Abstract: In a sampling tube-type smoke detector equipped with a smoke detection device detects smoke particles contained in the air suctioned from a monitored area through a sampling tube by an aspirator positioned in the downstream. The smoke detection device the sampling tube forms a lead-in tube and suctions air through the sampling tube in substantially a straight line. The lead-in tube is formed with a smoke sensor unit to detect smoke particles contained in the air. The aspirator comprises a rotating part which forms an actuator mechanism that discharges the air. The central axis of the lead-in tube and the rotational axis of the actuator mechanism of the aspirator are substantially on the same axis. The sampling tube-type smoke detector is provided to reduce pressure loss in the airflow traveling from the smoke detection device to the aspirator and to supply a low cost, compact smoke detection device driven by a small-sized fan.

Abstract: A method and apparatus for measuring relative humidity of a mixture that provides a quick response time for thermal lag while affording protection to fragile sensors. In one aspect, the invention is an apparatus comprising: a chamber having a membrane covering an opening in the chamber, the membrane being permeable to water vapor while impermeable to liquid water; a humidity sensor for measuring relative humidity of the mixture within the chamber; a first temperature sensor for measuring a temperature relating to the mixture within the chamber; a second temperature sensor for measuring temperature of the mixture at a point exterior to the chamber; and a processor for receiving signals representing the measurements taken by the humidity sensor, the first temperature sensor, and the second temperature sensor and programmed to calculate relative humidity of the mixture at the point exterior to the chamber as a function thereof.

Abstract: A method and system removes nuclear, biological and chemical (NBC) agents from an air stream from a facility HVAC. The system includes an irradiation zone, a saturation zone and a precipitation zone. A contaminant detection apparatus controls the irradiation, saturation and precipitation of the air stream. The irradiation destroys biological agents along with saturation of air stream with a water based solution. The biological debris and dissolved chemical agents are precipitated out of the air stream by condenser coils. Nuclear agents are removed from the air stream by a diverting the air stream though a bypass filter containing high mass particulate filters and activated charcoal. The contaminants are stored for later removal and destruction. The contaminate detection apparatus includes NBC sensors.

Abstract: This apparatus and method allows collection concentrated sample of content in shipping packages without unsealing the package by forcing airflow via existing hidden gaps or, if necessary, creating one by a small incision. The air is injected into the hidden gaps by either probe or socket device to disturb and agitate contents inside the package, causing the contents to loosen and blend particulates on the surface into the air stream. Airborne particles are channeled into detection device, where the particulates are concentrated. Display and warning apparatus receives and records the analysis results from detection device. If the analysis finds that predetermined selection and sensitivity criteria for target hazard or contraband is met, then the warning apparatus initiates appropriate alert protocols.

Abstract: A system for the retrieval and initial conditioning of sample gas for “on line” analyzers or filling of gas sample cylinders. The preferred embodiment of the present invention contemplates a system configured to obtain a representative gas phase sample from a process gas containing entrained liquid, or a process gas which generally is highly susceptible to partial condensation of some gas phase components. The preferred embodiment of the present invention teaches an assembly including a phase separation membrane and housing configured to facilitate the removal of entrained liquid from a sample gas stream. Accuracy of the sample is enhanced, and compositional changes are avoided by first extracting a sample from the process gas followed by removal of entrained liquid it may contain, with the entrained liquid removal being conducted at the prevailing process gas pressure and temperature. Thereafter the liquid free sample may be desaturated by lowering its pressure to reduce its susceptibility to condensation.

Abstract: A water trap system based on a thermoelectric cooling device is employed to remove a major fraction of the water from air samples, prior to analysis of these samples for chemical composition, by a variety of analytical techniques where water vapor interferes with the measurement process. These analytical techniques include infrared spectroscopy, mass spectrometry, ion mobility spectrometry and gas chromatography. The thermoelectric system for trapping water present in air samples can substantially improve detection sensitivity in these analytical techniques when it is necessary to measure trace analytes with concentrations in the ppm (parts per million) or ppb (parts per billion) partial pressure range. The thermoelectric trap design is compact and amenable to use in a portable gas monitoring instrumentation.

Abstract: A portable system for the detection of chemical particles such as explosive residue utilizes a metal fiber substrate that may either be swiped over a subject or placed in a holder in a collection module which can shoot a jet of gas at the subject to dislodge residue, and then draw the air containing the residue into the substrate. The holder is then placed in a detection module, which resistively heats the substrate to evolve the particles, and provides a gas flow to move the particles to a miniature detector in the module.

Abstract: A method and device for determining the concentration of analytes in a sample. The device has a surface with an extraction coating thereon. The method is carried out while the sample is highly agitated to maintain a substantially constant boundary layer. The sample is brought into contact with the coating for a limited time so that all the analytes that pass through the boundary layer are adsorbed by the coating. The amount of analytes in the coating is determined and the concentration of those same analytes in the sample is then calculated from the diffusion coefficient of the analytes. The device is first calibrated using analytes of known concentration.

Abstract: A system for the retrieval and initial conditioning of sample gas for “on line” analyzers or filling of gas sample cylinders. The preferred embodiment of the present invention contemplates a system configured to obtain a representative gas phase sample from a process gas containing entrained liquid, or a process gas which generally is highly susceptible to partial condensation of some gas phase components. The preferred embodiment of the present invention teaches an assembly including a phase separation membrane and housing configured to facilitate the removal of entrained liquid from a sample gas stream. Accuracy of the sample is enhanced, and compositional changes are avoided by first extracting a sample from the process gas followed by removal of entrained liquid it may contain, with the entrained liquid removal being conducted at the prevailing process gas pressure and temperature. Thereafter the liquid free sample may be desaturated by lowering its pressure to reduce its susceptibility to condensation.

Abstract: A denuder assembly is adapted for the collection and removal of a gaseous analyte from a sample gas. The denuder includes a housing including an internal cavity, a sample gas inlet fluidly coupled with a sample gas source, a denuder liquid inlet fluidly coupled with a denuder liquid source, a barrier sheet extending across the internal cavity and separating the internal cavity into a liquid reservoir and a gas flow-through channel fluidly coupled with and downstream of the sample gas inlet, and a denuder liquid disposed in the liquid reservoir and permeating the barrier sheet to coat the gas-channel surface of the barrier sheet thereby allowing the denuder liquid on the gas-channel surface to contact the sample gas flowing within the gas flow-through channel and allowing the analyte to diffuse through the barrier sheet into the liquid reservoir.

Abstract: A gas detection instrument comprises a combustible gas sensor and associated circuitry, which supplies power to the sensor and measures and displays resulting sensor response. The supplied power is switched between timed pulses of electricity and steady state electricity, with the intermittent electricity being employed only when no significant change in sensor output has been detected. Alternatively, timed pulses of electricity are maintained, and predictive software algorithms are used to give readings for gas concentration during interruption of the power supply. The sensor operation enables the instrument to respond to rapid changes in gas concentration while minimizing power consumption of the sensor.

Abstract: Systems and methods for the detection of substances (particularly particulate substances) within mail pieces, specifically letters and other “flats” of mail. In particular, the systems and methods are for the detection of residues of Chemical or Biological Warfare Agents (CBWAs) which may be present within the mail pieces. The system is principally designed to be included as part of Dual Pass Rough Cull System (DPRCS) for the collection and detection of the residue when the contaminated mail piece first enters a mail facility and before it is intermingled with other mail pieces.

Abstract: A vapor trap for detecting VOCs includes a housing, having a first end portion, a second end portion and at least one opening for receiving gas vapor. The housing is at least partially buried in ground with a vapor containment mechanism detachably connected to the first end portion of the housing. The vapor containment mechanism can be removed and replaced with a vapor sampling mechanism. An organic vapor analyzer can be connected in fluid relationship to the vapor sampling mechanism to measure VOCs. Optionally, a vacuum pump can be utilized to draw vapor into the vapor trap and then subsequently into the organic vapor analyzer. There can be a first selector valve located between the vapor sampling mechanism and the vacuum pump and a second selector valve located between the vapor sampling mechanism and the organic vapor analyzer. A preferred organic vapor analyzer is a photo-ionization detector.

Abstract: A dust sampling device having a sampling nozzle is provided. The nozzle is provided with an inlets the diameter of which is variable. The diameter of the nozzle can be instantaneously changed, while keeping constant a sampling flow rate within a measuring device as the nozzle is introduced into a chimney or a duct in response to a change in flue gas flow velocity, to thereby maintain an uniform sampling rate in the nozzle. The nozzle is connected to a dust measuring device and is inserted into an interior of an flue gas passage. The diameter of the nozzle can be changed so as to keeping sampling gas flow rate determined by the dust measuring device constant at the sampling velocity corresponding to the flow velocity of the flue gas. The flue gas sampled through the nozzle is introduced into the dust measuring device.

