Showing papers on "Spectrum analyzer published in 1990"

Analyzer of liquid sample and analyzing method of liquid sample using said analyzer

Abstract: This invention relates to a liquid sample analyzer used for analyzing various liquid samples such as blood and urine and an analyzing method by using the analyzer, and can make the analyzer compact, can automate the analysis and can improve accuracy. The analyzer has the construction wherein a flow path (102) is disposed on a disc (101), a reagent is fixed onto this flow path (102) to form a reagent portion (104), and liquid sample supply means (9) for supplying the liquid sample to the reagent portion (104) and means for measuring the reaction product are disposed. The analyzing method of the liquid sample uses this analyzer and conducts in succession the supply of the liquid sample, the reaction between the reagent and the liquid sample and the measurement of the reaction product obtained by the reaction, on the disc.

A high-resolution chirp transform spectrometer for microwave measurements

Abstract: A microwave heterodyne spectrometer consists of a radiometer front-end and a real-time spectrum analyser back-end. Common spectrometer types are filterbanks, autocorrelators and acousto-optic spectrometers (AOS). A high-resolution chirp transform spectrometer using reflective array compressor (RAC) filters with a time bandwidth product of 6400 is presented. The spectrometer has 1600 channels within a 40 MHz input bandwidth and a linear dynamic range of 63 dB for a CW input. It seems to be very promising for future space applications.

Improvement of the spherical mirror analyzer

Abstract: With the use of some obstacle rings and a set of retarding grids, the resolution of the prototype spherical mirror analyzer, which has been developed in a previous paper [H. Daimon, Rev. Sci. Instrum. 59, 545 (1988)], was improved. The uniformity of the resolution with respect to the emission angle was also achieved. Some examples of electron energy‐loss spectra and XPS spectrum were presented.

Noise characterization of mode-locked color-center laser sources

Abstract: By using an ultrahigh-speed photodetector and wide bandwidth spectrum analyzer combinations, a noise characterization of the pulse train from a mode-locked KCl:Tl color-center laser has been performed. Amplitude and phase (timing jitter) noise content are quantified and compared when the laser is operated in both synchronously mode-locked and coupled-cavity mode-locked configurations. By deliberately mismatching the color-center laser cavity frequency with respect to that of the Nd:YAG pump-laser and examining resultant noise burst power spectra, it has been confirmed that the coupled-cavity mode-locking process exhibits passive characteristics. >

Inexpensive portable rf spectrum analyzer with calibration features

Abstract: An inexpensive portable RF (radio frequency) microcontroller-based (76) digital spectrum analyzer (50) is automatically calibrated for passband amplitude tilt/variations. Resulting software-obtained (78) calibration parameters are used during operation to reduce or eliminate passband amplitude errors. The spectrum analyzer (52) also includes a PLL frequency synthesizer (100) arrangement, but the PLL (100) controls a VCO only during calibration to derive calibration values for controlling a digital-to-analog converter (92). During normal operation, the VCO is driven in an open loop configuration under software control using such calibration values -- achieving nearly the accuracy of closed loop operation while avoiding the penalty of long PLL lock time. These amplitude and frequency calibration techniques and arrangements permit the spectrum analyzer to have relatively inexpensive components and circuit arrangements and nevertheless achieve high accuracy over a wide band.

Waveform peak capture circuit for digital engine analyzer

Abstract: A digital engine analyzer has an oscilloscope display and is controlled by microprocessors operating under menudriven stored program control. The analyzer receives analog input signals from an engine being analyzed. Peak capture circuitry permits the display of a full cylinder period of a waveform, even though it contains very high frequency portions, by selectively switching between normal and high resolution modes. The circuitry samples the analog waveform at a very high rate and selects samples for display at a much slower display rate. The circuitry captures and stores the highest magnitude sample in each cylinder cycle by storing each sample only if its magnitude exceeds that of the previously stored sample. In the normal mode, at each display clock pulse the most recent sample is selected for display, irrespective of its magnitude. In the high resolution mode the stored peak value is selected for display at each display clock pulse.

High resolution electron energy loss spectrometer

Abstract: A method and an apparatus comprising an electron gun, two energy analyzers, an energy-selecting slit with intensity sensors, a feedback circuit, a sample, and an electron detector. The beam produced by the electron gun is dispersed according to the energies of the electrons by the first energy analyzer. The dispersed beam impinges on a slit which monochromates the beam by selecting a narrow pass-band of energies. The two halves of the slit are equipped with electron intensity sensors whose output is used by a feedback circuit to stabilize the position of the dispersed beam on the slit so as to counteract instabilities in the power supplies of the electron gun and of the analyzer. The monochromated electron beam then passes through a sample, and the transmitted beam is dispersed according to the energies of the electrons by the second energy analyzer. The power supplies of the two analyzers are linked so that the energy selected by the second analyzer tracks the energy selected by the first analyzer. The second analyzer therefore automatically tracks instabilities in the gun high voltage, and the whole apparatus is able to achieve much higher energy resolution than if all the power supplies were operated independently.

Interferometric analyzer for multiple substance detection

Abstract: An interferometric analyzer for the detection of substances having a structured absorption spectrum such as a periodic or quasiperiodic absorption line pattern, within a gas blend, and comprising a source of radiation for directing radiation into a radiation path that includes a container, cell or the like which contains the substances to be detected, the path includes further a filter system, which includes an electrically or temperature controlled Fabry Perot element such that the spacing between the transmission lines of the interference corresponds to spacing of absorption lines of different substances for different absorption bands of these substances; and a dispersion filter each circularly variable or another Fabry Perot filter is positioned in the radiation path for selecting a respective spectral region as far as a particular substance is concerned by means of the controlled disperging element.

Millimeter and/or submillimeter network vector analyzer

Abstract: A millimeter and/or submillimeter network vector analyzer comprises a millimeter source and a millimeter heterodyne receiver, and the network to be analyzed is placed between the source and the receiver. The millimeter source comprises a first microwave source feeding a millimeter harmonic generator. The millimeter heterodyne receiver comprises a millimeter harmonic mixer which is fed by a second microwave source which serves as a local oscillator for it, an HF (high frequency) vector receiver and a device for displaying the characteristics of the analyzed network. The analyzer includes a device for servocontrolling the frequency of emission of the second microwave source by the frequency of the first microwave source (or conversely), and a main HF (high frequency) oscillator activating this servocontrol device. The main oscillator is also directly used as a phase reference for the HF (high frequency) vector receiver. Both the millimeter harmonic generator fed by the first microwave source and the millimeter harmonic mixer of the millimeter heterodyne receiver operate at the same harmonic order. The analyzer makes possible vector measurements in all millimeter and submillimeter bands up to the terahertz frequency range without corresponding directional couplers or microwave frequency synthesizer.

An integrated optic RE spectrum analyzer in a ZnO-GaAs-AlGaAs waveguides

Abstract: A report is presented on the realization of an integrated optic RF spectrum analyzer (IOSA) that combines a wideband acoustooptic Bragg cell and a pair of waveguide lenses in ZnO/GaAs/Al/sub 0.15/Ga/sub 0.85/As composite waveguide 7*23 mm/sup 2/ in size. A total of 10 and 40 channels at the center frequencies of 167 MHz and 500 MHz, respectively, and a frequency resolution of 5.5 MHz were realized. The diffraction efficiencies of 11.5%/W and 4.0%/W of RF drive power at the center frequencies of 167 MHz and 500 MHz, respectively, and a dynamic range larger than 16 dB were measured. Further integration of this IOSA (integrated optic spectrum analyzer) with a laser source, a photodetector array, and electronic driving circuits could produce a monolithically integrated optic RF spectrum analyzer. >

Secondary electron energy analyzers for electron-beam testing

Abstract: Existing post-lens and through-lens analyzers for electron-beam testing are reviewed. A novel through-lens analyzer is proposed which can be operated in two modes: in the conventional retarding-field mode with a feedback technique or in a dispersive multichannel mode with an open-loop technique. In addition, an improved and fast ray-tracing method for the secondary electron trajectories is introduced, which uses Lenz's model field and series expansions for calculating the spatial magnetic field.

Method and apparatus for gas analysis

Abstract: There is provided a gas analyzer, including a radiation source (2), an analytical space (6) through which passes the gas to be analyzed, at least one detector (14) for detecting the intensity of radiation passing through the space, means (18,20,22,24) facilitating the alternating introduction, into the space (6), of the gas to be analyzed and a reference gas (RG) having a concentration located at least in the upper half of the range of concentrations to be measured by the gas analyzer. The analyzer further includes processing means (32), having memory means, to process signals originating in the detector (14), the memory means adapted to store in a first mode of operation signals representing instantaneous intensity values of the detected source and, in a second mode of operation, to store signals representing intensity values obtained when the analytical space (6) is filled with the reference gas, circuit means for comparing the instantaeous values with the reference value, and indicator means (38) for indicating concentration. A method for analyzing gases to establish their concentration is also provided.

Design Of A New In Situ Spectroscopic Phase Modulated Ellipsometer

Abstract: A new spectroscopic phase modulated ellipsometer (SPME) is presented. As compared to other ellipsometric techniques like rotating analyzer ellipsometry (RAE), the phase modulation uses a high frequency modulation (50 kHz) provided by a photoelastic modulator. Then SPME allows at least two orders of magnitude faster real-time mesurements than RAE. Thus, SPME is particularly suitable for in situ real-time applications. New insights on phase modulated ellipsometry are given. In particular, it is shown that an optical model, taking into account the presence of higher harmonics in the modulation, leads to an improvement of the precision measurement. Therefore, it can be inferred that both RAE and SPME provide comparable high precision measurements. Moreover SPME can be combined with numerical data processing systems. A new Fourier analysis of the signal, based on the use of a high precision analog digital converter and a fast digital processor, is presented. The adaptation of the SPME to a deposition chamber is illustrated. In particular, the use of optical fibers in both optical arms allows an increase of the compactness of the ellipsometer. Four detectors can be used simultaneously providing the spectroscopic capability for real-time applications. On-line connexions between the data acquisition system and external analog signals and triggers can also be used. Thus phase modulated ellipsometry appears a powerful technique for in situ control processing applications.

Methods of calibrating gas analyzers

Abstract: A method for calibrating a non-dispersive infrared gas analyzer especially adapted for measuring the concentrations of HC, CO and CO 2 in a vehicle exhaust is described. The analyzer includes a sample chamber (42) for holding a sample gas, a radiation emitter (48) for directing a beam through the chamber and a detector (70) for indicating the amount of radiation absorbed. A plurality of filters each of which transmits radiation at an absorption band of a gas component to be detected are alternatingly positioned in the radiation path to produce a time-multiplexed signal having concentration information for all gases. A calibration assembly is provided which includes a plurality of calibration cells (142) selectively positionable in the radiation path in order to provide an internal calibration standard for two-point calibration of each gas channel. The cells contain one or more of the gas components to be measured at concentrations and pressures predetermined to compensate for the difference in optical path length between the calibration cells and the sample chamber A technique is provided for characterizing the calibration cells in situ after a conventional calibration using bottled calibration gas is performed. The time-multiplexed detector output is corrected for gain and offset errors "on-the-fly" without requiring demultiplexing through the use of an analog multiplier circuit. The correction factors are themselves determined without demultiplexing the detector output signal.

Mass spectrometer having a multichannel detector

Abstract: The invention typically provides a double focusing mass spectrometer comprising an ion source (55), an ion momentum analyzer (56), a multichannel detector (58) and a multielectrode electrostatic ion-energy analyzer (57), wherein the energy dispersing field is generated by arrays of electrodes disposed in groups above and below the ion beam. By appropriate selection of the potentials applied to the electrodes, the focusing properties of the analyzer can be changed, allowing different extents of the mass spectrum to be accurately focused on the face of the detector (58) as it is tilted by the actuator (61) at different angles to the ion beam (64) emerging from the analyzer (57). This enables the spectrometer to simultaneously record either a small part of a mass spectrum at high resolution or a larger part at a lower resolution. Alternative arrangements of the detector which allow a similar result to be obtained are also disclosed.

Network analyzer performance verification

Abstract: A method to verify that a test and measurement system continues to operate within a predetermined acceptable range with respect to a given calibrated state previously defined for that system without the need for conventional external reference components. In accordance with one embodiment, performance verification of a network analyzer used to perform electrical measurements is achieved by storing RF "thru" measurement data (an RF thru measurement trace of the system) at the time of calibration at the factory or later repair and/or recalibration at a field service site. In accordance with another embodiment, performance verification of a lightwave component analyzer, used to perform electrical, electro-optical, opto-electrical, and optical measurements, is achieved by storing RF and optical thru measurement data (both an RF thru measurement trace of the system and an optical thru measurement trace of the system) at the time of calibration at the factory or later repair and/or recalibration. In both cases, at the time of manufacture, the key measurement paths (with calibrated reference components in the loop) of the test and measurement system are measured and stored in system memory or, alternatively, on a disc that is shipped with the system. Repeating these measurements with the same thru connection(s) at a later time(s) indicates how well the test and measurement system is reproducing the conditions of its initial calibration. Setting a range of allowable deviation (for measurement repeatability and normal system drift) between the initial and any later measurements establishes limits within which the integrity of the test and measurement system hardware performance is assured for subsequent measurements on an unknown device under test.

