copyright © 2002 delmar thomson learning chapter 13 understanding relay instructions and the...

Copyright © 2002 Delmar Thomson Learning

Chapter 13

Understanding Relay Instructions

and the Programmable Controller Input

Modules


ObjectivesExplain proper programming of normal

closed and normally open PLC input signals.

Describe hardware relay operation and its correlation to proper PLC interface and programming.

Convert a conventional start-stop schematic to a PLC ladder rung diagram.


Objectives (cont’d.)Explain why PLC ladder logic for

motor starter interface has an additional contact in comparison to a conventional schematic.

Hook up a start-stop station to a PLC input module.

Hook up and develop a PLC program to correctly control a motor starter.


Typical Hard-Wired Start-Stop Latching

Circuit


Incorrect Conversion of Conventional Start-Stop Schematic to PLC Control


Normally Open Push Button and Non-Energized Relay


Normally Open Push Button Energizing Relay Coil and Pilot

Light B


Normally Closed Push Button Energizing Relay Coil and Pilot

Light B


Normally Closed Stop Push Button Depressed


Relay Status in Conjunction with Input Push Buttons


Input and Output Separation


Separated Inputs Connected to PLC Input Screw Terminals


Start Push-Button Status Reflected in the Input Status

Table


Start-Stop Input Bit Status from Input Hardware in a Non-

Energized State


Normally Open Push Button Not Activated


Normally Open Push Button Input Pressed


Normally Closed Input Push Button


Normally Closed Push Button Input to PLC


Push Button Released Output Latched through CR

1-1


Conventional Schematic Start-Stop Logic


Conventional Motor Starter Schematic Diagram


Conventional Motor Starter Circuit Converted for PLC

System Management

copyright © 2002 delmar thomson learning chapter 13 understanding relay instructions and the...

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