Abstract: A sensor is driven at a first heating power value. The sensor generates a sensing signal that is indicative of a sensed entity. A possible onset of a sensor contamination condition is detected as a function of the sensing signal generated by the sensor. If such detecting fails to indicate onset of a sensor contamination condition, the sensor continues to be driven at the first heating power value. However, if such detecting indicates onset of a sensor contamination condition, a protection mode is activated. In the protection mode, the sensor is driven at a second heating power value for a protection interval, where the second heating power value is lower than the first heating power value. Furthermore, the operation may refrain from supplying power to the sensor for a further protection interval, wherein the further protection interval is longer than the protection interval.

Abstract: An exhaust sensor (10) includes a cylindrical sensor body (11) arranged outside of an exhaust pipe (5) of an engine (1), a gas inlet (12) formed at one end of sensor body (11), and a gas outlet (13) formed at the other end of sensor body (11). The gas inlet (12) communicates with the exhaust pipe (5) through an introduction pipe (16), while the gas outlet (13) communicates, through a return pipe (17), with the exhaust pipe (5) on the downstream side of a communication portion (16a) of the introduction pipe (16) in terms of flow of the exhaust gas, and the exhaust gas is introduced into the sensor body (11) through the gas inlet (12) and then discharged from the sensor body (11) through the gas outlet (13) by a pressure difference between the communication portions (16a), (17a) of the introduction pipe (16) and of the return pipe (17).

Abstract: A microfabricated TID comprises a microhotplate and a thermionic source disposed on the microhotplate. The microfabricated TID can provide high sensitivity and selectivity to nitrogen- and phosphorous-containing compounds and other compounds containing electronegative function groups. The microfabricated TID can be microfabricated with semiconductor-based materials. The microfabricated TID can be combined with a microfabricated separation column and used in microanalytical system for the rapid on-site detection of pesticides, chemical warfare agents, explosives, pharmaceuticals, and other organic compounds that contain nitrogen or phosphorus.

Abstract: Molecular sensing of target molecules is performed by using an electrode for molecular sensing in which detecting molecules which can shift a surface potential of the electrode by an interaction with the target molecules are bound directly or via coupling molecules to surface hydroxyl groups on a conductive metal oxide. By this molecular sensing, specific target molecules can be detected selectively and stably with high accuracy. It is also possible to detect an enantiomer selectively and stably with high accuracy. The present invention can provide a chemical sensing system which is useful in fields such as medicines, environments and foods.

Abstract: A process and apparatus for testing material libraries, in particular catalysts, by means of coupled use of at least two analytical methods, preferably IR thermography and mass spectrometry. Owing to the selected arrangement, the disadvantages of the two previously known individual methods are compensated for: the subsequent selectivity determination for selected sections by means of mass spectrometry invalidates the argument against IR thermography, of only being able to determine activities; the rapid integrated determination of potentially “good” materials via IR thermography prevents an excessive loss of time by needing to test all materials of a library successively with the mass spectrometer.

Abstract: New sensors and methods for qualitative and quantitative analysis of multiple gaseous substances simultaneously with both high selectivity and high sensitivity are provided. The new sensors rely on a characteristic difference in energy between the interaction of a particular substance with a catalyst coated heat transfer device (HTD) and a non-catalyst coated (or one coated with a different catalyst) reference HTD. Molecular detection is achieved by an exothermic or endothermic chemical or physical reaction between the catalytic surface of the sensor and the molecule, tending to induce a temperature change of the sensor. Both high temperature and non-destructive low temperature detection are possible. The magnitude and rate of endothermic or exothermic heat transfer from a specific molecule-catalyst interaction is related to molecular concentration.

Abstract: The invention relates to a process for the detection of hydrocarbons other than methane in a gas predominantly or essentially comprising oxygen, as well as methane and the said hydrocarbons other than methane, the said process comprising: a stage of detection of the combined hydrocarbons in the said gas, providing a first value for the combined hydrocarbons, a stage of combustion of the hydrocarbons other than methane, a stage of detection of methane in the said gas, providing a second value, a stage of calculation of the amount of hydrocarbons other than methane by the difference between the first value and the second value. The invention also relates to a device for implementing this process.

