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7. Use of “Guard” (G) terminal
Depending on the measurement to be made, the Guard (G) may be used or
not. During measurements, the equipment should be electrically grounded
to avoid unsteady readings. When insulation is measured regarding
grounding, the R terminal is connected to earth and the condition by means
of which the equipment potential setting is fulfilled. If the measurement is
performed between two parts, which are not grounded (for example,
between two phase conductors in a three-phase cable), the megohmmeter
GUARD terminal must be grounded This implies that whenever a
measurement is performed, one of the GUARD or R terminals must be
grounded, but not both of them simultaneously.
Technical Note #32, reproduced at the end of the manual, explains the
usage of GUARD terminal in order to eliminate the parasite resistance effect
over the result of measurements.
8. Setting tests
The megohmmeter MD-5075x is an extremely versatile instrument that
enables automatic performance of several types of insulation tests, and
records them in its internal memory and/or prints the results. Thus, it is
necessary to appropriately define the tests to be performed, setting the
following parameters before starting the measurement:
• Test voltage
• Test duration for “TIMER” mode test
• Maximum Voltage for step voltage test (SVT)
• Minimum resistance limit for “Pass/ Fail” tests
