Abstract: The amount of smog formed in air and the smog concentration in air is determined by measuring the consumption of nitric oxide.

Abstract: A mass flow meter for a gas dispenser includes apparatus and method for determining specific heat ratio of the gas as a function of two pressure measurements in relation to a nozzle and for determining mass flow rate as a function of the specific heat ratio, the two pressure measurements in relation to the nozzle, and a density measurement of the gas.

Abstract: Volumetric metering equipment, especially but not exclusively for use in metering the volume of fluid pumped through one or more injectors by a diesel-engine fuel injection pump, having means which serve to cause the inertia of a moveable member, and/or a return force applied to a moveable member to reduce the time taken for a desired back pressure to be built up following a draining operation.

Abstract: An apparatus and method for measuring differential oxygen concentration between two flowing gas streams is described. A reference gas and a sample gas in separate gas flow paths are passed, at selected temperature, pressure and flow rate over a respective one of a pair of electrically connected oxygen sensors which produce an output signal proportional to the differential oxygen concentration between the sensors. The output signal may be amplified and recorded by any conventional means. An internal calibration system is also described.

Abstract: A method for gas analysis includes the steps of extracting a gas sample from a gas to be analyzed with respect to one or more of its gas components, measuring the flow of the extracted gas sample, and adding a replacement gas to the gas in the same amount as the extracted sample in order to minimize the impact on the main gas flow of the extraction of the gas sample. The replacement gas can consist of the same gas components constituting the gas sample. A gas analyzer for performing the method is also disclosed.

Abstract: Provided is a method and apparatus for measuring evaporative vehicle emissions in a fixed-volume enclosure. The method comprises the steps of providing a volume compensation means in fluid communication with a test chamber for compensating for changes in the test chamber fluid volume, where n is a positive integer, measuring the temperature of the test chamber fluid at the sample times t.sub.n, measuring the absolute fluid pressure of fluid at the sample times t.sub.n, determining the density of the evaporative emissions and the test chamber fluid at selected sample times t.sub.n, determining the mass of evaporative emissions present in the chamber, determining the theoretical volume change of the test chamber fluid at said sample times t.sub.

Abstract: A system and method for using a gas detecting device that conducts electricity increasingly for increasing concentration of a gas being detected. The temperature of a gas sensor element is regulated to first burn-off impurities on the surface thereof, and then to cool down the gas sensor element to a temperature at or above which the gas catalyzes. During catalyzation, the sensor element conducts and electrically signals a microprocessor concentration data, which microprocessor controls a three color LED so as to emit a color pattern indicative of the concentration level of the gas. A sum of previously measured concentration levels is taken to gauge exposure to the gas over a period of time. The gas detection system includes a self-calibration routine that can be run prior to normal use by successive exposure to varying concentrations of gas to determine the sensor element-specific reaction.

Abstract: The present invention is directed to a smelling aid device including a nose member of a configuration to be at least partially insertable into a nostril and having a passageway therethrough, and means connected to the nose member for pumping an aroma of air and fine particulate emanating from a substance through the passageway.

Abstract: The present invention discloses a fluid relief device for relieving pressure of a fluid stored in a container or tank, or fluid used in a piece of equipment. In one aspect such a device has a body member with a primary channel therethrough in communication with a container of a contained fluid under pressure. When the pressure of the contained fluid under pressure exceeds a predetermined level, the pressure of the contained fluid moves a cover which is sealingly in place to close off the primary channel. During normal conditions the force of the contained fluid is insufficient to move the cover and leakage of the contained fluid past the cover is inhibited by the provision of a barrier fluid supplied into a barrier fluid chamber to oppose the contained fluid, the barrier fluid at a pressure greater than the normal pressure of the contained fluid.

Abstract: A video photometric color sensing system is provided for characterizing the color of a homogeneous substance on a real time basis. The sensing system includes a sample port for holding a homogeneous substance and a camera quantifies a color video image of the homogeneous substance and provides as outputs analog voltage signals representative of the amount of red, green and blue in the color video image. A peak detector circuit receives the analog voltage signals representative of the amount of red, green and blue in the color video image and generates peak red, green and blue analog voltage signals and uses these individual voltage values of each component to derive the luminance value from software generated nonadditive matrix.

