RESISTOMAT
®
Model 2302-V001
Page 20
Introduction &
applications
Description of functions
Brief guide
Operation
Calibration
Test and offset
instructions
RS232 data
output
Accessories and Circuit diagram
Operation
However, three such measurements should be performed
using the three possible wire combinations and the individual
values calculated as follows:
This method takes slightly more time but is least prone to interferences.
Test objects with a large inductive proportion
Measurements performed on large inductances (e.g. cable wound around steel drums or
power transformers) involve the problem of considerably high, self-induced voltages on
interruption of the measurement current. Although the RESISTOMAT
®
Model 2302 has a
protective input circuit, damage might nevertheless be caused by very high voltage peaks.
The Model 2371 protective switchover unit solves this problem. On the "contact" switch
setting, both the current and potential lines are bridged, thus short-circuiting the self-induced
voltages.
Attention!
Measurement ranges must only be switched over on
the "contact" setting (i.e. the current and potential
lines must be short-circuited).
Simply connect the Model 2371 protective switchover unit in parallel with the test object to
the terminals of the Model 2302 RESISTOMAT
®
.
R
1
=
R
2
=
R
3
=
A - B + C
A + B - C
B - A + C
2
2
2
A = R
1
+ R
2
B = R
2
+ R
3
C = R
1
+ R
3
2.
Also based on a reduction of inductance, the following method is very suitable
for three-wire cables:
Connect two wires at one end of the drum to the
RESISTOMAT
®
and join them together at the other
end so that these wires are measured in a series
connection.
As these two wires are connected in opposition,
(bifilar winding), this results in hardly any inductance
and, therfore, an immunity to magnetic interference.