Accurate measurement of low signal-to-noise ratios using a superheterodyne spectrum analyzer

Abstract: A modern superheterodyne spectrum analyzer measures RF power by the process of envelope detection, log amplification, and video averaging. This process is known to give an accurate power measurement for a noise-free sinusoidal tone signal and an error of 2.5 dB for additive white Gaussian noise (AWGN). For a tone combined with AWGN, the measurement of noise power N together with signal power S results in the need for two correction factors: one to compensate for the error in the measurement of combined signal and noise power, and another to take into account (on the logarithmic decibel scale) the subtraction of N from (S+N)/N to get the true signal-to-noise ratio (SNR identical to S/N). The first factor ranges from 0 to 2.5 dB; the second factor is >or=3 dB for SNR/0 dB. The results are extended to the measurement of SNR for phase-shift-keyed (PSK) digital communications signals combined with AWGN. >

Repetitive and Single Shot Pulse Microwave Six-Port

Abstract: The six-port reflectometer technique is extended to make pulsed-RF measurements. It is shown that a time resolution of the or- der of 1 ps is possible both in repetitive and single shot mode of oper- ation of the reflectometer. A proof of the principle of the method is made using passive and active loads. A simple method for the linear- ization of diode-detector response is also presented. HERE IS a need for precise characterization of active T microwave devices operating in pulsed modes. CW characterization of such devices using a conventional net- work analyzer is often inaccurate or even impossible be- cause of severe heating problems. In these cases, a pulsed network analyzer must be used to make measurements un- der polarization conditions similar to those used in oper- ating modes (I). Furthermore, thermal and burn-out ef- fects 121, (3) or turn-on behavior (3) of these devices can only be studied using a network analyzer having a time resolution of the order of 1 ps or better. To answer the need for pulsed measurements, various pulsed reflectometers were developed (3), (4), and a com- mercial vector network analyzer (VNA) with pulsed mea- surement capability became available recently (5). In this work, a new pulsed reflectometer using a six-port junction is presented. It is an interesting alternative to a costly commercial VNA or to other pulsed reflectometers devel- oped elsewhere. It requires simple hardware and can be fully automated. One of its important features is its unique capability of single shot operation. A new linearization method for diode detectors is also presented in this work. In contrast to other methods, this method does not require either a high precision power me- ter (6) or a high quality attenuator (7).

Novel acousto-optic systems for spectrum analysis and phased array radar signal processing

Abstract: Novel acousto-optic systems for spectrum analysis and phased array radar signal processing are proposed The pulsed source 2-D multiplicative time and space integrating spectrum analyzer is proposed and experimentally demonstrated This architecture is simpler, physically smaller, and less sensitive to mechanical vibrations than the pulsed source 2-D additive Mach-Zehnder interferometer based spectrum analyzer Simple and compact optical disk based systems for 1-D and 2-D spectrum analysis are presented The high data packing density, angular motion, and parallel read out capability of optical disks is uniquely exploited to generate the very high time bandwidth product reference signals required for temporal spectrum analysis, that are otherwise difficult to generate using electronics A continuous wave 1-D time integrating disk spectrum analyzer is successfully demonstrated in the laboratory The limited dynamic range due to huge bias levels in interferometric time integrating processors is alleviated by using photorefractive crystals as real time bias removers Continuous wave 1-D and 2-D bias free acousto-optic architectures for spectrum analysis are theoretically and experimentally investigated from a systems viewpoint Simple, compact, and powerful acousto-optic systems for control and signal processing in phased array radars are proposed that eliminate many system components like phase shifters, mixers, power dividers, and complex antenna feed networks, that are encountered in typical electronically controlled phased array radars Via a single control parameter, namely frequency, the optical technique provides appropriately phased signals for transmission and reception in phased array antennas The system is capable of continuous beam scanning, simultaneous multiple beam formation, and multi-target tracking, and can be integrated on a substrate to provide smaller and lighter phased array radars Also, the system is resistant to electromagnetic interference (EMI), and signal phase shifts are independent of the radar carrier frequency employed A 1-D linear phased array radar acousto-optic beam steerer is successfully demonstrated in the laboratory, and performance issues such as detector phase sampling error and phase linearity are highlighted The linear array design is extended to planar and multiple linear arrays

