# Process variable

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{{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](/source/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](/source/Control_system). 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](/source/setpoint_(control_system)) (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](/source/Negative_feedback) used to maintain PV = SP]]
Measurement of process variables is essential in [control system](/source/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 that affect chemical and physical processes are: [pressure](/source/pressure), [temperature](/source/Thermodynamic_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](/source/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](/source/PID_controller).

==References==
{{Reflist}}

{{DEFAULTSORT:Process Variable}}
Category:Control theory

{{Tech-stub}}

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Adapted from the Wikipedia article [Process variable](https://en.wikipedia.org/wiki/Process_variable) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Process_variable?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.