LIQUID LEVEL SENSING AND CONTROL SYSTEM

• US 3,757,317 A
• Filed: 09/15/1971
• Issued: 09/04/1973
• Est. Priority Date: 09/15/1971
• Status: Expired due to Term

• Current Assignee: Alexander Kahn, Charles Kahn, Warren Johannesen
• Original Assignee: Alexander Kahn, Charles Kahn, Warren Johannesen
• Inventors: Kahn, Alexander, Kahn, Charles, Johannesen, Warren
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Myer, Daniel
• Application Number:
  US05/180,613
• Time in Patent Office: 720 Days
• Field of Search: 340/244R,244C,239R 73/295,204 137/386,391,392 417/63,211.5
• US Class Current: 137/386
• CPC Class Codes: G01F 23/247 for discrete levels
• CPC Class Codes: G05D 9/12 characterised by the use of electric means
• CPC Class Codes: Y10T 137/7287 Liquid level responsive or maintaining systems
• CPC Class Codes: Y10T 137/7306 Electrical characteristic sensing

Abstract

Fluid sensing and control apparatus using solid state devices and capable of fluid sensing at spaced points to furnish output control signals to maintain fluid conditions within predefined limits. A feedback circuit between sensors is provided to minimize power consumption in quiescent periods and timed alarmactuating signals are generated in the event control functions are not achieved.

Claims

1. Fluid sensing and control apparatus comprising at least first and second electrical resistance sensors spaced apart in the direction of fluid control, each seNsor having an electrical impedance characteristic which varies with temperature, an electrical input power source and a controlled electrical power output, means to energize the first sensor continuously from the power source, circuit means to normally block the flow of electrical power to the second sensor, circuit means responsive to the changes of resistance due to the presence of the controlled fluid at the first sensor to initiate the power output, means responsive to the power output to energize the normally deenergized second sensor, feedback circuit means responsive to the energization of the second sensor to maintain the initiated power output in the absence of con-trolled fluid enveloping the first sensor, and circuit means responsive to change of resistance due to the absence of the controlled fluid at the second sensor to terminate the output power.

2. Apparatus according to claim 1 including timing circuit means responsive to the presence of controlled fluid at the first sensor for a predetermined time interval to furnish a second power output, said time interval being in excess of the time normally required for the controlled fluid to be cleared from the first sensor whereby the first and the second power output are sequentially derived with the second output affording an indication of failure of the first power output to change the fluid level.

3. Apparatus according to claim 1 including transistor switch means coupled to the first sensor to be actuated in the presence of the controlled fluid, and a power transistor responsive to the actuation of the transistor switch means to couple the power source to the output, said feedback circuit being connected between the second sensor and the transistor switch means to maintain the power transistor in operation while the controlled fluid envelops the second sensor.

4. Apparatus according to claim 3, the power source including a first power circuit for energizing the output and a parallel second power circuit for energizing at least the first of said sensors, a second output circuit responsive to the first sensor, and first and second overload protection means disposed respectively in the first and second power circuits, whereby the first and second output circuits can function independently.

5. Apparatus according to claim 4, said second output circuit including an alarm.

6. Apparatus according to claim 5, said second output circuit including a transistor switch to control the alarm, and a timing circuit to control the transistor switch.