Abstract: A powder filler is stuffed in a filler space defined between a housing and a gas sensing element so as to airtightly seal a clearance between the housing and the gas sensing element. The powder filler contains grains whose diameter is in a range from 80 ?m to 5,000 ?m when measured before being stuffed into the filler space. A weight percentage of the grains having the diameter of 80 ?m to 5,000 ?m is equal to or larger than 80% with respect to an overall weight of the powder filler.

Abstract: A liquid electrode mixture for use in a gas sensor having from about 60 to about 240 milligrams of platinum black catalyst; from about 900 to about 1100 milligrams of water; from about 300 to about 400 microliters of 1-propanol; and from about 100 microliters to about 150 microliters of a polymer mixture comprising from about 40% to about 80% PTFE by weight and water.

Abstract: A more efficient method for combustion or oxidation of samples containing nitrogen, phosphorus and/or sulfur to their corresponding oxides is disclosed, where method uses multi-staged addition of an oxidizing agent to enhance oxidation and liberation of nitrogen, phosphorus and/or sulfur oxides for subsequent detection. The method of the present invention allows for the injection of larger samples or the introduction of a greater amount of sample per unit of time which results in a larger amount of analyte being delivered to the detector per unit of time, thereby improving detection limits and detection efficiency.

Abstract: Apparatus 1 for evaluating catalyst performance according to the invention comprises a reaction vessel 2 in which a plurality of catalysts S are disposed at a distance, supply pipes 3 for supplying a reactant gas into the reaction vessel 2, a plurality of measuring instruments 7 provided with gas sensors 71 for sensing the gas formed by the contact of the reactant gas with a plurality of catalysts S, and outputting signals according to the kinds and concentrations of the formed gas, and a calculating unit 8 for receiving the output signals from the plurality of measuring instruments 7 and identifying the kinds of the formed gas and calculating the concentrations thereof. With such a constitution, performance evaluation on a plurality of catalysts can be made concurrently, quick and in simple steps.

Abstract: One of a pair of temperature sensor sections in a combustible gas sensor is covered with porous oxidizing catalytic layers (23, 24) for oxidizing a combustible gas, and the other is not covered with the oxidizing catalyst layers. The temperature sensor sections each have temperature sensitive portions (13, 14) made of a dense ceramic material, resistors (21, 22) buried therein and having a positive resistance temperature coefficient, current leads (31, 32, 41, 42) and voltage leads (33, 34, 43, 44). A method for detecting the deterioration of a catalyst which intends to eliminate the combustible gas, by the use of this combustible gas sensor is further disclosed. When a difference between temperatures of the pair of resistors or a difference between powers fed to the pair of resistors is in excess of a predetermined value, it is judged that the catalyst has been deteriorated.

Abstract: A method of and apparatus for detecting if a MOS gas sensor has been poisoned, the sensor having a sensor element for sensing a target gas and having a heater configured to heat the sensor element in response to a voltage being applied to the heater, the heater having an operating temperature which is selectively maintained by applying a first voltage thereto. The method includes reducing the voltage from the first voltage; and sensing a change in resistance of the sensor element, responsive to the reduction of the voltage from the first voltage, and comparing sensed changes with expected changes. The apparatus includes circuitry configured to reduce the voltage from the first voltage; and the same or different circuitry senses a change in resistance of the sensor element which is responsive to the reduction of the voltage from the first voltage, and compares sensed changes with expected changes.

Abstract: The invention includes systems and methods which allow reactivation of supported noble metal catalysts. The method involves heating the catalyst in the presence of a gaseous hydrocarbon in the absence of oxidizing agents. Systems of the invention provide for in situ reactivation of catalytic material.

