On line monitoring system of laser ammonia escape TDLAS technology (Tunable Diode Laser Absorption Spectroscopy) is adopted This instrument has the characteristics of high sensitivity, fast response, no interference from background gas, non-contact measurement, etc., which provides a reliable guarantee for real-time and accurate reflection of NH3 changes.
Main technical indicators
Measurement principle of LD-900 laser ammonia online monitoring system
On line monitoring system of laser ammonia escape The measurement principle of TDLAS is Tunable Diode Laser Absorption Spectroscopy, which was proposed in the 1970s
Tunable semiconductor laser spectral absorption technology TDLAS is essentially a spectral absorption technology. The concentration of gas is obtained by analyzing the selective absorption of laser by gas molecules. It differs from the traditional infrared spectral absorption technology in that the spectral width of the semiconductor laser is much smaller than that of the gas absorption line, as shown in the figure above. Therefore, semiconductor laser absorption spectroscopy is a high-resolution spectral absorption technology. The system uses a laser beam of a specific wavelength to pass through the measured gas. The attenuation of laser intensity and the concentration of gas meet Lambert Beer theorem, so the concentration of the measured gas can be obtained by analyzing the attenuation information of the detected laser intensity. The laser ammonia online monitoring system using semiconductor laser absorption spectroscopy technology can resist the interference of background gas in principle, and the measurement results are highly reliable.
system advantage
one . Not affected by background gas
The traditional nondispersive infrared spectral absorption technology uses a wide spectral band of the light source. In addition to the absorption spectral lines of the measured gas, there are many absorption spectral lines of other background gases within the spectral range. Therefore, the light emitted by the light source is not only absorbed by multiple spectral lines of the gas to be measured, but also by some background gas, which leads to measurement inaccuracy. However, the spectral width of the semiconductor laser used in the semiconductor laser absorption spectroscopy technology is less than 0.001 nm, far less than the spectral width of an absorption spectral line of the measured gas. The "single line absorption spectrum" data as shown in Figure 2-1. At the same time, when selecting the absorption spectrum line, it is ensured that there are no absorption lines of background gas components in the measurement environment within the range of about 10 times the spectral line width near the selected absorption spectrum line frequency, so as to avoid the cross absorption interference of these background gas components on the measured gas and ensure the accuracy of measurement.
2. No dust interference
As shown in Figure 2-1, the laser ammonia online monitoring system periodically scans the absorption spectral line of the measured gas by modulating the frequency of the laser. The scanning range of the laser frequency is set to be greater than the width of the absorption spectral line of the measured gas, so that the yellow green zone (Zone 1) in Figure 2-1 that is not attenuated by the gas absorption spectral line is included in a single scan And the red zone (zone 2) attenuated by the gas absorption spectrum. The measurement signal obtained from Zone 1 includes the transmittance of dust and window pollution, and the measurement signal obtained from Zone 2 includes the transmittance of dust and window pollution as well as the attenuation of light intensity absorbed by gas. Therefore, by measuring Zone 1 and Zone 2 simultaneously in a laser frequency scanning cycle, the transmittance absorbed and attenuated by the gas can be accurately obtained, so as not to be affected by the light intensity attenuation caused by dust and window pollution on the gas measurement concentration.
