-_l__l___- II ..-..--- “.--“” ._..* - -..-... .._, ,.,..,_ ., ,
, . I...+
Anyway, it is important’ to record the instruments used and measurement
results, and to always use the same instruments at inspection.
0 Oscilloscope
To measure high voltage (4OOV or higher) , insulate the power supply
of oscilloscope and use a high-voltage probe or insulate the point to
be measured with a potential transformer or current transformer.
In the latter case, the potential transformer or current transformer
should have a capacity large enough to prevent magnetic saturation.
(21 Measurements on control circuits
The measurements on control circuits include measurements of frequency
reference signal, inverter
control voltage and observation of waveforms.
For accurate measurement, note the followings:
@ Voltage measurement and waveform observation
Since the currents of these signals are
faint and the impedances of
the circuits are high, use an instrument, input resistance of which is
as high as possible (lOOkohm to
1 Megohm) .
It is recommended to use a digital multimeter or oscilloscope in the
measurements.
Since input resistance of multimeter set in a low range is significantly
low, value read by multimeter may be lower than the true value.
0 Common line connection
Connect the common terminal of instrument to an optimum point of
circuit (i.e. the common point nearest to the point measured) .
@ Instrument characteristics
f-
“,-
For waveform observation, use’ an oscilloscope which has characteristics
that meet the waveform to be observed.
-35-
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