Drives & Controls Magazine November/December 2022

n CONTROLGEAR AND ENCLOSURES I naccurate readings, runaway conveyors and crazy crankshafts are all potentially dangerous situations that can occur when electronic and electrical equipment is exposed to electromagnetic and radio frequency interference (EMI/RFI). Back in November 2000, a friend of mine attended an EMC seminar in Sydney, Australia, where one of the attendees told a story about the dangers of EMC gone wrong. He explained how, while he’d been repairing a diesel generator, the engine had sprung into life with the crankshaft whirring a few centimetres fromhis face. A powerful radio signal from a nearby emergency services vehicle had caused the generator’s PLC to initiate a start, despite the fact that the sump, the PLC and control panel were all set to their off positions. While safety-critical PLCs may have prevented this situation, the story demonstrates the potential of RFI and EMI to wreak havoc. Any device connected to the mains can be susceptible to EMC issues. This can include everything frommedical devices, HVAC equipment and control panels, to conveyor lines and evenmilitary equipment. These systems often incorporate switch-mode power supplies (SMPSs) or variable-speed drives (VSDs) that can generate high-frequency interference. If allowed to propagate through the mains power supply, these systems could create problems for other equipment connected to the same supply. This is where EMC filters can help. An EMC filter connects to the mains input and supresses interference. It can also provide immunity and protection to that equipment to allow it to operate as designed. Failing to address the potential risks of EMI and RFI – by not using an EMC filter, for instance – can lead to the type of problemdescribed earlier. A 4-20mA control signal, for example, can easily be upset if subjected to RFI from a nearby VSD cable. Interference can also compromise readings and sensors. A voltmeter may display inaccurate results or a conveyor line could end up running faster than intended. The EMC Directive 2014/30/EU was introduced to prevent these issues. The problem is that selecting harmonised test standards under the Directive is no longer sufficient for legal compliance. As the EMC expert Keith Armstrong explains: “If you are still choosing the most relevant test standards listed under the official EMC Directive, then passing those tests and listing them on your Declarations of EMC Conformity, you are five years out-of-date and your products might suffer costly delays in EU and UK customs. “Instead, since the EMC Directive – as well as the UK EMC Regulations – came into force in 2016, we have been required to perform and document an‘adequate analysis and assessment of the risks’of our products complying with the Directive’s Essential Requirements.” In practice, this means that buying a cheap EMC filter from a catalogue will probably not prevent EMC issues andmay be non-compliant. Understanding your equipment, how it interacts with other equipment and the environment in which it operates, is the best way to specifying the right EMC filter. A filter circuit is essentially a combination of inductors, capacitors and resistors. It needs to be configured in a way that takes into account cooling, ingress protection and terminal capabilities, among other factors. So, to avoid experiencing inaccurate readings, runaway conveyors or a crazy crankshafts, it could be time to reassess your EMC filters. n EMC filters come in variety of shapes, sizes and ratings. Choose the most appropriate type for your application. Steve Hughes, managing director of the power quality specialist REO UK, explains that not all electromagnetic compatibility (EMC) filters are the same, and why it may be time to re-assess yours if you want to avoid the dangers of radio frequency and electromagnetic interference. Not all EMC filters are the same