Abstract: An electrical-pneumatic transducer includes a pneumatic relay in which the pressure of the air at the outlet varies in accordance with the back pressure of the air at a bleed nozzle in the relay. This back pressure is changed by the armature of a solenoid with the armature opposing the nozzle outlet and being urged toward the latter with a force responsive to a signal in the form of current flowing through the solenoid coil. The magnitude of the current is correlated with the magnitude of a variable condition. The force on the armature, which is a permanent magnet, is selectively set to calibrate the transducer by means of a second permanent magnet which is axially aligned with the armature and is adjustably movable toward and away from the latter.

Abstract: A butterfly damper, controlling volume air flow through a duct, is biased toward a closed position at least partially by aerodynamic pressure and is moved against its bias by a small pneumatic actuator in response to a sensed condition. The position of the damper is stabilized by a feedback and oscillations are damped.