Two-wire connection
If only one pair of test leads is used, connected from the (+) and (-)
terminals of the DCX-127 to the unknown resistance, a 2-wire
measurement results. Current from the internal current source flows
through an internal resistor, through the test leads and resistance being
measured, and through another internal resistor back to the current
source. The two internal resistors are indicated schematically on the
front panel of the DCX-127. Voltage drop across these internal
resistors, produced by this current, is internally measured at the (+)
and (-) terminals. The resistance of the two test leads is thus included in
the measurement. For moderate and high values of unknown
resistance, the additional error introduced by resistance of the test leads
is usually negligible.
Resistance Measurements
Description
Page 4
DCX-127 Multifunction Module User’s Guide
Vmeas
Rw
(test lead)
Rw
(test lead)
Rx
(unknown)
Iref
Icomp
+INPUT
-INPUT
600
600
-SOURCE
Figure 1.
Simplified
diagram of
2-wire
ohmmeter
operation