Abstract: A dispenser for volatile liquids with a vapor collection system is disclosed which controls the rate of operation of a vacuum pump 118 so that a simple vacuum intake 148 disposed preferably inside, but not sealed with, the filler neck can be used to collect only the vapors displaced from the fuel tank 110 by the fuel 104. The vacuum pump 118 is controlled by a controller 114 which receives, from various sensors 124, 128, 132 and 136, signals representative of the fuel vapor/air ratio immediately outside the tank, inside the tank, and/or inside the vapor recovery conduit 122, and/or of the pressure relative to atmosphere inside the tank 110 and/or of the rate of flow of liquid being dispensed. Based on these input signals, the controller 114 operates the vacuum pump 118 at an optimal rate to collect fuel vapor displaced from the tank 110.

Abstract: A method for analyzing a gaseous mixture by means of microwave absorption including the steps of: generating microwave energy of at least one frequency known to be absorbed by the component of interest of the gaseous mixture for the presence of one specific gas component; transmitting two beams of the microwave energy simultaneously to a measuring cell and to a reference cell, both cells containing none of the specific gas component of interest; recombining the microwave energy through the matching arms of a waveguide "magic" tee with an "H" arm and an "E" arm; adjusting the phase and amplitude of the reference or measuring beam signals of microwave energy until a null is detected at the "E" arm of the waveguide "magic" tee and all microwave energy is detected at the "H" arm of the microwave tee; allowing the measuring cell to fill with the gaseous mixture to be analyzed; correlating the energy detected at the "H" arm to the concentration of the gaseous component of interest, according to Beer's law.

Abstract: The invention relates to a method for determining small quantities of carbon monoxide and nitrogen oxides in gaseous mixtures containing oxygen with the aid of a sensor whose electrical resistance changes at a higher temperature with the carbon monoxide and nitrogen oxide concentrations. It makes use of the fact that, with suitable sensors, on the one hand the resistance-temperature curve of the one of the gases to be determined is clearly different from that of the reference mixture over a broad temperature range (gaseous mixture without the two gases to be determined) and, on the other hand, the resistance-temperature curves of the two gases to be determined approach one another in one part of this temperature range, or coincide, and maintain a clear distance from one another in another part of this temperature range.

Abstract: A gas monitoring apparatus with a heatable hose assembly having a central polymer tube of polyether ether ketone wrapped with a layer of polymer tape is described which is used to provide hot gases to a gas monitoring device. Heating elements for heating the central polymer tube can be arranged on the layer of polymer tape as can be an element for monitoring and controlling the element for heating the central polymer tube. Surrounding the arrangement can be a layer of thermal insulation and a protective jacket.The assembly is of utility for use in systems for the monitoring of acid gases from emission stacks.

Abstract: An apparatus for remotely measuring and logging the flow rate of groundwater seepage into surface water bodies. As groundwater seeps into a cavity created by a bottomless housing, it displaces water through an inlet and into a waterproof sealed upper compartment, at which point, the water is collected by a collection bag, which is contained in a bag chamber. A magnet on the collection bag approaches a proximity switch as the collection bag fills, and eventually enables the proximity switch to activate a control circuit. The control circuit then rotates a three-way valve from the collection path to a discharge path, enables a data logger to record the time, and enables a pump, which discharges the water from the collection bag, through the three-way valve and pump, and into the sea. As the collection bag empties, the magnet leaves the proximity of the proximity switch, and the control circuit turns off the pump, resets the valve to provide a collection path, and restarts the collection cycle.

Abstract: A method and a system for analyzing gas samples employ at least two semiconductor sensor sets, used alternately. The sensor output signals are time-differentiated. As a result of these features, the time required for analysis can be reduced considerably, especially with an uninterrupted sequence of analyses to be performed in succession.

Abstract: A method and system for monitoring a concentration of volatile organic constituents in a test sample. A sparging vessel separates a volatile organic constituent sample from the test sample. A dryer dries the constituent sample to remove any vapor therein by mixing the constituent sample with a drying agent. A sorbent trap adsorbs the volatile constituents from the drying agent and concentrates the purged constituents. A microprocessor controlled director valve selectively directs the constituent sample from the dryer to the sorbent trap and from the sorbent trap to an organic vapor detector for determining the concentration of volatile constituents and for generating an electrical signal proportional to the total concentration of the volatile constituents in the sample.

