). But because of the old design of DOS system, only 1 MB (20 address lines) can be accesses by DOS (DOS run in real mode). To accesses the upper 1 MB, DOS must run in protected mode. These upper 1 MB memory are called XMS (Extended Memory Specification) and can be accesses if we installed EMM386.EXE in the CONFIG.SYS file too, or in the new system like windows system, it was used a DOS Extender program; DPMI, VCPM, etc ... etc. The first 64 kB memory location upper 1 MB memory also called HMA (High Memory Area). This location only for store the data not to execute the program. DOS also kept its data in it by the 'DOS=HI' statement. But the 'HIMEM.SYS' file must be installed first in the CONFIG.SYS file.
Fig. D-1. shows the memory map for the AT computer system. Its also included, memory location used by any programs and drivers, so we could see the whole system by hardware and software.


Fig. D-1. Memory Map of PC/XT/AT computer system.

E. HARDWARE INTERRUPT

In the earlier PC design, only 1 PIC (Programmable Interrupt Controller) implemented, and in the new design, it was added 1 more (cascade). These hardware interrupts have the priority level. Tabel. E-1. shows the complete hardware interrupts and their priority level in PC system design.

Hardware Int. No.	Desc. Master PIC	Desc. Slave PIC	Interrupt Vector Table No.	M A S T E R P I C
IRQ 0	Timer Int. (8253 PIT channel 0)		INT 08H
IRQ 1	Keyboard Int.		INT 09H
IRQ 2	Reserved (cascade), Clock Int.	Slave PIC (see below)	INT 0AH
IRQ 3	Serial Port 2 (COM-2)		INT 0BH
IRQ 4	Serial Port 1 (COM-1)		INT 0CH
IRQ 5	Fixed Disk Controller Int.		INT 0DH
IRQ 6	Floppy Disk Controller Int.		INT 0EH
IRQ 7	Parallel Printer Port Int.		INT 0FH
IRQ 8		Real Time Clock	INT 70H	S L A V E P I C
IRQ 9		Software Redirect to IRQ2	INT 71H
IRQ 10		Reserved	INT 72H
IRQ 11		Reserved	INT 73H
IRQ 12		Reserved	INT 74H
IRQ 13		Coprocessor	INT 75H
IRQ 14		Fixed Disk Controller	INT 76H
IRQ 15		Reserved	INT 77H

F. INTERRUPT VECTOR TABLE (IVT)

IVT is a table locate at 00000 hex. This table has 400 hex length. This table implemented on the Intel design architecture. In the begining, this location is to be used for the processor purpose, but in the PC design architecture the purpose is expanded. It's consist of a pair of pointer location; i.e.: CS:IP; where CS for code Segment and IP for Index Pointer. The size is 16 bit each. This pair of location consist of the routine program to do some task. The related function in the program is, location 00000 ~ 00003 hex used for INT 0, location 00004 ~ 00007 hex used for INT 1, and so on. The task for each interrupt is listed in Tabel. F-1. This table also a combined between hardware interrupt and software interrupt. We can also modified this interrupt to do some task for our purpose just by changing the interrupt pointer location not the whole routine.

Tabel F-1. Interrupt Vector Table for PC/XT/AT Computer.
INT. NO.	DESCRIPTION	INT. NO.	DESCRIPTION
INT 00 H	Division by Zero	INT 01 H	Single Stepping
INT 02 H	Non Maskable Interrupt	INT 03 H	Break Point
INT 04 H	Overflow (INTO)	INT 05 H	Print Screen
INT 06 H	Reserved	INT 07 H	Reserved
INT 08 H	Clock Tick (Hardware)	INT 09 H	Keyboard (Hardware)
INT 0A H	Reserved (Cascade PIC)	INT 0B H	COM-2 (Hardware)
INT 0C H	COM-1 (Hardware)	INT 0D H	Fixed Disk (Hardware)
INT 0E H	Floppy Disk (Hardware)	INT 0F H	LPT (Hardware)
INT 10 H	Video (Display)	INT 11 H	Device List
INT 12 H	Memory Size (for PC/XT system)	INT 13 H	Disk Drive (Software)
INT 14 H	COM (Software)	INT 15 H	Cassette (for PC/XT system)
INT 16 H	Keyboard Input (Software)	INT 17 H	LPT (Software)
INT 18 H	ROM BASIC (for PC/XT system)	INT 19 H	Bootstrap Startup
INT 1 H	Time of Day (TOD)	INT 1B H	Control Break
INT 1C H	Timer Tick	INT 1D H	Video Parameter Table
INT 1E H	Disk Drive Parameter Table	INT 1F H	CGA Video Graphic Character Table
INT 20 H	Program Terminate	INT 21 H	Various DOS Function
INT 22 H	End Routine Pointer	INT 23 H	DOS Control - C
INT 24 H	Critical DOS Error	INT 25 H	DOS Absolute Disk Read
INT 26 H	DOS Absolute Disk Write	INT 27 H	Terminate and Stay Resident
INT 28 H	Reserved	INT 29 H	Reserved
INT 2A H	Reserved	INT 2B H	Reserved
INT 2C H	Reserved	INT 2D H	Reserved
INT 2E H	Reserved	INT 2F H	DOS Multiplex Function
INT 30 H ~ INT 3F H		Reserved
INT 41 H	Reserved	INT 41 H	Fixed Disk Parameter Table
INT 42 H	Reserved	INT 43 H	EGA/VGA Video Graphic Character Table
INT 44 H ~ INT 5F H		Reserved
INT 60 H ~ INT 66 H	User	INT 67 H	LIM EMS Manager
INT 68 H ~ INT 7F H		Reserved (some used by slave PIC)
INT 80 H ~ INT 85 H		BASIC
INT 86 H ~ INT F0 H		BASIC Interpreter
INT F1 H ~ FF H		Reserved