Programmable Logic Controllers
Programmable Logic Controllers
5th Edition
ISBN: 9780073373843
Author: Frank D. Petruzella
Publisher: McGraw-Hill Education
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Concept explainers

Question
Chapter 12, Problem 1RQ
Program Plan Intro

Sequencers:

  • Programmable Logic Controller (PLC) sequencer performs ON or OFF output patterns using sequencer instructions.
  • The sequencer output instruction is used for controlling the output devices.
  • PLC sequencer instructions are used for controlling machines which provides a stepped sequence of repeatable operations.
  • It simplifies the ladder program by allowing the user to use a single or pair of instructions for performing complex operations.
  • Various sequencer instructions can be programmed based on the PLC manufacturer.

Drum switch:

  • Drum switch is also known as sequencer switch.
  • The drum switch includes a series of normally open contact blocks which are operated by pegs situated on a motor-driven drum.

Expert Solution & Answer
Check Mark

Explanation of Solution

Operation of a drum switch:

The operation of a drum switch is described as given below.

  • In a drum sequencer, the pegs are situated at specific locations around the circumference of the drum for operating the contact blocks.
  • When the drum starts rotating, no pegs will remain open and all the contacts that are arranged in a line with the pegs will remain closed.
  • Logic 1 or ON is used to indicate the presence of a peg and logic 0 or OFF is used to indicate the absence of a peg.

The mechanical drum-operated sequencer switch is depicted as follows.

Programmable Logic Controllers, Chapter 12, Problem 1RQ

  • The ON/OFF operation of 16 discrete outputs is controlled by the drum cylinder.
  • The data table given below is used to illustrate the logic state for the first four steps of the drum cylinder.
1111000100010101
0000111010100101
0000001010001110
0111000001010101

Here, each location where a peg is present is represented by 1 (ON) and the locations where there are no pegs are represented by 0 (OFF).

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