A drive fitted with a functional safety input allows
Answer: C
Certified circuitry inhibits the gate drives by two independent channels, which achieves a safe torque-off without the maintenance and wear of a main contactor. Holding a load, by contrast, still needs a mechanical brake.
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Safe torque off differs from switching off the supply in that it
Answer: D
Correct answer: leaves the dc link charged
Safe torque off removes the gate drive signals so that the inverter cannot produce torque, but it does not disconnect the supply or discharge the link, which remains at several hundred volts. It is therefore a safeguard against unexpected movement and not an isolation: work on the power circuit still requires the supply to be locked off.
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Which of these most often limits the life of a drive in service?
Answer: A
Both are wear-out items with lives measured in years and strongly dependent on temperature, whereas the semiconductors and the electronics usually outlast the installation. Planned replacement of both is cheaper than an unplanned failure.
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Preventive maintenance on a drive should include
Answer: B
Dust on a heatsink raises the thermal resistance and a failing fan raises it further, and both are easily checked. Devices are replaced on failure rather than on a schedule, and the firmware is left alone unless there is a reason to change it.
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