Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

20.2.1 Boolean Algebra for Circuit and Ladder Logic Design

 

· When we have logical decisions to make, truth tables and Boolean algebra allow formal methods to be used. The use of formal methods improves the overall quality of the design.

 

· Consider the example of a burglar alarm

  1. 1. If alarm is on, check sensors.
  2. 2. If window/door sensor is broken (turns off), sound alarm and turn on lights
  3. 3. If motion sensor goes on (detects thief) sound alarm and turn on lights.
  4.  
  5. A = Alarm and lights switch (1 = on)
  6. W = Window/Door sensor (1 = OK)
  7. M = Motion Sensor (0 = OK)
  8. S = Alarm Active switch (1 = on)
  9.  

 

 

 

 

 

· This example was quite simple. To do more complicated problems we will need to review some basic theory first.