Nonintrusive acoustic liquid level sensor

• US 4,901,245 A
• Filed: 12/01/1987
• Issued: 02/13/1990
• Est. Priority Date: 12/01/1987
• Status: Expired due to Fees

• Current Assignee: Moore Technologies
• Original Assignee: Moore Technologies
• Inventors: Christensen, Edward L., Olson, Rodney S.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Cosimano, Edward R.
• Application Number:
  US07/127,265
• Time in Patent Office: 805 Days
• Field of Search: 73/149, 73/290 V, 73/861.26, 340/621, 364/509, 364/562, 367/908
• US Class Current: 702/54
• CPC Class Codes: G01F 23/296 Acoustic waves
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level

Abstract

A non-intrusive acoustic sensor system for detecting and displaying the location of the level of a liquid in a tank uses a piezoelectric transceiver mounted to a bottom exterior location on the tank. The transceiver is an element of a driving and signal processing circuit which also includes a readout device for displaying liquid level location in selected terms. The system circuitry includes a microprocessor programmed to enable the velocity of sound in a liquid in the tank to be determined by the system at the site of use from a single distance measurement descriptive of the usage situation. The system automatically selects and uses the transceiver acoustic emission frequency which is best for the tank and liquid combination of interest at any time. The system, in a dual-transceiver configuration described, determines and uses speed of sound in the liquid as it in fact exists at any time. The system also rejects echo signals which are determined to described locations in the tank other than the liquid surface. A plurality of liquid levels can be defined at which control or alarm events are to occur.

Claims

1. Apparatus for measuring in selected terms the level of a liquid in a tank and the like from a location outside the tank and at the bottom thereof, the apparatus comprising energy transmitting means mountable to the bottom of a tank adapted to contain a liquid for transmitting an emitted signal in a selected liquid-surface-reflectable form of energy essentially vertically through a bottom tank wall and through a liquid in the tank to the surface of the liquid in the tank, energy receiving means mountable to the bottom of the tank for receiving a reflection of transmitted energy from the liquid surface and for generating a reflection signal in response to receipt of a reflection, driving means for the transmitting means operable for driving the transmitting means to transmit an emitted signal, signal processing means for the receiving means for processing a reflection signal to create information descriptive in said selected terms of the location of the surface of the liquid in the tank, and tuning means responsive to operation of the signal processing means and operable for adjusting a selected property of the emitted signal to an optimum value for the liquid in the tank.

2. Apparatus according to claim 1 wherein the selected terms are the absolute distance of the liquid level above the tank bottom.

3. Apparatus according to claim 1 wherein the selected terms are the distance of the liquid level above the tank bottom as a percentage of a selected full condition of the tank.

4. Apparatus according to claim 1 wherein the transmitting means and the receiving means comprise transceiving means.

5. Apparatus according to claim 4 wherein the transceiving means comprises a housing having therein a cavity which is open to an end of the housing, the housing is mountable to a tank exterior surface with the cavity opening toward the surface, a piezoelectric crystal assembly disposed in the cavity for movement toward the cavity opening, and force means coupled between the housing and the assembly for forcibly biasing the assembly to an extended position in which the assembly projects beyond the cavity opening, whereby the force means causes the assembly to forcibly contact the tank surface upon mounting of the housing to the tank surface.

6. Apparatus according to claim 1 wherein the selected property of the emitted signal is frequency, and the tuning means is operable for altering the frequency of the emitted signal.

7. Apparatus according to claim 6 wherein the selected form of energy is acoustic energy.

8. Apparatus according to claim 7 wherein the transmitting means comprises a piezoelectric device.

9. Apparatus according to claim 8 wherein the driving means is operable to cause the transmitting means to transmit an emitted signal at any one of several different frequencies within a range of frequencies, the tuning means is coupled to the driving means, and the tuning means is operable for causing the driving means to drive the transmitting means to transmit plural emitted signals each having a different frequency, for evaluating the amplitude of the reflection signal related to each emitted signal, and for identifying the reflection signal having the greatest amplitude.

10. Apparatus according to claim 9 wherein the tuning means includes means operable from time to time for verifying that the frequency of the emitted signal is productive of a maximum amplitude reflection signal and for causing the driving means to change the emitted signal frequency as appropriate.

