In this type of meters the electrical energy consumption is measured based on the induction principle recorded by the resolution of the counter. Ferraris invented this meter in the year 1884.Hence,these meters still called Ferraris meters.
The principle adopted by Ferraris was the principle of induction motor. Hence these meters are designed to carry the load current up to 80A in the whole current single and 100A in the three phase meters. For measuring high loads on the LT side, CT operated meters are used.
These meters have lo accuracy in the range of 0.2%.The life time of these meters varies from 15 years.
The driving system of this meter consist of two electromagnets. The coil of one of the electromagnet is excited by the load current. This coil is called current coil. The coil of second electromagnet is connected across the supply voltage.
This coil is called the pressure coil or voltage coil. An aluminium disc is positioned in between the electromagnets. The supply voltage is applied across the pressure coil. So a current proportional to the supply voltage is flowing through the pressure coil.
This current will produce a magnetic flux, major portions of this flux sweeps across the aluminium disc and is responsible for the production of driving torque. And the revolution of the disc is proportional to the load current.
The function of the registering or counting mechanism is to record the revolutions continuously a number which is proportional to the revolutions made by the moving system