Abstract: A gas detection device is provided comprising an exterior housing in which an active pelement and a compensating pelement are disposed. The gas detection device further comprises a porous frit seated within a distal end of the exterior housing to separate the active pelement and the compensating pelement from the surrounding environment. The porous frit is adapted to prevent flashback into the surrounding environment while allowing movement of environmental gas through the porous frit to contact the active pelement and the compensating pelement. The gas detection device further comprises a flow guide for directing flow of environmental gas into the gas detection device disposed adjacent the exterior side of the porous frit. The flow guide comprises an inlet port through which a forced flow of environmental gas is pumped to pass through the porous frit and into the exterior housing in a direction generally parallel to the axis of the exterior housing.

Abstract: An alumina substrate has a front surface with a semiconductor gas sensor main body attached thereon for specific detection of a surface exposed gas, and has a rear surface formed with a glass layer and a gold paste layer as superposed on the surface, and bonded to a gold plating layer on a frame by parallel gap welding. The gold paste layer is welded to the gold plating layer with the heat of welding. The glass layer prevents transmission of thermal impact of die bonding to the substrate.

Abstract: A compensated ionization-type sensor includes spaced apart active and reference electrodes. A center electrode is disposed between the active reference electrodes. A compensating electrode is disposed adjacent to the center electrode and, capacitively coupled thereto. The compensating electrode is electrically coupled to the active electrode. A compensating screen with a selected potential applied thereto surrounds the electrodes to compensate for velocity of the ambient atmosphere.

Abstract: Device for determining the Wobbe index of a first gas mixture, including a Wobbe index meter having a mixing chamber, and a feed system for supplying a first gas mixture and an oxidation gas to the mixing chamber of the Wobbe index meter. The feed system includes structure for supplying the first gas mixture to the mixing chamber via a first number of openings, structure for supplying an oxidation gas to the mixing chamber via a second number of openings, structure for keeping a constant ratio between the a quantity of first gas mixture and the a quantity of oxidation gas supplied to the mixing chamber, structure for burning the second gas mixture formed in the mixing chamber and structure for determining the oxygen content of the combustion gas obtained after combustion.

Abstract: An apparatus for analyzing spectral data of a mixture having a plurality of components by determining the pure variables, each of which has a contribution from only one of the mixture components, includes a programmed computer for performing steps of a) providing spectral data of the mixture, b) determining purity values of variables from said data to provide a first purity spectrum, c) finding the maximum of the purity values to determine the first pure variable, d) calculating a determinant-based weight function with respect to said first pure variable, e) multiplying the first purity spectrum by the determinant-based weight function to provide a second purity spectrum, f) finding the maximum in the second purity spectrum to yield the second pure variable, g) repeating steps d),e) and f) for successive determinant-based weight functions with respect to preceding pure variables to provide successive purity spectra from which successive pure variables are found.

Abstract: A catalyst composed of metal oxide particles among which are uniformly incorporated, in order to reduce the operating temperature of the catalyst, palladium particles.

Abstract: Methods and apparatus for in sire isolation of volatile organic compounds from groundwater using electrolytically-generated purge gas are disclosed. One preferred method includes electrolytically generating a purge gas from the ground water, passing the purge gas through the groundwater (in situ) to purge volatile organic compounds from groundwater, collecting the purge gas along with the purged volatile organic compounds, and detecting (in situ) the presence and/or amount of purged volatile organic compounds in the purge gas. One preferred apparatus includes a generally cylindrical cell incorporating the necessary electrodes, one or more ionization sources and detectors.

Abstract: The sonic velocity in a chamber which is filled with helium is measured by using ultrasonic waves, and the temperature in the chamber is also measured. Purity information relating to helium gas contained in the chamber is determined on the basis of the measured values of the sonic velocity and the temperature.

Abstract: A method and a system using that method are provided which employ a pattern ecognition algorithm to improve sensitivity in detecting hazardous vapors. The algorithm enables the discrimination of vapors of interest from non-hazardous substances at higher concentrations in varying relative humidity. A weight vector is generated corresponding to a N-space representation of a class comprising known vapors of interest, and a N-space representation of the unknown vapor is used to generate an unknown pattern vector. By calculating the dot product of the unknown pattern vector and the weight vector a determination can be made as to whether the unknown vapor is within the class. The weight vector is generated by selecting a training set comprising a subset of the known vapors of interest and background vapors and generating an N-space representation of the training set so as to create an associated weight vector.

Abstract: The efficiency of hydrocarbon vapor recovery installations used in gas stations is measured. A system for measuring a yield of recovery for hydrocarbon vapors emitted from the tank of a vehicle as it is being filled comprises at least one box for carrying a nozzle inside and for placement over a filler neck of the tank. The nozzle is connected through a conduit to a device for evaluating the recovered hydrocarbon vapor, wherein the recovered vapor evaluation device is a gas meter and a following orifice.

