Non-dispersive Infrared Gas Research Articles

New structure gas sensor using a modulation-type pyroelectric ir detector

Abstract We developed a new structure gas sensor using a new type of pyroelectric IR detector which contains a pyroelectric element (LiTaO3) and a small chopper using a piezoelectric material in the same package. The accuracy of measurement is ±0.2% in the 0 ∼ 20% concentration range of CO2 gas. The change in the output signal is within ±0.5% in a temperature range of 0 ∼ 40°C. The accuracy and stability of the new gas sensor are superior to those of the conventional non-dispersive IR gas sensor due to the new structure and the new type of pyroelectric IR detector.

Non-Dispersive Infra-Red Gas Analysers for Industrial Processes and the Protection of the Environment

Non-Dispersive Infra-Red Gas Analysers for Industrial Processes and the Protection of the Environment

Errors in atmospheric CO2concentration measurements arising from the use of reference gas mixtures different in composition to the sample air

Comparisons have been made between the URAS 2, UNOR 2 and Grubb Parson's SB2 non-dispersive infra-red gas analysers, involving the measurement of CO 2 concentration in gas mixtures containing N 2 and O 2 in varying proportions. The results imply that the CO 2 concentration in air when using CO 2 /N 2 mixtures as references, is under-estimated by 3.7 and 2.3 ppmv for the URAS and Grubb Parson's instruments respectively and over-estimated by 4.5 ppmv by the UNOR. The measurement of CO 2 concentration in air is not affected if CO 2 /air mixtures are used as references. The indicated CO 2 concentration of air relative to a CO 2 /N 2 reference mixture is found to depend on ambient pressure for both the UNOR and URAS analysers. Thus aircraft or high altitude in situ measurements need an additional correction, to be comparable with measurements made relative to the same CO 2 /N 2 reference mixtures at a standard (near sea-level) pressure of 1 000 mb. The results are similar to those obtained by Bischof (1973) and have important implications on the interpretation of carbon dioxide concentration measurements made at monitoring stations. DOI: 10.1111/j.2153-3490.1975.tb01656.x

Pressure Effect Determined with Use of the Nondispersive Infrared Gas Analyser

Abstract The pressure effect of nitrous oxide and nitric oxide due to nitrogen gas was investigated with use of a nondispersive infrared gas analyser. The results are in line with the theoretical curves derived from the Elsasser theory. The calculated expression is partly improved and the error of calculations is estimated in regard to carbon dioxide.

Book Review: Non-Dispersive Infra-Red Gas Analysis in Science, Medicine and Industry

Book Review: Non-Dispersive Infra-Red Gas Analysis in Science, Medicine and Industry

Paper 9: The Sampling and Measurement of Exhaust Emissions from Motor Vehicles

The development of apparatus and systems to reduce exhaust air pollution from motor vehicles was hampered initially by the lack of suitable quantitative measuring apparatus. Great improvements have taken place and accurate measurement of pollutants can now be made, either in the form of continuous records, or of an average value, over a period of time or cycle. The principal instrument in current use is the rapid response non-dispersive infrared gas analyser. Apart from carbon compounds it can also detect with accuracy oxides of nitrogen. Future trends in pollution measurements are orientated towards the evaluation of the mass emitted during a predetermined cycle instead of the average concentration. With this in view, new sample collection methods have been developed, such as total bag sampling, and variable dilution sampling. The B.T.C. Analytical Committee was formed four years ago to advise on and discuss exhaust gas measurement techniques. Amongst its achievements have been the establishment of gas and car correlation schemes and the laying down of instrument specifications.

The frequency response characteristics of some condenser microphone infra-red detectors

The frequency response characteristics for interrupted infra-red radiation are described for four condenser-microphone type detectors as used in nondispersive infra-red gas analysers. Three of the detectors are of conventional dimensions. The fourth is a subminiature type, and its use is described with a field-effect transistor amplifier. It is shown that markedly increased optical modulation frequencies can be used with infra-red pneumatic detectors, without radical reductions in output signal, if the dimensions of the device are drastically reduced. This has been accounted for on theoretical grounds. The frequency responses obtained are examined and shown to correlate adequately with mathematically predicted profiles. Low frequency attenuation is explained on the grounds of thermal conductivity effects and leakage paths across the transducer diaphragm, whereas a high frequency maximum for one detector is shown to arise from Helmholtz resonation due to the chamber configuration.

Cross-sensitivity effects in non-dispersive infra-red gas analysers using condenser microphone detectors

A pair of precision gas mixing pumps has been used to investigate the effect of spectral overlap and collision broadening by sample diluents on the accuracy of three commercial non-dispersive infra-red gas analysers, sensitized for carbon dioxide and having a condenser microphone type of transducer. These effects were investigated in respect of the composition of the sample mixture and the filling mixture of the condenser microphone chamber. The results are given as the ratio `actual%CO2 in sample/indicated%CO2 in sample'. In the case of broadening by helium, argon, oxygen and nitrogen this ratio is typically 1.125 ± 0.005, 1.030 ± 0.008, 1.000 and 0.950 ± 0.006, respectively, for the range 0-10% v/v CO2. This has been shown to be in accord with available spectroscopic data. Broadening by nitrous oxide indicates a value of 1.32 ± 0.06 for the foreign broadening coefficient F for this gas on the 2349 cm-1 band of carbon dioxide. Results for the vapours ether and halothane suggest a broadening ability similar to that of nitrous oxide.