Abstract:
A flow measurement cartridge assembly for measuring liquid flow in a partially filled channel and a method for measuring liquid flow using the cartridge assembly, the cartridge assembly comprising: a frame for insertion into a discharge opening of the channel; a level detector secured in the frame for determining a liquid level in the channel; and at least one flow measurement device secured in the frame.

Description:
FIELD OF THE INVENTION 
     The present invention relates to apparatuses and methods for measuring liquid flow in partially filled pipes and other channels. More particularly, but not by way of limitation, the present invention relates to apparatuses and methods for measuring velocities, rates, and other flow parameters in waste water treatment, irrigation, and other water and waste water systems. 
     BACKGROUND OF THE INVENTION 
     The systems heretofore used in the art for measuring the flow of water or waste water in a partially filled pipe or other channel have typically relied upon combinations of pressure cells and velocity sensors which are individually installed within the channel. In order to determine the depth of the flow in the partially filled channel, the pressure cell is mounted on the bottom of the channel to measure the amount of hydrostatic pressure head produced by the flowing fluid. Once the depth of fluid flow is known, the cross-sectional area of the flowing stream can be determined based upon the known cross-sectional shape and dimensions of the channel. The rate of fluid flow is then calculated by multiplying the cross-sectional area of the fluid flow by the flow velocity. 
     Unfortunately, the pressure cell systems heretofore used in the art have significant shortcomings. The accuracy of the pressure cell system depends upon the pressure cell being mounted precisely on the bottom of the channel and upon the pressure cell and the velocity sensor(s) being in precise vertical and horizontal alignment. Precisely mounting and aligning the pressure cell system components in the field is difficult and time consuming. In addition, considerable time and effort is required when using the prior art pressure cell systems for field calibration, validation, programming, and channel profiling. Moreover, the pressure cells used in these systems are highly susceptible to fouling and sediment build-up which affects the accuracy of the sensor and eventually renders the sensor inoperable. Consequently, the pressure cell must be frequently removed and cleaned. 
     One type of velocity sensor preferred for use in partially filled channels is a chordal, transit-time sensor comprising a pair of piezoelectric elements which are mounted on opposite sides of the channel. The elements must be beneath the fluid flow for operation and are typically mounted at a height of at least one-quarter, more preferably about one-third, of the vertical inside diameter of the channel. Transit-time velocity sensors are effective for determining the chordal velocity of the fluid across the entire path of the fluid flow. In addition, the sensor elements are highly resistant to fouling and are not susceptible to drift problems, variable water surface problems, or non-uniform particle distribution problems which are frequently encountered with other systems. The transit-time velocity sensor elements are also designed to prevent accumulation of rags, branches, and other debris. 
     Unfortunately, as indicated above, it has heretofore been difficult and time consuming to mount and precisely align the velocity sensor elements with each other and with the pressure cell for proper operation and accuracy. 
     As an alternative to the use of transit-time velocity sensors, trapezoidal flume structures have sometimes been used for measuring fluid flow in partially filled channels. Based upon the depth of flow through the trapezoidal flume, the rate of fluid flow can readily be determined using known flume equations recognized by the U.S. Bureau of Reclamation. Trapezoidal flumes are generally effective over a broad range and have a flat bottom design which is generally effective for preventing the accumulation of sediment or debris. 
     Although trapezoidal flume structures are resistant to fouling and sediment accumulation, the proper installation and alignment of these systems in the field is difficult and time consuming and typically requires that the operation of the water or waste water system in question be disrupted for a considerable period of time. 
     It is also known in the art that an ultrasonic transducer installed in the top of a partially filled pipe or other channel can be used to determine and monitor the fluid level in the channel by transmitting an ultrasonic signal directly downward onto the fluid surface. However, in addition to being difficult to properly install and align, the ultrasonic sensor systems heretofore known in the art have not been capable of operation, or have only been capable of limited operation, in many channel systems. Ultrasonic sensors typically require a minimum signal transmission distance of about 12 inches or more. Thus, in order to operate an ultrasonic level sensor in a partially filled channel, it has heretofore been necessary for the liquid level in the partially filled channel to remain at least one foot below the ultrasonic transducer. These systems therefore have generally not been acceptable for use, for example, in pipes having diameters of less than about 24 inches or in applications where the liquid level will sometimes rise to within at least one foot of the top of the channel. 
