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4. Application
4.1 Test Leads Connection
Auto balancing bridge has four terminals (H
CUR
, H
POT
, L
CUR
and L
POT
) to connect to the
device under test
(DUT).
It is important to understand what connection method will affect the measurement accuracy.
2-Terminal (2T)
2-Terminal is the easiest way to connect the DUT, but it contents many errors that are the inductance and
resistance as well as the parasitic capacitance of the test leads (Figure 4.1). Due to these errors in
measurement, the effective impedance measurement range will be limited at 100
to 10K
.
R
H
CUR
H
POT
DUT
(b) BLOCK DIAGRAM
DUT
V
A
Co
o
L
o
R
o
L
o
(a) CONNECTION
(c) TYPICAL IMPEDANCE MEASUREMENT RANGE(£[)
2T
1m 10m 100m 1 10
1K 10K 100K 1M
100
10M
L
POT
L
CUR
(c) Typical Impedance Measurement Range (Ω)
Figure 4.1
3-Terminal (3T)
3-Terminal uses coaxial cable to reduce the effect of the parasitic capacitor (Figure 4.2). The shield of the
coaxial cable should connect to guard of the instrument to increase the measurement range up to 10M
.
(c) Typical Impedance Measurement Range (Ω)
(d) 2T Connection with Shielding
Figure 4.2
4-Terminal (4T)
4-Terminal connection reduces the effect of the test lead resistance (Figure 4.3). This connection can improve
the measurement range down to 10m
. However, the effect of the test lead inductance can’t be eliminated.
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