Operation Manual

GMC-I Messtechnik GmbH 33
4.1.5 Measurements with the Guard Cable (feature G1)
The measurement of very high resistances necessitates extremely
minimal measuring current and may be rendered problematic as a
result of influences such as electromagnetic fields, humidity or
surface current. An accurate test set-up is thus absolutely essen-
tial.
A guard cable must be used for measurements within a range of
100 GΩ (10 GΩ) … 1TΩ, in order to prevent surface current from
distorting measurement results. The guard rings prevent current
at the surface of the insulation material from flowing from the
+measurement cable to the –measurement cable, instead of
through the insulation material itself.
Ð Insert the plug from the guard cable into the appropriate jack in
the test instrument.
Ð Plug the alligator clip onto the guard cable test probe.
Ð Connect the alligator clip to the guard ring between the two
measuring points at the insulation material under test.
Ð Refer to chapter 4.1.2 on page 31 regarding the measuring se-
quence
Note
The following materials can be used as guard rings: alu-
minum foil, copper foil or metallic hose clamps.
+Measurement Cable
–Measurement Cable
Guard Cable
Conductor
Insulation
Material
Guard Rings
Contact Ring