Abstract:
A method for measuring the flow rate of a fluid using a differential pressure sensor is presented. In this method, two pitot tubes are positioned within in flowing fluid, creating a pressure differential that is converted to a voltage by a differential pressure sensor. The voltage is transmitted to a programmable microcontroller for computation of flow rate based on a calibration procedure that was been used to determine the relationship between voltage and flow rate. The microcontroller may also be used to correct for temperature variations, store fluid flow rates, calculate the total volume of fluid that has passed, transmit data, display data, modify the fluid flow, or automatically run a calibration routine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     [Not Applicable] 
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to a system and method for measuring pressure differential created by flowing fluids. More particularly, the present invention relates to a system and method for using pressure differential measurements to measure fluid flow rate and to calculate volumes of fluids passing through a pipeline inexpensively and accurately. 
     Using integrated circuit technology to bring cheap and efficient solutions to problems in developing countries helps assist philanthropic and government organizations around the world that are building schools, clinics, or homes for poor families. For example, using integrated circuit technology and electronics to develop a low cost off-grid solar water heating system has allowed digital monitoring of a number of inputs such as water temperature and controlled switch pumps to optimally move water according to thermodynamics principles. In dry regions of the world, water is a major concern in terms of both efficient usage and the cost of building, monitoring and maintaining a water distribution system. Monitoring water usage remotely and electronically in real time in these regions is important for distribution and billing purposes and eliminates the need for an individual to report readings periodically. The ability to build an accurate, reliable, and inexpensive electronic device with no mechanical moving parts compatible with water delivery and storage systems in developing countries is desirable. 
     Prior art systems allow a user to measure fluid flow rate and volume using pressure differential created by flowing fluids. For example, in Columns 4-5, Paragraphs 0067-0068, Wang et. al., U.S. Pat. Appl. No. 2009/0221986A1, describe a system for delivering medical fluids to a patient using a flow sensor module which monitors fluid pressure differential across a flow restrictor downstream of a flow valve. As further described in Column 6, Paragraphs 0078-0079, the flow sensor module includes both a flow restrictor and a differential pressure sensor that directly or indirectly measures pressure differential. 
     As another example, Wiklund et. al., U.S. Pat. No. 6,725,731, describe a system to measure differential pressure created by flowing fluids. As described in Columns 3-4, a flow restriction member is placed inside a pipe and a differential pressure sensor is embedded in said flow restriction member. In the embodiments described in Columns 3-4, a pressure drop is created by the flow restriction member and this pressure drop is sensed by the embedded pressure sensor. Furthermore, a separate temperature sensor is placed in the pipeline as well as a static pressure sensor as described in Column 5. Another embodiment of the system described by in Column 7 and FIG. 14 allows a differential pressure sensor to be proximate to the exterior of a flow sensor by configuring a flow restriction member such that flow is constricted in the pipe by narrowing the walls of the pipeline toward the center of the pipe and placing ports on either side of this constricted portion. 
     Another example of a technique to measure flow rate of fluids using pressure differential is described by Wiklund et. al., U.S. Pat. No. 5,817,950. As described in Columns 3-4 and FIGS. 1A-1C, an averaging pitot tube having a plurality of openings on a forward-facing and backward-facing surface is used to average pressure measurements taken across the entire flow of fluid or gas in a pipe. To adjust fluid flow calculations for temperature changes in the fluid flowing in a pipe, a separate resistive temperature device is positioned downstream from the averaging pitot tube, as described in Column 3 and FIG. 1A. 
     Another example of using pressure differential to measure velocity of flowing fluids is described by Amir et. al., U.S. Pat. No. 3,678,754. One embodiment of the device disclosed in Amir et. al. described in Column 1, relies on the use of a plate orifice placed inside a pipe where fluid is flowing to create pressure differences at two separate measuring taps along the pipeline. A separate embodiment, described in Columns 2-3, relies on a concentric or double pitot tube placed in a single location in the pipeline to create pressure measurements that move a piston inside a cylinder. The movements of this piston reflect pressure differential measurements that are recorded either using a pen making a trace on paper, or by visually noting how far the piston moves relative to etchings on the glass column in which a piston moves, as described in as described in Column 2. As described in Column 3, the device is limited to detection of fluid flow rates of 0.36 liters per hour. 
     The prior art systems for measuring fluid flow rate and volume using pressure differential have several disadvantages. First, the systems of Wang et. al., Wiklund et. al. (&#39;731), and Amir et. al. require that a flow restriction is placed on the fluid that is flowing inside a pipe or tubing to generate a differential pressure. The systems of Wang et. al. and Wiklund et. al. (&#39;950) further require that a separate temperature measurement be taken to allow a user to obtain accurate fluid flow information. 
     Next, the systems of Wiklund et. al. (&#39;950) require that an averaging pitot tube be placed across the entire flow space of a pipe or tubing and require that a user place the plurality of openings in the averaging pitot tube at specific distances relative to the exterior and center of the pipe carrying a flowing fluid. Because the averaging pitot tubes employed by Wiklund et. al. (&#39;950) cross the entire diameter of the pipe through which fluid flows, they necessarily restrict fluid flow. Furthermore, because these systems utilize averaging pitot tubes with different shapes and sizes, they must be calibrated to the particular shape and size of the averaging pitot tube, must rely on a separate temperature measurements, and must include an estimate of the static pressure to be accurate. 
     Finally, the device of Amir et. al. requires that mechanical moving parts be employed to allows the measurement of pressure differential. Furthermore, the device of Amir et. al. requires that measurements be recorded with paper or by visualizing movement of a piston relative to glass etchings on the outside of a cylinder. 
     BRIEF SUMMARY OF THE INVENTION 
     One or more of the embodiments of the present invention provide systems and methods for measuring pressure differential. The system is comprised of a meter device, low pass filter, a microcontroller, and a control system. The meter device is comprised of fluid piping, a first pitot tube, a first tubing, a second pitot tube, a second tubing, and a pressure sensor. The first and second pitot tubes are connected to the pressure sensor with the first and second tubing. The low pass filter is connected in between the pressure sensor and microcontroller. The meter device is in unidirectional communication with the microcontroller. The microcontroller is in unidirectional communication with the control system. 
     In operation, the microcontroller is programmed using a control system to fit voltage to a second order polynomial representing fluid flow rate through a pipeline. The first and second pitot tubes are positioned in a fluid piping such that one end is inside the pipe and the other end passes through the exterior wall of the pipe. Fluid flowing across the first pitot tube creates positive pressure in the first pitot tube that is transferred through the first tubing to the pressure sensor. Fluid flowing through across the second pitot tube creates negative pressure that is transferred through the second tubing to the pressure sensor. The positive and negative pressure transferred from the first and second pitot tubes to the pressure sensor result in a pressure differential and create a voltage in the pressure sensor which is transmitted to through the low pass filter and then to the microcontroller. The microcontroller or control system may be used to store fluid flow rate data once data is fit to the polynomial and fluid flow rate is calculated. The control system or microcontroller may be used to monitor fluid flow rate and fluid volume flowing through a pipeline. In other embodiments, the control system or the microcontroller may be configured to open and close a control valve in a pipeline. A user may determine a volume or a time to close a pipeline and prevent fluid from flowing through a pipeline. A user may also program the microcontroller to calculate direction of fluid flow through a pipeline by using the magnitude of voltage output from the pressure sensor and transmitted to the microcontroller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of a system for measuring pressure differential according to an embodiment of the present invention. 
