User Manual

GMC-I Messtechnik GmbH 13
9 Milliohm Measurement (4-Pole-Measurement)
9.1 Compensation of Cable Resistance
Electrical resistance is a dipole quantity which can generally
only be measured using two poles. This is accomplished by
directing a measuring current of predetermined magnitude
through the device under test, and measuring the resultant
voltage drop. The respective resistance value is derived from
the quotient of these two values.
The two points between which voltage is measured are
decisive as regards the results of the measurement. All
resistances between these two points add to the measured
resistance value. These include contact resistance, as well as
cable resistance. If a very low resistance value needs to be
measured, for example contact resistance at a contactor with
a value of only a few milliohms, the points between which
voltage is measured must be moved out of the measuring
instrument and positioned as closely as possible to the
device under test. For this reason, the measuring instrument
is equipped with separate jacks for current feed and voltage
measurement. This type of 4-pole connection is known as
connection according to Kelvin.
KC4 Kelvin clips and KC27 Kelvin probes (available as
accessories) allow for easy, correct connection.
9.1.1 Measurement with Kelvin Probe KC27
9.2 Thermovoltage Compensation
Thermovoltages which occur as a result of material and
temperature differences may distort measurement results. For
this reason, the instrument is equipped with automatic
thermovoltage compensation in the relevant measuring
ranges.
Note!
If the measuring current is interrupted during 4-wire-
m-measurement or if the fuse is defective, the
message „leads open“ flashes on the display.
If fuse is defective, see chapter 14.2.
VC
m

S+S–
red
black
black
Milliohm measurement on
conductor bars, welds, coils
up to 1 H, etc. with Kelvin
probe KC27 (or Kelvin clip
KC4)
Direct the spring-loaded test
probes inward towards the DUT,
if possible, as they are con-
nected via the red plugs with S
+
or S
–
(Sense) .
01.180
m 
FUNC
MAN
00.010
termoC
m
FUNC
01.170
m
FUNC
m


ZERO
MAN
MAN
Measure
Thermo-
voltage
Thermo-
voltage
Compen-
sated
Measure-
ment
Results
long
30 m

/300 m

at 200 mA
Measuring Ranges:
MAN
FUNC
3  /30 at 20 mA
m
S+S–
VC
R
x
Voltage Drop Measuring Current
m: 0,001 m  30 
Overall Measuring Range:
+–
Measurement Cables,
KC27 or KC4
Note:
When using KC27 or
KC4 always set red
plug at S
+
or S
–
,
respectively.