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 EDM uses the current under measurement to produce the required field flux.

Linear Motor Working Principle. A fixed coil, split into two equal halves provides the magnetic field in which the movable coil rotates, as shown in Fig. A current flowing through the current coil generates an electromagnetic field around the coil. The scale is thus calibrated in terms of the square root of the average current squared i. The scale elctrodynamometer the EDM is usually calibrated in terms of the square root of the average current squared, and therefore reads the effective or electrodynamometrr value of the ac.

electrodynamometer – Wiktionary

The electrodynamometer can be used by slightly modifying the PMMC movement. This is done using an electrodynamometer EDM.

It is however very accurate at power line frequency and can be considered as a secondary standard. These coils are called the current coils of electrodynamometer type wattmeter. Measurements of very Large Currents by Thermocoupl Eoectrodynamometer email address will not be published. The coils are usually varnished.


Scale is uniform upto a certain limit. Such a transfer instrument has same accuracy for a. A modern electrodyhamometer wattmeter samples the voltage and current thousands of times a second. The low flux density of the EDM affects the developed torque and therefore the sensitivity of the instrument. Thus temperature compensating resistors can be used in the precise instrument to eliminate the temperature errors.

But moving system, due to inertia cannot follow rapid variations and thus finally meter shows the average torque.

The electrodynamometer at the right is one of the few pieces of apparatus that I have seen manufactuered by Elmer Willyoung of Philadelphia.

Electrical and electronic measuring equipment.

Electrodynamometer Wattmeter

The deflection of the pointer is directly proportional to the power flows through it. Thermistors and thermocouples are used to measure heat produced by RF power and electrodyanmometer be calibrated either directly or by comparison with a known reference source of power. So shielding is done to protect it from stray magnetic fields. This is great one to see your blog last time I see same design to my friend constraction building in chennai.

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.

Strain Gauge Transducer Types.

To have reasonable deflecting torque, mmf of the moving coil must be large enough. The torque acts on the coils becomes. The moving coils acts as a voltage coil or pressure oil and must be connected across the supply terminals. Also it introduces increased frictional losses. The fixed coils are spaced far apart to allow passage for the shaft of the movable coil. Moving Coil Moving coil moves the pointer with the help of spring control instrument.


The current and voltage of the fixed and moving coil generate the two magnetic fields. Another method is to use the heating effect of ac current to produce an indication of its magnitude. The instantaneous values of electrpdynamometer 2 are always electrodynamomter and torque pulsations are therefore produced.

It uses for measuring the power of both the AC and DC circuits. They move in sector shaped chambers. These springs act as leads to the moving leectrodynamometer.

Torque to weight ratio: Leave a Reply Cancel reply Your email address will not be published. The case is supported by adjustable levelling screws. This particularly affects low power e.


The instantaneous torque acts on the pointer of the wattmeter and is given by the equation. This may not be specified in the meter’s manual. The movable coil carries a pointer, which is balanced by counterweights.

The coil halves are connected in series with the moving coil and are fed by the current being measured. If ac current is sought to be measured, the current would flow through the coil with positive and negative half cycles, and hence the driving torque would be positive in one direction and negative in the other.

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