Fiber optic liquid sensing system

• US 5,684,296 A
• Filed: 06/17/1996
• Issued: 11/04/1997
• Est. Priority Date: 06/17/1996
• Status: Expired due to Fees

• Current Assignee: Optical Systems Industries Incorporated
• Original Assignee: Optical Systems Industries Incorporated
• Inventors: Prabhakar, Avinash, Hamblin, Jesse R.
• Primary Examiner(s): ALLEN, STEPHONE B
• Application Number:
  US08/664,711
• Time in Patent Office: 505 Days
• Field of Search: 250/573-577, 250/227.11, 250/904, 356/436-440, 340/619
• US Class Current: 250/227.11
• CPC Class Codes: G01F 23/2961 for discrete levels G01F23/2962 - G01F23/2968 take precedence

Abstract

An optical liquid sensing system for sensing liquids in contact with an optical sensing component is provided. The sensing system comprises an optical sensor connected to a control module by a fiber optic cable having two fiber optic strands, the first for receiving light emitted by the control module, and the second for receiving light reflected from a distal reflector. The strands terminate in a longitudinally oriented common ferrule within the optical sensor. The optical sensor is generally cylindrical and includes a distal reflector opposite and in a spaced relationship to the ferrule. A group of apertures is defined in the circumferential wall of the housing so as to permit entry of liquid into the housing and to draw liquid proximally located to the sensor into the housing via capillary action. When an amount of liquid insufficient to flood the sensor enters the housing, the shape of the sensor and the arrangement of interior components of the sensor cause the liquid to be formed into a liquid cylinder spanningly disposed between the ferrule and the reflector. The reflective inner surface of the liquid cylinder causes the amplitude of a light signal introduced into the housing by the first strand to be increased in amplitude before being received by the second strand. When the sensor is flooded with liquid, the light signal from the first strand is attenuated before being received by the second strand. The control module detects variances in the amplitude of light received by the second strand when the sensor is in contact with or is flooded by a liquid and indicates to a user that presence of a liquid has been detected by the sensor.

Claims

1. A system for sensing the presence of a liquid, comprising:

a light emitting device operable to emit a light signal of a pre-defined amplitude;

a transmitting fiber optic strand having a first end connected to said light emitting device and a second end, said transmitting strand being operable to transmit a light signal emitted by said light emitting device and to emit said first light signal through the second end;

a light sensing device operable to sense a plurality of light signals, each having a particular amplitude, and to derive, from each light signal of said plurality of light signals, a voltage value having a magnitude proportional to a magnitude of each light signal'"'"'s particular amplitude;

a receiving fiber optic strand having a first end connected to said light sensing device and a second end, said receiving strand being operable to receive said plurality of light signals through the second end;

an optical sensor comprising;

a housing having opposed proximal and distal ends and defining a hollow interior of a predetermined cross-sectional size and bounded by a peripheral wall in and through which a plurality of apertures of predetermined size are defined at predetermined locations intermediate to said proximal and distal ends for permitting entry of liquid into the housing interior;

a ferrule projecting a predetermined extension distance into said housing interior from said housing proximal end and terminating in an end wall disposed in spaced confronting opposition to said housing distal end, said ferrule having a cross-sectional size smaller than said cross-sectional size of the housing interior so as to define a predetermined ferrule spacing between said ferrule and said housing peripheral wall, said ferrule retaining said fiber optic transmitting and receiving strands such that the second end of said transmitting strand and the second end of said receiving strand terminate in the housing at and coincident with said ferrule end wall; and

a light reflector disposed in the housing interior proximate said distal end at a predetermined reflection distance from said ferrule end wall and oriented for receiving said light signal transmitted from said light source and entering the housing interior from said transmitting strand and for reflecting said received light signal onto the ferrule end wall for transmission of said reflected light signal through said receiving strand to said light sensing device, so that said light sensing device derives a first voltage corresponding to said predefined amplitude of said light signal;

at least a selected plurality of said reflection distance, said ferrule extension distance, said predetermined aperture locations and said aperture size being selected so that liquid entering the housing interior through said apertures forms a liquid conduit spanningly bridging said ferrule and said reflector and through and within which spanning liquid conduit said light signal entering the housing interior from said transmitting strand and reflected back to said receiving strand is also internally reflected by the liquid conduit such that an amplified reflected light signal transmitted to said light sensing device through said receiving strand has a greater amplitude than said light signal entering the housing through said transmitting strand from said light emitting device so that said light sensing device derives a second voltage corresponding to the greater amplitude of said amplified light signal;

comparing means, connected to said light sensing device, being operable to store a predefined third voltage, to compare said predefined third voltage to said first voltage and to said second voltage, to assert a first signal when said third voltage is substantially equal to said first voltage, and to assert a second signal otherwise; and

indicator means, connected to said comparing means, operable to receive said first and said second signals and to indicate a dry condition when said first signal is received, and to indicate a wet condition when said second signal is received.

