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 electrodynamometer for use as a wattmeter is shown in Fig. Wattmeter: Perhaps the most important use of the electrodynamometer is for the wattmeter. electrodynamometer (plural electrodynamometers). An instrument, having a fixed and a moveable coil, that measures the power flowing in an electric circuit;.

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The voltage across the pressure coil of the circuit is given as. Their working depends on the theory that the current carrying conductor placed in a magnetic field experiences a mechanical force.

Electrodynamometer Wattmeter

From Wikipedia, the free encyclopedia. The basic EDM shown in Fig.

Linear Motor Working Principle. The torque acts on the coils becomes. The complete assembly is surrounded by a laminated shield to protect the instrument from stray magnetic field which may affect its operation. The operation of the instrument may be understood from the expression for the torque developed by a coil suspended in electrodynamometerr magnetic fieldi.

The construction of moving coil is made light as well as rigid. To have reasonable deflecting electrodynamomfter, mmf of the moving coil must be large enough. The instrument whose working depends on the reaction between the magnetic field of moving and fixed coils is known as the Electrodynamo-meter Wattmeter. As operating field would be distorted by eddy current damping, it is not employed.

Errors may be due connections. 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 done by enclosing in a casing high permeability alloy. This is great one to see your blog last time I see same design to my friend constraction building in chennai. The instantaneous values of i 2 are always positive and torque pulsations are therefore produced.


Control System Out of two controlling systems i. Simple meters may be calibrated to meet specified accuracy only for sinusoidal waveforms. An electrodynamometer is often used in accurate voltmeter and ammeters not only at power line frequency but also at low AF range.

To get accurate results, these errors must be minimized. In order to measure the power dissipated in an electrical load, it is necessary to measure the current through the load and the potential drop across it. Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement.

The coils are usually varnished. The electrodynamometer instruments can be used as a voltmeter by connecting the fixed and moving coils in series with a high non-inductive resistance. This may not be specified in the meter’s manual. A typical wattmeter in educational labs has two voltage coils pressure coils and a current coil.

This principle is used in the electrodynamometer type instrument. The electrodynamometer at the right is one of the few pieces of apparatus that I have seen manufactuered by Elmer Willyoung of Philadelphia. The reduction in current required to maintain temperature is related to the incident RF power.

A transfer instrument is one which is calibrated with a d. Wattmeters vary considerably in correctly calculating energy consumption, especially when real power is much lower than VA highly reactive loads, e. These springs act as leads to the moving coil.

Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage. A uniform field is obtained near the center of coil due to division of coil in two sections. A modern digital wattmeter samples the voltage and current thousands of times a second.



Damping is provided by aluminium air vanes moving in a sector shaped chamber. Therefore, a wattmeter is rated not only in watts, but also in volts and amperes. This particularly affects low power e. But moving system, due to inertia cannot follow rapid variations and thus finally meter shows the average torque. In practice accuracy can be improved by connecting a fixed load such as an incandescent light bulb, adding the device in standby, and using the difference in power consumption.

Electrodynamometer | Basic EDM as a Voltmeter –

Leave a Reply Cancel reply Your email address will not be published. It may also serve as a transfer instrument, because it can be calibrated on dc and then used electrodynamometet on ac thereby equating ac and dc measurements of voltage and current directly. The temperature errors are caused due to the self heating of the coil, which causes change in the resistance of the coil.

A fixed coil, split into two equal halves provides the magnetic field in which the movable coil rotates, as shown in Fig.

It is most accurate type of voltmeter. The damping torque is provided by air friction, by a pair of aluminium vanes which are attached to the spindle at the bottom.

Electrodynamometer – definition of electrodynamometer by The Free Dictionary

Stray magnetic field error: For AC powercurrent and voltage may not be in phase, owing to the delaying effects of circuit inductance or capacitance. The EDM has the disadvantage of high power consumption, due to its construction. Where, x is the electrodynamometfr. They can be used for both to measure ac as well dc quantities as scale is calibrated for both.