SU1640727A1 - Passive infra-red intruder detection system - Google Patents

Abstract

The invention relates to infrared technology and can be used in alarm systems. The purpose of the invention is to extend the functionality, which is the ability of the detection system to determine the distance to the intruder. The passive infrared detection system consists of two completely identical channels and an arithmetic unit 11. The channels include modulators 3, 8 of radiation, optical filters 4, 9, receivers 1, 6 of infrared radiation, amplifiers 2, 7, and meters 5, 10 frequencies. The radiation modulator 3 (8) can be made, for example, in the form of a grating element, in the form of a ruled raster, or in the form of a grid of opaque lines deposited on the surface of the optical filter 4 (9). Receivers 1, 6 are located at opposite ends of the detection zone and facing each other. The infrared radiation of a moving intruder is interrupted by the lines of the modulator 3 (8) at a certain frequency, depending on many factors, including the distance from the disturber to the intruder. The interrupt frequencies from each channel are fed to the arithmetic unit 11, which determines their ratio and calculates the distance to the intruder. 4 il.

Description

1

The invention relates to infrared technology and can be used in alarm systems.

The purpose of the invention is to expand the functionality of the alarm system.

FIG. 1 is a functional system diagram; in fig. 2 - 4 - scheme of the system.

The passive infrared intruder detection system contains two channels. The first channel includes the first infrared receiver 1, the first amplifier 2 connected to the output of the radiation receiver, the first radiation modulator 3 located in front of the optical input of the receiver, the first optical filter 4 placed between the modulator and the receiver, and the first meter 5 is connected to the output of amplifier 2. The second channel of the system includes the second infrared radiation receiver 6, amplifier 7, radiation modulator 8, optical filter 9 and frequency meter 10 and is completely identical to the first a-lu. The device contains an arithmetic unit 11c output 12.

The embodiments of the radiation modulator may be different. For example, in the form of a lattice element, in the form of a linear raster, or in the form of a grid of opaque lines deposited on an optical filter, which is an integral part of the optical system.

The infrared receiver, modulator and optical filter can be structurally combined into one node, which will be referred to as a detector.

The essence of the proposed invention consists in using two detectors, with the help of which the angular velocity of the violator is measured, on the basis of which the calculator 10, whose inputs are connected to the outputs of the corresponding frequency meters 5 and 10, and the output is output 12 of the entire system, determines the distance to the intruder.

Two identical detectors are placed on spaced opposite supports, and are facing each other (Fig. 2). FIG. 2 the following notation is accepted: a - the angle of view of the detectors; a is the extent of the area not viewed by the detector; I - the extent of the controlled boundary.

FIG. 3 shows the detection zone of the infrared system from above. The shaded part denotes the zone

system performance, when the intruder penetrates, the system issues an alarm signal and determines the distance from it to one of the detectors.

Consider the operation of the system.

In the initial state, the intruder is absent in the field of view of the detectors, there is no frequency modulated signal at the outputs of the radiation receivers 1 and 6, there is no signal at the output 12 of the entire system.

Let the intruder, moving at a speed v at an angle c to the optical axis of the system, penetrate the detection zone. The principle of operation of one of the detectors is explained in FIG. 4. The optical filter is not shown. The image of the field of view using optics (also not shown in Fig. 4) through the modulator is focused on the radiation receiver. When the intruder, which is an infrared radiation source, moves in the field of view of the detector, the modulator lines interrupt this radiation with a certain frequency f, which depends on the distance d to the intruder, its speed v, the distance from the radiation receiver to the modulator p and on the distance between the modulator lines (linear period of the modulator) d. In mathematical form, this functional relationship looks like this: w vi y sine4 Jti where w is the angular velocity of the violator;

/ 3 - the angular period of the modulator, rad.

In turn, the angular period can be determined by the formula

P -Wa ™ -W An electrical signal with a frequency f appears at the output of the radiation receiver, which through an amplifier enters a frequency meter. The measured value of the frequency F is fed to the input of the arithmetic unit 11, which, if there is a frequency value at the second input, determines the range to the intruder.

Consider the algorithm for determining the distance to the intruder, implemented by the arithmetic unit 11. From formula (1), using simple transformations, you can obtain a formula for determining the distance to the violator, which looks like this:

  V f

From analysis (2) it follows that the only unknown quantity in it is

f sh

I -0

(one)

the speed of movement of the violator v. Knowing its value, it would be possible to determine the distance to the intruder from the measured interrupt frequency f. However, the difficulty lies in the fact that the speed of movement v depends only on the intruder, is unpredictable in advance and can vary in very wide limits 0.1-8 m / s. The way out of this uncertainty is the elimination of the variable v from the formula for determining the range, which is achieved by using two detectors simultaneously.

Let the distance from one of the detectors to the intruder be di. Then the distance from the intruder to the other detector in this case is equal to

da L-di,

where L 2a +1 is the distance between the detectors.

Obviously, when the intruder moves at a speed v at the output of the first radiation receiver, the pulse frequency is

f v sine

T1 Јdi and from the output of the second detector, v sirtc4

In relation to these two frequencies, we get

fi-d2 n Now it’s easy to determine

 or d2 J} L

di

-. For complete certainty, it is sufficient to know only one of these quantities.

Thus, by simple mathematical transformations, it was possible to obtain a formula for determining the distance to the intruder, which does not contain the variable v. In addition, it also follows from this that the direction of the vector D does not affect the determination of the distance. In other words, the infrared detection system that implements this principle is operable theoretically with the preferred direction of movement of the intruder in the field of view of the detectors.

The only exception to this will be the case when the intruder moves parallel to the optical axis of the system, in which the intruder does not intersect the modulator lines with the intruder's image. However, this case is almost impossible.

This range determination algorithm

before the intruder is implemented by an arithmetic unit 11, which can be created, for example, using a microprocessor or based on a microcomputer. When fi and f2 frequencies appear on

its two inputs are arithmetic blo. determines the ratio of these frequencies n and the range to the disturber ch or d. The appearance at output 12 of the distance to the intruder is also a signal

anxiety

Thus, the proposed intruder detection system can significantly increase the informativeness of the detection process by determining

distance to the intruder and, consequently, increase the effectiveness of the protection of objects.

Claims (1)

Invention Formula A passive infrared intruder detection system comprising a first infrared radiation receiver, a first amplifier connected to the output of the first infrared radiation receiver, the first radiation modulator, located in front of the optical input of the first infrared radiation receiver, and the first optical filter, located between the first modulator and the infrared radiation receiver, characterized in that in order to extend the functionality of the system by determining the distance before the intruder is detected, additionally introduced into it a second infrared receiver, a second amplifier, a second radiation modulator, a second optical filter, two frequency meters and an arithmetic unit, a second radiation modulator through the second optical filter is optically connected to the second radiation receiver, the output of which is connected to the input of the second amplifier; the outputs of the first and second amplifiers are connected respectively to the inputs of the first and the second frequency meters, the outputs of the first and second frequency meters are connected respectively to the first and second inputs of the arithmetic unit, the output of which is the output of the device. Fie.2 “Sto. 3 I infrared detector -. j i