| 摘要 |
An apparatus for monitoring and detecting a preselected liquid level of a liquid in a container comprises a light emitter element disposed at a height along the outer wall of the liquid container and a light sensitive element disposed in opposition to the light emitter element at such a height that the light beam emitted from the light emitter element will impinge onto the light sensitive element when the liquid level in the container has attained the preselected liquid level, wherein change in the output state of the light sensitive element is utilized for producing an alarm signal.
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