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Measurement of Capacitance by Schering Bridge
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Objective : To determine the capacitance of an unknown capacitor.

 

                                                         Fig. 1. Schering Bridge for Capacitance Measurement.

The circuit diagram is shown in Fig.1.

Let, C1=capacitor whose capacitance is to be measured.

r1= a series resistance representing the loss in the capacitor C1.

C2= a standard capacitor.

R3= a non inductive resistance.

C4= a variable capacitor.

R4= a variable non inductive resistance. 

At balance, 

 (r_1+\frac{1}{jwC_1})(\frac{R_4}{jwC_4R_4+1})=\frac{R_3}{jwC_2}.....(1) 

or r_1R_4-\frac{jR_4}{wC_1}=-\frac{jR_3}{wC_2}+\frac{R_3R_4C_4}{C_2}.....(2)

Equating the real and imaginary terms in equa. (2), we obtain

r_1= \frac{R_3C_4}{C_2}.....(3) 

and C_1= \frac{R_4C_2}{R_3}.....(4)

Two independent balance equations (3) and (4) are obatined if C4 and R4 are chosen as the variable elements.

Dissipation factor 

D_1= wC_4R_4.....(5).

 

Cite this Simulator:

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