Objective: To determine the relative permittivity of an unknown capacitor.
Fig. 1. Relative Permittivity measurement by Schering Bridge circuit.
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.
d= Spacing between electrodes,
A= effective area of electrodes,
= permittivity of free space.
Equating the real and imaginary terms in equ. (2), we obtain
Two independent balance equations (3) and (4) are obtained if C4 and R4 are chosen as the variable elements.
Dissipation factor ,
For, a parallel plate arrangement , relative permittivity,