2. LITERATURE REVIEW
2.1 ENERGY METERS
An electricity meter or energy meter is a device that measures the amount of electrical energy supplied to a specific consumer. This can be done for three phase or single phase supply. They are used by utility companies to measure billable services. They are usually calibrated in billing units, normally kilowatt hour (kWh). Periodic readings of electric meters establish billing cycles and energy used during a cycle.
2.1.2 ELECTRO-MECHANICAL METERS
Figure 1.1: Electromechanical meter 
Prof. a Thomson’s induction-type wattmeter, dubbed the Recording meter, was the precursor to modern electromechanical meters. The electromechanical ...view middle of the document...
A permanent magnet in the configuration exerts an opposing force on the disc proportional to the speed of rotation of the disc.
The principle used applies the equation:
F = Bil [1.1]
Where :F – Force (N/m2)
B - Magnetic flux (Wb/m)
i – Current (A)
l - Length of coil (m)
The equilibrium of the two opposing forces makes the disc rotate at a speed proportional to the power being consumed. The aluminium disc drives a register that integrates the speed of the disc over time by counting number of revolutions and hence giving a reading of the energy used over time.
2.1.3 ELECTRONIC (SOLID-STATE) METERS
With the advent of integrated circuits, meter designs started to change. Instead of relying on mechanical parts for acquisition of electric energy consumption, they rely on electronic sensors for measuring the current and voltage, analogue-digital converter to convert the information into digital data then a processor embedded in the system instantly calculates the amount of energy consumed over time.
They have gained a lot of acceptance worldwide due to their compact design and light weight compared to the earlier electromechanical meters. As the world moved more into integrated systems design, various integrated circuits became more available and cheaper in cost, and thus the world’s major electricity meter manufacturing companies started producing this kind of meters.
Figure 1.3: Electronic meter 
Electronic meters measure energy using highly integrated components or other customized integrated circuits. Generally, these devices digitize the instantaneous voltage and current. Computing the product of the voltage and current gives the instantaneous power in watts. Integration over time gives energy used, measured in kilowatt hours.
Two basic sensors are usually employed. These are voltage and current sensors. The voltage sensor is built around a step down element and potential divider network that senses both the phase voltage and load voltage. The step down relates with the real voltage linearly and tracks its variation, its value is only in a form that can be used for analysis.
The second sensor is a current sensor; this senses the current drawn by the load at any point in time. It is built around a current transformer and other active devices (such as voltage comparator) which convert the sensed current to voltage for processing.
The output from both sensors is then fed into a signal conditioner which ensures matched voltage or signal level (usually 5V DC) to the control circuit. The signal conditioner also contains multiplexers which enable sequential switching of both signals to the either analogue or digital (PWM) input of the microcontroller.
The signals from the voltage and current sensors once conditioned are then fed as inputs to the embedded software in the microcontroller. The microcontroller is then programmed. It uses the received data to calculate power consumption per hour, as well as the expected charges. These are...