Fluke 1537-II User Manual page 11

1535/1537/1537-II
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
8
Figure 1. Surface Leakage Current
Figure 2. Guard Terminal Connection
Leakage Current
Surface Leakage
Current
Optional
L
E
L
G
E