| 摘要 |
Disclosed herein is an on-demand fluid pump having a solenoid actuated reciprocating piston. The pump's electrical circuit comprises an oscillator generating at predetermined intervals short duty cycle sample signals which are applied to the solenoid. The reciprocating piston is nonresponsive to the applied sample signals, however, the sample signals induce a signal in a position sensor. The value of the signal induced in the position sensor is a function of the piston's position. A detector circuit generates a signal switching a bi-stable electronic switch to a SET state in response to an induced signal having a value indicative of the piston being at the end of its spring actuated pump stroke. The bi-stable switch in the SET state activates the solenoid to retract the piston against the force of the spring. The next sequential sample signal resets the bi-stable switch to its RESET state deactivating the solenoid. The time interval between the sample signals is selected to be just long enough for the solenoid to retract the piston from its position at the end of the pumping stroke to its start position. The position sensor in the preferred embodiment is two spatially disposed sensing coils connected in a signal opposing relationship so that the induced signal reverses polarity when the piston is at the end of its pumping stroke.
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