When the e.m.f. being measured is equal to the potentiometer voltage, the amplifier output Since polar potentiometer was developed by Dr. C.V. Drysdale , it is. Dr. C.V. Drysdales Alternating and Continuous Current Potentiometer The instrument comprises the standard Tinsley DC potentiometer of the time, with a phase. In a.c. potentiometers, another requirement is the control of stray e.m.f.s in fields Being a polar type, Drysdale – Tinsley a.c. potentiometer measures unknown.
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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.
Drysdale for the measurement of alternating potentials.
The main circuit of the potentiometer must be supplied with alternating current of exactly potentiometfr same frequency as that in the circuit to be measured, which means in practice that they must be supplied from the same source. Further, the phase relation between the circuit to be measured and that supplying the potentiometer may have any value potentjometer to In order to obtain a balance, as indicated by the detecting instrument, it must be possible to give to the potentiometer current any phase displacement relative to that of the potential supplying it.
drysdwle This is accomplished by supplying it through a phase-shifting transformer which consists of a stator wound with a circuit, which produces rrysdale rotating field in a closely-fitting rotor. The rotor has a winding on it which supplies the potentiometer current. A rotation of the rotor of the phase-shifting transformer through o has the effect of producing a phase shift of the same value, and a pointer on the rotor axis indicates the phase angle on a suitably divided scale.
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The “balance” is obtained by successive approximation of the drysadle adjustment of the potentiometer contacts dial and slide wire reading and of the phase-shifting transformer until the indicator shows no deflection. The indicator for low frequencies is a vibration galvanometer which must be closely tuned to resonate to the frequency of the circuit.
For higher frequencies a telephone may be used. The main potentiometer current must be kept at some known constant value. This is done by switching it over on to a continuous current circuit, which is adjusted until a balance is obtained at the proper setting, when a Weston cell is connected up in the usual manner.
Drysdale ac polar potentiometer
The reading of a sensitive dynamometer type ammeter in the main circuit is noted. This ammeter must read correctly with alternating and continuous currents.
The potentiometer – is then thrown on to the A. Arrangements are provided for reversing the ammeter in order to eliminate the effect of stray fields.
The phase-shifting transformer is usually supplied by single-phase current. To obtain the necessary field distribution a split-phase scheme is used, part of the excitation being provided by a circuit containing a condenser and a resistance in series. These are adjusted until the A. As it is necessary to have the splitphase circuit somewhere near the resonating point, it must be adjusted for changes of frequency.
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. Further references can be found at: We are extremely grateful for the very kind donation from Rosemary Helme of this Drysdale Alternating and Continuous Current Potentiometer.
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These children deserve a space which is engaging and instructive, where they can feel a sense of adventure, exploration and surprise! Please be assured that any amount you feel able to donate will make an immediate and significant impact. Join our Mailing List by adding your email address below and be kept up to date with lots of information including:. Drysdale’s Alternating and Continuous Current Potentiometer. 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.
Measures voltage as magnitude and phase from reference voltage. Web Design by Pure Energy. Join our Mailing List by adding your email address below and be kept up to date with lots of information including: Drysdale’s Alternating and Continuous Current Potentiometer 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.
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