Omron ZEN Operation Manual page 23

Circuit
Diode method
Power
supply
Varistor method
Power
supply
Current Characteristic
AC DC
No Yes The diode connected in
parallel with the load
changes energy
accumulated by the coil
into a current, which then
flows into the coil so that
the current will be
converted into Joule heat
by the resistance of the
inductive load.
This time lag, between
the moment the circuit is
opened and the moment
the load is reset, caused
by this method is longer
than that caused by the
CR method.
Yes Yes The varistor method
prevents the imposition of
high voltage between the
contacts by using the
constant voltage
characteristic of the
varistor. There is time lag
between the moment the
circuit is opened and the
moment the load is reset.
If the supply voltage is 12
to 48 V, insert the varistor
in parallel with the load. If
the supply voltage is 100
to 200 V, insert the
varistor between the
contacts.
Precautions
Required element
The reversed dielectric
strength value of the diode
must be at least 10 times as
large as the circuit voltage
value. The forward current of
the diode must be the same as
or larger than the load current.
The reversed dielectric
strength value of the diode
may be two to three times
larger than the supply voltage
if the surge protector is
applied to electronic circuits
with low circuit voltages.
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