Four-wire resistance measurement, also known as Kelvin or 4-wire measurement, is a method used to accurately measure the electrical resistance of a component or material with low resistance values. This technique overcomes the limitations of two-wire resistance measurement, providing more precise results, especially when dealing with resistances in the milliohm or microhm range.
In a two-wire resistance measurement, the resistance of the connecting wires can impact the measurement results. The resistance of the wires, along with the contact resistance at the junctions between the wires and the device under test (DUT), can create additional resistance components that add to the measured value. This can lead to significant errors, especially when dealing with small resistances.
The four-wire resistance measurement technique addresses this issue by using two additional current-carrying leads, known as the "sense" leads. The setup consists of:
Current-carrying leads (source leads): These leads carry the current to the DUT and are responsible for generating the voltage drop across it.
Voltage-sensing leads (sense leads): These leads are used to measure the voltage drop across the DUT. They are connected to the DUT independently of the current-carrying leads, thus bypassing any interference from the contact and wire resistances.
The working principle of four-wire resistance measurement involves passing a known constant current through the current-carrying leads and the DUT. The voltage drop across the DUT is then measured using the voltage-sensing leads. Since these sense leads are not in the current path, they experience a minimal voltage drop due to their very low resistance, ensuring that the measured voltage accurately represents the DUT's resistance without any significant error from the connecting wires.
Advantages of Four-Wire Resistance Measurement over Two-Wire Measurement:
Elimination of lead resistance errors: The four-wire method separates the current and voltage measurement paths, bypassing the resistance of the connecting leads and contacts. This ensures a more accurate and precise measurement of the DUT's resistance, especially for low-resistance components.
Higher accuracy: By avoiding lead resistance errors, four-wire resistance measurement provides significantly higher accuracy and repeatability compared to the two-wire method.
Applicable to low-resistance measurements: Four-wire resistance measurement is particularly valuable when measuring small resistances in the milliohm or microhm range. It enables accurate readings without the interference of lead resistances, which would otherwise be considerable relative to the small resistance being measured.
More reliable measurements: Since the measurement is less sensitive to contact resistance, the four-wire technique offers greater reliability and stability over time.
In summary, the four-wire resistance measurement technique is a superior method when high accuracy is required, especially for measuring low resistances. By minimizing errors introduced by the connecting leads and contacts, it provides more reliable and precise measurements compared to the conventional two-wire method.