Editing Chart recorder (section)

==Chart drive==
[[File:Chart recorders of a control panel.JPG|thumb|Chart recorders of a control panel at a water purification plant record water flow rates at different stages of the process.]]

The paper chart is driven past the pen at a steady rate by a clockwork or electrical drive mechanism. One common method is to use a miniature [[synchronous motor]] which turns at a constant speed related to the [[utility frequency|power frequency]]; a gear-train is used to propel the paper. Industrial strip-chart recorders may have two-speed gear trains that allow a higher speed to be used for initial adjustments of a process or to follow process upsets. Medical and scientific recorders allow a wide range of accurately-controlled speeds to be set.

An "X-Y" recorder drives the chart depending on the value of another process signal. For example, a [[universal testing machine]] may plot the tension force on a specimen against its length. Depending on the particular recorder, either the paper chart is moved or else the pen carriage has two axes of motion. Examples of an x-y recorder date back to the 18th century in the form of the [[Pressure volume diagram|steam indicator diagram]]s used to record pressure and volume in steam engines.