Instruments and Meters
Most devices used in the electrical industry to measure electrical properties are called "meters." For example, there are voltmeters, ammeters, as well as numerous other types of meters. The measurement of circuit amperage or voltage can be accomplished with meters by an easily understood procedure. Power in a single-phase circuit can be measured with a single-phase wattmeter. A customer of a three-phase electrical service, three-wire or four-wire, will have a permanently installed meter that measures at least energy consumption. An effective and practical means of measuring power in unbalanced three-phase three-wire circuits involves the use of only two wattmeters in what is commonly called the "two-wattmeter method." The term smart meter is commonly applied to not only electric meters but also to water meters and gas meters. Smart meters are electronic digital instruments with a wider range of capabilities than the electromechanical designs of the past.