The primary principle that has been used by our company for identifying and measuring gas concentrations has been well incorporated in a scientifically manner. The concept of DOAS (Differential Optical Absorption Spectroscopy) is entirely dependent upon the absorption law of Beer-Lambert. This law helps in the determination of relationship that occurs between molecules and amount of absorbed light within the light path. Due to different kind of molecules, each of the gas possess distinct properties of the absorption spectrum. By utilizing this concept, it is quite easy for simultaneously determination of concentrations of a number of gases that come within the path of light.
Light beam is transferred from the xenon lamp having high pressure over a certain path.
With the help of up-to-the-minute computer calculations, the evaluation and analysis of light is done and because of transfer, it loses molecular absorption.
Be it infrared wavelengths or the visible spectrum, both types emerge from the xenon lamp and is highly intense in nature.
Later, the receiver captures the light and conduct it to analyzer with the help of optical fiber. Moreover, the fiber helps the installation of the analyzer away from aggressive environments.
Analyzer consists of a computer, allied controls and spectrometer of high grade quality.
Spectrometer helps in the splitting of light into narrow bands of wavelength with the help of an optical grating. This comes with a adjustable so that wavelengths can be adjusted in order to obtain optimum array of wavelengths.
Later, the process of transforming light into electrical signals takes place.
When the slit passes through the detector speedily, several instantaneous values combine together for forming a spectrum in the required range of wavelength.
In order to register the image of spectra in the computer's memory, the mentioned scan is done hundred times per second.
The obtained spectrum is compared to the absorption one, from which the other spectrum is calculated which has well-balanced summation to be used for the analysis.
Until the best match is observed, computer keeps checking for it with the help of varying factors such as size.
Nevco has created an analyzer to monitor to monitor various compounds particularly in the area of infra red wavelength. The mentioned IR technique is similar to that of spectrometer technique, which helps in the identification and measurement of different concentrations. As both the techniques are based on same principle, thus their working is also same. In order to know the mechanism of this technique kindly refer to the mechanism mentioned in the UV DOAS.
The difference lies in the components of interferometer, where the beam splitter is used to divide the beam of light towards a couple of mirrors to form an interference pattern.
Bulletined below is the working of the mentioned technique:
Laser light is emitted by the LD500 within the near by wavelength spectrum section that includes infra red wavelength.
In order to measure this, rapid scanning of laser is done over an absorption line within the spectrum that absorbs gas.
For observing a slight change in the laser wavelength, the laser is continuously operated and can be easily tuned.
Electrical voltage is applied across the semiconductor diode for obtaining this change.
During the scan, the applied voltage is entirely based upon the ramp function because of which it varies and is precisely controlled.
A large amount of scans can be done on an average by the LD500, during a measurement. The interval of measurement ranges from 1 to 20 seconds and rate of scanning is measured in kilohertz range.
When the measurement interval is about to complete then the spectrum spectrum is entered into the procedure of evaluation.
The absorbent gas cross section is compared with the procedure of least squares fitting. At particular wavelengths, this cross section of the gas is related to the absorption strength of the gas. Once, path length is monitored, it helps to evaluate gas concentration.