| 摘要 |
A circuit for sensing and controlling the level of fluid within a reservoir includes a pump for controlling the level of fluid. The circuit further includes two sub-circuits each including a probe adapted to contact the fluid. Each sub-circuit further includes an SCR and an oppositely poled diode. Also included is a relay coupled to the sub-circuits for operating the pump. The relay is designed to energize the pump only upon submersion of both of the probes. The circuit is coupled to an AC transformer having, in one embodiment, an off-set center tap such that upon submersion of the first probe the first sub-circuit conducts a first magnitude of energy that is insufficient to pull in the relay but is sufficient to hold in the relay once it is actuated. In an alternative embodiment, the transformer includes first and second resistors coupled between the relay and the first and second sub-circuits, respectively. The resistors may be of the same or different impedance, such that a different energy level is imparted to the relay when the first probe is in contact with the fluid than when both probes are in contact with the fluid. |
