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Precautions for Maintenance and Inspection
6.3.8 Measurement of main circuit voltages, currents and
powers
! Measurement of voltages and currents
Since the voltages and currents on the inverter power supply and output sides
include harmonics, accurate measurement depends on the instruments used and
circuits measured.
When instruments for commercial frequency are used for measurement, measure
the following circuits with the instruments given on the next page.
Typical Measuring Points and Instruments
CAUTION
Use FFT (Fast Fourier Transforms) to measure the output voltage accurately.
It cannot be measured accurately with a meter or general measuring
instrument.
+-
Ar
As
At
Vr
Vs
Vt
W11
W12
W13
Au
Av
Aw
Vu
Vv
Vw
W21
W22
V
R
S
T
U
V
W
Inverter
PN
Input voltage
Input current
Output voltage
Output current
:Moving-iron type
:Electrodynamometer
type
:Moving-coil type
:Rectifier type
Three-phase 200V power input
Three-phase
power supply
To motor
Instrument
types