Ultrasonic Fog Detector for Greenhouse with Evaporative Fog Cooling System

摘要

To improve the spray control of evaporative fog cooling systems in greenhouses, we propose an ultrasonic fog detector. Conventional evaporative fog cooling systems have not been equipped with fog detectors and spray control has not been sufficient. The effect of fog on the amplitude and phase of ultrasonic waves between a loudspeaker and a microphone was electrically measured by quadrature detection. From the laboratory experiment using a sound probe with a 300 mm base line, the phase of the propagation characteristics showed marked lowering only while fog exists along the propagation path. In a greenhouse experiment using a sound probe with a 740 mm base line, similar results are obtained. In these experiments, the existence or nonexistence of fog was detected by the sound probe at the frequency of 40kHz.