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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From these data the relative wattmeter sensitivity at any point on the scale was computed by dividing the total deflection at the point by the moving-coil current required electroeynamic deflect the wattmeter to this point. The computed phase angle, 9 C9 For the derivation of this relation see appendix II.

electrodynamic wattmeter

In his next tutorial, Nasir is going to explain another very important measuring device. The maximum allowable current through the moving coils is limited by the heating due to this current. In order to provide an immediate and visible check on any gross misalinement of the two glass panels with respect to each other, two groups of fiducial marks were etched on the panels. Torque required to deflect moving system from mechanical zero to full scale position of zero mutual30 dyne cm.

Digital electronic instruments measure many parameters and can be used where a wattmeter is needed: The reason for this is that the potential coil is allowed to move whereas the current coil is kept fixed. Of these four, one was chosen which contained about the same amount of magnetic impurity as the glass or porcelain, and a new moving system was constructed using a tube of this material for mounting the moving-system parts.

The plotted points on this figure represent the values of ac-dc errors of the wattmeter at unity power-factor obtained by the tests just described.

These frames also allow the lack of squareness of the corners of the glass panels to be corrected for and concealed. Design and construction 1. The shank of each chuck is so milled as to allow the suspensions to come through under the shell.

They may therefore be lined up by eye so as to fall one upon the other. This may not be specified in the meter’s manual. The coils used in the shunt resistance 1, ohms and lower are much cheaper and less apt to give trouble than the 10,ohm coils that would be needed in the series resistance if a shunt resistance were not used.

The fixed coil connects in series with the circuit whose power consumption use to be measured. It would be almost im- possible to build up enough capitance by using air capacitors.


Wattmeter – Wikipedia

Errors due to stray magnetic field. What they are used for, what is their mechanical construction and how do they work. In simple words, a wattmeter is used for measuring the watts in the circuit. Deflections as large as 2 mm 0.

Electrodynamometer Wattmeter

Advantages of Electrodynamometer Type Wattmeter Following are the advantages of electrodynamometer type wattmeter and they are written as follows: The current supply was connected and current adjusted to 2. 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 Total weight of moving system, 18 g.

Possible sources of phase defect are 1 eddy current or skin effects in the fixed coils, 2 capacitance currents in the fixed coils, and 3 phase defect in the voltage circuit.

In case of DC current, the current is also in phase with its generated electromagnetic field. The small value of watts indicated by the wattmeter will be due to 1 any phase defect in the capacitor used as a load; 2 the current taken by the voltage circuit of the wattmeter, which necessarily flows through the wattmeter fixed coils; 3 the current taken by the voltmeter used to measure the drop across the capacitor; and 4 any phase defect in the wattmeter.

And the interaction of these two magnetic fields deflects the pointer of the instrument.

The balancing weights consist of small thumb nuts fitting these threaded rods. The possibility of warping was reduced to a minimum by carefully varnishing the mahogany inside and out. The pressure coil can also be tapped to change the meter’s range. At radio frequencies a common method is a rectifier circuit arranged to respond to current in a transmission line ; the system is calibrated for the known circuit impedance.

In order to obtain the most nearly linear relation between deflection and power being measured, the 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.

Even if the drift were not cancelled by the sequence of taking readings, the maximum error caused by it would be only 0. Eattmeter measurement of the resistance between this binding post and a moving-coil terminal thus serves as a check on the continuity of the shield. So the expression for the torque can be written as: The algebraic mean of these two deflections is the deflection caused by eddy currents, and one-half the algebraic difference between these two deflections is the deflection caused by capacitance currents.


The value of this shunt resistance may be set at oo wsttmeter 1,,or 50 ohms by means of a 6-step selector switch. The deflection due to capacitance currents elevtrodynamic a increase approximately as the square of the frequency of the fixed- coil current, b increase as the square of the current through the fixed coils, c depend upon the efficacy of the shield between the fixed and moving coils, d be approximately unchanged wattmetef magnitude but reversed in direction when the electrostatic tie between fixed and moving coils is changed from one terminal of the fixed coils to the other terminal, and e depend upon the fixed-coil connections, being largest for series and least for parallel.

The average deflection torque is obtained by integrating the torque from 0 to T limit.

Full text of “Standard electrodynamic wattmeter and ac-dc transfer instrument”

The internal construction of a wattmeter is such that it consists of two cols. Higher current values might be used, but their use is not anticipated at this time. As evident, they are of wattmetter importance and extensive use in electrical related industries and like other measuring devices, are quite easy to use and accurate.

These current ratings are conservative on a self-heating basis and might electrodyanmic exceeded by moder- ate amounts with some sacrifice in wattemter if necessary. The wattmetsr alternator was used to supply the current through the fixed coils of the wattmeter, and by also passing this current through a shunt and then stepping-up the drop across the shunt by means of a voltage transformer whose secondary was connected to the quadrants of the electrometer, a voltage was applied to the quadrants which bore a fixed relation to the current through the wattmeter fixed coils.

The only appreciable error, entering eq 1 as “Aa”, was found to be that due to eddy currents in the moving system and capacitance currents in the moving coils. The readings may be displayed on the device, retained to provide a log and calculate averages, or transmitted to other equipment for further use.

Construction of a Wattmeter Electrodynmic internal construction of a wattmeter is such that it consists of two cols. It uses for measuring the power of both the AC and DC circuits.

The hinges are attached to these frames. A limit to the number of turns in the fixed coils is set by the introduction of capacitance currents.