Method and apparatus for ultrasonic material level measurement

• US 4,000,650 A
• Filed: 03/20/1975
• Issued: 01/04/1977
• Est. Priority Date: 03/20/1975
• Status: Expired due to Term

• Current Assignee: Endress+Hauser GmbH+Co (ENDRESS)
• Original Assignee: Bindicator Company
• Inventors: Snyder, Ellery P.
• Primary Examiner(s): Swisher, S. Clement
• Application Number:
  US05/560,244
• Time in Patent Office: 656 Days
• Field of Search: 73/290 V, 73/67.7, 73/67.8, 340/1 L, 340/15.5 DP, 343/5 DP, 343/12 R
• US Class Current: 73/290.00V
• CPC Class Codes: G01F 23/2962 Measuring transit time of reflected waves
• CPC Class Codes: Y10S 367/90 Sonar time varied gain control systems
• CPC Class Codes: Y10S 367/901 Noise or unwanted signal reduction in nonseismic receiving system
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level

Abstract

Ultrasonic pulses are transmitted from the top of a tank or bin by a transducer and reflected by the material contained therein and received by the same transducer. In the short range mode, two millisecond pulses at sixty second intervals provide a measurment of from two to twenty one feet. Failure to detect a reflected pulse in the short range mode automatically switches the device to the long range mode utilizing ten millisecond pulses at three hundred millisecond intervals. After a pulse is transmitted the energy received by the receiver is converted to a digital value each millisecond and compared to the highest previously converted digital value so that the time of the largest received reflection signal and consequently the distance to the material surface may be determined. The echo signals from eight successive long range pulses are digitized and then integrated according to apparent object distance so that the sum of the true echo signals returned from the material surface is substantially greater than the sum of random noise signals for each transmitted pulse. After each eight-pulse long-range sequence, apparatus electronics automatically return to the short-range measurement mode to start a subsequent measurement sequence.

Claims

1. In a control system for use in monitoring the level of material in a storage tank, the combination comprising,

transducer means directing ultrasonic pulses toward and receiving echo response pulses reflected from the upper surface of said material,

means operatively connected to said transducer means to sample said echo response pulses at preselected intervals which are a function of distance,

means converting each of said sampled response pulses to digital signals having a numerical value indicative of the intensity of each said echo pulse relative to one another,

means integrating said sampled and digitizesd response pulses from successively transmitted pulses over a preselected pulse sequence according to apparent distance of said transducer means from said material surface,

means storing said integrated response pulses serially according to apparent distance, and

means monitoring said integrated pulses to provide an indication of actual distance, which is a function of material level, upon completion of said pulse sequence.

2. The combination set forth in claim 1 wherein said transducer means is mounted to the top of said tank and is disposed to direct said ultrasonic pulses downwardly toward and to receive said response pulses reflected upwardly from said surface.

3. The combination set forth in claim 1 wherein said integrated pulse monitoring means comprises,

first digital storage register means for storing digital data,

means operatively connected to said integrating means comparing an integrated pulse in said integrating means with digital data stored in said first storage register means,

means responsive to said comparing means for storing said integrated pulse in said first storage register means when said integrated pulse is greater than said stored data,

second storage register means for storing digital data, and

means responsive to said comparing means to store an apparent material surface distance associated with said integrated pulse stored in said second storage register means when said integrated pulse is greater than said stored data.

4. The combination set forth in claim 3 further comprising display means operatively connected to said second storage register means for providing a display of said actual distance upon completion of said pulse sequence.

5. The combination set forth in claim 4 wherein said display means comprises digital display means.

6. The combination set forth in claim 4 wherein said display means comprises a galvanometer and digital-to-analog signal converting means operatively connecting said second storage register means with said galvanometer.

7. The combination set forth in claim 3 wherein said pulse sequence comprises one pulse.

8. The combination set forth in claim 1 wherein said pulse sequence comprises eight pulses.

9. The combination set forth in claim 1 wherein said preselected sampling intervals are regulated as a function of temperature within said tank.

10. The combination set forth in claim 9 wherein each of said intervals corresponds to one-half foot of apparent distance between said transducer means and said material level.

11. The combination set forth in claim 1 wherein said sampling means samples said response pulses in a range of apparent distance from 14 to 158 feet.

