Automating Manufacturing Systems - Process Control and ...

plc electrical - 31.14
output
common
Control Relay (PLC)
inductive load
VDC+/VAC
VDC-/COM.
Power supply
Uncompensated
output
common
Relay or Triac
inductive load
L
+
C R Vs
-
VAC
COM.
Power supply
R = Vs*(.5 to 1) ohms
C = (.5 to 1)/Adc (microfarads)
Vcapacitor = 2(Vswitching) + (200 to 300) V
where,
Adc is the rated amperage of the load
Vs is the voltage of the load/power supply
Vswitching may be up to 10*Vs
Compensating
for AC loads
output
inductive load
+
Compensating
for DC loads
common
Relay or Transistor
-
Power supply
Figure 31.11
Surge Suppressors
31.2.5 PLC Enclosures
PLCs are well built and rugged, but they are still relatively easy to damage on the
factory floor. As a result, enclosures are often used to protect them from the local environment.
Some of the most important factors are listed below with short explanations.