Megger ATEC 210415 Series, Manual

Page: 40 / 82

OPERATION NOTES
33
AVTM21-415Ja Rev. A June 2005
CORRECTION FOR INTERNAL LEAKAGE
If the insulation resistance is high, arbitrarily over 20,000
megohms, a more accurate measurement can be made by
correcting for the internal leakage of the Test Set.
To do this first suspend the output terminal well clear of all
objects and raise the voltage to the value required by the test.
Read the resulting leakage resistance.
Make the required resistance measurement, then use the
equation:
R R
R R
R
L
L
T −
×
=
where:
R
L
= measured leakage resistance (typically above 100,000
megohms)
R = measured resistance of item under test.
R
T
= corrected measured resistance of item under test.
STABILIZING SWITCH
In most cases the motion of the Megohmmeter pointer is slow
and steady enough to permit a definite megohm reading.
In certain cases the Megohmmeter pointer will be observed to
swing rapidly and widely so that a definite resistance reading
cannot be made. This happens when the item under test has
significant capacity and resistance values on the order of
thousands of megohms. It is the result of line voltage
transients that cause small changes in the test voltage.
The readings can be significantly stabilized under these
conditions by switching the stabilizer "IN" during the test, and
readjusting the test voltage if necessary. The stabilizer is only