Abstract:
A flowmeter which clamps around and seals to a pipe with probes projecting into the pipe through holes in the pipe, the useful separation of the probes being achieved by their entering the pipe through separate holes.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority of Provisional application serial No. 60/336,659, filed on Dec. 5, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to instruments for measuring flow in pipes, and specifically to such an instrument that mounts on a pipe.  
         BACKGROUND OF THE INVENTION  
         [0003]    Flowmeters for measurement of flow through pipes may be divided into in-line types, in which the flowmeter interrupts the pipe, insertion types, in which a portion of the meter projects through the wall of the pipe, and external types, with which the pipe remains intact. Typically, insertion meters attach to the wall of the pipe at the point of entry, often by means of a fitting that is welded into the wall of the pipe. Consequently, the exact location of the sensing element within the pipe is dependent on the workmanship of the person installing the fitting, and this may compromise the accuracy of the measurement. Insertion flowmeters of the thermal type, which typically require a heated element and an unheated element, normally are designed to have the probes enter the pipe through a single opening. This requires that the hole in the pipe be large enough to accommodate both elements, and it constrains the spacing of the elements.  
         SUMMARY OF THE INVENTION  
         [0004]    This invention features a flowmeter for installation in existing compressed-air distribution systems. As compared with available flowmeters it provides advantages of low cost and ease of installation.  
           [0005]    The flowmeter operates on the well-known thermal principal by which one probe is heated and maintained warmer than a second probe, the amount of heat required to maintain the temperature difference being a measure of the fluid mass velocity. It incorporates novel features, primarily aimed at facilitating its installation. First, since the probes project individually into the pipe through separate holes, the holes that must be drilled are small, and the probes may be widely spaced to minimize interaction, particularly at low flow rates. Second, since the probes are located with reference to the outside surface of the pipe, their position is not dependent on the location of a fitting welded into the pipe. Further, since sealing means are incorporated into the device and it clamps securely onto the pipe, it can be installed without cutting or welding the pipe or adding fittings.  
           [0006]    One embodiment of the inventive flowmeter consists of two probes that project through drilled holes into a pipe, two split rings encircling the pipe in which the probes are mounted, and a control enclosure mounted on the rings. The rings resemble well-known shaft collars, each consisting of two halves that are pulled together by screws and thereby clamped onto a cylindrical surface. Each probe is mounted in a hole drilled in the corresponding ring. The control enclosure is attached to the rings with screws, and the wires from the probes pass through the rings and directly into the enclosure. A gasket is placed around each probe, between the ring and the pipe.  
           [0007]    A second embodiment of the flowmeter consists of two probes projecting through drilled holes into a pipe, a single split ring encircling the pipe in which the probes are mounted, and a control enclosure mounted on that ring. In other respects the second embodiment resembles the first.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Other objects, features, advantages and embodiments will occur to those skilled in the art from the following description of two embodiments and the accompanying drawings, in which:  
         [0009]    [0009]FIG. 1 is an overall view of one preferred embodiment of the inventive flowmeter mounted on a pipe.  
         [0010]    [0010]FIG. 2 is side view of one of the split rings of FIG. 1 that clamps to the pipe, with the associated probe and gasket.  
         [0011]    [0011]FIG. 3 is an enlarged view of one of the inventive probes.  
         [0012]    [0012]FIG. 4 is a sectional view showing the arrangement of the probes in the pipe for the embodiment of FIG. 1, and  
         [0013]    [0013]FIG. 5 is a functional block diagram of the inventive device.  
         [0014]    [0014]FIG. 6 is an overall view of the second embodiment of the inventive flowmeter mounted on a pipe, and  
         [0015]    [0015]FIG. 7 is a side view of the single split ring of FIG. 6 showing the associated probes and gasket. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    The invention constitutes a flowmeter of the thermal type designed in such a way that it is inexpensive to produce and easy to install on a pipe. Such a flowmeter typically employs two probes projecting into the fluid stream: an unheated probe that senses the temperature of the fluid, and a heated probe that is maintained at a temperature higher than that of the unheated probe, the amount of heat required being a measure of the flow rate. The invention concerns the arrangement of the probes and methods of mounting them so that the complete flowmeter may quickly and easily be installed on a pipe in a compressed-air distribution system.  
         [0017]    [0017]FIG. 1 is an overall view of one embodiment of the invention mounted on a pipe; FIG. 2 is a side view of one of the split rings that attach to the pipe with a probe mounted within the ring, and FIG. 4 is a sectional view of this embodiment mounted on a pipe. A control enclosure  101  is affixed by screws (not shown) to the upper portions  102  and  103  of two split rings. The lower portions of the rings  104  and  105  are attached by screws to the upper portions of the rings, these screws being tightened to secure the assembly firmly to the pipe  106 . The control enclosure includes a display  107  and a connector  108  for receiving power from an outside source.  