Abstract: This invention is directed to a method of monitoring the relative activity of various heterogeneous catalysts by analyzing their bulk electrical properties such as specific conductivity or resistance. The difference between the resistance of fresh and spent catalysts is to be large (as high as four orders of magnitude). These large differences make this invention a very sensitive indicator of changes that may happen at the surface and/or in the bulk of the catalyst. The simplicity of this new invention renders it to be a sensitive potential on-line testing method of catalyst activity.

Abstract: A sensor and method are provided for ascertaining a soot concentration in flowing, soot particle-bearing gases, wherein at least a component stream of a soot particle-bearing gas stream flows through at least one molded element which is open-pored at least in the flow direction, and wherein the temperature of the molded element is measured with at least one temperature probe. The sensor is a soot sensor, which has at least one molded element which is open-pored at least in the flow direction, at least one electric heating element and at least one temperature probe.

Abstract: An apparatus for identifying an unknown reactive gas in a carrier gas, utilizing a sensor with a diffusion limited inlet. The apparatus includes a manifold of predetermined volume having an inlet and outlet, an inlet valve in the manifold inlet, an outlet valve in the manifold outlet, a gas detector in communication with the manifold, a diffusion barrier disposed between the manifold and the gas detector for limiting diffusion of gas from the manifold into the gas detector, means for opening and closing the inlet and outlet valves, means for detecting an output signal from the gas detector, means for determining a coefficient of diffusion for the reactive gas from the output signal, and means for identifying and quantifying the reactive gas from the determined coefficient of diffusion.

Abstract: This is a method and apparatus for accurately determining a NOx concentration of a measurement gas that contains H2O and/or CO2, without being affected by a dissociation of H2O and/or CO2.

Abstract: Electronic odor detecting device (electronic nose) provided with a number of sensors. The gas that is to be subjected to the detection is brought to pass a number of similar or different sensors distributed on a surface. Between the sensors or actually extending between and past the sensors is a catalyst. The catalyst may be arranged on an opposing wall in a detection cell or in the same surface as the sensors. Constituents of the gas that react with the catalyst result in a different signal pattern for the sensors, depending on their location in relation to the catalyst. Since different substances in the gas will react with different rates in the presence of the catalyst, the sensed pattern will change along the catalytic surface. This makes it possible to evaluate a gas mixture with great precision and with a more limited number of sensors in comparison to prior art.

Abstract: A method and apparatus for identifying an unknown reactive gas in a carrier gas, utilizing a sensor with a diffusion limited inlet. After a signal is established for the carrier gas, a flow of the mixture of carrier gas and reactive gas is passed to the sensor and a steady state signal S is established. Then, the input to and output from the sensor are closed, and the steady state signal decays as a known volume of reactive gas is consumed. The decay curve of the signal is integrated to produce an integrated response .SIGMA., and the ratio S/.SIGMA. is proportional to the diffusion coefficient for the reactive gas. By comparing this ratio to the ratio for a known reactive gas, the identity of the unknown reactive gas can be determined.

Abstract: A method and apparatus is provided for modulating the flux of oxygen impinging on a calorimetric gas sensor. The method and apparatus are based on modulating the oxygen concentration of a gas mixture presented to the microcalorimeter between a predetermined high level and at a substantially zero value to create a modulated output to reduce the noise of the sensor and to eliminate its zero-offset.

Abstract: The invention provides a gas sensor for selective detection of hydrocarbons in low-oxygen gases, having a capacitive element and a gas-permeable sensitive layer as a dielectric. The sensitive layer is a precious-metal-doped zeolite which has a regular crystalline structure made of primary pores whose diameter is in the order of the gas-kinetic diameter of the gas molecules to be detected.

Abstract: A combustible gas sensor having a pair of temperature sensor sections is here disclosed. One of the pair of temperature sensor sections is covered with porous oxidizing catalytic layers (23, 24) for oxidizing a combustible gas, and the other is not covered with the oxidizing catalyst layers. In the one temperature sensor section, the combustible gas is burned, and in the other temperature sensor section, the temperature of a gas to be measured is compensated. The temperature sensor sections each comprises temperature sensitive portions (13, 14) made of a dense ceramic material, resistors (21, 22) buried therein and having a positive resistance temperature coefficient, current leads (31, 32, 41, 42) and voltage leads (33, 34, 43, 44). A method for measuring the concentration of the combustible gas by the use of this combustible gas sensor is also disclosed.

