RU2079888C1 - Fiber-optical security alarm system - Google Patents

Abstract

FIELD: optical devices, alarm systems for protection of perimeters of areas and rooms against intruders. SUBSTANCE: device has laser light source 1, which output is connected to input of photodetector 4 through piece of multiple-mode optical fiber 2 and light beam generation unit 3. Output of photodetector is connected to input of alarm signal generator 5, which is designed as separating capacitor 6, comparator 7, pulse duration generator 9 and indicator 13. In addition alarm signal generator 5 has integrator 10, signal duration selector 8, OR gate 12 and second comparator 11. Light beam generation unit 3 is designed as tube of specific length which is made from opaque material. EFFECT: increased stability to noise, self-monitoring of optical elements. 2 cl, 2 dwg

Description

 The present invention relates to signaling devices based on fiber optics and can be used in systems for protecting the perimeter of territories and premises from unauthorized access.

 Known fencing safety system [1] containing a number of tensioned wires, a coherent light source, an optical fiber as a sensing element and a terminal device with a photo detector and an alarm driver. When the fence is mechanically exposed, the optical fiber is deformed using special devices, while the intensity of coherent light passing through the fiber is attenuated, which is recorded as an alarm by the terminal device.

 The disadvantages of the described system are the complexity of the practical implementation and the limited scope, due to the fact that the implementation of the system in the form of a device of tensioned wires that create a physical barrier does not allow its use in conditions where the protected areas are surrounded by traditional elements of the fence (barbed wire, mesh, etc.) .P. ).

 These disadvantages are partially eliminated in the fiber-optic alarm system with an optical fiber buried in the ground as a sensitive element [2] This technical solution is the closest to the claimed one.

 The specified fiber-optic alarm system contains a coherent light source, a segment of a multimode optical fiber, a light shaper in the form of a plate with a hole, a photo detector and an alarm shaper, made in the form of a separation capacitor, a comparator, a pulse shaper, and an indicator element.

 The disadvantages of this system are the limited scope and lack of reliability due to the following reasons. One of the important parameters of alarm systems is immunity to environmental influences. There is no selection of the duration of the input signal in the alarm driver circuit of the known solution, which, given the high sensitivity of the sensors due to the effect of inter-mode interference, can lead to the triggering of the alarm system during random short-time single exposure. The indicated drawback does not allow to install the system on the elements of the territory fencing and open structural blocks of buildings and structures exposed to the environment. The insufficient reliability of the system is also due to the fact that the alarm driver circuit does not have a constant optical power control circuit. Thus, in real conditions, a smooth drop in optical power in the event of a degradation of a coherent light source or optical fiber leads to a failure of the alarm system without a warning signal.

 Another disadvantage of the known system is the complexity of its practical implementation, due to the use of the shaper of the light flux in the form of a plate with a diaphragm hole, difficult to manufacture and install.

 The objective of the invention is to expand the scope of the system, increasing the reliability of its operation and simplifying the practical implementation.

 The problem is solved as follows.

 A fiber-optic burglar alarm system is proposed, containing a coherent light source, the output of which is connected to the photodetector input through a segment of a multimode optical fiber and a light shaper, and the photodetector output is connected to the input of an alarm shaper made in the form of a separation capacitor, comparator, pulse duration shaper, and indicator element, the first lining of the isolation capacitor in this case is actually the input of the signal conditioner revogi and second plate coupled to the first input of the comparator, the second input of which is set a reference level.

 New in the proposed system is that the alarm driver is equipped with an integrator, a signal duration selector, an OR logic element and a second comparator, the first input of which is connected through the integrator to the first plate of the isolation capacitor, the reference level is installed at the second input of the second comparator, and the output is connected to the first input of the OR logic element, the second input of the OR logic element is connected through the pulse width former to the output of the signal duration selector, the input to orogo connected to the output of the comparator, the output of NAND gate OR is connected to the input of the indicator cell. New in the proposed device is also that the shaper of the light flux is made in the form of a tube of a certain length of optically opaque material, which is located between a segment of a multimode optical fiber and a photodetector with the ability to provide the necessary contrast to the speckle pattern of the light flux from the end of the optical fiber on the photosensitive surface of the photodetector.

 In FIG. 1 shows a functional diagram of the proposed system; in FIG. 2 shows plots of input and output signals block by block.

