Programmable Controllers: Theory and Implementation

Introduction to PLC Programming and Implementation—from relay logic to PLC logic- Master control relays turn ON and OFF power to certain logic rungs. In a PLCprogram, an END MCR instruction must be placed after the last rung an MCR willcontrol.- PLCs do not allow bidirectional power flow, so all PLC rungs must be programmedto operate only in a forward path.- PLCs do not provide instantaneous contacts; therefore, an internal output must beused to trap a timer that requires these contacts.- Complicated logic rungs should be isolated from the other rungs during programming.• Program coding is the process of translating a logic or relay diagram into PLC ladderprogram form.• The benefits of modernizing a relay control system include greater reliability, lessenergy consumption, less space utilization, and greater flexibility.REVIEW QUESTIONS1 What is the first step in designing an effective PLC control system?a–approach the system in a systematic mannerb–flowchart the processc–define the control taskd–define the control strategy2 A(n) __________________ is a procedure that uses a finite number of steps toachieve a desired outcome.3 List four guidelines that are recommended as an approach to modernizing acontrol system.4 In a modernization project, an existing __________________ often defines thesequence of events in the control program.5 System operation for new applications usually begins with:a–sample diagramsb–specificationsc–the control strategyd–logic diagrams6 A(n) __________________ is a graphical representation of a solution’s algorithm.7 Logic sequences for a control program can be created using:a–logic gatesb–relay ladder symbologyc–PLC contact symbologyd–all of the aboveIndustrial Text & Video Company www.industrialtext.com 1-800-752-839855