A mirror galvanometer is a mechanical meter that senses electric current, except that instead of moving a needle, it moves a mirror. The mirror reflects a beam of light, which projects onto a meter, and acts as a long, weightless, massless pointer.
The apparatus is also known as a spot galvanometer after the spot of light produced in some models.
Mirror galvanometers were used extensively in scientific instruments before reliable, stable electronic amplifiers were available. The most common uses were as recording equipment for seismometers and submarine cables used for telegraphy.
The mirror galvanometer was invented by William Thomson, later to become Lord Kelvin.
In the case of a moving-mirror galvanometer, a mirror is attached to the coil, and illuminated with light.
The mirrorgalvanometer was of major use in laying the transatlantic telegraph cable between the United States and Europe in 1866.
In some cases (the classical polygraph of movies or the electroencephalograph), the galvanometer is strong enough to move the pen while it remains in contact with the paper; the writing mechanism may be a heated tip on the needle writing on heat-sensitive paper or a fluid-fed pen.
Feeds |
Contact