Abstract: A high accuracy flowmeter for testing and calibrating flowmeters and the like, and more particularly a positive displacement flowmeter which may include a cylinder (12), a piston (10) within the cylinder (12) which makes a clearance seal with the inside of the cylinder, an encoder (40) associated with the piston, and a control valve (V) for controlling the supply of a fluid flow (A1) to be measured. The flowmeter may have an arrangement for receiving differently-sized interchangeable modules for measurement of different flow rate ranges, each module having for example a compatible piston and cylinder of a predetermined size. The flowmeter includes a channel for receiving a fluid flow so as to move the piston (10) within its cylinder (12); and a device (36, 38) including the encoder (40) for detecting movement of the piston and generating electrical signals representative of the fluid flow to be measured.

Abstract: The invention relates to a high accuracy flowmeter for testing and calibrating flowmeters and the like, and more particularly to a positive displacement flowmeter which may include a cylinder (12), a piston (10) within the cylinder (12) which makes a clearance seal with the inside of the cylinder, an encoder (40) associated with the piston, and a control valve (V) for controlling the supply of a fluid flow (A1) to be measured. More generally, the flowmeter includes a channel for receiving a fluid flow so as to move the piston (10) within its enclosure (12); and a device (36, 38, 40) for detecting movement of the piston and generating electrical signals representative of the fluid flow to be measured. The movement of the piston is detected as a function of a known volume of the enclosure traversed by the piston, and a measured variable elapsed time over which the piston traverses the volume. Preferably, the flowmeter system includes a damping device (FIGS. 6A-6D) which may be mechanical, pneumatic, or fluidic.

Abstract: A method for making vacuum components from plastic material, and in particular, PVC and CPVC, where the plastic component is exposed to a high vacuum or ultra high vacuum for an extended period of time, by which the outgas rate drops considerably to levels that are well within required limits for high vacuum and ultra high vacuum applications. Residual gas analysis may be used to certify this low outgas level for the plastic components.

Abstract: An air contamination detector for a scuba unit includes a transparent tube having a lumen, the lumen being user visible for a full 360.degree. about its circumference. A contamination indicator is positioned within the lumen and is exposed to air flow from the air supply of the scuba unit. The contamination indicator is responsive to a contaminant to manifest a change that is visible through the transparent tube. A quick connect/disconnect air connection is affixed to one end of the transparent tube and mates with a low pressure fitting that communicates with the scuba air tanks. A further quick connect/disconnect air filling is positioned at another end of the transparent tube and is connectable to a hose that provides air inlet control for a buoyancy control vest.

Abstract: Disclosed is a continuous emissions monitoring system for exhaust gas emissions containing HCl comprising a sampling subsystem with a sample probe in the effluent to collect effluent samples that are transmitted through heated conduits through one or more filters and pumps to a mass spectrometer. The sampling subsystem is maintained at a temperature no less than about 190.degree. C. and the flow rate through the-system is greater than about 10 liters per minute. The process for continuous monitoring of exhaust emissions containing HCl extracts an exhaust gas sample and maintains the temperature and physical state of the exhaust gas throughout transport of the sample from the exhaust effluent to a mass spectrometer.

Abstract: An early warning system for providing notice that seismic activity, such as an earthquake, is imminent. The earthquake early warning system includes a subterranean detector unit assembly having a plurality of detector units carried by a subterranean inverted conduit. The conduit is filled with a dense, dry inert aggregate and has a soil interface consisting of a perforated metal screen or porous fabric material thus allowing migrating gases to migrate into the conduit. Gas detectors carried by the conduit detect the gases as they migrate into the conduit. Access tubes are provided to allow access to the detectors from the surface of the ground without exhuming the conduit assembly. The conduit would carry a plurality of detectors and associated access tubes for monitoring migration of gases across a linear distance. The detectors are in communication with a monitoring facility for monitoring the rate of migration of gases.

Abstract: The apparatus for the automated fueling of a launch vehicle includes a mobile fuel line platform assembly for carrying a fuel line assembly. A gross mechanical actuation mechanism provides gross positioning of the platform assembly relative to a fuel tank inlet. A micro-positioning mechanism provides micro-positioning of the fuel line assembly relative to the fuel tank inlet. A floating plate assembly securely connects the fuel line assembly to the fuel tank inlet. Leak detector detects any leaks in the connection between the fuel line assembly and the fuel tank. The present invention augments existing space program hardware thereby removing human involvement and increasing vehicle/environment safety.

