Method for detecting combustible gases and device therefor

Claim 2

Method for detecting the concentration of combustible gas contained in an air mixture with aid of a measuring device equipped with an indicating unit, the measuring device operating according to both the heat-tone process and the heat-conductivity process and to give an indication pursuant to the heat-tone process only beneath a predetermined reference value for the measuring signal, the method comprising the steps of: at the start of measurement, holding a single individual sensor constant in said measuring device at a first temperature T 1 adequate for a heat-conductivity measurement, said sensor being catalytically active at a second temperature T 2 greater than said first temperature T 1 which enables a heat-tone measurement to be made; obtaining a first signal from said sensor indicative of the concentration of combustible gas in said air mixture; comparing the measuring signal emitted by said sensor with a first reference value R 1 corresponding to the presence of a predetermined concentration of the combustible gas; increasing the temperature of the sensor to said second temperature T 2 only when said measuring signal indicates that combustible gas is present and at a concentration below said predetermined concentration corresponding to said reference value R 1 and holding the temperature of the sensor constant at said second temperature T 2 to obtain a second measuring signal indicative of the concentration of combustible gas in said air mixture, said sensor now operating as a heat-tone sensor; comparing said second measuring signal emitted by said sensor with a load-limit value G corresponding to a concentration of the combustible gas higher than said value R 1 ; and, reducing the temperature of said sensor to said first temperature T 1 and holding the same constant as soon as said second measuring signal exceeds said load-limit value G to thereby again place said sensor in the heat-conductivity mode and obtain a further measuring signal indicative of the gas concentration of the combustible gas for concentrations thereof greater than that corresponding to said load-limit value G.

Claim 3

The method of claim 1, wherein said reference value R 1 and said load-limit value G lie approximately in the range of 100% to 140% of the lower explosion limit.

Claim 4

The method of claim 1, wherein said sensor signal emitted in response to the reduction of the temperature thereof to T 1 causes a full-scale reading of said indicator unit.

Claim 5

The method of claim 3, wherein said measuring device also includes an alarm unit and said last-mentioned signal also actuates said alarm unit.

Claim 6

Method for detecting the concentration of combustible gas contained in an air mixture with aid of a measuring device equipped with an indicating unit, the measuring device operating according to both the heat-tone process and the heat-conductivity process and to give an indication pursuant to the heat-tone process only beneath a predetermined reference value for the measuring signal, the method comprising the steps of: at the start of measurement, holding a single individual sensor constant in said measuring device at a first temperature T 1 adequate for a heat-conductivity measurement, said sensor being catalytically active at a second temperature T 2 greater than said first temperature T 1 which enables a heat-tone measurement to be made; obtainng a first signal from said sensor indicative of the concentration of combustible gas in said air mixture; comparing said measuring signal emitted by said sensor with a first reference value R 1 corresponding to the presence of a first predetermined concentration of the combustible gas; comparing said measuring signal with a second reference value R 2 corresponding to a second predetermined concentration of the combustible gas which lies beneath said first predetermined concentration of the gas corresponding to said first reference value R 1 ; increasing the temperature of the sensor to said second temperature T 2 only when said measuring signal indicates that combustible gas is present and at a concentration which is below said predetermined concentration corresponding to said reference value R 1 and which also exceeds said reference value R 2 to obtain a second measuring signal indicative of the concentration of combustible gas in said air mixture, said sensor now operating as a heat-tone sensor; comparing the measuring signal emitted by said sensor with a load-limit value G corresponding to a concentration of the combustible gas higher than said value R 1 ; and, reducing the temperature of said sensor to said first temperature T 1 and holding the same constant as soon as said measuring signal exceeds load-limit value G to thereby again place said sensor in the heat-conductivity mode and obtain a further measuring signal indicative of the gas concentration of the combustible gas for concentrations thereof greater than that corresponding to said load-limit value G.

