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 LI1 and
LI2 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 Lv, and its
multiplier resistor Rs, 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
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 = VrmsIrmscos(theta) or P = I2R