Ultrasonic flow sensor

• US 6,178,827 B1
• Filed: 12/10/1999
• Issued: 01/30/2001
• Est. Priority Date: 04/22/1999
• Status: Expired due to Term

• Current Assignee: ONICON, Inc. (TASI Holdings, Inc.)
• Original Assignee: Murray F. Feller
• Inventors: Feller, Murray F.
• Primary Examiner(s): PATEL, HARSHAD R
• Application Number:
  US09/458,315
• Time in Patent Office: 417 Days
• Field of Search: 738/612.7, 738/612.8, 738/612.9, 738/612.5, 738/612.2
• US Class Current: 73/861.27
• CPC Class Codes: G01F 1/662 Constructional details
• CPC Class Codes: G01F 1/667 Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• CPC Class Codes: G01F 5/00 Measuring a proportion of the volume flow

Abstract

A transit time ultrasonic fluid flow sensor is configured as a self contained modular unit that does not rely on acoustic transmissions through or reflected by a pipe for operation. A highly efficient transducer assembly transmits and receives signals which are well isolated from each other and which enables simplification of the supporting electronics. Continuous wave transmission and reception of the acoustic signals, and provision for acoustic path and electronic drifts enable the sensors to be physically small and yet to exhibit high sensitivity and measurement precision. Some versions of the apparatus sense flow along two orthogonal axes. In addition, electrolytic cleaning is provided for some versions of the sensor.

Claims

1. A transit-time flow sensor for measuring an acoustic propagation time difference between upstream and downstream acoustic transmissions in a fluid and for determining the flow rate of the fluid therefrom, wherein the fluid wets a probe portion of the sensor, the probe portion comprising;

first and second transducers, each of the transducers having a respective transmitting functional state and a respective receiving functional state, each of the transducers adapted to transmit acoustic energy at a first frequency along an axis parallel to a direction of flow of said fluid when said each transducer is in its respective transmitting state, each transducer adapted to receive said acoustic energy transmitted by the other transducer when said each transducer is in its receiving state; and

a reflector adapted to convey said acoustic energy between said transducers;

the sensor further comprising;

means for alternating the transmitting and receiving states of the transducers so as to always have one of the two transducers in its respective transmitting state and the other of the two transducers in its respective receiving state, the means for alternating adapted to act at a second frequency substantially less than the first frequency;

means for providing a continuous carrier signal at the first frequency to the transmitting one of said transducers; and

a phase detector containing a low pass filter for providing an output signal responsive to a phase difference between electrical signals corresponding to, and of the same frequency as, the transmitted and received acoustic energy.

2. The transit time flow sensor of claim 1, further comprising means to correct a drift in said phase difference between said transmitted and received acoustic energy by changing the first frequency.

3. The transit time flow sensor of claim 1, further comprising means to correct a drift in said phase difference between said transmitted and received acoustic energy by a phase shift change of the phase relationship of said electrical signals corresponding to the transmitted and received acoustic energy.

4. The transit time flow sensor of claim 1, wherein a surface of said reflector faces said transducers, said surface having a radius of curvature along an axis between said transducers that is equal to approximately two times the distance between a midpoint between said transducers and said rcflector.

5. The transit time flow sensor of claim 1, further comprising a third transducer and a fourth transducer which are mounted orthogonally as a pair to said first and said second transducers, said sensor further comprising processing means for determining a component of said flow rate which is orthogonal to an axis extending between the third and the fourth transducers.

6. The transit time flow sensor of claim 1, further comprising a third transducer and a fourth transducer which are mounted as a pair orthogonally to said first and second transducers, said sensor further comprising processing means responsive to changes in the speed of sound of said fluid, the processing means adapted to correct said output signal for said changes.

7. The transit time flow sensor of claim 1, further comprising third and fourth transducers which are mounted as a pair orthogonally to said first and second transducers so that a surface of the reflector comprises a portion of an acoustic path between the third and the fourth transducers.

8. The transit time flow sensor of claim 1 further comprising a bluff body for generating a Karman vortex street comprising a plurality of vortices that pass through an acoustic beam extending between said transducers, the sensor further comprising means for measuring a frequency of variation in said flow rate caused by said vortices.

