Download 1000 V

3.4. Error indications
The most common error in the case of an insulation measurement is the presence of a voltage on the terminals.
The instrument can make the measurement if the peak value of this voltage is less than 0.4UN or 1000 Vac maximum.
Above this value, it is necessary to eliminate the voltage and repeat the measurement.
If an external voltage appears on the terminals during the measurement, and its peak value is greater than 1.1UN, the measurement
is broken off and the error is indicated.
3.5. DAR (dielectric absorption ratio) and PI (polarization index)
In addition to the quantitative value of the insulation resistance, it is very useful to calculate the quality ratios of the insulation
(the DAR and the PI) because they can eliminate the influence of certain parameters likely to invalidate the “absolute” insulation
measurement. They also serve to predict the evolution of insulation quality over time.
The most important of these parameters are:
„„ temperature and relative humidity, with which insulation resistance varies according to a quasi-exponential law.
„„ the disturbance currents (capacitive charging current, dielectric absorption current) created by the application of the test
voltage. Even if they gradually fade, they perturb the measurement at the start, for a more or less long time depending
on whether the insulation is sound or degraded.
These ratios therefore complete the “absolute” insulation value and reliably reflect the condition, good or bad, of the insulation.
In addition, long-term observation of the evolution of these ratios is a way to monitor the ageing of the insulation. For example,
that of a revolving machine or of a long cable.
The values of DAR and PI are calculated as follows:
DAR = R 1 min/R 30s (2 values to be noted during a 1-min measurement)
PI = R 10 min/R 1 min (2 values to be noted during a 10-min measurement)
The times of 1 and 10 minutes for the calculation of the PI and the times of 30 seconds and 1 minute for the calculation of the
DAR can be modified using the CONFIG key or in SET-UP (see §5), to adapt to particular applications.
3.5.1. Measurement
There are several ways of measuring the DAR and the PI:
„„ In manual configuration
Press the START/STOP button.

Wait one minute for the DAR or ten minutes for the PI (if the default
values are used).
BURN
499 MΩ
502 V
START/STOP
978 nA
Set: 500 V
Elapsed Time 00:10:08
kΩ
1
10 100
21
MΩ
1
10 100
GΩ
1
10 100
TΩ
10