Level Control Loop

Level Control


  • Flow Indicator
  • Control Valve
  • Control Valve


This is a example of attempted feedforward control. The level in the tank is never measured. Changing the valve position does not affect the measured variable. The level is supposed to be kept constant by matching the outlet flow to the inlet flow.

There is no point in doing this usless for some reason the level in the tank cannot be measured.

  • Measured variable - Inlet flowrate
  • Manipulated variable - Outlet flowrate
  • Disturbances - Inlet flowrate


If the inlet flowrate increases then the outlet flowrate is increases by the same amount. If the inlet flowrate decreases then the outlet flowrate is decreased by the same amount.

This will not work! This is a bad control system. Feedforward should only be used to augment the performance of a feedback system. A correct control system is shown below.