Process variable: Difference between revisions

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

A '''process variable''', '''process value''' or '''process parameter''' is the current statusmeasured value of a particular part of a process underwhich control.is being monitored or 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.

==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 are 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 which affect chemical and physical processes are: [[pressure]], [[Thermodynamic temperature|temperature]], level and flow.{{cn|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]].

Measurement of process variables are important in [[Control system|controlling]] a process. The process variable is a dynamic feature of the process which may change rapidly. Accurate measurement of process variables is important for the maintenance of accuracy in a process. There are four commonly measured variables which affect chemical and physical process: [[pressure]], [[Thermodynamic temperature|temperature]], level and flow.{{cn|date=December 2011}}