| 摘要 |
PROBLEM TO BE SOLVED: To provide a highly reliable device by constructing a negative feedback control system as a whole and controlling automatically the pressure source so as to always and stably fix the liquid contained in a U-shaped tube at the position of a liquid level detector. SOLUTION: A liquid level detector 7 is fixed in touch at the position of liquid level difference 6 equivalent to the pressure to be controlled in a negative pressure underwater tube of a communicating tube. When the detector 7 detects no liquid at the position of the difference 6, a pressure control machine 9 is opened and the pressure of a pressure source 8 is applied into a connecting tube 10 to set the larger negative pressure at a pressure output port 11. However, when the negative pressure is increased and the liquid level reaches the detector 7, the output of the detector 7 functions contrarily to close the machine 9 and to suppress the rise of the negative pressure. As a result, the liquid level is balanced at the position of the detector 7 and the set pressure is generated at the port 11. This actual pressure is directly shown in the difference 6 by connecting the tube 10 to a negative pressure port 4 with the source 8 used as a negative pressure source.
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