Editing Chart recorder (section)

==Galvanometer instruments==
{{See also|Galvanometer}}
Many types of chart recorders use a [[galvanometer]] to drive the marking device. A light coil of wire suspended in the magnetic field of a permanent magnet deflects in proportion to the current through it; instead of the pointer and scale of a direct-reading meter, the recorder deflects a pen or other marking device. The writing mechanism may be a heated needle writing on heat-sensitive paper or a simple hollow ink-fed pen. If the pen is continuously pressed against the paper, the galvanometer must be strong enough to move the pen against the friction of the paper. To lessen the strain on the galvanometer the pen might instead only intermittently be pressed against the writing medium, to make an impression, and then move while pressure is released.{{citation needed|date=August 2012}}

Where greater sensitivity and speed of response is required a [[mirror galvanometer]], might be used instead, to deflected a beam of light which can be recorded photographically.