Bk-precision 889B - Manual Bedienungsanleitung PDF herunterladen (Seite 27)

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 100Ω to 10KΩ.

CUR

POT

DUT

(b) BLOCK DIAGRAM

DUT

(a) CONNECTION

1m 10m 100m 1 10 1K 10K 100K 1M100 10M

POT

CUR

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 10MΩ.

DUT

(d) 2T CONNECTION WITH SHILDING

CUR

POT

DUT

(b) BLOCK DIAGRAM

DUT

Co doesn't

effect

measurement

result

(a) CONNECTION

1m 10m 100m 1 10 1K 10K 100K 1M100 10M

POT

CUR

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 10mΩ. However, the effect of the test lead inductance can’t be eliminated.

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