Valve positioner with pressure feedback, dynamic correction and diagnostics

• US 5,549,137 A
• Filed: 08/25/1993
• Issued: 08/27/1996
• Est. Priority Date: 08/25/1993
• Status: Expired due to Term

• Current Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Warrior, Jogesh, Brown, Gregory C., Lenz, Gary A.
• Primary Examiner(s): LEE, KEVIN L
• Application Number:
  US08/112,694
• Time in Patent Office: 1,098 Days
• Field of Search: 137/486, 137/487.5, 137/82, 137/85, 137/86, 137/488
• US Class Current: 137/486
• CPC Class Codes: F16K 31/1262 one side of the diaphragm being spring loaded
• CPC Class Codes: F16K 37/0083 by measuring valve parameters
• CPC Class Codes: G05D 7/005 characterised by the use of auxiliary non-electric power combined with the use of electric means
• CPC Class Codes: Y10T 137/2452 With counter-counter balancing pressure feedback
• CPC Class Codes: Y10T 137/7759 Responsive to change in rate of fluid flow
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve

Abstract

In this invention, a valve positioner receives a setpoint from a master and provides a control pressure to a valve actuator for controlling a valve. A sensing circuit in the positioner senses the position of the valve and the control pressure, and a control circuit in the positioner uses both the sensed pressure and position to provide a command output to a pneumatic section which produces the control pressure. In another embodiment of the invention, a positioner receives a setpoint from a master and provides a control pressure to a valve actuator for controlling a valve. A sensing circuit in the positioner senses the valve position and pneumatics in the positioner provide the control pressure as a function of the sensed position and an output from a control circuit within the positioner. The positioner includes a diagnostic circuit which stores a valve attribute and provides a diagnostic output as a function of the stored valve characteristic and a selected one of the sensed variables. In another embodiment of the invention, a positioner includes a correction circuit for storing a valve attribute affected by one of a set of physical parameters and for receiving a selected one of the set of sensed physical parameters. The correction means compensates a command output from a control circuit as a function of the sensed physical parameter and the stored valve characteristic. In another embodiment, the positioner includes a benchset control circuit which ramps the control pressure between an initial control pressure and a final control pressure and back to the initial control pressure, while sampling specific control pressures and their corresponding positions, in order to provide an output indicating the proper spring preload force on an actuator spring.

Claims

1. A valve positioner for use in a process control system for providing a control pressure to a valve actuator mechanically coupled to a valve, comprising:

receiving means coupled to a communications loop for receiving an input representative of a desired valve position;

sensing means for providing state variables representative of a process, one state variable representative of the position of the valve and the other representative of the control pressure;

transducer means receiving a source of pressurized air and a command output, for providing the control pressure as a function of the command output;

control means coupled to the sensing means and the receiving means, for providing the command output as a function of the desired valve position, the sensed position and the time derivative of the sensed pressure; and

wherein the time derivative of sensed pressure provides reduced overshoot in the valve position.

2. The positioner of claim 1 where the input to the receiving means is a 4-20 mA current having a magnitude representative of the desired valve position.

3. The positioner of claim 1 where the input to the receiving means is formatted according to a digital communications protocol.

4. The positioner of claim 1 where the control means is implemented in a CMOS microprocessor.

5. The positioner of claim 1 where the control means uses an adaptive control algorithm having at least one PID constant which changes as a function of the sensed state variables.

6. The positioner of claim 1 where the state variable representative of the valve position is temperature compensated.

7. The positioner of claim 6 where the sensing means further comprise a sensor for detecting force.

8. The positioner of claim 1 further comprising diagnostic means coupled to the sensing means, for storing a attribute of the valve and providing a diagnostic output as a function of the stored valve attribute and at least one of the state variables.

9. A valve positioner for use in a process control system for providing a control pressure to a valve actuator mechanically coupled to a valve, comprising:

receiving means coupled to a communications loop for receiving an input representative of a desired valve position;

sensing means for providing state variables representative of a process, one state variable representative of the position of the valve and the other representative of a force required to move the valve;

transducer means receiving a source of pressurized air and a command output, for providing the control pressure as a function of the command output;

control means coupled to the sensing means and the receiving means, for providing the command output as a function of the desired valve position, the time derivative of the sensed force and the sensed position; and

wherein the time derivative of the sensed force and sensed position provide reduced overshoot in the valve position.