Omron CQM1H - 08-2005 Operation Manual page 22

Conformance to EC Directives
Countermeasures
Countermeasure Examples
Circuit
CR method
Power
supply
Diode method
Power
supply
Varistor method
Power
supply
put switching may not satisfy these Standards. In such a case, a noise filter
must be connected to the load side or other appropriate countermeasures
must be provided external to the PC.
Countermeasures taken to satisfy the standards vary depending on the
devices on the load side, wiring, configuration of machines, etc. Following are
examples of countermeasures for reducing the generated noise.
Refer to EN61000-6-4 for more details.
Countermeasures are not required if the frequency of load switching for the
whole system including the PC is less than 5 times per minute.
Countermeasures are required if the frequency of load switching for the whole
system including the PC is 5 times or more per minute.
When switching an inductive load, connect a surge protector, diodes, etc., in
parallel with the load or contact as shown below.
Current
AC DC
Yes Yes If the load is a relay or solenoid, there is
a time lag between the moment the
circuit 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.
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 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
contacts.
Characteristic Required element
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 testing,
and take into consideration that the
capacitance suppresses spark
discharge when the contacts are
separated 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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