Gas detector and automobile ventilation system

A gas detecting device using a gas sensor element changing an electrical characteristic depending on a concentration of a specific gas, comprising:

• acquiring means for acquiring a sensor output value by using the gas sensor element;
• concentration level signal switching generating means for switching and generating a plurality of concentration level signals corresponding to a plurality of concentration levels, respectively;
• first deciding means for deciding whether or not a first deciding object value calculated by using the sensor output value satisfies a first relationship for a first threshold;
• and
• second deciding means for deciding whether or not a second deciding object value calculated by using the sensor output value through a different calculating method from the method of calculating the first deciding object value and a plurality of interlevel thresholds corresponding to interlevel boundaries between the concentration levels with one to one satisfy predetermined relationships, respectively;
• wherein the concentration level signal switching generating means generates a concentration level signal corresponding to a concentration level which is higher than the lowest concentration level by one rank in place of a concentration level signal corresponding to the lowest concentration level when the first relationship is satisfied by the first deciding means for a period in which the concentration level signal corresponding to the lowest concentration level is generated, and generates the concentration level signal corresponding to a higher concentration level than a current concentration level when the second deciding object value satisfies the predetermined relationship for the interlevel threshold corresponding to the interlevel boundary between the current concentration level and the concentration level which is higher than the current concentration level by one rank, and
• generates the concentration level signal corresponding to a lower concentration level than the current concentration level when the second deciding object value does not satisfy the predetermined relationship for the interlevel threshold corresponding to the interlevel boundary between the current concentration level and the concentration level which is lower than the current concentration level by one rank.

A gas detecting device using a gas sensor element changing a sensor resistance depending on a concentration of a specific gas, comprising:

• a sensor resistance value converting circuit for outputting a sensor output potential depending on a change in a sensor resistance value by conducting to the gas sensor element, the sensor output potential being raised when the concentration of the specific gas is increased;
• A/D converting means for A/D converting the sensor output potential every predetermined time, thereby acquiring a sensor output value;
• first base value calculating means for calculating a base value from the sensor output value in accordance with the following equation (1),
• B(n)=B(n−1)+k1{S(n)−B(n−1)} (1)
• wherein S(n) represents a sensor output value, B(n) represents a base value, k1 represents a first coefficient, 0<k1<1 is set, and n is an integer indicative of an order of time series;
• difference value calculating means for calculating a difference value D(n) from the sensor output value S(n) and the base value B(n) in accordance with the following equation (2),
• D(n)=S(n)−B(n) (2)
• wherein D(n) represents a difference value;
• concentration signal generating means for generating either a low concentration signal or a high concentration signal,
• the concentration signal generating means generating the high concentration signal when the difference value is greater than a predetermined concentration threshold;
• and
• second base value calculating means for calculating the base value B(n) from the sensor output value S(n) in accordance with the following equation (3) in place of the equation (1) for a period in which the high concentration signal is generated,
• B(n)=B(n−1)+k2{S(n)−B(n−1)} (3)
• wherein k2 represents a second coefficient and 0≦k2<k1<1 is set.

A gas detecting device using a gas sensor element changing a sensor resistance depending on a concentration of a specific gas, comprising:

