Amprobe AMB-110 Insulation-Resistance-Tester - Manual (Page 25)

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Note
• When determining Riso (1min) pay close attention to the capacitance of the object under test.
It has to be charged-up in the first time section (1 min). Approximate maximum capacitance
using:
where:
t .............. period of first time unit (e.g. 1min)
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).
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.
DIELECTRIC DISCHARGE TESTING (DD)
DD is the diagnostic insulation test carried out after the completion of the Insulation Resistance
measurement. Typically the insulation material is left connected to the test voltage for 10 to 30
min and then discharged before the DD test is carried out. After 1 minute a discharge current
is measured to detect the charge re-absorption of the insulation material. A high re-absorption
current indicates contaminated insulation (mainly based on moisture):
where:
Idis 1min .......... discharging current measured 1 min after regular discharge
U ...................... test voltage
C ...................... capacitance of test object.
Measurement procedure:
• Select DIAGNOSTIC TEST function in MAIN MENU.
• Connect the test leads to the instrument and to the measured object.
• Press the START/STOP key to start the measurement.
• Wait until set timer runs out, the result is displayed.
• Wait until the object under test has discharged
• The result can optionally be saved by pressing the MEM key twice, see the section of Store,
Recall and Clear Operation.