IM 2768-01E
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(4) Power Source Voltage and Null Balance Sensitivity
Select the power source voltage of the bridge circuit depending upon
the resistor to be measured, and set the POWER SUPPLY function switch.
3 V for the resistor under test which resistance is lower than 100 kΩ, and 150 V for
those higher than 100 kΩ are typical setting of the function switch.
With this voltage, the null balance sensitivity (Resistance variation of Rs side
required to deflect one division from the balanced condition on the galvanometer) of
this instrument is shown in Fig. 4.3.
0.1
Ω
1
Ω
1 M
Ω
10 M
Ω
100 M
Ω
1 k
Ω
100 k
Ω
10 k
Ω
10
Ω
100
Ω
Fig. 4.3 Sensitivity and Accuracy
Sensitivity
Accuracy
0.001%
0.01%
0.1%
1%
10
-5
10
-4
10
-3
10
-2
10
-1
/div
R
R
Rx
3 V
15 V
4.2 Measurement
(1) Set the galvanometer to low sensitivity by turning the galvanometer SENSITIVITY
adjustment knob. (Turn the knob counter clockwise.)
(2) Set the measuring dials (Rs) to 1.9999.
(3) Observe the direction of the pointer deflection of the galvanometer by depressing momentarily
the GA switch after depressing the BA switch.
If the pointer of the galvanometer deflects the plus ( ) side, increase the value of Rs dial,
if the pointer is deflected to the minus (
) side, decrease Rs to make the indication to 0.
When it reaches closely to an equilibrium, increase the sensitivity of the galvanometer and
rebalance the bridge in the same manner as above.
When the galvanometer pointer indicates zero accurately, the value of unknown resistor can be obtained
from the following:
Rx = (Dial Reading) × Multiplying factor (Ω)