         [0018]    The split rings resemble commercially-available shaft collars. As such, the upper portion of each ring  201  (FIG. 2) has threaded holes  202 ,  203  for screws  204 ,  205 . The lower portion of each ring  206  has counterbored holes  207 ,  208  for the screws, and the screws are included with the assembly. The upper portion of each ring has a flat  209  and two threaded holes  210 ,  211  to facilitate mounting of the control enclosure, and stepped hole  212  large enough in its lower portion to accept a cylindrical probe  213 , and small enough in its upper portion to prevent the probe from being forced out. Each probe is affixed and sealed in the corresponding ring by an adhesive, such as epoxy. A gasket  214  is adhered to the inside of each ring, surrounding the probe. These gaskets form a seal against the pipe when the screws holding the halves of the split rings together are tightened. The gasket material may be oil-resistant rubber or a pliable fibrous material suitable for use with compressed air.  
         [0019]    [0019]FIG. 3 shows one of the probes. Each probe comprises a sensing tip  301  that includes an RTD for heating and temperature sensing, mounted within a plated copper body, and a supporting post  302 . The sensing tip is designed for good thermal conduction between the RTD and the outside surface of the tip, while the supporting post is designed for minimal heat flow between the sensing tip and the supporting ring. The post may be a thin-walled stainless steel cylinder. The post may extend over the cylindrical surface of the tip as long as a good thermal bond is provided between the post and the tip by means of thermally conductive epoxy or similar material.  
         [0020]    [0020]FIG. 4 is a sectional view showing the flowmeter of FIG. 1 mounted on a pipe, with the two probes projecting into the fluid. The heated probe  401  and the unheated probe  402  project through drilled holes  403  and  404  into the pipe  405 . The probes are displaced longitudinally along the pipe, making it possible to separate them further than would be possible with probes placed side-by-side, particularly in a relatively small diameter pipe. Doing so minimizes the interaction between the probes.  
         [0021]    The heated probe may be placed upstream or downstream of the unheated probe. If it is upstream, the unheated probe will be warmed slightly by fluid passing the heated probe. If it is downstream, the flow approaching it (the heated probe) will be somewhat disturbed by the presence of the unheated probe. In either case, if the probes are small in diameter in relation to their spacing (in a ratio of at least 1:15) the resulting errors are minimal and are largely eliminated by calibration. Also shown in section is the control enclosure  406  mounted on the upper portions of the split rings  407  and  408 . The gaskets  409  and  410  are shown between the rings and the pipe.  
         [0022]    [0022]FIG. 5 is a schematic illustration of the measurement process for the invention. The microcontroller  501  causes a switching circuit  502  to connect the heated probe  503  to a heating circuit  504  for a fixed period of time. The heating circuit compensates for the variation in resistance of the heated probe with temperature in order to provide a controlled amount of power for heating. At the end of the heating period, the microcontroller causes the heated probe to be connected to the comparison circuit  505 . Also connected to this circuit is unheated probe  506 . The comparison circuit determines the temperature difference between the probes on the basis of their resistances. When the heated tip has cooled so that it is within a pre-determined temperature differential of the unheated tip (typically within 10 degrees F.) the comparison circuit so indicates to the microcontroller, and the microcontroller initiates another heating cycle. On the basis of the amount of time since the start of the previous heating cycle, the microcontroller calculates the flow velocity (by interpolating in a lookup table) and it sends to the display  507  a signal representing the flow rate, calculated on the basis of the pipe size and the velocity. To minimize the heating of the tips by current used for measurement, the microcontroller causes the measurement circuit to be energized only when necessary for periodic comparisons of resistances.  
         [0023]    [0023]FIG. 6 and FIG. 7 show an alternative embodiment of the invention in which a single split ring is used to mount the probes and to support the enclosure. FIG. 6 is an overall view of the second embodiment of the invention mounted on a pipe; FIG. 7 is a side view showing the single split ring with two probes mounted within it. The control enclosure  601  is attached to the upper portion  602  of the split ring by screws (not shown). As with the first embodiment, the lower portion of the split ring  603  is attached to the upper portion by screws, securing the assembly onto a pipe  605 .  
         [0024]    [0024]FIG. 7 shows the single split ring of the second embodiment with two probes  701  and  702  mounted in drilled holes  703  and  704  in the upper portion of the split ring  705 . As in the first embodiment, a gasket  706  surrounds the probes; in this case a single gasket may be used to seal around both probes. In other respects the split ring(s) and the probes resemble those in the first embodiment. Other aspects of the invention, including the mode of operation and features of the control enclosure, are the same as in the first embodiment. To install the flowmeter, the user first removes air pressure from the air line where the meter is to be installed, and then drills the two holes required for the probes. Next he inserts the probes into the holes, and attaches the lower halves of the rings to the unit with the screws provided. Finally, he connects a suitable source of power to the unit, typically from a wall-plug adaptor, and turns on the compressed air. The display on the unit will now indicate air flow in units of mass flow rate (scfm).  
         [0025]    Although specific features of the invention are shown in some drawings and not others, this is for convenience only as some feature may be combined with any or all of the other features in accordance with the invention.  
         [0026]    Other embodiments will occur to those skilled in the art and are within the following claims: