Method for CO detection and its apparatus

• US 5,517,182 A
• Filed: 09/20/1994
• Issued: 05/14/1996
• Est. Priority Date: 09/20/1994
• Status: Expired due to Fees

• Current Assignee: FIGARO Engineering, Inc. (New Cosmos Electric Co., Ltd.)
• Original Assignee: FIGARO Engineering, Inc. (New Cosmos Electric Co., Ltd.)
• Inventors: Yasunaga, Susumu
• Primary Examiner(s): Swarthout, Brent A.
• Assistant Examiner(s): LIEU, JULIE BICHNGOC
• Application Number:
  US08/309,163
• Time in Patent Office: 602 Days
• Field of Search: 340/634, 340/632, 422/90, 422/94, 422/95, 422/98, 338/34, 338/35, 73/31.05, 73/31.06
• US Class Current: 340/634
• CPC Class Codes: G01N 27/124 varying the temperature, e.g. in a cyclic manner

Abstract

A CO detector, utilizing periodical temperature change of a metal oxide semi-conductor gas sensor, is equipped with a backup battery. When power cut of a commercial power supply is detected, the detector will be driven by the battery, and the gas sensor will be heated at 50°-100° C. for from 30 seconds to 1 minute and will be kept at room temperature for about 30 minutes. CO is detected by the minimum sensor output after the heating.

Claims

1. A method for CO detection comprising:

a step for operating a metal oxide semi-conductor gas sensor which comprises at least a heater and a metal oxide semi-conductor whose resistance changes upon contact with CO, with a first power supply under a first heating cycle, so that the metal oxide semi-conductor is heated at a relatively high temperature suitable for purging said semi-conductor, and at a relatively low temperature suitable for CO adsorption on said semi-conductor,

a step for detecting CO by measuring the resistance of the metal oxide semi-conductor at said relatively low temperature,

a step for detecting power cut of the first power supply and for outputting a power cut signal,

a step for connecting a backup battery to the gas sensor in place of the first power supply, based upon the power cut signal,

a step for operating the gas sensor under a second heating cycle repetitively upon the power cut signal so that the metal oxide semi-conductor is pulsively heated and is kept from being heated except for the pulse heating time,

a step for detecting CO by measuring the resistance of the metal oxide semi-conductor after the pulse heating in the second heating cycle, and

operating a micro-computer for controlling the heater and for detecting CO by measuring the resistance of the metal oxide semi-conductor under the second heating cycle in an operation mode both for controlling the heater and for detecting CO by measuring the resistance of the metal oxide semi-conductor, and also in a hold mode without operation alternately.

2. A method for CO detection as recited in claim 1, wherein the maximum heating temperature of the metal oxide semi-conductor during the second heating cycle is in the range of from ambient temperature plus 30°

C. to ambient temperature plus 150°

C.

3. A method for CO detection as recited in claim 1, wherein the pulse heating is performed for 5 seconds to 2 minutes and the gas sensor is kept from being heated for 5 minutes to 2 hours.

4. A method for CO detection as recited in claim 1, wherein the step for detecting CO under the second heating cycle includes sampling a maximum or stationary resistance of the metal oxide semi-conductor after the pulse heating.

5. A method for CO detection as recited in claim 4, wherein the step for detecting CO under the second heating cycle further includes a step for detecting CO by measuring the resistance of the metal oxide semi-conductor after the sampling of the maximum or the stationary resistance.

6. A method for CO detection in claim 1, wherein the backup battery is connected to the heater of the gas sensor intermittently during the pulse heating.

7. A method for CO detection as recited in claim 1, wherein an LED and a buzzer both for indicating the presence of CO are provided, and they are intermittently operated under the second heating cycle when the presence of CO is detected.

8. A method for CO detection as recited in claim 7, wherein the metal oxide semi-conductor is intermittently connected to the backup battery under the second heating cycle after the pulse heating for sampling its resistance.

9. A CO detector comprising;

a metal oxide semi-conductor gas sensor which includes a metal oxide semi-conductor whose resistance changes in contact with CO and at least a heater for heating the semi-conductor, a first power supply, and means for controlling the heater by inputting the output of the power supply to the heater so that the metal oxide semi-conductor is heated at a relatively high temperature and at a relatively low temperature alternately and periodically,

a backup battery,

means for detecting trouble of the first power supply,

a switch for connecting either of the first power supply and the backup battery to the heater control means,

a micro-computer both for controlling the heater control means and for sampling the resistance of the metal oxide semi-conductor for detecting CO, said micro-computer having at least two modes comprising an operational mode both for controlling the switch and the heater and for detecting CO by measuring the resistance of the metal oxide semi-conductor, and a data hold mode without operation but holding data stored in the micro-computer, and

a timer,

said micro-computer, when said trouble detecting means detects trouble of the first power supply, controlling both the switch and the heater control means so that the backup battery is connected to said heater control means and so that the metal oxide semi-conductor is heated pulsively and kept at ambient temperature alternately, and

the micro-computer detecting CO by measuring the resistance of the metal oxide semi-conductor after the pulse heating, and said micro-computer undergoes the two modes alternately with the timer, when the trouble of the first power supply is detected.

10. A CO detector as recited in claim 9, wherein said micro-computer detects CO by determining the maximum or stationary resistance of the metal oxide semi-conductor after the pulse heating, when the trouble of the first power supply is detected.

11. A CO detector in claim 10, wherein said micro-computer generates a plurality of sub-pulses during the pulse heating for connecting the backup battery to the heater during the each sub-pulse, when the trouble of the first power supply is detected.

12. A CO detector in claim 9, wherein the detector as recited further comprises a buzzer and LED both for alarming the presence of CO, and the buzzer and the LED are intermittently operated, when CO is detected during the trouble of the first power supply.

13. A CO detector comprising:

a metal oxide semi-conductor gas sensor which includes a metal oxide semi-conductor whose resistance changes in contact with CO and at least a heater for heating the semi-conductor, a first power supply, and means for controlling the heater by inputting the output of the power supply to the heater so that the metal oxide semi-conductor is heated at a relatively high temperature and at a relatively low temperature alternately and periodically,

a backup battery,

means for detecting trouble of the first power supply,

a switch for connecting either of the first power supply and the backup battery to the heater control means, and

a controller having a timer and a micro-computer, said micro-computer controlling the heater control means and sampling the resistance of the metal oxide semi-conductor for detecting CO, said micro-computer having at least two modes comprising an operational mode both for controlling the switch and the heater and for detecting CO by measuring the resistance of the metal oxide semi-conductor, and a data hold mode without operation but holding data stored in the micro-computer,

said micro-computer, when said trouble detecting means detects trouble of the first power supply, controlling both the switch and the heater control means so that the backup battery is connected to said heater control means and so that the metal oxide semi-conductor is heated pulsively and kept at ambient temperature alternately, and

the micro-computer detecting CO by measuring the resistance of the metal oxide semi-conductor after the pulse heating, and said micro-computer undergoes the two modes alternately with the timer, when the trouble of the first power supply is detected.