Abstract: Gas separation membranes, especially meniscus-shaped membranes for gas separations are disclosed together with the use of such meniscus-shaped membranes for applications such as thermal gas valves, pre-concentration of a gas stream, and selective pre-screening of a gas stream. In addition, a rapid screening system for simultaneously screening polymer materials for effectiveness in gas separation is provided.

Abstract: A system for the retrieval and initial conditioning of sample gas for “on line” analyzers or filling of gas sample cylinders. The preferred embodiment of the present invention contemplates a system configured to obtain a representative gas phase sample from a process gas containing entrained liquid, or a process gas which generally is highly susceptible to partial condensation of some gas phase components. The preferred embodiment of the present invention teaches an assembly including a phase separation membrane and housing configured to facilitate the removal of entrained liquid from a sample gas stream. Accuracy of the sample is enhanced, and compositional changes are avoided by first extracting a sample from the process gas followed by removal of entrained liquid it may contain, with the entrained liquid removal being conducted at the prevailing process gas pressure and temperature.

Abstract: A gas sampler (1) for a portable gas analyser, having a cooler or chiller (8) through which cooler or chiller (8) the gas sample is passed prior to being conveyed to a gas analyser, has the cooler or chiller (8) operable by means other than electrical power. The invention also includes a portable gas analyser provided with such a sampler (1).

Abstract: A sample handling system includes an inlet for receiving sample from a process, and a mixer for intermixing a solvent with the sample to dissolve undesirable components within a sample. A separator is provided that receives the solvent/sample mixture and separates the sample from the solvent and undesirable solutes. The so separated sample is then provided to a suitable analyzer for analysis.

Abstract: A sample handling system includes a sample probe that is adapted to intermix a solvent with a sample obtained from a process to dissolve undesirable components within a sample. A separator is provided in the sample handling system that receives the solvent/sample mixture and separates the sample from the solvent and undesirable solutes. The so separated sample is then provided to a suitable analyzer for analysis.

Abstract: A probe is provided that combines in one housing a pressure regulator and filter/dryer element. The probe may be connected to a conduit for the transfer of a fluid sample, such as natural gas, from the conduit to provide separation of the fluid such that a gaseous component may be then subsequently transferred to an instrument or the like. If liquid is separated it may be returned to the conduit via a return line.

Abstract: A vapor trap for detecting VOCs includes a housing, having a first end portion, a second end portion and at least one opening for receiving gas vapor. The housing is at least partially buried in ground with a vapor containment mechanism detachably connected to the first end portion of the housing. The vapor containment mechanism can be removed and replaced with a vapor sampling mechanism. An organic vapor analyzer can be connected in fluid relationship to the vapor sampling mechanism to measure VOCs. Optionally, a vacuum pump can be utilized to draw vapor into the vapor trap and then subsequently into the organic vapor analyzer. There can be a first selector valve located between the vapor sampling mechanism and the vacuum pump and a second selector valve located between the vapor sampling mechanism and the organic vapor analyzer. A preferred organic vapor analyzer is a photo-ionization detector.

Abstract: A modular aerosol sample detection system is provided comprising a sample collector couplable to an aerial vehicle and provided with at least one retrievable collection sample plate, which controllably rotates to collect aerosol samples on a multiplicity of collection spots arranged in multiple concentric tracks on the collection disk, and a multi-channel TOF removably couplable to the collection sampler to analyze the collected samples.

Abstract: An analytical system is provided which uses the kinetic energy of motion of the entire system to drive a fluid under analysis through the system. This is accomplished by use of a propulsion system which is attached to the analytical portion of the system. Various sensor detection systems may be used to analyze the sample collected within the confines of a sample isolation and concentration module contained within the system. Trace quantities of suspect materials may be detected or monitored by use of the instant system.

Abstract: A gas detector having an intake to let in the gas to be detected and detecting the gas let in through the intake by a gas sensor, in which a porous film is horizontally arranged over the gas intake, in order to prevent the gas permeability of the porous film from being affected by water, oil and/or dust riding on the porous film, wherein a water-repellant and oil-repellant porous film is horizontally provided in a stretched state over the upper end of the intake, and the outside of the outer circumferential edge of the porous film is so structured as to allow liquid on the porous film to fall externally.

