Measurement of fluid flow rates

Abstract

Apparatus and a method for measuring the flow rate of a fluid in which a beam of ultrasonic ≮, electromagnetic, optical or other radiant.]. energy is transmitted across the flow at each of two positions spaced apart in the direction of flow, the noise amplitude, frequency or phase modulation on each beam due to disturbances in the flow is detected, and the two resultant signals are cross correlated to determine the time delay therebetween producing maximum correlation, i.e. the mean fluid transport time between the beams, and thus the mean fluid flow rate.

I claim: 
     
       1. Apparatus for measuring the rate of flow of a fluid, comprising means for transmitting a beam of .[.radiant.]. .Iadd.ultrasonic .Iaddend.energy, into and across the fluid flow at each of two positions spaced apart in the direction of flow of the fluid, respective receiving means associated with each beam and each positioned to receive the associated beam after passage across the flow, each receiving means producing a beam-representative carrier signal modulated by a noise signal caused by disturbances in the fluid flow profile, a respective detector connected to each receiving means for detecting said noise signals, and a signal correlator for cross-correlating the two detected noise signals whereby the value of correlation delay producing maximum correlation between said two noise signals can be ascertained. 
     
     
       2. Apparatus as claimed in claim 1, wherein the signal correlator includes means for determining the value of correlation delay producing maximum correlation between said two noise signals. 
     
     
       3. Apparatus as claimed in claim 1, wherein said transmitting means is arranged to transmit the two beams in a common plane which also includes the direction of fluid flow. 
     
     
       4. Apparatus as claimed in claim 1, wherein the transmitting means is arranged to transmit the two beams in respective different planes each of which includes the direction of fluid flow. 
     
     
       5. Apparatus as claimed in claim 4, where said two planes are orthogonal. 
     
     
       6. Apparatus as claimed in claim 1, wherein said transmitting means includes a respective transmitting transducer for each beam and wherein said receiving and detecting means includes a respective receiving transducer for each beam. 
     
     
       7. Apparatus as claimed in claim 6, wherein an oscillator is connected to the input of each transmitting transducer. 
     
     
       8. Apparatus as claimed in claim 6, wherein the output of each receiving transducer is connected by a feedback loop to the input of the associated transmitting transducer, each feedback loop having sufficient gain to cause it to self-oscillate so as to produce the associated beam. 
     
     
       9. Apparatus as claimed in claim 8, wherein the parameters of the components of each feedback loop are selected so that it oscillates at a frequency which is near or equal to the resonant frequencies of the associated transmitting transducer and receiving transducer. 
     
     
       10. Apparatus as claimed in claim 6, wherein the output of the receiving transducer associated with a first of the beams is connected to the input of the transmitting transducer associated with the second of the beams and the output of the receiving transducer associated with the second beam is connected to the transmitting transducer associated with the first beam, whereby both beams are included in a single feedback loop having sufficient gain to cause it to self-oscillate to produce said beams. 
     
     
       11. Apparatus as claimed in claim 10, wherein the two transmitting transducers are mutually matched and wherein the two receiving transducers are mismatched both mutually and relative to the transmitting transducers. 
     
     
       12. Apparatus as claimed in claim 6, wherein said receiving and detecting means includes a respective AM detector connected to the output of each receiving transducer for detecting noise amplitude modulation on the beams to provide said two noise signals. 
     
     
       13. Apparatus as claimed in claim 6, wherein said receiving and detecting means includes a respective FM detector connected to the output of each receiving transducer for detecting noise frequency modulation on the beams to provide said two noise signals. 
     
     
       14. Apparatus as claimed in claim 6, wherein said receiving and detecting means includes, for each beam, a respective phase-to-voltage converter having a first input connected to the input of the associated transmitting trans-ducer and a second input connected to the output of the associated receiving transducer, each converter thereby measuring, in use, the changes of phase shift across the associated beam. 
     
     
       15. Apparatus as claimed in claim 14, wherein one or more intermediate transmitting transducers and one or more intermediate receiving transducers are provided for each beam whereby each beam can be passed through the flowing fluid two or more times. 
     
     
       16. Apparatus as claimed in claim 14, wherein each phase-to-voltage converter comprises a linear quarter period delay network having an input connected to said first input thereof, a level detector having an input connected to the output of the linear half period delay network, a half period monostable circuit having an input connected to the output of the level detector, a gate having a first input connected to the output of the half period monostable circuit and a second input connected to said second input of the converter, and an integrator having an input connected to the output of the gate, the output signal of the integrator being one of said two noise signals. 
     
     
       17. Apparatus as claimed in claim 16, wherein each phase-to-voltage converter includes a first divider connected between said first input thereof and the input of the linear half period delay network and a second divider of the same ratio as the first divider connected between said second input thereof and the second input of said gate. 
     
     
       18. Apparatus as claimed in claim 17, wherein each phase-to-voltage converter includes first and second gating means each having a first input connected to a respective one of said first and second inputs of the converter, and a pulse width detector having an input connected to the output of said gate and an output connected to a second input of each of said gating means and to reset terminals of each of said dividers.  .[.19. Apparatus as claimed in claim 6, wherein said transmitting transducers are of the type responsive to an electrical input signal and wherein said receiving trans-ducers are of the type producing electrical output signals..]. .[.20. Apparatus as claimed in claim 1, wherein said transmitting means is of the type such that the radiant energy is ultrasonic..]. .[.21. Apparatus as claimed in claim 1, wherein said transmitting means is of the type such that the radiant energy is electromagnetic..]. .[.22. Apparatus as claimed in claim 21, wherein said transmitting means is of the type such that the electromagnetic radiant 
     
     
        energy is within the optical band..]. 23. Apparatus as claimed in claim 1, including means for inducing turbulence in the flowing fluid, said means 
     
     
        being located upstream of both of the beams. 24. A method of measuring the rate of flow of a fluid, comprising the steps of transmitting a beam of .[.radiant.]. .Iadd.ultrasonic .Iaddend.energy into and across the fluid flow at each of two positions spaced apart in the direction of flow of the fluid, receiving the two beams after passage across the flow and producing, for each beam, a beam-representative carrier signal modulated by a noise signal caused by disturbances in the fluid flow profile, detecting said noise signals, cross-correlating the two detected noise signals, and determining the value of correlation delay producing maximum 
     
     
        correlation between the two noise signals. 25. A method as claimed in claim 24, wherein the two beams are transmitted in a common plane which 
     
     
        also includes the direction of fluid flow. 26. A method as claimed in claim 24, wherein the two beams are transmitted in respective different 
     
     
        planes each of which includes the direction of fluid flow. 27. A method 
     
     
        claimed in claim 26, wherein said two planes are orthogonal. 28. A method as claimed in claim 24, wherein noise amplitude modulation on the two 
     
     
        beams is detected to provide said two noise signals. 29. A method as claimed in claim 24 wherein noise frequency modulation on the two beams is 
     
     
        detected to provide said two noise signals. 30. A method as claimed in claim 24, wherein noise phase modulation on the two beams is detected to provide said two noise signals.  .[.31. A method as claimed in claim 24, wherein said radiant energy is ultrasonic..]. .[.32. A method as claimed in claim 24, wherein said radiant energy is electromagnetic..]. .[.33. A method as claimed in claim 32, wherein said electromagnetic radiant energy 
     
     
        is within the optical band..]. 34. A method as claimed in claim 24, having the further step of inducing turbulence in the flowing fluid upstream of both said beams.