Amprobe AMB-110 Insulation-Resistance-Tester - Manual (Page 24)

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DIELECTRIC ABSORPTION RATIO (DAR)
DAR is ratio of Insulation Resistance values measured after 15s and after 1 minute. The DC test
voltage is present during the whole period of the test (also an Insulation Resistance measurement is
continually running). At the end, the DAR ratio is displayed:
Some applicable values:
DAR value Tested material status
< 1.25 Not acceptable
< 1.6 Considered as good insulation
> 1.6 Excellent
Note
• When determining Riso (15s) pay attention to the capacitance of the test object. It has to be
charged-up in the first time section (15s). Approximate maximum capacitance using:
where:
t .............. period of first time unit (e.g. 15s)
U ............ test voltage.
To avoid this problem, increase the DIAG. Starting time parameter in CONFIGURATION menu,
because start of timer in the DIAGNOSTIC TEST functions depends on the test voltage. The timer
begins to run when test voltage reaches the threshold voltage, which is product of the DIAG.
Starting time and nominal test voltage (Unominal).
Using filters (fil1, fil2, fil3) in the DAR function is not recommended!
Analysing the change in the measured insulation resistance over time and calculating the DAR and
PI are very useful maintenance tests of an insulating material.
POLARIZATION INDEX (PI)
PI is the ratio of Insulation Resistance values measured after 1 minute and after 10 minutes. The
DC test voltage is present during the whole period of the measurement (an Insulation Resistance
measurement is also running). On completion of the test the PI ratio is displayed: