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Abstract

A boiler water level system comprises a plurality of electrodes arranged to sense the resistivity of the fluid at each of a plurality of different levels in a pressure vessel. The pressure vessel is coupled to one end of the boiler such that the level of the water in the pressure vessel is substantially the same as the level in the boiler, and each electrode senses the resistivity of the fluid (ie water or steam) between the tip of the electrode and the wall of the pressure vessel. Such a system on its own inherently produces a digital output of relatively low resolution, so to improve resolution, and to provide an analogue output if desired, additional circuitry is provided to sense the progressive change in the impedance sensed by each electrode as the water rises to progressively immerse that electrode and then carries on rising towards the next electrode.

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First Claim