For procedures, see your electrical laboratory manual.

Title: Measurement of Capacitance

By —
1. Using the Schering Bridge.
2. Measuring transient voltage and time of the RC circuit.

First Method - Schering Bridge

Apparatus

1. AF Generator.
2. Two Decade Resistance Boxes.
3. Two Decade Capacitance Boxes.
4. Headphones.
5. Capacitor of unknown value.

Aim

To find the value of the unknown capacitor C1 and its leakage resistance R1 by balancing the bridge.

Theory
The Schering Bridge is an electrical circuit used for measuring the insulating properties of electrical cables and equipment. It is an AC bridge circuit and it has the advantage that the balanced equation is independent of frequency.

The Schering bridge is used for measuring the unknown capacitance of the capacitor, dissipation factor, properties of an insulator, capacitor bushing, insulating oil, and other insulating materials. It is one of the most commonly used AC bridge. The Schering bridge works on the principle of balancing the load on its arm.

The dissipation factor of a capacitor is the ratio of its resistance to its capacitive reactance.

Advantages of the Schering bridge

1. Balance equations are free from frequency.
2. The arrangement of the bridge is less costly as compared to the other bridges.

Second Method - Measuring transient voltage and time of the RC circuit.

Apparatus

1. AF Generator.
2. Capacitor of unknown value.
3. A Resistor of known value.
4. Oscilloscope

Theory

A transient voltage is a spike, dip, or fluctuating voltage that occurs along with the intended signal.

Transient voltage is a temporary voltage imposed on power lines during other than normal operating conditions. It can be caused by switching on or off capacitors, starting a large customer motor, a fault on the power line, or a superimposed lightning stroke. In a well-designed distribution system, there are line devices that will operate automatically that will allow the transient voltage to settle off of the system.

Transient can reach an amplitude of tens of thousands of volts that can damage, degrade, or destroy electrical/electronic equipment within any home, commercial building, industrial, or manufacturing facility. Transient surges are generally measured in microseconds.

The waves can be viewed with an oscilloscope.



An oscilloscope is a type of electronic test instrument that graphically displays varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time.

An oscillator is an electronic circuit that produces a periodic oscillating electronic signal often a dime wave or a square wave. Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal.