초록 ▼

A circuit for controlling the level of a liquid in a tank between predetermined limits is disclosed. A low and high probe are provided, each connected in the tank at the desired limit levels, and each connected to a comparator associated therewith. The output of each of the comparators are connected

A circuit for controlling the level of a liquid in a tank between predetermined limits is disclosed. A low and high probe are provided, each connected in the tank at the desired limit levels, and each connected to a comparator associated therewith. The output of each of the comparators are connected as inputs to an OR gate, which provides the control signal for activating a pump to pump liquid from the tank, and further provides a latching signal to the lower limit comparator, to keep that comparator latched in an off position until the upper limit comparator is triggered by liquid coming into contact with the upper limit probe. Once activated, the upper limit comparator causes the OR gate to produce a pump activation signal, in addition to unlatching the lower limit comparator, which in turn produces an OR gate activating signal which remains set until the pump evacuates the tank below the level of the lower limit probe, thereby deactivating the OR gate and the pump and whereby the process may be reinitiated.

대표청구항 ▼

A control circuit controlling a medium between predetermined upper and lower limits in a system including medium control means operable to vary said medium at least from said upper limit below said lower limit, said circuit comprising: upper and lower limit single conductor electrical probes operabl

A control circuit controlling a medium between predetermined upper and lower limits in a system including medium control means operable to vary said medium at least from said upper limit below said lower limit, said circuit comprising: upper and lower limit single conductor electrical probes operable to detect the presence of said medium at upper and lower limits respectively; upper and lower limit differential comparator means connected at an input to said upper and lower limit probes respectively, producing upper and lower limit signals respectively when said medium is detected by said probes; p1 logic means receiving said upper limit signal and producing a control signal in response thereto, said control signal used to cause said medium control means to vary said medium toward said lower limit; reference voltage control means supplying a first reference voltage to a second input of said lower limit comparator in the absence of said control signal to prevent said lower limit comparator from producing said lower limit signal and operable in response to said control signal to vary said first reference voltage to permit said lower limit comparator to produce said lower limit signal when the presence of the medium is detected by said lower limit probe; and said logic means further receiving said lower limit signal and further responsive thereto to produce said control signal whereby said medium is automatically maintained below said upper limit.