Table of Contents
Advertisement
In measuring the resistance of a probe, the effect of lead wire resistances between probe
and measuring device must be compensated for. Normally, the change of the lead
resistance as its temperature changes must also be considered. Accurate
measurements require that the connecting cable have at least three, and preferably four,
conductors.
5.2 CONNECTING A RESISTANCE PROBE
Ideally, the best method of eliminating the effect of lead resistance is to use four
conductors when measuring the temperature with the probe. Two conductors are
required to carry the measurement current through the resistance, while the other two
are used to measure the voltage across the probe.
Constant current
Figure 5-1. Basic PtIOO Measuring Circuit
The CL521 uses this method in resistance measurements. By measuring potentials both
with and without current flow, the unit can also eliminate possible thermoelectric
potentials caused by conductor connections.
Figure 5-2. Connecting a 4-Wire Resistance Probe to the CL521
15
Advertisement
Table of Contents
