Measuring and testing – Gas analysis – Detector detail
Reexamination Certificate
1999-08-26
2001-10-23
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Detector detail
C073S023200, C073S431000, C204S412000, C204S415000
Reexamination Certificate
active
06305214
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a gas sensor used to detect the presence of gases, such as carbon monoxide.
Many commercially available gas sensors are of the amperometric type having two or more electrodes in which a catalytically active metal is fixed to a porous substrate. The porous substrate may operate as a gas permeable membrane and structural support for the electrode. The electrodes are located on the inside surface of the membrane where they make contact with an electrolyte such as sulfuric acid. External circuitry maintains one of the electrodes, the working electrode, at a selected electrical potential with respect to one of the other electrodes during operation.
When the gas of interest diffuses through the porous membrane to reach the working electrode, the diffused gas is oxidized or reduced at the interface of the working electrode and the electrolyte. That reaction generates an electrical current that is proportional to the concentration of the gas. In some cases, the gas of interest reacts with another chemical which, in turn, is oxidized or reduced at the electrode. In some cases, sensors are of a galvanic design wherein a metal such as lead is oxidized to provide the opposite current to that occurring at the working electrode.
In the prior art, the sensors were connected to the external circuit through wires. For example, a platinum contact wire was connected to the catalytically active electrode and passed through the sensor body to an external contact. Since most sensors contain a corrosive, liquid electrolyte, a difficulty with sensors has been providing secure electrical contact with the electrodes while maintaining an electrolyte-tight seal at the location where the conductor passes through the sensor body. In the prior art, seals around conductors have included Teflon gaskets. In other methods, the seal has been made of thermoplastic material or epoxy resin.
U.S. Pat. No. 5,744,697 to Martell, et al. discloses a gas sensor of the type described above. The Martell, et al. gas sensor has a plastic housing composed of a plurality of conductive housing portions integrally formed with a plurality of non-conductive housing portions. The housing has a receptacle disposed therein, and a gas-sensing agent is provided in the receptacle. A support sheet that has a plurality of electrodes formed thereon is disposed above the receptacle wherein electrical contact is made with electrodes to the conductive plastic portion, and a wick disposed in the receptacle causes the gas-sensing agent to maintain electrolytically conductive contact with the electrodes formed on the support sheet inside the sensor assembly.
SUMMARY OF THE INVENTION
In one aspect, the invention is directed to a gas sensor assembly having a housing with a receptacle formed therein. The housing has a non-conductive housing portion and a plurality of conductive housing portions, each of which is conductively separated from each other, with the conductive housing portions being composed of a conductive plastic material. A gas-sensing agent is disposed in the receptacle, and a plurality of electrodes are disposed in conductive contact with the gas-sensing agent and the conductive housing portions. The gas sensor housing has a conductive agent disposed on an area that contacts a first of the conductive housing portions and a conductive agent disposed on an area that contacts a second of the conductive housing portions. A first conductor is disposed in conductive contact with the conductive agent on the area on the first conductive housing portion, and a second conductor is disposed in conductive contact with the conductive agent on the area on the second conductive housing portion to complete the connection of the sensor to the electrical circuit.
The conductive agent may comprise a mixture of conductive ink and an adhesive, and more particularly, the conductive agent may comprise a mixture of about 15% to about 25% by volume of a conductive ink, about 15% to about 25% by volume of an adhesive, and about 50% to about 70% by volume of a thinner. This type of conductive agent may be spread on the outside of the conductive housing portions to facilitate electrical connection to the circuitry.
The invention is also directed to a method of forming a gas sensor assembly having a housing with a non-conductive housing portion and a plurality of conductive housing portions composed of conductive plastic material. The method includes the steps of: (a) forming the housing to have the non-conductive housing portion and the conductive housing portions, (b) applying a conductive agent comprising a mixture of a conductive ink and an adhesive to an area on a first of the conductive housing portions and to an area on a second of the conductive housing portions, (c) placing a contact surface of the first conductor in conductive contact with the conductive agent on the area on the first conductive housing portion, and (d) placing a contact surface of the second conductor in conductive contact with the conductive agent on the area on the second conductive housing portion.
In another aspect, the invention is directed to a gas sensor assembly with a non-conductive housing portion and a plurality of conductive housing portions, each of which are formed so that areas are conductively separated from each other, and the conductive housing portions are composed of a conductive plastic material. A gas-sensing agent is disposed in a receptacle formed in the housing, and a plurality of electrodes are disposed in conductive contact with the gas-sensing agent and the conductive housing portions. The gas sensor has an electrode support sheet with a plurality of electrodes formed thereon, and a seal is formed between the electrode support sheet and the housing, the seal being formed by the sealing of a portion of one of the electrodes to a portion of the housing.
The invention is also directed to a gas sensor assembly having a housing with a non-conductive housing portion and a plurality of conductive housing portions, each of which are conductively separated from each other, and the conductive housing portions are composed of a conductive plastic material. A gas-sensing agent is disposed in a receptacle in the housing, and a plurality of electrodes are disposed in conductive contact with the gas-sensing agent. The gas sensor has an electrode support sheet with a plurality of electrodes formed thereon, a seal is formed between the electrode support sheet and the housing, the seal being formed by the sealing of a portion of one of the conductive housing portions to the electrode support sheet.
In a further aspect, the invention is directed to a method of forming an electrode sheet for a gas sensor assembly. The method includes the steps of: (a) forming a support sheet having a first side and a second side, (b) applying a liquid electrode solution to a plurality of different areas on the first side of the support sheet, and then (c) subjecting the second side of the support sheet to a reduced pressure in order to pull the liquid electrode solution disposed on the first side of the support sheet towards the second side of the support sheet.
In another aspect, the invention is directed to a gas sensor assembly having a housing with a receptacle formed therein, a gas-sensing agent disposed in the receptacle, a wick disposed within the receptacle and being impregnated with the gas-sensing agent, and a plurality of conductive patterns formed on a surface of the wick, each of the conductive patterns extending from an interior portion of the wick to a peripheral portion of the wick.
The invention is also directed to a method of forming a gas sensor assembly which includes the steps of: (a) forming a wick composed of a gas sensing agent-adsorbent material having a first side and a second side, (b) applying a liquid electrode solution to a plurality of different areas on the first side of the wick, (c) subjecting the second side of the wick to a reduced pressure in order to pull the liquid electrode solution dispo
Martell Dennis
Schattke Nathan
Cygan Michael
Marshall Gerstein & Borun
Sensor Tek, LLC
Williams Hezron
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