The working principle of the Electrodynamometer Wattmeter is very simple disturbs the main magnetic field of the Electrodynamic Wattmeter. For example, in using an electrodynamic wattmeter on direct current, two readings are taken, the direction of current flow through the instrument being reversed. Dynamometer type wattmeter works on very simple principle and this principle We know that instantaneous torque in electrodynamic type.

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Details of design and construction a Supporting framework b Fixed coils c Moving system d Preliminary tests e Series resistor f Shielding g Wattmeter constants 1 Fixed coils 2 Moving system III. Another possible source of induced currents in the moving system is the mutual inductance between the wattmerer and moving coils.

The value of this shunt resistance may be elecyrodynamic at oo f 1,,or 50 ohms by means of a 6-step selector switch. One alternator was used to supply the voltage circuit of the standard wattmeter, and this Journal of Research of the National Bureau of Standards [Voi.

The purpose of the shunt resistance is to decrease the current through the moving coil, which, as regards voltage sensitivity, is the equivalent of increasing the series resistance. Circuit Globe All about Electrical and Electronics. The device consists of a pair of fixed coilsknown as current coilsand a movable coil known as the potential coil.

Park, Lewis Standard Electrodynamic Wattmeter These glass panels are hinged to each other, one being stationary and the other opening and closing like a door. The moving coils were then twisted around on the Bakelite tube until the position of zero mutual inductance between the fixed and moving coils the position near which the moving coils are held when the wattmeter is in use coincided with the position for minimum deflection of the moving system with current through the fixed coils only.

Hence the current flows through the pressure coil is considered as the total load current. They are also used in industries to check the power rating and consumption of electrical appliances.

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. The plotted points include “Aa” and “Am” errors. The direct current was adjusted until the watt- meter reading was equal to the average of the two readings obtained Journal of Research of the National Bureau of Standards [va.


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Holes of other shapes can be made by drilling a series of small round holes around the outline desired and then smoothing down the edges with a flat brass tool worked by hand with carborundum. This deflection was measured eleftrodynamic 60 ma the maximum value to be used electrodynmic the moving coils for various positions of the mov- ing system near the point of zero mutual inductance between the fixed and moving coils.

Electrodynamic wattmeter | Article about electrodynamic wattmeter by The Free Dictionary

Errors in Watteter Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: The mechanical construction of a wattmeter is shown in the figure below.

They are used with refrigerators, electric heaters and other equipment to measure their power ratings.

The hinges are attached to these frames. The minimum fixed-coil current with fixed coils connected in series at which the wattmeter is expected to be used is 0. Lewis] Standard Electrodynamic Wattmeter does not exactly coincide with the point of maximum sensitivity.

The central wire of this lead is connected through a binding post to the upper moving-coil suspension. You enjoy this post: This was the case of DC power.

And the value of current is given by the equation. In order to derive these expressions let us consider the circuit diagram given below: It was proposed to incorporate these characteristics in the construction of the new instrument so far as was compatible with their sometimes conflicting requirements. The results of these tests are shown in figure 1 1 as a plot of watt- meter phase defect against frequency.

The remainder of the wattmeter phase defect must be due to “skin effects” in the fixed coils. The wiring diagram for the equipment used in this test is shown in figure Tibbals, one of the Bureau’s mechanicians, who is responsible for many valuable suggestions relating to the design of important details of the instrument.

The difficulty of attaching hinges directly to the glass forced the use of supporting frames of mahogany for the two glass panels. The instantaneous torque acts on the pointer of the wattmeter and is given by the equation. Please keep doing this.

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Now the reason is very obvious of using two fixed coils instead of one, so that it can be constructed to carry considerable amount of electric current. The result is to minimize the zero shift, on steady deflections, resulting from the inelastic yielding of the spring and suspensions.

The heat and pressure of the press destroyed the insulation of the coils and the attempt had to be abandoned. A typical wattmeter in educational labs has two voltage coils pressure coils and a current coil.

Electrodynamometer Type Wattmeter

These current ratings are conservative on a self-heating basis and might be exceeded by moder- ate amounts with some sacrifice in accuracy if necessary. Under these conditions the current through the watt- meter fixed coils is small in value compared to the large capacitance current taken by and is in phase with the voltage, E, across the wattmeter voltage circuit, so that the effect of the wattmeter phase defect is negligible.

Construction and Working Principle of Electrodynamometer Type Wattmeter Now let us look at constructional details of electrodynamometer. Control System Out electrodynmic two electrodynamc systems i. A fixed resistance of ohms is connected electroynamic series with the wattmeter moving coil, and a capacitance of 0. The voltage is dropped across the potential coil and as a result of this complete process, the needle moves across the scale.

Arbitrary waveform wzttmeter Digital pattern generator Function generator Sweep generator Signal generator Video-signal generator. A switching arrangement was placed in the current and voltage supply such that the alternating current and voltage could be disconnected and a direct current and voltage substituted. The only prerequisite in working this glass was found to be patience.


As evident, they are of extreme importance and extensive use in electrical related industries and like other measuring devices, are quite easy to use and accurate. In order to obtain the most nearly linear relation between deflection and power being measured, electroodynamic moving coils are held near the position of zero mutual inductance between the fixed and moving coils when the moving coils are deflected to their full-scale position. A current of 0. The absolute wattmeter sensitivity is equal to the relative sensitivity to within 0.