Development of sapflow sensor and its application
การพัฒนาเครื่องวัดอัตราการไหลของน้ำในต้นพืชและการประยุกต์ใช้งาน
Chusak Limsakul, Asst. Prof., D. of Electrical Eng., F. of Eng., PSU.
Sayan Sdoodee, Assoc. Prof., D. of Plant Sci., F. of Natural Resources, PSU.
Witchanee Omsubsin, D. of Plant Sci., F. of Natural Resources, PSU.
Montep Kiatweerasakul, D. of Electrical Eng., F. of Eng., PSU.
Corresponding e-mail : lchusak@ratree.psu.ac.th
Grant : NECTEC
Presented : National Annual Conference 2000, Agricultural Engineering Association of
Thailand, 28-29 March 2000, Marou Garden Hotel, Bangkok
Key words : sapflow sensor, water use, heat pulse technique
This paper describes the development of a prototype of sapflow sensor using the heat pulse technique. The function of equipment is controlled by a microcontroller. The sensor set consists of 2 temperature probes and a heater probe. One temperature probe is located 10 mm above the heater
probe and another one is 5 mm below the heater probe. The sensor set is inserted into the stem and preferably placed in the sapwood of the stem. Then the short pulse of electric current is applied to the heater and the time is measured until the temperature of the two temperature probes is again equal.
This time interval is called delay time (t0). T0 is the time required for calculating the sap flow rate. The results in the laboratory show that the accuracy of measuring of t0 by the prototype is good enough. Finally the prototype was applied to determine the water use of 2 longkong trees (8-year-old) and 2 mangosteen trees (12-year-old) by comparing with the Greenspan sapflow sensor. The results show
that the average of water use by longkong tree measured by the prototype of sapflow sensor and Greenspan sapflow sensor is 16.85 and 16.53 liters, respectively. While the average of water use by mangosteen tree is 25.78 and 29.32 liters, respectively.
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