Dual reset controller

Claim 1

A dual reset pneumatic controller for providing a pneumatic control signal comprising: a pneumatic control signal bleed nozzle; a flapper associated with said nozzle; a pressure differential-to-mechanical force transducer for applying a force tending to move said flapper in one direction with respect to said nozzle; a bias member having a free end for applying a force tending to move said flapper in an opposite direction with respect to said nozzle, the position of said flapper with respect to said nozzle being determined by a balance of the opposed forces applied to said flapper, said pneumatic control signal varying as a function of said flapper position; a first pneumatic actuator for producing a first reset force as a function of a variable sensed controlled condition to alter the force applied by said bias member to said flapper; and a change-over pneumatic actuator for producing a second reset force as a function of a variable signal, a lever for transmitting force from said change-over pneumatic actuator to said bias member to alter the force applied by said bias member to said flapper, and bias means for applying force to said lever in opposition to the force produced by said change-over pneumatic actuator whereby the position of said lever is established by a balance of said forces, said lever being movable between inoperative and operative positions.