| 摘要 |
PROBLEM TO BE SOLVED: To measure the accurate level of a measured liquid even if the capacitance formed around an insulating tank is changed. SOLUTION: An auxiliary electrode 5 and a main electrode 7 covered with insulating layers 17, 19 are inserted into a conductive measured liquid 1 in the insulating tank 3. An AC signal is applied to the auxiliary electrode 5 from a signal source 9 to output a signal proportional to the liquid level from the main electrode 7. An AC signal Vq0 with the same potential as the potential Vq of the measured liquid 1 (liquid intersection) and having no capacitance Cx1 between the bottom section of the insulating tank 3 and the ground 21, no resultant capacitance Cv2 between the side section of the insulating tank 3 and the ground 21, and no resultant capacitance Cp between the liquid path of a pipe 25 and the ground 21 is generated from an auxiliary signal source 37 and connected to the ground 21. No signal current flows in the capacitance Cx1 and the resultant capacitance Cv1, Cv2, Cp formed around the insulating tank 3, thereby changes of the peripheral electrostatic capacitance have no relation with the measurement of the liquid level.
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