Clive’s PLC Failures

PEME Software Manager, Clive Wardle, was recently asked for his opinion on the top causes of PLC control system failure and how the risks can be minimised.

Clive advises that there are six common causes of PLC Control System failure that are avoidable with an appropriate Preventive Maintenance strategy:

  • I/O card or field device failures; Damaged field wiring or faulty devices can cause I/O card failures. These faults can be minimised by routine inspection of cables and cable containment systems and by regular maintenance of field devices
  • Program loss due to failed batteries; Program loss is usually the result of power failure with inadequate battery power but can also sometimes be caused by power supply spikes. Batteries have a finite life and this problem can be minimised by the scheduled replacement of PLC batteries
  • Poor back-up procedures; PLC programs should be backed-up and safely stored so that a PLC can be rapidly restored in the event of the PLC failing and requiring replacement or should the program be lost
  • Earthing problems; Earthing issues can be introduced by corrosion or poor connections. The earth integrity can be checked by regular inspection and measurement of any voltage between the earth point and a known ground
  • Power supply failures; Power supply problems may be the result of corroded or poor connections. These can be reduced by regular inspection and measurement of supply voltage to ensure that they are within the manufacturer’s tolerances for the equipment
  • Environmental factors such as heat, dust or moisture; These can be monitored by regular inspection and maintenance of panels to check the integrity of protection measures such as panel cooling / filtering and seals