A DC resistance measurement is based upon: 1) a supply of
current and 2) the measurement of the voltage drop. Using
Ohm's law this voltage drop is expressed in terms of resistance:
R=V/I.
Test leads of a multimeter typically have a resistance of
about 0.2 Ohms. When measuring resistances of less than two
Ohms, this could produce a large error of 10%. The simple
solution in this instance, would be to subtract the residual
resistance of the test leads but with less than ideal connections,
this method is at best, limited. Most manufacturers of dedicated
milli or micro ohmmeters use the 4wire Kelvin test lead method
to arrive at errorfree results.
In a 4wire Kelvin test lead, such as our STERLING Instruments
KTLS2M, the supply points for the current are placed outside
the voltage leads and an accurate measurement of resistance
is possible at the contact of the voltage leads. Pix 4 wire
hookup.
