Milliohm Meters

Milliohm Meter

What is a Milliohm?

The units of measure for resistances less than 1 Ohm are Milli- and Micro-Ohms. One milliohm (1mΩ) is equal to one thousandth of an ohm (0.001 Ω). One microohm (1μΩ) is equal to one millionth of an ohm (0.000001 Ω). For example, 0.5 ohms (one half an ohm) is equal to 500mΩ.

Why bother measuring resistances so low? 

It may seem like too small a resistance to be of any consequence but many safety standards (UL, CSA, VDE, etc.) require that such resistances be measured during the manufacture of consumer products, hand tools, and many appliances. A good example is the testing of kitchen appliances.

Many appliances require AC power (115 or 230VAC signals) and although AC signals are not supposed to come in contact with the user, accidents and faults can arise. To overcome these problems, manufacturers provide ground paths in appliances to carry high potentials to ground, away from the user in the event of a product fault. If even the slightest amount of resistance is present in such paths, injury can result. Milliohm measurements are also useful in the development of electronic components such as capacitors and inductors.

Milliohm Meter

Why are 4-wire connections required when making milliohm measurements?

Test leads always introduce a small amount of additional resistance into a measurement. This is acceptable in non-critical measurements such as megohm resistances. However, when measuring milliohms in a critical application, any additional
resistance can render the measurement useless. This is why 4-wire (Kelvin) connections are imperative.