{{Short description|Value of a given part of a monitored or controlled process}} {{about|the engineering indicator|the mathematical concept used in thermodynamics|process function}} {{more citations needed|date=May 2022}}
In control theory, a '''process variable''' ('''PV'''; also '''process value''' or '''process parameter''') is the current measured value of a particular part of a process which is being monitored or controlled. An example of this would be the temperature of a furnace. The current temperature is the process variable, while the desired temperature is known as the setpoint (SP).<ref name=Bequette> {{cite book |author=B. Wayne Bequette | title = Process Control: Modeling, Design, and Simulation | publisher =Prentice Hall Professional | year= 2003 | page = 5 |url=https://books.google.com/books?id=PdjHYm5e9d4C&pg=PA5 |isbn = 9780133536409 }} </ref>
==Control system use== [[File:Set-point control.png|thumb|Block diagram of a negative feedback control system used to maintain PV = SP]] Measurement of process variables is essential in control systems to controlling a process. The value of the process variable is continuously monitored so that control may be exerted.
Four commonly measured variables that affect chemical and physical processes are: pressure, 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 PID controller.
==References== {{Reflist}}
{{DEFAULTSORT:Process Variable}} Category:Control theory
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