Fluke 1535 User Manual page 15

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Users Manual
Figure 1 shows how to measure the resistance from one of the conductors to
the outer shield. In this case, there is a leakage current along the surface of the
inner insulation near the end of the cable. This leakage adds to the current that
the negative terminal senses, and causes the Tester to read a lower resistance
than it should.
Shield
Figure 2 shows how to prevent surface current leakage with a lead connected
from the Guard terminal to a conductor that surrounds the inner insulation. The
surface leakage current is directed to the Guard terminal. This removes the
leakage current from the measurement path between the positive and
negative terminals, and improves the accuracy of the test readings.
Shield
12
Figure 1. Surface Leakage Current
Figure 2. Guard Terminal Connection
Leakage
Current
Surface Leakage
Current
Optional
L
E
L
G
E