11. Apparatus according to claim 9 wherein the range of frequencies comprises a plurality of primary frequencies at substantially regular larger intervals through the range of frequencies and a plurality of secondary frequencies at substantially regular smaller intervals through the range, and the tuning means is operable for causing the transmitting means to transmit emitted signals at at least some of the primary frequencies and to identify therefrom a primary frequency productive of an apparent peak reflection signal amplitude, and for causing the transmitting means to transmit emitted signals at at least some of the secondary frequencies within a portion of the range associated with the identified primary frequency and to identify a frequency of emitted signal productive of a confirmed maximum reflection signal amplitude.

12. Apparatus according to claim 1 wherein the signal processing means includes discriminating means for creating liquid level descriptive information only from reflection signals associated with the liquid surface in the tank.

13. Apparatus according to claim 12 wherein the discriminating means includes means for determining the location of the liquid surface in the tank, for defining a selected distance range extending above and below said location, and for accepting for creation of said information only reflection signals originating within the distance range.

14. Apparatus according to claim 13 wherein the discriminating means includes means for averaging the information created from a selected number of successive reflection signals and for redetermining the location of the liquid surface based on the average.

15. Apparatus according to claim 14 wherein the discriminating means includes range adjusting means for detecting the presence or absence of an acceptable reflection signal for each emitted signal, for increasing the distance range in response to the detection of a selected number of absences until the next acceptable reflection signal is detected, and for using the information created in respect to said next acceptable reflection signal to redetermine the location of the liquid surface in the tank.

16. Apparatus according to claim 14 wherein the range adjusting means includes means responsive to detection of said selected number of presences of acceptable reflection signals for reducing the distance range toward a minimum distance range.

17. Apparatus according to claim 16 wherein the range adjusting means is operable for increasing and reducing the distance range in increments away from and toward the minimum distance range.

18. Apparatus according to claim 16 wherein the range adjusting means is operable for reducing the distance range in response to detection of the selected number of presences in succession.

19. Apparatus according to claim 18 wherein range adjusting means is operable for reducing the range in increments which vary in magnitude depending upon the extent of the range and the relation of the determined surface location to the range.

20. Apparatus according to claim 1 wherein the signal processing means includes memory means for storing data descriptive of a distance, and means for entering such data into the memory means.

21. Apparatus according to claim 20 wherein the means for entering the distance data includes manually operable means.

22. Apparatus according to claim 20 including transceiving means for transmitting and receiving said form of energy, the transceiving means is mountable to the exterior of a side wall of the tank for transmitting said form of energy along a selected path through the side wall and liquid in the tank to an opposite side wall, and for generating a separate reflection signal in response to receipt of a reflection of transmitted energy from the opposite side wall, and means for entering into the memory means data descriptive of the distance along the selected path between the tank side walls.

23. Apparatus according to claim 20 wherein the signal processing means includes means for describing the velocity of said form of energy through the tank and liquid therein over said distance by determining the time required for said form of energy to move said distance through the tank wall and said liquid, and by dividing said distance by said time.

24. Apparatus according to claim 23 wherein the distance is a known depth of liquid in the tank.

25. Apparatus according to claim 23 wherein the distance is the distance horizontally between opposite side wall locations on the tank, and including a second energy transmitting means mountable to an exterior side wall of the tank for transmitting an emitted signal in said energy form along a selected path through the wall and through liquid in the tank to the opposite side wall and a second energy receiving means mountable to the tank exterior essentially along said path for generating a signal in response to receipt of said energy form.

26. Apparatus according to claim 25 wherein the second transmitting and receiving means are mountable to the same side wall of the tank proximate each other for receipt by the second receiving means of a reflection from the opposite tank side wall of a signal emitted along the path by the second transmitting means.

