# How is electrical energy measured?

## The Ferraris meter

The Ferraris meter is an induction motor meter named after the Italian physicist and engineer
Galileo Ferraris. The meter is used to show the energy consumed.

It consists of an induction motor connected to a mechanical meter display.

The induction motor has a pivoted metal disc which runs over and/or through two electromagnets placed cross-wise (voltage and current coils). If an alternating current flows through the electromagnets, eddy currents are generated in the metal disc - physically induced - which work with the magnetic flows to generate a turning moment which makes the disc rotate.

A permanent magnet (braking magnet) is positioned over the disc at another point. If less energy is consumed, the braking magnet compensates for the acceleration and holds the rotation speed in proportion to the energy flow.

The disc drives a roller counter which shows the consumption. Energy consumption in kilowatt hours (kWh) can be found with the number of rotations of the disc, i.e. the number of disc rotations is proportional to the energy consumed. This is why the statement "rotation per kilowatt hour" is found on the meter. Thus, "600 R/kWh" means that the disc must rotate 600 times for the meter to show consumption of one kilowatt hour. Energy meters can vary in the number of rotations per kilowatt hour. Comparing rotations is therefore not an effective way to determine consumption.

The single-phase Ferraris meter is also colloquially known as an alternating current meter and the multi-phase meter as a three-phase current meter.

## The electronic meter

In an electronic meter, the energy used is not determined through moving mechanical elements, but with electrical components such as Rogowski coils, shunt resistors and the Hall sensor. Further processing of the measurement values received is carried out with an electronic switch.

The information received and processed is shown on a display.