FEEDBACK CONTROL OF LEAF TEMPERATURE

Abstract

To control the leaf temperature by means of setting the desired value of the leaf temperature, the feedback control of leaf temperature was carried out in a growth cabinet: The leaf temperature was detected by the use of a microthermistor which was inserted into the cotyledon of the Cucurbita seedling. This leaf temperature was used as the feedback signal for the temperature control system in the growth cabinet. In this system, air was used for heat transfer, and the program control of the leaf temperature was made possible by setting the desired value.For the analyses of the response characteristics in the leaf temperature control, conditions of light, air humidity and air movement were changed to give the disturbances to the leaf temperature control.From the results, the following points were ascertained.1) In this system, the ramp response in the feedback control of the leaf temperature conformed well to the desired value. At the leaf temperatures of 10°C, there was no difference between the leaf and air temperature in darkness. With the increased temperature, however, the air temperature became higher than the leaf temperature.2) When the leaf was irradiated to an intensity of 31 mW/cm2 by an incandescent lamp, the leaf temperature rose, while the air temperature fell. In proportion to this fall in air temperature, the leaf temperature settled within at least 15 min. The effect of this disturbance of irradiation on the leaf temperature control was larger in lower temperature condition than in higher temperature condition.3) When the air humidity was changed rapidly from 60% to 80% and from 80% to 40%, the leaf temperature control was disturbed. The effect of the air humidity change on the leaf temperature control was larger under higher temperature condition than under lower temperature condition. The leaf temperature settled within 10 min.4) The air movement decreased the difference between the leaf and air temperatures and made the settling time short.