         FIG. 2A  is a cross sectional view of the meter device of  FIG. 1 . 
         FIG. 2B  is a top view of the meter device of  FIG. 1 . 
         FIG. 2C  is an axial view of the meter device of  FIG. 1 . 
         FIG. 3  is an illustration the configuration of the pressure sensor, first pitot tube, and second pitot tube, and the fluid piping of the meter device of  FIG. 1 . 
         FIG. 4  is an illustration a full anterior view of the meter device of the system for measuring pressure differential of  FIG. 1 . 
         FIG. 5  is an illustration the posterior view of the pressure sensor connection ports to the microcontroller of  FIG. 1 . 
         FIG. 6  is a graph of unfiltered voltage over time output by the pressure sensor as fluid is flowing through the meter device of  FIG. 1  at a constant rate. 
         FIG. 7  is a graph illustrating the fit of voltage readings to a second order polynomial enabling the calculation of fluid flow rate through the meter device of  FIG. 1 . 
         FIG. 8  is a graph illustrating the variation of voltage over time under stepwise adjustment of the fluid flow rate through the meter device of  FIG. 1 . 
         FIG. 9  is a graph illustrating the comparison of voltage readings (representing pressure differential) measured by a pressure sensor as related to fluid flow rate in two separate meter devices  110  of  FIG. 1 . 
         FIG. 10  illustrates a block diagram of an alternative system for measuring pressure differential created by a flowing fluid further including a control valve according to an embodiment of the present invention. 
         FIG. 11  is a flow chart of an embodiment of the invention for a method for measuring pressure differential created by a flowing fluid. 
         FIG. 12  is a flow chart of an alternative embodiment of the invention for a method to control fluid flow through a meter device and pipeline. 
         FIG. 13  illustrates a block diagram of a calibration system used to adjust data measurements taken by an individual meter device of  FIG. 1  before use in an existing pipeline. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a block diagram of a system for measuring pressure differential  100  according to an embodiment of the present invention. The system for measuring pressure differential  100  includes a pipeline  108 , a meter device  110 , a low pass filter  135 , a fluid flow indicator  140 , a microcontroller  150 , and a control system  170 . The meter device  110  further includes a fluid piping  105 , a first pitot tube  120 , a first tubing  121 , a second pitot tube  125 , a second tubing  126 , and a pressure sensor  130 . 
     In the system for measuring pressure differential  100 , the pipeline  108  is connected to the fluid piping  105  of the meter device  110 . The first pitot tube  120  passes from the center of fluid piping  105  through the external wall of the fluid piping  105  and is connected to the first tubing  121 . The first tubing  121  is connected to the pressure sensor  130  (as illustrated in  FIGS. 3A  and B) on the external wall of the fluid piping  105 . The second pitot tube  125  passes from the center of fluid piping  105  through the external wall of the fluid piping  105  and is connected to the second tubing  126 . The second tubing  126  is connected to the pressure sensor  130  (as illustrated in  FIGS. 3A  and B) on the external wall of the fluid piping  105 . The pressure sensor  130  of the meter device  110  is in unidirectional communication with the low pass filter  135  and the low pass filter  135  is in unidirectional communication with the microcontroller  150 . The microcontroller  150  is in bidirectional communication with the control system  170 . The fluid flow travels in the direction of the fluid flow indicator  140 . 
     In operation, fluid passes through pipeline  108  in the direction of the fluid flow indicator  140 . As fluid in the pipeline  108  passes through the fluid piping  105  of the meter device  110 , it flows across the section of the first pitot tube  120  located inside fluid piping  105  (as illustrated in  FIG. 2 ) and creates a positive pressure that is transferred from the first pitot tube  120  through the first tubing  121  to the pressure sensor  130 . As fluid continues to flow through the fluid piping  105  of the meter device  110 , it next flows across the section of the second pitot tube  125  located inside fluid piping  105  (as illustrated in  FIG. 2 ) and creates a negative pressure that is transferred from the second pitot tube  125  through the second tubing  126  to the pressure sensor  130  of the meter device  110 . The difference in positive pressure created as water flows past the first pitot tube  120  and the negative pressure created as water flows past the second pitot tube  125  are combined at pressure sensor  130  to create a pressure differential. The pressure differential created at pressure sensor  130  creates a voltage in pressure sensor  130  which is transmitted to the low pass filter  135  and then to the microcontroller  150  in the system for measuring pressure differential  100 . 
     The microcontroller  150  is programmed by using the control system  170  to fit voltage transmitted over time (as illustrated in  FIG. 6 ) from pressure sensor  130  to microcontroller  150  to a second order polynomial, where pressure differential (voltage) goes as flow rate squared (as illustrated by  FIG. 7 ). The voltage in pressure sensor  130  of the meter device  110  changes as fluid flow rate changes in the pipeline  108  and the fluid piping  105  of meter device  110  as a result of the changes in pressure differential created by the positive pressure from the first pitot tube  120  and negative pressure from the second pitot tube  125  (as illustrated in  FIG. 8 ). The change in voltage as related to the change in pressure differential allows a user to measure the changes in fluid flow rate (as illustrated in  FIG. 8 ) and to calculate total fluid flow through the pipeline  108  of a system for measuring pressure differential  100  over time. 
     In another embodiment, the microcontroller  150  may be programmed to calculate the flow direction of a fluid flowing through the meter device  110  and the existing pipeline  108 . For example, programming the microcontroller  150  to calculate not only the pressure differential received from the pressure sensor  130 , but also to account for the magnitude of the pressure differential the microcontroller  150  may also provide a user with the fluid flow rate and direction in the existing pipeline  108 . 
     In another embodiment, the control system  170  may record the data calculations for flow rate, flow volume and flow direction transmitted from the microcontroller  150 . The control system may be in bidirectional communication with a plurality of microcontrollers  150  that may be in unidirectional communication with a plurality of meter devices  110 . The control system may be a central location for a user to record, look up, monitor, or otherwise use fluid flow rate and fluid volume data collected from a plurality of meter devices  110 . 
       FIG. 2A  is a cross sectional view of the meter device  110  of  FIG. 1 . The cross sectional view of the meter device  110  includes the fluid piping  105 , the first pitot tube  120 , the first tubing  121 , the second pitot tube  125 , the second tubing  126 , and the fluid flow indicator  140 . The cross sectional view of the meter device  110  further includes the external wall  210  of fluid piping  105 , the internal wall  220  of fluid piping  105 , an internal end  230  of the first pitot tube  120 , an exterior end  231  of the first pitot tube  120 , an internal end  235  of the second pitot tube  125 , and an exterior end  236  of the second pitot tube  125 . 