Abstract: A method and apparatus is provided for modulating flux of combustibles reacting with oxygen impinging on a calorimetric gas sensor. The method includes the steps of enclosing a sensing element and a reference element of a calorimetric gas sensor with an apparatus having at least one aperture to allow combustibles to enter and impinge on the sensing element and reference element, periodically restricting the aperture of the apparatus to modulate the flux of combustibles entering at a predetermined frequency to produce an AC output signal from the calorimetric gas sensor, and measuring the sensor output at the frequency at which the aperture is restricted.

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 method for detection of the performance reduction of an exhaust gas purification catalyst used for reducing the concentration(s) of combustible components or (and) nitrogen oxides all present in an exhaust gas, which method detects a reduction in the heat amount E.sub.g generated from the exhaust gas by the reaction of the exhaust gas catalyzed by the catalyst, or a reduction in the cumulative heat amount generated from the exhaust gas by said reaction in a predetermined temperature range taken by the catalyst during its temperature increase. This method can detect the performance reduction of the catalyst accurately without conducting constant-speed vehicle running for a long time.

Abstract: An NOx sensor for an exhaust gas is made from .beta.-Nb.sub.2 O.sub.5 as a primary component and TiO.sub.2 as a subsidiary component. The TiO.sub.2 content is in a range of 0.1% by weight .ltoreq.TiO.sub.2 .ltoreq. 20% by weight. In place of TiO.sub.2, Ru may be used in the NOx sensor. The Ru content is in a range of 0.1% by weight .ltoreq.Ru.ltoreq. 10% by weight. Thus, the NOx sensor has an excellent NOx adsorbing ability and is higher in sensitivity to NOx in an exhaust gas.

Abstract: The heating value of a sample gas is calculated by a microcontroller from the heating value of a reference gas, and from flow ratios determined as the gas is consumed by catalytic combustion. The combustible gas is mixed with a combustion supporting gas, such as air, and flowed to a catalytic apparatus. In one embodiment, a molar flow meter is connected in the supply line for the combustible gas to measure the molar flow rate of a reference gas and a sample gas. Molar flow rates of the reference gas and the sample gas are determined at maximum temperature of combustion of the gas. In a preferred embodiment, a valve chamber is charged with a gas to a predetermined pressure and then discharged. During the discharge cycle, the apparatus senses the maximum temperature of combustion which corresponds to the point of optimum fuel-to-air ratio for catalytic combustion.

Abstract: A transition metal oxide based calorimetric non-methane hydrocarbon sensor (100) is constructed by disposing a transition metal based catalyst (105), preferably chromium oxide (Cr.sub.2 O.sub.3), onto a carrier (101). A temperature measurement device (103) is positioned thermally coupled to the transition metal based catalyst (105). A preferred application includes sensing non-methane heavy hydrocarbons in an automotive exhaust gas stream (803) by exposing a transition metal oxide catalyst based sensor (805) to the exhaust gas stream (803) and providing a signal (811) indicative of a concentration of non-methane heavy hydrocarbons and carbon monoxide (CO). Then, exposing a compensating sensor (807) to the same exhaust gas stream (803) and providing a compensating signal (813) indicative of a concentration of carbon monoxide (CO). By combining the signal (811) and the compensating signal (813), a measure of non-methane heavy hydrocarbons can be provided.

Abstract: A system and method are provided for minimizing the effects of background signals in masking signals indicating the presence of substances to be detected such as contaminants in materials moving rapidly along a conveyor. The contaminants detected may include nitrogen containing compounds and hydrocarbons. The system and method of the present invention minimizes the number of falsely positive indications of the presence of such substances due to background signals and changes in background signals. The substances detected are divided into first and second sample portions and the respective portions are heated. The first heated portion is reacted with ozone to generate radiation by chemiluminescence having characteristic wavelengths related to substances in the first portion. The second portion heated is also reacted with ozone to generate radiation by chemiluminescence having characteristic wavelengths related to substances in the second portion.

