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Incontrol theory, aprocess variable (PV; alsoprocess value orprocess parameter) is the current measured value of a particular part of a process which is being monitored orcontrolled. 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 theset-point (SP).[1]
Measurement of process variables is essential incontrol 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] but there are in fact a large number of measurement quantities which for international purposes use theInternational 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 thePID controller.
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