Non-Periodic Control Communications in Wireless and Other Process Control Systems

• US 20090299495A1
• Filed: 08/07/2009
• Published: 12/03/2009
• Est. Priority Date: 10/25/2005
• Status: Active Grant

• Current Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Original Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Inventors: Blevins, Terrence L., McMillan, Gregory K., Nixon, Mark J., Chen, Deji
• Granted Patent: US 7,945,339 B2
• Time in Patent Office: Days
• US Class Current: 700/28
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 2219/31121 Fielddevice, field controller, interface connected to fieldbus
• CPC Class Codes: G05B 2219/33192 Radio link, wireless
• CPC Class Codes: G05B 2219/34306 Power down, energy saving
• CPC Class Codes: Y02P 70/10 Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Abstract

Disclosed is a controller having a processor and a control module adapted for periodic execution by the processor and configured to be responsive to a process variable to generate a control signal for a process. An iteration of the periodic execution of the control module involves implementation of a routine configured to generate a representation of a process response to the control signal. The routine is further configured to maintain the representation over multiple iterations of the periodic execution of the control module and until an update of the process variable is available. In some cases, the update of the process variable is made available via wireless transmission of the process signal. In those and other cases, the controller may be included within a process control system having a field device to transmit the process signal indicative of the process variable non-periodically based on whether the process variable has changed by more than a predetermined threshold. In some embodiments, the field device also transmits the process signal if a refresh time has been exceeded since a last transmission.

Claims

1. A process control system for a process having a process variable, comprising:

a field device to transmit a process signal indicative of the process variable of the process; and

,

a controller in communication with the field device to receive an update of the process variable via the process signal and generate a control signal for the process, the controller having a processor and a control module adapted for periodic execution by the processor;

wherein the field device wirelessly transmits the process signal non-periodically based on whether the process variable has changed by more than a predetermined threshold.

2. The process control system of claim 1, wherein the field device transmits the process signal if a refresh time has been exceeded since a last transmission.

3. The process control system of claim 1, wherein the periodic execution of the control module implements a routine configured to generate a representation of a process response to the control signal.

4. The process control system of claim 3, wherein the routine is further configured to maintain the process response representation over multiple iterations of the periodic execution of the control module and until the field device transmits the process signal.

5. The process control system of claim 4, wherein the control module comprises a closed-loop control scheme that utilizes the process response representation to determine the control signal.

6. The process control system of claim 4 wherein the routine comprises a positive feedback network to determine the process response representation based on past values of the control signal.

7. The process control system of claim 4, wherein the routine implements a filter algorithm to determine the process response representation.

8. The process control system of claim 4, wherein the routine is further configured for implementation based on non-periodic updates of the process variable.

9. The process control system of claim 4, wherein the process response representation comprises a process variable response representation, and wherein the routine is further configured to update the process variable response representation once the update of the process variable is available.

10. The process control system of claim 9, wherein the routine determines the expected response of the process based on a last update of the process variable, the control signal, and an elapsed time since the last update of the process variable.

11. A method of controlling a process having a process variable, the method comprising the steps of:

receiving wirelessly a process signal to obtain an update of the process variable; and

,

implementing periodically a process control routine to generate a control signal for the process based on the process signal;

wherein the receiving step occurs non-periodically such that the process control routine is configured to utilize non-periodic updates of the process variable received due to the process variable changing by more than a predetermined threshold or due to a time elapsed since a prior update of the process variable.

12. The method of claim 11, wherein the implementing step comprises the steps of executing a routine configured to generate a representation of a process response to the control signal, and maintaining the process response representation over multiple iterations of the implementing step and until the update of the process variable is available.

13. The method of claim 12, wherein the process control routine comprises a closed-loop control scheme that utilizes the process response representation to determine the control signal.

14. The method of claim 13, wherein the process response representation comprises a process variable response representation, and wherein the implementing step further comprises the step of updating the process variable response representation once the update of the process variable is available.

15. The method of claim 14, wherein the implementing step further comprises the step of determining the expected response of the process based on a last update of the process variable, the control signal, and an elapsed time since the last update of the process variable.

16. The method of claim 15, wherein the implementing step further comprises the step of determining an updated reset contribution based on the expected response of the process to the last update and the elapsed time since the last update.