Abstract: A system and method for minimizing the effects of background signals in masking signals indicating the presence of substances to be detected such as contaminants in materials moving rapidly along a conveyor. The contaminants detected may include nitrogen containing compounds and hydrocarbons. The system and method minimize, during detection of the presence or absence of such substances, the number of falsely positive indications of the presence of such substances due to background signals and changes in background signals. The substances detected are divided into first and second sample portions and the respective portions are heated. The first heated portion is mixed with ozone to cause a chemical action therewith in order to generate radiation by chemiluminescence having characteristic wavelengths related to substances in the first portion.

Abstract: A method of determining an analyte in the gaseous or vapour phase and in which a bioreceptor or biomimic is retained at an electrode. The bioreceptor or biomimic is preferably retained at a support at the electrode which comprises a solid or gel matrix of an electrolyte, especially organic salt electrolytes. Electrochemical detection of analytes in this way has several advantages over existing methods which rely on solution monitoring. For example gas sensors can be prepared for monitoring an analyte by the occurrence of a reaction with a bioreceptor or biomimic, in addition to monitoring the presence of toxins due to inhibition of the bioreceptor or biomimic reaction. Furthermore, the invention enables gas or vapour analyte monitoring with increased sensitivity and speed and greater stability of the sensors can be achieved. The invention also relates to novel media for carrying out bioelectrochemical reactions.

Abstract: A matched catalytically inactive compensator for use in a combustible gas sensor is made from a catalytically active detector. The catalytically active detector is exposed to a gas phase catalytic inhibitor such as hexamethyldisiloxane to completely destroy its catalytic ability thereby forming a compensator which has very similar chemical and physical properties to the untreated detectors.

Abstract: A semiconductor-type hydrocarbon sensor includes an oxide semiconductor, an outer electrode formed on an outside surface of the oxide semiconductor, an inner electrode formed on an inside surface of the oxide semiconductor, and a zeolite layer constructed of zeolite carrying at least one metal selected from the group consisting of platinum and copper. Small molecular weight hydrocarbons enter pores of the zeolite layer and are oxidized so that the small molecular weight hydrocarbons cannot reach the oxide semiconductor. Large molecular weight hydrocarbons cannot enter the small pores of the zeolite layer and, instead, pass through grain boundaries of zeolite particles of the zeolite layer to reach the oxide semiconductor. As a result, the large molecular weight hydrocarbons are selectively detected by the semiconductor-type hydrocarbon sensor.

Abstract: A selected component of a fluid mixture, for example a reduced sulfur compound vapor in air, is detected by selectively adsorbing the component onto a conductive thin layer of material having a chemical affinity for such component and observing the resultant change of electrical resistivity of the layer. The sensitivity of the detector changes with accumulation of the component on the sensor. The accumulation of the component on the sensor is removed by oxidizing and evolving the component from the sensor to restore the sensor to a linear operating region. The accumulated component is preferably oxidized by reacting the component with ozone. The dynamic range of the sensor is increased by counteracting the tendency for the component to accumulate by continuously feeding back ozone to or controlling the temperature of the sensor so that the sensor operates in a linear region near null.

Abstract: A selected component of a fluid mixture, for example a reduced sulfur compound vapor in air, is detected by selectively adsorbing the component onto a conductive thin layer of material having a chemical affinity for such component and observing the resultant change of electrical resistivity of the layer. The sensitivity of the detector changes with accumulation of the component on the sensor. The accumulation of the component on the sensor is removed by oxidizing and evolving the component from the sensor to restore the sensor to a linear operating region. The accumulated component is preferably oxidized by reacting the component with ozone. The dynamic range of the sensor is increased by counteracting the tendency for the component to accumulate by continuously feeding back ozone to or controlling the temperature of the sensor so that the sensor operates in a linear region near null.

