Table of Contents
Advertisement
Megohmmeter Models 5000N/5100/5110
Utilizing the Guard Terminal
Guard terminals are useful when measuring high resistance values and
for stabilizing readings.
A
When testing the insulation at the end of a cable, it is necessary to
eliminate the error from surface leakage that occurs, particularly at high
resistance values. The guard terminal provides a third terminal within the
path of the surface leakage. Connect the instrument as shown in Figure
7.
If there is no shield at "B", use a copper wire wound several times around
the exposed surface "B". (Note: If a shield is not available and you do
not make up a shield around "B" and connect to the guard terminal (-),
the measurement will be erroneous and lead to confusion as to the
cable's state).
If the guard terminal is not
connected
at
instrument measures the
current "I" flowing through
the
insulation
surface
leakage
"i
". See Figure 8.
1
B
C
Exposed
Surface
Conductor
Insulation
to
to
Line (-)
Guard
Terminal
Terminal
"B",
the
and
a
current
To EARTH
Terminal
Outer jacket
The guard terminal
is useful when
measuring very
high resistance
Shield
values.
to
Earth (+)
Terminal
Figure 7
A
- 24 -
No Connection to
Guard Terminal
i 1
Ry
Rz
Rx
i
Figure 8
B
To LINE
Terminal
C
Advertisement
Table of Contents
