| 摘要 |
Apparatus for monitoring the liquid contents of a container vessel 10 comprises a pair of pressure transducers 16.1, 16.2, 120, 192 arranged at different levels in the vessel or in an upright tube 114 leading from the vessel. The signals provided by the pressure transducers are processed in a processor 22, 122 to provide an output signal corresponding to the value @<1>/¦P1 - P2¦, where P1 is the pressure sensed by the one pressure transducer and P2 is the pressure sensed by the other pressure transducer. This corresponds to the level of the liquid in the vessel and is independent of the specific gravity of the liquid. In another embodiment two pressure values are obtained by a single pressure transducer 120 arranged at the bottom of an upright measuring tube 114 leading from the vessel. There is a solenoid operated valve 118 at the bottom of the tube and a solenoid operated valve 116 at the top of the tube. One pressure value is obtained with the pressure transducer subjected to the overall head of liquid in the vessel and in the measuring tube, and a second pressure value is obtained with the pressure transducer subjected to the head of liquid in the measuring tube only, the top of the measuring tube being vented to atmosphere. In yet a further embodiment, where the content of the vessel is subject to a varying gas pressure, a further pressure transducer 16.3 is provided to sense the gas pressure and to compensate for the effect which this has on the pressure measurements P1 and P2.
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