2. The system of claim 1, wherein:

when a quantity of liquid sufficient to obstruct said ferrule end wall enters the housing interior, said quantity of liquid causes the amplitude of said light signal light transmitted to said light sensing device through said receiving strand to decrease to a lower amplitude than the light entering the housing through said transmitting strand from said light emitting device, such that an attenuated reflected light signal transmitted to said light sensing device through said receiving strand has a lower amplitude than said light signal entering the housing through said transmitting strand from said light emitting device, so that said light sensing device derives a fourth voltage corresponding to the lower amplitude of said attenuated light signal; and

said comparing means are further operable to compare said third voltage to said fourth voltage.

3. The system of claim 1 wherein said light emitting device further comprises means for emitting a pulsed light signal of a pre-determined frequency and amplitude.

4. The system of claim 1 wherein said light signal is infrared.

5. The system of claim 1 wherein said transmitting strand and said receiving strand are formed into an insulated cable.

6. The sensor of claim 1 wherein said indicator means further comprises means for transmitting said first and second signals to an external computer.

7. The system of claim 1 wherein the liquid is one of water and a liquid having substantially similar properties to water.

8. The system of claim 7 wherein the predetermined cross-sectional size of the housing interior is approximately 4 mm.

9. The system of claim 7 wherein the predetermined distance of said ferrule projection is selected from a range of approximately 2.6 to 3.6 mm.

10. The system of claim 7 wherein the predetermined reflection distance from said reflector to said ferrule end wall is selected from a range of approximately 2--3 mm.

11. The system of claim 7 wherein said aperture size is approximately 2.5 mm.

12. The system of claim 1 wherein said indicator means comprises first visual indicator means representative of the dry condition and responsive to said first signal, and second visual indicator means representative of the wet condition and responsive to said second signal.

13. The system of claim 12 wherein said second visual indicator means further comprises an audible indicator means responsive to said second signal.

14. A sensor, operable in conjunction with a source of light transmitted to the sensor from the source through a fiber optic transmitting strand and a device for detecting a change in amplitude of a light signal transmitted from the sensor to the device through a fiber optic receiving strand, for identifying a presence of a liquid in contact with the sensor, said sensor comprising:

a housing having opposed proximal and distal ends and defining a hollow interior of a predetermined cross-sectional size and bounded by a peripheral wall in and through which a plurality of apertures of predetermined size are defined for permitting entry of liquid into the housing interior;

a ferrule projecting a predetermined extension distance into said housing interior from said housing proximal end and terminating in an end wall disposed in spaced confronting opposition to said housing distal end, said ferrule having a cross-sectional size smaller than said cross-sectional size of the housing interior so as to define a predetermined ferrule spacing between said ferrule and said housing peripheral wall, said ferrule retaining the fiber optic transmitting and receiving strands such that each of the strands terminates in the housing at and coincident with said ferrule end wall; and

a light reflector disposed in the housing interior proximate said distal end at a predetermined reflection distance from said ferrule end wall and oriented for receiving light transmitted from the source and entering the housing interior from the transmitting strand and for reflecting the received light onto the ferrule end wall for transmission of the reflected light through the receiving strand to the detecting device;

at least said ferrule spacing and said reflection distance being selected so that liquid entering the housing interior through said apertures forms a liquid conduit spanningly bridging said ferrule and said reflector and through and within which spanning liquid conduit light entering the housing interior from the transmitting strand and reflected back to the receiving strand is also internally reflected by the liquid conduit such that the reflected light transmitted to the detecting device through the receiving strand is of greater amplitude than the light entering the housing through the transmitting strand from the light source so that a detected increase in the amplitude of the light signal received by the detecting device indicates the presence of liquid in contact with the sensor.

15. The sensor of claim 14 wherein said light signal is infrared.

16. The sensor of claim 14 wherein said light signal is infrared.

17. The sensor of claim 14 wherein the liquid is one of water and a liquid having substantially similar properties to water.

18. The sensor of claim 17 wherein the predetermined distance of said ferrule projection is selected from a range of approximately 2.6 to 3.6 min.

