Abstract:
A magnetic flowmeter includes a pipe having a non-conductive liner, afield coil adjacent to the pipe and configured to generate a magnetic field across a fluid flowing through the pipe, a first electrode located in a first tunnel passing through the pipe and into the liner, and a second electrode located in a second tunnel passing through the pipe and into the liner. The electrodes are configured to sense a voltage induced by the magnetic field across the fluid flowing through the pipe. The flowmeter also includes a sealed compartment attached to the pipe and enclosing the field coil, the first electrode, or the second electrode. The flowmeter further includes a vapor sensor within the sealed compartment configured to sense relative humidity in the compartment, and an electronics compartment having transmitter circuitry connected to the field coil, the first electrode, the second electrode, and the vapor sensor.

Description:
BACKGROUND 
     The present disclosure relates to magnetic flowmeters, and in particular, to vapor permeation in a magnetic flowmeter. 
     In general, electromagnetic flow measurement techniques are applicable to water-based fluids, ionic solutions and other conducting flows. Specific uses include water treatment facilities, high-purity pharmaceutical manufacturing, hygienic food and beverage production, and chemical processing, including hazardous and corrosive process flows. Magnetic flowmeters are also employed in the hydrocarbon fuel industry, including hydraulic fracturing techniques utilizing abrasive and corrosive slurries, and in other hydrocarbon extraction and processing methods. 
     Magnetic flowmeters (or mag meters) measure flow by Faraday induction, an electromagnetic effect. The meter energizes a coil to generate a magnetic field across a pipe section, and the magnetic field induces an electromotive force (EMF) across the process flow. The resulting potential difference (or voltage) is measured using a pair of electrodes that extend through the pipe section and into contact with the process flow, or via capacitive coupling. The flow velocity is proportional to the induced EMF, and the volumetric flow rate is proportional to the flow velocity and flow area. 
     The coil and the electrode can be located in a hermetically sealed magnetics compartment in order to prevent damage to the electronics. However, a non-conductive liner lines the pipe section, and permeation of the liner can occur. In the event that permeation is occurring, vapor can build up in the magnetics compartment, increasing the relative humidity in the compartment. When the relative humidity reaches 100%, water droplets will form and can cause the magnetic flowmeter to fail due to the moisture shorting the electronics, such as the electrodes or the coil. Magnetic flowmeter failure is typically not noticeable until a short occurs and the flowmeter needs to be replaced. 
     SUMMARY 
     A magnetic flowmeter includes a pipe having a non-conductive liner, afield coil adjacent to the pipe and configured to generate a magnetic field across a fluid flowing through the pipe, a first electrode located in a first tunnel passing through the pipe and into the liner, and a second electrode located in a second tunnel passing through the pipe and into the liner. The electrodes are configured to sense a voltage induced by the magnetic field across the fluid flowing through the pipe. The flowmeter also includes a sealed compartment attached to the pipe and enclosing the field coil, the first electrode, or the second electrode. The flowmeter further includes a vapor sensor within the sealed compartment configured to sense relative humidity in the compartment, and an electronics compartment having transmitter circuitry connected to the field coil, the first electrode, the second electrode, and the vapor sensor. 
     A method includes sensing flow of a fluid through a pipe of a magnetic flowmeter and sensing a relative humidity in a sealed compartment with a vapor sensor. The sealed compartment is attached to the pipe and encloses at least one of a field coil, a first electrode, or a second electrode. The method further includes generating a first output representing a flow rate of the fluid through the pipe and a second output based upon the relative humidity sensed by the vapor sensor, the second output alerting a user to vapor permeation in the sealed compartment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a magnetic flowmeter. 
         FIG. 2  is a cross-sectional view of the magnetic flowmeter of  FIG. 1  along line  2 - 2  in  FIG. 1 . 
         FIG. 3  is a schematic diagram of the magnetic flowmeter of  FIG. 1 . 
         FIG. 4  is a perspective cut-away view of a magnetic flowmeter. 
         FIG. 5  is a front view of the magnetic flowmeter in  FIG. 4 . 
         FIG. 6  is a schematic diagram of the magnetic flowmeter of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     The magnetic flowmeter of the present disclosure includes a vapor sensor for detecting vapor permeation prior to flowmeter failure. The magnetic flowmeter includes a pipe section or flow tube with a pipe having an inner surface covered by a liner made of a non-conductive material. The vapor sensor senses moisture build up as water or fluid vapor permeates through the non-conductive liner into a sealed compartment containing a coil, electrodes, or both. The vapor sensor can sense a change in relative humidity in the sealed compartment. The vapor sensor is connected to transmitter circuitry circuitry in the electronics compartment of the magnetic flowmeter. The transmitter circuitry circuitry can generate an output to alert a user to permeation when the vapor sensor senses a predetermined change in relative humidity. This is advantageous as the user is alerted to permeation prior to failure of the flowmeter due to a short. The user can use the relative humidity data to estimate time to failure and replace the flowmeter prior to failure. 