       FIG. 2B  is a top view of the meter device  110  of  FIG. 1 . The top view of the meter device  110  includes the fluid piping  105 , the first pitot tube  120 , and the second pitot tube  125 . The top view of the meter device  110  further includes the external wall  210  of fluid piping  105 , the internal wall  220  of fluid piping  105 , an internal end  230  of the first pitot tube  120 , an exterior end  231  of the first pitot tube  120 , an internal end  235  of the second pitot tube  125 , and an exterior end  236  of the second pitot tube  125 . 
       FIG. 2C  is an axial view of the meter device  110  of  FIG. 1  viewed from the upstream end of fluid flow through a pipeline. The cross sectional view of the meter device  110  includes the fluid piping  105 , the first pitot tube  120 , and the first tubing  121 . The axial view of the meter device  110  further includes the external wall  210  of fluid piping  105 , the internal wall  220  of fluid piping  105 , an internal end  230  of the first pitot tube  120 , and an exterior end  231  of the first pitot tube  120 . 
     In the cross sectional view of the meter device  110  ( FIG. 2A ), the interior end  230  of the first pitot tube  120  has a single opening located inside the interior wall  220  of fluid piping  105 . The orientation of the interior end  230  of the first pitot tube  120  is further illustrated in  FIG. 2B  and  FIG. 2C . The first pitot tube  120  passes through the exterior wall  210  of fluid piping  105 , where the exterior end  231  of the first pitot tube  120  is connected to the first tubing  121  ( FIG. 2A ,  FIG. 2B , and  FIG. 2C ). The interior end  235  of the second pitot tube  125  has a single opening located inside the interior wall  220  of fluid piping  105 . The orientation of the interior end  235  of the second pitot tube  125  is further illustrated in  FIG. 2B . The second pitot tube  125  passes through the exterior wall  210  of fluid piping  105 , where the exterior end  236  of the second pitot tube  125  is connected to the second tubing  126  ( FIG. 2A  and  FIG. 2B ). The first pitot tube  120  and the second pitot tube  125  are aligned inside fluid piping  105  such that in the axial view ( FIG. 2C ), the second pitot tube  125  is aligned with and behind the first pitot tube  120  and in the opposite orientation (as illustrated in  FIG. 2A  and  FIG. 2B ). 
     In operation, fluid flows in the direction of the fluid flow indicator  140  inside the fluid piping  105  ( FIG. 2A  and  FIG. 2B ). The fluid in the fluid piping  105  first flows across the interior end  230  of the first pitot tube  120  and transfers a positive pressure to the exterior end  231  of the first pitot tube  125 , through the first tubing  121  ( FIG. 2A  and  FIG. 2B ). The fluid in the fluid piping  105  next flows across the interior end  235  of the second pitot tube  125  and transfers a pressure to the exterior end  236  of the second pitot tube  125 , through the second tubing  126  ( FIG. 2A  and  FIG. 2B ). The orientation of the first pitot tube  120  and the second pitot tube  125  allows exterior end  231  and exterior end  236  to be connected to the pressure sensor  130  of the meter device  110  on the exterior wall  210  of the fluid piping  105  (as illustrated in  FIG. 3 ,  FIG. 4 , and  FIG. 5 ). 
       FIG. 3  is an illustration the configuration of the pressure sensor  130 , first pitot tube  120 , and second pitot tube  125 , on an exterior wall of fluid piping  105  of the meter device  110  of  FIG. 1 . The view of the meter device  110  in  FIG. 3  includes the fluid piping  105 , the first pitot tube  120 , the first tubing  121 , the second pitot tube  125 , the second tubing  126 , and the pressure sensor  130 . The view of the meter device  110  further includes a first fastener  330 , a first connection port  350  of the pressure sensor  130 , and a second connection port  360  of the pressure sensor  130 . 
     In the illustration shown in  FIG. 3 , the portion of the first pitot tube  120  passing through the exterior wall of fluid piping  105  is connected to the first tubing  121  and the first tubing  121  is connected to the first connection port  350  of the pressure sensor  130 . The portion of the second pitot tube  125  passing through the exterior wall of fluid piping  105  is connected to the second tubing  126  and the second tubing  126  is connected to the second connection port  360  of the pressure sensor  130 . The first fastener  330  encircles the pressure sensor  130  and the exterior wall of fluid piping  105  of the meter device  110 . 
     In operation, fluid flowing through the fluid piping  105  creates a positive pressure in the first pitot tube  120  and a negative pressure in the second pitot tube  125  as described above ( FIG. 1  and  FIG. 2 ). The seal between the first pitot tube  120  and the first tubing  121  that allows positive pressure created when fluid flows across the first pitot tube  120  to be transferred to the first connection port  350  of pressure sensor  130 . Similarly, the seal between the second pitot tube  125  and the second tubing  126  that allows negative pressure created when fluid flows across the second pitot tube  125  to be transferred to the second connection port  360  of pressure sensor  130 . The first fastener  330  secures the pressure sensor  130  in place between the ends of the first pitot tube  120  and the second pitot tube  125  on the exterior wall of the fluid piping  105  of the meter device  110  of  FIG. 1 . 
       FIG. 4  is an illustration a full anterior view of the meter device  110  of the system for measuring pressure differential  100  of  FIG. 1 . The anterior view of the meter device  110  includes the fluid piping  105 , the first pitot tube  120 , the first tubing  121 , the second pitot tube  125 , the second tubing  126 , the pressure sensor  130 , and the first connection port  350  and the second connection port  360  of the pressure sensor  130 . The anterior view of the meter device  110  further includes a first treaded cap  410 , a second threaded cap  420 , and a second fastener  460 . 
     The first threaded cap  410  is connected to an end of the fluid piping  150  of the meter device  110  and the second threaded cap  420  is connected to the opposite end of the fluid piping  105  of the meter device  110 . The fastener  460  encircles the exterior wall of fluid piping  105  of the meter device  110 . 
     In operation, the first threaded cap  410  and the second threaded cap  420  allows the fluid piping  105  to be placed in line with the existing pipeline  108  of  FIG. 1 . The first threaded cap  410  and the second threaded cap  420  allows a seal to be formed between the fluid piping  105  of the meter device  110  and the existing pipeline  108  of the system for measuring pressure differential  100  of  FIG. 1 . The second fastener  460  encircling the fluid piping  105  secures wires that may be used to connect the pressure sensor  130  to the microcontroller  150 . 
       FIG. 5  is an illustration the posterior view of the meter device  110  in the system for measuring pressure differential  100  of  FIG. 1 . The posterior view of the meter device  110  includes the fluid piping  105 , the first pitot tube  120 , the first tubing  121 , the second pitot tube  125 , the second tubing  126 , the pressure sensor  130 , the first connection port  350  and the second connection port  360  of the pressure sensor  130 . The posterior view of the pressure sensor  130  of the meter device  110  further a wiring conduit  510 , a first wire  511 , a second wire  512 , a third wire  513 , and a first external contact  520 , a second external contact  530 , and a third external contact  540  of the pressure sensor  130 . 
