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The 4-wire ohms method is used in systems where lead resistances can
become quite large and variable and in automated test applications
where cable lengths can be quite long. The 4-wire ohms method has the
obvious disadvantage of requiring twice as many switches and twice as
many wires as the 2-wire method. The 4-wire ohms method is used
almost exclusively for measuring lower resistance values in any
application, especially for values less than 10
Ω and for high-accuracy
requirements such as
RTD temperature transducers.
I
test
V
meter
HI-Source
LO-Source
LO-Sense
HI-Sense
R =
V
meter
I
test
Chapter 8 Tutorial
Measurement Fundamentals
370