Improved accuracy when measuring low resistance

Taking measurements of low resistance components and printed circuit board tracks below 10 Ohms is a common requirement in electronics. However, most digital multimeters are not able to measure low resistances accurately as their resolution is inadequate. Whilst specialist digital meters are available they are normally reserved for professional use due to their high cost.

If an analogue meter is used it is unlikely that meter resolution would allow accurate measurements of small resistances. Analogue meters require the user to guess the value as the needle normally falls between scale markings. This is fraught with danger, as estimation by eye may not be accurate enough, especially as the scale is usually not linear.

Digital meters also have other major drawbacks. Most 3.5 digit meters can only display with a resolution of 0•1 Ohms. The measurement is rounded up or down inside the meter to allow it to be displayed, so the actual reading could have a considerable measurement error at low resistances. There is also an error caused by the test leads, which requires a special technique to gain accurate low resistance measurements.

This article presents an adaptor that can be connected to most multimeters to enable low resistance readings to be taken.