Pneumatic servo assembly for an electro-pneumatic converter

Claim 1

A pneumatic servo assembly for an electropneumatic closed loop control system providing a pneumatic output signal in response to a corresponding input signal comprising: variable restriction means for producing different pneumatic output signals from the pneumatic servo assembly; motor means for moving said variable restriction means to vary the pneumatic output from the pneumatic servo assembly, said motor means having a cam assembly connected thereto for variably restricting the pneumatic servo assembly depending on the position of the cam; a backpressure nozzle mounted proximately to said cam assembly to be variable restricted by said cam assembly; means for actuating said motor means in response to a control signal; means for establishing a set point signal in response to the electrical input signal indicative of a desired pneumatic output signal; means for establishing a feedback signal indicative of the pneumatic output signal; combining means for comprising the setpoint signal with the feedback signal to establish a control signal to said actuating means; and a nozzle clamp for exerting drag on the cam assembly to maintain a constant pneumatic output signal from said pneumatic servo assembly corresponding to the last control signal to said pneumatic servo assembly in response to an electrical failure.