9. A transit time flow sensor for determining a flow rate of a fluid from a measurement of an acoustic propagation time difference between upstream and downstream acoustic transmissions in the fuid, wherein the fluid wets a probe portion of the sensor, the probe comprising:

first and second transducers, each of the transducers having a respective transmitting functional state and a respective receiving functional state, each of the transducers adapted to transmit, when in its transmitting state, acoustic energy at first, controllable, frequency, the acoustic energy transmitted along an axis parallel to a direction of flow of said fluid, each transducer further adapted to receive said acoustic energy transmitted by the other transducer when said each transducer is in its receivg state; and

a reflector adapted to convey said acoustic energy between said transducers;

the sensor further comprising;

means for repeatedly alternating the transmitting and receiving states of the transducers so as to always have one of the two transducers in its respective transmitting state and the other of the two transducers in its respective receiving state, the means for alternating adapted to act at a second frequency substantially less than the controllable frequency;

means for providing a continuous carrier signal at the controllable frequency to that one of said transducers that is in its transmitting state;

a phase detector containing a low pass filter for providing an output signal responsive to a phase difference between electrical signals corresponding to, and of the same frequency as, said transmitted and received acoustic energy; and

a phase locked loop adapted to act responsive to the output signal to control the controllable frequency, so that said phase detector operates, on the average, at a center of its operating range.

10. The transit time flow sensor of claim 9, wherein the means for alternating the receiving and transmitting states comprises:

a first switch adapted to periodically switch, at a third frequency substantially less than the second frequency, so as to provide a momentary pulse from a voltage source to said low pass filter;

a second switch adopted to operate at said second frequency so as to synchronously detect a magnitude of said output signal from said phase detector; and

means to filter, amplify and process said synchronously detected output signal and provide it as an output flow rate signal.

11. The transit time flow sensor of claim 10, wherein said first switch is adapted to operate when the controllable frequency is not at a nominal center of its operating range.

12. The transit time flow sensor of claim 10, wherein said means to filter, amplify and process said synchronously detected output signal includes means for retaining said output signal during a reset pulse at the value existing prior to the commencement of said reset pulse.

13. The transit time flow sensor of claim 9, wherein said means for providing a controllable frequency is adapted to provide a fixed frequency and its output to said phase detector is phase controlled.

14. The transit time flow sensor of claim 13 wherein said first switch is adapted to operate when said phase detector is detected to be other than at a nominal center of its operating range.

15. The transit time flow sensor of claim 9, wherein a surface of said reflector faces said transducers, the surface having a radius of curvature along an axis between said transducers that is equal to approximately two times the distance betveen a midway point between said transducers and said reflector.

16. The transit time flow sensor of claim 9, further comprising a third transducer and a fourth transducer which are mounted as a pair orthogonally to said first and second transducers so that a surface of the reflector comprises a portion of an acoustic path between the third and the fourth transducers.

17. The transit time flow sensor of claim 9, further comprising a third transducer and a fourth transducer which are mounted as a pair orthogonally to said first and second transducers, said sensor further comprising processing means responsive to changes in the speed of sound of said fluid, the processing means adapted to correct said output signal for said changes.

18. A transit-time flow sensor for sensing an acoustic propagation time difference between upstream and downstream acoustic transmissions in a fluid and for determining the flow rate of the fluid therefrom wherein the fluid wets a probe portion of the sensor, the probe portion comprising:

first and second transducers, each of the transducers having a respective transmitting functional state and a respective receiving functional state, each of the transducers adapted to transmit acoustic energy at a first frequency along an axis perpendicular to a direction of flow of said fluid when said each transducer is in its respective transitting state, each transducer adapted to receive a portion of the acoustic energy transmitted by the other transducer when said each transducer is in its receiving state;

the sensor further comprising;

means for repeatedly alternating the transmitting and receiving states of said transducers so as to always have one of the two transducers in its respective transmitting state and the other of the two transducers in its respective receiving state; and

means responsive to a change in time between said transmitted and said received acoustic energy for indicating a flow rate component that is not along the axis.

19. A transit-time flow sensor for measuring an acoustic propagation time difference between upstream and downstream acoustic transmissions in a fluid and for determining a flow rate of the fluid therefrom wherein the fluid wets a probe portion of the sensor, the probe portion comprising:

first and second transducers, each of the transducers having a respective transmitting functional state and a respective receiving functional state, each of the transducers adapted to transmit acoustic energy at a first frequency when said each transducer is in its respective transmitting state, each transducer adapted to receive acoustic energy transmitted by the other transducer when said each transducer is in its receiving state; and

a reflector adapted to convev said acoustic energy between said transducers;

the sensor further comprising;

a bluff body for generating a Karman vortex street in said fluid and for therebv producing a plurality of vortices that pass through at least one acoustic pathlsl betveen said reflector and said transducers; and

means responsive to a change in time between said transmitted and said received acoustic energy caused by said Karman v ortex street for generating an electrical signal with a frequency representative of said flow rate.

20. The transit time flow sensor of claim 19, wherein said bluff body is a supporting member for said reflector.