Electric and pneumatic valve positioner

A control element positioning apparatus for positioning a piston in a cylinder, the cylinder having inlet ports at both ends and the piston being coupled to a shaft and the apparatus being coupled to a pneumatic supply and an exhaust and being activated by an external control signal, comprising:

• a balance beam, said balance being coupled to a pivot element and said balance beam being coupled to the shaft;
• a pneumatic force balance element having pneumatic output ports and being coupled to said balance beam so that when said balance beam moves in a first direction a first pneumatic output port is coupled to a pneumatic supply and a second pneumatic output port is coupled to an exhaust and when said balance beam moves in a second direction, the first pneumatic output port is coupled to an exhaust and the second pneumatic output port is coupled to a pneumatic supply;
• each of said pneumatic output ports being adapted to be coupled to an end of the cylinder;
• a control spring having two ends, the first end coupled to said balance beam;
• a drive unit having an input and an output, the output being coupled to the second end of said control spring;
• and
• a motor having a shaft coupled to the input of said drive unit and whose motion is controlled by the external control signal.

A positioning apparatus for positioning an actuator;

• the actuator being adapted to move bidirectionally, being responsive to pneumatic pressures and providing means for indicating the position of the actuator;
• and the apparatus being coupled to a pneumatic pressure source and a pneumatic pressure vent and being activated by an external control signal, comprising:
• means for summing a plurality of applied forces and being adapted for motion in response to an imbalance of the applied forces;
• actuator bias means for providing a force indicative of the actuator position;
• said actuator bias means being coupled to the actuator position indication means and coupled to said summing means;
• control bias means for providing a force indicative of the desired actuator position, said control bias means being coupled to said summing means and having an input for receiving a positional signal;
• drive means for providing a positional signal to said control bias means responsive to an input signal, said drive means having an input and an output, the output being coupled to said control bias means positional input;
• a motor having a shaft for providing a positional signal indicative of the desired actuator position and whose motion is controlled by the external control signal, said motor shaft being coupled to said drive means input;
• and
• pneumatic pressure control means for coupling the pneumatic pressure source and the pneumatic pressure vent to the actuator, said pressure control means being coupled to said summing means, to the actuator, to the pneumatic pressure source and to the pneumatic pressure vent, so that when said summing means moves in a first direction the pneumatic pressure source and the pneumatic pressure vent are coupled to the actuator to cause the actuator to move in one direction and when the summing means moves in a second direction the pneumatic pressure source and the pneumatic pressure vent are coupled to the actuator to cause the actuator to move in an opposite direction.