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5 reasons for PLC failure

Like all electronic equipment, a PLC (programmable logic controller) may occasionally fail. Here we look at five of the most commons reasons for PLC failure:

Power supply issues

Loose, corroded connections are often responsible for power supply faults, so carry out a visual inspection. Test the integrity of the ground by measuring the voltage between the PLC ground terminal and a known ground. Also check the PLC’s input voltage to ensure it is within the manufacturer's recommended range.

Communication problems

Many PLCs provide multiple communication protocols, so be certain you’re using the right one. Check diagnostic indicators which may reveal a CPU (central processing unit) fault.

Electromagnetic interference (EMI)

Along with radio frequency interference (RFI), EMI is another cause of PLC malfunction. These issues occur due to events such as large motor starting, nearby arc welding, lightning strikes and the use of handheld radio transmitters. Handheld radios emit RF radiation and if electronic equipment is not protected can cause serious disruption.

Conflict between internal PLC status and environment

Inputs and output issues occur when the PLC’s internal status does not agree with external conditions. Consult the manufacturer’s documentation or contact your service provider for assistance.

Corrupted memory

Interference and power supply issues may disturb and corrupt a PLC’s memory, so ensure the programme is valid and comparable with a backup copy. Backups can be stored on tape, disk or in the cloud, and physical copies should be stored away from heat and humidity and out of range of EMI and RFI.

For help with PLC fault finding, plus PLC installations and other associated services, call Barry Horsfall on 01621 868138 or email

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  • Date: 20 January 2017 Rajan Mahajan
    It's a short but an interesting blog. In short it tells many more about PLC failure. Thank you very much for sharing this blog.

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