Claim 7

Method for detecting the concentration of combustible gas contained in an air mixture with aid of a measuring device equipped with an indicating unit, the measuring device operating according to both the heat-tone process and the heat-conductivity process and to give an indication pursuant to the heat-tone process only beneath a predetermined reference value for the measuring signal, the method comprising the steps of: at the start of measurement, holding a single individual sensor constant in said measuring device at a first temperature T 1 adequate for a heat-conductivity measurement, said sensor being catalytically active at a second temperature T 2 greater than said first temperature T 1 which enables a heat-tone measurement to be made; obtainng a first signal from said sensor indicative of the concentration of combustible gas in said air mixture; comparing said measuring signal emitted by said sensor with a first reference value R 1 corresponding to the presence of a first predetermined concentration of the combustible gas; comparing said measuring signal with a second reference value R 2 corresponding to a second predetermined concentration of the combustible gas which lies beneath said first predetermined concentration of the gas corresponding to said first reference value R 1 ; increasing the temperature of the sensor to said second temperature T 2 only when said measuring signal indicates that combustible gas is present and at a concentration which is below said predetermined concentration corresponding to said reference value R 1 and which also exceeds said reference value R 2 to obtain a second measuring signal indicative of the concentration of combustible gas in said air mixture, said sensor now operating as a heat-tone sensor; comparing the measuring signal emitted by said sensor with a load-limit value G corresponding to a concentration of the combustible gas higher than said value R 1 ; and, reducing the temperature of said sensor to said first temperature T 1 and holding the same constant as soon as said measuring signal exceeds load-limit value G to thereby again place said sensor in the heat-conductivity mode and obtain a further measuring signal indicative of the gas concentration of the combustible gas for concentrations thereof greater than that corresponding to said load-limit value G.

Claim 8

The method of claim 5, wherein the combustible gas is methane and wherein said first reference value R 1 or said load-limit value G correspond to 100 to 140 percent Lower Explosion Limit of said combustible gas and said second reference value R 2 lies in the range between 2 and 5 percent Lower Explosion Limit.

Claim 9

The method of claim 5, wherein said sensor signal emitted in response to the reduction of the temperature thereof to T 1 causes a full-scale reading of said indicator unit.

Claim 10

The method of claim 7, wherein said measuring device also includes an alarm unit and said last-mentioned signal also actuates said alarm unit.

Claim 11

A measuring device for detecting the concentration of combustible gas contained in an air mixture, the measuring device comprising: single sensor means operable in both a heat-conductivity mode at a first temperature T 1 and a heat-tone mode at a second temperature T 2 greater than said first temperature T 1 and having a changeable sensor resistance; a controllable current source connected to said sensor for controlling current supplied to the latter; computer means connected to said sensor means for receiving an output signal thereof; measuring means for measuring said sensor resistance and for providing a measurement signal indicative of said sensor resistance and of the concentration of combustible gas in said air mixture; said computer means including a comparator for receiving said measurement signal for making a first comparison thereof with a first reference value R 1 corresponding to the presence of a first predetermined concentration of the combustible gas and for making a second comparison of said measuring signal with a second reference value R 2 corresponding to a second predetermined concentration of the combustible gas which lies beneath said first predetermined concentration of the gas corresponding to said first reference value R 1 and for issuing a first control signal to said current source only when said measuring signal indicates that combustible gas is present and at a concentration which is below said predetermined concentration corresponding to said reference value R 1 and which also exceeds said reference value R 2 ; said current source being adapted to respond to said first control signal for providing an increased supply current to increase the temperature of the sensor to said second temperature T 2 to cause said sensor to operate as a heat-tone sensor; said comparator also receiving said measurement signal for making a further comparison thereof to a load-limit value G corresponding to a concentration of the combustible gas higher than said value R 1 and for issuing a second control signal to said current source; and, said current source also being adapted to respond to said second control signal for providing a reduced supply current to reduce the temperature of the sensor to said first temperature T 1 to cause said sensor to operate as a heat-conductivity sensor.

