Page 30 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 7: Measurement of unknown resistance using

Wheatstone bridge

Objectives

At the end of this exercise you shall be able to:
• Identify the terminals of a Wheatstone bridge
• Operate / Set the Wheatstone bridge to get null deflection in galvanometer
• Calculate the value of unknown resistance using the Wheatstone bridge.

Requirements

Tools/Equipments/Instruments Materials/Components
• Combination plier 150mm -1 No. • PVC copper wire 1 sq mm - 2 mtr.
• Side cutter 150mm -1 No. • Resistance Unknown value - 2 No’s.
• Screw driver set 150mm -1No. • Known resistance Assorted value - 2 No’s.
• DC power supply 0-30 V DC -1 No.
• Wheatstone bridge -1 No.

Procedure

TASK 1: Measure the value of unknown resistance using the wheat stone bridge
1 Identify the terminals / parts of a Wheatstone bridge
2 Connect the unknown resistor across terminals X, XX
3 Set the ratio arm to the approximate value of the unknown resistor

4 Set the sensitivity control to ‘Low’
5 Close the switch and watch the deflection of the galvano meter.
6 Adjust the variable arm by closing the switch, to get a minimum deflection in the galvanometer. (In case the
galvanometer needle over shoots, reset the ratio arm.)
7 Increase the sensitivity and repeat step 6
8 When ‘Null’ deflection is achieved in the galvano meter, note the value of the ratio arm and position of the
variable resistance. Enter the values in Table 1.
Tabular column:

1 digit 2 digit multiplier Value of the resister
nd
st

13