Microhm Electronics' metal current sense resistors are popular devices used to measure current flow. When evaluating these products for a given application, designers will need to test their resistance value. To be assured of obtaining a correct reading when testing the resistance, it is important to employ the proper test method for the most accurate results.
 
Resistance value measurement tests typically use standard multimeters with two measuring wires. This measurement method is suitable for resistance values higher than 10 ohms, but is more prone to inaccurate results when measuring lower resistance values. This is especially true of current sense resistors with resistance values under 100 milliohms. Microhm Electronics' MPR series are most used in this kind of situation.
 
For measuring resistances under 100 milliohms, it is recommended to use the four-wire (Kelvin) method in order to eliminate inaccuracies caused by the resistance of the measuring wires. By using a four-wire connection, the test current (main current) is forced through the component under test via a pair of wires while the voltage drop across the subject component is measured through another pair of cables. MVR series of Microhm Electronics is typical four-wire resistors for current measurement.
Since the voltmeter internal resistance trends to infinite, the measuring current is very small, typically 10 to 100 pA. Thus, the voltage drop on the current sense wire is very low compared to the voltage drop on the subject component forced by the main current. This is the reason that the resistance of the current sense wire has no significant influence on the measuring result. Another advantage of using the four-wire method to measure resistance, is that it also helps to prevent the influence of any damaged wires or probes on the resistance measurement. Besides general MVR series, noninductive MVR4618 is also used for current sense of test equipment, reference resistor in laboratory and laboratory power supply.