Abstract:
A method and apparatus for measuring the flow rate of a fluid based on the fluid weight. A container is provided between a fluid source and a fluid removal system. A valve is arranged between the fluid source and the container, to control the admitting of fluid into the container from the source, and removal of fluid from the container by the removal system. The valve is controlled by a weight-responsive mechanism, which detects a change in weight of the container due to the admitting and removal of fluid, and opens or closes the valve accordingly. A flow rate of the fluid may be determined in terms of a time period between the closing and subsequent opening of the valve.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a method and apparatus for efficiently metering the flow of a fluid being removed from a container and, more particularly, to a method and apparatus for metering the flow rate by a weight of the fluid which is delivered per unit of time, in order to allow accurate measurement and control of the amount of fluid being removed.  
           [0002]    Fluids which are delivered in bulk quantities for various applications typically utilize metering systems for measuring and controlling the amount of fluid delivered. An example of such an application is in the delivery of water treatment chemicals to cooling towers, boilers and other similar systems. Such an application would typically use a fluid delivery system such as a metering pump. While metering pumps can be set up to accurately dispense the chemicals, over time the pump may lose accuracy due to conditions such as, but not limited to, changes in inlet or discharge pressure, losing pump prime, outgassing from the fluid product, causing “airlock”, or damage to the supply or delivery lines. These conditions can result in a reduction of metering accuracy, or even stopping fluid delivery entirely.  
           [0003]    In view of the foregoing, there is a need to verify that a fluid delivery system is functioning and how much fluid it has actually delivered. One existing system for metering fluid uses a volumetric method to measure fluid delivery. However, a volumetric system has disadvantages. For example, because fluid density and therefore volume are functions of temperature, equipment for measuring fluid in a volumetric system may need to be calibrated for temperature. Therefore, variations in temperature during product delivery over a period of time can introduce inaccuracies into measurement.  
           [0004]    Accordingly, a metering system is needed which is easily repeatable and maintains accuracy over a range of temperatures.  
         SUMMARY OF THE INVENTION  
         [0005]    A method and apparatus according to the present invention provides for improved accuracy of measurement of a rate of fluid delivery. A weight of a fluid being delivered is measured in timed cycles to provide for greater accuracy of measurement over a range of temperatures.  
           [0006]    In a preferred embodiment, a metering device is connected between a fluid source and a fluid removal system such as a pump. The device includes an intermediary container having an inlet from the fluid source controlled by a valve. Weight-responsive means engaging the container control the valve to admit fluid into the container from the source. The weight-responsive means detect a change in the weight of the content of the container due to the fluid, and close the valve in response to the change in weight. The fluid removal system subsequently removes fluid from the container. The weight-responsive means detect a change in the weight of the container due to the removal of fluid, and subsequently re-open the valve to admit fluid. Repeating time periods between the closing and opening of the valve can thus be used for measurement of the fluid flow rate in terms of its weight. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 shows a metering device according to the present invention in a state in which an intermediary container is being filled with fluid from a bulk fluid source;  
         [0008]    [0008]FIG. 2 shows the metering device in a state in which a control switch has opened in order to shut off an inlet valve from the fluid source;  
         [0009]    [0009]FIG. 3 shows the metering device in a state in which the inlet valve from the fluid source is closed, and fluid is being pumped from the container;  
         [0010]    [0010]FIG. 4 shows the metering device in a state in which enough fluid has been offloaded from the container to close a control switch;  
         [0011]    [0011]FIG. 5 shows the metering device in a state in which enough fluid has been offloaded from the container to disconnect a different or separate control switch to trigger the opening of the inlet valve;  
         [0012]    [0012]FIG. 6 shows the metering device with the inlet valve from the source open for refilling the container;  
         [0013]    [0013]FIG. 7 shows a timing diagram for switches for controlling the opening and closing of the inlet valve and for determining a timing period for measuring flow rate of the fluid;  
         [0014]    [0014]FIG. 8 shows a control system for the metering device; and  
         [0015]    FIGS.  9 - 14  show an alternative embodiment for the metering device. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Referring now to FIG. 1, an embodiment of a metering device according to the present invention is shown. The metering device comprises a valve  1  in a feed line  2  connected between a bulk fluid source (not shown) and a fluid removal system such as a pump (not shown). A feed line  3 , which may be a flexible connection, is connected to the feed line  2  between the valve  1  and the pump, and also connected to an intermediary container  4 .  
         [0017]    The container  4  is engaged by weight-responsive means for controlling the opening and closing of the valve  1  based on a change in weight of the container  4 . In an embodiment, the weight-responsive means includes a weight-triggered device such as balance arm  8 . The container  4  is positioned at one end of the balance arm  8 . At the other end of the balance arm  8 , a fixed weight  6  and an adjustable weight  7  are positioned. The balance arm is pivotable about a pivot point  10 .  
         [0018]    The weight-responsive means further include a separable fixed weight  6  having a member  11 , an adjustable weight  7 , and control switches  5  (S 2 ) and  9  (S 1 ). In FIG. 1, member  11  is shown in contact with control switch  5 . The fixed weight  6  is in contact with control switch  9  on the balance arm  8 .  
