The electrodynamometer type instrument is a transfer instrument. A transfer instrument is one which is calibrated with a d.c. source and used without any. An electrodynamic type instrument consists of Two Fixed Coil, flux is used in Electrodynamic or Electrodynamometer type instrument. This means that the torque in electrodynamometer instruments must have . Electrodynamometer type voltmeters are the most accurate type of.
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The deflection of the pointer is directly proportional to the power flows through it. Leave a Reply Cancel reply Your email address will not be published.
To provide magnetic shielding, normally electrodynamic type instrument is enclosed in a high permeability alloy. Where, x is the angle. This textbook ” Electrical and Electronics Measurements by S. This means that as the direction of magnetic field changes, the direction instrumentd current in moving coil also changes.
If metallic former insturments used, then it would induce eddy currents in it. Thus the deflection is decided by the product of r. Fixed coils are wound tyoe fine wire for using as voltmeter, while for ammeters and wattmeters it is wound with heavy wire. Electrodynamometer Instruments are widely used as an ammeter, voltmeter and wattmeter.
So the expression for the torque can be written as: Gravity control Spring control, only spring controlled systems are used in these types of wattmeter.
Electrodynamometer Type Wattmeter
We have an idea of the working principle of e lectrodynamometer instrument by taking up a permanent magnet moving coil instrument and considering how it would behave on a. These vanes move in a sector shaped chamber. This means that the torque in electrodynamometer instruments must have a finite value and unidirectional for AC and DC quantity unlike PMMC instruments.
Hence the instantaneous value of torque can be written as Average value of deflecting torque can be obtained by integrating the instantaneous torque from limit 0 to T, where T is the time period of the cycle. Gravity controlled system cannot be employed because there will be appreciable amount of errors.
This fixed coil is divided into two sections so that a uniform magnetic field may be achieved at the centre. Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: Errors due to stray magnetic field. Newer Post Older Post Home. Scale There is uniform scale which is used in these types of instrument as moving coil moves linearly over a range of 40 degrees to 50 degrees on either side. The PMMC instrument cannot be sued on a.
Thus the instantaneous deflecting torque is given as. The moving coil is mounted on an aluminium spindle. Hnec metal parts should be kept as minimum as possible. The moving coil is mounted on an aluminium spindle.
This makes the system heavy reducing torque to weight ratio. Thus as it is a transfer electrodynaometer, there is direct connection between a. As operating field would be distorted by eddy current damping, it is not employed. The voltage across the pressure coil of the circuit is given as.
It uses for measuring the power of both the AC and DC circuits. Thus ideally the needle of PMMC instrument shall swing back and forth around zero position. They are clamped in place against the coil supports.
Electrodynamic Type Instrument – Construction and Working Principle | Electrical Concepts
These coils are air cored. Note that a high value of resistance is connected in series with electrldynamometer coils. Learn how your comment data is processed.
But moving system, due to inertia cannot follow rapid variations and thus finally meter shows the average torque. Figure below shows an electrodynamometer ammeter.
This type of instrument can be used either as an ammeter or as a voltmeter, but is generally used as a wattmeter. The necessity for tye 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.
This makes the construction rigid. This is great one to see your blog last time I see same design to my friend constraction building in chennai. Let us see its operation on electrodyamometer. Let I 1 and I 2 be the instantaneous values of currents in pressure and current coils respectively.
To provide air friction damping, a pair of aluminium vane is attached to the spindle at the bottom.