In accordance with the claimed invention, the fiber-optic alarm system (Fig. 1) contains a coherent light source 1, the output of which through a segment of a multimode optical fiber 2 and a light shaper 3 is coupled to the input of the photodetector 4. The output of the photodetector 4 is connected to the input of the alarm driver 5. The shaper of the alarm 5 is equipped with a separation capacitor 6, the first comparator 7, a selector for the duration of the signal 8, a shaper of the duration of the pulses 9, an integrator 10, the second a parator 11, an OR gate 12 and an indicator element 13. The first input of the second comparator 11 is connected through the integrator 10 to the first lining of the isolation capacitor 6. At the second input of the second comparator 11, a reference level U _{op2 is installed} , and the output is connected to the first input of the OR gate 12 The second input of the OR gate 12 is connected via a pulse width former 9 to the output of the signal duration selector 8, the input of which is connected to the output of the first comparator 7, the first input of which is connected to the second plate of the coupling capacitor 6 and the second input is fed the reference voltage of the comparator. The output of the logic element OR 12 is connected to the input of the indicator element 13.

 The proposed system works as follows.

 The radiation of a coherent light source 1 (Fig. 1) is introduced into a segment of a multimode optical fiber 2 and, through a light shaper 3, is fed to the input of the photodetector 4. As a result of intermodal interference in the optical fiber, a discrete picture of bright and dark spots is formed on the photosensitive surface 4 ( speckles), which is static in the absence of mechanical stress and changes under the influence of shock, vibration or deformation of the optical fiber. The light shaper 3 provides the necessary contrast speckle pattern to increase the sensitivity of the system.

The signal from the output of the photodetector 4 (position a in Fig. 2) is fed to the input of the alarm driver 5. Depending on the intensity and duration of the mechanical impact on the optical fiber, the photocurrent is modulated, the level of which corresponds to the optical power at the input of the photodetector 4. Next, in the signal conditioner alarm 5 there is a double-circuit conversion of the input signal by a variable and a constant component. The variable component is separated by a separation capacitor 6 and fed to the first input of the first comparator 7, at the second input of which a reference level U _{op1 is installed} . The pulses from the output of the first comparator 7 (position b in Fig. 2) are fed to the input of the signal duration selector 8, which has a selection time τ _c . In the case when τ _c <τ _{2, the} selector starts the pulse shaper 9, while τ _{f is} set depending on the required duration of the alarm (position in Fig. 2). In the case where τ _c > τ ₁ , the selector locks the circuit.

The constant component through the integrator 10 is fed to the first input of the second comparator 11, at the second input of which a reference level U _{op2 is installed} . Depending on the level of optical power at the input of the photodetector 4, the second comparator 11 generates a corresponding signal (position g in Fig. 2). This signal is fed to the first input of the OR gate 12, to the second input of which a signal is output from the first comparator 7. When a signal appears at the first or second input of the OR gate 12 from the output of the OR gate 12, the alarm signal (position e in Fig. 2) after the double-circuit conversion is supplied to the indicator element 13.

 Thus, the claimed invention allows to increase the stability of the system to random external influences, which, in turn, allows you to install it on the open elements of the fencing of the territory, structural blocks of buildings and structures. The dc component of the input signal processing introduced into the alarm driver 5 increases the reliability of the system and allows diagnosing its potential failure.

 A tube of any optical opaque material as a shaper of light flux is simpler to implement, install, and configure, which simplifies the practical implementation of the system.

Claims (2)

 1. Fiber-optic alarm system containing a coherent light source, the output of which through a segment of a multimode optical fiber and a light shaper is coupled to the photodetector input, the photodetector output is connected to the input of the alarm driver, made in the form of a separation capacitor, the first comparator, the duration shaper pulses and indicator element, the first lining of the isolation capacitor is the input of the alarm driver, and the second lining and connected to the first input of the first comparator, at the second input of which the reference level of the first comparator is installed, characterized in that the alarm driver is equipped with an integrator, a signal duration selector, an OR logic element and a second comparator, the first input of which is connected through the integrator to the first lining of the isolation capacitor , at the second input, the reference level of the second comparator is installed, and the output is connected to the first input of the OR gate, the second input of the OR gate is connected inen through the pulse width generator with the output of the signal duration selector, the input of which is connected to the output of the first comparator, the output of the OR gate is connected to the input of the indicator element.  2. The system according to claim 1, characterized in that the shaper of the light flux is made in the form of a tube of optically opaque material, the length of which is determined by the length and type of segment of a multimode optical fiber.

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