Abstract:
A system for testing and calibrating gas sensors with gas stored in a strip of packets. The strip may be fed into a chamber having a defined volume of air. A packet may be punctured with a mechanism to release one or more gases into the volume of air to result in an air-gas mixture. New air may be moved into the chamber to push the mixture out of the chamber to a sensor for testing and/or calibration. Then another packet may be punctured to release one or more gases into the volume of new air in the chamber for another air-gas mixture. This mixture may be moved out of the chamber, in the same manner as the previous mixture, to another sensor for testing and/or calibration. This procedure may be repeated with additional packets on the strip.

Description:
BACKGROUND 
       [0001]    The invention relates to gas sensors, and particularly to testing and calibration of sensors. 
       SUMMARY 
       [0002]    The invention is a mechanism that provides a stored amount of gas released into a defined volume of air. The gas and air mixture may be transported to a sensor for testing and/or calibration of the sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]      FIG. 1  is a diagram of a storage unit for holding a defined amount of gas for sensor testing; 
           [0004]      FIG. 2  is a diagram of an overall mechanism for gas sensor testing; 
           [0005]      FIG. 3  is a diagram showing a gas transport from a source to a gas sensor; 
           [0006]      FIG. 4  is a diagram of a thermal transport for gas from a source to a gas sensor; and 
           [0007]      FIG. 5  is a diagram of an example pump transport for gas from a source to a gas sensor. 
       
    
    
