Portable TDLAS Sensor for Online Monitoring of CO2 and H2O Using a Miniaturized Multi-Pass Cell

Abstract

We designed a tunable diode laser absorption spectroscopy (TDLAS) sensor for the online monitoring of CO2 and H2O concentrations. It comprised a small self-design multi-pass cell, homemade laser drive circuits, and a data acquisition circuit. The optical and electrical parts and the gas circuit were integrated into a portable carrying case (height = 134 mm, length = 388 mm, and width = 290 mm). A TDLAS drive module (size: 90 mm × 45 mm) was designed to realize the function of laser current and temperature control with a temperature control accuracy of ±1.4 mK and a current control accuracy of ±0.5 μA, and signal acquisition and demodulation. The weight and power consumption of the TDLAS system were only 5 kg and 10 W, respectively. Distributed feedback lasers (2004 nm and 1392 nm) were employed to target CO2 and H2O absorption lines, respectively. According to Allan analysis, the detection limits of CO2 and H2O were 0.13 ppm and 3.7 ppm at an average time of 18 s and 35 s, respectively. The system response time was approximately 10 s. Sensor performance was verified by measuring atmospheric CO2 and H2O concentrations for 240 h. Experimental results were compared with those obtained using a commercial instrument LI-7500, which uses non-dispersive infrared technology. Measurements of the developed gas analyzer were in good agreement with those of the commercial instrument, and its accuracy was comparable. Therefore, the TDLAS sensor has strong application prospects in atmospheric CO2 and H2O concentration detection and ecological soil flux monitoring.

Vertical Distribution Mapping for Methane Fugitive Emissions Using Laser Path-Integral Sensing in Non-Cooperative Open Paths

“…Allan variance analysis is the most common and widely used tool for estimating the minimum detection limit of TDLAS sensor systems [ 43 ]. The variance supplies detailed information, including the signal stability and noise characteristics of monitoring over different time scales.…”

“…A transparent balloon, filled with methane at a path-integral concentration of 300 ppm•m, is monitored at a detection distance of 10 m for 1200 s. The sampling interval for the TDLAS telemetry sensor is 0.2 s. The 6000 concentration data are successively recorded as shown in Figure 4. Allan variance analysis is the most common and widely used tool for estimating the minimum detection limit of TDLAS sensor systems [43]. The variance supplies detailed information, including the signal stability and noise characteristics of monitoring over different time scales.…”

Infrared Non‐Invasive Exhaled Biomarker Sensing: A Review

“…[97] The CO 2 sensing with detection limit of 0.13 ppm at 18 s response time has been achieved by TDLAS along DFB laser at 2.004 μm and 430 cm multipass cell. [98] 4.1.2. Helicobacter pylori Infection CO 2 and 13 C isotope are the biomarkers of H. pylori infection, bacterial activity in the body and liver malfunction.…”

“…[ 97 ] The CO 2 sensing with detection limit of 0.13 ppm at 18 s response time has been achieved by TDLAS along DFB laser at 2.004 µm and 430 cm multipass cell. [ 98 ]…”

Online Monitoring of Seawater Carbon Dioxide Based on an Infrared Rear Beam Splitter

“…Schroder et al in 2022 proposed a new multispectral NDIR gas sensor capable of achieving a 90% decrease in signal intensity in ten seconds when the concentration was changed and set up for the direct conversion of values to ppm units [ 16 ]. In fact, most of the carbon dioxide detection is focused on air, using optical paths with multiple reflective devices [ 17 , 18 , 19 ]. It is well known that carbon dioxide molecules are polar and interact with other molecules, which affects the sensitivity and accuracy of the sensor.…”