Abstract: A gas sampling separator 29 for the separation of liquid or other contaminants from gas received from a pipeline may be easily inspected visually and cleaned. A cylindrical body 62 forming a separation chamber 64 is threaded onto a base 40. A tube 68 within the separation chamber receives gas from a port in the base and directs the gas into the separation chamber for separation of the gas from the contaminants. The separated contaminants collect in a sump 58 formed by the base and may be vented upon actuation of a manually actuated valve 76.

Abstract: Sidestream gas sampling assembly that does not substantially degrade the waveform of expired gases. The gas sampling assembly includes a sample cell portion integrated with a filter portion for separating undesired liquid condensate from respiratory gases to be monitored. The gas sampling assembly is configured to receive expired gases through a gas sampling line, filter undesired liquid condensate from the expired gases through hydrophobic fiber elements and communicate the filtered gases to a sample chamber which is in close proximity to the filter where measurements may be taken thereof e.g., optical or infrared sensing mechanisms. The gases that are substantially free of liquid condensate are then exhausted from the sample chamber.

Abstract: A hydrogen gas indicator system that provides various substrate materials (4) that support hydrogen gas sensor (1) materials with discrete indicia (7) that provide information separate from any change in the physical properties of the hydrogen gas sensor itself.

Abstract: The present invention is a novel collection device that allows constituents of air to collect on a test strip included within the collection device. Specifically, the collector allows a removable test strip to be inserted in the collector while an air sample passes therethrough. Thereafter, the test strip is removed from the collector and analyzed to determine the constituents of air that passed through the test strip and collector. When using the collector to inspect for trace amounts of explosives within a piece of baggage, the collector is connected to a baggage-collector interface because the shape of the baggage-collector interface corresponds to that of the collector. The baggage-collector interface is secured to the baggage and an air sample is extracted from the interior of the baggage and through both the interface and the collector, including the test strip. As the air is extracted, the constituents of air collect on the test strip.

Abstract: The present invention is a novel collection device that allows constituents of air to collect on a test strip included within the collection device. Specifically, the collector allows a removable test strip to be inserted in the collector while an air sample passes therethrough. Thereafter, the test strip is removed from the collector and analyzed to determine the constituents of air that passed through the test strip and collector. When using the collector to inspect for trace amounts of explosives within a package, the collector is connected to a package-collector interface because the shape of the package-collector interface corresponds to that of the collector. An air sample is extracted from the interior of the package and through both the interface and the collector, including the test strip. As the air is extracted, the constituents of air collect on the test strip.

Abstract: An apparatus and method for monitoring a source gas for detection of phosgene and/or chlorine dioxide therein, in which the source gas is filtered for removal of hydrogen sulfide and/or chlorine and/or hydrogen chloride prior to monitoring of the source gas by a gas sensor specific for phosgene or chlorine dioxide detection. The filter includes a support having Ag2O thereon, and when the source gas contains chlorine dioxide, chlorine also is present in the source gas prior to its filtration.

Abstract: A device according to the related art for determining at least one parameter of a medium flowing in a line is unable to prevent pollutants from getting out of the line into the atmosphere. The device of the present invention has a filter which is able to take up the pollutants and thus prevent them from getting into the atmosphere.

Abstract: A vapor trap for detecting VOCs includes a housing, having a first end portion, a second end portion and at least one opening for receiving gas vapor. The housing is at least partially buried in ground with a vapor containment mechanism detachably connected to the first end portion of the housing. The vapor containment mechanism can be removed after a predetermined time period and replaced with a vapor sampling mechanism. An organic vapor analyzer can be connected in fluid relationship to the vapor sampling mechanism to measure VOCs. Optionally, a vacuum pump can be utilized to draw vapor into the vapor trap and then subsequently into the organic vapor analyzer. There can be a first selector valve located between the vapor sampling mechanism and the vacuum pump and a second selector valve located between the vapor sampling mechanism and the organic vapor analyzer. A preferred organic vapor analyzer is a photo-ionization detector.

Abstract: Sensors are provided which are selective for a specific gas. The sensors include a substrate, electrodes, and a thin film metal oxide. Methods for choosing the metal oxide to be utilized in the sensor with selectivity for the specific gas are also provided, as are methods for determining the presence of a specific gas in a gaseous mixture.