     The first wire  511 , the second wire  512  and the third wire  513  pass through the wiring conduit  510  and are individually soldered to the first external contact  520 , the second external contact  530 , and the third external contact  540  of the pressure sensor  130  as illustrated in  FIG. 5 . 
     In operation, the first wire  511  provides power to the pressure sensor  130 , the second wire  512  provides a ground, and the third wire  513  transmits voltage readings from the pressure sensor  130  of the meter device  110  to the microcontroller  150  in the system for measuring pressure differential  100  ( FIG. 1 ). As fluid flows through fluid piping  105  in the direction of the fluid flow indicator  140 , positive pressure is created as fluid flows past the first pitot tube  120  and negative pressure is created as water flows past the second pitot tube  125 . The positive and negative pressure are transferred through the first tubing  121  and the second tubing  126  to the pressure sensor  130  which causes a voltage to be produced in the pressure sensor  130 . This voltage is communicated through the third wire  513  to the microcontroller  150  ( FIG. 1 ) in the system for measuring pressure differential  100 . 
     In the preferred embodiment, the fluid piping  105  of the meter device  110  may be ¾ inches in diameter and 6 inches in length and may be polyvinyl chloride (PVC) material or any other material suitable for carrying fluids. In the preferred embodiment, the first threaded cap  410  and the second threaded cap  420  may be pre-made polyvinyl chloride threaded caps and may have ¾ inch diameter. In alternative embodiments, fluid piping  105 , the first threaded cap  410  and the second threaded cap  420  may be any other diameter suitable for connection to an existing pipeline  108 . 
     In the preferred embodiment, the first pitot tube  120  and the second pitot tube  125  of the meter device  110  may be elbow tube fittings with classic series barbs, may have a 3/16 inch (4.8 mm) inner diameter and may be made of polyvinylidene fluoride. The first pitot tube  120  and the second pitot tube  125  may be threaded such that they form a seal between the wall of the fluid piping  105 . In the preferred embodiment, the first pitot tube  120  and the second pitot tube  125  are positioned inside the fluid piping  105  such that the portions of the first pitot tube  120  and the second pitot tube  125  that pass through the exterior wall of the fluid piping  105  at an angle that is perpendicular to the exterior wall of fluid piping  105 . In the preferred embodiment, the open end of the first pitot tube  120  that is inside the fluid piping  105  faces in the opposite direction to the open end of the second pitot tube  125  that is inside the fluid piping  105 . In the preferred embodiment, the ends of the first pitot tube  120  and the second pitot tube  125  that are on the interior wall of the fluid piping  105  (in contact with fluid passing through the meter device  110 ) are radially centered inside the fluid piping  105 . Furthermore, by radially centering the ends of the first pitot tube  120  and second pitot tube  125  inside the fluid piping  105  where the flow rate inside fluid piping  105  or the existing pipeline  108  are maximal, this maximizes the pressure differential sensed by pressure sensor  130  and transmitted to the microcontroller  170 . 
     In an alternative embodiment, the first pitot tube  120  and the second pitot tube  125  may be positioned toward the top or bottom of the inner wall of the fluid piping  105 . In other embodiments, the first pitot tube  120  and the second pitot tube  125  may be located in different portions of the fluid piping  105  and may have ends that do not directly oppose one another. In other embodiments, the first pitot tube  120  and the second pitot tube  125  may have orthogonal portions that are equal in length whereas in other embodiments, these lengths may differ based on the size of the meter device  110  constructed. 
     In another embodiment, the first pitot tube  120  and the second pitot tube  125  may be installed directly into an existing pipeline  108  rather than a separate fluid piping  105 . In this embodiment, the pressure sensor  130  may be connected to the first tubing  121  and the second tubing  126  as described above, for example in  FIG. 1 . The first tubing  121  and the second tubing  126  may be connected to the first pitot tube  120  and the second pitot tube  125  and pressure differential measurements may be taken as described above in  FIG. 1 ,  FIG. 2A ,  FIG. 2B ,  FIG. 2C ,  FIG. 3 ,  FIG. 4 , or  FIG. 5 . 
     In the preferred embodiment, the first pitot tube  120  and the first tubing  121  may be coupled together using a threaded adapter that fits around the first pitot tube  120  and forms a seal with the exterior wall of the fluid piping  105  and with the first tubing  121 . Similarly, the second pitot tube  125  may be coupled to the second tubing  126  using a threaded adapter that fits around the second pitot tube  125  and forms a seal with the exterior wall of the fluid piping  105  and with the second tubing  126 . For example, the threaded adapter may be ⅛-27 national pipe thread and may have a 7/16 inch hex to 200 series barb, may have a 1/16 inch (1.6 mm) inner diameter, and may be made of polyvinylidene fluoride. 
     In the preferred embodiment, the first tubing  121  and the second tubing  126  of the meter device  110  may be Tygon tubing with a diameter suitable for connecting to the first pitot tube  120  and the second pitot tube  125 . In an alternative embodiment, the first tubing  121  and the second tubing  126  may be any silicone or plastic tubing of suitable size and length. 
     In the preferred embodiment, the first tubing  121  may be connected to a threaded adapter that fits over the first pitot tube  120  using ear clamps, for example, OETIKER 4.1 mm clamps at each connection point. Similarly, an ear clamp may be used to connect a threaded adapter that fits over the second pitot tube  125  to the second tubing  126 . In an alternative embodiment, epoxy, paste, bonding, or other sealant may be used to connect the first tubing  121  and the second tubing  126  to the first pitot tube  120  and the second pitot tube  125 , respectively (or an adapter if used), as well as the first connection port  350  and the second connection port  360  of the pressure sensor  130 . 
     In the preferred embodiment, the first fastener  330  and second fastener  460  of the meter device  110  may be zip ties, tape, wire, or other types of fasteners. In an alternative embodiment, first fastener  330  and second fastener  460  may be glue, epoxy, paste, or other types of adhesives or bonding agents. 
     In the preferred embodiment, where the first pitot tube  120  and second pitot tube  125  pass through the exterior wall of fluid piping  105 , a seal may be created by wrapping Teflon tape around the threads of first pitot tube  120  and the second pitot tube  125 . In alternative embodiments, glue, paste, epoxy, or any other types of sealants may be used to create a seal and prevent leaking in the fluid piping  105  where the first pitot tube  120  and the second pitot tube  125  are positioned. 
     In the preferred embodiment, the low pass filter  135  of the meter device  110  may be a 1 kohm resistor in series and a 1 μF capacitor in parallel with the output from the pressure sensor  130 . In alternative embodiments, the low pass filter  135  may be any other suitable device that may be connected to the pressure sensor  130  of the meter device  110  and the microcontroller  150 . 
     In the preferred embodiment, the pressure sensor  130  may be a piezoresistive transducer, may have monolithic silicon pressure sensors designed for a wide range of applications, and may be temperature compensated or calibrated to operate in temperatures between −40 to +125 degrees Celsius. An example of a piezoresistive transducer may be a Freescale Semiconductor series MPX5010, MPXV5010, or MPVZ5010 transducer. In the preferred embodiment, the pressure sensor  130  may, for example, offer 0 to 10 kPa or 0.2 to 4.7 V output. In alternative embodiments, the sensitivity and voltage output of the pressure sensor  130  may be changed depending upon the size of the existing pipeline  108  with which the meter device  110  is being used. 
