Electricity meter

An electricity meter, electric meter, electrical meter, energy meter, or kilowatt-hour meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device. Electric meter or energy meter measures the total power consumed over a time interval. Electric utilities use electric meters installed at customers' premises for billing and monitoring purposes. They are typically calibrated in billing units, the most common one being the kilowatt hour (kWh). They are usually read once each billing period. When energy savings during certain periods are desired, some meters may measure demand, the maximum use of power in some interval. "Time of day" metering allows electric rates to be changed during a day, to record usage during peak high-cost periods and off-peak, lower-cost, periods. Also, in some areas meters have relays for demand response load shedding during peak load periods. As commercial use of electric energy spread in the 1880s, it became increasingly important that an electric energy meter, similar to the then existing gas meters, was required to properly bill customers, instead of billing for a fixed number of lamps per month. DC meters measured charge in ampere hours. Since the voltage of the supply should remain substantially constant, the reading of the meter was proportional to actual energy consumed. For example, if a meter recorded that 100 ampere hours had been consumed on a 200-volt supply, then 20 kilowatt-hours of energy had been supplied. Many experimental types of meter were developed. Thomas Edison at first worked on a direct current (DC) electromechanical meter with a direct reading register, but instead developed an electrochemical metering system, which used an electrolytic cell to totalise current consumption. At periodic intervals the plates were removed and weighed, and the customer billed. The electrochemical meter was labor-intensive to read and not well received by customers. An early type of electrochemical meter used in the United Kingdom was the 'Reason' meter.