West Control Solutions CALogix - Manual (Page 8)

EMC GUIDELINES
We make a number of general recommendations that can reduce the possibility of EMC problems
.
1) It is important to suppress CALogix relay contacts, this will reduce switching interference and also prolongs life
of the contacts.
RC Networks fitted across the relay contacts are recommended for resistive and larger inductive loads, values
such as 0.1
μF capacitor in series with a 100Ω resistor.
For small inductive loads, a suitable rated VDR is recommended.
For small inductive dc loads, relays etc, a suitably rated diode fitted in parallel with the load is recommended.
2) CALogix should be mounted into a metal cabinet which is properly earthed, good all round metal shielding is
important.
3) It should be borne in mind that the wiring of the installation can significantly reduce the efficiency of the
instrumentation immunity. This is due to the ease with which high frequency RF can enter via unprotected
incoming and outgoing cables.
Earthed thermocouples or sensors with screened cable, should be earthed at the cabinet entry point.
Any long cables entering the control cabinet should be protected at the point where they enter the cabinet, large
diameter ferrite sleeves are an economical and effective method of reducing high frequency RF, looping the
cables through ferrite sleeves a number of times will improve the efficiency of the filtering.
Alternatively for mains cables, the fitting of a suitable mains filter can provide good results.
Data or communications cables should be screened. If using Belden 8132 connect drain wire to PIN 5 of a
shielded RJ45 connector.
Ideally data and sensor cables should be routed separately from power cables and away from inverters or other
high power/frequency devices.
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