A Study Of Sap Flow Detection System Based On Heat Balance

Plant transportation and consumption are an important topic of agricultural research. The following methods:heat pulse velocity, heat balance, thermal dissipation and heat field deformation can be use to measure sap flow in plants.. Heat balance is the most mature theory and widely using for measuring sap flow in all of the thermodynamics method. But heat balance also has some disadvantages in application for measuring the sap flow such as high-precison installation of sensor, high-precison temperature control and low-power heating conditions.According to the theory and methods of heat balance for measuring sap flow, we Simplified the measuring method via analyzing the parameters of heat balance relationship and the sap flow in actual measurement. More importantly, the linear regression method has been put forward to measure sapflow based on the principle of heat balance.For the proposed method, it is designed to achieve a simplified heat balance measurement system in using1710HG multifunction data acquisition card of Advantech and LabVIEW programming platform with PID control algorithm and the PWM variable power output system. Thermistor is used to detect temperature. So a negative feedback control system is constituted.We adopted non-invasive installation by using high-precision and thin-film thermal sensor for temperature measurement and flexible electric heating film as a heating element that avoid the plant injury. This system achieved high-precision control with low-power heating film and simple temperature control system on virtual instrument with0.1℃precision and temperature feedback control program which was viable and practical.After the detection system has completed, thesap flow of Radermachera hainanensis has been measured and Linear Regression Analysis has been done between the system’s energy consumption and plant’s water consumption on the basis of simulation experiments. The coefficient of determination (R2) is0.793. The predict test has been done to analyze the expected value and the actual value of water consumption by the empirical equation. The result showed that the average error ratio is12%under with plant water consumption greater than1.8g in60minutes.Because of the limite of the flexible electric heating film size and power (2W), this sap flow detection system only can be used to the plant stem which diameter was less than2cm and sap flow velocity was in1.8g/h-13g/h.For the plants which have larger diameter,this system need to change the size of the flexible heating film and revise the control parameters of PID in this system.