Patent Publication Number: US-7581427-B2

Title: Workspace analyte sensing system and method using a fan to move samples from the workspace to the sensor

Description:
BACKGROUND 
     Industrial processes often require maintenance of an atmospheric analyte within a workspace above or below a given concentration range. Analytes of interest or concern are typically reactive analytes such as O 2 , CO or VOCs. One such example is the modified atmosphere packaging (MAP) of foods where the workspace in which the foods are packaged is flushed with an inert gas, such as nitrogen, to reduce the oxygen concentration within the resultant packaging and thereby increase the shelf life of the packaged product. 
     Analyte concentration within a workspace is typically measured by pumping atmospheric samples from the workspace to a remotely located on-line analyte reading analyzer. While generally effective, such systems are relatively expensive, prone to frequent failures, and have a short life-span. While repair and replacement of these systems is problematic, the greater business concern is the time and cost involved in preventing potentially defective product, produced while the analyte sensing system was not functioning, from reaching consumers. Of even greater concern is that defective product will reach consumers, resulting in a tarnishing of the business&#39; reputation. 
     Accordingly, a need exists for an inexpensive yet reliable atmosphere analyte sensing system possessing an extended useful life. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention is a system for sensing and reporting atmospheric analyte levels in a workspace. The system includes (i) a remotely located gas analyte sensor, (ii) a tube attached to the sensor and defining a lumen through which the sensor is placed in fluid communication with a workspace, and (iii) a fan in fluid communication with the lumen of the tube for continuously moving gaseous content from the workspace through the lumen and into operative engagement with the sensor. 
     A specific embodiment of the first aspect of the invention is a system for sensing and reporting O 2  levels in the workspace of a form, fill, and seal machine. The system includes (i) a form, fill, and seal machine defining a workspace open to the atmosphere wherein packaging is filled with a product and sealed, (ii) a flush system for flushing the workspace with an inert gas to reduce oxygen levels in the workspace, (iii) an oxygen sensor remotely located relative to the workspace, (iv) a tube attached to the oxygen sensor and defining a lumen through which the oxygen sensor is placed in fluid communication with the workspace, and (v) a fan in sealed fluid communication with the lumen of the tube for continuously moving gaseous content from the workspace into operative engagement with the oxygen sensor. 
     A second aspect of the invention is a method for sensing and reporting analyte levels in a workspace. The method includes the steps of (i) placing a distal end of a tube attached to an analyte sensor within a workspace, (ii) activating a fan in sealed fluid communication with the lumen of the tube so as to continuously move gaseous content from the workspace through the tube and into operative engagement with the sensor, and (iii) sensing and reporting analyte levels in the workspace with the sensor. 
     A specific embodiment of the second aspect of the invention is a method for controlling inert gas flushing of a form, fill, and seal machine workspace. The method includes the steps of (i) placing the distal end of a tube attached to an oxygen sensor within the workspace of a form, fill, and seal machine, (ii) activating a fan in sealed fluid communication with the lumen of the tube so as to continuously move gaseous content from the workspace through the tube and into operative engagement with the oxygen sensor, (iii) sensing and reporting O 2  levels in the workspace with the oxygen sensor, and (iv) adjusting a flow rate of inert gas into the workspace based upon the reported level of O 2  in the workspace. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of one embodiment of the invention. 
         FIG. 2  is a cross-sectional side view of the fan portion of the invention shown in  FIG. 1 . 
         FIG. 3  is a perspective view of the fan portion of the invention shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     Nomenclature 
     
         
           10  Gas Analyte Sensing System 
           20  Analyte Sensor 
           30  Fan 
           31  Housing 
           32  Rotar 
           33  Blades 
           40  Tube 
           49  Lumen of Tube 
           50  Workspace 
           60  Gas Introduction System 
           61  Introduced Gas 
           70  Flow Control Valve 
           100  Microcontroller 
       
