IA PPT 4.pdf - Programmable Logic Control Systems VIT/E&TC/FINAL YEAR/B TECH/INDUSTRIAL AUTOMATION 1 Introduction 1 Many control applications do not

IA PPT 4.pdf - Programmable Logic Control Systems...

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Introduction 1. Many control applications do not involve analog process variables, that is, the ones which can assume a continuous range of values, but instead variables that are set valued, that is they only assume values belonging to a finite set. 2. The simplest examples of such variables are binary variables, that can have either of two possible values, (such as 1 or 0, on or off, open or closed etc.). 3. These control systems operate by turning on and off switches, motors, valves, and other devices in response to operating conditions and as a function of time. 4. Such systems are referred to as sequence/logic control systems. 5. For example, in the operation of transfer lines and automated assembly machines, sequence control is used to coordinate the various actions of the production system ( e.g., transfer of parts, changing of the tool, feeding of the metal cutting tool, etc. ). VIT/E&TC/FINAL YEAR/B. TECH,/INDUSTRIAL AUTOMATION 2
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Structure of a PLC program 1. PLC programs are structured in their composition. i.e. they consist of individual, separately defined programs sections which are executed in sequence. These programs sections are called ‘blocks” . 2. Each program section contains statements. The blocks are supposed to be functionally independent. Assigning a particular (technical) function to a specific block, which has clearly defined and simple interfaces with other blocks, yields a clear program structure. The testing of such programs in sections is substantially simplified. 3. Various types of blocks are available according to the function of the program section. 4. Users can also define separate data blocks for special purposes, such as monitoring, trending etc., and perform read/write on such areas. VIT/E&TC/FINAL YEAR/B. TECH,/INDUSTRIAL AUTOMATION 5
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A Relay Ladder Logic (RLL) 1. A Relay Ladder Logic (RLL) diagram, also referred to as a Ladder diagram is a visual and logical method of displaying the control logic which, based on the inputs determine the outputs of the program. 2. The ladder is made up of a series of “rungs” of logical expressions expressed graphically as series and parallel circuits of relay logic elements such as contacts, timers etc. 3. Each rung consist of a set of inputs on the left end of the rung and a single output at the right end of each rung. . VIT/E&TC/FINAL YEAR/B. TECH,/INDUSTRIAL AUTOMATION 6
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RLL operands In RLL Programs, inputs are represented as contacts. Two types of contacts are used, namely, normally open and normally closed contacts. The difference in the sense of interpretation between these contacts is shown.
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  • Spring '18
  • Prof. S. S. Bhatlawande

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