EP0724245B1 - Passive infra-red detector evaluating the spectrum of heat radiation emitted by an object - Google Patents

Abstract

The sensor (3) breaks down the incident infrared radiation into four spectral channels for which corresp. wavelength-dependent electrical signals (A1-A4) are produced. These signals are filtered (4) and their amplitudes are evaluated (5) for presentation to a logic unit (6). The spectral fundamental patterns of emission characteristics of a variety of infrared sources are stored in the memory (7). The mean voltage amplitude over the entire wavelength range is used as a basis for comparison. If correspondence to the stored patterns lies within allowed limits, the source is identified and an alarm given.

Description

The invention relates to a passive infrared detector according to the The preamble of claim 1. Such a detector is known for example from US-A-4,245,217.

Passive infrared detectors are generally used to cover a room area to monitor and a person entering here as a heat source capture. The reporting of such a heat source can depending on the type of task on switching on the lighting restrict a room or trigger an alarm. Common passive infrared detectors do not allow differentiated spectral assessment of a heat source, but perform independently whether this is an intruder, the outbreak a fire, or a strong headlight, to a message as soon as the heat source reaches a minimum level Thermal radiation reached. However, a warning should appear on it restrict, e.g. B. only register intruders, so it is very annoying if it is also a strong one Headlights succeed in triggering an alarm. A passive infrared detector, which is the heat emission of an intruder from the would be able to distinguish between a strong headlight of great advantage.

Now it is not only interesting, a human being of one Distinctive light source to distinguish, but there are a number of Radiation sources, in particular an unwanted one Fire counts with very different reactions require and should therefore be distinguished. So far to respond to heat radiation sensors so constructed that they only determined from the entire frequency range, for such a Radiation object capture specific wavelength ranges and evaluate. However, this technique requires several different sensors to different radiation objects, e.g. B. people on the one hand and fire on the other.

The object of the invention is therefore a passive infrared detector to improve according to the preamble of claim 1 that it is possible to use different radiation objects with one device Kind of differentiating spectrally at the same time and thus on the one hand to reduce the false alarm rate and on the other hand to create an expanded functional area.

This object is characterized by those in claim 1 Features resolved. Appropriate refinements and training of the subject matter of the invention are mentioned in the subclaims.

Because behind the optics of a passive infrared detector the place where normally an optoelectric conversion element is arranged, now acting as a multispectral sensor Infrared sensor lies, it succeeds, the incident heat radiation in several discrete wavelength ranges (spectral channels) disassemble. Each of these spectral channels enables generation a special wavelength-dependent electrical signal, which in turn is fed to an evaluation circuit, which is capable of making the different wavelength dependent electrical signals depending on the specific emission characteristics of the radiation objects to be detected at the same time to rate. After identifying in this way, it is the passive infrared detector possible, the type of radiation object submit identifying report. By splitting up of the entire spectrum of a radiation object into several discrete ones spectral channels succeed in a relatively accurate analysis Determination of the type of radiation object. Sources of interference, such as Headlights can be quite accurate from an unwanted one Intruder can be distinguished, so that the number of False alarms inevitably reduced. But also the type of alarm can provide information about whether a fire has broken out or an unwanted intruder enters the monitored room has entered.

In an appropriate detailed design of the evaluation circuit it is provided that this has a memory in the basic pattern the emission characteristics of various types distinguishing radiation objects are stored. Usually it is sufficient to use the individual spectral channels To record voltage amplitudes. It is advantageous in everyone spectral channel to store an average of the voltage amplitude. The basic pattern to be recorded depends on what discrete wavelength ranges the multispectral sensor is able to differentiate between them.

Furthermore, it is provided that as the central functional unit Evaluation circuit serves a logic unit, the z. B. as a microprocessor can be built, and the individual, from Multispectral sensor coming with wavelength-dependent signals compares the signal spectra coming from the memory. An identification can according to the size match between the Measured and stored values are done.

It is also provided that the logic unit is an output unit controls which in turn controls the identified radiation object characteristic message generated, this immediately can be spent, or by appropriate means is transmitted remotely.