       FIG. 1  is a perspective view of magnetic flowmeter  10 .  FIG. 2  is a cross-sectional view of magnetic flowmeter  10  along line  2 - 2  in  FIG. 1 . Magnetic flowmeter  10  includes pipe  12 , magnetics compartment  14 , and electronics compartment  16 . Pipe  12  and magnetics compartment  14  form the flow tube of magnetic flowmeter  10 . The inner surface of pipe  12  is lined with liner  18 . Magnetics compartment  14  surrounds pipe  12  and encloses tunnels  20  with electrodes  22 , field coils  24 , and vapor sensor  26 . In the embodiment shown, magnetic flowmeter  10  includes two tunnels  20 , two electrodes  22 , and two field coils  24 . Hermetic seal  28  provides a primary seal between magnetics compartment  14  and electronics compartment  16 . Hermetic seal  28  can be made of glass or any other suitable material. Seal  30  provides a secondary seal between magnetics compartment  14  and electronics compartment  16 . Seal  30  can be made of rubber or any other suitable material. 
     Pipe  12  can be made of a conductive material, such as stainless steel. Liner  18  is made of a non-conductive material such as polyurethane, polytetrafluoroethylene (PTFE), or an insulating rubber material in order to prevent a short in the voltage induced across a fluid flowing through pipe  12 . Liner  18  can be glued, pressed, injection molded, or rotationally molded to the inner wall of pipe  12 . In an alternative embodiment, liner  18  can be formed by pouring a material into pipe  12  and allowing the material to harden. Tunnels  20  are holes drilled through pipe  12  and into liner  18  on opposite sides of pipe  12 . Electrodes  22  placed in tunnels  20 , and embedded into liner  18 , such that electrodes  22  are sealed against liner  18  and can be in direct electrical contact with a fluid flowing through pipe  12 . Tunnels  20  provide clearance around electrodes  22 , preventing electrodes  22  from contacting pipe  12  and shorting out. Field coils  24  are located opposite each other on the outside of pipe  12  (generally above and below pipe  12 , as shown in  FIG. 2 ). Vapor sensor  26  can be located anywhere within magnetics compartment  14 , preferably in a location with lower temperature, such as the top portion of magnetics compartment  14  (as shown in  FIG. 2 ). 
     Magnetic flowmeter  10  measures the flow velocity of a conductive fluid flowing through pipe  12  as well as vapor permeation in magnetics compartment  14 . When a conductive fluid flows through pipe  12 , field coils  24  generate a time varying magnetic field across the fluid. The fluid flowing through pipe  12  functions as a moving conductor inducing a voltage in the fluid. Electrodes  22  are in direct electrical contact with the fluid and therefore sense voltages present in the fluid. The voltages sensed by electrodes  22  can be used to calculate the flow rate of the fluid flowing through pipe  12 . 
     The fluid flowing through pipe  12  can be caustic and hot. High temperature and caustic fluids can facilitate vapor permeation through liner  18 . Water vapor molecules pass through liner  18  and into tunnels  20  of magnetics compartment  14 . As stated above, magnetics compartment  14  is hermetically sealed; therefore the water vapor molecules build up in magnetics compartment  14  and cause an increase in relative humidity within magnetics compartment  14 . Once the relative humidity reaches 100%, water droplets will form within magnetics compartment  14 . The water droplets can short out the electronics within magnetics compartment  14 , including electrodes  22  and field coils  24 . For example, water droplets will form in tunnels  20 , between electrodes  22  and pipe  12  and cause a short. 
     Magnetic flowmeter  10  is advantageous, because it includes vapor sensor  26  in magnetics compartment  14 . Vapor sensor  26  can be a relative humidity probe or sensor, such as a microelectromechanical systems (MEMS) chip. Vapor sensor  26  can sense vapor build up, such as relative humidity, within magnetics compartment  14 . The relative humidity measurement can be used to alert a user to vapor permeation in magnetics compartment  14 . This allows the user to replace magnetic flowmeter  10  before a short occurs and causes magnetic flowmeter  10  to lose functionality. 
       FIG. 3  is a schematic diagram of magnetic flowmeter  10 . Magnetic flowmeter  10  includes pipe  12 , magnetics compartment  14 , and electronics compartment  16 . Magnetics compartment  14  encloses electrodes  22 , field coils  24 , and vapor sensor  26 . Electronics compartment  16  includes transmitter circuitry  32 . Electrodes  22 , field coils  24 , and vapor sensor  26  are connected to transmitter circuitry  32 . 
