Active power meter circuit

A power meter is an instrument used to directly measure electrical power. Electrical power in a DC circuit is the product of voltage and current . The electric
power (also called active power ) in the AC circuit is not only related to the effective value of the voltage and current, but also related to the cosine of the phase difference between them. Therefore,
the instrument that can directly measure the electric power must be able to reflect the relationship between them. The performance of the electric system measurement mechanism meets this requirement, so
most of the current power meters are electric system instruments.
    The structure and working principle of a power meter. In the sinusoidal AC circuit shown in Figure 5-8a , the active power
absorbed by the negative intercept is     P=U∞ printed in Eq. U and J are the effective values ​​of the sinusoidal voltage and current on the load respectively; J is the impedance angle of the load, that is, the phase difference angle of the voltage and current on the load } cos is the power factor of the load.