RF generator, RF power amplifier, transmitting antenna, and various other instruments to measure the reaction of equipment under test (EUT) to the suddenly radiated RF. They also examine how cables, internal circuitry, EMI shielding, and enclosures are affected by the external frequency and determine ‘susceptibility thresholds’ at which EUT stops functioning normally due to EMI. For conducted susceptibility, testers check
the EUT’s power mains and any interfacing ports that support cables greater than three metres to gauge the conductivity levels at which interference occurs. Test personnel use a signal generator connected to a bulk current injection clamp (BCIC) alongside an RF amplifier with analysis tools and software to measure susceptibility thresholds.
• Electrical fast transient and surge testing This test focuses on powermains and interfacing ports for large cables. Testers generate a fast transient and use a coupler-decoupler network (CDN) to ensure the simulation doesn’t send an excessively strong signal back into the building’s power network. A grounding plane further ensures stability in the testing environment. Functionally, the lightning surge test is almost
identical to its fast-transient counterpart, but the event being simulated is far more powerful and potentially recurrent. As such, it can be necessary to generate multiple strokes or burst pulses of current to accurately measure
EUT susceptibility to lightning.
• Unintentional radiated and conducted emissions To assess radiated emissions, an engineer uses an antenna and other supporting equipment (e.g., a conductive ground plane made of an electromagnetically absorbent metal) to examine a typical frequency range from 30 MHz to 6 GHz, which is subject to change based on the highest RF initially measured. For conducted emissions, a set of line impedance stabilisation networks (LISNs) and grounding plane is used, or alternatively, a voltage probe.
• Electrostatic Discharge (ESD) test Assuming a normal work environment, this assessment simulates the results of an ESD on the EUT devices. This determines how much damage such a transient event would cause and how much must be done to increase device immunity. If the EUT surface isn’t electrically conductive, the test simulates a discharge that directly contacts the surface, while an air- discharge simulation is used if surfaces are conductive.
• Power frequency magnetic field testing
Ian Wright
This test is critical for determining the magnetic-field influence of power lines in close proximity to the EUT. For laboratory testing of smaller devices, a coil surrounds the equipment to generate a uniform magnetic field. For on-site EMC investigations, or those involving large equipment, testers use the coil to form a perimeter around the EUT and determine what level of electromagnetism will cause interference. While most EMI incidents cause little more
than brief irritation for workers and engineers, if these occur with any regularity the downtime can add up. Even more seriously, it could indicate future disturbances that might endanger employees or equipment.
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