    
     DEFINITIONS 
     As utilized herein, including the claims, the term “fan” means a machine including at least a rotor, blades and a housing for moving gases at relatively low pressure differentials wherein the blades do NOT sealingly engage the housing. 
     Description 
     Construction 
     The gas analyte system  10  of the present invention is effective for measuring the concentration of a gaseous analyte in a workspace  50 . Common analytes of interest include specifically, but not exclusively, carbon dioxide, carbon monoxide, oxygen, ozone, water vapor, and volatile organ compounds such as propane, benzene, toluene, methanol, etc. 
     Referring to  FIG. 1 , the gas analyte system  10  of the present invention is depicted in fluid communication with a generic workspace  50 . The workspace  50  may be defined by any of a number of different pieces of equipment including horizontal and vertical fill and packaging machines. One such piece of equipment is a standard form, fill, and seal machine (not shown) where packaging film (not shown) is fed from a master roll (not shown) into the workspace  50  where the film is formed into individual bags (not shown). The fill unit (not shown) and seal unit (not shown) of the form, fill, and seal machine are located within the workspace  50 . The product to be packaged (not shown) (e.g., potato chips) is stored within a hopper (not shown) and directed by feeder tubes (not shown) into bags after the bags have been formed. The filled bags are moved through the workspace  50  by a first conveyor (not shown) and, upon exiting the workspace  50 , are moved away from the workspace  50  for further handling by a second conveyor (not shown). 
     An inert gas  61 , typically N 2 , CO 2  or a combination thereof, is pumped into the workspace  50  through a gas introduction system  60  for purposes of reducing O 2  levels in the workspace  50 . By way of example, snack food such as potato chips are typically packaged with an O 2  concentration of less than about 3% in the headspace (not shown) of the bag. By reducing O 2  levels in the workspace  50 , the O 2  levels in the headspace of the sealed bags formed by the form, fill, and seal machine will contain reduced O 2  levels corresponding to the O 2  concentration within the workspace  50  as the headspace is filled with air from the workspace  50 . 
     Referring to  FIG. 1 , an analyte sensor  20  effective for sensing the concentration of an analyte of interest is placed in fluid communication with the workspace  50  via suitable tubing  40 . The sensor  20  can be provided with a display (not shown) for reporting sensed analyte levels to an operator and/or placed in electrical communication with a microcontroller  100  for reporting sensed analyte levels to the microcontroller  100 . 
     The gas introduction system  60  is equipped with a flow-control valve  70  for allowing manual or automatic control of gas flow through the gas introduction system  60  based upon the sensed and reported concentration of analyte within the workspace  50 . The gas introduction system  60  can be used to introduce an inert gas within the workspace  50  in order to maintain a reduced concentration of an analyte within the workspace  50  (i.e., a flushing system), or alternatively can be used to introduce a reactive gas within the workspace  50  in order to maintain a desired reactive environment within the workspace  50  (i.e., reactant supply system). An exemplary use of the gas introduction system  60  as a flushing system places the flow-control valve  70  and the analyte sensor  20  into electrical communication with a microcontroller  100  programmed to open valve  70  in order to increase the flow of inert gas into the workspace  50  when the analyte sensor  20  senses an analyte level above a defined upper threshold value (e.g., 4%) to prevent contamination of product processed within the workspace  50 , and close valve  70  in order to decrease the flow of inert gas into the workspace  50  when the analyte sensor  20  senses an analyte level below a defined lower threshold value (e.g., 2%) to prevent overuse of inert gas. 
     An exemplary use of the gas introduction system  60  as a reactant supply system places the flow-control valve  70  and the analyte sensor  20  into electrical communication with a microcontroller  100  programmed to open valve  70  in order to increase the flow of analyte into the workspace  50  when the analyte sensor  20  senses an analyte level below a defined lower threshold value (e.g., 40%) to ensure the presence of sufficient analyte within the workspace  50 , and close valve  70  in order to decrease the flow of the gaseous analyte into the workspace  50  when the analyte sensor  20  senses an analyte level above a defined upper threshold value (e.g., 50%) to prevent overuse of analyte. 
     Gas samples for testing by the analyte sensor  20  are withdrawn from the workspace  50  through tubing  40  on a continuous basis by a fan  30  in sealed fluid communication with the lumen  49  of the tube  40 . The fan  30  includes a housing  31 , rotor  32  and blades  33  for continuously pulling gases at relatively low pressure differentials through the tube  40 . I have surprisingly discovered that suitable samples may be pulled from a workspace  50  and passed by an analyte sensor  20  utilizing a fan  30  (i.e., a machine for moving gases at relatively low pressure differentials wherein the blades do not sealingly engage the housing) rather than a pump (i.e., a machine for moving fluids at relatively high pressure differentials wherein the blades sealingly engage the housing), resulting in a significant cost savings and substantial increase in the useful life of the gas analyte sensing system  10 . 
     A wide range of fans  30  may suitably be used in the gas analyte sensing system  10 . Preferred fans  30  are the small fans (i.e., typically about 1-10 inches wide by about 1-10 inches tall and about ½-2 inches thick) with an RPM of between about 1,500 and about 15,000 widely used on CPUs and in similar applications. 
     The sensing system  10  should be constructed, configured and arranged to provide a gas flow rate from the workspace  50  through the sensor  20  of at least 0.1 liters/minute as a flow rate of less than 0.1 liters/minute can significantly delay detection of a change in analyte concentration within the workspace  50 . For most applications, the flow rate should be kept below about 5 liters/minute, preferably well below 5 liters/minute as a flow rate of greater than about 5 liters/minute depletes the concentration of desired gases from the workspace  50  without a corresponding benefit. The primary variables affecting flow rate are the performance rating of the fan  30  employed and the size of the lumen  49  in the tube  40 . 
     Use 
     The gas analyte system  10  may be effectively deployed and used to sense and report analyte levels in a workspace  50  by simply (i) placing the distal end  40   b  of the tube  40  into fluid communication with the workspace  50 , (ii) activating the fan  30  so as to continuously move gaseous content from the workspace  50  through the tube  40  and into operative engagement with the sensor  20 , and (iii) sensing and reporting analyte levels in the gaseous samples pulled from the workspace  50  with the sensor  20 .