Abstract:
The present invention includes a clamp-on housing for encapsulating or confining a flexible tube or pipe. The housing includes transducers therein for transmitting and receiving sonic energy. A sonically matched plate is provided to function as a waveguide for the sonic energy to form a coherent wide beam such that flow characteristics may be measured in the flexible tube. An apparatus for measuring flow in flexible tubes, in accordance with the present invention, includes a housing including a first portion configured and dimensioned for receiving a first transducer and a second transducer therein and a second portion adapted to attach to the first portion to encapsulate a flexible tube between the first and second portion without cutting off flow within the tube. A plate is disposed within the housing in contact with the tube. The plate is sonically matched to the transducers to permit sonic energy transmitted from the first transducer to travel along the plate to provide sonic radiation from the plate to be received by the second transducer to measure flow characteristics within the tube.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Provisional Application Ser. No. 60/132,757 filed May 6, 1999. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This disclosure relates to flow measurements and, more particularly, to sonic flow measurement devices for flexible vessels. 
     2. Description of the Related Art 
     All metallic pipes may be considered sonic waveguides. This means that there is a mode of transmission of sonic energy, which preserves the relationship between Group and Phase velocities as sonic energy is transmitted down a pipe wall. 
     A transducer may be attached to a pipe such that the Phase velocity of sonic energy produced by the transducer is matched to a shear mode propagation velocity of the pipe material, and the transducer is operated at a frequency dependent on the round trip echo time in the radial direction. This will result in radiation of a coherent sonic wave into a liquid contained within the pipe at a constant angle to the pipe axis as the energy travels down the pipe. The sine of this angle is dependent, by Snell&#39;s law, on the sonic propagation velocity of the liquid and the propagation velocity of the sonic energy down the wall of the pipe, since that energy travels axially, rather than at an angle within the pipe wall. 
     Since most non-metallic materials, such as plastics, do not support or only marginally support shear waves, pipes and tubes made of these materials do not typically exhibit waveguide properties. Accordingly, if sonic measurements are to be taken, it is not necessary for a sonic transducer to exhibit any particular Phase velocity or frequency to optimize the coherency of the liquid sonic beam. Unfortunately, the sonic impedance of plastic and other non-metallic materials are typically close to the impedance of most liquids. This is unlike metallic pipes in which the impedance is much higher than liquids. In sonic flow measurement systems, this results in a receive transducer obtaining sonic energy reflected from both the inner and outer pipe wall when operated with reflect mode transducers, which are desirable for crossflow correction. This reflection distorts the sonic signal with consequent miscalibration effects. 
     An additional problem presents itself when operating on plastic tubes, rather than metallic tubes. When operating on metallic tubes, a waveguide matched transducer may be excited to a waveguide mode of the tube or pipe at a location of a transmit transducer. This results in the injection of a Wide Beam signal, (i.e., waveguide matched), even though a limited aperture of the transmit transducer actually produces energy which is not, at the edges of the injection footprint, at a different phase velocity. 
     When clamped to a plastic pipe, however, these edges are not discriminated against. This results in the receive signal obtaining sonic signals that travel at a variety of angles in the liquid. The resultant multipath signals, each arrive at the receive transducer at a slightly different time, and cause further distortion and calibration instability. 
     Therefore, a need exists for an apparatus for accurately measuring flow in flexible vessels, such as plastic or rubber tubes and pipes. 
     SUMMARY OF THE INVENTION 
     An apparatus for measuring flow in flexible tubes, in accordance with the present invention, includes a housing including a first portion configured and dimensioned for receiving a first transducer and a second transducer therein and a second portion adapted to attach to the first portion to encapsulate a flexible tube between the first and second portion without cutting off flow within the tube. A plate is disposed within the housing in contact with the tube. The plate is sonically matched to the transducers to permit sonic energy transmitted from the first transducer to travel along the plate to provide sonic radiation from the plate to be received by the second transducer to measure flow characteristics within the tube. 
     In other embodiments, the first and second transducers may be disposed on a same side of the tube to operate in a reflect mode. A second sonically matched plate may be disposed on the same side of the tube as the first and second transducers to carry Sonically transmitted signals through the second plate to provide a reference signal. 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will be described in detail in the following description of preferred embodiments with reference to the following figures wherein: 
     FIG. 1 is partial cross-sectional view of a housing showing aspects of an apparatus for measuring flow in flexible vessels in accordance with the present invention; 
     FIG. 2 is a side view of a housing showing a flexible tube in cross-section with a cover in an open position in accordance with the present invention; 
     FIG. 3 is a side view of a housing showing a flexible tube in cross-section with a cover in a closed position in accordance with the present invention; 
     FIG. 4 is a side view of a housing showing a rigid tube in cross-section with a cover in a closed position and the pipe being held by a biasing means in accordance with the present invention; 
     FIG. 5 is a side view of a housing showing a rigid tube in cross-section with a cover in an open position after releasing the cover from biasing the pipe in accordance with the present invention; and 
     FIG. 6 is partial cross-sectional view of another embodiment of an apparatus for measuring flow in flexible vessels in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention relates to flow measurements and, more particularly, to sonic flow measurement devices for flexible vessels. The present invention includes an apparatus for measuring flow in flexible vessels such as tubes and pipes. The present invention encapsulates or confines a portion of the flexible vessel to maintain contact with the vessel and to fix the geometry of the flexible vessel. The present invention employs sonic energy propagated through the flexible vessel wall and into the fluid stream within the flexible vessel using transducers. The sonic energy that passes through the far wall of the flexible tube is incident on a sonically matched surface which permits the sonic energy to travel along the sonically matched plate. This, in turn, produces a wide beam as the sonic energy travels along the sonically matched plate. The wide beam is reinjected into the liquid and is received by another transducer downstream of the propagation area of the sonic energy on the same side of the flex tube at the first transducer. An echo time can be measured which results in the flow parameters of the fluid being determined. 
     Referring now in specific detail to the drawings in which like reference numerals identify similar or identical elements throughout the several views, and initially to FIG. 1, an apparatus  10  in accordance with the present invention is shown. A transducer  12 , described in more detail below and in U.S. Pat. No. 4,425,803 incorporated herein by reference, produces a signal that meets the criteria for phase detection and phase correlation as described in U.S. Pat. No. 5,117,698, incorporated herein by reference. Transducer  12  contacts a flexible tube or pipe  14  to produce a sonic wave therein for measuring flow within tube  14 . Since tube  14  is flexible, it is necessary to encapsulate or restrict the volume of tube  14 . This assures the dimensions of tube  14  for flowrate computation purposes as well as for sonic transmission as will be described. Tube  14  is encapsulated in a housing  16 . Housing  16  includes mounting positions for at least two transducers, i.e., transducer  12  and transducer  18 . 
     Housing  16  may include a clam shell design as shown in FIGS. 2 and 3 where a cover  20  is hingedly connected to housing  16 . Alternately, housing may include a split half design or other design which may be placed on a mid-section of a tube. To accommodate the various tube sizes, transducers may be adjustable in tube diameter increments and/or and may be biased to compress tube  14 . As shown in FIG. 1, housing  16  includes a slot  22  and cover  20 , which when closed, fixes the axial and normal dimensions of tube  14  to conform to the slot dimensions. 
     In a preferred embodiment, slot  22  (see FIG. 2) dimensions may be adjusted to accommodate different tube sizes. It is expected that slot  22  may be slightly smaller than tube  14  so as to compress tube  14  to conform the dimensions thereof. Dependent on wall thickness of tube  14 , the area of the interior of tube  14  will be known, and taken into account for flow computations. Other pertinent information includes tube material, nominal diameter and wall thickness. This information is taken into account in the computation of flow from transit-time information obtained from the transducers, as is described below. 
     Transducer  12  is a transmit transducer which propagates the sonic energy in the fluid stream. Transducer  18  is a receive transducer which receives the propagated sonic energy (e.g., wide beam) further along tube  14 . The roles of transducers  12  and  18  may be switched, i.e., the receive transducer becomes the transmit transducer and vice versa. The receive transducer may be placed directly across tube  14  from the transmit transducer, (direct mode), or positioned to receive a reflected signal, (reflect mode) as depicted in FIG.  1 . 
     In direct mode, the receive transducer will not have to deal with multipath signals which are produced due to signal reflection from both the inner and outer pipe walls, as described above. This mode may be used only when poor sonic transmission of a tube wall minimizes a reflect mode signal excessively. 
     A preferred embodiment of the present invention employs reflect mode operation as shown in FIG. 1. A sonically matched plate  26  is included oppositely disposed relative to the placement position of transducers  12  and  18 . In one embodiment, sonically matched plate  26  includes a metal plate or other material capable of reflecting sonic waves. Sonically matched plate  26  is placed in contact with a wall of tube  14 . Sonically matched plate  26  has the material, wall thickness and waveguide velocity which matches the frequency and phase velocity of transducers  12  and  18  (hence, sonically matched). 
     Accordingly, when a sonic wave  31 , which passes through a fluid  28  from the transmit transducer (transducer  12  in this case), also passes through walls  30  of tube  14  and onto plate  26 , the waveguide properties of plate  26  are excited. Sonic energy travels down plate  26  in the direction of arrow “A”. This results in the re-transmission of sonic energy with full coherency as if the sonic signal was originating in a metallic pipe, rather than a flexible tube. 
     The result of the present invention is that a coherent signal  32  originating from an outer wall of tube  14  has much more amplitude than any of the other signals, say, reflected from an inner wall, or having a phase velocity different from the waveguide properties of plate  26 . Advantageously, edge waves radiated from the transmit transducer due to its non-infinite aperture are also discriminated against, i.e., the coherent signal is recognizable over edge waves due to end effects of the transmit transducer. Accordingly, the receive signal exhibits singlepath, rather than multipath, characteristics, that are of excellent shape, coherency and low resonance. 
     Another aspect of the present invention is that the Wide Beam generated by sonic energy ( 32 ) flowing in sonically matched plate  26  retains its coherency regardless of the sonic propagation of the fluid. Typically, the sonic propagation of fluid in tube  14  may vary with chemical or physical properties of the fluid as well as the temperature of the fluid. The present invention will act as if a flexible tube, for example, plastic, rubber, etc., was a liner within a metallic pipe wall. Computing flow for the present invention may be performed using a computer or data acquisition device. The computer or data acquisition device retains its calibration accuracy and sonic waveshape even as a liquid sonic beam angle varies with the sonic propagation velocity of the fluid. 
     Receive transducer  18  may be spaced apart sufficiently from transmit transducer  12  such that an initial reflection  17  of the transmitted ultrasound is not directed to receiver transducer- 18 . In this way, the internal reflections of the flexible tube  14  are sufficiently attenuated and have little influence on the measured signal. 
     Referring to FIGS. 2 and 3, a particularly useful embodiment of apparatus  10  is shown. Apparatus  10  includes housing  16  with cover  20  attached by a hinge  34 . A cable connection  36  is provided for powering transducers  12  and  18  (FIG. 1) and transmitting signals for calculating flow measurements. Flow measurements may include echo times or other information used in determining fluid velocity and flow rate. Other signals may also be transmitted. The transmitted signals are preferably received by a computer or data acquisition device (not shown) through cable  38  to be processed or stored to be processed at a later time. 
     A flexible tube  14  is placed within slot  22 . Cover  20  is then rotated in the direction of arrow “B” to close cover  20  and encapsulate tube  14 . Cover  20  includes a recess  40  for mounting sonically matched plate  26 . Sonically matched plate  26  is brought into contact with tube  14  by closing cover  20 , and sonically matched plate  26  is locked in place using a latch  42  or other locking device to maintain cover  20  is a closed position. Sonic flow measurements may now be made for fluids flowing in tube  14 . 