     Transmitter circuitry  32  includes a coil driver, which provides power to field coils  24  in order for field coils  24  to generate a magnetic field across the fluid flowing through pipe  12 . Transmitter circuitry  32  also includes a signal processor, a digital processor, and a communications interface. The signal processor measures a voltage difference in potential between electrodes  22  and converts the voltage into a digital signal representing the electrode voltage. The digital signal can be processed by the digital processor, and the digital processor supplies a flow measurement value to the communication interface, which communicates the value to a monitoring or control system. The communication interface can communicate the value through a wired connection or a wireless connection. 
     Transmitter circuitry  32  also receives relative humidity measurements from vapor sensor  26 . The signal processor produces a relative humidity measurement sensed by vapor sensor  26  and converts the measurement into a digital signal. The digital processor can process the signal and supply a relative humidity measurement, such as a percentage of relative humidity in magnetics compartment  14 , to the communication interface, which communicates the measurement to the read out or control system. The communication interface can therefore alert a user to vapor permeation in magnetics compartment  14 . Additionally, the communication interface can alert the user to replace magnetic flowmeter  10  when a threshold level of relative humidity is sensed by vapor sensor  26  in magnetics compartment  14 . For example, the communication interface can alert the user when a 20% change in relative humidity occurs, or when absolute relative humidity reaches a level such as 80%. 
       FIG. 4  is a perspective cut-away view of magnetic flowmeter  40 .  FIG. 5  is a front cut-away view of magnetic flowmeter  40 . Magnetic flowmeter  40  is substantially similar to magnetic flowmeter  10  of  FIG. 1 , except magnetic flowmeter  40  includes vapor sensors located in electrode wells instead of a vapor sensor located in a magnetics compartment. Magnetic flowmeter  40  includes pipe  42 , magnetics compartment  44 , and electronics compartment  46 . The inner surface of pipe  42  is lined with liner  48 . Magnetics compartment  44  surrounds pipe  42  and partially encloses electrode wells  50 . Electrode wells  50  enclose tunnels  52 , electrodes  54 , and vapor sensors  56 . Each electrode well  50  includes a tunnel  52 , an electrode  54 , and a vapor sensor  56 . Electrode wells  50  are hermetically sealed and separate electrodes  54  from magnetics compartment  44  to prevent electrode leakage into magnetics compartment  44 . Magnetics compartment  44  also encloses field coils  58 . In the embodiment shown, magnetic flowmeter  40  includes two electrode wells  50 , two tunnels  52 , two electrodes  54 , two vapor sensors  56 , and two field coils  58 . 
     Magnetic flowmeter  40  is advantageous, because it includes vapor sensors  56  in in electrode wells  50 . Vapor sensors  56  can be relative humidity probes or sensors, such as MEMS chips. Vapor sensors  56  can sense vapor build up, such as relative humidity, within electrode wells  50 . The relative humidity measurements can be used to alert a user to vapor permeation in electrode wells  50 . This allows the user to replace magnetic flowmeter  40  before a short occurs in one of electrode wells  50  and causes magnetic flowmeter  40  to lose functionality. 
       FIG. 6  is a schematic diagram of magnetic flowmeter  40 . Magnetic flowmeter  40  includes pipe  42 , magnetics compartment  44 , and electronics compartment  46 . Magnetics compartment  44  surrounds pipe  42  and partially encloses electrode wells  50 . Electrode wells  50  enclose tunnels  52 , electrodes  54 , and vapor sensors  56 . Magnetics compartment  44  also encloses field coils  58 . Electronics compartment  46  includes transmitter circuitry  60 . Electrodes  54 , vapor sensors  56 , and field coils  58  are connected to transmitter circuitry  60 . 
     Like transmitter circuitry  32  of magnetic flowmeter  10  ( FIGS. 1-3 ), transmitter circuitry  60  includes a coil driver, a signal processor, a digital processor, and a communications interface. Transmitter circuitry  60  can process voltage sensed by electrodes  54  to generate an output representing the flow rate of the fluid flowing through pipe  42 . Transmitter circuitry  60  can also process relative humidity measurements from each vapor sensor  56  in each electrode well  50  and generate outputs based upon the relative humidity sensed by vapor sensors  56 . The communication interface can alert a user to vapor permeation in one or both of electrode wells  50 , and can output the relative humidity percentage sensed by vapor sensors  56  in one or both of electrode wells  50 . Additionally, the communication interface can alert the user to replace magnetic flowmeter  40  when a threshold level of relative humidity is sensed by vapor sensors  56  in one or both of electrode wells  50 . For example, the communication interface can alert the user when a 20% change in relative humidity occurs, or when absolute relative humidity reaches a level such as 80%. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.