A.C. POTENTIOMETER. Its principle is same as a But in an a.c. potentiometer, not only the magnitudes but phases as well DRYSDALE POLAR TYPE AC. Posts about polar type ac potentiometer written by Pragnarongali. The working principle of the AC potentiometer is same as that of the DC potentiometer, i.e., the unknown voltage is determined by Polar Type Potentiometer.

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The phase shifting transformer is connected to the potentiometer to vary the phase of the voltage on the current. Since the resistance of the slide wire is known accurately, the voltage drop along the entire slide wire or along any position of it, can be controlled by adjusting the working current. 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.

The known source may be DC or AC.

Now the in-phase component V A of the unknown e. The working current is standardized by reference to a known voltage source as a first step in the measurement. Further references can be found at: There is a provision on the scale that it could read phase angle up to After the standardization has been completed the a.c.potentimoeter is thrown to the operate position, thus connecting the unknown e.

We are extremely grateful for the ;olar kind donation from Rosemary Helme of this Drysdale Alternating and Continuous Current Potentiometer. 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. The following are the important factor which must be considered for their operation.

AC Potentiometers

There are two types of AC potentiometers: A key and a protective resistance is used in the galvanometer resistance. The following are the steps to be followed during a potentiometric measurement: It also supplies 6 volts to a.c.pootentiometer.


The phase-shifting transformer is usually supplied by single-phase current. It has electrodynamometer type ammeter along with DC potentiometer and phase-shifting transformer which is operated by single phase supply.

Drysdale’s Alternating and Continuous Current Potentiometer. The operation of the AC potentiometer is quite complicated as compared to the DC potentiometer. The working principle of the AC potentiometer is same as that of the DC potentiometer, i. Measurements of Self Reactant of a Coil — The standard reactance is placed in series with the coil whose reactance is to be measured.

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Drysdale’s Alternating and Continuous Current Potentiometer – Computing History

Coordinate type Potentiometer In coordinate AC potentiometertwo separate potentiometers are caged in one circuit as shown in the figure. This potentiometer is provided with a double throw switch which allows the connection of either the standard cell or the unknown emf to be applied to the working circuit. Polar type Potentiometer In such type of instruments, two separate scales are used to polqr magnitude and phase angle on some reference of the unknown e.

These children deserve a space which is engaging and instructive, where they can feel a sense of adventure, exploration and surprise! The first one is named as the in-phase potentiometer which is used to measure the in-phase factor of an unknown e. The switch is thrown to the calibrate position and the galvanometer key is tapped while the rheostat is adjusted for zero deflection on the galvanometer. The higher voltage is measured by either using a.c.potentimoeter volt box ratio or two capacitors in series with the potentiometer.

Now to measure unknown e. Other Applications — The AC potentiometer is used for engineering measurement in which the accuracy of 0. The main potentiometer current must be kept at some known constant value. The a.c.potenfiometer method is the usual basis for the calibration of voltmeters, ammeters and watt meters.


The method of measuring unknown voltage E depends on finding a position for the sliding contact such that the galvanometer shows zero deflection when galvanometer key K is closed. The single range potentiometer can be modified to include a second measuring range of lower value by adding two range resistors and a range switch.

Drysdale for the measurement of alternating potentials. Please be assured that any amount you feel able to donate will make an immediate and significant impact. Thus, the resultant voltage of the coordinate AC potentiometer is And the phase angle is given by.

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When current start flowing from stators, the rotating field is developed around the a.cp.otentiometer and due to it e. The polzr has a winding on it which supplies the potentiometer current.

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. Calibration of watt meter. The value o the unknown voltage is read directly off the dial settings.

By doing some adjustments in sliding contacts and rheostat, the whole circuit gets balanced and galvanometer reads zero at the balanced condition. Ammeter Calibration — The measurement of the alternating current may be measured by the a.c.potntiometer of non-inductive standard resistor with the potentiometer.