AskDefine | Define ammeter

Dictionary Definition

ammeter n : a meter that measures the flow of electrical current in amperes

User Contributed Dictionary



  1. A device that measures the magnitude of an electric current, especially one calibrated in amperes


device that measures an electric current
  • Croatian: ampermetar
  • Russian: амперметр
  • Spanish: amperímetro

Extensive Definition

An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes, hence the name. The word "ammeter" is commonly misspelled or mispronounced as "ampmeter" or "ameter" by some.
The earliest design is the D'Arsonval galvanometer or moving coil ammeter. It uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The voltage drop across the coil is kept to a minimum to minimize resistance across the ammeter in any circuit into which it is inserted.
Moving iron ammeters use a piece or pieces of iron which move when acted upon by the electromagnetic force of a fixed coil of (usually heavy gauge) wire. This type of meter responds to both direct and alternating currents (as opposed to the moving coil ammeter, which works on direct current only).
To measure larger currents, a resistor called a shunt is placed in parallel with the meter. Most of the current flows through the shunt, and only a small fraction flows through the meter. This allows the meter to measure large currents. Traditionally, the meter used with a shunt has a full-scale deflection (FSD) of , so shunts are typically designed to produce a voltage drop of when carrying their full rated current.
Zero-center ammeters are used for applications requiring current to be measured with both polarities, common in scientific and industrial equipment. Zero-center ammeters are also commonly placed in series with a battery. In this application, the charging of the battery deflects the needle to one side of the scale (commonly, the right side) and the discharging of the battery deflects the needle to the other side.
Digital ammeter designs use an analog to digital converter (ADC) to measure the voltage across the shunt resistor; the digital display is calibrated to read the current through the shunt.
Since the ammeter shunt has a very low resistance, mistakenly wiring the ammeter in parallel with a voltage source will cause a short circuit, at best blowing a fuse, possibly damaging the instrument and wiring, and exposing an observer to injury. In AC circuits, a current transformer converts the magnetic field around a conductor into a small AC current, typically either 1 or 5 Amps at full rated current, that can be easily read by a meter. In a similar way, accurate AC/DC non-contact ammeters have been constructed using Hall effect magnetic field sensors. A portable hand-held clamp-on ammeter is a common tool for maintenance of industrial and commercial electrical equipment, which is temporarily clipped over a wire to measure current.
ammeter in Arabic: أميتر
ammeter in Bulgarian: Амперметър
ammeter in Catalan: Amperímetre
ammeter in Czech: Ampérmetr
ammeter in Danish: Amperemeter
ammeter in German: Strommesser
ammeter in Modern Greek (1453-): Αμπερόμετρο
ammeter in Spanish: Amperímetro
ammeter in Persian: آمپرسنج
ammeter in French: Ampèremètre
ammeter in Galician: Amperímetro
ammeter in Italian: Amperometro
ammeter in Hebrew: מד זרם
ammeter in Lithuanian: Ampermetras
ammeter in Hungarian: Villamos műszerek
ammeter in Dutch: Ampèremeter
ammeter in Japanese: 電流計
ammeter in Polish: Amperomierz
ammeter in Portuguese: Amperímetro
ammeter in Russian: Амперметр
ammeter in Simple English: Ammeter
ammeter in Slovenian: Ampermeter
ammeter in Finnish: Ampeerimittari
ammeter in Swedish: Amperemeter
ammeter in Vietnamese: Ampe kế
ammeter in Turkish: Ampermetre
ammeter in Ukrainian: Амперметр
ammeter in Chinese: 安培计
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