Research On Acquisition System Of Plant Sap Based Oil Temperature Excitation

The stem-flow speed on the sapwood is an important indicator of transpiration rate of a whole tree. Among the current major measurements, thermal diffusion method and thermal pulse method need to get zero-stem-flow speed reference, and calculate stem flow according to the empirical formula, so they tend to import big error and have gross universality between different tree species; as for the existed stem-flow products, these usually are expensive and unstable.Targeting at all those drawbacks above, in this thesis we present an improved thermal pulse method based on heat tracer principle– called “temperature peak-to-peak value” measurement which can avoid the acquisition of standard parameter, and overcome the problem of poor generality, and develop a set of complete stem-flow collecting device with a portable construct and simple installation of sensor. Following are the main points:(1) According to the request of “peak-to-peak value” measurement, a pin-inserted type of stem flow sensor is designed; moreover, by structural optimization, three key elements are realized that are high accuracy of thermal injection, repeatable control and high sensitivity of temperature change in the sapwood liquid flow. On this basis, corresponding signal processing circuit and data collecting model is devised and upper computer system is designed based on MCGS software.(2) According to the analysis of sapwood stem flow, along with the variation of temperature curve caused by heat conduction, we bring out methods to catch the peak value such as high-frequency sampling, threshold detection, software filter and multiple examinations. The best interval among peak-to-peak phenomenon is from 30 mm to 35 mm based on the experiments which take aspen, sycamore trees, jujube trees, and platycladus orientalis as samples in Beijing agricultural and forest academy.(3) The wound mechanism of plants and the influence of environmental factors on the measurement accuracy are clearly researched; wound repairing model has been concluded according to the numerical calculation model proposed by Swanson, and also error has been corrected.By the test of stimulated system and practical measurement, the gap between stimulation and actual flow speed is less than 0.01 mm/s. This stem-flow sensor and its data collecting system prove to be reliable and stable because the test data has great repetition and daily stem flow curve shows good consistency according to multiple tests taking aspen as samples.