Fluid sensing systems

A pair of vertically spaced rubber diaphragm covered bellows are employed with output means to produce a DC voltage directly proportional to the movement of the free end of one bellows. The upper bellows and diaphragm are inverted from their conventional positions. A conduit connects the two bellows together. The conduit, both bellows and both diaphragms are filled with an incompressible fluid. The fixed ends of both bellows are fixed relative to each other. This arrangement may be employed with a DC voltmeter calibrated in linear measure to indicate the level of a liquid in a storage tank. In this case, one bellows is located inside of and fixed relative to the tank at the top. The other bellows is located inside the tank at the bottom and fixed relative thereto thereat. A two bellows densitometer is also provided which may be employed with or without the liquid level system.