The nature of a radiation object is essentially determined by this recognizable that in certain spectral channels with a relatively higher or lower voltage amplitude occurs than that is the case with other radiation objects. The evaluation circuit is therefore provided with an amplitude evaluator, to record the respective mean value of the voltage amplitudes of the individual spectra. The amplitude evaluator can be connected upstream of the logic unit or integrated into it become.

So that the most accurate possible amplitude evaluation is achieved, it is appropriate, in addition to that by the individual spectral Channels formed signals to provide a base signal that the can capture the entire wavelength range and that of the logic unit is supplied as a comparison variable. This can cause errors to be avoided, otherwise by very different strong sources of radiation could be caused.

The base signal can be calculated from the remaining the signals representing the wavelength ranges used derive or analog directly to the other signals generate in the multispectral sensor by using one accordingly broadband channel that include everyone else can, provides.

If the radiation sources are of very different strengths, the logic unit must be used ensure the correct relation by taking the mean the voltage amplitude of the total frequency range as Base value for comparison with a corresponding one from memory coming value used and the amplitude ratio of this both values taken into account in the overall evaluation.

Sometimes it can be useful if the logic unit allows it other criteria for the one to be carried out Evaluation to take into account. It is therefore envisaged that in addition to the signals of the individual spectral channels at least a special signal is provided to the logic unit feeds at least one piece of special information. This can either be such that they identify the radiation object facilitated or the way of their output to the output unit influenced. With such special signals, the time of day, the ambient brightness and other factors are taken into account.

Regarding the construction of the passive infrared detector it is provided that the multispectral sensor has an aperture possesses that approximately in the image plane of the focusing optics lies. It is advisable to set up the multispectral sensor so that the incident total radiation is initially spatial and then spectrally decomposed and then optoelectric Transducer elements arrives. For spatial separation you can in Suitable splitter optics behind the aperture arrange and between this and the transducer elements in each at least one of the partial beam paths thus formed is selective arrange the bandpass element. The bandpass element must be for this ensure that only a relatively narrow wavelength range can happen. In principle, there are several options here on. So they could already be needed for spatial separation reflective mirrors selective with regard to their reflection act, or the transducer element could also be constructed in such a way that it only responds to a very specific wavelength range. Usually, however, you will be using an optical filter work at a suitable point in the radiation path between the Divider optics and the transducer element is arranged. To increase The selective effect can also be behind the optoelectric Electrical bandpass filters are arranged that only pass signals of a certain frequency spectrum to let.

Fig. 1

einen Ausschnitt aus einem Passiv-Infrarot-Melder seitlich im Schnitt,

Fig. 2

einen Multispektralsensor,

Fig. 3

ein Blockschaltbild der zum Passiv-Infrarot-Melder gehörigen elektrischen Schaltung.

Embodiments of the invention are shown in the drawings and are described in more detail below. Show it:

Fig. 1

a section of a passive infrared detector on the side in section,

Fig. 2

a multispectral sensor,

Fig. 3

a block diagram of the electrical circuit belonging to the passive infrared detector.

As can be seen in FIG. 1, behind a lens 1 is a passive infrared detector a multispectral sensor 3 in the area of Image plane of this optics 1 arranged. From an unspecified Radiation object 9, thermal radiation 2 is emitted and focused on the multispectral sensor 3 by the optics 1.

2 shows the most important details of a multispectral sensor, as described in DE 41 33 481 A1. After that is the Multispectral sensor 3 in a commercially available TO 8 housing 11 arranged. The housing 11 consists of a housing pot 12 whose end 14 has a central inlet opening 16 for the Entry of radiation 18 to be measured into the interior of the housing 11 is arranged. The housing 11 is on its Front side 14 opposite side of a housing base 20 completed and has a broadband on the entry side infrared transparent window 15.

Pins 22 are perpendicular to the housing base 20 down from. A wiring carrier 24 is on the housing base 20 arranged, on which in turn an approximately cubic cage 26 is mounted is. The one facing the inlet opening 16 of the housing pot 12 Top of the cage 26 is designed as an aperture diaphragm 28, which has a central aperture 30.

