## De Sauty Bridge

De Sauty Bridge measures an unknown capacitance in term of a standard capacitance i.e. comparing two capacitance’s Two ratio arm of this bridge consist pure resistor and two consist capacitor where one is of known value and another is standard capacitor.

Let,

C_{1} = Capacitor whose capacitance is to be measured

C_{2} = a standard capacitor

R_{1}, R_{2} = non-inductive resistors

Balance is obtained by varying either R_{1} or R_{2}. For balance, point B and D are at the same potential.

**I _{1}R_{1} = I_{2}R_{2} and (–j/ωC_{1}).I_{1} = (-j/ωC_{2}).I_{2}**

Dividing one equation by the other, we get

**R _{1}/R_{2} = C_{1}/C_{2}; C_{1} = C_{2}R_{1}/R_{2}**

The bridge has maximum sensitivity when **C _{1}=C_{2}**. The simplicity of this method is offset by the impossibility of obtaining a perfect balance if both the capacitors are not free from the dielectric loss. A perfect balance can only be obtained if air capacitors are used.