US 3631439 A
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Description (OCR text may contain errors)
United States Patent  Inventor Edward W. Nichols 2,582,483 1/1952 l-la11erberg.. ,200/83 X Monroeville, Pa. 2,5 87,482 2/1952 Keller 317/144 X  Appl. No. 857,961 2,868,300 1/1959 .loerren et a1.. 310/8.8 X  Filed Sept. 15, 1969 3,268,683 8/1966 Palmer 200/83 R  Patented Dec. 28, 1971 3,307,052 2/1967 Neilson et al. 310/8  Assignee Westinghouse Electric Corporation 3,336,573 8/1967 Gallaway et a1. 310/82 X Pittsburgh, Pa. 3,359,386 12/1967 Howard 200/83 R 3,438,021 4/1969 Nelkin 340/409 X 54 PRESSURE-SENSITIVE SECURITY APPARATUS 'f' Y I claim 2 Drawing Figs. Assistant Examiner-Scott F. Partridge Att0rneys-F. H. Henson, M. P. Lynch and C. F. Renz  U.S. C1 340/240, 200/83, 310/8, 340/272, 340/261  Int. Cl ..G08b13/20, CT; A e ure-sensitive security signal apparatus of Holh 35/ 34 the type in which a receiving transducer responds to pressure  Field of Search 340/272, applied to fl id fi]] d tubes by deve|oping an electrical Signal ZOO/33 83 A, 33 C, 83 which is a function of the applied pressure. More particularly 317/144; 310/8, the invention is directed to a pressure-sensitive security signal apparatus comprising two fluid-filled tubes and a single pres-  Reterences Cited sure transducer means for developing an electrical signal as a UNITED STATES PATENTS function of the difference in pressures applied to each of the 1,986,479 1/1935 Lowe et a1. 340/240 X fluid-filled tubes.
. N PREAMPLIFIER N l4 \I z Patented Dec. 28, 1971 MONITORING 22/- UNIT PROTECTED REGION INTERROGATING SIGNAL GENERATOR DIFFER NFAL T PRESSUERE PREAMPLIFIER TRANSDUCER FE m n-" 34 J 32 PREAMPL l Fl ER FIG.2.
lNI/ENTOR Edward W. Nichols /MMM U i ATTORNEY PRESSURE-SENSITIVE SECURITY APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to pressure-sensitive security apparatus and has particular relationship to apparatus for detecting the penetration of a boundary of a predetermined region. The principal component of this apparatus is a fluid-filled pressure conductor or tube terminating in a pressure transducer means which responds to applied pressure by developing an electrical signal as a function of the magnitude of the applied pressure.
2. Description of the Prior Art A basic pressure-sensitive security apparatus is disclosed and claimed in Pat. No. 3,438,021 issued Apr. 8, I969 andassigned to the assignee of the present invention. A pair of fluid-filled tubes positioned in a spaced-apart relationship, typically .of the order of 2 to 5 feet are utilized to render the security apparatus insensitive to remote sounds or disturbances while retaining sensitivity to local sounds and disturbances. Individual transducer means are operatively connected to each of the two fluid-filled tubes.
The theory of operation of the two-tubes system is that a remote disturbance or a change in atmospheric conditions will affect each tube similarly and that by providing an electrical balance circuit at the output of the transducer means equal applied pressure to the two tubes will result in a net zero electrical output signal. In the event of a local disturbance which results in a change in applied pressure to only one of the two tubes the balance circuit will develop an electrical signal which is a function of the difference in the applied pressures at the tubes. This signal is available for intruder detection alarm.
The transducer system disclosed in the above-identified U.S. patent discloses the use of two separate pressure transducers the outputs of which are electrically combined in a bucking relationship. Each transducer comprises a deflection element and a deflection sensitive transducer element operatively associated with the deflecting element. The electrical response of each transducer is combined so that equal electrical signals corresponding to equal applied pressures tend to cancel each other.
An inherent shortcoming of this system is that exact electrical balance cannot be maintained between the respective transducer element inasmuch as the elements of each detector exhibit peculiar sensitivity to mechanical stress, temperature variation and aging.
Furthermore each pressure transducer functions as a gaugetype pressure transducer in which one surface of the deflecting element is subjected to the static line pressure of the fluidfilled tube whereas the opposite surface is subjected to an ambient pressure. The static line pressure resulting from fluid head pressure produced when the tubes are used in a nonhorizontal position may be sufficient to rupture the deflecting element or over stress and permanently damage the deflection sensitive transducer element.
SUMMARY OF THE INVENTION The invention is directed to the use of a single combination of a bidirectional pressure-responsive element and a deflection sensitive transducer element which functions as a differential pressure transducer by responding to the net difference in fluid pressure in the fluid tubes of the above identified system by developing a single electrical signal in response to a local disturbance.
The static line pressure present in eachv of the two fluid cables is transmitted to opposite surfaces of the bidirectional pressure-responsive element thus eliminating detector failure due to excessive fluid static line pressure.
The elimination of a second pressure transducer disposes of the problem of matching or balancing electrical and mechanical characteristics encountered in the dual transducer system of the referenced patent.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view showing a preferred embodiment of the invention;
FIG. 2 is a view in section showing the connection of the fluid-filled tubes of FIG. I to the differential pressure transducer means.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 there is illustrated diagrammatically a pressure-sensitive security apparatus 10 concealed beneath the surface of the earth to provide intrusion protection. The security apparatus 10 comprises essentially a pair of fluidfilled tubes 12 and 14 and a differential pressure-sensitive device I6. The tubes 12 and 14 are composed of compliant material such as rubber and the fluid with which each tube is filled is uncompressible gas or liquid.