Abstract: A bismuth molybdate gas sensor which provides stable sensitivity to gases such as alcohol, ketones, alkenes, and long chain alkanes is disclosed. Sensors comprising a mixture of the Bi.sub.2 Mo.sub.3 O.sub.12 and Bi.sub.2 MoO.sub.6 phases of bismuth molybdate; or, bismuth iron molybdate are particularly effective. The bismuth molybdate mixture; or, the bismuth iron molybdate may be deposited as a thin film on a substrate or may take the form of a sintered powder.

Abstract: A catalytic combustion type CO gas sensor which is composed of an electrical circuit by serially arranging two coils composing an active section and a compensating section, and by providing serial bridge resistances, r.sub.1 and r.sub.2, opposing to the said coils, respectively, and via a gas sensitometer, and which determines the CO concentration based on the difference in value of resistance of both coils of the active section and the compensating section on catalytic combustion of CO, characterized by:(A) that the values of the resistance of coils of the active section and the compensating section and bridge resistances, r.sub.1 and r.sub.2, at a definite temperature are made substantially the same, and thus the temperature coefficients of the coil of the active section and the bridge resistance r.sub.1, and of the coil of the compensating section and the bridge resistance r.sub.2 are made approximately the same.(B) that the value of resistance of the coil of the active section at 150.degree.-200.degree.

Abstract: An oxygen gas concentration-detecting apparatus in an internal combustion engine using an alcohol fuel includes a ceramic substrate having one surface falling in contact with a reference gas and the other surface falling in contact with an exhaust gas of the engine and generating an electromotive force according to oxygen gas concentrations of both the gases. A pair of electrode members are arranged on the ceramic substrate to take out the electromotive force. A first oxidation catalyst layer is formed on the outer surface of the ceramic substrate to promote oxidation reaction of unburnt components. A laminate of a protecting layer of a metal oxide and a reduction catalyst layer of promoting reduction reaction of nitrogen oxides is formed on the outer surface of the first oxidation catalyst layer, and a second oxidation catalyst layer is arranged on the outer side face of the laminate to promote oxidation reaction of hydrogen gas.

Abstract: Apparatus and methods for measurement of total organic carbon content of water, particularly of low relative organic content, are described, featuring a single sample cell for exposure of a static sample to ultraviolet radiation and comprising electrodes for measuring the conductivity of the water. The conductivity is monitored as a function of time and the second time derivative of the conductivity signal is monitored to indicate when the oxidation reaction has been completed. Compensation for the contribution to conductivity of the water sample made by the instrument is achieved by subtracting a quantity proportional to the first time derivative of the conductivity at a time when the second time derivative reaches zero, indicating that the oxidation reaction is complete, from the change in the total conductivity measurement, the remainder being equal to the contribution to conductivity made by oxidation of the organic content of the water.

Abstract: Apparatus for detecting a combustible gas which comprises a Wheatstone bridge circuit having a detector element comprising an electrically conducting member coated with a refractory and having on the surface of said refractory a catalyst for the oxidation of said gas, said detector element constituting one leg of said bridge, and a reference element comprising an electrically conducting member coated with a refractory, said reference element constituting a second leg of said bridge, whereby upon catalytic oxidation of said gas an electrical signal approximately proportional to the amount of said gas present at the detector element is produced. The improvement comprises a reaction control block having a cover in the form of a dust shield and having two chambers, one containing said detector element, and the other containing said reference element.

Abstract: A laminar gas-sensitive thick film consisting of ceramic semiconductor and metallic catalyzer is formed across a pair of electrodes carried by a ceramic substrate, and the nature of metallic catalyzer on an outer surface layer of the thick film is different from that of metallic catalyzer in that portion of the thick film which is in the proximity of the electrodes.

Abstract: A structure and method for sensing oxides of nitrogen in a gas. The gas is first passed through an oxidation catalyst and any reducing species in the gas are oxidized. The output gas from the oxidation catalyst is received by a sensor which generates an output responsive to oxides of nitrogen because the sensor has been isolated from any reducing species in the gas.

