Design and experiment of assembled soil temperature sensor

Abstract: Soil temperature is one of most important physical parameters of the soil. It effects the physical, chemical and biochemistry characteristics of the soil. Soil temperature also associates with the crop's growth and physiological process. The soil temperature measurement technology and sensors which are widely used come from the industry. But in the application of soil humidity and meteorological environment geography fields, Soil temperature sensor has the disadvantages of unsuitable structure, selection in sensitive element blindness and unscientific measure method. Based on the analysis of soil temperature measurement requirements in agriculture, sensor structure and sensitive element choice, the paper promoted the assembled structure which had optimization in the design of soil temperature sensor. The temperature sensing region length was reduced to 2 cm. The new design of soil temperature sensor was composed of sensing region and glass fiber reinforced plastics catheter. Lower coefficient of temperature conductivity material was used as catheter could decrease the influence of traditional long sleeve type sensor. The new design can be assembled to measure the single point, multi point and multi－layers' soil temperature. Experiments had been designed to compare the new designed sensor with the traditional sensors in sensing structures (stainless steel sleeve type & sensing region and supporting rod separation type), packaging materials (epoxy resin & silicone rubber) , measurement accuracy and insert approach (horizontal & vertical). Soil temperature sensor's selection for application could be brought out according to the experiments. The soil temperature measured by traditional insert sensor has big differences in vertical and horizontal methods. The experiment indicated that the accuracy requirements of single point measurement and multi-layer measurement are different. The result showed that the assembled sensor had the accuracy below ±0.2℃, and the response time is less than 100 seconds in the span of 20 centigrade. Influence of temperature in probe insert methods was about 0.2℃, and the horizontal approach was lower than vertical approach. The new sensor decreased the influence in structure, package and measurement approach. It improved applicability and flexibility of soil temperature sensor, and also raised the scientificity and accuracy in soil temperature measurement technology.