FLUID LEVEL DETECTION SYSTEM

• US 3,766,395 A
• Filed: 12/27/1971
• Issued: 10/16/1973
• Est. Priority Date: 12/27/1971
• Status: Expired due to Term

• Current Assignee: Alexander S. Keir
• Original Assignee: Alexander S. Keir
• Inventors: Keir, Alexander S.
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Corr, Denis E.
• Application Number:
  US05/212,078
• Time in Patent Office: 659 Days
• Field of Search: 73/293 307/305,311 250/214,218 340/244R
• US Class Current: 250/214.00R
• CPC Class Codes: G01F 23/2925 using electrical detecting means

Abstract

A system is disclosed for detecting the presence or absence of a medium and includes a radiation emitting means and a radiation responsive means selectively coupled to the radiation emitting means responsive to the absence of the medium. The radiation responsive means has an electrical property which varies in response to the incidence of radiation thereon. In addition, a selectively energizable switch means having a control element is coupled to the radiation responsive means through a selectively energizable coupling means having a predetermined substantially constant voltage threshold level, whereby the state of energization of the switch means is controlled responsive to variations in the electrical property of the radiation responsive means substantially independently of variations in power being supplied to the system.

Claims

1. A system for detecting the presence or absence of a medium comprising:

radiation emitting means, radiation responsive means selectively coupled to said radiation emitting means responsive to the absence of the medium, said radiation responsive means having an electrical property which varies in response to the incidence of radiation thereon, a selectively energizable switch means comprising a transistor having a control element, energization of said selectively energizable switch means being controlled responsive to preselected variations in the electrical property of said radiation responsive means, selectively energizable coupling means having a predetermined substantially constant voltage threshold level coupling said radiation responsive means and said control element of said selectively energizable switch means for controlling the state of energization of said selectively energizable switch means responsive to variations in the electrical property of said radiation responsive means substantially independently of variations in power being supplied to said system, and a gate-controlled output switch means having a gate, said gate connected in parallel relationship with the collector-emitter circuit of said transistor, whereby gating signals are shunted through said collector-emitter circuit preventing conduction of said output switch means when said transistor is conductive and are applied to said gate to render said output switch conductive when said transistor is non-conductive.

2. A system in accordance with claim 1 wherein said radiation emitting means comprises an electrically energizable light emitter adapted to emit light in response to electrical energization and said radiation responsive means comprises a light responsive device having a resistance which varies in response to the incidence of light thereon, said light emitter being optically coupled to said light responsive device only in the absence of said medium.

3. A system in accordance with claim 2 wherein said light responsive device comprises a photoelectric cell having a relatively high resistance mode in the absence of light incident thereon and a relatively low resistance mode in response to the presence of light incident thereon.

4. A system in accordance with claim 3 wherein a resistor is provided connected to said photoelectric cell to define a first voltage divider including a junction between said resistor and said photoelectric cell, said first voltage divider being adapted to be connected across a source of electrical power, said junction being coupled to one terminal of said coupling means for controlling the state of energization thereof responsive to the voltage established at said voltage divider junction, the other terminal of said coupling means being coupled to said control element.

5. A system in accordance with claim 4 wherein said coupling means comprises a zener diode, said zener diode being maintained in an energized state and supplying an energizing signal to said control element of said selectively energizable switch means when the voltage at said junction is at a first predetermined level responsive to operation of said photoelectric cell in its high resistance mode.

6. A system in accordance with claim 5 wherein said zener diode has a substantially lower resiStance when in its energized state relative to the resistance of said photoelectric cell in the absence of light incident thereon so as to shunt current away from said photoelectric cell and maintain said selectively energizable switch energized.

7. A system in accordance with claim 6 wherein said zener diode is maintained in a de-energized state and blocks the application of energy to said control element of said selectively energizable switch means when the voltage at said junction is at a second predetermined level responsive to operation of said photoelectric cell in its low resistance mode, said photoelectric cell, when in its low resistance mode shunting current from said zener diode to prevent energization thereof.

8. A system in accordance with claim 7 wherein said transistor has its base connected to said zener diode.

9. A system in accordance with claim 1 wherein said radiation responsive means is connected to said gate and to the collector-emitter circuit of said transistor, whereby gate current for said output switch is supplied through said photoelectric cell when said transistor is non-conductive and said photoelectric cell is operative in its low resistance mode and gate current is shunted away from said gate through said photoelectric cell and the collector-emitter circuit of said transistor when said transistor is conductive and said photoelectric cell is operative in its high resistance mode.

10. A system for detecting the presence or absence of a medium comprising:

radiation emitting means, said radiation emitting means comprising an electrically energizable light emitter adapted to emit light in response to electrical energization, radiation responsive means comprising a photoelectric cell having a relatively high resistance mode in the absence of light incident thereon and a relatively low resistance mode in response to the presence of light incident thereon said radiation responsive means being optically coupled to said radiation emitting means only in the absence of said medium, a selectively energizable switch means having a control element, energization of said selectively energizable switch means being controlled responsive to preselected variations in the resistance of said radiation responsive means, selectively energizable coupling means having a predetermined substantially constant voltage threshold level coupling said radiation responsive means and said control element of said selectively energizable switch means for controlling the state of energization of said selectively energizable switch means responsive to variations in the resistance of said radiation responsive means substantially independently of variations in power being supplied to said system said coupling means comprising a zener diode, said zener diode being maintained in an energized state and supplying an energizing signal to said control element of said selectively energizable switch means when the voltage at said junction is at a first predetermined level responsive to operation of said photoelectric cell in its high resistance mode, said zener diode having a substantially lower resistance when in its energized state relative to the resistance of said photoelectric cell in the absence of light incident thereon so as to shunt current away from said photoelectric cell and maintain said selectively energizable switch energized, a resistor connected to said photoelectric cell to define a first voltage divider including a junction between said resistor and said photoelectric cell, said first voltage divider being adapted to be connected across a source of electrical power, said junction being coupled to one terminal of said coupling means for controlling the state of energization thereof responsive to the voltage established at said voltage divider junction, the other terminal of said coupling means being coupled to said control element, and another resistor connected to said light emitter to define a second voltage divider having a junctioN defined therebetween, said second voltage divider being connected across said first voltage divider, and means are coupled between said junctions of said first and second voltage dividers for maintaining said junctions electrically isolated from each other only when said light emitter is operable and for shunting current from said junction of said first voltage divider to prevent energization of said selectively energizable switch means responsive to improper operation of said light emitter.

