xxii
Precautions
Relay Output Noise Reduction Methods
The ZEN conforms to EN 61131-2 of the EMC Directives. However, noise generated by
relay output 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 ZEN.
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.
Countermeasures
(Refer to EN61131-2 for more details.)
• Countermeasures are not required if the frequency of load switching for the whole
system with the ZEN included is less than 5 times per minute.
• Countermeasures are required if the frequency of load switching for the whole
system with the ZEN included is 5 times per minute or higher.
Countermeasure Examples
When switching an inductive load, connect an surge protector, diodes,
etc., in parallel with the load or contact as shown below.
Circuit Current Characteristic Required element
AC DC
CR method 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 12
to 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.
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 experiments, 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.
Power
supply
Inductive
load
C
R
Z211-E1-03.book Page xxii Friday, November 21, 2008 10:38 AM
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