Abstract: Apparatus for monitoring gaseous oxygen concentration that includes an oxygen sensor for providing an electrical sensor signal that varies as a function of oxygen concentration at the sensor. Processor circuitry compares oxygen concentration indicated by the sensor signal to at least one threshold level, and indicates when such oxygen concentration at the sensor departs from such threshold concentration level. The apparatus is calibrated by exposing the sensor to a calibration gas having an oxygen concentration equal to the desired threshold concentration level, and storing in the processor circuitry electrical indicia indicative of operating characteristics of the sensor at such threshold oxygen concentration level.

Abstract: Method and apparatus for thermal desorption wherein a carrier liquid is circulated around a desorption chamber when a sample to be desorbed in heated, whereby the desorbed substance is dissolved into the carrier liquid for transport to a region where the substance is analyzed. The carrier liquid circulation is performed at high pressure sufficient to maintain the carrier liquid in the liquid phase during heating of the sample.

Abstract: Apparatus for preconcentrating trace amounts of organic vapors in a sample of air for subsequent detection, comprising a metallic substrate; a thin film of fullerenes deposited on the metallic substrate for adsorbing the organic vapors on the thin film of fullerenes, thereby preconcentrating the organic vapors; and apparatus for heating the metallic substrate to a predetermined optimum temperature for desorbing the vapors from the thin film of fullerenes to form desorbed organic vapors for subsequent detection.

Abstract: Air to be introduced into the cabin of a motor vehicle passes over a measuring device, in which parameters such as temperature, humidity and pollution are measured. The measuring device comprises a housing having an air inlet, which is supplied with a fraction of the air stream, and an air outlet for evacuating this fraction. The housing has an internal chamber which communicates with both the air inlet and the air outlet, and air circulating means such as a pump are provided for setting up a differential pressure between the inlet and outlet so that the fraction of the air stream to be measured flows through the chamber in the housing. The sensor or sensors are arranged in this chamber, so that they are always ventilated by the air passing through the latter.

Abstract: A resealable gas concentration sensor for determining the concentration of a particular gas within a gaseous environment. The sensor is constructed of a housing and a cap. The cap is adapted to be temporarily coupled with the housing while in the environment to define a sealed sample chamber, thereby capturing a sample of the environment. A venturi tube having a narrow passage is affixed to the housing which is adapted to allow fluid flow through venturi tube into test equipment for determining the concentration of the gas in the sample. The housing and cap may be repeatedly uncoupled and resealed to capture additional samples and measure other concentrations.

Abstract: In order to increase the reliability of detection of gaseous contamination in containers, gas (G) from the container is subject to several different methods of analysis (54a to 54d), each of which emits differing output signal courses (I.sub.1 to I.sub.4), depending on the contaminants and their concentration. A vector of the state vector type (P.sub.GAS) is formed with the output signals (I.sub.1 to I.sub.4) as a state variable and checked to see whether it defines a permissible or an unacceptable state of contamination (56). On the basis of this examination the decision is taken whether a container is acceptably or unacceptably contamined.

Abstract: Provided is a method and apparatus for measuring evaporative vehicle emissions in a fixed-volume/variable temperature test chamber. The method comprises the steps of providing a volume compensation device in fluid communication with a test chamber for compensating for changes in the test chamber fluid volume, determining the density of the evaporative emissions and the test chamber fluid in mass per unit volume at selected sample times t.sub.n, where n is a positive integer, measuring the temperature of the test chamber fluid at the sample times t.sub.n, measuring the absolute fluid pressure of fluid at the sample times t.sub.n, determining the difference in the test chamber fluid volume between successive sample times t.sub.

Abstract: A method of monitoring, while on board an automotive vehicle, one or more of catalyst performance, engine misfire, and combustion quality, the vehicle having an internal combustion engine equipped with a catalyst for converting noxious emissions of the engine, comprising: (i) exposing at least one pair of EGO sensors to substantially the same emissions either exiting from the engine or from the catalyst, one of the EGO sensors having its electrode highly catalytic, and the other sensor having its electrode low-to-noncatalytic; (ii) comparing the outputs of the sensor electrodes (amplitude, frequency, or phase shift) to determine if there is a sufficient differential to indicate a misfire or poor combustion in the case of the sensors being located downstream of the engine exhaust but upstream of the catalyst, or indicating poor catalyst efficiency in the case of the sensors being placed substantially immediately downstream of the catalyst. The catalyst may be a three-way catalyst (or an oxidation catalyst).