11. A system in accordance with claim 10 wherein said means coupled between said junctions comprises a normally reverse biased diode which is operative to shunt current from said photoelectric cell and through said another resistor responsive to improper operation of said light emitter.

12. A system in accordance with claim 10 wherein said means coupled between said junctions comprises a zener diode.

13. A system for detecting the presence or absence of a medium comprising:

radiation emitting means comprising an electrically energizable light emitter adapted to emit light in response to electrical energization, radiation responsive means comprising a photoelectric cell having a relatively high resistance mode in the absence of light incident thereon and a relatively low resistance mode in response to the presence of light incident thereon said radiation responsive means being optically coupled to said radiation emitting means only in the absence of said medium, a selectively energizable switch means having a control element, energization of said selectively energizable switch means being controlled responsive to preselected variations in the resistance of said radiation responsive means, selectively energizable coupling means having a predetermined substantially constant voltage threshold level coupling said radiation responsive means and said control element of said selectively energizable switch means for controlling the state of energization of said selectively energizable switch means responsive to variations in the resistance of said radiation responsive means substantially independently of variations in power being supplied to said system, a resistor connected to said photoelectric cell to define a first voltage divider including a junction between said resistor and said photoelectric cell, said first voltage divider being adapted to be connected across a source of electrical power, said junction being coupled to one terminal of said coupling means for controlling the state of energization thereof responsive to the voltage established at said voltage divider junction, the other terminal of said coupling means being coupled to said control element, said coupling means comprises a zener diode, said zener diode being maintained in an energized state and supplying an energizing signal to said control element of said selectively energizable switch means when the voltage at said junction is at a first predetermined level responsive to operation of said photoelectric cell in its high resistance mode, said zener diode having a substantially lower resistance when in its energized state relative to the resistance of said photoelectric cell in the absence of light incident thereon so as to shunt current away from said photoelectric cell and maintain said selectively energizable switch energized, said zener diode maintained in a de-energized state blocking the application of energy to said control element of said selectively energizable switch means when the voltage at said junction is at a second predetermined level responsive to operation of said photoelectric cell in its low resistance mode, said photoelectric cell, when in its low resistance mode shunting current from said zener diode to prevent energization thereof, said selectively energizable switch means comprising a transistor having its base connected to said zener diode, and a gate-controlled output switch means having a gate, said gate being connected in parallel relationShip with the collector-emitter circuit of said transistor, whereby gating signals are shunted through said collector-emitter circuit preventing conduction of said output switch means when said transistor is conductive and are applied to said gate to render said output switch conductive when said transistor is non-conductive.

14. A system in accordance with claim 13 wherein said photoelectric cell is connected to said gate and to the collector-emitter circuit of said transistor, whereby gate current for said output switch is supplied through said photoelectric cell when said transistor is non-conductive and said photoelectric cell is operative in its low resistance mode and gate current is shunted away from said gate through said photoelectric cell and the collector-emitter circuit of said transistor when said transistor is conductive and said photoelectric cell is operative in its high resistance mode.

15. A system in accordance with claim 14 wherein said output switch means comprises a silicon controlled rectifier.

16. A system in accordance with claim 14 wherein said output switch means comprises a triac.

17. A system in accordance with claim 14 wherein said output switch means comprises a silicon controlled rectifier.

18. A system in accordance with claim 14 wherein said output switch means comprises a triac.

19. A system for detecting the presence or absence of a medium comprising:

radiation responsive means, a resistor connected to said radiation responsive means to define a first voltage divider having a junction defined therebetween, radiation emitting means, another resistor connected to said emitting means to define a second voltage divider having a junction defined therebetween, said voltage dividers being adapted to be connected across a source of electric power, first coupling means coupled between said junctions for maintaining said junctions electrically isolated from each other only when the radiation emitting means is operable and for shunting current from said junction of said first voltage divider to prevent energization of said selectively energizable switch means responsive to improper operation of said radiation emitting means, a selectively energizable switch means having a control element, energization of said selectively energizable switch means being controlled responsive to preselected variations in the electrical property of said radiation responsive means, and selectively energizable second coupling means having a predetermined substantially constant voltage threshold level coupling said radiation responsive means and said control element of said selectively energizable switch means for controlling the state of energization of said selectively energizable switch means responsive to variations in the electrical property of said radiation responsive means substantially independently of variations in power being supplied to said system.

20. A system in accordance with claim 19 wherein said second coupling means comprises a zener diode, said zener diode being maintained in an energized state and supplying an energizing signal to said control element of said selectively energizable switch means when the voltage at said first junction is at a first predetermined level responsive to operation of said photoelectric cell in its high resistance mode.