     Thus, a need currently exists for a flow measurement system for partially filled channels which is accurate over a broad range of flows and is not susceptible to fouling or sediment buildup. A need particularly exists for a system of this type which can be quickly and easily installed in existing or new channel systems while ensuring that all of the system components are properly and precisely oriented and aligned. There is also a need for a system for measuring flows in partially filled channels which can be installed and activated substantially without the need for field calibration, flow profiling, and field programming and which does not require a significant amount of field validation. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the needs and alleviates the problems discussed above. In one aspect, there is provided an inventive ultrasonic level sensor assembly which is capable of operation in generally any size channel or container for accurately determining liquid levels in the channel or container ranging from 0% to substantially 100% of full. The inventive ultrasonic level sensor assembly preferably comprises (a) an ultrasonic transmitter which is oriented for transmission of an ultrasonic signal horizontally in the top of the channel or container and (b) a reflector which deflects the horizontal signal vertically downward toward the fluid surface. In order to allow the inventive ultrasonic sensor assembly to continue to operate as the liquid level approaches the top of the channel or container, the reflector will preferably be spaced horizontally from the ultrasonic transmitter a sufficient length to account for the necessary signal transmission distance of the ultrasonic transmitter. Consequently, in most applications, the horizontal distance between the ultrasonic transmitter and the reflector will preferably be at least 12 inches. 
     In another aspect, there is provided a flow measurement apparatus comprising a cartridge assembly which can be removably inserted into a pipe or other flow channel. The cartridge assembly comprises a cartridge frame having a trapezoidal flume and a level sensor, both of which are preinstalled in the frame in correct orientation and alignment. The level sensor is preferably an inventive ultrasonic level sensor assembly of the type described above comprising an ultrasonic transmitter installed in the top portion of the frame for longitudinal transmission and a reflector positioned in the frame for directing the ultrasonic transmission signal downward onto the fluid surface. 
     The inventive cartridge assembly is preferably pre-sized for the specific application and can be conveniently inserted into any accessible channel discharge opening. As will be understood by those in the art, accessory discharge openings suitable for insertion of the cartridge assembly are commonly provided in water and waste water systems, for example, in manhole cavity structures. The cartridge assembly will preferably also include a built-in leveling device which will ensure that the cartridge is precisely installed in its correct horizontal and vertical orientation. 
     In another aspect, there is provided a dual range flow measurement apparatus which is similar to the inventive flow measurement apparatus described above but which also includes a velocity sensor which is preinstalled in the cartridge assembly. The velocity sensor is preferably a transit-time velocity sensor comprising a pair of velocity sensor elements which are preinstalled on opposite sides of the frame. Thus, when the fluid level within the channel is below the velocity sensor elements, the inventive dual range apparatus is operable for accurately measuring flow using the trapezoidal flume. However, when the liquid level is above the velocity sensor elements, the transit-time velocity sensor will be used for accurately determining flow within the channel. 
     Further aspects, features, and advantages of the present invention will be apparent to those in the art upon examining the accompany drawings and upon reading the following Detailed Description of the Preferred Embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational front view of a first embodiment  2  of the inventive flow measurement apparatus. 
         FIG. 2  is a cutaway elevational side view showing the inventive flow measurement apparatus  2  installed in a partially filled flow channel  4 . 
         FIG. 3  is an elevational front view of a second embodiment  102  of the inventive flow measurement apparatus. 
         FIG. 4  is a cutaway elevational side view showing the inventive flow apparatus  102  installed in a partially filled flow channel  104 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment  2  of the inventive flow apparatus utilizing an insertable cartridge assembly  6  is depicted in  FIGS. 1 and 2 . The cartridge assembly  6  comprises: a cartridge frame  8  having a flange  10  at its outer end; a trapezoidal flume  12  which extends from the outer flange  10  along a portion of the bottom of the frame  8 ; an ultrasonic transducer  14  secured to the outer flange  10  and oriented for transmitting an ultrasonic signal  16  longitudinally adjacent to the top of the frame  8 ; a reflecting surface  18  provided in the top of the frame  8  for directing the longitudinal/horizontal ultrasonic signal  16  vertically downward onto the fluid surface  22  as illustrated by the signal direction arrows  20 ; a leveling bubble element  24  secured in proper alignment to the outer flange  10  to correctly indicate the true horizontal and vertical alignment of the cartridge assembly  6 ; and a pair of outer handles  26  provided on the flange  10  for inserting and removing the cartridge assembly  6  and for rotating the cartridge assembly  6  to achieve the correct vertical and horizontal alignment as indicated by the leveling element  24 . 
