KYORITSU 3128 - Manual (Page 53)

KEW3128
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KEW3128 6. Measurement
6. 4 PI Measurement (Polarization Index)
6.4.1 Polarization Index
PI : Polarization Index
This is a test to check a temporal increase of leakage currents flowing on
insulations. To determine a Polarization Index, first, measure insulation
resistance at 1 min intervals for 10 min. Then, divide the final value by
the initial reading and calculate a ratio. PI is dependent on the shape of
insulations and influenced by moisture absorption, therefore, a check of PI
is important to diagnosis the insulation of cables.
Polarization index =
TIME 2
Insulation resistance value 3 or 10 min
after starting measurement
TIME 1
Insulation resistance value 30 sec or 1 min
after starting measurement
PI 4.0 or more 4.0 ～ 2.0 2.0 ～ 1.0 1.0 or less
Criteria Best Good Warning Bad
6.4.2 How to measure PI
1. Select the “PI（Polarization Index）” on the Mode Selection Screen.
Refer to Basic Operation (=>P.21) and operate the Screen.