CO gas detecting device and circuit for driving the same

• US 4,792,433 A
• Filed: 09/04/1986
• Issued: 12/20/1988
• Est. Priority Date: 08/27/1982
• Status: Expired due to Fees

• Current Assignee: Tokyo Shibaura Denki Kabushiki Kaisha
• Original Assignee: Tokyo Shibaura Denki Kabushiki Kaisha
• Inventors: Shiratori, Masayuki, Katsura, Masaki
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/903,839
• Time in Patent Office: 838 Days
• Field of Search: 73/23, 73/27 R, 324/71.5, 338/34, 338/225 D, 422/94-98, 422/90, 436/134, 436/151, 436/152, 436/159
• US Class Current: 422/98
• CPC Class Codes: G01N 27/12 of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid , for detecting components in the fluid
• CPC Class Codes: G01N 33/0031 comprising two or more sensors, e.g. a sensor array
• CPC Class Codes: G01N 33/004 CO or CO2

Abstract

Disclosed is a CO gas detecting device which comprises a CO gas sensor provided with a gas sensitive member made of SnO₂, ZnO, Fe₂ O₃ or the like, a pair of electrodes provided on said gas sensitive member, and a catalyst layer comprising at least one kind of catalyst metals of Pt, Pd and Rh and at least one kind of carriers of Al₂ O₃, ZrO₂ and SiO₂, provided on said gas sensitive member; and a reference sensor substantially without sensitivity to CO gas provided with a gas sensitive member similar to the above gas sensitive member, a pair of electrodes provided on said gas sensitive member and a catalyst layer comprising Ag and at least one kind of carriers of Al₂ O₃, ZrO₂ and SiO₂, provided on said gas sensitive member. Also disclosed is a circuit for driving the device.

Claims

1. A CO gas detecting device comprising:

a CO gas sensor provided with a gas sensitive member comprising an oxide semiconductor whose resistance value is changed when contacted with a reducing gas, a pair of electrodes provided on said gas sensitive member, and a catalyst layer comprising one or more catalyst metals selected from the group consisting of Pt, Pd and Rh and at least one carrier selected from the group consisting of Al₂ O₃, ZrO₂ and SiO₂, provided on said gas sensitive member; and

a reference sensor substantially without sensitivity to CO gas provided with a gas sensitive member comprising an oxide semiconductor whose resistance value is changed when contacted with a reducing gas, a pair of electrodes provided on said gas sensitive member, and an insulative catalyst layer comprising Ag and at least one carrier selected from the group consisting of Al₂ O₃, ZrO₂ and SiO₂, provided on said gas sensitive member

wherein said catalyst layers of each of said sensors comprise said catalyst metals in an amount of from about 0.05 to 20 wt. % based on the catalyst carrier in a thick film of from 10 to 50 μ

m and from about 1 to 90 wt. % based on the catalyst carrier in a thin film of from about 5 to 1000 nm, such that the amounts of said catalyst metals are below levels at which the electroconductivity of said layers hampers measurement of said resistance value.

2. The CO gas detecting device according to claim 1, wherein the oxide semiconductor used in each of said gas sensitive members comprises at least one oxide semiconductor selected from the group consisting of SnO₂, ZnO and Fe₂ O₃.

3. The CO gas detecting device according to claim 2, wherein the oxide semiconductor further comprises Nb or Sb within the range of from 0.005 to 0.05 in terms of atomic ratio to the oxide semiconductor.

4. The CO gas detecting device according to claim 1, wherein each of said gas sensitive members is a thin film.

5. The CO gas detecting device according to claim 4, wherein each of said gas sensitive member has a film thickness of from 100 Å

to 1 μ

m.

6. The CO gas detecting device according to claim 4, wherein each of said gas sensitive members comprises a SnO₂ thin film or a SnO₂ thin film comprising Nb or Sb.

7. The CO gas detecting device according to claim 1, wherein the catalyst carrier of said CO gas sensor comprises Al₂ O₃.

8. The CO gas detecting device according to claim 1, wherein the catalyst layer of said CO gas sensor comprises a thick film.

9. The CO gas detecting device according to claim 1, wherein the catalyst metal of said CO gas sensor is a material selected from the group consisting of Pt-Pd, Pd-Rh and Pt-Rh wherein the proportion of Pt/Pd, Rh/Pd and Rh/Pt=0.05 to 1.0, respectively, in terms of atomic ratio.

10. The CO gas detecting device according to claim 1, the catalyst layer of said CO gas sensor further comprising a moisture protective metal containing 0.05 to 20 wt.% of Ag based on the carrier(s).

11. The CO gas detecting device according to claim 1, further including another layer comprising at least one carrier of Al₂ O₃, ZrO₂ and SiO₂ and 0.05 to 20 wt.% of Ag based on the carrier(s).

12. The CO gas detecting device according to claim 1, wherein the carrier of the catalyst layer of said reference sensor is Al₂ O₃.

13. The CO gas detecting device according to claim 1, wherein the catalyst layer of said reference sensor comprises a thick film.

14. The CO gas detecting device according to claim 1, wherein the CO gas sensor and the reference sensor are secured and suspended within a cut area provided in an insulating supporting plate comprising a glass epoxy resin or Al₂ O₃ and having conductor patterns comprising Cu foil formed on both of front and rear surfaces thereof, by means of lead wires in such a manner that they are respectively located on the faces corresponding to the front surface and the rear surface of the supporting plate or that they are provided in parallel on the same face corresponding to one surface of the supporting plate;

said supporting plate being provided with a cut at an area adjacent to and along one side of the plug portion in such a manner that it may be inserted to an external plug socket having a shape corresponding to the sectional shape of the plug.

15. A circuit for driving the CO gas detecting device of claim 1, which comprises the CO gas sensor connected to a resistance-voltage converting circuit, the reference sensor connected to another resistance-voltage converting circuit which is further connected to an alarm level-setting circuit, a voltage comparison circuit to compare signals from the CO gas sensor and signals from the alarm level-setting circuit, and an alarm circuit to which an alarm signal from the voltage comparison circuit is inputted.

16. The CO gas detecting device according to claim 1, wherein said CO sensor and said reference sensor have similar sensitivities to reducing gases other than CO.