Claim 12

A measuring device for detecting the concentration of combustible gas contained in an air mixture, the measuring device comprising: single sensor means operable in both a heat-conductivity mode at a first temperature T 1 and a heat-tone mode at a second temperature T 2 greater than said first temperature T 1 and having a changeable sensor resistance; a controllable current source connected to said sensor for controlling current supplied to the latter; computer means connected to said sensor means for receiving an output signal thereof; measuring means for measuring said sensor resistance and for providing a measurement signal indicative of said sensor resistance and of the concentration of combustible gas in said air mixture; said computer means including a comparator for receiving said measurement signal for making a first comparison thereof with a first reference value R 1 corresponding to the presence of a first predetermined concentration of the combustible gas and for making a second comparison of said measuring signal with a second reference value R 2 corresponding to a second predetermined concentration of the combustible gas which lies beneath said first predetermined concentration of the gas corresponding to said first reference value R 1 and for issuing a first control signal to said current source only when said measuring signal indicates that combustible gas is present and at a concentration which is below said predetermined concentration corresponding to said reference value R 1 and which also exceeds said reference value R 2 ; said current source being adapted to respond to said first control signal for providing an increased supply current to increase the temperature of the sensor to said second temperature T 2 to cause said sensor to operate as a heat-tone sensor; said comparator also receiving said measurement signal for making a further comparison thereof to a load-limit value G corresponding to a concentration of the combustible gas higher than said value R 1 and for issuing a second control signal to said current source; and, said current source also being adapted to respond to said second control signal for providing a reduced supply current to reduce the temperature of the sensor to said first temperature T 1 to cause said sensor to operate as a heat-conductivity sensor.

Claim 13

A measuring device for detecting the concentration of combustible gas contained in an air mixture, the measuring device comprising: single sensor means operable in both a heat-conductivity mode at a first temperature T 1 and a heat-tone mode at a second temperature T 2 greater than said first temperature T 1 and having a changeable sensor resistance; a controllable current source connected to said sensor for controlling current supplied to the latter; computer means connected to said sensor means for receiving an output signal thereof; measuring means for measuring said sensor resistance and for providing a measurement signal indicative of said sensor resistance and of the concentration of combustible gas in said air mixture; said computer means including a comparator for receiving said measurement signal for making a comparison thereof with a first reference value R 1 corresponding to the presence of a predetermined concentration of the combustible gas and for issuing a first control signal to said current source only when said measuring signal indicates that combustible gas is present and at a concentration below said predetermined concentration corresponding to said reference value R 1 ; said current source being adapted to respond to said first control signal for providing an incresaed supply current to increase the temperature of the sensor to said second temperature T 2 to cause said sensor to operate as a heat-tone sensor; said comparator also receiving said measurement signal for making a further comparison thereof to a load-limit value G corresponding to a concentration of the combustible gas higher than said value R 1 and for issuing a second control signal to said current source; and, said current source also being adapted to respond to said second control signal for providing a reduced supply current to reduce the temperature of the sensor to said first temperature T 1 to cause said sensor to operate as a heat-conductivity sensor.

Claim 14

A measuring device for detecting the concentration of combustible gas contained in an air mixture, the measuring device comprising: single sensor means operable in both a heat-conductivity mode at a first temperature T 1 and a heat-tone mode at a second temperature T 2 greater than said first temperature T 1 and having a changeable sensor resistance; a controllable current source connected to said sensor for controlling current supplied to the latter; computer means connected to said sensor means for receiving an output signal thereof; measuring means for measuring said sensor resistance and for providing a measurement signal indicative of said sensor resistance and of the concentration of combustible gas in said air mixture; said computer means including a comparator for receiving said measurement signal for making a comparison thereof with a first reference value R 1 corresponding to the presence of a predetermined concentration of the combustible gas and for issuing a first control signal to said current source only when said measuring signal indicates that combustible gas is present and at a concentration below said predetermined concentration corresponding to said reference value R 1 ; said current source being adapted to respond to said first control signal for providing an incresaed supply current to increase the temperature of the sensor to said second temperature T 2 to cause said sensor to operate as a heat-tone sensor; said comparator also receiving said measurement signal for making a further comparison thereof to a load-limit value G corresponding to a concentration of the combustible gas higher than said value R 1 and for issuing a second control signal to said current source; and, said current source also being adapted to respond to said second control signal for providing a reduced supply current to reduce the temperature of the sensor to said first temperature T 1 to cause said sensor to operate as a heat-conductivity sensor.