GOSSEN-METRAWATT
11
7
Measuring the insulation resistance
7.1
ISO-
Ω
measurement up to 3 G
Ω
with autoranging
í
Set the rotary switch (6) to one of the three „ISO-
Ω
“ posi-
tions. Depending upon the nominal voltage of the device
under test, you can measure the insulation resistance
with a nominal voltage of 250 V, 500 V or 1000 V. With a
nominal voltage of 1000 V selected, the LCD display (5)
shows the following:
When there is no voltage applied to the probes, the digital
display only shows the decimal point together with the
numeral 3 and the symbol for the unit M
Ω
. Depending upon
the nominal voltage selected, the analog indicator shows
the 250 V, 500 V or 1000 V measuring range.
When the „ISO-
Ω
“ function is switched on, or when chang-
ing to this function, the tester always switches to autorang-
ing. The LCD then shows „AUTO“.
Detecting external voltages
You can measure insulation resistances on electrically dead
devices only. That is why it is necessary to detect external
voltages.
í
Apply the two probes to the measuring points. If a
voltage > approximately 25 V exists, the presentation on
the LCD display (5) changes as follows:
• The warning triangle signals a hazardous contact poten-
tial > 25 V.
• Four horizontal lines are shown in the middle of the
numerals of the digital display.
• The pointer of the analog indicator shows the value of
the DC or AC voltage applied. If this is the voltage of a
charged capacitive device under test, the device under
test is discharged. You can observe the drop in voltage
on the analog indicator.
If the measurement pushbutton (8) is already pressed
before you apply the probes to the measuring points – e.g.
to illuminate the measuring points – a sound signal points to
an external voltage on the device under test.