Liquid level control apparatus

• US 4,600,844 A
• Filed: 06/07/1984
• Issued: 07/15/1986
• Est. Priority Date: 06/07/1984
• Status: Expired due to Fees

• Current Assignee: The Rival Company (Newell Brands Inc.)
• Original Assignee: The Marley-Wylain Company
• Inventors: Atkins, Donald G.
• Primary Examiner(s): Pellinen, A. D.
• Assistant Examiner(s): DEBOER, TODD
• Application Number:
  US06/617,957
• Time in Patent Office: 768 Days
• Field of Search: 307/118, 307/116, 361/178, 340/620, 364/509, 364/510, 137/392, 137/395, 137/396
• US Class Current: 307/118
• CPC Class Codes: G05D 9/12 characterised by the use of electric means
• CPC Class Codes: Y10T 137/7306 Electrical characteristic sensing

Abstract

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.

Claims

1. Apparatus controlling a liquid between predetermined levels in a grounded vessel comprising:

pumping means operable when energized to pump the liquid from the grounded vessel;

upper and lower limit single conductor electrical probes mountable in the vessel at upper and lower limit levels respectively, said probes producing upper and lower limit sense signals respectively when the liquid is sensed at the respective level;

an upper limit comparator connected at one input thereof to said upper limit probe, said upper limit comparator responsive to said upper limit sense signal and a fixed reference signal connected at a second input thereof to produce a first control signal in reponse to the difference between said fixed reference signal and said upper limit sense signal;

a lower limit comparator connected at one input thereof to said lower limit probe and selectively responsive to said lower limit sense signal and a variable reference signal connected at a second input thereof to produce a second control signal; and

OR gate means receiving said first and second control signals for producing a control means energizing signal in response to the presence of either control signal, and further responsive to the absence of both control signals to vary said variable reference signal to prevent said lower limit comparator from producing said second control signal until said first control signal is present to permit the liquid to fill said vessel from below said lower limit to said upper limit and to cause said pumping means to empty said liquid from said vessel down to below said lower limit.

2. 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.

3. A control circuit controlling a conductive medium between predetermined limits in a system including medium control means operable when energized to vary said medium from an upper limit toward a lower limit, said circuit comprising:

upper and lower limit single conductor electrical probes biased to a predetermined voltage contacting the medium at upper and lower limits respectively whereby the voltage on the contacting probe varies;

upper limit differential comparator means connected at an input to said upper limit probe and responsive to the variance of the voltage thereon away from said predetermined voltage to produce a first control signal;

lower limit differential comparator means connected at an input to said lower limit probe and responsive to the variance of the voltage thereon away from said predetermined voltage and further responsive to a latching signal applied at the other input to produce a second control signal; and

logic means receiving said first and second control signals for producing a control means energizing signal in response to the presence of either control signal, and further responsive to the transition from the presence to the absence of said second control signal to produce said latching signal until said first control signal is present to permit said medium to vary from below said lower limit to said upper limit and to cause said medium control means to vary said medium from said upper limit to said lower limit.

4. A control circuit, controlling a conductive liquid medium between predetermined upper and lower limits in a grounded vessel in a system including medium control means operable to vary said medium at least from said upper limit to 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 by sensing an electrical path between the probe and the grounded vessel;

upper and lower limit voltage 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;

logical OR means receiving said upper limit signal and said lower limit signal and producing a control signal in response thereto for enabling said medium control means to vary said medium toward said lower limit; and

variable 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 a second 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.

5. The circuit according to claim 4 wherein said control signal is optically coupled to said medium control means.

6. A control circuit controlling a conductive liquid medium between predetermined upper and lower limits in a grounded vessel in a system including medium control means operable to vary said medium at least from said upper limit to below said lower limit, said circuit comprising:

a single conductor upper limit probe operable to detect the presence of said conductive medium at the upper limit by sensing an electrical path between the probe and the grounded vessel;

an upper limit bias resistor connected between said upper limit probe and a voltage potential;

upper limit voltage differential comparator means connected at the inverting input to the upper limit probe and connected at the noninverting input to a fixed reference voltage;

a single conductor lower limit probe operable to detect the presence of said conductive medium at the lower limit by sensing an electrical path between said lower limit probe and said grounded vessel;

lower limit bias resistor connected between said lower limit probe and the voltage potential;

lower limit voltage differential comparator means connected at the inverting input to said lower limit probe and at the noninverting input to a pull-down resistor connected on the other side to a ground potential;

logical OR means receiving said upper limit voltage differential comparator output and lower limit voltage differential comparator output producing a medium control signal used for energizing said medium control means; and

said control signal further connected to the noninverting input of said lower limit voltage differential comparator so that said control signal operates to change the reference voltage potential on the inverting input of said lower limit comparator.