     In other embodiments the pressure sensor  130  may include a memory chip that may be in bidirectional communication with the microcontroller  150 . In this embodiment, the voltage data from the pressure sensor  130  may be transmitted to the microcontroller  150  to calculate a fluid flow rate. The microprocessor  150  may transmit fluid flow rate to the memory chip in the pressure sensor  130  where it may be stored. 
     In the preferred embodiment, the pressure sensor  130  may have microcontroller  150  or microcontroller A/D inputs. In alternative embodiments, a wide range of pressure sensors  130  that produce an accurate, high level analog output signal that is proportional to the applied pressure may be used. In alternative embodiments, a pressure sensor  130  with axial ports modified to accommodate industrial grade tubing may be used. In alternative embodiments, the pressure sensor  130  may be an integrated silicon pressure sensor and may be on-chip signal conditioned, and may be temperature compensated and calibrated. 
     In the preferred embodiment, the microcontroller  150  may be an open-source single-board microcontroller. Examples of open source single-board microcontroller may be an Arduino, Parallax Basic Stamp, Netmedia BX-24, Phidgets, Handyboard, and others with similar functionality. Other inexpensive microcontrollers or those that operate using cross platform software which may be, for example, Windows, Macintosh OSX, and Linux operating systems, may be used. The microcontroller  150  may use a simple, clear programming environment or it may use open-source and extensible software. The language of the microcontroller  150  may be programmed using for example, language similar to C, C++ libraries, or the AVR C programming language. The microcontroller  150  may use open-source and extensible hardware which may be, for example, Atmel ATMEGA8 or ATMEGA168. 
     In the preferred embodiment, the microcontroller  150  may be in connection with the low pass filter  135  using a wired connection, or if a low pass filter  135  is not used, the microcontroller  150  may be in connection with the pressure sensor  130  using a wired connection. The microcontroller  150  may stand alone and may store data and process instructions or the microcontroller  150  may communicate with software running on a computer using for example, Flash, Processing, or MaxMSP. 
     In the preferred embodiment, microcontroller  150  may be connected to the control system  170  using either a wireless or wired connection. For example, the microcontroller  150  may transmit data to the control system  170  using wireless communication. Examples of wireless communication may include Bluetooth, ZigBee, WiFi wireless connection or the microcontroller  150  may be wired directly to the control system  170  or may be connected using a USB port. 
     In the preferred embodiment, the control system  170  may be a laptop computer or other portable computing device. For example, the control system  170  may be an iPad, notebook, notepad, or other portable computing device. The control system  170  may also be a stationary computer or computing system. The control system  170  may have a display screen on which a user could view fluid flow rate or fluid volume or both in real time. The control system  170  may further be used to display graphically the data received from the microcontroller  150  in real time so that a user may instantly view his or her fluid use over time or during a predetermined time period. 
     In an alternative embodiment, the control system  170  may be a mobile hand held device that is able to use an application that communicates wirelessly with the microcontroller  150 . Examples of mobile handheld devices may include the iPhone, Android phone, Blackberry, or other smart phones. 
     In another alternative embodiment, the control system  170  may communicate with a plurality of microcontrollers  150 , one or more of which may be connected to an individual meter device  110  or several meter devices  110 , for example in the same household or in a plurality of households. 
     In another alternative embodiment, the microcontroller may be programmed using a control device  170  and then may be connected using a wired or wireless connection to a screen capable of displaying data collected by the meter device  110  to a user. 
       FIG. 6  is a graph of unfiltered voltage over time as output by the pressure sensor  130  of the meter device  110  in the system for measuring pressure differential  100  of  FIG. 1  as fluid is flowing through the meter device  110 . The graph illustrates a plot of voltage measurements  625  over time without signal filtering. As discussed above in  FIG. 1 , the difference in positive pressure created as water flows past the first pitot tube  120  and the negative pressure created as water flows past the second pitot tube  125  are combined at pressure sensor  130  to create a pressure differential ( FIG. 1 ). As discussed above in  FIG. 5 , the pressure differential created at pressure sensor  130  creates a voltage in pressure sensor  130  which is transmitted through the first wire  510 , the second wire  520 , and the third wire  530  to the microcontroller  150  in the system for measuring pressure differential  100  ( FIG. 1 ). 
     In operation of the preferred embodiment, a low pass filter, which may be a 1 kohm resistor in series and a 1 μF capacitor in parallel with the output from the pressure sensor  130 , is used to reduce variation in the voltage transmitted from the pressure sensor  130  to the microcontroller  150 . As shown in  FIG. 6 , when a low pass filter is not used, variation is generated in the voltage measurements  625  even when sampled frequently over time. In other embodiments, the frequency of voltage sampling by the microcontroller  150  can be varied such that measurements are taken more frequently or less frequently. For example, the microcontroller  150  may be programmed to take 85 measurements of voltage every second as shown in  FIG. 6 . Therefore, in absence of using a low pass filter, changing sampling frequency improves the accuracy of the meter device  110 , as more data points are fit to a second order polynomial. For example, by using the sampling frequency depicted in  FIG. 6  whereby approximately 600 data points are collected for each flow rate and used to fit a polynomial curve, the error in calculation of fluid flow rate can be reduced to less than 0.5%. 
       FIG. 7  is a graph illustrating the fit of voltage readings (representing pressure differential) to a second order polynomial enabling the calculation of fluid flow rate through the meter device  110  of the system for measuring pressure differential  100  of  FIG. 1 . The graph illustrates raw voltage data  750  and a polynomial curve fit to the raw voltage data  725 . These data are obtained during a calibration process (described below in  FIG. 13 ) whereby the meter device  110  is connected to existing pipeline  108  of the system for measuring pressure differential  100  and a standard meter is placed in line with the meter device  110  in the same existing pipeline  108  configured as described below in  FIG. 13 . The general equation used to fit the data and calculate flow rate after the calibration process ( FIG. 13 ), where voltage (pressure differential) generally varies with the square of the flow rate is: voltage (pressure differential)=ax 2 +bx+c, where a, b, and c are constants and x is the flow rate. 
     As shown in  FIG. 7 , a second order polynomial curve  725  is fit to the raw voltage data  750 , collected from the pressure sensor  130  representing pressure differential created when fluid flows across the first pitot tube  120  and the second pitot tube  125  ( FIG. 1 ), to calculate flow rate of fluid passing through the meter device  110 . Once raw data are fit to a polynomial in the calibration process as described below in  FIG. 13 , the relationship between voltage and fluid flow rate are simplified and the variation in the raw data is reduced so that the polynomial fit for an individual meter device  110  may be stored on the microcontroller  150  or the control system  170  as the reference relationship for conversion of voltage to flow rate when the meter device  110  is in use. 
