Process variable: Difference between revisions

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==Control system use==

[[File:Set-point control.png|thumb|Block diagram of a [[Negative feedback|negative feedback control system]] used to maintain PV = SP]]

Measurement of process variables areis essential in [[control system]]s to controlling a process. The value of the process variable is continuously monitored so that control may be exerted.

Four commonly measured variables whichthat affect chemical and physical processes are: [[pressure]], [[Thermodynamic temperature|temperature]], level and flow.{{citation needed|date=December 2011}} but there are in fact a large number of measurement quantities which for international purposes use the [[International System of Units]] (SI)

The SP-PV error is used to exert control on a process so that the value of PV equals the value of the SP. A classic use of this is in the