         [0019]    Adjustable weight  7  may be provided for adjusting the metering device in accordance with the fluid density in order to compensate for fluid products of different densities, but it is noted that adjustable weight  7  is not necessary to the operation of the metering device.  
         [0020]    A description of a metering process according to the invention follows. In a phase of the process, the metering device may have the state shown in FIG. 1. In FIG. 1 control switches  5  and  9  are both ON, causing valve  1  to be open. When valve  1  is open, fluid flows from the source, for example, by means of a gravity feed, through feed line  2 , through the valve  1 , through feed line  3  and into the container  4 .  
         [0021]    When sufficient fluid has entered the container  4 , the metering device may assume the state shown in FIG. 2. In FIG. 2, sufficient fluid has been delivered to the container  4  that the container  4  is heavier than the combined weight of the fixed weight  6  and the adjustable weight  7 , causing the balance arm  8  to pivot about pivot point  10  in a counterclockwise direction. The pivoting of the balance arm causes member  11  to break contact with control switch  5 , turning switch  5  OFF.  
         [0022]    When control switch  5  changes from ON to OFF, the metering device may assume the state shown in FIG. 3. In FIG. 3 valve  1  is closed and thus no fluid enters the container  4  from the fluid source.  
         [0023]    Fluid may then be removed from the container  4  using the pump. In FIG. 4 sufficient fluid has been removed from the container  4  that the content of container  4  has substantially the same weight as the combination of fixed weight  6  and adjustable weight  7 , causing balance arm  8  to pivot in a clockwise direction. The pivoting of the balance arm  8  brings member  11  into contact with control switch  5 , turning control switch  5  ON. Control switch  9  has remained ON due to its contact with fixed weight  6 .  
         [0024]    In typical actual practice, the closing of the valve  1  is not instantaneous and pressure from the fluid source is a factor in causing fluid to continue to enter the container  4  during the transition from the state shown in FIG. 2 to the state shown in FIG. 3. Accordingly, for repeatability and accuracy of measurement, a timing cycle for measuring the rate of fluid removal from the container  4  would preferably begin substantially at the instant the device assumes the state shown in FIG. 4, when the container  4  and weights  6  and  7  are balanced. It is noted that the moment arms between the centers of gravity of the container  4  and weight  6  may not be equal.  
         [0025]    After sufficient fluid has been removed from container  4 , the metering device may assume the state shown in FIG. 5. In FIG. 5 sufficient fluid has been removed from container  4  that container  4  is now lighter than adjustable weight  7 . This condition causes balance arm  8  to rotate in a clockwise direction sufficiently to break the contact between control switch  9  and fixed weight  6 , turning control switch  9  OFF. Control switch  5  remains ON due to its contact with member  11 . When the metering device assumes the state shown in FIG. 5, measurement of the timing cycle may end.  
         [0026]    When control switch  9  is turned OFF, the valve  1  is again opened as shown in FIG. 6. When the valve  1  is opened, fluid again flows from the fluid source through the feed line  2 , the valve  1  and feed line  3  into the container  4  to refill the container  4 . Subsequently, the metering device resumes the state shown in FIG. 4 and an identical measuring cycle begins.  
         [0027]    A timing diagram for control switches  9  and  5  (S 1  and S 2 , respectively) is shown in FIG. 7. A fill period I corresponds to the states of the metering device shown in FIG. 6 through FIGS. 1, 2 and  3 , in that order. At the end of a cycle as shown in FIG. 5, S 1  is OFF and S 2  is ON, causing valve  1  to be open and fluid to enter the container  4  from the fluid source, as shown in FIG. 6. Then, when enough fluid enters container  4 , balance arm  8  pivots to bring S 1  into contact with fixed weight  6  as shown in FIG. 1, and filling of container  4  continues. As noted above, because the valve typically does not close instantaneously, the fill period I may include a period in which fluid continues to enter the container  4  while the valve is closing as shown in the transition from FIG. 2 to  3 .  
         [0028]    Next, in time period II, measurement of a repeatable time versus change-in-weight cycle begins. The time period is triggered by S 2  being turned ON as shown in FIG. 4. When S 2  is turned ON following the closing of valve  1 , the container  4  and the known weights  6  and  7  are substantially balanced. Subsequently, fluid is removed from container  4  until contact is broken with S 1  as shown in FIG. 5. The time between S 2  turning ON and S 1  turning OFF is measured, and the weight of fluid removed during that time can be calculated since the moment arms between the pivot point  10  and centers of gravity of the container  4  and weights  6  and  7  are known.  
         [0029]    When contact is broken with S 1 , causing valve  1  to open and allow fluid to enter container  4  again, a fill period III identical to fill period I begins. Then, a timing cycle IV identical to timing cycle II is entered. Alternating fill periods followed by timing periods identical to periods I and III, and II and IV, respectively, may continue as long as fluid is being pumped.  
