Sampling method and apparatus for use with ultrasonic flowmeters

Claims

What is claimed is:

1. In a fluid parameter measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical input signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second state in which said second transducer is a transmitting transducer and said first transducer is a receiving transducer, in combination:

a driver circuit for alternately applying bursts of electrical drive pulses to said first and second transducers to establish the first and second states of said apparatus;

a receiver circuit coupled to the receiving transducer for generating a received signal having transitions that correspond to the zero crossings of the AC output signal of the receiving transducer;

a reference signal generator for generating, for said bursts of drive pulses, reference transitions which occur controllable times after the beginnings of those bursts of drive pulses;

a sampling signal generator for generating, for said bursts of drive pulses, sampling signals that define a plurality of sampling windows each beginning with a sampling transition for use in timing respective transitions of said received signal, said sampling windows having durations that are related to the periods of said drive pulses;

wherein the first of said sampling transitions occurs at substantially the same time as the respective reference transition.

2. The apparatus of claim 1 in which said driver circuit includes first and second switching means for controllably establishing said first and second states and means for connecting said switching means to respective transducers, further including means for connecting said receiver circuit to both of said transducers.

3. The apparatus of claim 2 in which said first and second switching means comprise tri-state buffers.

4. The apparatus of claim 1 in which said controllable times are selected so that said reference transitions occur after the occurrences of predetermined numbers of the transitions of the received signals.

5. The apparatus of claim 1 in which said reference transitions initiate the generation of respective sampling signals.

6. The apparatus of claim 1 in which the occurrence times of said reference transitions are changed as necessary to cause the transitions of said received signals to remain within respective sampling windows of respective sampling signals.

7. The apparatus of claim 1 in which the occurrence times of said reference transitions are changed as necessary to prevent the occurrence of phase ambiguities between said sampling signals and said received signals.

8. The apparatus of claim 1 further including a timing signal generator for generating a train of clock pulses having a frequency which is high in relation to the frequency of said sampling transitions, and a counter circuit for counting the number of clock pulses which occur between said sampling transitions and the corresponding transitions of the received signals, the numbers of clock pulses counted during said first and second states comprising the up and down sample counts, respectively, of said received signals.

9. The apparatus of claim 8 in which said controllable time is controlled by controlling the number of equal time periods that separate the beginning of a burst and the respective reference transition, the numbers of said time periods occurring during said first and second states comprising the up and down window counts, respectively, of the apparatus, said sampling windows and said time periods each having durations corresponding to different integer numbers of said clock pulses.

10. The apparatus of claim 9 in which said sampling signals may be shifted with respect to respective bursts of drive pulses by changing said up or down window counts and making compensatory changes in said up or down sample counts.

11. The apparatus of claim 10 in which said sampling signals are shifted as necessary to prevent the transitions of the received signals from occurring outside of respective sampling windows, whereby tracking relationships are maintained between the transitions of the received signals and the transitions of the sampling signals in spite of substantial changes in the magnitude of said fluid parameter.

12. The apparatus of claim 10 in which said sampling signals are shifted as necessary to prevent phase ambiguities from arising between said sampling signals and said received signals.

13. The apparatus of claim 8 in which each of said sampling windows includes a target window of acceptability bounded by upper and lower target counts, and in which said sampling signals are shifted as necessary to cause said up and down sample counts to approach and enter said window of acceptability.

14. The apparatus of claim 9 in which the temporal position of each transition of the received signal is fixed, with a resolution comparable to the period of said clock pulses, by adding together the number of clock pulses corresponding to the window counts for a measurement and the number of sample counts for the same measurement.

15. The apparatus of claim 9 in which each window count is equal to the sum of a fixed window count and a variable window count.

16. An apparatus of the type set forth in claim 1 in which said fluid may flow bidirectionally.

17. In a fluid parameter measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical input signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second state in which said second transducer is a transmitting transducer and said first transducer is a receiving transducer, in combination:

driving means for applying first bursts of electrical drive pulses to said first transducer to establish the first state of said apparatus, and for applying second bursts of electrical drive pulses to said second transducer to establish the second state of said apparatus;

receiving means for generating a first received signal having transitions that correspond to the zero crossings of the output signal of said second transducer, and for generating a second received signal having transitions that correspond to the zero crossings the output signal of said first transducer;

