Research On Near Infrared Moisture Measurement Based On LED

Moisture content is an important indicator to determine the physical, chemical and biological properties of the material and the accurate determination of moisture content is of great significance. As a common device to detect the moisture content of the material, the research and development of the moisture meter received widespread attention. The near infrared moisture meter has been widely used in many areas because it has the advantages of continuous measurements, non-contact measurement and fast response speed. The light sources of the conventional near infrared moisture meter are usually incandescent lamp or halogen lamp and the meter modulates the optical signal in the mechanical modulation way with a motor and a modulating disk. The conventional near infrared moisture has the disadvantage of high power consumption, too many movable members and its modulation frequency is limited by the mechanical rotational speed.For the shortcomings of the traditional infrared moisture meter, this thesis proposed a moisture detection solution which uses the modulated LED light source and electrical modulation instead of the traditional light sources and mechanical modulation. This solution is without the movable members such as the motor and modulating disk. And on this basis, the hardware and software platform of the near infrared moisture detection system was built and the related tests and experiments were operated on it. This thesis made the following research:(1) This thesis studied the near infrared moisture detection theory and analyzed the shortcomings of the conventional near infrared moisture meter. A new moisture detection solution without movable members was proposed based on the feature of the LED light source and InGaAs detector.(2) For the case of low power LED light source, the weak optical signal and strong interference, this thesis studied and used the lock-in amplifier to detect the weak optical.(3) This thesis designed and made the LED driving circuit, preamplifier circuit, filter circuit, lock-in amplifier circuit and conducted a systematic debugging.(4) This thesis wrote the microcontroller procedures of signal acquisition, de-noising and filtering。The PC software platform was completed in the LabVIEW development environment, which includes data display and storage procedure.(5) This thesis built the moisture measurement detection platform and calibrated the moisture system. The moisture content of the sinter mixture were detected. For the moisture content of 2% to 9% of the sinter mixture, the measurement error is less than 0.32% absolute moisture content.