KYORITSU 3323A - Manual (Page 18)

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6−5 Using Guard Terminal (only for MODEL3321A)
Shown below is an example of the insulation resistance
measurement of an electric wire. If Line probe is simply
connected to the wire conductor and Earth probe to the woven
metal shield as shown, a measurement error will be introduced
as this results in the measurement of the combined resistance
of insulation resistance and the surface leakage resistance at
the cut end of the electric wire. In order to remove this surface
leakage current, wind a guard wire around the cut end of the
conductor and connect it to the guard terminal of the instrument
using Guard Connection lead. Then, the surface leakage
current will bypass the meter of the instrument.
6−6 Backlight function
To facilitate working in dimly lit situations, a backlight function is
provided which illuminates the scale plate. Press the backlight
switch to operate this function. The backlight will light up for
about 60 sec., and then turned off automatically.
Meter
Voltage
Generator
Leakage Current
Core Conductor
Insulation
Guard Wire
Sheathed
Cable
Insulalion Resistance Tester