Abstract:
Devices and methods are disclosed that can adjust a hydration level in an electrochemical sensor or an instrument which includes such a sensor. The device can include a chamber which can, at least in part, surround an inflow port of the sensor. An adjacent reservoir of water can provide a source of water vapor which can be infused into the sensor.

Description:
FIELD 
     The invention pertains to electrochemical gas sensors. More particularly, the invention pertains to devices and methods to adjust levels of hydration in such sensors subsequent to exposure to an ambient environment. 
     BACKGROUND 
     Electrochemical gas sensors of the type that are commonly used in portable and fixed instrumentation are frequently employed in diverse and sometimes extreme operating environments. Most sensors would be expected to function continuously at temperatures between −20 degrees C. to 40 degrees C. and 15% to 85% ambient humidity, and intermittently at even more extreme conditions. 
     Operating electrochemical cells at the extremes of the their respective operating range for extended periods of time can lead to performance degradation as the internal electrolyte composition responds to the external environmental conditions. For example such cells may lose or gain water in response to their respective working environments. 
     The recent trends towards smaller cell package size means that cell performance is even more susceptible to extremes of environmental conditions. Under continued operation this might result in significant degradation in cell performance or even failure. 
     There thus continues to be a need for systems and methods which support gas sensor operability at or in extreme external environmental conditions. Preferably, such enhanced operability could be provided relative to known types of electrochemical gas sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a system in accordance with the invention; and 
         FIG. 2  is an enlarged diagram illustrating additional aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated. 
     Applicant has recognized that there is a need to be able to modify hydration of electrochemical-type sensors. Modification can take place, in accordance with the invention via various exemplary processes. An assumption as to the environmental history of usage a sensor can be made and that sensor can be exposed to a controlled RH environment that is deemed appropriate for the respective history. Alternately, a measurement can be made of one or more parameters which indicate the state of humidity of the sensor, and the sensor can then be exposed to an appropriate RH environment. Multiple measurements could of course be made during the course of exposure to the environment. In yet another alternate, information can be collected during operation of the sensor to subsequently determine the appropriate remedial RH environment. 
     In accordance with the invention electrochemical gas sensors can be hydrated or dehydrated after use to adjust the sensor&#39;s electrolyte concentration to a predetermined range. This process can be conveniently carried out when the respective sensor, or associated detector is receiving routine service or battery charging. In this regard, those of skill will understand that either the entire detector or the sensor element alone could be exposed to a hydrating/dehydrating environment. 
     Electrolyte adjustment can be implemented by exposing the sensor to water vapor, to moving streams of mixed wet or dry air, exposing the sensor to solid dryers or any other way which provides the desired hydration or dehydration. 
     Effective electrolyte adjustment can include adjusting the electrolyte to its allowable operable range. Those of skill in the art will recognize that it is not necessary to readjust the respective sensor to its original, out the factory door condition, in view of that fact that electrolytes for such sensors are usually chosen partly on the basis that they continue to function adequately across as wide a range as possible. In addition, where cells have been exposed to a common environment, an open loop hydrating/dehydrating methodology could be developed which could be applied to a plurality of cells which have been exposed to the common environment. 
     In a preferred method of practicing the invention, an electrochemical gas sensor component within a gas detector is hydrated, or dehydrated, through modification of the local humidity external to the sensor, while the detector, or, instrument is not in use. For example, hydration, or dehydration, could take place while the batteries of the detector are being re-charged. In accordance herewith, the present method would replenish or extract an equivalent amount of water vapor to that lost/gained by the sensor during a period of operation, thereby significantly reducing or eliminating environmental effects on sensor performance. 
     In one aspect, the detector can be placed in a sealed chamber in which the local humidity is modified/controlled in a fixed or dynamic fashion so as to restore the electrolyte concentration within the sensor to the manufacturer&#39;s intended composition. The relative humidity, RH of the modified instrument environment may be static and set at an appropriate level to compensate for the working conditions of the instrument/cell, or the modified RH environment may be dynamic and capable of being changed or controlled to an optimum level. 
     The optimum level may be determined by measurement of a physical characteristic of the cell that varies with degree of hydration of the electrolyte. For example, pH of the electrolyte could be measured as an indicator of hydration. 
