Field device with capability of calculating digital filter coefficients

• US 20090055457A1
• Filed: 08/23/2007
• Published: 02/26/2009
• Est. Priority Date: 08/23/2007
• Status: Active Grant

• Current Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Original Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Inventors: Miller, John P.
• Granted Patent: US 8,301,676 B2
• Time in Patent Office: Days
• US Class Current: 708/300
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 19/0426 Programming the control sequence
• CPC Class Codes: G05B 2219/25014 Fieldbus general name of bus connected to machines, detectors, actuators
• CPC Class Codes: G05B 2219/25243 Digital filter

Abstract

A digital filter design algorithm is implemented directly within a process control field device or other process related equipment. Filter design parameters are exposed so that filter design parameter values may be provided to the digital filter design algorithm so that the digital filter design algorithm may calculate digital filter coefficients for a digital filter having desired frequency response characteristics. The digital filter design parameter values may be provided by a user, or may be provided as process variable data output from a process control field device or other process related equipment. Once the coefficients of the digital filter having the desired frequency response characteristics have been calculated, the digital filter may be applied to process variable data received by the process control field device or other process related equipment.

Claims

1. A system for implementing a digital filter for filtering process variable data, the system comprising:

an intelligent device adapted to receive process variable data, implement a digital filter design algorithm, and apply a digital filter to the received process variable data; and

an interface adapted to expose digital filter design parameters such that digital filter design parameter values may be provided to the digital filter design algorithm to design a digital filter having desired frequency response characteristics to be applied to the received process variable data.

2. The system for implementing a digital filter of claim 1 wherein the digital filter design algorithm comprises an equiripple filter design algorithm.

3. The system for implementing a digital filter of claim 1 wherein the digital filter design algorithm comprises a Remez Exchange filter design algorithm.

4. The system for implementing a digital filter of claim 1 wherein the digital filter design algorithm comprises a Parks-McClellan filter design algorithm.

5. The system for implementing a digital filter of claim 1 wherein the exposed digital filter design parameters comprise a filter type.

6. The system for implementing a digital filter of claim 5 wherein the filter type comprises one of a highpass or a lowpass filter.

7. The system for implementing a digital filter of claim 6 wherein the exposed filter parameters further comprise a cut-off frequency.

8. The system for implementing a digital filter of claim 5 wherein the filter type comprises a bandpass filter.

9. The system for implementing a digital filter of claim 8 wherein the exposed digital filter design parameters further comprise a passband center frequency and a passband width.

10. The system for implementing a digital filter of claim 8 wherein the exposed digital filter design parameters further comprise a low frequency cut-off frequency and a high-frequency cut off frequency.

11. The system for implementing a digital filter of claim 5 wherein the filter type comprises an infinite impulse response filter.

12. The system for implementing a digital filter of claim 5 wherein the filter type comprises a finite impulse response filter.

13. The system for implementing a digital filter of claim 1, further comprising a communication channel between the intelligent device and the interface.

14. The system for implementing a digital filter of claim 13 wherein the communication channel comprises a communication bus connecting the intelligent device to a computer workstation, the computer or workstation executing an interface application adapted to display the digital filter design parameters on a display device, receive digital filter design parameter values from a user, and forward the received digital filter design parameter values to the intelligent device.

15. The system for implementing the digital filter of claim 13 wherein the communication channel comprises a temporary connection between the intelligent device and a hand held configuration tool.

16. The system for implementing a digital filter of claim 1 wherein the interface comprises a process control variable input, such that at least one frequency response characteristic of the digital filter is determined by a value of the process control variable.

17. The system for implementing a digital filter of claim 1 wherein the intelligent device comprises a process control field device.

18. A process control device comprising:

a processor;

a memory storing a digital filter design algorithm;

a first input adapted to receive digital filter design parameter values for specifying desired frequency response characteristics of a digital filter; and

a second input for receiving process variable data;

the processor adapted to execute the digital filter design algorithm to create a digital filter having the desired frequency response characteristics, and apply the digital filter to the process variable data.

19. The process control device of claim 18 wherein the digital filter design algorithm comprises an equipple filter design algorithm.

