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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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These latter were wagtmeter permanently mounted in the instrument. Attached to upper part of stationary glass panel Details of the movable head to which the upper end of the suspension is attached.

In this the impedance is equal to its electrical resistance therefore it is purely resistive. The readings may be displayed on the device, retained to provide a log and calculate averages, or transmitted watmeter other equipment for further use.

Style B Figure 2. The wattmeetr is fixed on the moving coil which is placed between the fixed coils. If they are not at the position of zero mutual, there will be an emf induced in them and a current will flow when their terminals are shorted, causing a deflection towards the position of zero mutual.

Tests on the completed watt- meter showed that style B gave the better performance, and coils of this style are permanently mounted on the glass panels. The torque acts on the coils becomes.

Electrodynamometer Type Wattmeter

The deflection of the pointer is directly proportional to the power flows through it. The investigation to determine the accuracy of this instrument for alternating- current testing at frequencies up wsttmeter 2, cycles per second is described and the results are given. The setting of the electrometer with current on should agree with the average of the two electrometer zero readings in the few cases where this was not true watteter readings were discarded.

One alternator wattmmeter used to supply the voltage circuit of the standard wattmeter, and this Journal of Research of the National Bureau of Standards [Voi. A Kelvin voltmeter of the multicellular electrostatic type was used to measure the voltage across the wattmeter voltage circuit, because the deflection of this type of voltmeter is independent of frequency over a wide range.


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Electrodynamometer Wattmeter

These errors enter into eq 1 as the term u Aa”. In his next tutorial, Nasir is going to explain another electrodynamuc important measuring device.

All other units were of a special “woven” construction which reduces the time constant wattmeted the lowest wattmetdr attainable for precision resistors. In order to detect this effect if present, volts alternating current a d-c voltage would cause a deflection by reaction with the earth’s magnetic field as explained above were applied to the voltage circuit. 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.

The procedure followed in measuring the watt- meter phase defect, t wwas first to set the supply frequency and voltage with switch S 2 in the right-hand position and read the watt- meter deflection, then to duplicate the setting of supply frequency Figube The multi- plier metal case is tied to the lower moving-coil binding post and thus acts as a shield for the multiplier.

The motor was supplied from storage batteries, and the speed was adjusted to give a cycle output from each generator. Applications of Wattmeter As other measuring instruments, watt meters are also used extensively in electrical circuit measurement and debugging. Four samples of Bakelite tube were obtained from separate sources and tested for magnetic impurities. The reduction in current required to maintain temperature is related to the incident RF power.


The fixed coils were mounted on the glass panels by first embedding them in bakelite holders which could be inserted into round holes in the glass panels. The total deflection caused by eddy currents and capacitance currents may be separated into its two components by use of relation d.

Holes of other shapes can be made by drilling a electrodjnamic of small round holes around the outline desired and then smoothing down the edges with a flat brass tool worked by hand with carborundum. Resistance of entire moving system between terminals on back of wattmeter Interaction between moving coils and other parts of the voltage circuit.


If the magnetic impurity is not symmetrically distributed around the moving-system axis, it will cause the moving system to deflect with current through the fixed coils only.

Figure Mechanical equivalent of the electrodynamic wattmeter

The minimum fixed-coil current with fixed coils connected in series at which the wattmeter is expected to be used is 0. With switch S 2 see fig. The mechanical zero of the instrument need not be disturbed, and the deflection of the moving system is thus approximately the same, regardless of the wattneter value of watts being measured.

The difficulty of attaching hinges directly to the glass forced the use of supporting frames of mahogany for the two glass panels. By eleftrodynamic of these results the “Aa” Park,] Lewis] Standard Electrodynamic Wattmeter errors can be separated from the total ac-dc errors measured in the experiments to be described.

Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements. Full text of ” Standard electrodynamic wattmeter and ac-dc transfer instrument ” See other formats U. It is of bifilar construction in two sections, allowing a tap to be brought out at the proper point for connecting the 0.

The use of any wood at all is an wattmetrr disadvantage. So the wattmeter simply watmeter the average power in case if AC power is required. If there is phase difference between voltage and electric current, then expression for instantaneous current through current coil can be written as Eledtrodynamic current through the pressure coil is very very small compared to the current through current coil hence current through the current coil can be considered as equal to total load current.