1. Modulated spectrum detection technology
Modulated spectrum detection technology is the most widely used TDLAS technology that can achieve higher detection sensitivity. It analyzes the absorption of the gas by rapidly modulating the laser frequency to sweep across a fixed frequency range of the absorption spectrum line of the gas being measured, and then using phase-sensitive detection technology to measure the harmonic components in the transmission spectrum line after being absorbed by the gas. There are two types of modulation schemes: external modulation and internal modulation. The external modulation scheme uses an electro-optical modulator outside the semiconductor laser to achieve modulation of the laser frequency. The internal modulation scheme achieves the modulation of the laser frequency by directly changing the injection working current of the semiconductor laser. modulation. Due to the convenience of use, the internal modulation scheme is more widely used. Its measurement principle is briefly described below.
While the laser frequency scans the gas absorption spectrum line, the laser operating current is modulated with a higher frequency sinusoidal modulation. The instantaneous laser frequency can be expressed as: where (t) represents the laser frequency Low-frequency sweep; a is the frequency change amplitude produced by sinusoidal modulation; w is the sinusoidal modulation frequency. The transmitted light intensity can be expressed in the form of the following Fourier series.
Harmonic components can be detected using phase sensitive detectors (PSD). Modulated spectroscopy technology significantly reduces the impact of laser optical noise (1/f noise) on measurement through high-frequency modulation. At the same time, a very narrow-bandwidth bandpass filter can be obtained by setting a larger time constant for PSD, thereby effectively compressing Noise bandwidth. Therefore, modulated spectroscopy technology can achieve better detection sensitivity.
3. Technical features and advantages (1) Not affected by background gas
(2) Not affected by dust and window pollution
(3) Automatically corrects the effects of temperature and pressure on measurement
Laser gas online analyzer is used for continuous industrial process and gas emission measurement. It is suitable for harsh industrial environment applications, such as various steel furnaces, aluminum and non-ferrous metal industries. Metals, chemicals, petrochemicals, cement, power generation and waste incineration, etc.
Features
High resolution (laser scanning frequency is several times that of traditional laser analyzers)
Modular design, on-site modular replacement, quick maintenance and maintenance
High light penetration capability, suitable for applications in high dust barrier environments
Patented aerodynamic principle insertion tube, suitable for applications in extremely high dust barrier environments
< p>No cross-interferenceNo sampling required, direct on-site measurement
Fast measurement (response time can be less than 1 second)
Compact structure, sturdy and durable< /p>
According to different application requirements, there are mainly the following configuration models:
In-situ type
Laser in-situ measurement, fast response speed and high measurement accuracy< /p>
Integrated positive pressure explosion-proof design, safe and reliable
Modular design, all functional modules can be replaced on site, easy to maintain
Highly intelligent and easy to operate< /p>
Bypass laser bypass measurement has high measurement accuracy and strong anti-interference ability
Optical non-contact measurement can directly measure high temperature and highly corrosive gases
The bypass treatment device is simple and reliable, and can be installed directly at the process pipeline
The entire system is explosion-proof and supports automatic compensation of gas temperature and pressure
Distributed type
Distributed Type laser measurement, supports eight measurement channels, high cost performance
Independent laser measurement module for measurement channels, high reliability
Networked centralized display and control, convenient monitoring
< p>Measure gas composition and detection limitPipeline measurement
Remote measurement
Sampling measurement
Pipeline measurement
p>Remote measurement
Sampling measurement