Abstract: An instrument provides a quantitative measurement of an analyte in a gas. It includes a detection cell that provides an indication of an amount of analyte present in the gas, and a valve having a closed position, a sample gas position, and a calibration gas position. There is a calibration gas inlet orifice in communication with a gas outlet through a first flow path including the valve and the detection cell, and a sample gas inlet orifice in communication with the gas outlet through a second flow path including a scrubber, the valve, and the detection cell. Two orifices of different sizes, a sample gas orifice along the second flow path, and a bypass orifice positioned between the sample gas orifice and the gas outlet, prevent a build up of excessive pressure in the instrument when the valve is in the closed position or the calibration gas position.

Abstract: A self contained field sampling system for measuring engine exhaust emissions includes a mini-dilution tunnel adapted for the collection of proportional samples of emissions to be analyzed, an engine air intake flow measurement instrument, a system controller and data acquisition system, and an optionally portable generator to provide electrical power. Several probes withdraw dilute and undiluted exhaust for emission analysis. Various engine emissions may be isolated. As well, engine emissions mass rate may be calculated by reference to engine RPM, inlet flow rate, exhaust temperature and emissions output rate.

Abstract: A vapor trap for detecting VOCs includes a housing, having a first end portion, a second end portion and at least one opening for receiving gas vapor. The housing is at least partially buried in ground with a vapor containment mechanism detachably connected to the first end portion of the housing. The vapor containment mechanism can be removed after a predetermined time period and replaced with a vapor sampling mechanism. An organic vapor analyzer can be connected in fluid relationship to the vapor sampling mechanism to measure VOCs. Optionally, a vacuum pump can be utilized to draw vapor into the vapor trap and then subsequently into the organic vapor analyzer. There can be a first selector valve located between the vapor sampling mechanism and the vacuum pump and a second selector valve located between the vapor sampling mechanism and the organic vapor analyzer. A preferred organic vapor analyzer is a photo-ionization detector.

Abstract: The invention is directed to a silver/palladium (AgPd) cell for adjusting or measuring a level of hydrogen in a high pressure environment, a high temperature environment, and/or an environment incompatible with stainless steel. The inventive cell includes a hollow diffusion tube of a AgPd alloy operably associated with a hollow connecting member and a connected tube, also operably associated with the hollow connecting member. The cell is operable in environments having a pressure of up to 3,600 p.s.i.

Abstract: A collector is provided which is capable of simultaneously capturing and collecting particulate and gaseous chlorinated organic compounds contained in a fluid. The collector 3 includes a housing 6 and a captor 7 disposed within the housing 6. The captor 7 includes a tubular porous core member 7a of a sintered glass having one end closed with a close member 7c, and a gas-permeable sheet 7b fitted around the core member 7a. The gas-permeable sheet 7b is, for example, a paper-like sheet having a fibrous activated carbon and inorganic fibers. The particulate and gaseous chlorinated organic compounds contained in a gas sample flowing into the captor through a sampling tube 2 are simultaneously collected and removed from the gas sample by the core member 7a and the gas-permeable sheet 7b, and the gas sample free from the chlorinated organic compounds is then discharged from an outlet port 6b.

Abstract: An apparatus and method are provided for continuously monitoring the operation of electrical equipment and preventing critical operational failures. The invention quantitatively determines the concentrations of gas and/or vapor (including water) components in an insulating fluid on a real time basis. An increase of one or more detected chemical components signifies an actual or potential electrical problem with the equipment. The preferred apparatus consists of a gas extractor, an infrared gas analysis instrument, and a gas diaphragm pump. Gas and water vapor components are extracted from the insulating fluid by permeating through a membrane in a gas extractor. The gas and/or vapor components are then brought into an infrared gas analyzer by the gas diaphragm pump. A quad detector in the analysis instrument identifies and determines the concentration of three specified gases and/or the vapor simultaneously.

Abstract: An apparatus for, and a method of, sampling and analyzing thermally-labile chemical species, comprises a quartz tube having a filter member positioned in the bore of the tube. The filter member comprises a plug of quartz beads having a layer of quartz frits on either side. A fluid (gas or liquid) carrying one or more chemical substances associated with particulate matter is passed through the tube, the particulate material being collected by the quartz beads. After sample collection, the material remaining/retained from the original sample is removed, as for example by thermal desorption, and the material is then analyzed.

