Simple Watt Meter Review

Electronic Electrical Devices

The wattmeter is an instrument which measures DC power or true AC power. The wattmeter uses fixed coils to indicate current, while the movable coil indicates voltage illustrated below. Coils L_I1 and L_I2 are the fixed coils in series with one another and serve as an ammeter. The two I terminals are connected in series with the load. The movable coil L_v, and its
multiplier resistor R_s, are used as a voltmeter, with the V terminals connected in parallel with the load. The meter deflection is proportional to the VI, which is power.

Wattmeters are rated in terms of their maximum current, voltage, and power. All of these ratings must be observed to prevent damage to the meter.

The equation below is the mathematical representation of calculating power in a DC circuit.

P = VI or P = I²R

Equation (14-16) is the mathematical representation for calculating power in an AC circuit.

P = V_rmsI_rmscos(theta) or P = I²R