Abstract:
A foam detector generally including a pair of leads positioned adjacent to a surface layer of a fluid so that foam created on a surface layer of the fluid contacts at least one lead and sends a signal to a controller connected to the leads.

Description:
This application is a 35 U.S.C. 371 Application of PCT/US01/07698 filed Mar. 9, 2001, which is a divisional application of U.S. Provisional Patent Application No. 60/188,639, filed Mar. 10, 2000 and a divisional application of U.S. Provisional Patent Application No. 60/224,242, filed Aug. 10, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to foam detectors and, more particularly, to foam detectors used in conjunction with a concentrator for gas chromatographs. 
     2. Brief Description of the Prior Art 
     When a gas is diffused through a fluid, bubbles can form and collect on a surface layer of the fluid. The accumulation of bubbles is commonly referred to as foam. 
     In some applications, such as in gas chromatography sample preparation, sample vessels are used to extract volatile organics from water samples or the like. A pressurized sparging gas is introduced into the water sample and diffuses through the water sample. The volatile organics are carried out of the water sample by the sparging gas and concentrated by a trap in a sample concentrator. The concentrated organics are then released from the trap and passed to an analyzing instrument, such as a gas chromatograph. If the bubbling action of the sparging gas creates foam over the surface layer of the water sample, the foam may or may not be contained or dissipated by a bubble breaker defined by the sample vessel. The presence of foam can lead to erroneous measurements or contamination of the sample concentrator. U.S. Pat. No. 4,910,996 to Pfisterer et al. discusses foaming problems in gas chromatographs used in beer processing. To combat the foam problem, the Pfisterer patent discloses using pressure regulators to pressurize a beer sample and prevent outgassing of the beer. However, if outgassing does occur, there is no way to test for the presence of the foam prior to the advancement of the concentrated prepared sample into internal tubing housed within the sample concentrator or the gas chromatograph. 
     Another problem not addressed by the prior art is the process of cleaning the sample concentrator if inadvertent contamination of the internal tubing does occur. Cleaning a contaminated sample concentrator generally takes a few weeks and includes the steps of taking the contaminated sample concentrator offline, shipping the sample concentrator to a cleaning facility, and reinstalling the cleaned sample concentrator. 
     SUMMARY OF THE INVENTION 
     To help obviate the disadvantages of the prior art, the present invention generally includes a device for detecting the presence of foam positioned adjacent to a surface layer of a fluid. The device generally includes a first lead positioned adjacent to the surface layer of the fluid, a second lead positioned adjacent to the surface layer of the fluid and spaced apart or electrically insulated from the first lead, and a controller connected to the first lead and the second lead. The first lead and the second lead may be thermocouples, with the first lead spaced at a further linear distance from the surface layer of the fluid than the second lead. Alternatively, the first lead and the second lead may be made from an electrically conductive material. 
     A method for the detection of foam positioned adjacent to a surface layer of a fluid is also provided. The method generally includes the steps of positioning a pair of leads adjacent to the surface layer of the fluid, with the leads each spaced apart or electrically insulated from one another. Additional steps include forming foam on the surface layer of the fluid, bringing the foam in physical contact with one or both of the pair of leads after the step of forming foam on the surface of the fluid, and registering a presence of the foam. Still further steps include (1) reducing the temperature of one of the leads after the step of bringing the foam in physical contact with one of the pair of leads and (2) flowing an electrical current from one of the pair of leads, through the foam, to another of the pair of leads, after the step of bringing the foam in physical contact with both of the pair of leads. 
     One particular application of the present invention is a system for detecting the presence of foam in gas chromatography. The system generally includes a gas chromatograph, a sample concentrator, such as a modular sample concentrator fluidly connected to the gas chromatograph, a sample vessel defining an internal cavity fluidly connected to the, sample concentrator, a pair of leads positioned in the internal cavity of the sample vessel, and a controller connected to the pair of leads. A fluid and foam may also be included, the fluid contained in the internal cavity of the sample vessel and the foam positioned on a surface layer of the fluid, wherein the foam physically touches at least one of the pair of leads. The modular sample concentrator may generally include a first body section housing, internal tubing, and a second body section housing control electronics, wherein the first body section and the second body section are removably connected to one another. Cleaning the sample concentrator includes the steps of removing a contaminated first body section from a second body section, replacing the contaminated first body section with a clean first body section, and resuming operation of the sample concentrator. 
     The present invention allows foam to be detected by one or both of the pair of leads, through the controller, and alert the operator so that the system can be shut down or continue to operate, depending on preprogram settings. Moreover, if the sample concentrator is contaminated by foam, the sample concentrator can be easily and quickly returned to operative service. 
     These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the attached drawings in which like reference numerals represent like elements throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a first embodiment foam detector assembly according to the present invention; 
     FIG. 2 is a sectional view of a second embodiment foam detector assembly according to the present invention; 
     FIG. 3 is a first end view of a modular sample concentrator according to the present invention; 
     FIG. 4 is a side view of the modular sample concentrator shown in FIG. 3; and 
     FIG. 5 is a second end view of the modular sample concentrator shown in FIGS.  3  and  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Applicants previously filed U.S. Provisional Patent Application Serial Nos. 60/188,639 and 60/224,242, which are both incorporated herein by reference in their entireties. 
     A foam detector  10  according to a first embodiment of the present invention is shown in FIG.  1 . The first embodiment foam detector  10  shown in FIG. 1 is shown in conjunction with a gas chromatography sample vessel  12  to help aid in the understanding of the present invention, but gas chromatography is only one possible type of application. 
     As shown in FIG. 1, the foam detector  10  generally includes a first lead  14 , a second lead  16  electrically insulated from the first lead  14 , and a controller  18  connected to the first lead  14  and the second lead  16 . In the particular application shown in FIG. 1, the sample vessel  12  defines an internal cavity  20  and a bubble breaker  22 , the internal cavity  20  receiving a fluid  24  having a surface layer  26 . Moreover, the first lead  14  is a sensor wire  32  and the second lead  16  is a dip tube  30 , which is electrically grounded  28 . 
     The sample vessel  12  forms a first end  34  and a second end  36 , and is generally made from glass or other electrically non-conductive material. A first collar  38  is preferably positioned adjacent to the first end  34  of the sample vessel  12  for receiving a housing  40 . The housing  40  is generally a hollow structure defining an evacuation branch  42 , a fill branch  44  with an optional septum retainer to allow for syringe injections, and a dip tube passageway  46 , with the dip tube passageway  46  receiving the dip tube  30 . An optional sensor conduit  48  is preferably fluidly connected to the dip tube passageway  46 , and preferably extends away from the housing  40  at an angle α generally between 1 and 179 degrees. However, the sensor conduit  48  is not required if the housing  40  defines a sealed orifice or is otherwise configured to receive a sensor wire  32 , discussed below. A second collar  50 , configured to provide a fluid seal with the dip tube  30 , is also positioned adjacent to the housing  40 . As previously stated, the dip tube  30  preferably extends through the dip tube passageway  46  defined by the housing  40  and continues to extend in a direction away from the sample vessel  12  and the housing  40 . 
     One end of the sensor wire  32  extends through the sensor conduit  48  connected to the housing  40  and is fluidly sealed to the housing  40  by a third collar  52 . The other end of the sensor wire  32  is electrically connected to a vessel ferrule  56 . The sensor wire  32  is preferably electrically conductive, such as a 0.010 inch diameter wire made from stainless steel or other suitable electrically conductive material. The vespel ferrule  56  is generally made from plastic and metal, metal, or any other suitable material or materials. A carrier wire  58 , preferably made from 22-gauge copper or any other diameter of suitable material, is also connected to the vespel ferrule  56 . An electrically insulated material  60 , such as PEEK brand heat shrink tubing, preferably encompasses all of the electrically conductive parts. More specifically, the PEEK brand heat shrink tubing is sealingly captured in the vespel ferrule  56  and extends along with the sensor wire  32  through the sensor conduit  48 , the dip tube passageway  46  in the housing  40 , and into the internal cavity  20  defined by the sample vessel  12 , terminating above the bubble breaker  22 . The sensor wire  32  extends out of the electrically non-conductive material  60  and is bent back over the material  60 . An exposed end  62  of the sensor wire  32  is arranged as not to contact the dip tube  30 , which is preferably electrically grounded. 
     With continuing reference to FIG. 1, a sparging gas  64  flows through the dip tube  30  in the direction shown by arrow A 1  and into the second end  36  of the sample vessel  12 . The sparging gas  64  percolates through the fluid  24  introduced into the sample vessel  12 , captures volatile organic analytes or other substances from the fluid  24 , and carries the analytes out of the sample vessel  12  through the evacuation branch  42 . If foam forms on the surface layer  26  of the fluid  24 , the foam rises in a direction indicated by arrow A 2  and enters the bubble breaker  22 . When foam moves up beyond the bubble breaker  22  and contacts the exposed end  62  of the sensor wire  32  and the dip tube  30 , current is drawn through the sensor wire  32  as the electrical discontinuity present between the spaced apart sensor wire  32  and dip tube  30  is closed by the foam. This current, produced by a current source  66  in the controller  18 , is sensed by the controller  18  and a signal is generated indicative of foam beyond the bubble breaker  22 . The signal passes though an isolation circuit  68  and foam detection logic is applied. The controller  18  is programmed to respond to the signal in a way specified by the user which may, for example, include shutting down the gas chromatography application to allow cleaning of sample vessel  12 . The current source  66  is designed so that when foam contacts the sensor wire  32 , current flows in a range of approximately 1-10 micro amps. The current is controlled by the voltages applied across the sensor wire  32  in the dip tube  30  and the additional series resistance. The current is so limited to minimize hydrolysis of the fluid  24  in the sample vessel  12 . 
