page_title: Galvanometer
section_title: Edward Weston
hierarchical_section_title: Galvanometer / History / Edward Weston
caption_attribution_description: English: Weston Galvanometer Rectangular wooden box; brown leather handle attached to top with metal fasteners; front has a steel lock screwed to it; lock is stamped with manufacturer; four hard black rubber feet on bottom; top attached with two brass hinges; black painted aluminium instrument panel with raised meter; meter has a glass window over measurement bar; metal plaque attached to meter identifying the manufacturer; on flat part of panel are two plastic knobs; around each knob is a piece of copper wire; typed instructions are included. Galvanometers detect and measure small amounts of electrical current through the use of a magnetic needle or a coil in a magnetic field.
context_page_description: A galvanometer is an electromechanical instrument used for detecting and indicating an electric current. A galvanometer works as an actuator, by producing a rotary deflection, in response to electric current flowing through a coil in a constant magnetic field. Early galvanometers were not calibrated, but their later developments were used as measuring instruments, called ammeters, to measure the current flowing through an electric circuit.
  Galvanometers developed from the observation that the needle of a magnetic compass is deflected near a wire that has electric current flowing through it, first described by Hans Christian Ørsted in 1820. They were the first instruments used to detect and measure small amounts of electric currents. André-Marie Ampère, who gave mathematical expression to Ørsted's discovery and named the instrument after the Italian electricity researcher Luigi Galvani, who in 1791 discovered the principle of the frog galvanoscope – that electric current would make the legs of a dead frog jerk.
  Sensitive galvanometers have been essential for the development of science and technology in many fields.
context_section_description: Edward Weston extensively improved the design. He replaced the fine wire suspension with a pivot, and provided restoring torque and electrical connections through spiral springs rather like those of a wristwatch balance wheel hairspring. He developed a method of stabilizing the magnetic field of the permanent magnet, so the instrument would have consistent accuracy over time. He replaced the light beam and mirror with a knife-edge pointer that could be read directly. A mirror under the pointer, in the same plane as the scale, eliminated parallax observation error. To maintain the field strength, Weston's design used a very narrow circumferential slot through which the coil moved, with a minimal air-gap. This improved linearity of pointer deflection with respect to coil current. Finally, the coil was wound on a light-weight form made of conductive metal, which acted as a damper. By 1888, Edward Weston had patented and brought out a commercial form of this instrument, which became a standard electrical equipment component. It was known as a "portable" instrument because it was affected very little by mounting position or by transporting it from place to place. This design is almost universally used in moving-coil meters today.
  Initially laboratory instruments relying on the Earth's own magnetic field to provide restoring force for the pointer, galvanometers were developed into compact, rugged, sensitive portable instruments essential to the development of electro-technology.
caption: Weston galvanometer in portable case
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