研究目的
To develop an open-path non-dispersive infrared (NDIR) sensor for in-situ measurement of Halon 1301 concentration in aircraft fire protection systems, incorporating a novel cavity-type absorption module for faster response and more compact structure, and to study a temperature compensation algorithm to improve accuracy over a temperature range of 25°C to 105°C.
研究成果
The developed open-path NDIR sensor with a cavity-type absorption module achieved faster response and a more compact structure compared to previous designs. The temperature compensation algorithm effectively reduced measurement errors within 25°C to 105°C, with significant improvements at higher temperatures. Future work should address low-temperature effects, pressure influences, and explore the use of quantum cascade lasers for enhanced performance.
研究不足
The influence of low temperature due to gasification of liquefied agents during spraying was not studied. The effect of pressure on infrared absorption spectrum remains unresolved. The compensation algorithm was validated only for the specified temperature range and may not account for other environmental factors like humidity or pressure variations.
1：Experimental Design and Method Selection:
The study involved designing an NDIR sensor based on infrared absorption principles, using a cavity-type open-path absorption module to avoid sampling delays. A temperature compensation algorithm (Slope-Bias method) was applied to correct for temperature effects.
2：Sample Selection and Data Sources:
Standard gases of Halon 1301 with concentrations from 0% to 25% were used, prepared with nitrogen as the balance gas. Experiments were conducted at temperatures of 25°C, 45°C, 60°C, 75°C, 90°C, 105°C, 50°C, and 100°C.
3：List of Experimental Equipment and Materials:
Equipment included an infrared source, collimator, optical chopper, HgCdTe photodetector, pre-amplifier, lock-in amplifier, mass flow controller (MFC), heating tape, T-type thermocouple thermometer, gas cell, pipes, fan, and computer for data processing. Materials included high-purity nitrogen (
4：999%) and Halon 1301 standard gases. Experimental Procedures and Operational Workflow:
Calibration was done at 25°C and 1 atm using the gas cell. The cell was purged with nitrogen, then standard gas flowed through at a constant rate (1 SLM). For temperature tests, a heating tape was used to heat the gas, with temperature monitored by a thermocouple. Measurements were taken at various temperatures, and data were processed using the NDIR principle and compensation algorithms.
5：Data Analysis Methods:
Data were analyzed using nonlinear fitting based on Johnson's formula for calibration. The Slope-Bias compensation method was applied, with polynomial fitting and least squares method used to derive compensation equations. Relative and absolute errors were calculated to evaluate performance.
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