Omron CJ - 09-2009 Operation Manual page 47

Conformance to EC Directives
Countermeasure Examples
Circuit
Yes
CR method
Power
supply
No
Diode method
Power
supply
Yes
Varistor method
Power
supply
When switching an inductive load, connect an surge protector, diodes, etc., in
parallel with the load or contact as shown below.
Current Characteristic
AC DC
Yes If the load is a relay or solenoid, there is
a time lag between the moment the cir-
cuit is opened and the moment the load
is reset.
If the supply voltage is 24 or 48 V, insert
the surge protector in parallel with the
load. If the supply voltage is 100 to
200 V, insert the surge protector
between the contacts.
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 The varistor method prevents the impo-
sition of high voltage between the con-
tacts by using the constant voltage
characteristic of the varistor. There is
time lag between the moment the cir-
cuit is opened and the moment the load
is reset.
If the supply voltage is 24 or 48 V, insert
the varistor in parallel with the load. If
the supply voltage is 100 to 200 V,
insert the varistor between the con-
tacts.
When switching a load with a high inrush current such as an incandescent
lamp, suppress the inrush current as shown below.
Countermeasure 1
OUT
COM
Providing a dark current of
approx. one-third of the rated
value through an incandescent
lamp
The capacitance of the capacitor must
be 1 to 0.5 µF per contact current of
1 A and resistance of the resistor must
be 0.5 to 1 Ω per contact voltage of 1 V.
These values, however, vary with the
load and the characteristics of the
relay. Decide these values from experi-
ments, and take into consideration that
the capacitance suppresses spark dis-
charge when the contacts are sepa-
rated and the resistance limits the
current that flows into the load when
the circuit is closed again.
The dielectric strength of the capacitor
must be 200 to 300 V. If the circuit is an
AC circuit, use a capacitor with no
polarity.
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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Countermeasure 2
OUT
R
COM
Providing a limiting resistor
Required element
R
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