PROXIMITY DETECTOR

• US 3,829,850 A
• Filed: 12/17/1971
• Issued: 08/13/1974
• Est. Priority Date: 12/17/1971
• Status: Expired due to Term

• Current Assignee: John W. Guetersloh
• Original Assignee: John W. Guetersloh
• Inventors: Guetersloh, John W.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Wannisky, William M.
• Application Number:
  US05/209,333
• Time in Patent Office: 970 Days
• Field of Search: 340/258C,244C,228R,258R 328/116,147 324/6C,61R,71R 317/123,153
• US Class Current: 340/515
• CPC Class Codes: G08B 13/26 by proximity of an intruder causing variation in capacitance or inductance of a circuit
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/96075 involving bridge circuit

Abstract

A capacitive proximity detector protects against injury, damage or unauthorized entry into a protected area. It comprises an unbalanced capacitive bridge including an antenna or sensor which produces an output proportional to the capacitance of the antenna to ground. A change in capacitance is detected and the resulting signal is applied to a pair of '"'"''"'"''"'"''"'"'windows'"'"''"'"''"'"''"'"' having maximum and minimum values which, if exceeded, operate a pair of relays and produce a suitable visual indication. Many fail-safe and other safety features are provided in the detector.

Claims

1. A protector device comprising a capacitive balancing circuit, means for coupling an antenna located adjacent an area to be protected electrically into said balancing circuit, said antenna having a capacitive reactance which causes said balancing circuit to be normally unbalanced, means coupled to said balancing circuit for exciting it with alternating electrical energy, a demodulaTor coupled to said balancing circuit for producing a DC output indicative of unbalance in said balancing circuit, a pair of electrical windows having maximum and minimum limits coupled to the output of said demodulator, and a pair of relays coupled to said windows for actuation when the output of said demodulator is greater than the maximum limit or less than the minimum limit of either window.

2. Apparatus according to claim 1 wherein said balancing circuit comprises a bridge.

3. Apparatus according to claim 2 wherein said bridge comprises only capacitive elements.

4. Apparatus according to claim 3 wherein said bridge includes a variable capacitor.

5. Apparatus according to claim 4 including a variable balance detector coupling the output of said bridge to said demodulator.

6. Apparatus according to claim 1 wherein said demodulator comprises a synchronous detector, and means for coupling a squarewave output from said exciting means to said synchronous detector.

7. A protective device comprising a capacitive bridge, means for coupling an antenna located at an area to be protected electrically into an arm of said bridge, said antenna having a capacitive reactance which causes said bridge to be normally unbalanced, an oscillator, a buffer coupling an output of said oscillator across said bridge, a balance detector coupled to the output of said bridge, a synchronous detector having a first input coupled to said balance detector and a second input coupled to said oscillator, a difference amplifier coupled to said synchronous detector, a control relay, and an electrical window having maximum and minimum limits coupling the output of said difference amplifier to said relay.

8. Apparatus according to claim 7 including a meter coupler to the output of said difference amplifier.

9. Apparatus according to claim 7 including a rectifier diode coupling the output of said difference amplifier to a reference potential whereby said difference amplifier output can not fall below said reference potential.

10. Apparatus according to claim 7 comprising a pair of control relays coupled to the output of said difference amplifier, each of said relays having mechanically interconnected control and monitor contacts, a time delay circuit coupled to said monitor contacts, and means for feeding a disabling signal from said time delay circuit to said electrical window when said relays do not work substantially in unison.

11. A protective device comprising a capacitive bridge, means for coupling an antenna located at an area to be protected electrically into an arm of said bridge, an oscillator, a buffer coupling an output of said oscillator across said bridge, a balance detector coupled to the output of said bridge, a synchronous detector having a first input coupled to said balance detector and a second input coupled to said oscillator, a difference amplifier coupled to said synchronous detector, a pair of control relays coupled to the output of said difference amplifier, an electrical window having maximum and minimum limits coupling the output of said difference amplifier to said relays, each of said relays having mechanically interconnected control and monitor contacts, a time delay circuit coupled to said monitor contacts, means for feeding a disabling signal from said time delay circuit to said electrical window when said relays do not work substantially in unison, said electrical window comprising a pair of voltage comparators, said time delay circuit including an RC circuit, and means for feeding a disabling signal from said RC circuit to an input of one of said voltage comparators.

12. Apparatus according to claim 11 including means cross-coupling the inputs and outputs of said voltage comparators.

13. A protective device comprising a capacitive bridge, means for coupling an antenna defining an area to be protected into an arm of said bridge, said antenna having a capacitive reactance which causes said bridge to be normally unbalanced, a Radio frequency oscillator, a buffer coupling the output of said oscillator across said bridge, a demodulator coupled to the output of said bridge for producing a DC signal indicative of bridge unbalance, a pair of electrical windows having maximum and minimum limits coupled to said demodulator, each window comprising a pair of voltage comparators, a pair of control relays, a solid state switch coupled to the coils of each of said relays, and means coupling said switches to the outputs of all of said voltage comparators.

14. Apparatus according to claim 13 including an antenna, and a coaxial cable coupling said antenna into said bridge.

15. Apparatus according to claim 14 wherein said antenna comprises a thin-walled conduit.

16. Apparatus according to claim 13 including a DC reference voltage source, and means coupling reference voltages from said source to the reference input of each of said voltage comparators.

17. Apparatus according to claim 16 wherein the reference voltage coupled to the maximum limit comparators of said windows is variable.

18. Apparatus according to claim 17 including a solid state switch coupling said reference voltage source to the coils of said relays whereby a break in the circuit of said reference voltage source operates through said switch to actuate said relays.

19. Apparatus according to claim 13 including at least one variable test capacitor, and a test switch for coupling said test capacitor into said bridge.

20. Apparatus according to claim 13 including a reset switch coupled between the input and output of the maximum limit comparators of said windows whereby said reset switch must be opened and reclosed to reset said protective device when the maximum limit of said windows has been exceeded.

21. A protective device comprising a capacitive bridge, an antenna located at an area to be protected, means for coupling said antenna electrically into an arm of said bridge, said antenna having a capacitive reactance, said bridge with said antenna being normally unbalanced, an oscillator, a buffer coupling an output of said oscillator across said bridge, a balance detector coupled to the output of said bridge, a synchronous detector having a first input coupled to said balance detector and a second input coupled to said oscillator, a difference amplifier coupled to said synchronous detector, a control relay, and an electrical window having maximum and minimum limits coupling the output of said difference amplifier to said relay.

22. A protective device comprising a capacitive bridge, an antenna located at an area to be protected having a capacitive reactance, means for coupling said antenna into an arm of said bridge, said bridge with said antenna normally being unbalanced, a radio frequency oscillator, a buffer coupling the output of said oscillator across said bridge, a demodulator coupled to the output of said bridge for producing a DC signal indicative of bridge unbalance, a pair of electrical windows having maximum and minimum limits coupled to said demodulator, each window comprising a pair of voltage comparators, a pair of control relays, a solid state switch coupled to the coils of each of said relays, and means coupling said switches to the outputs of all of said voltage comparators.