32
Have series resistors R
0
, R
1
, R
2
,…R
n
. Therefore, a measurement of R
0
only
is very difficult. It is said that, with some insulation resistance
measurements, it takes several hours to a few days for the leakage current
to stabilize. This is not practical.
To avoid this problem, a method is customarily used in the insulation
resistance measurement for convenience to read the resistance value one
minute after charging the test voltage to the sample. This value is called
minute rate value for the resistance value of an insulator, and is widely
employed among a variety of electrical standards.
In the 1-minute rate insulation resistance measurement, the measured
values may vary when a measurement is repeated once or twice with the
same sample. To minimize such a deviation, it is important to completely
discharge the sample before the start of each measurement. The required
discharge time mainly depends upon the charging voltage and the size of
C
0
in Fig. 6.7.1, but, generally it can be said to be 5 to 6 times longer than
the time of test voltage charging.
6.8 Connectivity Precautions
6.8.1 When the Screen Shows LOCK and Measurement Cannot Be Started
The super megohmmeter can output measurement voltages of up to 1,000 V.
Consequently, failure to wire the instrument correctly may pose hazards such
as electric shock. The instrument provides an interlock function in order to
prevent these risks. An HV-EN (high-voltage enable) connector is provided for
interlock function use on the rear of the instrument.
When using the measuring rods (red/black) that come with the instrument,
insert the shorting plug into the HV-EN connector on the rear of the
instrument. If LOCK is displayed at the bottom left of the instrument’s screen,
check the following:
(1) Has the measuring rod (black) been properly inserted into the Rx+
terminal?
(2) Has the shorting plug been properly inserted into the HV-EN connector
on the rear of the instrument?
Display of the LOCK indicator at the bottom left of the screen indicates that
the instrument has detected an issue with the measuring rod or shorting plug
wiring.
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