Instrumentation & Measurement Lab Experiments

Measurement of capacitance De Sauty’s Bridge

May 28 2023

Aim

To determine unknown capacitance of given capacitor by De sauty’s Bridge Method.

Apparatus Required:

S.No	Name	Type	Quantity
1	De sauty’s Bridge training kit	EE-123	1
2	Patch cords	-	5-8
3	Multimeter	Digital	1
4	Audio oscillator		1

Theory

The De sauty’s Bridge is one of the most important A.C bridge which is extensively Used for the measurement of unknown capacitance. De sauty’s Bridge contains four arms each having a resistance or capacitor or a combination of both.

Circuit Diagram :

C₂= Capacitor whose capacitance is to be measured

C₃= Standard capacitor

R₁= Non inductive resistor of one arm

R₄= Non inductive resistor of other arm

Balance is obtained by varying either R₁ or R₄

So For balance, points B & D are at the same potential

I₁R ₁= I ₂R ₄

R₁[1/jwc₃] = R₄[1/jwc₂]

R₁C₃= R₄C₂

∴C₂= C₃R₄/R₁

Where,

I₁= Current in the resistor R₁of one arm

I₂= Current in the resistor R₄of one arm

Procedure:-

Select one of the standard capacitor C ₃& connect on the appropriate place using two Patch cords.
Select one of the unknown capacitor C ₃using band switch.
Select 5 KΩ value of R ₄using band switch.
Connect headphone provided with this model at the place indicated.
Connect audio oscillator at the appropriate place indicated & switch it ON.
Now vary R₁using Pot and select the value for null point in the head phone. If the null point does not detect for selected one value of C₃& R₄change the value of C ₃& R ₄now again vary R ₁ using Pot and select the value for null point in the head phone.
Now switch OFF the supply and detach all patch chords.
Measure the resistances R₁& R ₄using multimeter and note down various value into the observation table.
Change the value or unknown capacitor C₂ using band switch & repeat all above steps.