Can anyone suggest a typical electronic analogue control system that can be used to control the flow of air in a duct. The control system will control the pressure of the air by using pressure transducers then compare the actual pressure to a nominal value then use the error signal to drive the system and will probably employ an electrically actuated valve. There is also a requirement for the valve to be shut off if problems arise. I am assuming that the system will make use of differential amplifiers but I am currently trying to understand them. The system cannot make use of digital control only electronic analogue control. Thank you for taking time to read this request.