2-Wire Resistance Measurement: Advantages and Disadvantages

This page covers the 2-Wire Resistance Measurement schematic, outlining its benefits and drawbacks.

What is Two-Wire Resistance Measurement?

Two-wire resistance measurement, typically performed using Source Measurement Units (SMUs) and Digital Multimeters (DMMs), is a method where resistance is determined using just two wires connected to the resistor under test. DMMs often employ a constant current method for resistance measurement. In this approach, the resistance value is calculated by dividing the measured voltage by the source current. DMMs usually have very high internal input impedance.

The following table illustrates typical test currents used for various resistance ranges when employing the constant current method:

Figure 1 shows a typical 2-wire resistance measurement setup.

In the schematic:

• V_M = Voltage measured by the meter
• V_R = Voltage across the resistor

Therefore, the measured resistance = V_M / I = R + (2 * R_LEAD)

Benefits or Advantages of 2-Wire Resistance Measurement

The following are the benefits or advantages of 2-Wire Resistance Measurement:

• It is a simpler measurement technique compared to 4-wire methods.
• It requires fewer lead wires; only two are needed for the measurement.

Issues or Disadvantages of 2-Wire Resistance Measurement

• The main drawback or disadvantage or issue with 2-wire resistance is found with low resistance measurement. Here total lead resistance is added to measurement. As test current ‘I’ causes significant voltage drop across lead resistances, measured voltage and voltage across ‘R’ is not equal. Typical range of lead resistance is from 10mΩ to 1Ω. Hence it is difficult to measure accurate two wire resistance for RUT (Resistance Under Test) below 100Ω. Lead resistance used are dominant source of error in two wire resistance measurement method in addition to instrument error.

• It is a less accurate method compared to 4-wire resistance measurement.