Hioki RM3542-50, Instruction Manual

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Appendix 1 Four-Terminal (Voltage-Drop) Method
A
1
Appendix
The Four-Terminal method is essential for measuring very small resistance values.
With two-terminal measurements (Fig. 1), the resistance of the test leads is included in the measured resis-
tance, resulting in measurement errors.
The Four-Terminal method (Fig. 2) consists of the current source terminals (H
CUR
, L
CUR
) for providing a con-
stant current, and the voltage detection terminals (H
POT
, L
POT
) for detecting the voltage drop.
Because of the high input impedance of the voltmeter, measurement requires essentially no current flow
through the leads connecting the voltage detection terminals to the test object, practically eliminating the
effects of lead and contact resistance on the measurement probe.
Appendix
Appendix 1 Four-Terminal (Voltage-Drop)
Method
Figure 1
r
1
r
2
E
I
Constant current
source
Voltmeter
Resistance R
0
Two-Terminal Measurement Method Four-Terminal Measurement Method
Measurement current I flows through the test object re-
sistance
R
0
as well as lead resistances r
1
and r
2
.
Therefore, voltage measured will be given by E =
I ( r
1
+ R
0
+ r
2
) which includes lead resistances r
1
and r
2
.
Figure 2
r
1
r
2
E
I
r
3
r
4
E
0
Constant current
source
Voltmeter
Resistance R
0
Current I flows from r
2
to r
1
through test object resistance
R
0
. The voltmeter has an extremely high input resistance,
so the measurement current will flow to r
3
and r
4
. There-
fore, voltage drop across r
3
and r
4
is zero, and the volt-
age measured as E across the measurement terminals,
and the voltage drop E
0
between the test object resis-
tance R
0
are essentially equal, allowing test object resis-
tance to be measured without being affected by r
1
to r
4
.