AC Potentiometer

The term “AC potentiometer” refers to a type of potentiometer that is used to determine the phase and magnitude of an unknown emf by comparing it to a known emf. The AC potentiometer operates on the same principles as the DC potentiometer, which is to compare the unknown voltage to the known voltage in order to determine it. And the galvanometer shows the null point when they are both equal. As a result, the unknown emf’s value is known.

Compared to a DC potentiometer, the AC potentiometer has a much more complicated operating system. The following are crucial elements that must be taken into account for their operation.

1. The frequency and waveform of the current in an AC potentiometer must match those of the voltage being measured. As a result, the same source from which the current or voltage is measured is also used to transfer potential in an AC potentiometer.
2. The non-inductive element is used for making the sliding wire and the resistance coil of the AC potentiometer which reduces the reading error.
3. The magnetic field outside has an impact on the AC potentiometer’s reading. As a result, they are disregarded when measuring.
4. Because it is difficult to achieve balance when there are harmonics present, the supply source should be sinusoidal and free of them.

Types of AC Potentiometer

The value determined by the potentiometer dial and scales is used to categorize AC potentiometers. The AC potentiometers can be categorized broadly as.

Polar Type Potentiometer

In this potentiometer, the unknown voltage’s magnitude is determined by the first scale, and its phase angle is determined by the second scale. The setup is designed to read phase angles up to 360 degrees. The voltage is represented by the symbol V∠θ.

Coordinate Type Potentiometer

Two scales on the coordinate type potentiometer can be used to read the inphase V1 and quadrature V2 components of the unidentified voltage V. The phase between these voltages is 90 degrees out of phase. The potentiometer’s design allows it to read both positive and negative values for V1 and V2 and to cover an angle range of up to 360°.

Applications of Potentiometer

There are numerous uses for the AC potentiometers. Below are detailed explanations of a select few of them.

1. Voltmeter Calibration – Low voltages up to 1.5V are directly measured by the AC potentiometer. Either the volt box ratio or two capacitors connected in series with the potentiometer are used to measure the higher voltage.

2. Ammeter Calibration – By combining a non-inductive standard resistor with a potentiometer, it is possible to measure alternating current.

3. Wattmeter and Energy Meter Testing – The testing circuit for energy meters and wattmeters is the same as for DC measurements. To change the phase of the voltage on the current, a potentiometer is connected to a phase shifting transformer. As a result, the voltage and current may change depending on the power factor.

4. Measurements of Self Reactance of a Coil – The coil whose reactance is being measured is connected in series with the standard reactance.

5. Other Applications –

The accuracy of 0.5 to 1% is crucial for engineering measurements, which is why the AC potentiometer is used. The voltage, which needs to be broken down into two components, is also measured using the AC potentiometer. It provides precise results for testing instrument transformers and magnetic components.