Abstract: An organic fluid detection instrument having great sensitivity to low concentrations or organic fluids in a fluid stream comprise a conduit adapted for the one-way flow therethrough a mixture of an oxygen-containing carrier fluid and organic fluids; a first electrical resistance element disposed in the conduit and carrying a material catalyst for promoting exothermic oxidation reactions of the organic fluid of the mixture; a second resistance element also disposed in the conduit for temperature sensing, consisting of a material with an electrical resistivity that varies with its induced temperature; each element is connected to a pair of electrical leads for operatively producing electrical signals representative of the amplitude of the output signal to be measured; a measuring circuit means is joined to both pairs of leads for processing both a synchronous signal and the second output signal in a manner whereby variations in the differential resistance of the second sensing element serve as a measure of the

Abstract: A detector for detecting leaks of a corrosive liquid such as strong acids or bases is provided comprising a light guide core having a covering which generates heat upon contact with the liquid to the detected, thereby changing the light transmissivity of the light guide, which change can be measured. The covering comprises a porous polymer having a salt within its pores such as an ammonium salt which dissolves in the liquid to be detected and generates heat thereby.

Abstract: A method and apparatus to automatically compensate for temperature variation in a vapor detection system. In one embodiment, two identical organic semiconductor film sensors in close thermal contact with each other are used in the feedback circuit of an inverting amplifier supplied by constant voltage. One of the sensors is isolated from vapor exposure to act as a reference for the other sensor which is used for vapor sampling. The output of the inverting amplifier provides an indication of the presence and relative concentration of vapor exposure. Variation in sample sensor resistance due to a change in temperature is accompanied by the same corresponding change in the reference sensor, which stabilizes the ratio of the feedback circuit resistances and therefore the gain of the inverting amplifier to exactly compensate for the temperature induced resistance variations automatically.

Abstract: A pyroelectric substrate is provided with a heater and at least one set of electrodes for sensing charge redistributions due to changes in the substrate temperature. In a preferred embodiment, there are two interdigitated electrodes, one coated with an absorber/desorber material. The heater pulsatingly raises the temperature of the substrate past the desorption temperature of a fluid of interest. If the fluid was exposed to the absorber/desorber material prior to heating, a portion of the fluid will have been absorbed. When the substrate reaches the desorption temperature, additional heat pulses will not increase the substrate temperature significantly until the fluid has desorbed. Thus, heat used in changing state does not raise the substrate temperature and, lacking a temperature change, reduces the charge redistribution sensed by the electrode coated with the material.

Abstract: Apparatus for the detection of carbon monoxide concentration of a gas. The apparatus comprises a base from which a pair of arms extend, a resistance layer disposed on each arm serving both to measure the difference in temperature between the arms and to heat a catalyst layer; a protective layer on the resistance layers to prevent electrical shorts caused by deposit of conductive particles in the gas to be detected; and a catalyst layer on one and only one of the arms in contact with the protective layer.

Abstract: A method and apparatus for controlling a chemical reaction by heterogeneous catalysis, in which a surface acoustic wave (SAW) is propagated along a surface of a piezoelectric element in contact with liquid or gaseous substances to be chemically reacted, to thus generate an electric field at the surface of the element which initiates and sustains the desired reaction. The catalysis rate can be varied by varying the frequency and/or intensity of the surface acoustic wave. The surface of the element may be coated with a very thin film of a catalytic group 8 metal which can be penetrated by the SAW electric field. In such an embodiment, normal catalysis proceeds via chemisorption, and the SAW element field acts to increase the catalysis rate.

Abstract: A laminar gas-sensitive thick film consisting of ceramic semiconductor and metallic catalyzer is formed across a pair of electrodes carried by a ceramic substrate, and the nature of metallic catalyzer on an outer surface layer of the thick film is different from that of metallic catalyzer in that portion of the thick film which is in the proximity of the electrodes.