Abstract: A method and apparatus for in situ measurement of the concentration of a gas with a frequency modulated tunable diode laser is disclosed. The sampling cell, which is mounted in the flow of gases to be measured, is a Herriott cell. Gas enters the sampling cell through sintered metal filters that prevent entrance of particulates. Signals from a sample detector and a null detector are compared to eliminate interference patterns from the laser optics. High accuracy dynamic calibration of the apparatus is also disclosed.

Abstract: An apparatus and method are disclosed for measuring the concentration of gases that are unstable or difficult contain in a sample cell. A frequency modulated laser is tuned to the frequency of a first spectral feature of a gas of interest and a laser beam is projected through a reference cell containing, at a selected pressure, a selected second gas that has a second spectral feature near the first spectral feature of the gas of interest. The laser is line-locked to an outer zero crossing of a third harmonic of the detected laser beam coincident with the first spectral feature. The concentration of the gas of interest is calculated from a second harmonic of a portion of the laser beam projected through a transmission medium containing the gas.

Abstract: Dilution stack sampling apparatus, for analyzing gaseous components of a gas stream from a stack containing particulate material of varying size therein. A passageway has a first end communicating at an angle with the probe intermediate its ends to receive a sample of gas and to change its flow direction to inertially remove most of the particulate material. An eductor connected to the second end of the passageway mixes dilution air with the sample of gas to provide a diluted sample. A filter upstream of the second end of the passageway removes remaining particulate material from the sample of gas which is not the inertially separated. Instrument air can be provided in a back-flow direction at the upstream side of the filter to periodically remove particulate material from the filter. The diluted sample and the dilution gas are supplied to gas analyzer, and the mass flow rate of the dilution gas and diluted gas are measured.

Abstract: In accordance with this invention, a misalignment detector apparatus is provided for a transmissometer with an underfilled reflector. The transmissometer has a transceiver that projects a collimated beam of light of small diameter across a smokestack to a circular reflector of substantially greater diameter than the collimated beam of light so that the reflector is underfilled. The reflector includes apparatus for sensing the position of the collimated beam of light with respect to the center of the reflector and its position on the reflector when it is not on center which allows operator notification of when the beam is on the reflector and when the beam is off the reflector thereby requiring maintenance/realignment.

Abstract: A sulfur monitor analyzer is disclosed and utilizes a burner or flame holder, a burner or reaction chamber, a photomultiplier tube, a light collimator, and chopper blade members with openings so as to permit a flame disposed in the burner or reaction chamber to be seen by the photomultiplier tube at all times. A chemiluminescent radiation mask is disposed operatively between a portion of the chemiluminescent radiation and the photomultiplier tube so as to provide a chopper open mode of operation at which time the photomultiplier tube receives the flame radiation and a fraction of any chemiluminescent radiation surrounding the flames with any remaining fraction of any chemiluminescent radiation being obscured permanently by the chemiluminescent radiation mask. When the chopper is in the closed mode of operation, the photomultiplier tube receives only the radiation from the flame through an aperture defined by an opening in the opaque segment of this chopper or chemiluminescent radiation mask.

Abstract: Sample air is divided into two paths. One path leads through a thermal converter where ambient NO.sub.2 is changed into NO. The other path passes through equivalent tubing to keep the air samples synchronized. Both samples then go to separate cells where each combines with ozone. The resulting chemical reaction produces light, chemiluminescence, which is measured by separate photo-multiplier tubes. Electronic circuits translate the results into simultaneous readings of NO.sub.x and NO concentrations. A difference amplifier subtracts the NO from the NO.sub.x to give a continuous NO.sub.2 value.