Abstract
AN important class of instruments among those required for scientific purposes as well as for the many accurate measurements which are now an essential feature in industrial and engineering undertakings is that which is designed for indicating, recording and controlling liquid levels. Many devices have been adopted for these purposes, one being the employment of compressed air which is arranged to be slowly discharged through an open tube the end of which is submerged in the liquid. As the head of liquid above the open end varies, so does the pressure of air, thus giving an indication of the level. Instruments of this type are suitable for almost any fluid and give single or multi-point readings, or they may be adapted for continuous records. Where the provision or use of an air supply presents difficulty or is undesirable for special reasons, depth indicators and level recorders may be of the self-contained pressure bulb type. The bulb is installed at the zero of the level to be measured and is connected by tubing to the instrument, which may be at any desired height above or below the liquid and at any reasonable distance from it.
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Level Measurement and Control. Nature 145, 314–315 (1940). https://doi.org/10.1038/145314b0
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DOI: https://doi.org/10.1038/145314b0