Abstract: A method of monitoring, while on board an automotive vehicle, one or more of catalyst performance, engine misfire, and combustion quality, the vehicle having an internal combustion engine equipped with a catalyst for converting noxious emissions of the engine, comprising: (i) exposing at least one pair of EGO sensors to substantially the same emissions either exiting from the engine or from the catalyst, one of the EGO sensors having its electrode highly catalytic, and the other sensor having its electrode low-to-noncatalytic; (ii) comparing the outputs of the sensor electrodes (amplitude, frequency, or phase shift) to determine if there is a sufficient differential to indicate a misfire or poor combustion in the case of the sensors being located downstream of the engine exhaust but upstream of the catalyst, or indicating poor catalyst efficiency in the case of the sensors being placed substantially immediately downstream of the catalyst. The catalyst may be a three-way catalyst (or an oxidation catalyst).

Abstract: Gas flux rate from a surface is measured using an elongated tubular housing having a lower open end and an upper open end with a support positioned within the housing a predetermined distance from the lower open end. A gas sampling wand extends into the housing from the upper open end and is supported on the support. The wand has a lower open end at the support generally co-planar with the lower open end of the housing. An air baffle is coupled to the upper open end of the housing for reducing velocity and pressure fluctuations of atmospheric air entering the housing from the upper end. A detector is coupled to the wand for measuring the concentration of selected gases within the housing. A funnel-shaped hood circumscribes the lower open end of the wand and increases the sample collection area of the wand. An air pump is coupled to the wand for drawing air and gases into the wand from the area adjacent the lower open end of the housing.

Abstract: The amount of smog formed in air and the smog concentration in air is determined by measuring the consumption of nitric oxide.

Abstract: Selective detection of microorganisms is achieved by a screening technique in which radioactively labeled, low-molecular-weight metabolites produced by microorganisms to be detected reach an adsorption medium through a semipermeable medium which passes the labeled metabolites but blocks the labeled incubation medium. The adsorption medium is then subject to analysis, such as antoradiography, to detect the presence of the labeled metabolites.

Abstract: Selective detection of microorganisms is achieved by a screening technique in which radioactively labeled, low-molecular-weight metabolites produced by microorganisms to be detected reach an adsorption medium through a semipermeable medium which passes the labeled metabolites but blocks the labeled incubation medium. The adsorption medium is then subject to analysis, such as autoradiography, to detect the presence of the labeled metabolites.

Abstract: An explosive detection screening system used for the detection of explosives and other controlled substances such as drugs or narcotics. The screening system detects the vapor and/or particulate emissions from the aforementioned substances and reports that they are present on an individual or object and the concentration of each substance detected. The screening system comprises a sampling chamber for the collection of the vapor and/or particulate emissions, a concentration and analyzing system for the purification of the collected vapor and/or particulate emissions and subsequent detailed chemical analysis of the emissions, and a control and data processing system for the control of the overall system.

Abstract: An industrial process oxygen analyzer, and method of using same, incorporates an automotive oxygen sensor to minimize the criticalness of controlling heater temperature during operation. Higher sensor heater temperature, required to accommodate the automotive oxygen sensor, is achieved by application of higher supply voltage to the sensor heater. Current limiting of the heater supply circuit reduces stress on the sensor heater, even at the higher operating temperature.

Abstract: An in-line detector system for real-time detection of impurity concentration in a flowing gas stream. In a specific aspect, the system may comprise a purifier unit for selective purification of gas from the gas stream, and an impurity addition unit for imparting a predetermined concentration of impurity to the gas stream, whereby the resulting concentration sensings of the purified gas, and the impurity-enhanced gas are usefully employed to calibrate an impurity concentration sensor, for continuous accurate sensing of impurity concentration in the flowing gas stream. The system may utilize hygrometric sensors in the case of water as a critical impurity, or surface acoustical wave (SAW) devices coated with suitable impurity-affinity coatings. The system has particular utility in monitoring low impurity concentration levels (e.g., from about 0.1 ppm to about 100 ppm) in gas streams employed in vapor-phase processes such as chemical vapor deposition in the manufacture of semiconductor devices.