The Potentiometer is an instrument which measures unknown voltage by balancing it with a known voltage. The known source may be DC or. Definition of DRYSDALE POTENTIOMETER: An ac potentiometer of the polar type, comprising a phase-shifting transformer and resistive voltage divider. Definition: The potentiometer which is used for measuring the phase and the magnitude of the unknown emf by comparing it with the known emf such type of.

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Since opening at the end ofover 5, children have visited the Centre. It gives the accurate results in magnetic testing and precise testing of instrument transformers. S 1 and S 2 are signs changing switches which are used to change the polarity of the test voltage if it is required for balancing the Potentiometer.

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AC Potentiometers

Arrangements are provided for reversing the ammeter in order to eliminate deysdale effect of stray fields. As it is necessary to have the splitphase circuit somewhere near the resonating point, it must be adjusted for changes of frequency. Where as, AC potentiometer measures both the magnitude and phase of unknown voltage by comparing it with known reference.

The known source may be DC or Pitentiometer. The phase displacement of the rotor emf is equal to rotor movement angle from its original position and it is related to the stator supply voltage. One is directly connected to power supply and the other one is connected in series with variable resistance and capacitor.

There are two step-down transformers T 1 and T 2 which isolate potentiometer from the line and give an earthed screens protection between the winding.

But there is one major difference between potentoometer measurements, DC potentiometer only measures the magnitude of the unknown voltage. The function of the series components is to maintain constant AC supply in the potentiometer by doing small adjustments in it. The indicator for low frequencies is a vibration galvanometer which must be closely tuned to resonate to the frequency of the circuit.


Measures voltage as magnitude and phase from reference voltage. Hence the value of the unknown emf is known.

Drysdale’s Alternating and Continuous Current Potentiometer. Now to measure unknown e.

Applications of AC Potentiometer Measurement of self-inductance. The rotor has a winding on it which supplies the potentiometer current. The potentiometer, which is the universal instrument by which currents are determined in terms of a difference of potential between the end of a known resistance, has been developed by C.

These children deserve a space which is engaging and instructive, where they can feel a sense of adventure, exploration and surprise! Drysdake the stators, there is laminated rotor having slots and winding which supplies voltage to the slide-wire circuit of the Potentiometer. It also supplies 6 volts to potentiometers. As the vibration galvanometer has also to be adjusted for such changes, it is necessary to have a source of a very steady frequency and voltage for satisfactory working.

Click on the Images For Detail. When current start flowing from stators, the rotating field is developed around the rotor and due to it e. Measurements of Self Reactant of a Coil — The standard reactance is placed in series with the coil whose reactance potentjometer to be measured.

We are extremely grateful for the very kind donation from Rosemary Helme of this Drysdale Alternating and Continuous Current Potentiometer. There is a provision on the scale that it could read phase angle up to Circuit Globe All about Electrical and Electronics.

Drysdale’s Alternating and Continuous Current Potentiometer – Computing History

This is accomplished by supplying it through a phase-shifting transformer which consists of a stator wound with a circuit, which produces a rotating field in a closely-fitting rotor. Other Applications — The AC potentiometer is used for engineering measurement in which the accuracy of 0.

In this potentiometer, the magnitude of the unknown voltage is measured from one scale, and its phase angle is directly on the second scale.

Coordinate type Potentiometer In coordinate AC potentiometertwo potenriometer potentiometers are caged in one circuit as shown in the figure. The “balance” is obtained by successive approximation of the usual adjustment of the potentiometer contacts dial and slide wire reading and of the phase-shifting transformer until the indicator shows no deflection.


In a phase-shifting transformer, there is a combination of two ring-shaped laminated steel stators connected perpendicularly to each other as shown in the figure.

Voltmeter Calibration — The AC potentiometer directly measures the low voltages up to 1. The AC potentiometers are classified by the value measured by the potentiometer dial and scales.

The coordinate type potentiometer has two scales to read the inphase V 1 component, and the quadrature component V 2 of the unknown voltage V. Leave a Reply Cancel reply Your email address will not be published.

The higher voltage is measured by either using the volt box ratio or two capacitors in series with the potentiometer. The main circuit of the potentiometer must be supplied with alternating current of exactly the same frequency as that in the circuit to be measured, which means in practice that they must be supplied from the same source.

Now the in-phase component V A of the unknown e. The instrument comprises the standard Tinsley DC potentiometer of the time, with a phase shifter, Weston dynamometer voltmeter, selection and change-over switches and terminal panels for connection of galvanometers, DC and AC measuring and supply voltages.

Join our Mailing List by adding your email address below and be kept up to date with lots of information including: The potentiometer – is then thrown on to the A. There are two types of AC potentiometers: Polar type Potentiometer In such type of instruments, two separate scales are used to measure magnitude and phase angle on some reference of the unknown e. The AC potentiometer may be broadly classified as.