A Wattmeter or power meter measures the amount of power flow in a circuit. These wattmeters are used to measure the power usage, both in industries and household usage. Unit of power is watt that’s why this meter is known as wattmeter.
Wattmeter connection to circuits
Connection for single phase 2-wire connection:
The single phase line is a 2 wire connection, the measuring element should consist of one voltage sensor and current sensor connected parallel and in series respectively. The connection must be such that all connection coils have a common tie to the conductor in which there is no current coil. Detailed discussions of measuring circuits for various power distribution schemes is beyond the context of the present text.
Connection for 3 phase wire circuit:
##Wattmeter/Electricity measuring devices:
A fundamental electricity measuring device consists of a sensor, multipliers, numerical conversion and registers. There are mainly two types of measuring meters, electromechanical type and Electronic Meters.
The electromechanical meter consists of an ac motor which spins in a speed according to the amount of current passing through it.
The number of rotation of a motor is measured using an “odometer”. The “motor” used in these meters has a rotor made of a thin aluminium disk, with the rotating magnetic field established by sets of coils energized by line voltage and load current so that the rotational speed of the disk is dependent on both voltage and current.
The electronic meter contains additional components as multiplexers, analog to digital converter, microprocessor, display/registers, communication and input/output ports, LED’s and clocks.
Two basic forms of electronic metering measurement have been introduced to the industry:
- Analog multiplying
- Digital sampling