Omron NX-ID User Manual page 211

Inductive Load
The life of the Relay varies with the load inductance.
If any inductive load is used, we recommend that you use a contact protection circuit.
tion Circuit on page 7-21).
Be sure to connect a contact protection circuit in parallel with every DC inductive load that is connected
to the Contact Output Unit because the usage of a contact protection circuit has a significant effect on
the service life of the contact.
Contact Protection Circuit
Contact protection circuits are used with the Contact Output Unit in order to prolong the life of each
relay mounted to the Contact Output Unit, prevent noise, and reduce the generation of carbide and
nitrate deposits caused by arcs. However, if contact protection circuits are used incorrectly, they can
reduce relay service life. Using a contact protection circuit can also cause a delay in the resetting time
(shut-off time).
Contact protection circuit examples are listed in the following table.
Circuit
CR
method
NX-series Digital I/O Unit User's Manual (W521)
Current
AC DC
Yes Yes If the load is a relay or
C
Power
supply
R
Feature
The capacitance of the capaci-
solenoid, there is a delay tor should be approx. 1 to 0.5
in the resetting time. μF per contact current of 1 A
and resistance of the resistor
If the power supply volt-
should be approx. 0.5 to 1 Ω
age is 24 or 48 V, con-
per contact voltage of 1 V.
nect the contact
protection circuit in paral- C: The capacitance of the
lel with the load. If the capacitor should be approx. 0.5
supply voltage is 100 to to 1 μF per contact current of 1
200 V, connect the con- A.
tact protection circuit
R: The resistance of the resis-
between the contacts.
tor should be approx. 0.5 to 1 Ω
per contact voltage of 1 V.
These values, however, vary
depending on the load and the
characteristics of the relay.
Decide these values from
experiments, and take into con-
sideration that the capacitance
suppresses spark discharge
when the contacts are sepa-
rated and the resistance
restricts 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.
7 Digital Output Units
Contact Protec-
(
Required element
7 - 21
7