An FPGA-based lock-in detection system to enable Chemical Species Tomography using TDLAS

Abstract

This paper presents the design, implementation and test of a compact, low-cost and fully digital signal recovery system for tunable diode laser absorption spectroscopy (TDLAS) in narrow line-width gas sensing applications. An FPGA-based digital lock-in amplifier (DLIA), in conjunction with TDLAS using the wavelength modulation spectroscopy (WMS) technique, is utilized to demodulate and extract first (1f) and second (2f) harmonic signals for a narrow CO 2 feature in the spectrum region of 1997.2nm. The spectrum in this wavelength region shows suitably weak water absorption, enabling CO 2 detection with high resolution. Gas-cell experiments were carried out using the DLIA and a conventional rack-mounted commercial lock-in amplifier. The comparison between the two systems shows good agreement, validating the feasibility of this approach and demonstrating the prospect for extension to a massively multichannel system to implement Chemical Species Tomography.

Cost-Effective Quasi-Parallel Sensing Instrumentation for Industrial Chemical Species Tomography

“…To achieve the CF-WMS scheme, the WMS-1f and WMS-2f signals are extracted from the digitised 𝐼 , (𝑡), denoted as 𝐼 , (𝑑), using the DLI module. The in-phase and quadrature components of the WMS-1f, 𝑋 , and 𝑌 , , and WMS-2f, 𝑋 , and 𝑌 , , can be obtained by [29] 𝑋…”

Laser driving and data processing concept for mobile trace gas sensing: Design and implementation

“…The respective progress has led to many implementations also in the field of laser spectroscopy, e.g., in the form of digital lock-in amplifiers (DLIA) on FPGA platforms. 20,26,27 In this work, we take the advantage of a recently available, integrated, and open-source platform and show how to adopt this SoC (Red Pitaya 28 ) for laser driver control and data processing. This system is based on a Xilinx ZYNQ-7010 processor, featuring an integrated dual-core ARM Cortex A9 processor with Xilinx 7-series FPGA logic.…”

An open-source high-frequency lock-in amplifier

“…First described in 1941, early LIAs were based on heaters, thermocouples and transformers 3 . More modern LIAs have been fully digital [4][5][6][7] or implemented on field programmable gate array (FPGA) devices [8][9][10][11][12][13][14] , which are able to exceed the performance of their analog counterparts 15 . However, the cost of modern LIAs may prove prohibitive, particularly in cases where large numbers of input channels are required.…”

“…Research into low-cost FPGA based LIAs has produced a number of alternatives 25 , including high resolution designs operating at up to 6 MHz demodulation 31,32 , and simulations have been presented for a high frequency LIA based on the Red Pitaya STEMlab 33 . Typically, FPGA LIAs have been developed with specific experimental objectives 13,14,34 . The STEMlab is the basis for a range of related measurement instrumentation from PyRPL, including an LIA [35][36][37] .…”