     In  FIG. 2 , the cartridge assembly  6  of the inventive system  2  is shown as inserted into an outlet opening  28  of a pipe of other flow channel  4  which discharges into a manhole cavity  32 . Given the size of the flow channel  4 , the inventive cartridge assembly  6  can be completely preassembled and all of the components thereof can be precision aligned, precalibrated, and preprogrammed at the factory prior to delivery and installation. The inventive system  2  will also preferably include a flow meter, a flow chart, or a combination thereof (not shown) which can be of generally any type known in the art for displaying, logging, and/or transmitting fluid flows, levels, velocities, and/or other desired parameters. 
     The inventive ultrasonic level sensor assembly  15  comprising (a) the ultrasonic transducer  14  which transmits a horizontal signal  16  above the fluid surface and (b) the reflector  18  which redirects the ultrasonic signal downwardly toward the fluid surface, is particularly well suited for use in the inventive flow measurement system  2 . However, it also will be understood that the inventive ultrasonic level sensor assembly  15  can alternatively be installed and used independently for determining levels in pipes or other channels, containers, tanks, or other systems. The inventive ultrasonic level sensor assembly  15  is accurate to within ±0.02 inches and is not susceptible to the fouling and sediment buildup problems experienced with the prior art pressure sensor assemblies. 
     In the inventive level sensor assembly  15 , the ultrasonic transducer  14  is preferably positioned for transmitting the ultrasonic signal  16  horizontally above the fluid surface  22  and the reflector surface  18  is preferably oriented at a 45 degree angle for reflecting the ultrasonic signal directly downward onto the fluid surface  22 . In order to accurately determine the fluid level, the reflector surface  18  is horizontally spaced a known distance from the ultrasonic transducer  14 . 
     In addition, to ensure that the inventive ultrasonic sensor assembly  15  will continue to operate as the fluid level  22  approaches the top of the flow channel, container, or other system, the horizontal distance from the transducer  14  to the reflecting surface  18  will preferably be greater than the minimum required transmission distance for the ultrasonic transducer  14 . Thus, in most applications, the distance from the ultrasonic transducer  14  to the reflecting surface  18  will preferably be at least 12 inches. As the fluid level  22  approaches the top of the flow channel  4 , the inventive flow measurement system  2  is preferably programmed to detect a full channel flow condition when the reflector surface  18  is submerged and the reflector ultrasonic echo is thus lost. 
     The reflector surface  18  can be formed of any material effective for redirecting the ultrasonic signal onto the fluid surface. In the inventive flow measurement system  2 , the reflector surface  18  will preferably be a stainless steel surface provided by an upper support member  38  of the cartridge frame  8 . 
     Using the built-in trapezoidal flume  12  provided in the bottom of the cartridge assembly  6  in conjunction with the inventive ultrasonic level sensor assembly  15 , the rate of flow in the flow channel  4  can be determined to an accuracy of within ±3-5%. As indicated above, the determination of flow through the flume  12  is based upon known flow equations recognized by the U.S. Bureau of Reclamation. The trapezoidal flume system also provides accurate flow determinations over a broad turn down ratio (full to minimum flow) of 60:1. In addition, the flat bottom  40  of the trapezoidal flume  12  is effective for preventing fouling and sediment buildup. 
     A second embodiment  102  of the inventive flow measurement system is depicted in  FIGS. 3 and 4 . The inventive system  102  is essentially identical to the inventive system  2  except that the cartridge assembly  106  of the inventive system  102  also includes a transit-time velocity sensor  105  comprising a pair of transit-time velocity sensor elements  108  and  110  which are preinstalled on opposite sides of the cartridge frame  112  upstream of the built-in trapezoidal flume  114 . The transit-time sensor elements  108  and  110  will preferably be vertically spaced above the bottom of the flow channel  104  a distance of at least one-fourth of the vertical inside diameter of the flow channel  104 . The transit-time sensor elements  108  and  110  will more preferably be vertically positioned above the bottom of the flow channel  104  at about one-third of the vertical inside diameter of the flow channel  104 . 
     The inventive system  102  is thus a dual range measurement device which (a) provides accurate flow measurement at levels below the velocity sensor elements  108  and  110  using the trapezoidal  114  and the ultrasonic level sensor assembly  116  and (b) accurately determines flow at fluid levels above the velocity sensor elements  108  and  110  using the transit-time velocity sensor  105  and the ultrasonic level sensor  116 . The measurement accuracy of the inventive system  102  in the lower range is within ±3-5% with an effective turndown ration of 60:1. The measurement accuracy of the inventive system  102  in the upper range is within ±1-2% with an effective turndown ratio of 60:1. In addition, the inventive flow measurement system  102  is effective for accurately determining flow at liquid levels ranging from essentially 0% to 100% of full. 
     Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.