Inventors:
Everett O. Olsen - Wrentham MA
Robert F. Estes - Foxboro MA
Paul W. Rezendes - New Bedford MA
George F. Williams - Rumford RI
Assignee:
The Foxboro Company - Foxboro MA
International Classification:
F15B 500
G05D 1620
Abstract:
An electro-pneumatic current-to-position transducer includes an electric motor having a permanent magnet for a stator and spring restrained coil pivotally suspended about the magnet for a rotor. An input current to the coil induces a mechanical rotation of the coil about the magnet which is proportional to the applied current. Fastened to the coil for rotary movement therewith is a flapper positioned to cover the nozzle of a pneumatic circuit. As current is applied to the coil, the flapper moves toward the nozzle thereby changing the back pressure in the pneumatic circuit. This change in pressure is amplified, then sensed by appropriate pressure-responsive devices and subsequently fed back to a control lever on which the nozzle is mounted, thereby repositioning the nozzle so as to maintain an essentially constant separation between the flapper and the nozzle. The pressure signal developed by this pneumatic control circuit is proportional to the applied current, and can serve as a pneumatic output signal for any of various purposes. Two embodiments of the transducer are disclosed, one arranged to convert an input current signal into a corresponding pressure output; the other adapted to receive an electrical input for proportionally controlling the position of a process control valve stem.
