Almost every home today has an electricity connection. Electric energy is a primary need and it is not free of cost. Electricity generation and supply companies have to bear various costs. You have to pay for the amount of energy used to your electricity supplier.
With an electricity connection, you get a device called electricity meter or energy meter or kilowatt hour meter or electric meter. It measures the amount of electrical energy you have consumed so that you will pay for only what you have used. Basically, energy meters can be classified into two main types as (i) electromechanical energy meter and (ii) electronic energy meter. Both the types are further explained below.
Electromechanical Energy Meter
The conventional electromechanical energy meter works on the principle of electromagnetic induction. It has a rotating non-magnetic but electrically conductive metal disc (usually aluminum disc). The disc is mounted on a spindle between two electromagnets. It rotates at a speed proportional to the power passing through the meter. Thus, the number of revolutions of the disc are proportional to the energy usage.
There are two coils placed near the metal disc, one coil produces magnetic flux proportional to the voltage and another coil produces magnetic field proportional to the current. These two magnetic fields act on the metal disc which cause eddy currents in the disc (this is similar to a two-phase induction motor). Few other gear wheels are coupled to this metal disc and arrangement is made so that it will show appropriate readings in the display section.
Since many mechanical parts are used in such type of energy meter, mechanical defects like friction, wear & tear etc problems are noticeable in such meters. These mechanical defects directly affect the accuracy of the meter.
Electronic Energy Meter
Electronic energy meters can further be classified as electronic analog energy meter and digital energy meter.
In analog type electronic energy meters, voltage and current values are obtained by voltage dividers and current transformers. An ‘analog to digital converter’ converts these analog values into digitized samples. These samples are then converted into corresponding frequency signals by a frequency converter. These frequency pulses are then fed to a counter which displays the amount of used energy.
A digital energy meter displays the readings of energy used on a digital display (LCD or LED). No moving parts are present in this type of energy meters. Thus, these are also called as ‘static energy meters‘. A digital meter consists of instrument transformers (to sample current and voltage), analog to digital converters, microcontroller etc. The input voltage/current is compared to with a programmed reference voltage and current and then the data gets converted into digital form. The digital data is the processed with appropriate operations in a microcontroller which is then displayed on an LCD or LED display.
Electronic meters are much more accurate than electromechanical meters. There are no moving parts and, hence, mechanical defects like friction are absent.
In addition, electronic energy meters come with indicating LEDs for phase/neutral ok, earth/leakage loss, kilowatt-hour pulse etc.