The battery level indicator is
located at the top right of the
display and contains four pairs of
segments depicting charge level.
Battery level indication of 50% of
battery life.
Battery level indication of a flat
battery.
Use of guard terminal (G)
For basic insulation resistance tests where there is little possibility
of surface leakage affecting the measurement, it is not necessary
to use the guard terminal i.e. if the insulator is clean and there are
unlikely to be any adverse current paths. However in cable testing
for example, there may be surface leakage paths across the insula-
tion between the bare cable and the external sheathing due to the
presence of moisture or dirt. To obtain an accurate measurement,
particularly at high testing voltages, a bare wire may be bound
tightly around the insulation and connected via the third test lead
to the guard terminal ‘G’.
As illustrated in the diagram, the guard terminal is at the same
potential as the negative terminal. Since the leakage resistance is
effectively in parallel with the resistance to be measured, the use
of the guard causes the current flowing through surface leakage to
be diverted from the measuring circuit. The instrument there-
fore reads the leakage of the insulator, ignoring leakage across its
surface.
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