FPGA-Based Real-Time Implementation of Temperature Measurement via Tunable Diode Laser Absorption Spectroscopy

In this paper, a real-time temperature measurement system was implemented using a field programmable gate array (FPGA) via tunable diode laser absorption spectroscopy. The system can be used to measure the average temperature along the laser path. The wavelength modulation spectroscopy (WMS) method was applied to realize temperature measurement. First, a recursive peak detection algorithm was proposed to improve the accuracy of main peak detection of WMS signal and reduce the computational complexity. Second, an FPGA was facilitated to realize: 1) a real-time quadrature demodulator to extract the signals at frequencies of 2 f and 1 f and calculate the WMS-2 f/1 f signals on chip and 2) in-situ accurate main peak detection of the WMS-2 f/1f signals and hence target gas temperature measurement. Third, experiments were conducted to verify the real-time performance of the system. Experimental results show that the proposed algorithm and hardware design can implement continuous temperature measurement with a temporal resolution of up to 0.25 ms and the measuring rate can reach 4 kHz.

I. Introduction

Temperature is an essential parameter to be measured online in various combustors, which exist widely in power plants, engines and turbines [1]–[4]. It can be utilized to infer the combustion efficiency and analyze the combustion conditions. A variety of detection techniques have been applied to capture the temperature of target gas molecules, e.g. water vapor and carbon dioxide. Among all currently available techniques, the thermocouple and thermistor are the most popular temperature detectors for their high reliability and low cost. As intrusive sensors, they usually disturb the gas flow and are prone to be damaged.