Hitachi L100 Instruction Manual page 138

Inverter Output Voltage Measurement Techniques
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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.
Voltage measurement with load
L1(L) U/T1
L2 V/T2
Inverter
L3(N) W/T3
220 k
2W
V class Diode bridge
200V class 600V 0.01A min. 300V range
400V class 1000V 0.1 A min. 600V range
HIGH VOLTAGE: Be careful not to touch wiring or connector terminals when working
with the inverters and taking measurements. Be sure to place the measurement circuitry
above in an insulated housing before using them.
Voltage measurement without load
L1(L)
L2
L3(N)
Additional resistor
5 k
+ –
Voltmeter V class
200V class 600V 0.01A min. 300V range
400V class 1000V 0.1 A min. 600V range
L100 Inverter
U/T1
V/T2
Inverter
W/T3
30W
220 k
2W
+ –
Diode bridge Voltmeter
6–13