reference signal generating means for generating a first reference signal having a first reference transition a first adjustable number of time intervals after said first bursts, and for generating a second reference signal having a second reference transition a second adjustable number of time intervals after said second bursts;

sampling signal generating means for generating first sampling signals that each define a plurality of first sampling windows including first sampling transitions that are synchronized with said first reference transitions for timing respective zero crossings of the output signal of said second transducer, and for generating second sampling signals that each define a plurality of second sampling windows including second sampling transitions that are synchronized with said second reference transitions for timing respective zero crossings of the output signal of said first transducer; and

means for adjusting said first and second adjustable numbers of time intervals to maintain an unambiguous phase relationship between said first and second sampling transitions and the transitions of the first and second received signals.

18. The apparatus of claim 17 in which said adjusting means adjusts said first and second adjustable numbers to maintain the transitions of the first and second received signals within respective sampling windows.

19. The apparatus of claim 17 further including timing signal generating means for generating a succession of timing pulses having a frequency which is high in relation to the frequencies of said sampling signals, and counting means for counting the number of timing pulses which occur between said first and second sampling transitions and corresponding zero crossings of the output signals of said second and first transducers, respectively, the counts counted by said counting means comprising the upcounts and downcounts, respectively, of said zero crossings.

20. The apparatus of claim 19 in which the sampling windows of said sampling signal have durations that correspond to a first predetermined number of said timing pulses, and in which the time intervals of said first and second reference signals have durations that correspond to a second predetermined number of said timing pulses, said first predetermined number being large in relation to said second predetermined number.

21. The apparatus of claim 20 in which the temporal positions of said zero crossings may be specified, with an uncertainty comparable to the period of said timing pulses, by adding together numbers of timing pulses corresponding to the occurrence times of said reference transitions and to said upcounts and downcounts.

22. The apparatus of claim 19 in which the first and second sampling windows may be shifted with respect to said first and second bursts by increasing or decreasing the number of said timing intervals and making a corresponding decrease or increase in said upcounts and downcounts.

23. The apparatus of claim 22 in which the durations of said time intervals are small in relation to the durations of said sampling windows.

24. The apparatus of claim 22 in which said first and second sampling windows are shifted with respect to said first and second bursts as necessary to maintain the transitions of the received signals within said sampling windows in spite of substantial changes in said fluid parameter.

25. The apparatus of claim 22 in which each of said sampling windows includes an inner, target window bounded by first and second target counts, and in which said sampling windows are shifted with respect to the respective burst when said upcounts and downcounts fail to have values that remain between said target counts.

26. The apparatus of claim 19 in which said first and second reference signals each include a fixed component and a variable component, said fixed and variable components each having a duration that corresponds to a whole number of said time intervals.

27. The apparatus of claim 26 in which the occurrence times of said zero crossings may be specified, with an uncertainty comparable to the period of said timing pulses, by adding together numbers of timing pulses corresponding to the durations of said fixed and variable components to said upcounts and downcounts.

28. The apparatus of claim 17 in which each reference transition is timed to occur after a preselected number of transitions of the respective received signal.

29. The apparatus of claim 17 in which said reference transitions initiate the generation of respective sampling signals.

30. The apparatus of claim 17 in which said driving means and said receiving means are both directly coupled to said transducers.

31. The apparatus of claim 30 in which said driving means includes first and second tri-state buffers.

32. An apparatus of the type set forth in claim 17 in which said fluid may flow bidirectionally.

33. In a fluid parameter measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical input signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second state in which said second transducer is a transmitting transducer and | said first transducer is a receiving transducer, in combination:

a driver circuit for alternately applying bursts of electrical drive pulses to said first and second transducers to establish the first and second states of said apparatus;

a receiver circuit coupled to the receiving transducer for generating a received signal having transitions that correspond to the zero crossings of the AC output signal of the receiving transducer;

a reference signal generator for generating, for each of said bursts of drive pulses, a reference transition which occurs a controllable time after the beginning of that burst of drive pulses;

a sampling signal generator for generating, for each of said bursts of drive pulses, a sampling signal that defines a plurality of sampling windows each beginning with a sampling transition for use in timing respective transitions of said received signal, the first of said sampling transitions occurring at substantially the same time as the respective reference transition, said sampling windows having durations that are equal to the periods of said drive pulses;

a timing circuit, responsive to said sampling transitions and to the transitions of said received signals, for generating data indicative of the transit times of said acoustic signals along said path;

a microcomputer, connected to said reference signal generator and to said timing circuit, for controlling said controllable time so that an unambiguous phase relationship is maintained between said sampling transitions and the respective transitions of said received signals, and for calculating the magnitude of said fluid parameter from transit time data received from said timing circuit.

