Galvanometer, << `gal` vuh NOM uh tuhr, >> is a delicate instrument used primarily to detect and measure small electric currents. Most galvanometers operate on the principle that an electric current flowing through a wire in the presence of a magnetic field produces a force in the wire.
A typical galvanometer has a scale with a zero in the center and numbers at regular intervals on either side. It also has an indicator such as a needle or a beam of light. The indicator remains at zero until a current passes through the galvanometer. A current in one direction causes the indicator to move to one side of the zero point. A current in the opposite direction causes the indicator to move to the other side of the zero point. The stronger the current, the farther the indicator moves across the scale. When the scale is marked in standard units of current, such as amperes or milliamperes, the instrument is called an ammeter or milliameter.
One of the most commonly used galvanometers is the D’Arsonval galvanometer. This instrument uses a coil of fine wire suspended between the poles of a permanent magnet. Current is applied through a small wire attached to the top of the coil and exits through a springlike wire attached to the bottom. With no current applied, the springlike wire keeps the coil in the zero position. When the current is introduced, it establishes a magnetic field in the coil. This field interacts with the magnetic field of the permanent magnet, causing the coil to turn. In some D’Arsonval galvanometers, a fine needle is attached to the moving coil to serve as the indicator. In others, a small mirror is attached to the coil, and a beam of light is reflected off the mirror and onto a scale a distance away.
Hans Christian Oersted, a Danish physicist, investigated the effect of electric currents on a magnetic needle in 1820. Also in 1820, Johann Salomo Christoph Schweigger, a German physicist, constructed the first simple galvanometer. In 1882, Jacques Arsene d’Arsonval, a French physiologist, made significant improvements in the performance of the galvanometer. The most common type of galvanometer is named for him.