     A foam detector  10 ′ according to a second embodiment of the present invention is shown in FIG.  2 . The second embodiment foam detector  10 ′ is also shown in connection with a gas chromatography application, but other applications are also contemplated. Moreover, when compared to FIG. 1, like parts in FIG. 2 are represented by like reference numerals. 
     In the second embodiment foam detector  10 ′, as shown in FIG. 2, the housing  40 ′ preferably has two sensor conduits  48 ,  48 ′. The first lead  14 ′, such as a first thermocouple  70 , is inserted through the sensor conduit  48 , is sealed by fourth collar  54 , and extends away from the housing  40 ′ in a direction A 3  toward the bubble breaker  22 . The second lead  16 ′, such as a second thermocouple  72 , is inserted through the second sensor conduit  48 ′, is sealed by a second fourth collar  54 , and also extends away from the housing  40 ′ in a direction toward the bubble breaker  22 . The first lead  14 ′ extends further away from the housing  40 ′ than the second lead  16 ′, so that the first lead  14 ′ is spaced closer to the bubble breaker  22  than the second lead  16 ′. 
     With continuing reference to FIG. 2, sparging gas  64  flows through the sample vessel  12  in the direction of arrow A 3  through the fluid  24 . As the sparging gas  64  percolates through the fluid  24 , volatile organic analytes or other substances are captured from the fluid  24  and exit the sample vessel  12  through a dip tube  30  (FIG. 1) which extends through the housing  40 ′. If foam forms on the surface layer  26  of the fluid  24 , the foam rises in a direction indicated by arrow A 4  and enters the bubble breaker  22 . When foam moves up beyond the bubble breaker  22  and contacts the first lead  14 ′, which is spaced closer to the bubble breaker  22  than the second lead  16 ′, the foam cools the first lead  14 ′, which, in this embodiment, is a first thermocouple  70 . The cooling creates a temperature differential between the first thermocouple  70  and the second thermocouple  72 . Any temperature difference between the first thermocouple  70  and the second thermocouple  72  results in a corresponding electrical differential. The electrical differential is measured by a controller  18 ′ having a balanced bridge circuit  74  which is zeroed at startup using an autotear circuit  76 . The balance bridge circuit  74  compares the electrical output of the first thermocouple  70  and the electrical output of the second thermocouple  72 . The comparison of the first thermocouple  70  and the second thermocouple  72  can be adjusted using a user deviation circuit  78 . The deviation circuit  78  can be used to correct for drift and other problems. Thermocouples  70 ,  72  are preferred in this embodiment because the thermocouples  70 ,  72  are in the same thermal environment in their respective electrical outputs are generally equal to one another. Therefore, if both the first and second thermocouples  70 ,  72  are heated or cooled equally, both will produce a zero output voltage or an output voltage normalized to zero. 
     If the difference between the electrical output of the first thermocouple  70  and the second thermocouple  72  exceeds the deviation entered by the user, the process or operation stops, holds, or shuts down, thereby preventing contamination and erroneous results. However, if the difference between the electrical output of the first thermocouple  70  and the second thermocouple  72  is within the tolerances set by the user, the process keeps running for the desired allotted period of time, stops, and the comparison zeroed itself. Only a sudden rise or fall in voltage outside the set tolerances causes shutdown. Continuous slow drift is neutralized by a periodic rezeroing of the output signals of the first and second thermocouples  70 ,  72 . 
     In the unlikely event that the first and second embodiment foam detectors  10 ,  10 ′ become incapacitated due to wear, a modular sample concentrator  80 , shown in FIGS. 3-5, can be used either in conjunction with the first and second embodiment foam detectors  10 ,  10 ′ or without the first and second embodiment foam detectors  10 ,  10 ′. As shown in FIG. 3, the modular sample concentrator  80  generally includes a first body section  82  removably connected to a second body section  84 . As shown generally in FIGS. 3 and 5, and with more detail in FIG. 4, the first body section  82  preferably houses internal tubing  85  which is fluidly connected at one end  86  to a sample vessel  12  and is fluidly connected at a second end  88  to a gas chromatograph  90 . Referring again to FIG. 3, the second body section  84  houses electronic control circuitry and may also contain an input control panel  92 . The first and second body sections  82 ,  84  are preferably electrically connected to each other via a wiring harness  94 , an integrated circuit board  96 , and one or more spring loaded attachment posts  98 . 
     Referring generally to FIGS. 3-5, one method of repairing the modular sample concentrator  80  includes the steps of operating the modular sample concentrator  80 , allowing the first body section  82  internal tubing  85  to become contaminated, stopping the modular sample concentrator  80 , removing the first body section  82 , replacing the removed first body section  82  with another first body section  82  having clean internal tubing  85 , restarting the modular sample concentrator  80 , and cleaning the contaminated first body section  82 . This method allows the modular sample concentrator  80  to become operational quickly, without taking the entire modular sample concentrator  80  offline for one or more days. 
     The invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.