An Online Humidity Transducer Based on Near-Infrared Radiation

Abstract

In various sectors, humidity measurement is a crucial task, for instance in the food industry, grain processing/crushing, sugar plants, etc. The conventional humidity measurement method requires a lab sample analysis. This is a destructive, expensive and slow process. Besides, as raw material humidity may vary considerably during the day, many measurements are required throughout the period. On the other hand, with an online humidity measurement process, the water amount is known instantly, without physical contact with the sample. Thus, the production process control can be carried out without losses, with maximum profit and quality. In this work, a humidity transducer based on near-infrared radiation is presented. During its development, the main project focus was cost reduction. Due to this, LEDs were used for producing infrared radiation. This has eliminated typical problems in conventional online measurement tools, such as reduced useful life and too many moving parts which may complicate equipment installation in vibrating places. Through the inclusion of a temperature control system, problems with ambient temperature variation were solved. The equipment was tested on a laboratory, measuring coffee powder humidity. However, the system can be easily adapted to measure humidity on a variety of other substances. Our tests indicate that the proposed transducer has a high sensitivity and robustness to temperature variations and external radiation sources (solar and incandescent light, etc.) Besides, the measured equipment uncertainty is in the order of 0.2 %.