| 摘要 |
PURPOSE:To monitor a liquid level accurately and certainly, by emitting a laser beam having a beam path inclined with respect to a predetermined liquid level surface and detecting the change in the beam patch of laser beam generated by the refraction on the surface of a liquid. CONSTITUTION:When the level of a liquid 11 is below a predetermined value and a beam receiving part 15 is exposed above the surface of the liquid, the laser beam 13 from a laser beam emitting part 14 is incident on the part 15. When the liquid level rises above the predetermined one and the part 15 is positioned under the surface of the liquid, the laser beam 13 is refracted on the surface of the liquid 11 and not incident on the part 15. Therefore, on the basis of the change in the signal from the part 15 measured in a measuring part 17, it can be detected whether the level of the liquid 11 is above or below the predetermined value. |
