Abstract: A control force input system for a balance beam pneumatic valve positioner which does not allow the controlled apparatus to make a full travel motion when the overall control signal is removed. The control force is transmitted to the balance beam or other force summing bar using a linear solenoid coupled to a control spring coupled to the balance beam. When the motive power control signal is removed from the linear solenoid, the balance beam establishes an equilibrium position based on the existing position of the linear solenoid. The solenoid shaft extends into a captive cylinder. A piston connected to the solenoid shaft is located in the captive cylinder and forms two chambers in the cylinder. A solenoid valve connects a port in each chamber. When the solenoid valve is activated, the piston is free to travel. When the solenoid valve is deactivated, as when the control signal is removed, the piston is held in position, locking the solenoid shaft in position.

Abstract: A control force input system for a balance beam pneumatic valve positioner which does not allow the controlled apparatus to make a full travel motion when the overall control signal is removed. The control force is transmitted to the balance beam or other force summing bar using a linear solenoid coupled to a control spring coupled to the balance beam. When the motive power control signal is removed from the linear solenoid, the balance beam establishes an equilibrium position based on the existing position of the linear solenoid. Split wedges are repelled from the linear solenoid when a control signal is applied, releasing the solenoid shaft for movement. Alternatively, split slides are repelled from each other when a control signal is applied, releasing the solenoid shaft bias spring. When the control signal is removed, the split wedges or split slides are biased and attracted to the solenoid, locking the solenoid shaft in position. A variation for use with a current to pressure transducer is detailed.

Abstract: A control force input system for a balance beam or pivot arm pneumatic positioner which does not allow the controlled apparatus to make a full travel motion when the overall control signal is removed. The control force is transmitted to the balance beam by the coupling of the magnetic fields produced by a fixed magnet located on the balance beam and a variable magnet located away from the balance beam. When the motive control signal is removed from the variable magnet, the balance beam returns to an equilibrium or zero position due to the action of a pair of zero springs, stopping the controlled apparatus at its position when the control signal is removed.

Abstract: A control force input system for a balance beam pneumatic valve positioner which does not allow the controlled apparatus to make a full travel motion when the overall control signal is removed. The control force is transmitted to the balance beam or other force summing bar using a motor coupled to a drive unit which compresses or extends a control spring coupled to the balance beam. When the motive power control signal is removed from the motor, the balance beam establishes an equilibrium position based on the existing position of the motor.