Noninvasive valve monitor using alternating electromagnetic field

• US 5,193,568 A
• Filed: 06/20/1991
• Issued: 03/16/1993
• Est. Priority Date: 06/20/1991
• Status: Expired due to Term

• Current Assignee: Martin Marietta Energy Systems, Inc.
• Original Assignee: Martin Marietta Energy Systems, Inc.
• Inventors: Eissenberg, David M., Haynes, Howard D., Casada, Donald A.
• Primary Examiner(s): CHAMBERS, A MICHAEL
• Application Number:
  US07/718,453
• Time in Patent Office: 635 Days
• Field of Search: 137/554, 137/1, 324/207.2, 340/686
• US Class Current: 137/1
• CPC Class Codes: F16K 37/0041 for measuring valve parameters F16K37/0033 takes precedence
• CPC Class Codes: Y10T 137/0318 Processes
• CPC Class Codes: Y10T 137/8242 Electrical

Abstract

One or more electrical coils are carefully located on the outside of a valve body. An alternating current passing through the coil(s) results in an alternating electromagnetic field being transmitted into the valve body and valve internals. The electromagnetic field varies in intensity and polarity in the valve. As the position of a valve internal part is changed, the electromagnetic field throughout the valve body and its internals is altered. A passive receiver coil carefully located on the outside of the valve body detects the intensity of the electromagnetic field at that location as an induced electrical voltage in the coil. With the change in position of the valve internal part, there is a corresponding change in the induced voltage as a result of the alteration in the alternating electromagnetic field at that location. Changes in the voltage provide an indication of the position and motion of valve internals.

Claims

1. A method for monitoring a valve having an obturator mounted within a valve housing and being movable therein between open and closed positions, the method comprising:

positioning at least one transmitter coil exterior of said valve housing;

providing an alternating current at a selected frequency to said transmitter coil so tat said transmitter coil produces an alternating electromagnetic field which penetrates into said valve housing; and

positioning at least one passive receiver coil exterior of said valve housing such that said receiver coil is within the influence of said alternating electromagnetic field, said alternating electromagnetic field inducing an electrical voltage in said receiver coil which varies in accordance with variations in the position of the obturator.

2. A monitor for a valve having an obturator mounted within a valve housing and being movable therein between open and closed positions, the monitor comprising:

at least one transmitter coil situated external to said valve housing;

a signal generator providing an alternating current at a selected frequency to said transmitter coil so that said transmitter coil produces an alternating electromagnetic field, said alternating electromagnetic field extending into said valve housing, and said obturator being movable through said electromagnetic field; and

at least one passive receiver coil disposed external to said valve housing, situated such that said receiver coil is within the influence of said alternating electromagnetic field, said receiver coil producing an alternating voltage signal which varies in accordance with variations in the position of the obturator.

3. The monitor of claim 2 further including means coupled to said passive receiver coil for detecting said alternating voltage signal.

4. The monitor of claim 3 wherein said means for detecting said alternating voltage signal is an ac voltmeter.

5. The monitor of claim 3 wherein said selected frequency involves at least two frequencies.

6. The monitor of claim 5 wherein said means for detecting said alternating voltage signal involves separate means for detecting said two frequencies.

7. The monitor of claim 5 wherein said at least one receiver coil comprises separate receiver coils for each of said two frequencies, and wherein said means for detecting said alternating voltage signal involves separate means for detecting said frequencies from said separate receiver coils.

8. The monitor of claim 5 wherein said at least one transmitter coil comprises separate transmitter coils for producing said alternating electromagnetic field from said two frequency signals.

9. The monitor of claim 2 further including a power amplifier connecting said signal generator to said transmitter coil.

10. The monitor of claim 9 further including a receiver coil tuning circuit connected to said receiver coil.

11. The monitor of claim 10 wherein said receiver coil tuning circuit includes a capacitor connected in parallel with said receiver coil.

12. The monitor of claim 10 wherein said receiver coil tuning circuit includes a frequency band-pass filter connected to said receiver coil.

13. The monitor of claim 10 wherein said receiver coil tuning circuit includes a frequency band-pass filter and a parallel-connected capacitor.

14. The monitor of claim 9 further including a transmitter coil tuning circuit connecting said power amplifier to said transmitter coil.

15. The monitor of claim 14 wherein said transmitter coil tuning circuit includes a capacitor connecting said power amplifier to said transmitter coil.

16. The monitor of claim 9 further including a gain amplifier connected to said receiver coil for amplifying said alternating voltage signal.

17. The monitor of claim 16 further including a means connected to said gain amplifier for converting said amplified alternating voltage signal to a dc signal.

18. The monitor of claim 17 wherein said converting means is an rms-to-dc converter.

19. The monitor of claim 7 further including a dc voltage offsetting source connected to said converting means for bringing said dc signal to zero volts.

20. The monitor of claim 19 further including a second gain amplifier connected to said dc voltage source for boosting said dc signal to the volts range during valve monitoring.

21. The monitor of claim 20 further including a low pass filter connected to said second gain amplifier for eliminating unwanted electronic noise on said dc signal.

22. The monitor of claim 2 wherein at least one of said transmitter coil and said receiver coil is an insulated wire wrapped around said valve housing.

23. The monitor of claim 2 wherein at least one of said transmitter coil and said receiver coil is a plurality of wire segments wrapped at least once around said valve housing, and connected at their ends such that all of said wire segments become connected together in series when said connection is made.

24. The monitor of claim 2 wherein at least one of said transmitter coil and said receiver coil is a pancake coil.

25. The monitor of claim 2 wherein at least one of said transmitter coil and said receiver coil is an air core solenoid.

26. The monitor of claim 25 further including a plurality of ferromagnetic inserts within said core.

27. The monitor of claim 26 wherein said inserts are ferromagnetic rods.

28. The monitor of claim 27 wherein said ferromagnetic rods extend axially substantially beyond the coil portion of said solenoid.

29. The monitor of claim 2 wherein at least one of said transmitter coil and said receiver coil is a ferromagnetic core solenoid.

30. The monitor of claim 29 wherein said ferromagnetic core extends axially substantially beyond the coil portion of said solenoid.

31. The monitor of claim 2 wherein at least one of said transmitter coil and said receiver coil is an insulated wire wrapped around a bolt.

32. The monitor of claim 2 wherein at least one of said transmitter coil and said receiver coil is a ferrite core solenoid.

33. The monitor of claim 2 wherein said selected frequency is a sine wave or square wave of fixed discrete frequency.

34. The monitor of claim 2 wherein said selected frequency is a broadband noise signal.

35. The monitor of claim 2 wherein said at least one transmitter coil comprises two transmitter coils, and said signal generator provides voltage signals of the same frequency but opposite ac phase generation to said two transmitter coils.

36. The monitor of claim 35 wherein one of said ac phase generation signals is stronger than the other.