Four-Wire Measurement: Precision in Electrical Resistance Measurement

Four-wire measurement is a proven method for highly accurate electrical resistance measurement. It is an important technique in electronics manufacturing, ensuring maximum precision and the high quality standards associated with FIXTEST. Simply put, four-wire measurement separates the current-carrying leads from the voltage-sensing leads. This virtually eliminates the influence of lead and contact resistance on the measurement result. As a result, even very low resistance values can be measured reliably.

Fundamentals of Four-Wire Measurement

Four-wire measurement, also known as Kelvin measurement, four-wire sensing, or 4-wire measurement, differs fundamentally from conventional two-wire measurement. While two-wire measurement is affected by the inherent resistance of the test leads, four-wire measurement uses separate current and voltage paths to largely eliminate this effect. This enables accurate measurements even at very low resistance values.

What is Four-Wire Measurement?

Four-wire measurement uses four separate leads: two for supplying current and two for measuring voltage. The resistance value is calculated from the voltage drop across the measurement points and the current flowing through them. Since virtually no current flows through the voltage-sensing leads, practically no interfering voltage drops occur in these leads, enabling highly accurate measurement results.

How Is Resistance Calculated in Four-Wire Measurement?

The calculation follows Ohm’s law: R = U / I. U is the voltage measured directly across the device under test, while I is the known test current. For example, if a test current of 1 A flows and the measuring instrument reads 10 mV, the resistance is 10 mΩ.

The advantages of four-wire measurement are clear:

• High precision by eliminating lead resistance
• Suitable for very low resistance measurements down to the milliohm range
• Repeatable results, even in automated production testing

However, there are also some challenges:

• Higher technical complexity
• Need for specialized measuring equipment
• More space required for additional wiring
• Twice the number of contact points on the device under test

Two-Wire, Three-Wire, and Four-Wire Measurement Compared

In two-wire measurement, the test current flows through the same leads that are also used to measure the voltage. As a result, the measuring instrument always includes the resistance of the leads and contact points in the measurement.

An example: A component has a resistance of 0.1 Ω. The leads and contacts add a combined resistance of 0.5 Ω. The two-wire measurement therefore shows 0.6 Ω, which is six times the actual value. Four-wire measurement measures the voltage directly across the component and provides the correct value of 0.1 Ω.

For high resistance values in the kiloohm range, a few tenths of an ohm have little impact. In such cases, two-wire measurement is usually sufficient. Three-wire measurement provides an intermediate solution and is mainly used for resistance thermometers such as the Pt100. It compensates for lead resistance mathematically but requires leads with equivalent characteristics.

Successful four-wire measurement requires precise components. These include specialized test equipment such as high-precision spring-loaded contacts that ensure reliable electrical contact. Kelvin contacting requires two contacts per measurement point, which must make reliable, electrically isolated contact within a very small space. FIXTEST offers customized solutions for demanding measurement applications.

Learn more about spring-loaded contacts

FIXTEST Solutions for Four-Wire Measurement

As an expert in test equipment manufacturing, FIXTEST offers high-quality spring-loaded components specifically developed for demanding measurement requirements: our TEKOFLEX® solutions . They provide a reliable and durable connection for measurement applications requiring maximum precision.

Learn more about TEKOFLEX® solutions

Frequently Asked Questions About Four-Wire Measurement

How does four-wire measurement work?

In four-wire measurement, the current supply and voltage measurement are routed through separate leads. This largely eliminates lead and contact resistance from the measurement result, allowing very low resistance values to be measured more accurately.

What is the difference between two-wire and four-wire measurement?

In two-wire measurement, the test current and voltage measurement use the same two leads. As a result, the resistance of the leads and the contact resistance are included in the measurement. Four-wire measurement separates the two paths and measures the voltage directly across the device under test. This makes it significantly more accurate for measuring low resistance values.

Where is four-wire measurement used?

Four-wire measurement is used in electronics manufacturing, battery technology, and medical technology, among other applications, for example when testing printed circuit boards, battery cells, shunts, and connectors. Suitable contacting solutions can be found in our spring-loaded contacts for printed circuit boards , battery spring-loaded contacts , and spring-loaded contacts for medical technology

When is four-wire measurement worthwhile?

Four-wire measurement is particularly useful when lead and contact resistance can no longer be neglected in relation to the actual resistance being measured. It is especially relevant for measurements in the milliohm range.

What measuring instrument is required for four-wire measurement?

A measuring instrument with a four-wire connection is required, such as a milliohm meter, a precision multimeter with 4-wire measurement, or a test system with a constant-current source and a high-impedance voltmeter. Reliable contacting is equally important: only when the current and voltage contacts make secure contact with the device under test can the measurement provide reliable results.

What advantages does FIXTEST offer for four-wire measurement?

FIXTEST offers specially developed spring-loaded components for reliable and precise four-wire measurements.
The contacts have been developed and manufactured in Engen since 1984, either as standard solutions or customized for your specific testing application.