The electro optical sensor consists of a robust metalhousing and a fused glass prism which contains aninfrared LED and a light receiver. When rising liquidimmerses the prism the light is refracted out into the liquidleaving lithe or no light to reach the receiver. Sensing thischange the receiver actuates electronic switching withinthe unit to operate an external alarmunit.* small size* solid state integrated elctronics* no moving parts* simple installation