Abstract
A wavelength modulation spectroscopy- (WMS-) based gas sensing system was established to measure concentration of carbon monoxide (CO) in the range 0–100%. The CO absorption line at 1563.06 nm was scanned with a tunable distributed feedback (DFB) laser, and two InGaAs photodiodes were applied to perform optic-electric conversion. Without using commercial instruments, essential electrical circuits were self-developed and integrated, including laser temperature controller, laser current driver, signal generator, and digital lock-in amplifier. The gas cell deployed in the system was fiber coupled with a total effective optical path length of 50 cm. The second-order harmonic signal was extracted, and experiments of gas detection were carried out to investigate the performance of the sensor, including detection repeatability, detection accuracy, response time, and limit of detection (LoD). Experiment results show that the sensor is reliable and has acceptable probing performance. The maximum relative detection error is less than 3.8%, suggesting good detection stability. Benefiting from the self-developed sensor, the whole CO detection system has small size, affordable expense, and application potential.
Highlights
Carbon monoxide, which is odorless and colorless, is an important indicator gas of preventing spontaneous combustion of coal seam [1–4]
It can be seen that the detection error is measured 20 times in a period of 100 seconds and the maximum error is under 0.7% which suggests good stability
With the increasing of concentration, the relative error tends to be decreasing and within the whole detection range, the relative detection error is within the range of −2.9%~3.8%
Summary
Carbon monoxide, which is odorless and colorless, is an important indicator gas of preventing spontaneous combustion of coal seam [1–4]. Among the numerous gas sensing techniques, optical methods have been studied worldwide in recent years due to its advantages including high sensitivity, fast response time, nonintrusive nature, wide sensing range, and long lifespan [5–7]. Tunable diode laser absorption spectroscopy (TDLAS) using lasers as light sources is a powerful and widely used technique for gas sensing applications including environmental monitoring, industrial process control, chemical analysis, and combustion diagnostics [8–12]. In order to achieve highly gas sensing ability, wavelength modulation spectroscopy technique is widely adopted to achieve high signal-to-noise ratio (SNR). This technique using harmonic detection is one of the most effective methods to suppress the background noises. TDLAS-WMS technology has been widely studied and reported in the trace gas detection field [13–16]
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