Author:
Bill Dull, Triad Magnetics
Date
01/16/2025
PDF
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Precision digital multimeters (DMMs) and source measurement units (SMUs) offer two methods of measuring resistance: 2-wire resistance measurement and 4-wire resistance measurement. However, these techniques are not interchangeable because their readings vary in accuracy. While a small margin of error is acceptable for certain applications, other applications require greater accuracy to prevent serious issues, like energy loss or overheating.
DMMs typically measure resistance using a constant-current method. This technique sources a constant current to the device under test (DUT) and measures the voltage. Resistance can then be calculated and displayed using the known current and measured voltage. However, you'll need to understand how each process works before you can identify the best testing method for your device. In this article, we'll discuss 2-wire and 4-wire resistance measurement and how we measure resistance at Triad Magnetics.
In the 2-wire testing method, two wires connect the device under test to the measurement equipment. This technique is the simplest way to measure resistance. The voltage measurement is done in the DMM, with the lead wire resistance included in the reading.
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While the 2-wire resistance measurement method is fast and easy, it is not perfectly accurate since the wires themselves have some resistance, which is included in the measurement results. The voltmeter not only measures the voltage drop across the device under test but the test lead wires as well. This small degree of error might be acceptable for higher resistance measures, but it creates a more serious concern when measuring low resistances. It is possible to adjust out the lead resistance, but you will need to recalculate the DCR each time.
With 4-wire measurements, the voltmeter features four leads instead of two. Two of these leads, called force wires, send current to the DUT while the other two, known as sense wires, connect to the voltmeter. Since voltage is measured at the device under test, the resistance of the leads is excluded from the measurement.
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The 4-wire resistance measurement method is more precise, as it eliminates the variance that results from the power source and ohmmeter sharing a connection. When the current path is separated from the voltage measurement like this, it's possible to obtain a more accurate measurement. This is very important when taking low-resistance measurements, such as anything below 10 ohms.
At Triad Magnetics, we test everything using the 4-wire measurement technique to ensure the highest accuracy, quality, and reliability. While 4-wire testing is a standard option in specialized benchtop testing equipment, it is uncommon in handheld multimeters. Our experienced team uses the most sensitive and advanced technology to achieve more accurate measurements.
The greater accuracy of 4-wire measurements results in safer and more reliable devices that adhere to even the most rigorous industry standards. Some of the most common applications for this type of resistance testing include:
While 2-wire measurements are simple to perform, many applications require a greater degree of accuracy. At Triad Magnetics, we obtain precision readings using the 4-wire measurement technique on every device we test. This approach ensures that the part will perform as expected without excessive power loss or overheating. We conduct all testing, design, and prototyping operations from our Perris, California facility, overseen by our experienced design engineers.
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