Multimeter Low Ohms Adapt or Introduction Most digital multimeters (DMMs) have problems reading low resistances. The Fluke 179 for example (not an inexpensive meter) has a resistance accuracy of +/-1% which sounds ok but it also has an uncertainty of +/-2 least significant digits. For example, when measuring a 0.8 Ohm resistance with the Fluke 179 the resistance value displayed could be anywhere between 0.6 and 1.0 Ohms as the meter's resolution (least significant digit) is 0.1 Ohms on the lowest range. The following device will enable even cheap multimeters able to accurately measure milli-Ohm resistances. The Circuit The circuit is adapted from a design by Peter Chamberlain. The circuit is based around an LM317T adjustable voltage regulator configured as a 100mA constant current source. The 100mA current is applied across a low-value resistor of unknown value (i.e. the resistance to be measured) and the resulting voltage drop can then be measured accurately by a digital multimeter. The circuit is short circuit proof as the maximum current into a short is 100mA. No on/off switch is required since no current will be drawn when no external resistance or meter is connected. NOTE: Before using the adaptor, check that your meter is not likely to be damaged by having the full output (6 to 8V+) applied when it is set to a low voltage range.