     By calculating the flow rate, the total volume of fluid passing through the meter device  110  can also be calculated over time. As discussed above, the microcontroller  150  of the system for measuring pressure differential  100  of  FIG. 1  stores flow rate over time and returns total volume in the preferred embodiment. 
       FIG. 8  is a graph illustrating the variation of voltage (representing pressure differential) over time under stepwise adjustment of the fluid flow rate through the meter device  110  in the system for measuring pressure differential  100  of  FIG. 1 . The graph illustrates a plot of voltage measurements  825  taken over time as fluid flow rate is varied in a pipeline. As shown in  FIG. 8 , the pressure differential created as fluid flows through the meter device  110  is represented by voltage sensed by the pressure sensor  130 . When no fluid is flowing through the meter device  110  the voltage is zero. As the rate of fluid flowing through the meter device  110  changes, the voltage responds quickly, allowing accurate calculation of flow rate and volume as desired (as illustrated by voltage measurements  825 ). As discussed above, the in the preferred embodiment, a low pass filter, which may be a 1 kohm resistor in series and a 1 μF capacitor in parallel with the output from the pressure sensor  130  is used to generate smoothed voltage data as are presented in  FIG. 8 . 
       FIG. 9  is a graph illustrating the comparison of voltage readings (representing pressure differential) measured by the pressure sensor  130  as it relates to fluid flow rate in two separate meter devices  110  of  FIG. 1 . The graph illustrates voltage measurements taken from a first meter device  925  as compared with voltage measurements taken from a second meter device  950 . As shown in  FIG. 9 , each individual meter device  110  produces a curve (voltage measurements  925  and  950 ); however, as is shown in  FIG. 9 , the voltage measurements  925  and  950  do not overlap. Therefore, variation due to construction of each meter device  110 , indicates the importance of the calibration of individual meter devices  110  (as illustrated above in  FIG. 8  and as described below in  FIG. 13 ) before they are used to measure fluid flow rate in an existing pipeline  108 . 
       FIG. 10  illustrates a block diagram of an alternative embodiment of a system for measuring pressure differential  1000 . The alternative system for measuring pressure differential  1000  includes a pipeline  1008 , a meter device  1010 , a low pass filter  1035 , a microcontroller  1050 , a control system  1070 , and a control valve  1080 . The meter device  1010  further includes a fluid piping  1005 , a first pitot tube  1020 , a first tubing  1021 , a second pitot tube  1025 , a second tubing  1026 , and a pressure sensor  1030 . 
     In the system for measuring pressure differential  1000 , the pipeline  1008  is connected to the fluid piping  1005  of the meter device  1010 . The first pitot tube  1020  passes from the center of fluid piping  1005  through the external wall of the fluid piping  1005  and is connected to the first tubing  1021 . The first tubing  1021  is connected to the pressure sensor  1030  (as described in  FIG. 3 ) on the external wall of the fluid piping  1005 . The second pitot tube  1025  passes from the center of fluid piping  1005  through the external wall of the fluid piping  1005  and is connected to the second tubing  1026 . The second tubing  1026  is connected to the pressure sensor  1030  (as described in  FIG. 3 ) on the external wall of the fluid piping  1005 . The pressure sensor  1030  of the meter device  1010  is in unidirectional communication with the low pass filter  1035  and the low pass filter  1035  is in unidirectional communication with the microcontroller  1050 . The microcontroller  1050  is in bidirectional communication with the control system  1070 . The microcontroller  1050  is in unidirectional communication with the control valve  1080 . 
     In operation, fluid passes through pipeline  1008  in the direction of the fluid flow indicator  1040 . As fluid in the pipeline  1008  passes through the fluid piping  1005  of the meter device  1010 , it flows across the section of the first pitot tube  1020  located inside fluid piping  1005  (as described in  FIG. 2A ,  FIG. 2B , and  FIG. 2C ) and creates a positive pressure that is transferred from the first pitot tube  1020  through the first tubing  1021  to the pressure sensor  1030 . As fluid continues to flow through the fluid piping  1005  of the meter device  1010 , it next flows across the section of the second pitot tube  1025  located inside fluid piping  1005  (as described in  FIG. 2A  and  FIG. 2B ) and creates a negative pressure that is transferred from the second pitot tube  1025  through the second tubing  1026  to the pressure sensor  1030  of the meter device  1010 . The difference in positive pressure created as water flows past the first pitot tube  1020  and the negative pressure created as water flows past the second pitot tube  1025  are combined at pressure sensor  1030  to create a pressure differential. The pressure differential created at pressure sensor  1030  creates a voltage in pressure sensor  1030  which is transmitted to the low pass filter  1035  and then to the microcontroller  1050  in the system for measuring pressure differential  1000 . 
     The microcontroller  1050  is programmed by using control system  1070  to measure voltage transmitted over time (as described in  FIG. 6 ) from pressure sensor  1030  to microcontroller  1050  to a second order polynomial where pressure differential (voltage) goes as flow rate squared (as described in  FIG. 7 ). The voltage in pressure sensor  1030  of the meter device  1010  changes as fluid flow rate changes in the pipeline  1008  and the fluid piping  1005  of meter device  1010  as a result of the changes in pressure differential created by the positive pressure from the first pitot tube  1020  and negative pressure from the second pitot tube  1025  (as described in  FIG. 8 ). The change in voltage as related to the change in pressure differential allows a user to measure the changes in fluid flow rate (as described in  FIG. 8 ) and to calculate total fluid flow through the pipeline  1008  of a system for measuring pressure differential  1000  over time. 
     In operation, the preferred embodiment of a system to measure pressure differential  1000 , the control system  1070  may be used to program the microcontroller  1050  to open or close control valve  1080  based on how much fluid flows through the meter device  1010 . For example, if the microcontroller  1050  records flow rate over time and stores total volume flowing through the meter device  1010  over time, once a desired volume has been reached for a specified time period, the microcontroller  1050  may be programmed to send a signal to the control valve  1080  to stop the pipeline  1008  from carrying more fluid to a downstream user. 
     In an alternative embodiment, the control system  1070  may be in bidirectional communication with a plurality of microcontrollers  1050 . For example, the pipeline  1008  may be one of many pipelines that deliver fluid to individual households from a storage tank. In this example, a meter device  1010  may be used for an individual household, whereby the microcontroller  1050  may be programmed to allow a predetermined volume of fluid to flow from a storage tank through the pipeline  1008 . Once a predetermined volume has flowed through the meter device  1010 , the microcontroller  1050  may send a signal to the control valve  1080  to close the pipeline  1008 . After a predetermined time elapses, the microcontroller  1080  may be programmed to send a signal to the control valve  1080  to open the pipeline  1008  and allow fluid to flow to an individual household. 
     In another embodiment, the control system  1070  may be used to program the microcontroller  1050  to allow a predetermined fluid flow rate to pass through the pipeline  1008 . For example, the microcontroller  1050  may send a signal to the control valve  1080  so that it may open or close to reach a predetermined fluid flow rate in the pipeline  1008 . Alternatively, after a predetermined time elapses, the microcontroller  1050  may be programmed to send a signal to the control valve  1080  to open the pipeline  1008  and allow fluid to flow irrespective of the predetermined fluid flow rate. In another embodiment, the microcontroller  1050  may be programmed to send a signal to the control valve  1080  to fully close off fluid flow through the pipeline  1008  once a flow rate in the pipeline  1080  had persisted for a predetermined time. 
