LED-Absorption-QEPAS Sensor for Biogas Plants

Abstract

A new sensor for methane and carbon dioxide concentration measurements in biogas plants is presented. LEDs in the mid infrared spectral region are implemented as low cost light source. The combination of quartz-enhanced photoacoustic spectroscopy with an absorption path leads to a sensor setup suitable for the harsh application environment. The sensor system contains an electronics unit and the two gas sensors; it was designed to work as standalone device and was tested in a biogas plant for several weeks. Gas concentration dependent measurements show a precision better than 1% in a range between 40% and 60% target gas concentration for both sensors. Concentration dependent measurements with different background gases show a considerable decrease in cross sensitivity against the major components of biogas in direct comparison to common absorption based sensors.

Quartz-enhanced photo-acoustic spectroscopy for breath analyses

“…6 A number of different light sources (QCLs, LEDs, DFBs, OPOs and more) have been reported used in QEPAS experiments. [15][16][17][18][19][20] OPOs seem to be the optimal choice for providing large wavelength tunability, high energy, molecular selectivity and cost-effective device for the generation of infrared light in the 1.5 to 5 µm spectral range. 21 Therefore, a pulsed single mode mid-infrared (MIR) OPO has been developed.…”

“…11 Standard low cost QTFs with resonance frequencies at 32.7 kHz are typically used as sensors, however, also custom made QTFs have been reported. [12][13][14][15][16][17][18] The PA signal is proportional to the Q-factor: S ∝ QP α/f 0 , where P is the optical power, α is the molecular absorption coefficient and f 0 is the resonant frequency of the QTF. The stiffness of quartz provides an efficient means of confining the acoustic energy in the prongs of the QTF, resulting in large quality factors (Q-factors) of the order 100000 in vacuum and 3-8000 at atmospherical pressures.…”

Investigating flexible feeding effects on the biogas quality in full‐scale anaerobic digestion by high resolution, photoacoustic‐based NDIR sensing

“…Modulation of the light source leads to the exiting soundwave whose amplitude is related to the amount of target gas in the measurement channel. About a decade ago, the first attempt to miniaturize this simple concept did use a micro-electro-mechanical system pressure sensor to gauge the light intensity of a thermal emitter [22], and since then different combinations of various types of broad band light sources and devices for determining the photoacoustic signal have been developed [23][24][25][26][27][28][29][30][31]. While the use of lasers in combination with acoustic resonators in setups of direct photoacoustic spectroscopy allow for ultra-sensitive trace gas detection, the use of such devices outside the laboratory is challenging [32][33][34][35][36].…”

Thin‐film Potentiometric Sensor to Detect CO2 Concentrations Ranging Between 2 % and 100 %

“…Hence, researchers worldwide are trying to meet the demand of devices that can be used to monitor the network condition at reduced cost. Recently, Kö hring et al [2] have shown the feasibility of a light emitting diodebased quartz enhanced photoacoustic sensor for methane and CO 2 detection in biogas plants with fast response time, broad concentration range and low cross sensitivities. However, the sensor showed temperature and pressure dependent signal variations.…”