FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY
sponsored by THE IMPORTANCE OF EMC TESTING
FOR INDUSTRIAL MACHINERY Ian Wright, chief engineer at TÜV SÜD, examines why EMC
matters when it comes to industrial machinery
A
s per International Electrochemical Commission (IEC) criteria, a machine that produces electromagnetic
emissions can only be formally classified as having achieved electromagnetic compatibility (EMC) if it functions effectively alongside other electromagnetic devices without disrupting their operation. If an electromagnetic emission does interrupt
other systems, it becomes electromagnetic interference (EMI). If it detrimentally affects inert matter or harms any living thing, the interference constitutes an electromagnetic disturbance. Furthermore, if unwanted electromagnetic emissions contain any elements within the radio frequency (RF) spectrum (lower than 3,000 GHz), they’re also classifiable as RF interferences or disturbances. Any machine that emits or receives
electromagnetic emissions and radio waves (or both) can cause problematic interference. There are several particularly common sources: • Switching power supplies • Programmable logic controllers (PLCs) • Variable speed drives (VSDs) for motor-driven equipment • RF transceivers or transmitters • Devices operating on the industrial, scientific and medical (ISM) radio band – ultrasonic equipment, electrodeless lamps, welding machinery and other industrial heating tools. All of those sources can also be victimised by EMI. Interference usually enters through the devices’ enclosure, power, signal or I/O ports. Although active circuitry is usually localised, interface cables often act as unintentional interference amplifiers. The four EMC disruptions below are the most notable to consider:
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1. Electrostatic discharges Most electrostatic discharges (ESDs) come from the enclosure port at high frequencies and amplitudes. These events pose a severe failure risk to any susceptible circuitry in the vicinity, particularly logic circuitry. More alarmingly, discharge sparks can cause an electric shock to human workers and potentially trigger explosions in industrial settings where gas is present. Bonding circuit connections and insulating (or isolating) them are common strategies for mitigating ESD risks, along with grounding and instituting safety procedures for employees to follow.
2. Electrical bursts A burst is similar to a discharge in that it is high-frequency, high-amplitude and disruptive to logic circuits or other susceptible surgery. However, bursts typically affect interfacing rather than enclosure ports. In theory, transient voltage suppression (TVS) devices should mitigate bursts, but their frequency is much higher than the surges TVS are designed for.
3. Power surges Often the result of lightning strikes, surges are perhaps the least predictable EMI event. A surge transient manifests as a high-amplitude transient received by a main AC or DC port, or possibly a signal I/O port interfacing with a cable directly connected to outside power lines. Sudden surges can catastrophically damage unprotected or underprotected circuits and even cause machine failure, facility outages and data loss. In addition to TVS devices that help keep surges isolated, backup systems (either physical or cloud) must be in place to safeguard data.
4. Electromagnetic field modulation Based on the principle of reciprocity, if a machine tends to radiate or conduct unintentional internal RF along its interface conductors, it will be equally receptive to unwanted external RF (and resultant disturbances). This is known as electromagnetic susceptibility (as opposed to immunity, which is the EMC ideal engineers strive for). While this is among the less dangerous and most common forms of EMI, it can still disrupt data processing or routing and interrupt logic circuitry, causing frustrating downtime. Audio signals are also likely to break up. Devices with high susceptibility should, as much as possible, be isolated from power supply lines, machines that generate RF on the ISM band, or any other devices prone to RF or electromagnetic noise. Filtration can also help reduce noise levels.
TAKE EMC TESTING SERIOUSLY EMC testing is mandatory in most countries and regions, and regulations dictate how organisations should ensure their machinery complies. While you’re only legally required to meet whatever standards apply in your jurisdiction, this bare-minimum approach may not be enough to significantly mitigate electromagnetic interference (EMI) risks. Failure to take EMI seriously enough to
incorporate it into risk management strategies and address it through voluntary EMC testing can be disastrous. Equipment or facility failure, product recalls, financial losses, regulatory fines and penalties, and mandatory government-conducted assessments, are just a few possible consequences. EMC testing must take place in an authorised
setting. This should ideally be a laboratory compliant with ISO/IEC 17025:2017 standards or one recognised by a relevant national regulator, such as a UK Market Conformity Assessment Bodies. If a laboratory setting isn’t possible, authorised testing personnel can conduct tests in situ – with the machine installed as desired by its end user – or at the device manufacturer’s facility before the product goes to market. An EMC investigation may involve one, two, several, or all of the following tests:
• Radiated and conducted RF susceptibility Testers create an electromagnetic field with an
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