Research On Smartphone-based Infrared Thermal Imaging System For Temperature Measurement

Temperature is a physical quantity to describe the degree of object’s hot and cold, and the approach of measuring temperature is one of the vital indicators to judge the progress of science and technology. Uncooled infrared thermal technology, as a non-contact measurement method, characterized by non-invasive and fast measurement and other advantages, has been widely used in all walks of life, and developing to the trend of low cost, intelligent and miniaturization. However, the implementation platform of traditional thermal imager is previously marked by high-price, large-volume and so on. With fast running speed, strong operability and high cost-effective, smart phone has been changing people’s lifestyle and consuming habits. Android system, as the main operating system of smartphone, is easy to be applied in other fields by virtue of its opening sources. It realizes the sharing of resources and reducing the cost meanwhile. Based on the trend of development and advantages of these two systems, it is imperative to develop an infrared thermal imaging system on Android smartphone. However, there is no such system or has the temperature measurement components but the accuracy is unguaranteed. Therefore, our work has great practical significance.In this paper, we launched the project from infrared radiation theories of the blackbody, and introduced the emissivity to establish the infrared radiation theory of the actual object. This paper presented the components of the uncooled infrared thermal imaging system in detail, and established the infrared thermal imaging temperature measurement model of the actual object by theoretical deduction, also analyzed the errors during the process of temperature measuring reasonably. By using Hongmi note smartphone, infrared detector components and Eclipse development environment, we had accomplished infrared thermal imaging temperature measurement technology on smartphone. According to the usage scenario of this system, we designed the night vision mode and temperature measurement mode processed by pseudo color algorithms. We established the relationship between thermal image and temperature with blackbody radiation to realize temperature measurement, in this mode, users can measure target’s temperature by moving smartphone. In addition, according to the needs of this system, we designed some practical functions, such as take thermal picture, parameter settings and so on.In this work, we have improved the temperature measurement precision from three aspects, particularly. For the temperature drift phenomenon caused by the infrared detector, we designed a constant temperature source correction system to refrain from it, and the device is fixed to the outside of the optical lens, and the algorithm is integrated in the interface of thermal imaging. For the case that the emissivity is unknown when measuring, we designed a variable spectrum device to measure temperature. It is accomplished by changing the temperature band, which makes the optical filter in and out of the light path through bluetooth communication technology. This paper also put forward an exact instantaneous method to measure the target’s emissivity and confirm it on the surface of different pig specimen. Besides, infrared temperature measurement, as a non-contact temperature measurement method, we furthermore studied the influence of distance and angle on it, among the many influences angle is easy to be neglected.The infrared temperature measurement system smartphone-based we developed has the advantage of low cost, small volume, and moving conveniently. The accuracy of temperature measurement of this system is ensured by three approaches, it achieves to 0.3℃. In this project, the measuring method of emissivity designed and the influence of the angle factors to temperature has a great significance of guidance and reference to actual temperature measurement.