34. A fluid parameter measuring apparatus as set forth in claim 33 in which the maintenance of said unambiguous phase relationship comprises the maintenance of the transitions of the received signals within respective sampling windows.

35. A fluid parameter measuring apparatus as set forth in claim 33 in which said driver circuit and said receiver circuit are both directly coupled to said transducers.

36. A fluid parameter measuring apparatus as set forth in claim 33 in which said microcomputer controls said controllable time by specifying the number of window counts of equal duration that occur between said bursts and the respective reference transitions.

37. A fluid parameter measuring apparatus as set forth in claim 33, further including a clock pulse generator, in which said timing circuit generates said transit time data by counting the number of clock pulses which occur between said sampling transitions and the transitions of said received signals.

38. A fluid parameter measuring apparatus as set forth in claim 36, further including a clock pulse generator, in which said timing circuit generates said transit time data by counting the number of clock pulses which occur between said sampling transitions and the transitions of said received signals.

39. A fluid parameter measuring apparatus as set forth in claim 38 in which said microcomputer is programmed so that changes in the number of said window counts are accompanied by compensating changes in transit time data received from said timing circuit.

40. A fluid parameter measuring apparatus as set forth in claim 39 in which said sampling windows have durations that are large in relation to the durations of said window counts.

41. A method for measuring a fluid flow parameter in conjunction with an apparatus of the type including first and second transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical input signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first, up state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second, down state in which said second transducer is a transmitting transducer and said first transducer is a receiving transducer, including the steps of:

a.) alternately applying bursts of electrical drive pulses to said first and second transducers to alternately establish said first and second states;

b.) generating, for the bursts of said first and second states, reference signals having reference transitions which occur at controllable times after the beginnings of the respective bursts;

c.) generating sampling signals having frequencies equal to the frequency of said drive signal, each sampling signal defining a plurality of sampling intervals which include sampling transitions that bear predetermined phase relationships to the respective reference transitions;

d.) generating a clock pulse signal having a frequency substantially greater than the frequency of said drive pulses;

e.) counting and storing as count values for said sampling intervals the number of clock pulses which occur between said sampling transitions and corresponding zero crossings of the AC output signals of the receiving transducers; and

f.) changing said controllable times as necessary to maintain an unambiguous phase relationship between said sampling transitions and the respective zero crossings.

42. The method of claim 41 in which step (f.) comprises the step of changing said controllable times so that said zero crossings remain within respective sampling intervals.

43. The method of claim 41 in which generating step (b) includes the steps of generating a first reference signal having a reference transition which occurs a first controllable time after the bursts of said first state, and generating a second reference signal having a reference transition which occurs a second controllable time after the bursts of said second state.

44. The method of claim 43 in which said controllable times are defined by the numbers of time delay intervals which occur between said bursts and the respective reference transitions.

45. The method of claim 44 in which the number of said time delay intervals is such that said reference transitions occur predetermined times after the beginnings of respective received signals.

46. The method of claim 44 in which the durations of said time delay intervals are small in relation to the durations of said sampling intervals.

47. The method of claim 44 in which changes in the number of said time delay intervals are made in conjunction with offsetting changes in said count values.

48. The method of claim 44 in which said reference signal includes a fixed component and a variable component, each component including a whole number of said time delay intervals.

49. The method of claim 41 which the numbers of clock pulses counted during the sampling intervals of said first and second states are stored as upcount and downcount values, respectively.

50. The method of claim 49 in which said sampling intervals have a maximum capacity of N counts and a mid point having a count value approximately equal to N/2, and in which said controllable times are changed when said upcount and downcount values fail to remain within a predetermined range of values that includes N/2.

51. The method of claim 50 in which said predetermined range includes a number of counts, which is relatively small in relation to N.

52. The method of claim 41 in which said sampling signals begin with the occurrences of the respective reference transitions.

