Method and apparatus for operating a gas sensor

Claim 3

A method according to claim 1 wherein the response is a modification of the sensor''s conductivity and indication of the response is derived by sensing the change in current through the sensor by monitoring the voltage across a resistor and by activating a signal circuit when the voltage exceeds a given level.

Claim 4

A method according to claim 2 wherein separate signal circuits are activated when the voltage exceeds different levels.

Claim 5

Apparatus for sensing gases, comprising: a gas sensor of the class which is modified conductively by contact with a given first class of gases when operated in a lower temperature range and which purges itself of said gases and restores itself toward original conductivity when operated in a temperature range higher than said lower temperature range; means for operating said sensor alternately and repetitively in said lower temperature range to sense said gases and in said higher purging temperature range to purge said sensor; and means for selectively measuring and indicating said conductive response of said sensor occurring when it is operated in said lower temperature range.

Claim 6

Apparatus for sensing gases, comprising: a gas sensor of the class which is modified conductively by contact with a given first class of gases when operated in a lower temperature range and which purges itself of said gases and restores itself toward original conductivity when operated in a temperature range higher than said lower temperature range; means for operating said sensor alternately and repetitively in said lower temperature range to sense said gases and in said higher purging temperature range to purge said sensor; and means for selectively measuring and indicating said conductive response of said sensor occurring when it is operated in said lower temperature range.

Claim 7

Apparatus according to claim 4 wherein said measuring and indicating means comprises means causing current flow through said sensor, means measuring said flow and a plurality of signal circuits respectively activated at different levels of current flow measured through said sensor.

Claim 8

The apparatus of claim 4, wherein said first class of gases comprises CO and methane, said sensor responds many times more strongly in said lower temperature range to said first class of gases than to a second class of gases comprising more complex hydrocarbons, and said sensor responds many times more strongly to said second class of gases than to said first class of gases in a third temperature range higher than said lower temperature range but lower than said purging temperature range.

Claim 9

The apparatus of claim 6, in which said response comprises a change in electrical resistance of said sensor.

Claim 10

The apparatus of claim 6, in which said means for selectively measuring and indicating said response comprises means for passing a current through said sensor to provide a signal which is a measure of the resistance thereof, means for sampling said signal during intervals of predetermined duration when said sensor is in said lower temperature range, and means responsive to said sampled signal for determining when said sampled signal reaches a predetermined threshold level.

Claim 11

The apparatus of claim 8, in which said last-named means comprises hold-circuit means responsive to said sampled signal for producing a continuous signal varying with the amplitude of said sampled signal and indicator means responsive to said continuous signal for producing indications of when said continuous signal reaches a predetermined level.

Claim 12

The apparatus of claim 9, in which said means for passing a current through said sensor comprises a pair of spaced electrodes in contact with said sensor and means for applying a direct voltage between said electrodes, and in which said means for operating said sensor alternately in said higher and lower temperature ranges comprises means for applying an alternating signal to one of said electrodes, said apparatus also comprising test means manually-operable to disable said sampling means to cause application of said signal to said indicator means without sampling thereof.

Claim 13

Apparatus for automatically producing an alarm when the concentration of CO in the air exceeds a predetermined level, comprising: a gas sensor deviCe responsive to contact by air containing CO to reduce its electrical resistance substantially when operated in a lower temperature range, said gas sensor tending to exhibit progressively increasing response as the period of its exposure to CO increases, said gas sensor being purgable of CO by operating it at a temperature in a range higher than said lower temperature range; timing generator means for producing a periodic timing signal; a heater oscillator and heating means associated with said sensor for heating said sensor into said higher temperature range when said oscillator is operating; means responsive to said periodic timing signal for rendering said heater oscillator alternately operating said non-operating, thereby alternately to heat said sensor into said higher temperature range and to cool it into said lower temperature range; means for passing a current through said sensor to develop a signal which varies with changes in electrical resistance of said sensor; sampling means responsive to said timing signal for interrupting said signal except during sampling intervals of predetermined duration during which said sensor is operating in said lower temperature range; hold circuit means responsive to said output signal from said sampling means for producing a continuous signal varying with the amplitude of said sampled signal; electrically-operable alarm means; and threshold circuit means responsive to said continuous signal for operating said alarm means when said continuous signal reaches a predetermined level.

Claim 14

Apparatus for automatically producing an alarm when the concentration of CO in the air exceeds a predetermined level, comprising: a gas sensor deviCe responsive to contact by air containing CO to reduce its electrical resistance substantially when operated in a lower temperature range, said gas sensor tending to exhibit progressively increasing response as the period of its exposure to CO increases, said gas sensor being purgable of CO by operating it at a temperature in a range higher than said lower temperature range; timing generator means for producing a periodic timing signal; a heater oscillator and heating means associated with said sensor for heating said sensor into said higher temperature range when said oscillator is operating; means responsive to said periodic timing signal for rendering said heater oscillator alternately operating said non-operating, thereby alternately to heat said sensor into said higher temperature range and to cool it into said lower temperature range; means for passing a current through said sensor to develop a signal which varies with changes in electrical resistance of said sensor; sampling means responsive to said timing signal for interrupting said signal except during sampling intervals of predetermined duration during which said sensor is operating in said lower temperature range; hold circuit means responsive to said output signal from said sampling means for producing a continuous signal varying with the amplitude of said sampled signal; electrically-operable alarm means; and threshold circuit means responsive to said continuous signal for operating said alarm means when said continuous signal reaches a predetermined level.

Claim 15

The apparatus of claim 11, wherein said means for passing a current through said sensor comprises a pair of spaced electrodes in contact with said sensor and means for applying a direct voltage between said electrodes, said apparatus also comprising test switch means manually operable to discontinue said interrupting of said signal for testing the operation of said apparatus.

Claim 16

The apparatus of claim 11, in which said sensor is many times more responsive to CO when in said lower temperature range than when in said higher temperature range.