Signal Reconstruction Techniques for Improved Measurement of Transient Emissions

Abstract: Conventional exhaust gas analyzers are of limited use in transient engine testing as the dynamics of the analyzers cause distortion of the emissions measurement during transients. An advanced technique is presented which uses signal reconstruction to determine the actual emissions during engine transients from the distorted output of a conventional exhaust gas analyzer. The reconstruction technique is based on the design of a finite horizon filter which is a dual of generalized predictive control theory. Results are presented which demonstrate the use of this technique for reconstruction of instantaneous emissions from a diesel engine over a part of the US heavy duty test cycle. The results show that the reconstructed emissions recover significant information which is otherwise obscured by the distortion introduced by the analyzer dynamics. In addition, the reconstructed emissions can be corrected for exhaust gas mass flow rate, enabling a more accurate evaluation of the instantaneous and cumulative mass emissions during complex transient cycles to aid in engine development. (A)

High speed optical modulator for application in instrumentation

Abstract: For high speed frequency domain instrument applications, a large bandwidth, efficient, and calibrated modulation source is required. Our primary interest was in developing a modulation source for a 20-GHz lightwave component analyzer (HP8703A). The use of a lithium niobate Mach-Zehnder external modulator for this application has the advantages of large modulation bandwidth, narrow linewidth, operation over a large wavelength range, and the ability to self-calibrate the modulation frequency response.

Rugged multiwavelength NIR and IR analyzers for industrial process measurements

Abstract: This paper discusses the advantages that can be achieved by using integrated multichannel detectors instead of the traditional filter wheel construction in process analyzers and presents four accomplished applications. Integrated multichannel detectors include several parallel detector elements each equipped with a specific interference filter and a Peltier cooler in one hermetic package. Advantages gained by filter integration are good withstanding of ambient stresses and low price due to small size. Multichannel detectors enable the use of different chopper techniques and rugged miniature and highly reliable analyzer constructions. Furthermore multichannel detectors provide exactly simultaneous measurement at each wavelength. This minimizes noise caused by rapid variations in fast moving nonhomogeneous process streams. The first application described is a two wavelength water monitor designed for on-line measurement of water content in lubricating oils. It has to meet high temperatures and high relative humidities in production plant environments. The oil analyzer is an advanced instrument that continuously measures oil content of water effluents in marine and land based applications. The peat moisture meter is a rugged portable NIR instrument constructed without any moving parts. Finally a four-wavelength NIR reflectance instrument is described. In a pilot application in a wood grinding plant the instrument with fibre optics is used to achieve a true in-line moisture measurement of the pulp stream having a speed of 15 - 40 rn/s and temperature of 125 - 145 OC. 1.

Improvements in a chemiluminescent ozone analyzer for respiratory applications

Abstract: The performance characteristics of a previously developed analyzer utilizing the homogeneous chemiluminescent reaction of ozone (O3) with a stoichiometric excess of 2‐methyl‐2‐butene were improved with the eventual goal of measuring the distribution of O3 in a single human breath. By increasing the sampling flow from 200 to 400 ml/min and utilizing a combination of analog and digital filtering, it was possible to improve the signal‐to‐noise ratio at 0.5 ppm O3 from 5.5 to 28, the minimum detection limit from 0.02 to 0.01 ppm, the sensitivity from 1.5 to 2.3 na/ppm, and the 10%–90% step‐response time from 200 to 100 ms. Humidity, temperature, and inlet gas composition interferences were also evaluated. While temperature and humidity have no influence on the analyzer output, the substitution of carbon dioxide for oxygen increased the analyzer sensitivity by 3.8% for each percent of CO2 that was present. Thus, provided that an appropriate correction for carbon dioxide is made, these improvements allow the instrument to monitor inhaled and exhaled O3 concentrations with a rapid dynamic response and over a broad range of physiologically relevant values.

