Avoiding EMC problems in control panels
Electromagnetic disturbances are potential sources of malfunctions for all electronic equipment from PLCs and inverter drives to measuring and processing devices. They can affect the performance of equipment causing it to malfunction and possibly crash. Because problems due to electrical noise are often transient they are notoriously difficult to identify and correct and good practice is recommended.
Conducted interference of various frequencies can be superimposed on the original signal. The signal may be unreadable by the equipment that receives it and consequently its processing will be uncertain or impossible. If a processing device such as a microprocessor is disturbed by high-frequency waves it can crash or produce abnormal results: when it restarts there is no apparent reason for the problem.
To help equipment users, Schneider Electric has produced a 24 page booklet on “How to protect a machine from malfunctions due to electromagnetic disturbance” which is now available as a download from 999inverters.co.uk.
It comprises three sections covering:
- Panel design in accordance with EMC rules
- Assembly – panel wiring
- Guide for selection of “EMC” products
Variable speed drives may affect other equipment by causing interference problems conducted through cables or radiated by the device. The most appropriate treatment is to arrange a filter on the disturbed line, as close as possible to the drive. The appropriate filter characteristics are given by the manufacturers according to the voltage, the line current and the frequency of the disturbance to be reduced.
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