Chapter 8, Problem 1RQ

Name the three forms of PLC counter instructions, and explain the basic operation of each.

Program Plan Intro

Programmable Logic Controller (PLC):

• Programmable Logic Controller (PLC) is a specialized computer used in industrial segments to control machines and process.
• PLC is program that consists of a set of instructions which resembles the controlling functions needed to perform specific tasks.
• The function of PLC is similar to that of a relay and hence, in an industrial segment a relay is greatly replaced by a suitable PLC.
• When compared to general Personal Computer (PC), a PLC is available in small and tiny sizes.
• The basic architecture of a PLC consists of an input-output interface module and a small Central Processing Unit (CPU) that runs by control programming language.

PLC counter:

A counter is a PLC instruction which counts up or down when the input transfers from an off state (false) to an on state (true).

Explanation of Solution

Forms of PLC counter instructions and its operation:

The PLC counter instructions are basically classified into three different categories as follows:

• Up Counter
  • This is an instruction whose count will be incremented by one each time when an event occurs.
• Down Counter
  • This is an instruction whose count will be decremented by one each time when an event occurs.
• Combined Counter
  • This is an instruction whose count will be either incremented or decremented by one, based on which count input is triggered, each time an even occurs.
  • It is also known as up-down counter.