Part NO. :	TDLAS-WMS-A-A
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Availability :	In store

TDLAS–WMS based near-infrared 1650.9nm DFB Laser diode methane sensor system

Figue1 The TDLAS whole system

Description

A new developed tunable diode laser spectrometer for the measurement of methane Gas mole fractions in exhaust gas matrices by the use of methane transitions in the ν2 + ν3 near-infrared band around 1650.9nm. We chose A fiber-coupled TL-DFB-1-A82-1650.9-SA 1650.9nm distributed feedback laser diode Provided By Idealphotonics. Connected with 20m optical path Multipass Herriott Type Cell (FOGMPC20-A),Together with Lock In amplifier we finish the measurement of CH4 concentration According to Beer’s Law.

About Beer’s Law: 

As indicated above, the amount of light absorbed by the gas is proportional to amount of the gas present in the light’s path. Beer’s Law says that light will be absorbed by molecules such that the absorbance (A) is a function of the light beam’s path length (l), the density of the gas being measured (d), and the particular absorptivity coefficient (ε) of the chemical species and that the absorbance (A) is a function of the initial light power (P0) and the power at the detector (P) as shown in these equations: 
A = ldε & A = -Log10(P/P0) Æ d (P0-P)/P0 
Since P is relatively close to P0 (or P/P0 is close to 1), and the path length and the absorptivity coefficient are fixed values, you can substitute, expand the log and simplify the equations to show that d is proportional to (P0-P)/P0. In essence, the target gas density (d) can be determined by measuring P0 and P with the spectrometer.

Figure 2 Typical transmitted laser intensity and corresponding normalized second harmonic signal.

Working Theory:

Wavelength modulation spectroscopy with second harmonic (2f) detection for sensitive tracespecies detection is one Higher Precision method for detecting Gases. A fast kHz sine wave modulation is added to drive the laser, and a lock-in amplifier is employed to detect the harmonic component at twice the modulation frequency (2f). By using wavelength modulation with 2f detection, the measurement sensitivity is improved by shifting the detection to higher frequencies where laser excess noise and detector thermal noise are both much smaller; in addition flow-generated noise outside the detection bandwidth is suppressed using phase-sensitive detection. The bottom graph in Figure 2 shows the normalized second harmonic (2f) signal. The concentration of the absorbing species can be determined from the measured 2f peak height. Since the scan range is much wider than the absorption feature, it is assured that the center of the absorption peak will be found in the scan. if only 10% or 50% of the light were getting through, the normalized 2f signal would not be different and the measurement would not be affected. If the mirror becomes very dirty, not enough light will get to the detector and the power cannot be measured at all. The system checks during every scan for a minimum amount of light. If that test fails, the system will show a “power fail” error.

TDLAS–WMS based near-infrared sensor system GUI:

Packing List：

Ordering Information:

The testing Result shows：

Through Building the TDLAS-WMS and testing, Our system has a High SNR Value at 100dB.This system will be the good Choice for Those Companies who Monitoring the gas in the environment and College Research. Judging from the CH4 concentration we use in our experiment, we can evaluate the lowest Precision will reach 0.5ppm

Gases measurement system support