12. In the method of monitoring the level of material in a storage tank on the basis of the roundtrip transit time of an ultrasonic pulse between a transudcer and the upper surface of said material, the improvement comprising the steps of:

transmitting a sequence of ultrasonic pulses toward an upper surface of said material,

receiving echo response pulses reflected from said surface,

converting each of said echo response pulses to a digital number having a value indicative of the intensity of each of said pulses relative to one another,

integrating said response pulses from successively transmitted pulses of said sequence according to apparent distance to said surface,

selecting an integrated response pulse having highest digital value after termination of said pulse sequence, and

identifying the apparent material surface distance which is associated with said highest-value integrated pulse and treating said apparent distance as actual material surface distance.

13. The method set forth in claim 12 wherein said sequence of ultrasonic pulses comprises eight pulses.

14. In a control system for use in monitoring the level of material in a storage tank the combination comprising,

transducer means mounted to the top of said tank transmitting ultrasonic pulses downwardly toward and receiving echo response pulses reflected upwardly from the upper surface of said material, and

means responsive to elapsed time between a first of said transmitted pulses and a corresponding response pulse for regulating the pulse width of a second transmitted pulse subsequent to said first transmitted pulse as a function of said elapased time.

15. In a control system for use in monitoring the level of material in a storage tank the combination comprising,

transducer means transmitting ultrasonic pulses toward and receiving echo response pulses reflected from the upper surface of said material, and

means responsive to elapsed time between a first of said transmitted pulses and a corresponding response pulse for regulating the pulse width and the pulse repetition period of a second transmitted pulse subsequent to said first transmitted pulse as a function of said elapsed time.

16. The combination set forth in claim 15 wherein said transducer means is mounted to the top of said tank and is disposed to direct said ultrasonic pulses downwardly toward and to receive said response pulses reflected upwardly from said surface.

17. The combination set forth in claim 15 wherein said subsequent pulse regulating means comprises,

means monitoring said response pulses to provide a first control signal when elapsed time between said first transmitted pulse and said corresponding received pulse indicates an apparent distance from said transducer means to said material surface within a preselected range interval,

means monitoring said response pulses to provide a second control signal when said apparent distance is outside of said preselected range interval, and

means responsive to said first and second control signals for regulating said pulse width and said pulse repetition period of said second transmitted pulse.

18. The combination set forth in claim 17 wherein said first and second signal responsive means comprises,

means operatively connected to said transducer means and responsive to said first control signal to produce a second transmitted pulse having a pulse width and pulse repetition period identical to that of said first transmitted pulse, and

means operatively connected to said transducer means and responsive to said second control signal to provide a second transmitted pulse having a second pulse width and a second pulse repetition period directly proportional to said apparent distance.

19. The combination set forth in claim 18 wherein said preselected range interval is a short-range interval and wherein said second control signal responsive means is responsive to said apparent distance being beyond said short-range interval to provide a second transmitted pulse having a greater pulse width and a greater pulse repetition period than said first transmitted pulse.

20. The combination set forth in claim 19 wherein said short-range interval is between 2 to 21 feet.

21. The combination set forth in claim 18 wherein said first pulse width is substantially equal to two milliseconds and said first pulse repetition period is substantially equal to 60 milliseconds, and wherein said second pulse width is substantially equal to 10 milliseconds and said second pulse repetition period is substantially equal to 300 milliseconds.

22. In a method of monitoring the level of material in a storage tank as a function of the round-trip transit time of an ultrasonic pulse between a transducer and the upper surface of said material, the improvement comprising the steps of:

a. transmitting a first ultrasonic pulse having a first pulse width and a first pulse repetition period vertically toward said upper surface of said material,

b. monitoring for an echo pulse in response to said first transmitted pulse for a preselected time after said transmitted pulse which corresponds to a preselected distance range to said surface,

c. retransmitting said first ultrasonic pulse in response to an echo pulse within said preselected time,

d. transmitting a second ultrasonic pulse having a second pulse width different from said first pulse width and a second pulse repetition period different from said first pulse repetition period vertically toward said surface in response to an absence of said echo pulse within said preselected time, and

e. monitoring for an echo pulse in response to said second transmitted pulse.

23. The method set forth in claim 22 further comprising the step of retransmitting said first pulse in accordance with said step (a) after transmitting a preselected number of said second pulses in accordance with said step (d).

24. The method set forth in claim 23 wherein said preselected number of said second ultrasonic pulses is eight.

25. The method set forth in claim 22 wherein said second pulse width is greater than said first pulse width.

26. The method set forth in claim 25 wherein said second pulse repetition period is greater than said first pulse repetition period.

27. The method set forth in claim 26 wherein said first pulse width is substantially equal to 2 milliseconds, said first pulse repetition period is substantially equal to 60 milliseconds, said second pulse width is substantially equal to ten milliseconds and said second pulse repetition period is substantially equal to 300 milliseconds.

