The wattmeter is an instrument for measuring the electric power in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements. Contents. 1 Electrodynamic; 2 Electronic. Dynamometer Type Wattmeter Principle: If two coils are connected such Hence an electrodynamic instrument, when connected as shown in. In electrodynamometer type wattmeter, moving coil works as pressure coil. We know that instantaneous torque in electrodynamic type instruments is directly.

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Dynamometer Type Wattmeter Working – your electrical guide

Now let the applied value of voltage across the pressure coil be Assuming the electrical resistance of the pressure coil be very high hence we can neglect reactance with respect to its resistance. Because fairly large currents are required to set up the necessary field flux, the dynamometer instrument is not as sensitive as a PMMC instrument. Consider the arrangement shown in figure 1. In order to derive these expressions let us consider the circuit diagram given below: The current coils are connected in series with the circuit, while the potential coil is connected in parallel.

This may not be specified in the meter’s manual. It consists of following parts There are two types of coils present in the electrodynamometer. Digital electronic instruments measure many parameters and can be used where a wattmeter is needed: The real power divided by the apparent volt-amperes VA is the power factor. The reduction in current required to maintain temperature is related to the incident RF power. Instruments of this type are used throughout the RF spectrum and can even measure visible light power.


Therefore, a wattmeter is rated not only in watts, but also in volts and amperes.

We know that instantaneous torque in electrodynamic type instruments is directly proportional to the product of instantaneous values of currents flowing through both the coils and the rate of change of flux linked with the circuit. If there is phase difference between voltage and electric current, then expression for instantaneous current through current coil can be written as As 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.

These coils are called the electric current coils of electrodynamometer type wattmeter. Errors in the pressure coil inductance.

Retrieved from ” https: In other words, when the field produced by the current carrying moving coil F r tries to come in line with the field produced by the current carrying fixed coil F ma deflecting torque is exerted on the moving system and deflection takes place as shown in figure b. By limiting the current, the moving coil is made of light weight which in turn increases the sensitivity of the instrument.

The dynamometer type wattmeters are very important because they are commonly employed for measuring power in AC circuits.

wattmeetr Wattmeters vary considerably in correctly calculating energy consumption, especially when real power is much lower than VA highly reactive loads, e. Gravity control Spring control, only spring controlled systems are used in these types of wattmeter.

Dynamometer Type Wattmeter Working

Generally, a high resistance is connected in series with the moving coil to limit the current through it. The fixed coil is splitted into two equal parts which are placed parallel to each other. The scale of the wattmeter is illustrated in figure 2 in which upper scale is calibrated in milli-watts while the typee one measures the power in watts range.


The resistor controls the current across the moving coil, and it is connected in series with it. The magnetic field in which the lightweight moving coil is situated is generated by passing current through the fixed field coils. Let I 1 and I 2 be the instantaneous values of currents in pressure and electric current coils respectively.

Ahmed Faizan Sheikh, M.

Electrodynamometer Type Wattmeter

Moving coil moves the pointer with the help of spring control instrument. In electrodynamometer type wattmetermoving coil works as pressure coil. The readings may be displayed on the device, retained to provide a log and calculate averages, or transmitted to other equipment for further use. Did you find apk for android? This particularly affects ttpe power e. Then, when a current is passed through the moving coil, the moving coil electroodynamic the meter pointer are deflected.

Now let the applied value of voltage across the pressure coil be Assuming the electrical resistance to the pressure coil be very high hence we can neglect reactance with respect to its resistance. In other projects Wikimedia Commons.

Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: The controlling torque wattjeter provided by springs which also serve the additional purpose of leading current into and out of the moving coil. The moving coil of the instrument has a series resistor and is connected in parallel with the load.

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