Hioki BT3554-50 - AC Four-Terminal Method Measurement

155
AC Four-Terminal Method Measurement
11.3 AC Four-Terminal Method
Measurement
The instrument uses the AC four-terminal method for resistance
measurement to cancel out wire resistance of the test lead and
contact resistance between the test lead and the object under
measurement. The following gure shows the principle of the AC
four-terminal measurement method.
Constant-
current source
DC-
elimination
capacitor
R
1
R
2
V
IS
R
3
R
4
I
S
Resistance measurement circuit
R
1
to R
4
:
Wire resistance value
of test lead and contact
resistance at contacts
Voltmeter
Resistance
R
The instrument applies the AC current I
S
from the instrument’s
SOURCE terminals to the object under measurement. The voltage
drop V
IS
, due to the impedance of the object under measurement,
is measured across the SENSE terminals. At this time, the SENSE
terminals connects to the internal high-impedance voltmeter.
Thus, little current ows through the resistances R
2
and R
3
, a wire
resistance and a contact resistance, respectively. As a result,
little voltage drops across the resistances R
2
and R
3
. In this way,
the voltage drop due to the resistances R
2
and R
3
is canceled
out. The instrument uses synchronous detection to separate the
internal impedance of the object under measurement into e󰀨ective
resistance and reactance and displays the e󰀨ective resistance
alone.
HIOKI BT3554F961-00HIOKI BT3554F961-00