Use Of Guard Terminal (G); Setup Procedure - Megger BM5200 Manual Del Usuario

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 insulation 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
therefore reads the leakage of the insulator, ignoring leakage
across its surface.

Setup procedure

The setup function is used to set the internal timer (t). Default
value is set at 1 minute and can be adjusted using the up and
down arrows. When the desired time setting is displayed the PI-t
(left
arrow) key is pressed and a beep confirms the new setting.
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