28. A control system for use in monitoring the level of material in a storage tank comprising,

transducer means mounted at the top of said tank directing ultrasonic pulses downwardly through air toward and receiving echo response pulses reflected upwardly through air from an upper surface of said material,

means operatively connected to said transducer means to sample said echo response pulses at preselected intervals corresponding to apparent distance from said transducer means to said material surface,

means converting said sampled response pulses to digital signals each having a numerical value indicative of the intensity of a corresponding response pulse relative to the other sampled response pulses,

means operatively connected to said transducer means transmitting a first ultrasonic pulse having a first pulse width and a first pulse repetition period downwardly toward said material surface,

means operatively connected to said converting means comparing digitized echo response pulses from said first transmitted pulse to a preselected response threshold within a preselected time interval after said transmitted pulse, said time interval corresponding to a preselected distance range from said transducer means to said surface,

means operatively connected to said comparing means and to said first pulse transmitting means retransmitting said first pulse in response to a digitized echo pulse from said first transmitted pulse above said threshold and within said interval,

means operatively connected to said transducer means and to said comparing means transmitting a second ultrasonic pulse having a second pulse width and a second pulse repetition period in response to an absence of a digitized response pulse from said first transmitted pulse above said threshold and within said interval,

means operatively connected to said converting means integrating digitized response pulses from said second transmitted pulse over a predetermined pulse sequence of second transmitted pulses according to apparent distance of said transducer means from said surface,

means operatively connected to said comparing means to provide an indication of actual distance to said surface in response to a digitized echo response pulse from said first transmitted pulse within said interval, and

means operatively connected to said integrating means to provide an indication of actual distance to said surface upon completion of said pulse sequence.

29. Apparatus for measuring distance to an object on the basis of round-trip transit time of a transmitted pulse to said object and back comprising, in combination,

transducer means directing pulses toward and receiving echo response pulses reflected from said object,

means operatively connected to said transducer to sample said echo response pulses at preselected intervals which are a function of distance from said transducer means to said object,

means converting said sampled response pulses to digital signals each having a numerical value indicative of the intensity of a corresponding response pulse relative to the other sampled response pulses, and

echo peak detector means monitoring said digitized pulses to provide an indication of actual distance, said echo peak detector means comprising first digital storage register means for storing digital data, means operatively connected to said digitizing means comparing a digitized pulse in said digitizing means with digital data stored in said first storage register means, means responsive to said comparing means for storing said digitized pulse in said first storage register means when said digitized pulse is greater than said stored data, second storage register means for storing digital data, and means responsive to said comparing means to store an apparent distance associated with said digitized pulse stored in said second storage register means when said digitized pulse is greater than said stored data.

30. The combination set forth in claim 29 further comprising means integrating said sampled and digitized response pulses from successively transmitted pulses over a preselected pulse sequence according to apparent distance of said transducer means from said object, and means storing said integrated pulses serially according to apparent distance, said echo peak detector means monitoring digitized pulses at the output of said integrating means to provide said indication of actual distance upon completion of said pulse sequence.

31. The combination set forth in claim 30 further comprising display means operatively connected to said second storage register means for providing a display of said actual distance upon completion of said pulse sequence.

32. The combination set forth in claim 30 wherein said pulse sequence comprises eight pulses.

33. In an apparatus for measuring distance to an object on the basis of round-trip transit time of a transmitted pulse to and from said object, the combination comprising,

transducer means transmitting pulses toward and receiving echo response pulses reflected from said object, and

means responsive to elapsed time between a first of said transmitted pulses and a corresponding response pulse for regulating the pulse width of a second transmitted pulse subsequent to said first transmitted pulse as a function of said elapsed time, said subsequent pulse regulation means comprising means monitoring said response pulses to provide a first control signal when elapsed time between said first transmitted pulse and said corresponding received pulse indicates an apparent distance from said transducer means to said object within a preselected range interval, means monitoring said response pulses to provide a second control signal when said apparent distance is outside of said preselected range interval and means responsive to said first and second control signals for regulating said pulse width of said second transmitted pulse.

34. The combination set forth in claim 33 wherein said first and second signal responsive means also regulates the pulse repetition period of said second transmitted pulse, and wherein said first and second signal responsive means comprises means operatively connected to said transducer means and responsive to said first control signal to produce a second transmitted pulse having a pulse width and pulse repetition period identical to that of said first transmitted pulse and means operatively connected to said transducer means and responsive to said second control signal to provide a second transmitted pulse having a second pulse width and a second pulse repetition period directly proportional to said apparent distance.

