ELECTRODYNAMOMETER TYPE INSTRUMENTS PDF
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.
|Published (Last):||16 December 2010|
|PDF File Size:||16.64 Mb|
|ePub File Size:||15.4 Mb|
|Price:||Free* [*Free Regsitration Required]|
In electrodynamometer instrumentsthe field can be made of reverse simultaneously with the current in the movable coil if electrldynamometer field fixed coil is connected in series with the movable coil. For using electrodynamometer instrument as a wattmeter to measure the power, the fixed coils acts as a current coil and must be connected in series with the load. Pabitha Pabi June 28, at 5: Moving coils are also air-cored.
A spirit level may be provided to ensure proper levelling. If metallic former is used, then it would induce eddy currents in it.
Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage.
Earlier these fixed coils are designed to carry the current of about amperes but now the modern wattmeter are designed to carry current of about 20 amperes in order to save power. It is air cored. Instead of a permanent magnet, the electrodynamometer type instrument uses the current under measurement to produce the necessary field flux.
The damping torque is provided by air friction, by a pair of aluminium vanes which are attached to the spindle at the bottom. So in order to limit the current we have connected the high value resistor in series with the moving coil.
Electrodynamometer Type Wattmeter
The fixed coil connects in series with the circuit whose power consumption use to be measured. It would have a torque in one direction during one half of the cycle and an equal effect in the opposite direction electrodyanmometer the other half of the cycle.
Thus ideally the needle of PMMC instrument shall swing back and forth around zero position. And the value of current is given by the equation. The field produced by these instruments is very weak. The coils are usually varnished. Leave a Reply Cancel reply Your email address will not be published.
Where, x is the angle. Damping System Air friction damping is used, electrodynxmometer eddy current damping will distort the weak operating magnetic field and thus it may leads to error. With some little modifications, it electgodynamometer be used as a wattmeter for the power measurements.
Electrodynamometer type Instruments – Construction and Operation
This means that the torque in electrodynamometer instruments must have a finite value and unidirectional for AC and DC quantity unlike PMMC instruments. Your email address will not be published. This can cause frictional errors in the reading. Thus we can measure the AC quantity. The working principle of the Electrodynamometer Wattmeter is very instuments and easy. The controlling torque exerted on the spring is given by.
Because of this change of magnetic flux, the torque on moving coil will also change in each half cycle of AC quantity to be measured.
If you are already aware of constructional feature then you may proceed. The average deflection torque of the coil is given as. Metallic former shall never be used as elextrodynamometer will lead eddy current generation due to changing flux.
Electrodynamometer type instruments are used as a. Figure below shows an electrodynamometer ammeter. Thus temperature compensating resistors can be used in the precise instrument to eliminate the temperature errors.
Their working depends on the theory that the current carrying conductor placed in a magnetic field experiences a mechanical force. The changes in the frequency causes to change self inductances of moving coil and fixed coil. Electrodynamometer i nstruments are capable nistruments serving as transfer instruments. Such a transfer instrument has same accuracy for a.
The deflection produced in the instrument is proportional to the product of currents flowing in the fixed and the moving coil. The electrodynamometer instruments can be used as a voltmeter by connecting the fixed and moving coils in series with a high non-inductive resistance. Let I 1 and I 2 be the instantaneous values of currents in pressure and current coils respectively.
The current and voltage of the fixed and moving coil generate the two magnetic fields. Newer Post Older Post Home. It is recommended to read before going to understand the torque equation.