53. In a fluid parameter measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when driven by a suitable electrical input signal and to generate an AC output signal when driven by a suitable acoustic input signal, said apparatus having a first state in which said first transducer is a transmitting transducer and said second transducer is a receiving transducer, and a second state in which said second transducer is a transmitting transducer and said first transducer is a receiving transducer, in combination:

driving means for alternately applying bursts of electrical drive pulses to said first and second transducers to establish the first and second states of said apparatus;

receiving means coupled to the receiving transducer for generating a received signal having transitions that correspond to the zero crossings of the AC output signal of the receiving transducer;

sampling means for generating, for each of said bursts of drive pulses, a sampling signal including a plurality of sampling transitions for use in measuring the occurrence times of respective transitions of said received signals, said sampling signals each having a frequency equal to that of said electrical drive pulses;

timing means responsive to the transitions of the sampling signal and to the transitions of the received signal for generating a first plurality of zero crossing time values for a burst transmitted when the apparatus is in its first state and for generating a second plurality of zero crossing time values for a burst transmitted when said apparatus is in its second state; and

calculating means for calculating a first average of the zero crossing time values for a burst transmitted when the apparatus is in its first state, for calculating a second average of the zero crossing time values for an adjacent burst transmitted when said apparatus is in its second state, and for calculating the magnitude of said fluid parameter from said calculated first and second average zero crossing time values.

54. The apparatus of claim 53 in which said fluid parameter is the volume rate of flow of said fluid.

55. The apparatus of claim 53 which said fluid parameter is the volume rate of flow value of said fluid, and in which said fluid is the air breathed by a living creature.

56. The apparatus of claim 55 in which said calculating means is responsive to a series of said rate of flow values and to the durations of the time periods during which said rate of flow values are maintained to calculate the volume of air breathed by a living creature.

57. The apparatus of claim 53 in which said timing means includes a timing pulse generator for generating timing pulses at a frequency substantially greater than the frequency of said electrical drive pulses, in which said zero crossing time values comprise the numbers of timing pulses which occur between the transitions of the sampling signal and the corresponding transitions of the received signal, the average number of timing pulses occurring when the apparatus is operating in said first state comprising an average upcount value, and the average number of timing pulses occurring when the apparatus is operating in said second state comprising an average downcount value.

58. The apparatus of claim 57 further including means for storing a calibration coefficient determined from a known rate of flow of said fluid and from the difference between the average upcount and downcount values associated with said known rate of flow, in which the calculation of the magnitude of said fluid parameter includes the multiplication of the measured difference of said average upcount and downcount values by said calibration coefficient.

59. The apparatus of claim 57 further including means for storing a zero flow upcount and a zero flow downcount determined from average upcount and average downcount values measured when the rate of flow of fluid through the apparatus is equal to zero, in which said calculating means uses said zero downcount and zero upcount values to calculate said rate of flow.

60. The apparatus of claim 58 further including means for storing a zero flow upcount and a zero flow downcount determined from average upcount and average downcount values measured when the rate of flow of fluid through the apparatus is equal to zero, in which said calculating means uses said zero upcount and zero downcount values to calculate said rate of flow.

61. The apparatus of claim 53 in which said calculating means is arranged to interleavedly calculate the magnitude of said fluid parameter each time that a new average zero crossing time value becomes available, whereby the number of calculated fluid parameter values is approximately equal to the number of said bursts.

62. The apparatus of claim 53 in which said calculating means comprises a computer having a L stored program that includes instructions for coordinating the operation of said driving means, said receiving means and said sampling means.

63. The apparatus of claim 62 in which said stored program includes instructions for performing said calculations, and in which said computer and said instructions for performing said calculations comprise said calculating means.

64. The apparatus of claim 63 in which said instructions for performing said calculations include instructions that the computer calculate said fluid parameter using the then most recently calculated average zero crossing time value and the then next-most recently calculated average zero crossing time value, whereby the number of calculated fluid parameter values is approximately equal to the total number of said bursts.

65. The apparatus of claim 63 in which said fluid parameter is the volume rate of flow of said fluid, and in which said instructions for performing said calculations include instructions for calculating a series of volume rate of flow values, and then integrating said volume rate of flow values with respect to time to determine the total volume of fluid flow through the apparatus.

66. The apparatus of claim 53 in which said transducers have a resonant frequency approximately equal to the frequency of said drive pulses.

67. In a fluid parameter measuring apparatus of the type including first and second sound transducers for transmitting and receiving acoustic pulses along a path through said fluid, each of said transducers serving to transmit an acoustic output signal when