35. The combination set forth in claim 34 wherein said preselected range interval is a short-range interval and wherein said second control signal responsive means is responsive to said apparent distance being beyond said short-range interval to provide a second transmitted pulse having a greater pulse width and a greater pulse repetition period than said first transmitted pulse.

36. In a system for monitoring the level of a material on the basis of the round-trip transit time of an ultrasonic pulse between a transducer and a surface of said material, the combination comprising,

means transmitting a sequence of ultrasonic pulses toward a surface of said material,

means receiving echo response pulses reflected from said surface,

means converting each of said echo response pulses to a digital number having a value indicative of the intensity of each of said pulses relative to one another,

means integrating said response pulses from successively transmitted pulses of said sequence according to apparent distance to said surface,

means selecting an integrated response pulse having highest digital value after termination of said pulse sequence, and

means identifying which apparent material surface distance is associated with said highest-value integrated pulse and treating said apparent distance as actual material surface distance.

37. The combination set forth in claim 36 wherein said sequence of ultrasonic pulses comprises eight pulses.

38. The combination set forth in claim 36 further comprising display means for providing a display of said actual distance upon completion of said pulse sequence.

39. In a system for monitoring the level of a material as a function of the round-trip transit time of an ultrasonic pulse between a transducer and a surface of said material, the combination comprising,

means transmitting a first ultrasonic pulse having a first pulse width and a first pulse repetition period vertically toward said surface of said material,

means monitoring for an echo pulse in response to said first transmitted pulse for a preselected time after said transmitted pulse which corresponds to a preselected distance range to said surface,

means retransmitting said first ultrasonic pulse in response to an echo pulse within said preselected time,

means transmitting a second ultrasonic pulse having a second pulse width different from said first pulse width and a second pulse repetition period different from said first pulse repetition period vertically toward said surface in response to an absence of said echo pulse within said preselected time, and

means monitoring for an echo pulse in response to said second transmitted pulse.

40. The combination set forth in claim 39 further comprising means retransmitting said first pulse after transmitting a preselected number of said second pulses.

41. The combination set forth in claim 40 wherein said preselected number of said second ultrasonic pulses is eight.

42. In a control system for use in monitoring the level of material in a storage tank, the combination comprising,

transducer means directing ultrasonic pulses toward and receiving echo response pulses reflected from the upper surface of said material,

means operatively connected to said transducer means to sample said echo response pulses from each transmitted pulse at preselected intervals which are a function of the distance of said material surface from said transducer means,

means converting each of said sampled response pulses to digital signals having a numerical value indicative of the intensity of each said echo pulse relative to other echo pulses similarly received, and

means monitoring said sampled and digitized response pulses to provide an indication of actual distance, which is a function of material level, upon completion of said pulse sequence, said monitoring means comprising first digital storage register means for storing digital data, means operatively connected to said converting means comparing said converted pulses with digital data stored in said first storage register means, means responsive to said comparing means for storing a converted pulse in said first storage register means when said converted pulse is greater than said stored data, second storage register means for storing digital data and means responsive to said comparing means to store an apparent material surface distance associated with said converted pulse stored in said second storage register means when said converted pulse is greater than said stored data.

43. In a control system for use in monitoring the level of material in a storage tank including a transducer directing ultrasonic pulses toward and receiving echo response pulses reflected from the upper surface of said material, and a control circuit operatively connected to said transducer to provide an indication of material level on the basis of the round-trip transit time of an ultrasonic pulse from said transducer to said material surface and back again, the improvement wherein said control circuit comprises means converting said echo response pulses to digital signals having a numerical value indicative of the intensity of each of said echo pulses relative to one another, and level indicating means responsive to said converting means to provide said indication of material level on the basis of the relative numerical value of said digitized response pulses.

44. The improvement set forth in claim 43 wherein said level indicating means comprises means integrating said digitized response pulses from successively transmitted pulses over a preselected pulse sequence according to apparent distance to said material surface and means monitoring said integrated pulses to provide an indication of actual distance upon completion of said pulse sequence.

45. The improvement set forth in claim 44 further comprising means operatively connected to said transducer to sample said echo response pulses at preselected intervals which are a function of distance from said transducer means to said material surface, said converting means being connected to said sampling means to convert sample response pulses to said digital signals.

46. The improvement set forth in claim 43 wherein said transducer is mounted to the top of said storage tank and is directed to transmit pulses downwardly toward and to receive pulses reflected upwardly from said material surface through an air space between said tank top and said material surface.