19. The sensor of claim 17 wherein the predetermined reflection distance from said reflector to said ferrule end wall is selected from a range of approximately 2-3 mm.

20. The sensor of claim 14 wherein the liquid is one of water and a liquid having substantially similar properties to water.

21. The sensor of claim 20 wherein the predetermined cross-sectional size of the housing interior is approximately 4 mm.

22. The sensor of claim 20 wherein the predetermined distance of said ferrule projection is selected from a range of approximately 2.6 to 3.6 min.

23. The sensor of claim 20 wherein the predetermined reflection distance from said reflector to said ferrule end wall is selected from a range of approximately 2-3 mm.

24. The sensor of claim 20 wherein said aperture size is approximately 2.5 mm.

25. A sensor, operable in conjunction with a source of light transmitted to the sensor from the source through a fiber optic transmitting strand and a device for detecting a change in amplitude of a light signal transmitted from the sensor to the device through a fiber optic receiving strand, for identifying a presence of a liquid in contact with the sensor, said sensor comprising:

a housing having opposed proximal and distal ends and defining a hollow interior of a predetermined cross-sectional size and bounded by a peripheral wall in and through which a plurality of apertures of predetermined size are defined at predetermined locations intermediate said proximal and distal ends for permitting entry of liquid into the housing interior;

a ferrule projecting a predetermined extension distance into said housing interior from said housing proximal end and terminating in an end wall disposed in spaced confronting opposition to said housing distal end, said ferrule having a cross-sectional size smaller than said cross-sectional size of the housing interior so as to define a predetermined ferrule spacing between said ferrule and said housing peripheral wall, said ferrule retaining the fiber optic transmitting and receiving strands such that each of the strands terminates in the housing at and coincident with said ferrule end wall; and

a light reflector disposed in the housing interior proximate said distal end at a predetermined reflection distance from said ferrule end wall and oriented for receiving light transmitted from the source and entering the housing interior from the transmitting strand and for reflecting the received light onto the ferrule end wall for transmission of the reflected light through the receiving strand to the detecting device;

at least a selected plurality of said reflection distance, said ferrule extension distance, said predetermined aperture locations and said aperture size being selected so that liquid entering the housing interior through said apertures forms a liquid conduit spanningly bridging said ferrule and said reflector and through and within which spanning liquid conduit light entering the housing interior from the transmitting strand and reflected back to the receiving strand is also internally reflected by the liquid conduit such that the reflected light transmitted to the detecting device through the receiving strand is of greater amplitude than the light entering the housing through the transmitting strand from the light source so that a detected increase in the amplitude of the light signal received by the detecting device indicates the presence of liquid in contact with the sensor.

26. A sensor, operable in conjunction with a source of light transmitted to the sensor from the source through a fiber optic transmitting strand and a device for detecting a change in amplitude of a light signal transmitted from the sensor to the device through a fiber optic receiving strand, for identifying a presence of a liquid in contact with the sensor, said sensor comprising:

a housing having opposed proximal and distal ends and defining a hollow interior of a predetermined cross-sectional size and bounded by a peripheral wall in and through which a plurality of apertures of predetermined size are defined at predetermined locations intermediate said proximal and distal ends for permitting entry of liquid into the housing interior;

a ferrule projecting a predetermined extension distance into said housing interior from said housing proximal end and terminating in an end wall disposed in spaced confronting opposition to said housing distal end, said ferrule having a cross-sectional size smaller than said cross-sectional size of the housing interior so as to define a predetermined ferrule spacing between said ferrule and said housing peripheral wall, said ferrule retaining the fiber optic transmitting and receiving strands such that each of the strands terminates in the housing at and coincident with said ferrule end wall; and

a light reflector disposed in the housing interior proximate said distal end at a predetermined reflection distance from said ferrule end wall and oriented for receiving light transmitted from the source and entering the housing interior from the transmitting strand and for reflecting the received light onto the ferrule end wall for transmission of the reflected light through the receiving strand to the detecting device;

wherein when a quantity of liquid sufficient to obstruct said ferrule end wall enters the housing interior, said quantity of liquid causes the amplitude of the reflected light transmitted to the detecting device through the receiving strand to decrease to a lower amplitude than the light entering the housing through the transmitting strand from the light source, so that a detected decrease in the amplitude of the light signal received by the detecting device indicates the presence of liquid in contact with the sensor.

27. The sensor of claim 26 wherein said light signal is infrared.

28. The sensor of claim 26 wherein the liquid is one of water and a liquid having substantially similar properties to water.