Abstract: Sensing particular gases in a mixture uses precise modulated heating. Sensor relative responses are compared at different temperatures and compared with known relative responses to identify gases and concentrations. Heater current sensors provide feedback control and microprocessor inputs. A processor controls complex impedances and varied frequencies in the sensors. Sensor responses at varied complex impedances and at varied frequencies are compared with known responses at those impedances and frequencies to determine existence and concentration of particular gases. Heater and sensor buses are separate or combined.

Abstract: Sensing particular gases in a mixture uses precise modulated heating. Sensor relative responses are compared at different temperatures and compared with known relative responses to identify gases and concentrations. Heater current sensors provide feedback control and microprocessor inputs. A processor controls complex impedances and varied frequencies in the sensors. Sensor responses at varied complex impedances and at varied frequencies are compared with known responses at those impedances and frequencies to determine existence and concentration of particular gases. Heater and sensor buses are separate or combined.

Abstract: A sensor for detecting hydrogen or ammonia gas uses a gas sensitive material based on Cr2O3 with a small percentage of the chromium replaced by transition metal ions having a valency greater than four, but still having a corundum crystal structure. Electrodes in contact with the gas sensitive material are connected by conductors to electrical measuring means for measuring the resistance, conductance, capacitance, or impedance of the gas sensitive material. A temperature sensing means and heating means allow the temperature of the gas sensitive material to be regulated. The gas sensitive material is formed on an insulator substrate over one or both electrodes. One electrode can be on the non-substrate side of the gas sensitive material. The gas sensitive material can be formed by deposition from a suspension or colloidal dispersion and firing. The gas sensitive material is contacted with gas and changes in electrical properties of the material are observed.

Abstract: An air quality monitor having multiple sensors deployed in an electric circuit returns a single sign indication of atmospheric impurity regardless of whether the impurity gas is of the oxidizing or reducing type. Each sensor employs a gas sensitive material that exhibits a response in the form of a change in electrical resistance of the material in the presence of a gas and that exhibits a negligible response to changes in the moisture content of the atmosphere. A powder is dried and calcined and the result is ground into a fine powder and pressed into a desired shape to make the gas sensitive material. Adding a binder during the pressing and firing the shaped powder results in a gas sensitive material with porosity. Gas is flowed to the gas sensitive material and the resulting change in resistance is measured and returned as a single sign indication of atmospheric impurity.