Electricity supply companies obviously require some method of metering the demand for electricity in homes and industry, so that they can charge accordingly. This is achieved by the installation of a meter on the consumer's premises which records electricity usage. The meters are periodically `read' and the displayed value used to calculate the billing cost.
There are two variations on standard electric meters. `Slot' meters will dispense electricity to the value of money inserted and then cut off when further payment is required. Card meters work in a similar fashion to slot meters but payment is taken from an electronic card, which is inserted into the meter and debited as electricity is used. The operation of the meter remains the same as the standard meter, but additional components are added to handle these two additional payment methods.
The electricity meter has a horizontal revolving disc of aluminium, which has electromagnet coils both above and below. Eddy currents produced by the coils, enable the disc to rotate. The upper coil has a magnetic flux, which is equal to the voltage being supplied. The magnetic flux of the lower coil depends on the load current. The rate at which the disc gyrates, is proportional to the power passing through the meter. Gears are also utilised to drive the counter, which determines the amount of electricity used.
