| 摘要 |
PROBLEM TO BE SOLVED: To provide the subject detector eliminating the need for a long electrode rod even if the control of a liquid level is in a wide range, formed small in size, superior in mounting stability, and permitting highly precise liquid level control. SOLUTION: An automatic operation circuit 3 of a pump motor M is stored in a holder 1 having an upper liquid level sensor 2A and a lower liquid level sensor 2B opposed to each other at a vertically limited space and a base 1a of the holder 1 is formed on a mounting portion on the upper face of a submersible motor-driven pump. The circuit is set to start the pump motor M by using an ON signal from the upper liquid level sensor 2A while computing a time t2 for a liquid level to be lowered to a predetermined stop level L based on a time t1 required to detect an OFF signal from the lower liquid level sensor 2B after the OFF signal from the upper liquid level sensor 2A is detected, so that the pump motor M can be continuously operated within the limits of the computed time t2 and stopped at time-up.
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