| 摘要 |
A pump control system (10) which can distinguish between water and oil so that a pump (11) can be controlled to pump water and deactivated before oil is pumped. Sensing is accomplished by a pair of capacitive sensors (30 and 30a). A dual mode frequency oscillator (U1A) is associated with each sensor. Each sensor reacts to the dielectric constant of the liquid at the sensor by changing its capacitance, to thus detect the presence of a conductive substance, such as a liquid, to cause the sensor's oscillator to switch its mode of oscillation. The circuit turns on the pump (11) only when both sensors (30 and 30a) are in water and the pump (11) remains on until both sensors (30 and 30a) are out of water.
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