Non-Dispersive Infrared (NDIR) sensor design and its application on alcohol detection

Alcohol concentration measurement becomes very important in mixing a chemical solution. The measurement in general uses a conventional method that requires direct contact and a long time of measurement period, such as using a capacitive sensor. Another method is Non-Dispersive Infrared (NDIR) which is capable of measuring the concentration of alcohol without any direct contact and within relatively short test period. In NDIR system, infrared light generated by an infrared source passes through the sample tube. Then, the infrared light that can be absorbed by the hydrocarbon particles of the alcohol is sensed by an infrared detector. In this paper, the infrared source is made of inexpensive 19 Gauge nichrome wire heated at different temperatures to find the best alcohol absorption. PID controller system is employed to maintain constant temperature of the infrared source. The infrared light absorbed is then detected by a thermopile sensor. The result showed that the best alcohol absorption is at 60 °C, and it is proportional to the magnitude of the concentration, the greater the concentration, the higher the value of its absorbance. Absorbance value for distilled water is 0 while the absorbance value for 20% alcohol is at 0.15 and for 60% alcohol is 0.26. This proves that the higher the concentration of alcohol, the infrared light absorbed will be higher. Overall, the inexpensive NDIR system is capable of observing and detecting alcohol that may be used for other solutions in further research.