Abstract: The selectivity of response of resistive gas sensors to specific gases or vapors is improved by the selection of specified gas-sensitive materials which are not previously known for the applications described, which include detection of hydrocarbons in the presence of CO, H.sub.2 S, SO.sub.2, chlorine, NO.sub.2, CO.sub.2 (especially in low concentrations), CFC's, ammonia, free oxygen by determination of partial pressures, and numerous organic gases and vapors.

Abstract: A resistive gas sensor has a gas sensing layer (11) overlaid as a layer on an array of electrodes (12, 14, 16) with unequal gaps (22, 24) between them. Signals from the different electrodes represent resistances in different regions of the sensing layer. The layer is applied as a succession of sub-layers, with application of each sub-layer modifying the microstructure of the preceding sub-layers. The resulting variation in microstructure within the sensing layer (11) is used for distinguishing between a reactive gas and a less reactive gas. The sensor has domestic applications for carbon monoxide detection.

Abstract: A method for determining the presence of a first gas in a second gas uses a gas sensor made up of at least two pairs of electrodes, each pair of electrodes having different spacing between the electrodes. The electrodes of the gas sensor have surfaces that are reactive to the gases under investigation. The gas sensor is exposed to the gases, and the electrical resistances between the pairs of electrodes are measured over a period of time. `The results are compared with a calibration curve to determine if the first gas is present in the second, and to determine of the sensor is malfunctioning.

Abstract: A fire detector, for connection in a fire protection/alarm system, comprises an array of sensors, or a single sensor, of the semiconductor resistor type impregnated with a noble metal. The detector is responsive, by way of a decrease in its resistance, to an increase in any one or more parameters indicative of a fire, namely the atmospheric concentrations of carbon monoxide, hydrogen and water vapor, and temperature, so that a fire is detected regardless of which of these indicators is present. The sensor responds to all of the parameters, and the output signal simultaneously represents changes in all the parameters.

Abstract: A resistive gas sensor has a porous semiconducting oxide body in which the pore surfaces are decorated with a precious metal. The sensor operates at ambient temperatures for detection and measurement of target gases, especially carbon monoxide. The porous sensor body is formed of primary crystallites agglomerated together, the agglomerate size being less than 10 times the primary crystallite size, and the primary crystallite size having an average diameter of less than 5 micrometer. From 0.05 to 80% of the pore surfaces are covered by the metallic phase, the metallic phase consisting of particles having an average size of less than 50 nanometers. Presence of the target gas is indicated by a change in electrical resistance of the sensor.

Abstract: A resistive gas sensor having a WO.sub.3 sensing element is especially useful for detection of low concentrations (1 ppm or less) of ozone in air. The WO.sub.3 element is a porous layer with a 30-60% porosity and less than 50 micrometer thick, having in general a sufficiently open porous microstructure and high surface area to give satisfactory response to ozone. The sensor is used for detection of low ozone concentrations at a working temperature in the range from ambient to 600.degree. C.

Abstract: A gas sensor, suitable for use under non-steady state conditions, has a gas-sensitive resistor with pairs of electrodes which either have different spacings between the electrodes of a pair, or comprise a pair at the active surface and further pairs buried in the resistor at different distances from the active surface. The sensor can be used in place of a sensor array, and is coupled to a processor for processing the resistance signals to detect and/or measure at least one target gas. The sensor is self-diagnostic, and factors such as relative humidity and ambient oxygen, that can otherwise affect the readings, can be compensated for without the aid of additional sensors for that purpose.

Abstract: A sensing element, for use in determining the presence and/or concentration of a species in a solution, comprises a flat insulating substrate (10) having at least one thin metallic electrode (16) deposited on it and overlaid with an insulating layer (20). The electrode (16) and insulating layer (20) bridge a weakening groove (12) formed in the substrate. Immediately before use, the element is broken along the groove to expose a cross-sectional surface (24) of the element, and thus a cross-sectional working surface (26) of the electrode. The thickness (T) of the element is comparable to or less than the concentration boundary layer thickness of the solution. This exposed working surface is the only part of the electrode in contact with the solution. In use, the element can be vibrated so as to improve its sensitivity.