27. Apparatus according to claim 26 wherein the second transmitting and receiving means comprise a transceiver.

28. A method for determining the location in a tank of the surface of a quantity of liquid in the tank from a position outside the tank, the method comprising the steps of

(a) directing a pulse of sound energy essentially vertically through a bottom wall of the tank and through liquid in the tank from a selected place on the bottom of the tank,

(b) receiving at substantially the same place on the tank bottom an echo of a sound energy pulse from the liquid surface and generating an echo signal in response thereto,

(c) determining from the echo signals associated with a series of sound pulses of differing frequency an optimum frequency of sound pulse for use with the liquid in the tank and thereafter performing directing step (a) with pulses of said optimum frequency,

(d) ascertaining the velocity of sound through liquid in the tank and through the tank wall,

(e) measuring the time between direction of a sound pulse into the tank and the liquid and receipt of an echo of the pulse from the liquid surface,

(f) computing the distance of the liquid surface above said place on the bottom of the tank, and

(g) developing a representation of the computed distance.

29. The method according to claim 28 wherein performance of the step (c) of claim 28 includes

(h) defining a range of frequencies at which sound can be directed through the tank and into liquid in the tank,

(i) defining a plurality of first frequencies at relatively large intervals over the range and a plurality of second frequencies at relatively small steps over each interval,

(j) for each first frequency generating an echo signal in response to direction of a sound pulse of that frequency and receipt of an echo thereof, and identifying at least one first frequency productive of an echo signal of greatest amplitude, and

(k) for each second frequency in the intervals adjacent said identified first frequency generating an echo signal, and identifying the frequency productive of the echo signal of highest amplitude as the optimum frequency.

30. The method according to claim 28 wherein performance of step (d) of claim 28 includes measuring the time required for a sound pulse to travel through a tank wall and through liquid in the tank over a known distance.

31. The method according to claim 30 wherein the known distance is known by manual measurement of the distance from said place to the liquid surface.

32. The method according to claim 30 wherein the known distance is a distance across the tank along a selected path between opposite sides of the tank.

33. The method according to claim 32 including periodically reascertaining the velocity of sound through the tank wall and through liquid in the tank.

34. The method according to claim 28 including, in practice of the measuring step, eliminating from consideration for generation of an echo signal echoes of sound energy pulses from locations in the tank other than the liquid surface.

35. The method according to claim 34 wherein the elimination process includes determining the location in the tank of the liquid surface, establishing a distance range spanning the liquid surface location from within which sound echoes are acceptable as emanating from the liquid surface and from outside which sound echoes are not so acceptable, and testing each sound echo received for emanation from a source within the established range.

36. The method according to claim 35 including determining the location in the tank of the liquid surface from an average of a selected number of said computed distances.

37. The method according to claim 35 including increasing the distance range in the event a selected number of consecutive sound pulses do not produce a sound echo emanating from within a previously established range.

38. The method according to claim 37 including further increasing the distance range for each additional consecutive sound pulse not productive of a sound echo from within the last previously established range until a sound echo is received from within the increased range or until the range is at a maximum value.

39. The method according to claim 35 including defining a minimum value of the distance range and, in the event the established range is greater than the minimum value thereof, reducing the range by a selected amount upon receipt of a sound echo from a source within the established range.

40. The method according to claim 39 including defining the amount of range reduction dependent upon the amount by which the range distance exceeds the minimum value thereof.

41. A method for determining the location in a tank of the surface of a quantity of liquid in the tank, the method comprising the steps of

(a) directing pulses of sound energy form a source thereof in an essentially vertical direction toward a liquid surface in the tank and detecting substantially at said source echoes of the pulses from the liquid surface,

(b) for each pulse, measuring the time between direction of the pulse and the detection of the echo thereof,

(c) providing information about the speed at which sound travels from the sound pulse source to the liquid surface,

(d) using said information and the time measurements to determine the distance from the sound pulse source to the liquid surface, thereby to determine the location of the liquid surface, and

(e) for subsequent sound pulses, disregarding for determination of source-to-surface distance any sound pulse echo which does not have an origin within a defined range of distances above and below the liquid surface.

42. The method according to claim 41 including redefining the range distance upwardly or downwardly dependent upon a given sound pulse echo having an origin respectively outside or inside the last defined range.

43. The method according to claim 42 including redefining the range distance upwardly to a greater distance toward a maximum thereof upon the occurrence of a predetermined number of consecutive sound pulses not having associated with them echos with origins within the last defined range.

44. The method according to claim 42 including redefining the range distance downwardly to a lesser distance toward a minimum thereof upon the occurrence of a predetermined number of consecutive sound pulses having associated with them echos with origins within the last defined range.