• a sensor resistance value converting circuit for outputting a sensor output potential depending on a change in a sensor resistance value by conducting to the gas sensor element, the sensor output potential being raised when the concentration of the specific gas is increased;
• A/D converting means for A/D converting the sensor output potential every predetermined time, thereby acquiring a sensor output value;
• first base value calculating means for calculating a base value from the sensor output value in accordance with the following equation (1),
• B(n)=B(n−1)+k1{S(n)−B(n−1)} (1)
• wherein S(n) represents a sensor output value, B(n) represents a base value, k1 represents a first coefficient, 0<k1<1 is set, and n is an integer indicative of an order of time series;
• difference value calculating means for calculating a difference value from the sensor output value and the base value in accordance with the following equation (2)
• D(n)=S(n)−B(n) (2)
• wherein D(n) represents a difference value;
• concentration level signal switching generating means for switching and generating a plurality of concentration level signals corresponding to a plurality of concentration levels, respectively,
• the concentration level signal switching generating means having a plurality of interlevel thresholds which correspond to level boundaries between a plurality of concentration levels with one to one and are increased corresponding to higher concentration interlevel boundaries,
• generating the concentration level signal corresponding to a higher concentration level than a current concentration level when the difference value is greater than the interlevel threshold corresponding to the interlevel boundary between the current concentration level and the concentration level which is higher than the current concentration level by one rank, and
• generating the concentration level signal corresponding to a lower concentration level than a current concentration level when the difference value is smaller than the interlevel threshold corresponding to the interlevel boundary between the current concentration level and the concentration level which is lower than the current concentration level by one rank;
• and
• second base value calculating means for calculating a base value from the sensor output value in accordance with the following equation (3) in place of the equation (1) for a period in which a concentration level signal corresponding to a higher concentration level than a predetermined concentration level is generated by the concentration level signal switching generating means,
• B(n)=B(n−1)+k2{S(n)−B(n−1)} (3)
• wherein k2 represents a second coefficient and 0≦k2<k1<1 is set.

A gas detecting device using a gas sensor element changing a sensor resistance depending on a concentration of a specific gas, comprising:

• a sensor resistance value converting circuit for outputting a sensor output potential depending on a change in a sensor resistance value by conducting to the gas sensor element, the sensor output potential being raised when the concentration of the specific gas is increased,
• A/D converting means for A/D converting the sensor output potential every predetermined time, thereby acquiring a sensor output value;
• third base value calculating means for calculating a base value from the sensor output value in accordance with the following equation (4),
• B(n)=B(n−1)+k3{S(n)−B(n−1)} (4)
• wherein S(n) represents a sensor output value, B(n) represents a base value, k3 represents a third coefficient, 0<k3<1 is set, and n is an integer indicative of an order of time series;
• difference value calculating means for calculating a difference value D(n) from the sensor output value S(n) and the base value B(n) in accordance with the following equation (5),
• D(n)=B(n)−S(n) (5)
• wherein D(n) represents a difference value;
• concentration signal generating means for generating either a low concentration signal or a high concentration signal,
• the concentration signal generating means generating the high concentration signal when the difference value is greater than a predetermined concentration threshold;
• and
• fourth base value calculating means for calculating the base value B(n) from the sensor output value S(n) in accordance with the following equation (6) in place of the equation (4) for a period in which the high concentration signal is generated,
• B(n)=B(n−1)+k4{S(n)−B(n−1)} (6)
• wherein k4 represents a fourth coefficient and 0≦k4<k3<1 is set.

A gas detecting device using a gas sensor element changing a sensor resistance depending on a concentration of a specific gas, comprising:

• a sensor resistance value converting circuit for outputting a sensor output potential depending on a change in a sensor resistance value by conducting to the gas sensor element, the sensor output potential being reduced when the concentration of the specific gas is increased;
• A/D converting means for A/D converting the sensor output potential every predetermined time, thereby acquiring a sensor output value;
• third base value calculating means for calculating a base value from the sensor output value in accordance with the following equation (4),
• B(n)=B(n−1)+k3{S(n)−B(n−1)} (4)
• wherein S(n) represents a sensor output value, B(n) represents a base value, k3 represents a third coefficient, 0<k3<1 is set, and n is an integer indicative of an order of time series;
• difference value calculating means for calculating a difference value from the sensor output value and the base value in accordance with the following equation (5)
• D(n)=B(n)−S(n) (5)
• wherein D(n) represents a difference value;
• concentration level signal switching generating means for switching and generating a plurality of concentration level signals corresponding to a plurality of concentration levels, respectively,
• the concentration level signal switching generating means having a plurality of interlevel thresholds which correspond to level boundaries between a plurality of concentration levels with one to one and are increased corresponding to higher concentration interlevel boundaries,
• generating the concentration level signal corresponding to a higher concentration level than a current concentration level when the difference value is greater than the interlevel threshold corresponding to the interlevel boundary between the current concentration level and the concentration level which is higher than the current concentration level by one rank, and
• generating the concentration level signal corresponding to a lower concentration level than a current concentration level when the difference value is smaller than the interlevel threshold corresponding to the interlevel boundary between the current concentration level and the concentration level which is lower than the current concentration level by one rank;
• and
• fourth base value calculating means for calculating a base value from the sensor output value in accordance with the following equation (6) in place of the equation (4) for a period in which a concentration level signal corresponding to a higher concentration level than a predetermined concentration level is generated by the concentration level signal switching generating means,
• B(n)=B(n−1)+k4{S(n)−B(n−1)} (6)
• wherein k4 represents a fourth coefficient and 0≦k4<k3<1 is set.

A gas detecting device using a gas sensor element changing a sensor resistance depending on a concentration of a specific gas, comprising:

• a sensor resistance value converting circuit for outputting a sensor output potential depending on a change in a sensor resistance value by conducting to the gas sensor element, the sensor output potential being raised when the concentration of the specific gas is increased;
• A/D converting means for A/D converting the sensor output potential every predetermined time, thereby acquiring a sensor output value;
• differential value calculating means for calculating a differential value from the sensor output value in accordance with the following equation (7),
• V(n)=S(n)−S(n−1) (7)
• wherein S(n) represents a sensor output value, V (n) represents a differential value, and n is an integer indicative of an order of time series;
• base value calculating means for calculating a base value B(n) from the sensor output value S(n) in accordance with the following equation (8),
• B(n)=B(n−1)+k{S(n)−B(n−1)} (8)
• wherein k represents a coefficient and 0<k<1 is set;
• difference value calculating means for calculating a difference value D(n) from the sensor output value S(n) and the base value B(n) in accordance with the following equation (9);
• and
• D(n)=S(n)−B(n) (9)
• concentration signal generating means for generating either a low concentration signal or a high concentration signal, the concentration signal generating means generating the high concentration signal when the differential value V(n) is greater than a first threshold for a period in which the low concentration signal is generated and generating the low concentration signal when the difference value D(n) is smaller than a second threshold for a period in which the high concentration signal is generated.

A gas detecting device using a gas sensor element changing a sensor resistance depending on a concentration of a specific gas, comprising:

• a sensor resistance value converting circuit for outputting a sensor output potential depending on a change in a sensor resistance value by conducting to the gas sensor element, the sensor output potential being reduced when the concentration of the specific gas is increased;
• A/D converting means for A/D converting the sensor output potential every predetermined time, thereby acquiring a sensor output value;
• differential value calculating means for calculating a differential value from the sensor output value in accordance with the following equation (10),
• V(n)=S(n−1)−S(n) (10)
• wherein S(n) represents a sensor output value, V(n) represents a differential value, and n is an integer indicative of an order of time series;
• base value calculating means for calculating a base value B(n) from the sensor output value S(n) in accordance with the following equation (11),
• B(n)=B(n−1)+k{S(n)−B(n−1)} (11)
• wherein k represents a coefficient and 0<k<1 is set;
• difference value calculating means for calculating a difference value D(n) from the sensor output value S(n) and the base value B(n) in accordance with the following equation (12);
• and
• D(n)=B(n)−S(n) (12)
• concentration signal generating means for generating either a low concentration signal or a high concentration signal, the concentration signal generating means generating the high concentration signal when the differential value V(n) is greater than a first threshold for a period in which the low concentration signal is generated and generating the low concentration signal when the difference value D(n) is smaller than a second threshold for a period in which the high concentration signal is generated.