         [0030]    A possible control system for controlling the opening and closing of the valve  1  and measuring time periods therebetween is shown in FIG. 8. In FIG. 8, a control unit  12 , which could be embodied, for example, as a microprocessor is shown. The control unit  12  is connected to switches S 1  and S 2  and valve  1 . The control unit would include time measurement capabilities, calculation capabilities, and control capabilities for turning valve  1  on and off in response to changes in state of switches S 1  and S 2  as shown in the timing diagram in FIG. 7.  
         [0031]    In a preferred embodiment, the time periods when the valve  1  is open and the intermediary container  4  is being refilled, as shown in periods I and III, are short compared with the time spent pumping fluid from container  4 , as shown in periods II and IV.  
         [0032]    Alternative methods for programming the above-described control system could be used. For instance, continuous pumping at a constant rate could be assumed. In this case, fluid could be pumped both from the fluid source and the container  4  during fill periods. The control system would be programmed to measure the time periods between S 2  turning ON following the closing of the valve, and S 1  turning OFF, calculate the weight of the fluid removed during that time, and calculate the corresponding rate of fluid removal. The time for the fill period would also be measured, and the weight of fluid removed would be assumed to correspond to the calculated flow rate. For example, if a fill period was one minute long, and a time period between S 2  ON and S 1  OFF was 9 minutes and 9 pounds of fluid was pumped, a flow rate of 1 pound per minute would be calculated.  
         [0033]    Alternatively, the control system could be programmed to control the pump to operate only when the valve  1  was fully closed following the filling of container  4 . In this way, it would be assured that fluid was only being removed from the container. Means also exist for controlling the fluid source to ensure that a negligible amount of fluid enters the container during the closing of the valve. This would permit calculations based on the assumption that the container  4  and the weights  6  and  7  are substantially balanced immediately following the breaking of contact with S 1  as shown in FIG. 2 to be reasonably accurate.  
         [0034]    Other possible embodiments for the metering device include using two valves, or a larger valve, to fill the container  4 , to ensure that container  4  fills at a much greater rate than it empties.  
         [0035]    Also, instead of weights  6  and  7  as described above, force-exerting means such as an adjustable spring could be used in connection with a pivoting end of the balance arm  8 , to exert a force on the pivoting end. The spring would extend within a short range which would cause it to exert an essentially linear force. Because the switch points are stationary, the metering process would be repeatable.  
         [0036]    An embodiment using an adjustable spring is illustrated in FIGS.  9 - 14 . The status of switches  5  (S 2 ) and  9  (S 1 ) in FIGS.  9 - 14  correspond to the status of the same-numbered switches in FIGS.  1 - 6 , respectively. However, the weight responsive means utilizes an adjustable spring  15  connected to a pivoting end of the balance arm, rather than weights  6  and  7 .  
         [0037]    As can be seen in FIG. 9, adjustable spring  15  is connected between an end of balance arm  8   a  and a fixed point  16 . The spring is connected to a pivoting end  18  of balance arm  8   a . Pivoting end  18  pivots about a second pivot point  17 .  
         [0038]    In FIG. 9, the metering device is in a state in which pivoting end  18  is in a non-pivoted state, causing it to be in contact with both switch  5  and switch  9 . Thus, switches  5  and  9  are both on, allowing fluid to enter container  4  from a fluid source.  
         [0039]    Subsequently, as shown in FIG. 10, sufficient fluid has entered container  4  to cause pivoting end  18  of balance arm  8   a  to break contact with switch  5 , while switch  9  is still on. The change in switch  5  from an ON status to an OFF status causes valve  1  to close so that the metering device assumes the state shown in FIG. 11. Pivoting end  18  is still in a non-pivoted state.  
         [0040]    Fluid is then removed by pumping from container  4  through line  3 , causing contact to be reestablished with switch  5  as shown in FIG. 12. At this point, a timing cycle for measurement of the rate of removal of fluid from container  4  would begin.  
         [0041]    As shown in FIG. 13, as fluid is removed from container  4 , adjustable spring  15  exerts a linear pressure on pivoting end  18  of balance arm  8   a , causing it to pivot in a counter-clockwise direction about second pivot point  17 , thereby breaking contact with switch  9 , while switch  5  remains on. When switches  5  and  9  assume this state, valve  1  opens again as shown in FIG. 4 to permit re-filling of container  4 .  
         [0042]    As timing diagram for the embodiment shown in FIG. 9- 14  would be the same as that shown in FIG. 7.  
         [0043]    In yet another embodiment of the invention, the adjustable spring  15  shown in the embodiment described in FIG. 9- 14  could be replaced by a weight.  
         [0044]    It may be appreciated from the foregoing discussion that the metering device described in the foregoing provides for an easily repeatable method of determining a flow rate of a fluid based upon the weight of the fluid, and therefore offers improved accuracy of measurement over a range of temperatures.  
         [0045]    The foregoing description of the invention illustrates and describes the present invention. Additionally, the disclosure shows and describes only the preferred embodiments of the invention, but is to be understood that the invention of capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings and/or the skill or knowledge of the relevant art. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention. Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments.