Chemical sensing apparatus and methods

Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:

• a polymer whose physical structure changes upon exposure to said chemical species,
• electrically conductive elements interspersed within and at least partly separated by said polymer, and
• an impedance-measuring means for measuring the impedance between two of said conductive elements,
• wherein a change in said polymer's physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements, and
• wherein said conductive elements comprise two spaced electrical contacts on an electrically insulating substrate, said contacts being electrically connected to, and bridged by, a layer of said polymer admixed with a multiplicity of said conductive elements.

Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:

• a polymer whose physical structure changes upon exposure to said chemical species,
• electrically conductive elements at least partly separated by said polymer, and
• an impedance-measuring means for measuring the impedance between two of said conductive elements,
• wherein a change in said polymer's physical structure upon exposure to said chemical species results in an increase in the impedance between said two conductive elements and
• wherein said conductive elements form two substantially parallel layers separated by said polymer, one of said layers having a vapor-permeable structure permitting permeation of vapor to said polymer.

Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:

• a polymer whose physical structure changes upon exposure to said chemical species,
• electrically conductive elements at least partly separated by said polymer, and
• an impedance-measuring means for measuring the impedance between two of said conductive elements,
• wherein a change in said polymer's physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements, and
• wherein said conductive elements comprise two spaced electrical contacts on an electrically insulating base, said contacts being bridged by a vapor-permeable conductor that is separated from said base by said polymer.

Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:

• a polymer whose physical structure changes upon exposure to said chemical species from said air,
• discrete electrically conductive elements at least partly separated by said polymer, and
• an impedance-measuring means for measuring the impedance between two of said conductive elements,
• wherein a change in said polymer's physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements,
• wherein said polymer appertains to the family of polymers that consists of ethylene propylene polymer, styrene butadiene resin, polybutadiene, isobutylene-isoprene polymer, chloroprene polymer, fluorocarbon polymer, and polyacrylate.

Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:

• a polymer whose physical structure changes upon exposure to said chemical species from said air,
• discrete electrically conductive elements at least partly separated by said polymer, and
• an impedance-measuring means for measuring the impedance between two of said conductive elements,
• wherein a change in said polymer's physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements,
• wherein said sensor is a first sensor and further comprising a second sensor similar to said first sensor exposed to substantially the same temperatures and humidities, only one of the two sensors being accessible to vapor of said chemical species,
• wherein said polymer in one of said sensors is covered by a selectively permeable membrane, said membrane being permeable to water vapor but not to said chemical species.

Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:

• a polymer whose physical structure changes upon exposure to said chemical species from said air,
• discrete electrically conductive elements at least partly separated by said polymer, and
• an impedance-measuring means for measuring the impedance between two of said conductive elements,
• wherein a change in said polymer's physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements,
• wherein said polymer is covered by a selectively permeable membrane that is permeable to said chemical species but not to water vapor, and
• wherein said membrane comprises a fluorinated polymer.