Logic Gates and Related Devices
103
A
B
Y
Figure 4.46 Example 4.15.
&
A
B
>1
1
=1
Y
Figure 4.47 Solution to example 4.15.
4.13.1 OR Gate
An OR gate can be used in all those situations where the occurrence of any one or more than one
event needs to be detected or acted upon. One such example is an industrial plant where any one or
more than one parameter exceeding a preset limiting value should lead to initiation of some kind of
protective action. Figure 4.48 shows a typical schematic where the OR gate is used to detect either
temperature or pressure exceeding a preset threshold value and produce the necessary command signal
for the system.
Shutdown
command
PLANT
Temp Pressure
Reference
Reference
Comparators
+
–
+
–
Sensors
Figure 4.48 Application of an OR gate.