InstrumentationEngg.Com - Instrumentation is the branch of engineering that deals with measurement and control

PLC – programmable logic controller (part 1)

Nagaraj Kanoor — Thu, 10 Sep 2009 09:26:18 +0000

PLC Pinball Machine

Nagaraj Kanoor — Thu, 10 Sep 2009 09:21:39 +0000

PLC Machine Control

Nagaraj Kanoor — Thu, 10 Sep 2009 09:17:13 +0000

PLC and Ladder Logic

Nagaraj Kanoor — Thu, 10 Sep 2009 09:06:43 +0000

[PPT]PROGRAMMABLE LOGIC CONTROLLER

Nagaraj Kanoor — Sun, 06 Sep 2009 17:11:18 +0000

Control Systems Types
Programmable Logic Controllers
Distributed Control System
PC- Based Controls
Programmable Logic Controllers
Sequential logic solver
PID Calculations.
Advanced Subroutines
BIT Operations.
Data Transfer.
Text Handling.

Applications :
Machine controls, Packaging, Palletizing, Material handling, similar Sequential task as well as Process control
Advantages of PLC :
They are fast and designed for the rugged industrial environment.
They are attractive on Cost-Per-Point Basis.
These Devices are less Proprietary ( E.g.. Using Open Bus Interface.)
These Systems are upgraded to add more Intelligence and Capabilities with dedicated PID and Ethernet Modules.
Disadvantages of PLC :
PLC were Designed for Relay Logic Ladder and have Difficulty with some Smart Devices.
To maximize PLC performance and Flexibility, a number of Optional Modules must be added

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[PPT]Programming PLCs using LADDER Logic

Nagaraj Kanoor — Sun, 06 Sep 2009 16:54:15 +0000

Review of Ladder Programming
Keyence PLC Ladder Builder
Example 1: Motor Control
Example 2: Drill Control
Example 3: Traffic Light
Ladder Logic Diagrams
Diagrams
Sequential Function Charts
Instruction ListFunction Block
Structured Text
High-Level Language

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[PPT]Introduction toIEC1131-3 Ladder Diagram

Nagaraj Kanoor — Sun, 06 Sep 2009 16:33:55 +0000

Origins of Ladder Diagram

The Ladder Diagram (LD) programming language originated from the graphical representation used to design an electrical control system
Control decisions were made using relays
After a while Relays were replaced by logic circuits
Logic gates used to make control decisions
Finally CPUs were added to take over the function of the logic circuits
I/O Devices wired to buffer transistors
Control decisions accomplished through programming
Relay Logic representation (or LD) was developed to make program creation and maintenance easier
Computer based graphical representation of wiring diagrams that was easy to understand
Reduced training and support cost

What is a Rung?
A rung of ladder diagram code can contain both input and output instructions
Input instructions perform a comparison or test and set the rung state based on the outcome
Normally left justified on the rung
Output instructions examine the rung state and execute some operation or function
In some cases output instructions can set the rung state
Normally right justified on the rung

A Full Presentation File :

Programmable Logic Controllers-Fourth Edition by W. Bolton

Nagaraj Kanoor — Sun, 06 Sep 2009 16:20:50 +0000

This chapter is an introduction to the programmable logic controller, its
general function, hardware forms and internal architecture. This overview
is followed up by more detailed discussion in the following chapters.
What type of task might a control system have? It might be required to
control a sequence of events or maintain some variable constant or follow
some prescribed change. For example, the control system for an automatic
drilling machine (Figure 1.1(a)) might be required to start lowering the
drill when the workpiece is in position, start drilling when the drill reaches
the workpiece, stop drilling when the drill has produced the required
depth of hole, retract the drill and then switch off and wait for the next
workpiece to be put in position before repeating the operation. Another
control system (Figure 1.1(b)) might be used to control the number of
items moving along a conveyor belt and direct them into a packing case.
The inputs to such control systems might be from switches being closed or
opened, e.g. the presence of the workpiece might be indicated by it
moving against a switch and closing it, or other sensors such as those used
for temperature or flow rates. The controller might be required to run a
motor to move an object to some position, or to turn a valve, or perhaps a
heater, on or off.

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PROGRAMMABLE CONTROLLERS HAND BOOK – L.A.BRYAN

Nagaraj Kanoor — Sun, 06 Sep 2009 12:45:04 +0000

Programmable logic controllers, also called programmable controllers or
PLCs, are solid-state members of the computer family, using integrated
circuits instead of electromechanical devices to implement control functions.
They are capable of storing instructions, such as sequencing, timing,
counting, arithmetic, data manipulation, and communication, to control
industrial machines and processes. Figure 1-1 illustrates a conceptual
diagram of a PLC application

Programmable controllers have many definitions. However, PLCs can be
thought of in simple terms as industrial computers with specially designed
architecture in both their central units (the PLC itself) and their interfacing
circuitry to field devices (input/output connections to the real world).
As you will see throughout this book, programmable logic controllers are
mature industrial controllers with their design roots based on the principles of
simplicity and practical application.

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Instrumentation

Nagaraj Kanoor — Sun, 06 Sep 2009 05:47:50 +0000

Instrumentation is the branch of engineering that deals with measurement and control.

An instrument is a device that measures or manipulates variables such as flow, temperature, level, or pressure. Instruments include many varied contrivances which can be as simple as valves and transmitters, and as complex as analyzers. Instruments often comprise control systems of varied processes. The control of processes is one of the main branches of applied instrumentation.

Control instrumentation includes devices such as solenoids, valves, circuit breakers, and relays. These devices are able to change a field parameter, and provide remote or automated control capabilities.

Transmitters are devices which produce an analog signal, usually in the form of a 4–20 mA electrical current signal, although many other options using voltage, frequency, or pressure are possible. This signal can be used to control other instruments directly, or it can be sent to a PLC, DCS, SCADA system, or other type of computerized controller, where it can be interpreted into readable values and used to control other devices and processes in the system.

Instrumentation plays a significant role in both gathering information from the field and changing the field parameters, and as such are a key part of control loops.