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GMC-I Messtechnik GmbH

3.3.2

Insulation Resistance Measurement

➭

Switch insulation measurement on by pressing the

ISO

SPD

key.

Figure 3.7:

Setting Test Voltage

➭

Select the required measuring voltage with the help of the

▲

TEST

and

▼

TEST

keys. By briefly pressing the respective

key, voltage is increased or decreased to one of the following
nominal values: 50, 100, 250, 500 or 1000 V. The selected
test voltage appears at the display in the

TEST

field. For indi-

vidualized value settings, press and hold either the

▲

TEST

▼

TEST

key until the value can be changed in 1 V steps

within a range of 50 to 1000 V. The desired value is then se-
lected by once again briefly pressing the respective key. Sev-
eral seconds after one of these two keys has been activated
for the last time, the test instrument is returned to the mode
which allows for switching amongst nominal values of 50,
100, 250, 500, 1000 V only.

➭

Contact the device under test with both test probes.

Figure 3.8:

Connection Example

Note

If an interference voltage of greater than about 10 V is
present in the measured electrical circuit, its value is dis-
played and the

START

key is disabled (see section 3.3.1

on page 4). Eliminate the source of interference voltage
before continuing with the measurement.

➭

Trigger measurement by pressing the

START

key. Release the

key as soon as measurement is started.
Rising measuring voltage is displayed by means of a bar
graph (this may take several tens of seconds in the case of
large capacitances). At the same time, the value appears at
the display in the

field. The measuring cycle is ended auto-

matically.

Note

If measurement needs to be continued for a longer period
of time, the

START

key has to be pressed and held for the

entire duration.
In contrast to this, the automatic cycle can be ended pre-
maturely by briefly pressing the

START

key. No results are

displayed in this case.

➭

Read the measured insulation resistance value.

Note

The device under test may not be disconnected from the
test instrument as long as the “!” warning symbol is lit up.
Discharging large capacitances may take several tens of
seconds!

Note

Whistling or hissing noises may emanate from the test
instrument during measurement.

3.3.3

Measurements at Varistors (surge protection devices)

For this measuring function, the test instrument generates a rising
direct voltage within a range of 50 to 1000 V and, at the same
time, measures current flowing through the device under test. As
soon as current reaches a level of 1 mA, voltage is no longer
increased and the voltage value for the so-called milliampere
point appears at the display. In accordance with the respective
function which has been selected with the

FUNC

key, results for

overcurrent protection devices are also evaluated automatically
and listed as shown in the following table.

Note

If the

DCMAX

function has been selected, the upper voltage

limit for automatic results evaluation can be adjusted with the

▲

TEST

and

▼

TEST

keys.

If the

DCMIN

function has been selected, the lower voltage

limit for automatic results evaluation can be adjusted with the

▲

TEST

and

▼

TEST

keys.

For actual measurement or evaluation, it doesn’t matter which of
these two functions is selected, i.e. either

DCMAX

DCMIN

* Table for Surge Protection Device

If the

SPD LIST

function is selected (SURGE PROTECTION DEVICE

TABLE), a specific type and manufacturer/distributor is suggested
at the display, voltage at the milliampere point is displayed and
further information may appear as well.
The required type of surge protection device can be selected with
the

▲

TEST

and

▼

TEST

keys.

Switch to off position!

Figure 3.9:

Sample Results for an

Insulation Measure-
ment (the DUT is
being discharged)

Figure 3.10:

Insulation Measure-
ment Results (the DUT
has been fully
discharged: U