Electronic Electrical Devices  Electronic Electrical Components
Simple Watt Meter Review
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 = I^{2}R
Equation (1416) is the mathematical representation for calculating power in an AC circuit.
P = V_{rms}I_{rms}cos(theta) or P = I^{2}R
