| 摘要 |
PROBLEM TO BE SOLVED: To obtain a liquid-level sensor by which a liquid level can be detected precisely with a simple configuration by detecting a collector output voltage at a PNP transistor whose base is connected to the collector of a phototransistor. SOLUTION: When liquid level is lowered and the prism reflecting face 31 of a liquid-level sensor is separated from a liquid, an optical coupling passage is formed across a light-emitting diode 2a and a phototransistor 2b, and incident light from the diode 2a is photoelectrically transduced by the phototransistor 2b. Since a transduced signal biases its base, the phototransistor 2b is turned on, and a current flows to its collector. A base current at an L-level flows to the base of a PNP transistor Q which is connected to it, and an output current is generated from its collector. On the other hand, when the reflecting face 31 is immersed in the liquid, the optical coupling passage is opened due to change in a refractive index, and the phototransistor 2b does not receive light so as to be turned off. As a result, the base of the transistor Q is set to an H-level, and no output is available from its collector. Consequently, on the base of whether an output from the collector of the transistor Q exists or not, the liquid level can be detected. |
