8
4-Wire Resistance Measurement
The four-terminal configuration of the Alpha 4314 eliminates errors normally caused by test lead and
contact resistances. In many applications the contact resistance can exceed the value of the load by
several orders of magnitude. The Alpha 4314 bypasses this potential error source by providing two
terminals of constant current and an additional two terminals for high impedance voltage measurement.
The result is a fast, accurate resistance measurement of the load, independent of the resistance of the
current carrying leads.
Figure
1 - Error Sources in Resistance Measurements
Figure 1 illustrates how the 4-wire principle is used to eliminate lead, wire and contact resistances as
potential error sources. The internal current source inherently overcomes all series resistance (within
compliance voltage limits) and delivers a precise constant current.
The internal high-impedance DVM senses the voltage drop across the load. There is negligible contact and
lead resistance error created by the voltage measurement because the high input impedance of the DVM
limits current flow in the voltage leads.
