6.4 Mesuring instrument selection and usage
To observe the condition of insulation, voltage, current, signal level, waveform,
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etc., select an adequate instrument and use it in accordance with the
following description:
(1) Measurements on main circuit
The measurements include power supply and output voltages and
current measurements, load (motor) continuity check, insulation check,
voltage and current waveform observation.
The followings are particularly important to be checked carefully with
the specified instrument(s):
0 Multfmeter
For continuity check with a multimeter, be careful of sneak path
circuit. Do not make continuity check for the inverter circuit transistor
module with the motor connected, and for the converter circuit diode
module with the power connected.
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Make continuity check only for components to be checked with the
wiring to other components disconnected.
@ Voltmeter and ammeter
The input power supply voltage is sine-wave of the commercial
frequency. To measure the input voltage, any appropriate instrument
may be used.
Since the input and output current waveforms include various high-
harmonic components, use a moving-iron type ammeter, as it indicates
values in r.m.s., to measure the input and output currents.
To measure the output voltage, use a rectifier type voltmeter because
it reads nearly the basic wave
component of the voltage waveform
which is used as the reference value of torque generated by the motor.
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