<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2016) (Learn how and when to remove this template message) </Td> </Tr> <P> The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) 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 . </P> <P> The traditional analog wattmeter is an electrodynamic instrument . The device consists of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil . </P> <P> The current coils are connected in series with the circuit, while the potential coil is connected in parallel . Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement . A current flowing through the current coil generates an electromagnetic field around the coil . The strength of this field is proportional to the line current and in phase with it . The potential coil has, as a general rule, a high - value resistor connected in series with it to reduce the current that flows through it . </P>

Function of current coil and pressure coil in wattmeter