58
When an inductive load is connected to the input or output of the CPU, it is
necessary to connect a surge suppressor or a diode in parallel with the load,
as shown below, to absorb the counter-electromotive force produced by the
load.
L
Surge suppressor
OUT
COM
Relay, or triac
output
COM
IN
DC Input
L
Diode
L
OUT
COM
Relay, or transistor
output
+
Diode
Resistor: 50 W
Capacitor: 0.47 mF
Voltage: 200 V
Diode: Must withstand
voltages more
than three times
the load voltage
and an average
current of 1 A
Output Loads Be sure to take appropriate measures when any electrical device likely to
produce noise is connected to the CPU as a load. For example, electromag-
netic relays and valves generating noise of more than 1,200 V require noise
suppression. For AC noise sources, connect a surge suppressor in parallel
with the coil of each device. For DC noise sources, connect a diode in paral-
lel with the coil of each device. When mounting a CPU and an Expansion I/O
Unit on a control panel, be sure to completely ground the intermediate
mounting plate. The mounting plate must be finished with high-conductivity
plating to ensure noise immunity.
RR
–
+
Surge
suppressor
AC power source DC power source
Diode
Inductive Load Surge
Suppressors
Preventive Measures Section 3-4
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