Terminology » Measurements » 4-Wire Resistance Measurement: Advantages and Disadvantages

4-Wire Resistance Measurement: Advantages and Disadvantages

measurement resistance accuracy dmm four wire

This page covers the 4-Wire Resistance Measurement schematic, outlining its benefits and drawbacks.

What is Four-Wire Resistance Measurement?

Digital Multimeters (DMMs) and Source Measurement Units (SMUs) are commonly used for four-wire resistance measurements. A DMM typically employs a constant current method. It determines resistance by calculating the ratio of the measured voltage to the source current. The source current varies depending on the resistance measurement range. For instance:

  • 100 Ω and 1 KΩ: 1 mA
  • 10 KΩ: 100 µA
  • 100 KΩ: 10 µA
  • 1 MΩ: 1 µA
  • 10 MΩ / 100 MΩ: 0.1 µA

Figure 1 illustrates a typical four-wire resistance measurement setup.

Schematic of 4 wire resistance measurement

In the schematic:

  • VM = Voltage measured by the meter
  • VR = Voltage across the resistor (R)
  • Measured resistance = VM / I = VR / I

Lead resistances, a factor in two-wire resistance measurements, can introduce significant errors, especially when measuring low-value resistances. Therefore, a method that minimizes the effect of lead resistance is preferable in these cases.

The four-wire resistance measurement method is generally used for resistances of 1 KΩ or less.

As shown in the diagram, the voltmeter is connected close to the Device Under Test (DUT). This eliminates voltage drops in the test leads. The setup forces current ‘I’ to flow through the test resistance ‘R’ via one set of test leads, while the voltage across the DUT is measured through a separate set of leads (sense leads). The current flowing through the sense leads is negligible and can be ignored. Consequently, the voltage measured by the voltmeter (VM) or DMM is virtually identical to the voltage across the resistor (VR). This makes the resistance measurement more accurate.

Benefits or Advantages of 4-Wire Resistance Measurement

Here are the key benefits of using the 4-Wire Resistance Measurement technique:

  • Higher Accuracy: It provides more accurate measurements compared to the two-wire method.
  • Simplicity: It’s a straightforward measurement technique, similar to two-wire resistance measurement, when using a Digital Multimeter (DMM).

Drawbacks or Disadvantages of 4-Wire Resistance Measurement

Despite its advantages, the four-wire method has some drawbacks:

  • Lead Resistance Impact: If the voltage sensing leads are connected too far from the resistor under test (RUT), the resistance of the test leads can still affect the measurement.
  • Complexity: It requires four wires and four lead resistors, adding to the complexity of the setup.

Schematic of 2 wire resistance measurement