Читать книгу Automation of Water Resource Recovery Facilities - Water Environment Federation - Страница 209

Closed-loop systems are also called feedback control because they provide direct feedback of the process variable to the control system to allow manipulation of the controlled variable. Feed-forward control is an open-loop control that contains a prediction or model of how the process is expected to respond based on data other than the actual process variable. The aforementioned flow-pacing example represents feed-forward control. In this instance, the prediction is that the chemical effect will be the same if the dosage rate is constant. The chemical flowrate is then varied in accordance with facility flow to maintain a constant dosage rate.