3-2
TEST LEAD CONNECTIONS (continued)
3. In “Normal Mode”, current on the “Return” and the “Ground” terminal is measured by the “DC
Microammeter.”
4. If the “Guard Mode” is activated, current flowing through only the test lead attached to the “Return”
terminal on the unit will be measured by the “DC Microammeter”, unless the specimen return is not
isolated from ground in which case the currentmeter will be inoperative.
5. Current flowing through the test lead attached to the “Ground” terminal on the unit will be measured by
the “DC Microammeter” only when “Normal Mode” is activated. Ground current associated with the
“Ground” terminal will not be measured when “Guard” Mode is activated.
6. To use the “Guard Mode”, the specimen must be isolated from ground. If the low potential side of the
specimen will not or cannot be isolated from ground, the “Guard Mode” cannot be used.
7. The use of appropriately rated discharge and grounding devices is recommended to ensure that the test
object is fully discharged and grounded before removing leads after testing is complete. A minimum
discharge time which is approximately 4 times that of the voltage application duration is recommended.
SPECIMEN SETUP CAUTION
Sensitivity Effects of Measuring High Resistance
In cases where high voltage electrical test equipment is being used to measure high resistance values of
Megohms or higher, any change in the voltage field during a test will cause a change in the capacitance that
the meter sees and faulty readings may occur. It is because of this phenomenon related to high resistance
measurement methods that any movement of personnel (including operator movement), movement of other
equipment, or equipment leads within the vicinity will cause changes in resistance readings seen on the
display of the PM15-4A. This effect is greatest at the maximum resistance values that the PM15-4A is
capable of measuring, as well as timed tests. It is strongly recommended that a stable test set up is ensured
for obtaining the most accurate readings.
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