# Advantages of 4 Wire Resistance Measurement | Disadvantage of Four Wire resistance measurement

## What is Four Wire Resistance ?

Digital Multimeters and Source Measurement units are used for four wire measurement. Digital Multimeter uses constant current method of measurement in which it takes ratio of measurement voltage with source current to determine resistance. There is different source current for different resistance measurement range.

For 100 Ω and 1 KΩ it is 1mA, for 10 KΩ it is 100 µA, for 10 KΩ it is 10 µA, for 1 MΩ it is 1 µA and for 10 MΩ/100 MΩ it is 0.1 µA.

The figure-1 depicts four wire resistance measurement schematic.

Following labels are used in the 4-wire schematic.
VM = Voltage measured by meter
VR = Voltage across resistor (R)
➨Measured resistance = VM/ I = VR/ I

Lead resistances used in 2-wire resistance measurement method lead to measurement error to considerable amount for low value resistance measurement. Hence for such low resistances, method which reduces effect of lead resistance is employed. The 4-wire resistance measurement method is used for resistances less than or equal to 1KΩ

As shown, volt meter is connected closer to the DUT (Device Under Test). Hence voltage drop in test leads are eliminated. This schematic forces current 'I' to pass through test resistance 'R' via one set of test leads where as voltage across DUT is measured through second set of leads i.e. sense leads. Current flowing through sense leads is negligible and can be ignored. Hence voltage measured by volt-meter (VM) or DMM is same as voltage across resistor (VR). Hence measured resistance by this method is more accurate.

## Benefits or Advantages of 4 Wire Resistance Measurement

Following are the benefits or advantages of 4 Wire Resistance Measurement:
➨It offers more accurate measurement compare to 2-wire method.
➨It is simple measurement method using DMM (Digital Multi-Meter) like 2 wire resistance measurement.

## Drawbacks or disadvantages of 4 Wire Resistance Measurement

➨Resistance of test leads get added to the measurement when voltage sensing leads are connected far away from the resistor under test (RUT).
➨The other drawback is it requires four wires for measurement and four lead resistors.

Also refer 2-Wire resistance measurement and advantages of two wire resistance measurement technique.