| Summary: | 碩士 === 南台科技大學 === 機械工程系 === 99 === This study investigates the characteristics of optical coupler and capacitive sensor used for non-contact liquid level sensing on intravenous drip. The studied items are:（I）Analyzing the wavelength characterization of light emitting devices in optical couplers,（II）Measuring sensing distance of optical coupler ,（III）Measuring the voltage variation of different targets by capacitive sensors,（IV）Measuring sensing distance of different targets by capacitive sensors,（V）Using impedance analyzer to measure the capacitance variation of different targets by capacitive sensors.
From literature report, the use of optical coupler or capacitive sensor to monitor the change of liquid level is possible. The change of light signal from optical coupler may identify different targets between light emitter and receiver. The change of capacitance from capacitive sensor may identify different targets by dielectric constant changes. Based on this principle, experimental analysis were carried out by different detection circuits and equipments to explore the characteristics of two kinds of sensors, which were proposed to use on the non-contact liquid level sensing circuit.
Experimentally explored the optical coupler and capacitive sensor for identifying whether the empty plastic or glass bottles contained the water, showed that: (1) Model EE-SG3 optical coupler can sense the liquid level descending or arising to the desired level, however the sensing distance is about 20 mm only, if liquid containers beyond this size or attached paper labels are not applicable, (2) The ring-shaped capacitive sensor, Rc-2, can distinguish whether the empty bottles contain the water, the other designed capacitive and comb-shaped sensors fairly perform this property, (3) The gap distance of the ring-shaped electrodes is the key parameter affecting the sensing capacitance and the correspondent voltage output in the sensing circuit. Besides, the closer for the sensing distance from target to the sensors would produce the better identification and stable signals.
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