Microcomputer-based system for the measurement of transpiration rate in trees by the heat pulse method

A microcomputer-based system was designed to measure water transport in trees by the heat pulse method. The system comprises a heater probe as a heat source and a thermistor, incorporated into a bridge which is automatically balanced by the microcomputer. The overall dynamic range of the system for temperature is 22 bits and the resolution for temperature determination is about 1.45×10^-4°C. The elapsed time between the heat pulse injection and the thermal peak at the thermistor is calculated by the microcomputer. The computation program includes algorithms for base-line slope correction and a noise immune derivative evaluating routine for peak recognition. The system was tested in the laboratory and in the field on a citrus tree.