Flow Control Loop
- Flow Indicator - Orifice Meter
- Control Valve
- Flow Controller
Although the measurement is before the manipulation this NOT feedforward control. Like all examples of useful control systems in this course it is standard feedback control. The position of the measurement relative to the adjustment does not matter in this case because the flow must be the same on both sides of the valve.
- Measured variable - the flowrate
- Manipulated variable - the flowrate via the control valve
- Disturbances - the flowrate upstream of the measurement
If the flow increases then the valve is closed and if the flow decreases then the valve is opened.
It is usual to measure flows upstream of valves since, especially with gases, valve position can affect the calibration of certain types of flowmeter.
This is the standard way of regulating flows. There are virtually no situations in which the flow though the control valve is not the one which is measured.