     DESCRIPTION  
       [0008]    Gas sensors should be functionally tested and calibrated periodically. In some places, functional testing and some calibration may be a requirement for sensors, for example, personnel sensor badges in a facility where a potential for a presence of a harmful gas exists. 
         [0009]    A mechanism that is capable of providing multiple gases in one run for health determination and, in some instances, for calibration of one or more sensors is desired. The present invention may provide a mixture of test gases in air, and to check and also calibrate sensors for CO, H 2 S, combustible gases, and other gases. 
         [0010]    The gases of significant interest may include CO, CH 4 , and H 2 S. These three gases should not react with each other at ambient conditions. The three gases may be put together or mixed for incorporation and sealed inside of a blister pack. The pack may be made of low permeability plastics or their metalized derivatives. These blisters may be punctured open at one per run to test and calibrate a sensor module. A number of blister packs may be made and stored in the form of a strip and wound into a roll. Single blisters may be rolled off and punched or punctured open in a manner similar to a way that a cap gun pops small explosive-like and noisy caps. To assure reproducible gas pulses to the sensors, a release of the gases may be released into a fixed amount or volume of air. Then this volume of air, mixed with a determined or fixed amount of released gases, may be transported as a particular air-gas mixture to a gas sensitive area of one or more sensors. 
         [0011]    Each single blister pack may be sealed or bonded with a cold working aluminum onto aluminum (for a good seal) or with an adhesive having a long diffusion length. A provision for transport of the gases to the sensors may also be provided. 
         [0012]    A generation or providing of gases for checking gas sensors may be effected electrochemically, thermally, or in some other manner. An illustrative example here may include a bubble foil, blister, or similar enclosure for holding and providing the gas. Gas is not necessarily generated but may be stored in a form that makes a release of the gas easy and reproducible. 
         [0013]    The present system may provide an alternative to gas generation. Current bump tests may be performed with a gas mixture from a tank (2.5 percent of CH 4 , 100 ppm CO, 40 ppm H 2 S, 15 percent of O 2 ). One may provide for a similar gas mixture from a small unit. To fill 1 mL of air with 1 percent of CH4, 100 ppm CO, and 40 ppm H 2 S, one may need a volume of 10 uL of CH 4 . 
         [0014]    An approach of the present system may include the following items. First, one may make long band of bubble foil with bubbles of about 20 uL out of aluminized polymer like Mylar, and fill them with a gas mixture without overpressure. Second, one may roll the band of bubbles onto a cylinder and pull off one bubble at a time. Third, for each bump test, one may puncture one bubble with a “hammer”, like a cap gun does when it generates a shooting sound from a roll, with chemicals. Fourth, one may let the gas mix with 2 mL of air in an enclosed volume, and pump air through the volume. Fifth, one may pump the gas mixture over the sensors. 
         [0015]    A roll for 800 2 mL-pulses could have a width of about one inch and a diameter of about two inches, which does not seem prohibitively large for fixed sensors. Bubble foil appears to be the easiest approach for fixed sensors. This approach may be used for testing portable sensors such as those implemented in personal badges. 
         [0016]    An alternative to gas generation may include some of the following items.  FIG. 1  shows a blister pack or bubble foil  10 . The bubble foil  10  may have bubbles  13  made out of aluminum foil  11  for a base and have aluminum or an aluminized polymer (e.g., Mylar)  12  for the bubble side. The aluminum foil  11  and the aluminum or aluminized polymer  12  may be joined and sealed by heat or ultrasound at a border  14  of the bubble to contain a gas  15 . The bubble  13  may be filled with a desired gas or gases  15  before or after the sealing of the border  14 . A design of the bubble or blister may be one among other approaches, packets or packages for keeping or storing gases until needed for testing and/or calibration of sensors. 
         [0017]    As indicated in  FIG. 2 , the foil  10  may be rolled up into a coil  16  and installed in a mechanism or source  20  on a coil or spool holder  17 . The foil may be fed from coil  16  through a container  21  via slots  18  and  19 , respectively. The slots  18  and  19  are such so as to provide somewhat air tight integrity to container  21  with the foil  10  moving through the slots. Roller  24  may guide the foil  10  through slot  18 . Roller  25  may guide a punctured foil  10  out of slot  19  to be wound as a coil  26  on a wind-up spool  26 . Container  21  may have an input port  22  and an output port  23  for air to enter and for a gas air mixture to exit, respectively. 
         [0018]    For each bump test, one bubble  13  may be punctured and emptied into a defined volume  28  of container  21 . There may be a plate  29  situated to keep foil  14  flat against an inside surface  31  of container  21 . A device  32  may have a pointed object  33  attached and facing plate  29 . Device  32  may be rotated about a hinge or anchor  34  towards the plate  29 . During this rotation, pointed object  33  may puncture a bubble  13  formed by foil  12 , or other material, by going through a hole  35  of plate  29  as the bubble passes by the hole. During this puncture of bubble  13 , a certain or defined amount of a particular gas  15  may be released into the chamber  28 . Upon the release of the gas, air may be pumped through port  22 , for instance with an air mover  45 , into the volume  28  and the certain or defined volume of air with the bubble  13  of gas  15  may be pushed out of volume  28  through port  23  to one or more gas sensors  30  to be tested (e.g., a health check) and/or calibrated. 
         [0019]    Permeability and chemical resistance of the bubble  13  may be noted for preservation of the gas  15 . For instance, an all-metal enclosure should keep CH 4  with traces of CO and H 2 S inside each bubble  13 . A desired permeability of the material containing the bubble or blister  13  may about 10 −15 /cm 2 . Aluminum may be reported to be stable in conjunction with H 2 S. However, a question is whether the aluminum may deplete some of the H 2 S. Depending on layout and circumstances of the setup and testing, the answer may be no. However, if the answer is assumed to be yes, H 2 S might be generated separately and/or provided outside of bubble  13 . Or bubble  13  may be made with other materials. One may further note whether H 2 S is safe and compatible, and whether H 2 S is sufficiently inexpensive for use with the present system in testing and/or calibration of sensors. The answer may depend on an application of the system or source  20 . 
         [0020]    A gas transport  37  from a gas source  20  to a sensor  30  may be noted in  FIG. 3 . Fixed and portable sensors may require different approaches. For fixed gas sensors, there may be transport of gases  15  through or from the ambient  36  to the sensor  30  by diffusion and/or convection. There may be some space available and full automatization may be desired. For portable gas sensors, transport of gases  15  from the ambient  36  to the sensor may often be effected by pumping. Space may be at a premium and human action possible or desirable for effecting transport. 
         [0021]    A flow design for fixed gas sensors might include reproducible gas pulses by an active transport, as diffusion may appear unacceptably slow and convection be unpredictable. Heat convection for gas transport  38  is shown by a diagram of a setup in  FIG. 4 . A heating element  39  may be placed proximate to the output port of gas source  20  to heat the gas  15  which will rise to follow the path of the gas transport  38  of the ambient  36 . The gas  15  may eventually reach gas sensor  30  to be sensed. Heat convection appears easy but not necessarily optimal for reproducibility. 
         [0022]    A pumping a gas pulse may result in the highest reproducibility for calibration. For example, a pump  41  may be included in a fixed gas sensor arrangement as shown in  FIG. 5 . Pump  41  may take air from the ambient  36  and push the air into a gas container  42  via a channel  43 . Container  42  may be for receiving gas  15  from a gas source  20 . Gas  15  may be pushed from container  42  by air from pump  41  through a channel  44  to a gas sensor  30  for detection. A fixed volume of air may be determined and pumped according to a volume or amount of gas released into container  42 . The overall system with the pump may relax space requirements for a gas source  20  (which could fit in a flameproof housing for safety purposes). Further, the present pump system may be economical if the pump  41  is inexpensive. An example of such a pump may be a Mesopump™ produced in a 10,000 unit volume (by a company like Honeywell). A number of mesopump units may be connected together for increased capacity. A mesopump arrangement may have a capacity to provide 12 mL/min at about 40 uW. It may have a size of about 10×10×2 mm and operate at a temperature up to 100° C. The pump may provide a 3 kPa pressure difference or differential. 
         [0023]    A flow design may be provided for portable gas sensors. The design may be more complex for portables than for fixed sensors. Reproducible gas pulses may be provided by an active transport in a portable design. It may be noted that dominant gases could include combustibles, H 2 S, and the like. An existing pump  41  may be utilized for gas transport from a gas source  20 . Or, one may let a manual operator press a button that drives pumping (which may be difficult in that the sensor or sensors should feel the gas). An integration of a source  20  may need a stronger interaction with the design of a sensor system. One may instead begin with fixed sensors rather than portable sensors, and make frequent visits to them unnecessary. 
         [0024]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0025]    Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.