In providing intrusion protection for any Protected Region a plurality of security apparatuses 10 each including a preamplifier 18 are disposed around the perimeter of the region. In the practice of the invention a monitoring unit 22 is connected to respond to and a signal generator is connected to actuate the security apparatus 10.
For the purpose of checking the in-line operation of the differential pressure-sensitive device 16 an interrogating signal from signal generator 36 is impressed on the interrogating transducers 30 and 32 located within a housing 34. This signal may be of the altemating-current-type and typically may be of 60 hertz potential derived from an available commercial source. The interrogator signal may be impressed in common on the fluid-filled tubes 12 and 14 to check the zero balance of the differential pressure-sensitive device 16 or may be impressed alternately on tubes 12 and 14 to check the positive and negative deflection calibration of the pressure-sensitive device 16. The description and operation of the interrogating transducer is presented in the referenced U.S. patent.
A typical embodiment of the diflerential pressure sensitive device 16 is illustrated sectionally in FIG. 2, as comprising'essentially a fluid-filled reference chamber 50 and a differential pressure detector 60 sealed within a wall of the housing. The differential pressure detector 60 can be described as a bidirectional differential pressure transducer.
The detector 60 is comprised of electrical transducer element 62 operatively associated with a pressure responsive element 64. In operation the transducer element 62 responds to the mechanical deflection of the bidirectional pressureresponsive element 64 by developing an electrical signal in the preamplifier 18 which is a function of the deflection. The deflection of element 64 may be as a result of an increase in fluid pressure in tube 14 which would result in an electrical signal of one polarity, or it may be the result of an increase in the fluid pressure in the fluid-filled cavity 52 of the reference chamber 50 which would result in an electrical signal of opposite polarity.
The electrical transducer element 62 may take the form of a piezoelectric ceramic disc, as described in the referenced U.S. patent, which is secured centrally to the pressure-responsive element 64. Tension and compression of the disc caused by positive and negative deflection of element 64 results in electrical signals of corresponding polarity. The pressure-responsive element 64 can be implemented with the deflection diaphragm element of the referenced U.S. patent, a bellows assembly, etc. Electrical conductors 66 and a hermetically sealed electrical interconnect 68 provide means for transmitting the electrical response of the transducer element 62 to the preamplifier I8. I
In an embodiment of the security system 10 in which the tubes 12 and 14 are filled with an electrically conductive or corrosive fluid such as water, or a water-antifreeze solution, it is necessary to isolate the electrical transducer element 62 from the fluid within tubes 12 and I4. This isolation is accomplished by sealing a reference deflection element, which is illustrated in the form of a highly compliant diaphragm 70, in the wall of the chamber 50 so as to expose one surface of the diaphragm 70 to the fluid in the tube 12 and the opposite surface of the diaphragm 70 to the fluid in cavity 52.
By selecting a suitable electrically nonconductive, incompressible fluid, such as an insulating oil, for filling cavity 52 through a conduit 54, the fluid pressure presentin tube 12 is transmitted by the diaphragm 70 through the fluid in cavity 52 to the differential pressure detector 60. The fluid selected for filling cavity 52 may be any one of numerous incompressible electrically nonconductive liquids or gases. Since the fluid in cavity 52 is virtually incompressible, the pressure of the fluid in tube 12 is transmitted to the detector 60 without significant loss in pressure sensitivity. The application of the fluid static line pressure in tubes 12 and 14 to opposite surfaces of the detector 60 substantially eliminates detector 60 failure due to excess fluid static line pressures.
in the event the fluid within tubes 12 and 14 is not electrically conductive then the reference diaphragm may be eliminated and the fluid in tube 12 permitted to contact the detector 60 directly.
In either of the above instances a single detector 60 is utilized, thus eliminating matching or balancing of electrical and mechanical characteristics of several detectors.
Various modifications may be made within the scope of this invention.
1. In apparatus for detecting penetration of a boundary of a predetermined region having a first and second fluid-filled tube means, the combination comprising,
a reference chamber filled with an inert, incompressible,
electrically nonconductive fluid, a bidirectional pressureresponsive element having a first and second surface, said bidirectional pressure-responsive element sealed in a wall of said reference chamber with the first surface of said bidirectional pressure-responsive element being in contact with the fluid'in said reference chamber and the second surface of said bidirectional pressure-responsive element being in contact with the fluid in said second fluid-filled tube, a reference deflection element sealed in a wall of said reference chamber, the surface of said reference deflection element external to said reference chamber being in contact with the fluid in said first fluidfilled tube, said reference deflection element transmitting fluid pressure changes occurring in said first fluid-filled tube through the fluid in said reference chamber to the first surface of said bidirectional pressure-responsive element, a piezoelectric pressure-responsive means disposed on said first surface of said bidirectional pressure-responsive element in contact with said fluid in said reference chamber to produce an electrical signal proportional to the magnitude of the difference in fluid pressure between said first and second fluid-filled tubes, and an electrical interconnected means sealed in a wall of said reference chamber to provide access to said piezoelectric pressureresponsivemeans.