We're all familiar with the electricity meter hidden away in the garage, basement, or other out-of-view location. We may even have looked at it once or twice to phone an up-to-date reading to the utility company in place of an estimate. Thanks to technology, a quiet revolution is taking place inside this innocuous looking meter.
The figure below shows an example of a traditional electromechanical meter -- first developed in the late 19th century -- that has a spinning disc and a mechanical counter display. This type of meter operates by counting the revolutions of a metal disc that rotates at a speed proportional to the power drawn through the main fuse box. Nearby coils spin the disc by inducing eddy currents and a force proportional to the instantaneous current and voltage. A permanent magnet exerts a damping force on the disc, stopping its spin after power has been removed.
|Electromechanical energy meter|
The first step in meter evolution was the replacement of electromechanical meters with solid-state electronic meters. Electronic meters measure energy using highly integrated components, such as those from Analog Devices and other vendors. These devices digitize the instantaneous voltage and current via a high-resolution sigma-delta ADC. Computing the product of the voltage and current gives the instantaneous power in watts. Integration over time gives energy used, which is usually measured in kilowatt hours (kWh). The energy data is displayed on a liquid-crystal display (LCD), as shown in below.
|Solid-state electronic energy meter|
Electronic meters offer several benefits. In addition to measuring instantaneous power, they can measure other parameters such as power factor and reactive power. Data can be measured and stored at specific intervals, allowing the utility to offer price plans based on time-of-day of usage. This allows smart consumers to save money by running major appliances, such as washers and dryers, during lower-cost, off-peak periods; and utility companies can avoid building new power plants because less capacity is required during peak periods. Electronic meters are not influenced by external magnets or orientation of the meter itself, so they are more tamper-proof than electromechanical meters. Electronic meters are also highly reliable.