Not all EMC filters are born equal

26Oct

Here, Steve Hughes, Managing Director of REO UK, explains how not all electromagnetic compatibility (EMC) filters are born equal and why it may be time to reassess yours.

Inaccurate readings, runaway conveyors and crazy crankshafts: all potentially dangerous situations that can occur when electronic and electrical equipment is exposed to electromagnetic and radiofrequency 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 working on repairing a diesel generator the engine sprang into life with the crankshaft whirring within a few centimetres of his face. The powerful radio signal from a nearby emergency services vehicle had caused the generator’s PLC to initiate a start command, despite the fact that the sump, PLC and control panel were all set to their off positions.

While safety-critical PLCs may likely have prevented this situation, the story demonstrates the power of RFI and EMI to wreak havoc in industrial settings.

Any device connected to the mains is susceptible to EMC issues. Everything from medical devices, HVAC equipment, control panels in process manufacturing, conveyor lines and even military equipment.

These devices generally use switch mode power supplies (SMPS) or variable speed drives (VSDs), generating high-frequency interference which, if allowed to propagate to the mains power supply, 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 device and is used to suppress interference, but also to provide immunity and protection to that equipment to allow it to operate as designed. Failing to address EMI and RFI, by not using an EMC filter, for instance, can lead to the kinds of problems our generator engineer experienced earlier.

A control signal, for example, that operates between 4-20mA is easy to upset when subjected to RFI from a nearby VSD cable. It 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 industry-leading 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 the cheapest off-the-shelf EMC filter from a catalogue will likely not prevent EMC issues and may mean non-compliance. Understanding your equipment, how it interacts with other equipment and the environment in which it operates is the best way to make a justified engineering decision and specify the right EMC filter.

Our expertise at REO UK is taking that filter circuit, which is essentially a mixture of inductors, capacitors and resistors, and configuring it in a way that considers cooling, ingress protection and terminal capability among other factors. We have a strong history of operating a 500kW railway test site, where we can test a variety of supply voltages and load conditions as well as emulate longer cable runs.

So, to avoid experiencing an inaccurate reading, a runaway conveyor or a crazy crankshaft, it could be time to reassess your EMC filters.

To find out more about REO’s newly redesigned range of EMC filters, visit the REO website or call 01588 673411.