programmable logic controller.pptx

7/29/2019 PROGRAMMABLE LOGIC CONTROLLER.pptx

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PROGRAMMABLE LOGIC CONTROLLER

Mukhlizar

20213048

ELEKTRONIKA INDUSTRIcopy right 2013


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Overview of Programmable Controllers

The programmable controllers has become the most powerful change to occur inthe electronics world for factory automation. The programmable controller (P/C)

is also called the programmable logic controller (PLC). Since the personal

computer is called a PC, the programmable controller is referred to as a PLC to

prevent confusion. As an electronics technician, you will run into the PLC in a

number of places such as on the factory floor, in a repair facility, or you might

work for a company that manufactures components and boards that are used to

interface with PLCs.

In this chapter you are going to study PLCs from two different perspectives. First,

you will see how the PLCs can be programmed to perform the same logic

functions that the IC logic chips and relay in Chapter 1 and 2 performed. Second,you will see the large amount of electronics involved in the input and output

modules that the controller uses for interfacing a variety of industrial voltages.



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Overview of Programmable Controllers

The programmable logic controller (PLC) is a computer that is designed to solve

logic (AND, OR, NOT) that specifically controls industrial devices such as motors

and switches and allow oher control devices of varied voltages to be easily

interfaced to provide simple or complex machine control.

The computer part of the PLC, which is called a central processing unit (CPU),

allows a program to be entered into its memory that will represent the logic

functions. The program in the PLC is not a normal computer programming

language like BASIC, Fortran, or C. Instead the PLC program uses contact and coil

symbols to indicate which switches should control which output. These symbols

look similar to a typical relay ladder diagram shown in chapter 1.



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Figure 1.1 Example of a typical programmable controller program called ladder

logic. This program uses to generic addresses of input 1, input 2,

output 1, and so on.



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Basic Parts of Simple Programmable Controller

All PLCs have four basic major parts: power supply, processor, input modules, andoutput modules. A fifth part, a pogramming device, is not considered a basic part

since some PLCs will not have one if its program is loaded from an EPROM

(erasable programmable read-only memory) chip.

Figur 1.2 Block diagram showing the

four major parts of a programmable

controller. The programming panel is

the fifth part of the system, but it is not

considered a basic part of the PLC since

it can be disconnected when it is not

needed.



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The Programming Panel

At the bottom of the diagram in figure 1.2 you can also see a programming panel. Today theprogramming panel is a computer and is necessary to program the PLCs, but it is not considered to be

one of the parts of a PLC because the programming panel or device can be disconnected after the

program is loaded and the PLC will run by itself. The programming device is used so humans can make

changes to the program, troubleshoot the inputs and outputs by viewing the status of contacts and coils

to see if they are energized or deenergized, and for saving programs to disk, or loading programs from

disk.

The programming panel can be a dedicated device or it can be a personal or portable computer with PLC

programming software loaded on it. The ladder logic program is able to be displayed on the

programming device where it can become animated. This feature is unique to the PLC and it helps the

technician troubleshoot very large logic circuits that control complex equipment.

Another feature that makes a PLC so desirable is the fact that it has most of the logic functions found in

the machine language program of any miroprocessor chip. This means that functions such as timing andcounting can be executed by the PLC rather than using electromechanical or electronic timers and

counters.



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An Example Programmable Controller Application

Figure 1.3 Input and output diagram that shows all switches that are connected to the PLC input module

and motor starters that are connected to the PLC output modules. The input and outputnumbering is generic and does not represent any brand-name programmable controller



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Scanning a PLC program When

It is The Run Mode

The PLC processor examines its program line by line, which is the way it solves its logic. The processor in

the PLC actually performs several additional functions when it is in the run mode. These functions

include reading the status of all inputs, solving logic, and writing the results of the logic to the output.

When the processor is performing all of these functions, it said to be scanning its program.

Image Register

The Run Mode and the Program Mode

On-line and Off-line Programming



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Equating the PLC with Traditional Solid-State Logic

Figure 1.4 Solid-state logic gates used to provide the same logic as the PLC box-sorting program

It may be easier to equate the operation of a PLC-controlled program with the same program using solid-

state logic (AND, OR, and NOT) functions.



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Features of the Programmable Controller



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Operation of Programmable Controller



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Operation of the Heat-Treating Part of the System



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Using Timers to Stage the Electric Heat



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Counter Operation in a PLC



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Timing and Counting Large Values



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Circuits for Input and output Modules



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Wiring Input Switches and Output Devices to the PLC



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Analog Input Modules



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Master Control Reset and Zone Control Last State



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Using a Hand-Held Programmer



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Advanced Instructions Found in Larger PLCs



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Addressing Other Allen Bradley PLCs



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Documenting a PLC Program with Software


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