Appendices
A - 80
NX-series Digital I/O Unit User’s Manual (W521)
A-4 EMC Directive Measures for Relay
Outputs
Conformance to EC Directives
The NX-series I/O Units conform to the Common Emission Standards (EN 61131-2) of the EMC
Directives. However, when incorporating in the system, noise generated by relay output switching
may not satisfy these Standards.
In such a case, appropriate countermeasures must be provided externally to the Output Unit, such
as by connecting a contact protection circuit. Countermeasures taken to satisfy the standards vary
depending on the devices on the load side, wiring, configuration of machines, etc.
Countermeasures
• Countermeasures are not required: the switching frequency of the entire system incorporating the
Output Unit is less than 5 times per minute
• Countermeasures are required: the switching frequency of the entire system incorporating the
Output Unit is more than 5 times per minute
Refer to EN 61131-2 for details.
Countermeasure Example
The following measures must be taken.
Use the measures to reduce the noises that are occurred.
• When switching an inductive load, connect a contact protection circuit in parallel with the load or
contact. (Refer to Inductive Load on page 7-22.)
• When switching a load with a high inrush current such as an incandescent lamp, use either of the
following methods to reduce the inrush current.
<Method 1. Draw about 1/3 of the current consumed by the load.>
<Method 2. Mount a limiting resistor.>
IOG
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Power supply
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