     It should be understood that the present invention has a wide range of applications. For example, non-metallic tubes or pipes are used in a variety of application where metallic pipes are not suitable, for instance, in the medical arts where sterilization is important, in the food industry, sanitation, pharmaceutical or other industries or application. The present invention is a likely candidate for installation into machines made by others for measurement and control of fluid flow as may be required by their device. Accordingly, it is intended that there be many embodiments, each configured for the benefit of a special purpose device. The “clamshell” embodiment may be modified accordingly. In some cases direct mode transmission may be needed, and in others reflect mode. 
     Referring to FIG. 4, the present invention may be applied to rigid pipes  102  such as thin metal pipes, glass pipes or other pipes in the form of a removable apparatus  110 . Cover  120  is biased using a biasing means  121  which may include a coil spring, rubber band or a similar device made of an elastic material which is hingedly attached to cover  120 . A latch  124  is provided to capture biasing means  121 . Alternately, the latch  124  may be placed on cover  120  and biasing means  121  may be hingedly attached to housing  16 . In operation, biasing means  121  is released from latch  124  to open cover  120  to install or remove pipe  102  from apparatus  110 . Cover  120  may be made from a compliant material to prevent damage to pipe in closing cover  120 . In alternate embodiments, hinge  130  may be omitted and replaced by a biasing means  121  and a latch  124  such that installation and removal is performed by securing both sides of cover  120  with two or more biasing means  121  and latches  124 . 
     Referring to FIG. 5, another embodiment of the present invention may be applied to rigid pipes  102  such as thin metal pipes, glass pipes or other pipes in the form of a removable apparatus  112 . Cover  120  is biased using a biasing means  123  which may include a leaf spring, Belleville spring or a similar device which is attached to cover  120 . Latches  124  are provided to capture arms  128  which are hingedly attached to cover  120 . Alternately, the latches  124  may be placed on cover  120  and arms  128  may be hingedly attached to housing  16 . In operation, arms  128  are released from latches  124  to open cover  120  to install or remove pipe  102  from apparatus  112 . In an alternate embodiment, cover  120  may be made from a compliant material with a raised portion of the cover as a biasing means  123  to prevent damage to pipe in closing cover  120  to thereby secure pipe  102 . 
     In FIGS. 4 and 5, slot  122  is dimensioned and configured to receive the rigid pipe  102 . Cover  120  is then closed to secure the pipe  102  in place. Since the pipe is rigid a matched plate  26  is no longer needed as the pipe itself can provide needed reflections to measure flow therein. Apparatus  110  and apparatus  112 , may also be used with a matched plate  26  for flexible tubes or pipes as described above. 
     Referring to FIG. 6, an apparatus  210  in accordance with another embodiment of the present invention is shown. Apparatus  210  includes a plate  208  on a same side of transducers  12  and  18 . Transducer  12  contacts plate  208  to produce a sonic wave therein for measuring flow within tube  14 . Ultrasonic energy from transducer  12  not only travels in tube  14  and the fluid flowing thereon, but travels in plate  208  in the direction of arrow “C”. Plate  208  functions as a beam splitter, permitting some sonic energy to flow into tube  14  and through the fluid therein and some sonic energy travels in plate  208 . Plate  208  preferably includes the properties described for plate  26  (e.g., sonically matched, etc.). The sonic signal traveling along plate  208  may be employed as a built-in reference signal. This signal may be employed to zero out noise, temperature effects or any other discrepancies encountered during flow characteristic measurements. The signal traveling down plate  208  is a high velocity, short path signal that does not travel through the fluid of tube  14 . This enables independent viewing of the transmitted ultrasonic signal. 
     For example, if one of transducers  12  or  18  is subjected to a higher temperature than the other transducer, zero drift may be experienced when comparing the transmitted and received signals. That is, a higher or lower flow may erroneously be measured. This error may be zeroed out by employing the sonic energy (signal) in plate  208  as a reference. This makes the ultrasonic measurements very robust and highly reliable by eliminating detrimental effects which may cause error in the measurements. The embodiment described with reference to FIG. 6 may be employed with or without plate  26 . Plate  208  may be employed in any ultrasonic system where a reference signal would be useful. 
     Having described preferred embodiments of an apparatus for sonic flow measurements for flexible vessels (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.