Appx.
3
AC 4-terminal Measurement Method
Appx. 3 AC 4-terminal Measurement
Method
The instrument uses the AC 4-terminal method, so that it can measure
resistance by canceling the resistance of the leads and the contact resistance
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the principle of the AC 4-terminal measurement method.
Constant current source
DC-elimination
capacitor
n
R
R
2
V
IS
R
3
R
4
I
S
Resistance
measurement
circuit
R
to R
4
:
Resistance values of the
test leads and contact
resistance values
Voltmeter
Resistance R
The AC current I
S
is applied to the measurement target from the instrument’s
SOURCE terminals. The voltage drop, V
IS
, due to the internal impedance of
the measurement target is measured at the SENSE terminals. The SENSE
terminals are connected to an internal voltmeter with a high impedance.
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2
and R
3
, which represent
the lead resistances and contact resistance, is almost zero. As a result,
the voltage drop across the resistances R
2
and R
3
is almost zero. Thus,
the voltage drop due to the resistances R
2
and R
3
is canceled out. In the
instrument, a synchronized wave detection is used, whereby the internal
impedance of the measurement target is separated into effective resistance
and reactance, and only the effective resistance is displayed.
If one of the following resistances increases, the instrument can no longer
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Lead resistance
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Contact resistance between the lead and the instrument
1
2
3
4
5
6
7
Appx.
Index
Appx.
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