20. The process control device of claim 18 wherein the digital filter design algorithm comprises a Remez Exchange filter design algorithm.

21. The process control device of claim 18 wherein the digital filter design algorithm comprises a Parks-McClellan filter design algorithm.

22. The process control device of claim 18 wherein the digital filter design parameters comprise a filter type.

23. The process control device of claim 22 wherein the filter type comprises one of a low pass filter or a high pass filter.

24. The process control device of claim 23 wherein the filter design parameters further comprise a cut-off frequency.

25. The process control device of claim 23 wherein the filter design parameters further comprise a transition width.

26. The process control device of claim 22 wherein the filter type comprises a bandpass filter.

27. The process control device of claim 26 wherein the filter design parameters further comprise a passband center frequency and a passband width.

28. The process control device of claim 26 wherein the filter design parameters further comprise a low frequency cut off frequency and a high frequency cut off frequency.

29. The process control device of claim 26 wherein the filter design parameters further comprise a transition width.

30. The process control device of claim 18 wherein the first input comprises a communication bus implementing a communication protocol for communicating data between the intelligent process control device and a configuration tool.

31. The process control device of claim 18 wherein the first input comprises a temporary communication link between the intelligent process control device and a hand-held configuration tool.

32. The process control device of claim 18 wherein the first input comprises an operating parameter value associated with the process.

33. The process control device of claim 32 wherein the operating parameter value comprises a process variable value.

34. A method of filtering process variable data comprising:

implementing a digital filter design algorithm in a process related control device;

exposing one or more filter parameters to an interface whereby filter parameter values may be provided to the digital filter design algorithm;

providing filter parameter values to the digital filter design algorithm;

calculating digital filter coefficients using the digital filter design algorithm based on the provided filter parameter values; and

applying a digital filter having the calculated digital filter coefficient to the process variable data.

35. The method of claim 34 wherein implementing a digital filter design algorithm comprises implementing a digital filter design algorithm adapted to generate filter coefficients of an infinite impulse response filter.

36. The method of claim 34 wherein implementing a digital filter design algorithm comprises implementing a digital filter design algorithm adapted to generate filter coefficients of a finite impulse response filter.

37. The method of claim 34 wherein implementing a digital filter design algorithm comprises implementing an equiripple filter design algorithm.

38. The method of claim 34 wherein implementing a digital filter design algorithm comprises implementing a Remez Exchange filter design algorithm.

39. The method of claim 34 wherein implementing a digital filter design algorithm comprises implementing a Parks-McClellan filter design algorithm.

40. The method of claim 34 wherein implementing a digital filter design algorithm comprises configuring the digital filter design algorithm in an abnormal situation prevention block associated with a process control device.

41. The method of claim 34 wherein exposing filter parameters comprises exposing a selectable filter type.

42. The method of claim 41 wherein the selectable filter type comprises one of a highpass filter and a lowpass filter.

43. The method of claim 42 wherein exposing filter parameters further comprises exposing a cut-off frequency parameter and a transition width parameter.

44. The method of claim 41 wherein the selectable filter type comprises a bandpass filter.

45. The method of claim 44 wherein exposing filter parameters further comprises exposing a passband center frequency parameter and a passband width parameter.

46. The method of claim 44 wherein exposing filter parameters further comprises exposing a low frequency cut off frequency parameter and a high frequency cut off frequency parameter.

47. The method of claim 44 wherein exposing filter parameters further comprise exposing a transition width parameter.

48. The method of claim 34 wherein exposing filter parameters comprises communicating filter parameters to a configuration tool.

49. The method of claim 48 wherein the configuration tool comprises a software application executed by a computer, and exposing the filter parameters comprises communicating the filter parameters to the computer over a network or bus.

50. The method of claim 48 wherein the communication tool comprises a handheld communicator, and exposing the filter parameters comprises communicating the filter parameters to the handheld communicator over a temporary communication link.

51. The method of claim 48 wherein providing parameter values to the digital filter design algorithm comprises communicating user entered parameter values to the digital filter design algorithm from the configuration tool.

52. The method of claim 34 wherein providing filter parameter values to the digital filter design algorithm comprises providing a process variable value to a process control function block implementing the digital filter design algorithm.