Process variable: Difference between revisions

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{{Short description|Measured valueValue of a particulargiven part of a processmonitored which is being monitored,or controlled, or regulatedprocess}}

{{about|the engineering indicator|the mathematical concept used in thermodynamics|process function}}

{{more citations needed|date=May 2022}}

AIn [[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 [[Control system|controlled]]. An example of this would be the temperature of a furnace. The current temperature is called the process variable, while the desired temperature is known as the [[setpoint (control system)|set-point]]. The set point is usually abbreviated to (SP, and the process value is usually abbreviated to PV).<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 }}

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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