Electromagnetic Compatibility

International English

·The output of all inverters generates high frequency, high voltage switching waveforms in the output cables between the motor and inverter.

·A lot of EMI occurs at high frequency. At high frequencies the shape and length of the cable has a big effect on its impedance. Therefore short, thick, braided leads will be most effective in grounding, and high quality screened cable, grounded at both ends, will be needed to limit effects on signal leads.

·If equipment is badly grounded, high levels of EMI may connect from the power part of equipment into the control connections. Similar effects can occur when badly grounded equipment is connected together and EMI is conducted via the control cables.

·Particular care is needed when equipment is used with low signal sensors such as load cells and capacitive sensors.

·Conducted interference is more likely to cause problems than radiated interference.

·The signal and control leads in any electronic system are generally low voltage, high impedance, and are therefore particularly sensitive to the high level of EMI present in industrial systems.

·Switching inductive loads, such as electro-mechanical brakes, relay and contactor coils generate severe EMI.

6.2.1Immunity and Immunity testing

Immunity is very important as damage and nuisance tripping will cause failure and service costs irrespective of where the fault lies. Therefore the tests carried out during product development are quite severe, and represent conditions encountered in industry.

Tests include:

·Electrostatic Discharge testing of all exposed surfaces, terminal and buttons using high voltage discharge gun. This simulates the effect of discharge from a human body electrostatically charged from a carpet for example.

·High voltage very high frequency discharges capacitively coupled into the control lines. This simulates the interference that couples from power switching (contactors etc.) into control leads.

·Similar discharges directly into the supply leads, line to line and line to ground. This simulates conducted interference from arcing contacts in other equipment.

·High energy, lower frequency interference in the supply leads, line to line and line to earth. This simulates lightning strike interference and similar supply disturbance.

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MICROMASTER Applications Handbook