     In another embodiment, the control valve  1080  may be used to recalibrate the system for measuring pressure differential  1000 . For example, the microcontroller  1050  may be programmed to close the control valve  1080  at a certain time interval, stopping flow of fluid through the pipeline  1008 , resulting in a static voltage reading sensed by the pressure sensor  1030  and sent to the microcontroller  1050 . The microcontroller  1050  may then reset or recalibrate to the static voltage reading sensed by the pressure sensor  1030 . The microcontroller  1050  may then send a signal to reopen the control valve  1080  to allow fluid to flow through the meter device  1010  and pipeline  1008 . 
     In another embodiment, the control system  1070  may be used to program the microcontroller  1050  to perform a full flow range calibration procedure. For example, the microcontroller  1050  may be programmed to send a signal to close the control valve  1080  at a predetermined time, stopping the fluid flow through the pipeline  1008 . A static voltage may be sensed by the pressure sensor  1030  and transmitted to the microcontroller  1050 , and the microcontroller  1050  may be programmed to send a signal to the control valve  1080  to open the control valve  1080  in small increments, allowing changes in fluid flow rate through the pipeline  1008  to increase over time, for example, until the maximal fluid flow rate in the pipeline  1008  is achieved. Alternatively, the maximal fluid flow rate in the pipeline  1008  may not be achieved during calibration and the microcontroller  1050  may be programmed using the control system  1070  to complete calibration using a predetermined acceptable error rate. The full flow range calibration may occur in regular or irregular intervals or alternatively may occur once a predetermined flow volume is recorded by the microcontroller  1050  and transmitted to the control system  1070 . The control system  1070  may be used to monitor calibration and adjust the calibration process as needed in a particular pipeline  1008 . 
       FIG. 11  illustrates a flow chart of an embodiment of the invention for a method for measuring pressure differential created by a flowing fluid using the meter device  110  in the system for measuring pressure differential  100  of  FIG. 1 . First, in step  1110 , the microcontroller  150  is programmed using the control system  170  to fit pressure measurements to a curve representing fluid flow rate. 
     Next, in step  1120 , the microcontroller  170  is connected to the pressure sensor  130 . 
     Next, in step  1130 , the first pitot tube  120  and the second pitot tube  125  are connected to the pressure sensor  130  on the external wall of the fluid piping  105 . 
     Next, in step  1140 , ends of first pitot tube  120  and the second pitot tube  125  are passed through the wall of the fluid piping  105  and positioned in fluid flowing inside the fluid piping  105 . 
     Next, in step  1150 , positive pressure is created when fluid flows over the first pitot tube  120  and is sensed by the pressure sensor  130 . 
     Next in step  1160 , negative pressure is created when fluid flows over the second pitot tube  125  and is sensed by the pressure sensor  130 . 
     Next, in step  1170 , the positive pressure and negative pressure sensed by the pressure sensor  130  are transmitted to the microcontroller  150 . 
     Next, in step  1180 , the microcontroller  170  uses the stored formula coefficients programmed in step  1110  to convert the pressure data to a fluid flow rate. 
       FIG. 12  illustrates a flow chart of an alternative embodiment of the invention for a method to control fluid flow through a meter device  1010  and pipeline. First, in step  1210 , fluid flow rate is monitored in a pipeline with the meter device  110  of  FIG. 1 . 
     Next, in step  1220 , the microcontroller  1050  of  FIG. 10  is programmed to calculate fluid volume flowing through the pipeline. 
     Next, in step  1230 , the fluid volume is compared with a predetermined volume stored on the microcontroller  1050 . If the volume that has flowed through the pipeline is less than the predetermined volume stored on the microcontroller  1050 , the control valve  1080  remains open and the method repeats at step  1210 . If the fluid flow volume is greater than or equal to the predetermined volume stored on the microcontroller  1050 , the microcontroller sends a signal to close the control valve  1080  in step  1245 . 
     Next, in step  1250 , the microcontroller monitors time that has passed since closing control valve  1080 . If the preset time has elapsed, a signal is sent from the microcontroller  1050  to the control valve  1080  in step  1260  and the valve is open as in step  1240  and the method repeats at step  1210 . If the preset time has not elapsed, the valve remains closed in step  1265  and step  1250  repeats until the preset time has been reached. 
     In the preferred embodiment, the predetermined volume of fluid in step  1230  may be determined based on the use of a community of users that share the same fluid source or pipeline in individual households. In an alternative embodiment, the predetermined volume in step  1230  may be based on different sources of fluid use within a household, for example, these sources may be a sink or bathtub. 
     In the preferred embodiment, the preset time in step  1250  may be based on the length of one day and may be programmed for individual households. In an alternative embodiment, the preset time in step  1250  may be based on shorter increments, for example, hours since last use. 
       FIG. 13  illustrates a block diagram of a calibration system  1300  used to adjust data measurements taken by the meter device  110  of  FIG. 1  (or the meter device  1010  of  FIG. 10 ) before use in an existing pipeline. The calibration system  1300  for includes the meter system  110 , the existing pipeline  108 , the low pass filter  135 , the fluid flow direction indicator  140 , the microcontroller  150 , and the control system  170  of  FIG. 1 . As described above in  FIG. 1 , the meter device  110  further includes the fluid piping  105 , the first pitot tube  120 , the first tubing  121 , the second pitot tube  125 , the second tubing  126 , and the pressure sensor  130 . The calibration system  1300  further includes a standard meter  1310  and a flow valve  1380 . 
     In the calibration system  1300 , the first pitot tube  1020  passes from the center of fluid piping  105  through the external wall of the fluid piping  105  and is connected to the first tubing  121 . The first tubing  121  is connected to the pressure sensor  130  (as described in  FIG. 1  and  FIG. 3 ) on the external wall of the fluid piping  105 . The second pitot tube  125  passes from the center of fluid piping  105  through the external wall of the fluid piping  105  and is connected to the second tubing  126 . The second tubing  126  is connected to the pressure sensor  130  (as described in  FIG. 1  and  FIG. 3 ) on the external wall of the fluid piping  105 . The pressure sensor  130  of the meter device  110  is in unidirectional communication with the low pass filter  135  and the low pass filter  135  is in unidirectional communication with the microcontroller  150 . The microcontroller  150  is in bidirectional communication with the control system  170 . The microcontroller  150  is in unidirectional communication with the control valve  180 . The standard meter  1310  is connected to the existing the pipeline  108  and the standard meter is in unidirectional communication with the microcontroller  150 . The flow valve  1380  is positioned in the existing pipeline  108  and the flow valve  1380  is in unidirectional communication with the microcontroller  150 . 