Process and system for rapid analysis of the spectrum of a signal at one or several points of measuring

Abstract: In electron beam measuring, it is often also necessary to measure the frequency range in addition to the measuring time range. In order to do this, according to the invented process, the output signal of the local oscillator of a spectrum analyzer, as is known from conventional high-frequency measuring, undergoes a first frequency conversion and subsequently is utilized for modulating the primary beam. Based on the potential contrast as a multiplicative interaction and the modulated primary beam, the under circumstances very high-frequency signal to be analyzed is transformed to an easily detected low intermediate frequency. Subsequently this intermediate frequency signal is transferred into an input frequency plane of the spectrum analyzer by a second frequency conversion. Both the variable input selection frequency or the fixed intermediate frequency of the spectrum analyzer may be the frequency . The measured result appears in the usual manner on the display of the spectrum analyzer.

Micro photoreflectance semiconductor wafer analyzer

Abstract: An apparatus for measuring local carrier concentration in a preselected area of a semi-conductor is shown and described. An exciting light (preferably a laser) alters the sample's band-gap by photo injecting electron hole pairs in the area being measured. Because of the Franz-Keldysh effect, the photo injected carriers alter the sample's reflectivity. An optical fiber conducts a broad band source of probing light to the excited area on the sample. The sample reflects some of the broad band light back into a fiber that conducts the reflected light to an optical analyzer. The optical analyzer includes a dispersive element that disperses the reflected light onto a linear array of detectors. The analyzer thus simultaneously samples multiple wavelengths in the reflected spectrum. From the resulting samples, a computer deconvolutes the spectral line shape into a measurement of the local electric field and the local carrier concentration.

Infrared analyzer with improved calibration

Abstract: An improved infrared analyzer is provided wherein an unknown specimen gas can be subjected to a measuring infrared ray and a comparative infrared ray to provide resulting signals. The system can be initially calibrated when a zero gas state is initially achieved in the sample cell, and correction factors are achieved by holding the zero gas instrument signal and an output difference between a zero gas comparison signal and the measuring signal for subsequent processing of the actual measurement of the specimen gas to provide a calibrated output signal representative of the concentration of the unknown gas.

Electric field studies of a 2 MeV electrostatic energy analyzer

Abstract: An energy analyzer based on the Proca and Green parallel‐plate design is being developed for use with the 2 MeV heavy ion beam probe on TEXT. In a departure from the conventional configuration, guard ring electrodes will not be used. Instead, a shaped top plate will provide for comparable, or improved, uniformity of the analyzer electric field region. To quantify this effect, and to characterize the electrostatic field, numerical solution methods have been utilized. Simulations have included effects of top plate shape, wire screens, vacuum chamber design, and dielectric support structures. The modeling has permitted us to design an analyzer electrode structure that is an integral part of a uniquely shaped vacuum vessel. The design electric field is 20 kV/cm with less than 1% error in uniformity within the parallel plate region. To examine the electric field structure experimentally, a quarter‐scale prototype analyzer has been constructed and tested. The electric field characteristics are examined by varying the path of a heavy ion beam through the analyzer and examining the resulting analyzer performance. A simulated vacuum wall can be positioned to examine the effects of different vessel configurations and to determine the sensitivity of the analyzer to this boundary condition. The experimental results show excellent agreement with the numerically predicted fields and confirm the validity of the shaped top plate electrode concept.

Lightwave component analyzer

Abstract: A lightwave component analyzer comprising at least an internal optical receiver and preferably also comprising an internal optical source which are selectively connectable by switches configurable by means of an internal or an external instrument controller for calibration and performance of electro-optical, opto-electrical, and optical measurements. The switches are arranged in a switch matrix. The configurable switch matrix is connected by the instrument controller in response to selection of a measurement by a user to facilitate calibration of, and test measurements of devices under test with, the lightwave component analyzer.

Improved pressure-modulated infrared gas analyzer and method

Abstract: A gas analyzer (10) for detecting low concentrations of a specific gas which has a sample chamber comprising passages (14, 30, and 32) through which radiant energy is directed and which is pressure modulated by a loud speaker (36) both of which provide a radiant energy signal which is detected by a beam splitter (82) having a measurement channel (86) directed to a measurement detector (92) and a reference channel (84) with a reference cell (94), containing gas of the type being analyzed, directed to a reference detector (90). Both detectors (92, 90) produce a signal which is processed by an algorithm. The loudspeaker (36) is isolated from the sample chamber by a flexible diaphragm (42) to eliminate phase changes in the pressure modulated output of the loud speaker (36). Means are provided for measuring the modulation or AC pressure and the steady state or DC pressure in the sample chamber, the radiant energy modulation, the humidity in the sample chamber and the temperature of the analyzer as parameters for processing. by the algorithm. Also disclosed is a method of detecting low concentration of a specific gas.