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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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The internal construction of a wattmeter is such that it consists of two cols. In the present wattmeter with a cm scale and a total normal deflection from mechanical electrodyamic position of cm, it is not feasible to obtain an accurate value of a at normal deflection. The traditional analog wattmeter is an electrodynamic instrument. This would account for the results obtained with the first moving system in the wattmeter.

electrodynamic wattmeter

After some discussion it was decided to use glass for the supporting framework, since it is nonwarping and nonmagnetic, permits a certain amount of vision within the instrument, can be obtained readily in slabs of almost any reasonable size, and can be readily worked if care is used.

Electrodynamiv it electrodgnamic concluded that the filler used in making the Bakelite tube and not the Bakelite itself contained the magnetic impurity. Simple meters may be calibrated to meet specified accuracy only for sinusoidal waveforms.

Criteria of design 2. Tibbals, one of the Bureau’s mechanicians, who is responsible for many valuable suggestions relating to the design of important details of the instrument. These latter were therefore permanently mounted in the instrument. This material should lend itself to a sufficiently sturdy and permanent construction to avoid future diffi- culties resulting from warping of the instrument frame and consequent sticking of the moving system.

A modern digital wattmeter samples the voltage and current thousands of times a second. 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. So the wattmeter simply measures the average power in case if AC power is required. The above procedure was repeated with switch S 2 in the reversed position. It would be almost im- possible to build up enough capitance by using air capacitors.

The curve is a plot of “Aa” errors only. A measurement of the resistance between this binding post and a moving-coil terminal thus serves as a check on the continuity of the shield. The wattmeter moving coil is connected to the multiplier by a single-conductor Journal of Research of the National Bureau of Standards [vol. Control System Out of two controlling systems i. Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage.


In his next tutorial, Nasir is going to explain another very important measuring device. The deflection due to eddy currents will 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; but it will be independent of a the efficacy of the shield between the fixed and moving coils, b the location of the electrostatic tie between the fixed and moving coils, and c the connection of the fixed coils series, series-parallel, or parallel.

In case of DC current, the current is also in phase with its generated electromagnetic field. Mutual inductance between any two of the four fixed coils, 85 juh. Instruments with moving coils can be calibrated for direct current or power frequency currents up to a few hundred hertz.

Wattmeter – Wikipedia

The 25,ohm resistor in series with the lead to the elec- trometer needle was inserted to protect the needle suspension from possible short circuits between needle and quadrant during preliminary adjustments. Limited of current flows through the moving coil so as to avoid heating. Electromagnetic watt meters are used to measure utility electrodynwmic. Views Read Edit View history.

The “shunt resistance” is connected electrodtnamic parallel with the moving coil and the ohm resistor. Imperfection of the astatic construction of the wattmeter results- in a small deflection of the moving system with direct current through the moving coils only, because of interaction with the earth’s magnetic field. 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 wattmeter would then be expected to indicate the power corresponding to 90 degrees minus the phase difference between the current through the fixed coils of the wattmeter and the quadrant voltage of the electro- meter. This procedure very completely eliminates all sources of error — such as heating, shift of zero, and reading error of either instrument — and leaves in the net difference only those errors which arise from sources such as inductance, capacitance, and eddy currents, in which the effect on alternating current differs from that on direct current.

A Kelvin voltmeter of the multicellular electrostatic type was used to measure the voltage across the wattmeter voltage circuit, because the deflection of this wartmeter of voltmeter is independent of frequency over a wide range. The a-c supply was disconnected and the d-c supply was connected, the voltage being adjusted to v. Connected in series 2. The results of these measurements are shown by the curve plotted in figure 8. The difference between the average a-c steps 1 and 4 above and the average d-c 8 A quadrant electrometer connected to measure power could be used as a standard instrument for this purpose, but a considerable amount of time and patience would be required to set up and calibrate an instru- ment of this electrodynzmic so that the desired accuracy could be attained.


How does a Wattmeter work? (back to basics)

The possibility of warping was reduced to a minimum by carefully varnishing the mahogany inside and out.

These induced currents will flow only when the moving-coil circuit is closed and when the position of the moving system is not at the point of zero mutual inductance.

Electrodynsmic two pressure coils can be connected in series or parallel to change the ranges of the wattmeter. Wattmeetr of this type are used throughout the RF spectrum and can even measure visible light power. When the present wattmeter was first assembled, one of the tests consisted in putting current through the fixed coils, the wattemter circuit being open, and noting the deflection of elsctrodynamic moving system. So the expression for the torque can be written as: Attached to upper part of stationary glass panel Wattmrter of the movable head to which the upper end of the suspension is attached.

For high-power measurements, a calorimeter directly measures heat produced by RF power. The central wire of the shielded lead is connected to the Upper moving-coil binding post. The Electrodynamometer Wattmeter has two types of coils; fixed and the moving coil. 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.

With magnetic impurities of zero retentivity, the deflection of the moving system would be the same for alternating current as for direct current through the fixed coils but would vary as the square of the magnitude of this current. One end of this series circuit is connected to the moving-coil lead going to the bottom suspension the damping vane is soldered to the lead from this suspension to the lower moving coil.

Wattmeer page was last edited on 27 Novemberat 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. The relative sensitivity this obtained is in electgodynamic in centi- meters per milliampere in the moving coils with rated current in the fixed coils.

The lower suspension ribbon extends 8 in.