**Measurement of Capacitance By DeSauty’s Bridge:**

**DeSauty’s Bridge** is the simplest method of comparing two **capacitances**. The connections and the phasor diagram of **DeSauty’s Bridge** are shown in the below figure.

#### Let C1 = capacitor whose **capacitance is to be measured**,

#### C2 = a standard capacitor, and

#### R3, R4 = non-inductive resistors.

#### At balance,

#### The balance can be obtained by varying either R3 or R4. The advantage of **DeSauty’s Bridge** is its simplicity. But this advantage is nullified by the fact that it is impossible to obtain balance if both the capacitors are not free from dielectric loss. Thus with **DeSauty’s Bridge,** only loss-less capacitors like air capacitors can be compared.

In order to make measurements on imperfect capacitors (i.e., capacitors having a dielectric loss), **DeSauty’s Bridge** is modified as shown in the below figure. This modification is due to Grover.

#### Resistors R1 and R2 are connected in series with C1 and C2 respectively. r1 and r2 are resistances representing the loss component of the two capacitors.

#### At balance,

#### The balance may be obtained by variation of resistances R1, R2, R3, R4. The above figure (b) shows the phasor diagram of the **DeSauty’s Bridge** under balance conditions. The angles δ1 and δ2 are the phase angles of **capacitors** C1 and C2 respectively.

#### Dissipation factors for the capacitors are :

#### ** D1 = tan δ1 = ωC1r1** and

#### ** D2 = tan δ2 = ωC2r2**

#### From the above equation, we have

#### Therefore, if the **dissipation factor** of one of the capacitors is known, the dissipation factor for the other can be determined.**De Sauty’s Bridge** does not give accurate results for dissipation factor since its value depends on the difference of quantities R1R4/R3 and R2.

These quantities are moderately large and their difference is very small and since this difference cannot be known with a high degree accuracy, the **dissipation factor** cannot be determined accurately.