This coil is divided into 2 sections to give a more uniform field near the centre and to allow passage of the instrument shaft. Grab it now for very less price.Ĭonstruction of Electrodynamometer type instrument: This textbook “ Electrical and Electronics Measurements by S. In electrodynamometer instruments, the field can be made of reverse simultaneously with the current in the movable coil if the field(fixed) coil is connected in series with the movable coil. If, however, we were to reverse the direction of the flux each time the current through the movable coil reverses, a unidirectional torque would be produced for both positive and negative halves of the cycle. However, for an ordinary meter, the inertia is so great that on power frequencies the pointer does not go very far in either direction but merely stays(vibrates slightly) around zero. If the frequency were very low, the pointer would swing back and forth around the zero points. It would have a torque in one direction during one half of the cycle and an equal effect in the opposite direction during the other half of the cycle. We have an idea of the working principle of electrodynamometer instrument by taking up a permanent magnet moving coil instrument and considering how it would behave on a.c.
Operation Principle of Electrodynamometer type instrument: They are used as watt-meters,varmeters and with some modification as power factor meters and frequency meters. Indeed, their principal use as ammeters and voltmeters in laboratory and measurement work and as standards for calibration of other instruments as their accuracy is very high.Įlectrodynamometer type instruments are used as a.c voltmeters and ammeters both in the range of power frequencies and lower part of the audio frequency range. A transfer instrument is one that may be calibrated with a d.c source and then used without modification to measure a.c.This requires the transfer type instrument to have the same accuracy for both a.c and d.c, which have electrodynamometer instruments have.Įlectrodynamometer i nstruments are capable of serving as transfer instruments. The necessity for the AC calibration of moving iron instruments as well as another type of instruments which cannot be correctly calibrated requires the use of a transfer type of instrument.
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