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Maintenance and Inspection
Troubleshooting
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6–14
Inverter Output Voltage Measurement Techniques
Taking voltage measurements around drives equipment requires the right equipment and
a safe approach. You are working with high voltages and high-frequency switching
waveforms that are not pure sinusoids. Digital voltmeters will not usually produce
reliable readings for these waveforms. And, it is usually risky to connect high voltage
signals to oscilloscopes. The inverter output semiconductors have some leakage, and
no-load measurements produce misleading results. So, we highly recommend using the
following circuits to measure voltage for performing the equipment inspections.
HIGH VOLTAGE: Be careful not to touch wiring or connector terminals when work-
ing with the inverters and taking measurements. Be sure to place the measurement cir-
cuitry components above in an insulated housing before using them.
220 kΩ
2W
+–
220 kΩ
2W
+–
Voltage measurement with load
Inverter
U/T1
V/T2
W/T3
Voltage measurement without load
U/T1
V/T2
W/T3
Additional resistor
L1(L)
L2
L3(N)
L1(L)
L2
L3(N)
Inverter
5 kΩ
30W
V Class Diode Bridge Vol tmete r
200V Class 600V 0.01A min. 300V range
400V Class 100V 0.1A min. 600V range
V Class Diode Bridge Voltmeter
200V Class 600V 0.01A min. 300V range
400V Class 100V 0.1A min. 600V range