Claims
- 1. A gas concentration detector for detecting a pollutant gas concentration, comprising:
an oxide-semiconductor gas sensor having a stable region and an unstable region in detecting a gas concentration, the gas sensor outputting a detected level by sensing the gas concentration; heater for supplying heat to the gas sensor; means for calculating a comparison level that follows the detected level with a delay; and means for determining that the gas concentration is high when a ratio of the detected level to the comparison level or a difference between both levels exceeds a predetermined value, wherein:
the calculating means calculates the comparison level so that the delay becomes smaller in the unstable region compared with that in the stable region.
- 2. The gas concentration detector as in claim 1, further including a memory, wherein:
the gas sensor periodically outputs a present value of the detected level with predetermined intervals; the calculating means periodically calculates a present value of the comparison level with the same intervals as the gas sensor; the memory memorizes each present value of the detected level and each present value of the comparison level; and the present value of the comparison level is calculated by adding a value less than a difference between the present value of the detected level and an immediately previous value of the comparison level to an immediately previous value of the comparison level.
- 3. The gas concentration detector as in claim 1, further including means for counting a heater-operated time during which the heater supplies heat to the oxide-semiconductor, wherein:
the calculating means calculates the comparison level so that the delay becomes smaller before the heater-operated time reaches a predetermined time than after the heater-operated time exceeds the predetermined time.
- 4. The gas concentration detector as in claim 3, further including means for detecting an amount of moisture absorbed on an surface of the oxide-semiconductor, wherein:
the predetermined time is set according to the amount of moisture absorbed.
- 5. The gas concentration detector as in claim 1, further including means for detecting an amount of moisture absorbed on an surface of the oxide-semiconductor, wherein:
the calculating means calculates the comparison level to make the delay in the unstable region small when the detected amount of moisture is large.
- 6. The gas concentration detector as in claim 4, wherein:
the calculating means calculates the comparison level to make the delay in the unstable region small when the detected amount of moisture is large.
- 7. The gas concentration detector as in claim 4, wherein:
the means for detecting an amount of moisture absorbed is a timer that counts a period of time during which the heater is not operated.
- 8. The gas concentration detector as in claim 5, wherein:
the means for detecting an amount of moisture absorbed is a timer that counts a period of time during which the heater is not operated.
- 9. The gas concentration detector as in claim 1, wherein:
the oxide-semiconductor gas sensor is a sensor for sensing NOx concentration.
- 10. The gas concentration detector as in claim 1, wherein:
the gas concentration detector is used in an automobile air conditioner operated by introducing air inside the automobile or by introducing air outside the automobile; and the inside air is introduced when the gas concentration detector determines that the gas concentration in the outside air is high, and the outside air is introduced otherwise.
- 11. The gas concentration detector as in claim 4, wherein:
the predetermined time is set to a first level when the detected amount of moisture exceeds a predetermined amount and is set to a second level which is shorter than the first level when the detected amount of moisture is less than the predetermined amount.
- 12. The gas concentration detector as in claim 10, wherein:
the gas sensor is mounted on a front grill of the automobile, so that the gas sensor is sufficiently exposed to the outside air.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2000-8737 |
Jan 2000 |
JP |
|
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-8737 filed on Jan. 18, 2000, the content of which is incorporated herein by reference.