Abstract: A two-level detector for an electrically conductive liquid having a common electrode serving as a potential reference and situated at a low level, a high electrode situated at a high level, and a low electrode situated at the low level, the electrodes being connected by conductors to electronic apparatus for detecting the liquid at said two levels by means of currents flowing through the liquid. The high and low electrodes are made of metals that have different electrode potentials. A first conductor and a second conductor interconnect the electrodes to constitute an electrical primary cell that is short-circuited when both electrodes are simultaneously in contact with the liquid. The second conductor is extended to connect the electrode assembly to a signal terminal of the electronic apparatus. The common electrode is made of a metal whose electrode potential is different by about 0.

Abstract: An electronic circuit that controls the operation of a motor whose output shaft drives an impeller for pumping a liquid includes a common grounded electrode positioned for immersion in the liquid, and a stopping electrode positioned above the common electrode. A first, latching transistor is connected to the stopping electrode which is connected to ground through the liquid when the level thereof reaches or exceeds the level of the stopping electrode. A second, power transistor operates the motor when the second transistor conducts in response to its grounding, the second transistor being connected to the starting electrode so as to be grounded when the level of liquid reaches the starting electrode.

Abstract: A suction pump has a suction pipe extending into a tank for receiving liquid. A detector, connected to a control circuit for the pump, is arranged to initiate operation of the pump when the liquid in the tank rises above a predetermined level. The detector comprises a hollow member of insulating material connected to the free end of the suction pipe. The member has a transverse dimension which is greater than that of the suction pipe whereby a shoulder is defined which connects the member to the pipe. Two or more electrodes are mounted on the member and the pump is operated when the liquid completes a circuit between the two electrodes. The electrodes are protected by the shoulder from liquid running backwardly within the suction pipe when the pump has stopped. In addition, a time delay means is included in the control circuit to delay restarting of the pump once it has stopped.

Abstract: An electronic alarm circuit for operating an audible alarm, such as a bell, has a trigger circuit arranged to continuously activate the alarm if a sensor is activated. The circuit also includes a capacitor arranged to be discharged if a normally closed test switch is opened. Closure of the test switch recharges the capacitor and renders the trigger circuit conductive. The alarm is thus activated but only for a restricted period dependent upon the time constant of the capacitor. Accordingly, it is possible to distinguish between a real alarm and the sound of the alarm when the circuit is tested.