April 2019

with a multimeter. By checking the resistance of the PLC earth terminal to a main earth bonding point in the equipment enclosure, you can establish if this is the root of the problem. Interference Electromagnetic interference (EMI) and radio frequency interference (RFI) are common in industrial environments that contain a variety of electrical equipment. Electrical noise needs to be controlled because it can lead to intermittent faults or unusual behaviour – or even complete PLC failures. There are many ways to mitigate the risk of downtime caused by electrical noise. For example, you can minimise noise by relocating sensitive equipment, segregating systems with high power components and adding barriers, grounding, or shielding cable between sensitive equipment. Network and communications Most PLC systems need to communicate with peripheral devices such as HMIs, typically via an industrial network, which are increasingly based on industrial Ethernet. Any loss of communications between devices can result in immediate plant downtime. You can mitigate against the risk of communications failures by ensuring the physical network infrastructure is installed and terminated correctly, that your network devices are suitable for purpose, and that firmware patches are installed regularly to maintain reliable and secure operation. Managing the risks By following a best practice routine, companies can minimise the chance of PLC system failures. You should ensure that the environment in which your control system is operating is sound. Through systematic inspections, you should be able to identify problems such as overheating or electrical noise. Obsolescence management is also important because PLC manufacturers regularly cycle their product ranges. If a component is several years old, it is important to have a readily available replacement. Businesses can manage this internally or can turn to third-party suppliers who can indicate which areas of a control system are most likely to lead to failure and put contingency plans in place to mitigate that risk, including sourcing legacy components. Although the PLC has been around for a long time, it is not invincible. However, with proactive maintenance, environment control and contingency plans, PLC control systems can keep operations up and running every day of the year. n .c o.uk r w.eplancoginee ww .er .cimat ehc Seor M.onimat otu Aeor LPE orM AN Se eingo M.de C ep Software analysis can help to pinpoint the cause of PLC system failures INDUSTRIAL CONTROLS n