Frequency multiplexed water leak detection system

• US 4,090,193 A
• Filed: 11/24/1976
• Issued: 05/16/1978
• Est. Priority Date: 11/24/1976
• Status: Expired due to Term

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Hinkle, Francis E. Jr.
• Primary Examiner(s): Waring, Alvin H.
• Application Number:
  US05/744,560
• Time in Patent Office: 538 Days
• Field of Search: 340/52 F, 340/59, 340/58, 340/242, 340/244 R, 340/244 C, 340/253 Y, 340/324 R, 340/409, 340/412, 340/413
• US Class Current: 340/524
• CPC Class Codes: G01M 3/16 using electric detection means G01M3/045, G01M3/06, G01M3/12, G01M3/20, G01M3/24, G01M3/26 take precedence
• CPC Class Codes: G08B 21/20 responsive to moisture
• CPC Class Codes: G08B 25/04 using a single signalling line, e.g. in a closed loop

Abstract

An active leak detector which uses frequency multiplexing to indicate the cation of water leaks. The circuit is composed of any number of satellite leak detectors and a master indicator circuit which monitors all detectors simultaneously. Each detector unit is identified by a unique frequency warning signal which allows the indicator circuit to isolate and display the location of the leak. Only two wires are needed to connect all the detectors to the master indicator as well as supply the necessary power to the detectors.

Claims

1. A system for detecting and locating a fluid leak comprising:

a plurality of sensing means for detecting a fluid, each situated in a different location;

circuitry coupled to respective sensing means for providing an electrical signal indicative of a fluid sensed by the sensing means coupled thereto, said signal having a unique frequency different from any other sensing circuitry in the system; and

an indicator unit electrically coupled in parallel to all of said sensing means through their respective circuitry for providing an indication and location of said fluid leak.

2. A system as recited in claim 1 wherein said circuitry includes an astable multivibrator to provide said unique frequency, said unique frequency determined by the RC time constant of said multivibrator.

3. A system as recited in claim 2 wherein said sensing means comprises a pair of electrodes and said fluid comprises water, whereby when water is present between said electrodes, current flows therebetween to cause said circuitry to provide said unique oscillator frequency.

4. A system as recited in claim 3 further including a power source;

and

only a single pair of lines to provide said power to said sensing means, said circuitry and said indicator unit, as well as provide the output signals of said circuitry to said indicator unit.

5. A system as recited in claim 4 wherein said circuitry comprises a CMOS unit arranged in a detecting, inverting and astable multivibrator arrangement.

6. A system as recited in claim 5 wherein said indicator unit comprises a CMOS unit arranged in a gate amplifier arrangement and an aural indicator to provide a tone indicative of said unique circuitry signals thereby identifying the location of the leak.

7. A system as recited in claim 4 further including:

an isolation network coupled between said power source and said circuitry whereby each circuit is isolated from said power source and each of the other circuits.

8. A system as recited in claim 6 further including:

filter means comprising an inductor in parallel with a resistor to isolate the power source from circuit output signals.

9. A system as recited in claim 8 wherein said indicating means includes a visual display to provide the frequency of oscillation of said circuit.

10. A system as recited in claim 9 wherein said power source comprises a 9 volt DC source and wherein said isolation network includes a capacitor chosen to be 1/1000 F_L farads, where F_L is the lowest frequency of oscillation of an astable multivibrator in said system.