Abstract: An air monitoring system is disclosed having an air monitoring unit with at least one sensor for measuring data of an air quality parameter and a computer for storing the air quality parameter data received from the sensor. The air monitoring unit may use an installed or a portable system, or a combination of both, for measuring the air quality parameters of interest. A remote data center may be provided, and the data may be uploaded to the data center from the unit by a communications media such as the Internet. Information or instructions may also be downloaded from the data center to the unit via the communications media for controlling or modifying the function of the unit. An expert system may be provided with the air monitoring system for controlling the unit. The information or instructions downloaded to the unit may be generated by the expert system.

Abstract: A gas sensor device including a housing provided with an inlet for introducing a gas to be measured, a sensor element capable of detecting oxygen gas or the like contained in the gas and a base element supporting the sensor element within the interior of the housing. The base element is integrally assembled to the housing by means of a seal.

Abstract: The mass of particulate of an effluent gas flowing in a stack is measured with a mass measurement assembly in which sampling is isokinetically controlled by determining in real-time the molecular weight of the effluent gas, and in particular, determining the moisture content of water vapor in the effluent gas. Readings from a pair of flow sensors connected in series and separated by a dryer are compared to provide a real-time moisture measurement of the effluent gas. The moisture measurement is used to determine a total molecular weight of the effluent gas in real-time and the velocity of the effluent gas in real-time for isokinetic sampling during measurement of the mass of particulate flowing in the effluent gas.

Abstract: A concentrator and sensor assembly are disclosed that use phased heaters to multiply the concentration levels that can be eluted, relative to operation with a single interactive element having a sorbent material to increase the concentration of desired gas constituents at a detector. This is accomplished here by providing two or more interactive concentrator elements that are selectively heated in a time phased sequence so that each of the interactive elements becomes heated and desorbs gas constituents into the sample fluid stream at substantially the same time that an upstream concentration pulse, produced by heating one or more upstream interactive elements, reaches the interactive element. This produces a multiplication effect that significantly increases the concentration of the gas constituents at the detector, thereby increasing the effective sensitivity of the detector.

Abstract: An aerosol lab-on-a-chip (ALOC) integrates one or more of a variety of aerosol collection, classification, concentration (enrichment), and characterization processes onto a single substrate or layered stack of such substrates. By taking advantage of modern micro-machining capabilities, an entire suite of discrete laboratory aerosol handling and characterization techniques can be combined in a single portable device that can provide a wealth of data on the aerosol being sampled. The ALOC offers parallel characterization techniques and close proximity of the various characterization modules helps ensure that the same aerosol is available to all devices (dramatically reducing sampling and transport errors). Micro-machine fabrication of the ALOC significantly reduces unit costs relative to existing technology, and enables the fabrication of small, portable ALOC devices, as well as the potential for rugged design to allow operation in harsh environments.

Abstract: A fuel dispenser system having a storage tank and a fuel delivery hose extending from the storage tank and terminating at a nozzle. A vapor recovery line extends between the nozzle and the storage tank. The vapor recovery line extends between the nozzle and the storage tank and has a section with a first larger diameter and a second section having a smaller diameter. A vapor pump is operatively connected to the vapor recovery line for moving vapor along said vapor recovery line. A chamber is positioned along the vapor recovery line and includes inlet and outlet ports, and a main sensor chamber. The inlet port connects to the vapor recovery line at a point having the larger diameter. The outlet port connects a point of the smaller diameter. Each of the ports connects to the main sensor chamber where a sensor is positioned for determining the vapor concentration.

Abstract: This invention relates to a gas sensor arrangement in which one or more gas sensors (4) are placed into rooms for monitoring or measuring gas or vapor concentrations or mixtures, a (diffusion body (5) is placed in front of the gas sensors (4), the responsiveness of the gas sensors, is impaired by structural) (design or contamination and/or the gas atmosphere is static. The sensor (4) or sensors (4 l to 4.n) are placed in, on. or in front of a duct (1) located in the room and thus are within the flow area of said duct (1), and a flow is present in the duct (1) during measuring or monitoring.

Abstract: The mass of particulate matter in a particle laden gas stream is measured using a first mass detector and a second mass detector. Switching means causes the particle laden gas stream and a substantially identical but particle-free gas stream to alternately engage the first mass detector and the second mass detector respectively during successive measurement time periods. A difference between a reading provided by the first mass detector and a reading provided by the second mass detector for each of the successive measurement time periods is determined. This difference intrinsically corrects for volatilization losses occurring during the measurement time periods. A measure of the mass or concentration of particulate matter in the particulate laden gas stream is determined from this difference.