     In operation of the calibration system  1300 , fluid flows through pipeline  108  in the direction of the fluid flow indicator  140 . At the time calibration is initiated, the flow valve  1380  is in a position that closes the pipeline  108  to stop fluid flow rate through the pipeline  108 . The microcontroller  150  is programmed by the control system  170  to open the flow valve  1380  at a controlled rate to gradually increase fluid flow rate through the pipeline  108  until a maximal flow rate is reached. During operation of the calibration system  1300 , as fluid in the pipeline  108  passes through the standard meter  1310 , the standard meter detects fluid flow rate and transmits fluid flow rate to the microprocessor  1310 . 
     The fluid in the pipeline next flows through the fluid piping  105  of the meter device  110 , where it flows across the section of the first pitot tube  120  located inside fluid piping  105  (as described in  FIG. 2A ,  FIG. 2B , and  FIG. 2C ) and creates a positive pressure that is transferred from the first pitot tube  120  through the first tubing  121  to the pressure sensor  130 . As fluid continues to flow through the fluid piping  105  of the meter device  110 , it next flows across the section of the second pitot tube  125  located inside fluid piping  105  (as described in  FIG. 2A  and  FIG. 2B ) and creates a negative pressure that is transferred from the second pitot tube  125  through the second tubing  126  to the pressure sensor  130  of the meter device  110 . The difference in positive pressure created as water flows past the first pitot tube  120  and the negative pressure created as water flows past the second pitot tube  125  are combined at pressure sensor  130  to create a pressure differential. The pressure differential created at pressure sensor  130  creates a voltage in pressure sensor  130  which is transmitted to the low pass filter  135  and then to the microcontroller  150  in the calibration system  1300 . 
     During operation of the calibration system  1300 , the microcontroller  150  simultaneously monitors the output from the standard meter  1310  and the output voltage from the pressure sensor  130  of the meter device  110  to produce the data shown in  FIG. 7  and  FIG. 9 , voltage versus fluid flow rate. As described above in  FIG. 7 , these data fit well with a second order polynomial, thus eliminating the need to store large amounts of raw data on the microcontroller  150  or the control system  170 . Once calibration data are collected for an individual meter device  110 , the microcontroller  150  is programmed using the control system  170  to store at least three fitting coefficients for calculation of fluid flow rate through a pipeline  108 . The standard meter  1310  and the flow valve  1380  may be removed from the existing pipeline  108  and the meter device  110  may be used to measure the pressure differential created by flowing fluids to calculate the fluid flow rate through a pipeline. 
     In another embodiment, the microcontroller  150  may be programmed to calculate the total volume of fluid flow through a pipeline  108  by multiplying fluid flow rate by a time increment between each fluid flow rate measurement and adding each of these incremental fluid flow rate measurements together to return a total volume which may be stored on the microcontroller  150  or transmitted to the control system  170 . 
     In the preferred embodiment, the standard meter  1310  may be a displacement meter and may have pulsed output, for example of one pulse per gallon of fluid flow. In other embodiments, the standard meter  1310  may be a velocity meter, such as a turbine meter or compound meter, or may be an electromagnetic meter, or ultrasonic meter, or any other meter that may be used to accurately transmit fluid flow rate to the microcontroller  150 . The standard meter  1310  may be located either upstream or downstream of the meter device  110  relative to the direction of fluid flow  140  through the existing pipeline  108 . 
     In the preferred embodiment, the flow valve  1380  may be a faucet valve that may be located in the existing pipeline. In alternative embodiments, the flow valve  1380  may be installed inside the existing pipeline or in any other configuration that effectively allows fluid flow through the existing pipeline  108  to be controlled. The flow valve  1380  may be located either upstream or downstream of the meter device  110  relative to the direction of fluid flow  140  through the existing pipeline  108 . 
     In view of the forgoing teaching, embodiments of the present invention provide numerous advantages over other known systems, methods, and devices for allowing a user to measure flow rate and flow volume of fluids. Importantly, the pressure differential measurement system  100  and the meter device  110  allow a user to accurately measure fluid flow rate and volume from existing pipelines in real time without the need for restricting fluid flow, without the need for extensive calibration, and without maintaining mechanical moving parts. Furthermore, the meter device  110  is easily and inexpensively adaptable and tunable for various uses, for example, adjusting the sensitivity of the meter device  110 , or controlling fluid flow in a pipeline, or for use in very low fluid flow rates where the sensitivity of mechanical metering devices is inadequate for accurate fluid flow rate measurements. 
     First, unlike the systems of Wang and Wiklund (&#39;731), the instant invention does not require that the fluid flow be restricted to measure fluid flow rate through a pipeline. Unlike the systems of Wiklund (&#39;950) that require an averaging pitot tube be placed across the entire flow space of a pipe or tubing, necessarily restricting flow in the pipeline, the instant meter device  110  requires that a single opening on each of two pitot tubes be used, minimally restricting fluid flow through the pipeline. Restricting fluid flow requires that extra fluid restriction members be placed in the pipeline, which requires extra calibration to account for the static pressure around the flow restriction member placed in the pipeline. Also, flow restriction necessarily causes unwanted loss of fluid pressure. The instant invention relies on a moderate restriction of fluid flow based on the size of the pitot tubes used in the meter device  110 . Because of this, the instant device is accurate and easily calibrated without the need for placing extra components in the pipeline. Furthermore, unlike the systems of Wiklund et. al. (&#39;950) which utilize averaging pitot tubes with different shapes and sizes and must be calibrated to the particular fluid or pipeline used, the instant meter device  110  is easily adapted to different sizes of pipelines and fluid flow with minimal calibration needed before first use. 
     Next, unlike the system of Wiklund (&#39;731), where the pressure sensor is embedded in a flow restriction member, the instant invention allows the pressure sensor  130  to be placed on the exterior wall of the meter device  110 . If the embedded pressure sensor in Wiklund malfunctions or different pressure sensitivity is needed, the entire system must be taken apart and the flow restriction member must be removed and replaced and recalibrated. In the instant system, however, if the pressure sensor malfunctions or a higher or lower flow rate is desired in a pipeline, the pressure sensor is easily disconnected and replaced from the outside of the meter device. 
     Next, the systems of Wang and Wiklund (&#39;950) further require that a separate temperature measurement be taken to allow a user to obtain accurate fluid flow information. By using a temperature compensated pressure sensor in the meter device  110  of the instant system, no further sensor placement or calibration is needed. 
     Finally, unlike the device of Amir, which requires mechanical moving parts be employed to allows the measurement of pressure differential or to record pressure measurements, the instant meter device  110  operates using no moving parts. Furthermore, unlike the device of Amir which requires measurements to be recorded on paper or to be visualized and recorded by a user, the instant meter device  110  transmits pressure differential measurements to a microcontroller which may be programmed to calculate, store, save, or display fluid flow rate in real time. 
     While particular elements, embodiments, and applications of the present invention have been shown and described, it is understood that the invention is not limited thereto because modifications may be made by those skilled in the art, particularly in light of the foregoing teaching. It is therefore contemplated by the appended claims to cover such modifications and incorporate those features which come within the spirit and scope of the invention.