     In a disclosed embodiment, a shroud/jacket can provide an interface with a detector&#39;s front panel to provide a seal against the external environment. The seal can be maintained with respect to the detector, or sensor element, using a variety of different types of seals such as O-rings, a gasket material, or a molded rubber insert. 
     The jacket can contain a salt solution, water or other hydrating solution, whose temperature is/can be controlled via a heater element. The jacket can also include a vapor permeable membrane through which moisture vapor can pass into an air space enclosed between the instrument sensor and the shroud. Suitable materials for the membrane material include micro-porous polymers such as PTFE or polyethylene. The shroud containing the solution could include an aperture to enable replenishment of lost water. 
     In accordance with the above, various embodiments include: 
     I) Configuring the shroud/Jacket so that it will totally enclose the instrument. 
     II) Using the shroud to enclose multiple instruments. 
     III) Providing a saturated salt solution in the shroud. 
     IV) Providing an unsaturated solution in the shroud. 
     V) The shroud can contain a salt solution with an RH between 5 and 95% RH that is non-temperature controlled. Preferably, the imposed RH would be in the range 40 to 60% to match that of the original electrolyte solution within the cell. However, the RH of the shroud could be chosen and adjusted to compensate for the local working environment. For example. If the cells have been operating in a dry warm environment then a shroud might be chosen to provide a high RH environment to compensate for higher than average loss of water vapor from the cell and vice versa. 
     VI) The applied RH % may be controlled by varying the temperature of the salt solution via a heater element. 
     VII) The temperature and applied humidity might be specifically controlled and adjusted to an optimum level by measuring a characteristic of the cell that varies with degree of electrolyte hydration. Examples include electrolyte pH, cell capacitance, impedance, or noise. Alternately, cell response to an applied current or voltage pulse can be sensed. 
     VIII) The local RH environment of the instrument/cell could be modified remotely, provided the instrument is in an enclosed chamber. In addition to the above, other suitable methods might be to blend two air streams of differing humidity to a single flow of a specific humidity. 
       FIG. 1  illustrates an apparatus  10  which embodies the invention. A hydrating housing  12  can partially, via section  12   a , or fully, as illustrated by expansion section  12   b  (in phantom), provide a hydrating/dehydrating environment for a plurality of electrochemical gas detectors  14 , having members  14   a ,  14   b  . . .  14   n . Electrolyte adjustment can take place while a battery of the respective detector, such as detector  14   i  is being recharged. 
     In  FIG. 2  detector  14   i  is illustrated positioned adjacent to section  12   a  to be hydrated. Detector  14   i  includes, for example, a sensor component  20  having a cylindrically extending portion  22  with an environmental access aperture  24 . 
     An electrochemical sensing element  26  is carried within the portion  22  exposed to the environment via aperture  24 . Those of skill will understand that the detector  14   i  will also include other conventional elements which need not be illustrated here. 
     Apparatus  12   a  includes a housing section  30  with a cylindrical, hollow, protruding member, or jacket,  32 . Member  32  has an interior peripheral surface  32   a , and also carries a seal  34 , for example an O ring or other type of seal such as a gasket or molded insert. 
     When detector  14   i  is positioned against the seal  34 , the external environment is excluded and the electrolyte of the sensor element  26  can be adjusted by apparatus  12   a.    
     The jacket  32  contains, for example, a salt solution  36  whose temperature is/can be controlled via a heater element  40 . The heater element  40  can be energized from an exterior source via a connector  42 . It will be understood that other solutions could be used to carry out a hydrating or dehydrating process. 
     The apparatus  12   a  also contains a vapor permeable membrane  38  through which moisture vapor can pass into an air space  44  sandwiched between the sensor element  26  and the jacket  32 . Suitable materials for the membrane&#39;s material include micro-porous polymers such as PTFE or polyethylene. The apparatus  12   a  containing the salt solution  36  has an aperture  44  usable to replace lost water. 
     Once a suitable period of time has elapsed, detector  14   i  can be removed from apparatus  12   a  and placed back into service. On removal, the sensor element  26  should exhibit improved operational characteristics. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.