Abstract

An optical sensor, having serviceable electronics, for monitoring the level of a liquid within a vessel having an exterior and an interior and for providing an electrical signal on the traverse of the liquid level past the sensor. The sensor comprises a fitting adapted to traverse the vessel wall, the fitting including a window having a prism shaped interior face and a planar exterior face sealed into the fitting and providing a fluid-tight optical path from the vessel interior to the vessel exterior. The fitting includes a chamber adjacent the planar face of the window and an electronic module shaped to fit the chamber. The module has an optical face. A light source and a light detector are positioned in the optical face to provide substantially zero clearance light communication between the window and both the source and the sensor, when the module is positioned within the chamber. The module includes electronics for supplying power to the light source and for providing different electrical signals on the presence, and on the absence of light at the detector. The sensor further includes means for resiliently securing the module against the window whereby intimate light communication between the window and the light source and the light sensor is achieved, and for readily removing the module for servicing ory replacement.