On the bottom of the cage is a pyramid 34 with a square base arranged. The lateral surfaces facing the aperture 30 of the pyramid 34 have a high degree of reflection for the through the total radiation 18 entering the aperture 30. The total radiation 18 turns on after passing through the aperture 30 the surface of the pyramid 34 toward the side walls of the cage 26, which in turn is reflected by infrared bandpass filters 36 are formed. These filters 36 each have mutually different transmission areas outside of them are highly reflective. Therefore, it arrives in the transmission area spectral part of the radiation 18 of the filter 36 through the filter 36 to a radiation sensitive Element 38, which is in the beam path behind the filter 36, i. H. on the outside of the cage 26 is arranged.

In Fig. 3 is a schematic representation of the optical parts shown an evaluation circuit 4 to 8, with the help of which an evaluation of the multispectral sensor 3 coming signals. From the connector pins 22 of the multispectral sensor 3 signals A1 to A4 via filter 4 and amplitude evaluators 5 fed to a logic unit 6. The logic unit 6 is simultaneously connected to a memory 7, in the basic spectral pattern of the emission characteristic radiation objects of a different type but different from one another 9 are stored. So that the basic pattern for comparison are suitable with the help of a multispectral sensor of the type used and therefore contain an exact Image of the spectra selected by the multispectral sensor 3 become. An important distinction is made here the amplitudes in the different spectral channels that can be detected with the aid of the amplitude evaluator 5. To be different strong radiation objects the relation of that of the multispectral sensor signal strengths recorded in the different spectra to relativize, a summer 10 is provided, which consists of the signals A1 to A4 generates a base signal A0, which is used as a comparison signal can serve.

Is the match determined by the logic unit 6 between one of the basic patterns stored in the memory 7 and one Signal analysis within the multi-spectral sensor permissible limits, this is an identification of the radiation object 9 accepted and reported to an output unit. This in turn can now be used for an identifying one Provide notification, or the notification using appropriate tools prepare for remote transmission.

Claims (16)

1. A passive infra-red detector with an optical system (1) which focuses a thermal radiation (2) onto an infrared sensor (3), which radiation incident from the area of a room is emitted from a radiation object (9) to be detected, which sensor generates an electric signal which is used for an alarm which makes the appearance of a radiation object (9) recognisable in a monitored room, characterised in that a multi-spectral sensor is used as an infra-red sensor (3) which breaks down the incident heat radiation into several discrete wavelength ranges and produces for the same respective wavelength-dependent electric signals (A1 to A4) and that an evaluation circuit (4 to 8) evaluates the electric signals (A1 to A4) depending on the radiation objects (9) to be proven with specific emission characteristics and emits an alarm identifying the type of the radiation object (9).
2. A passive infra-red detector as claimed in claim 1, characterised in that the evaluation circuit (4 to 8) comprises a memory (7) in which the basic patterns of the emission characteristics of different radiation objects (9) to be distinguished are stored.
3. A passive infra-red detector as claimed in claim 2, characterised in that the respective basic pattern defines the signals in the individual spectral channels and a mean value of their voltage amplitudes and the determination of the respective basic pattern occurs according to the wavelength spectra selectable by the multi-spectral sensor (3).
4. A passive infra-red detector as claimed in claim 2 or 3, characterised in that the evaluation circuit comprises a logic unit (6) which compares the individual signal spectra coming from the multi-spectral sensor (3) with the signal spectra coming from the memory (7) and determines the radiation object (9) with the highest coincidence between the measured values and the stored values.
5. A passive infra-red detector as claimed in claim 4, characterised in that the logic unit (6) controls an output unit (8) in such a way that the same generates an alarm characterising the identified radiation object (9) and emits the same directly or by way of remote transmission.
6. A passive infra-red detector as claimed in claim 4 or 5, characterised in that the evaluation circuit (4 to 8) is provided with amplitude evaluators which are integrated in the logic unit (6) or are connected in the incoming circuit with the same and are used for detecting the respective mean values of the voltage amplitudes in the individual spectral channels.
7. A passive infra-red detector as claimed in claim 4 or 5, characterised in that in addition to the signals (A1 to A4) formed by the individual spectral channels, a base signal (A0) is provided which detects the entire spectral range and supplies this to the logic unit (6) as a reference value.
8. A passive infra-red detector as claimed in claim 7, characterised in that a summer (10) is used for producing the base signal (A0) which sums up the remaining signals (A1 to A0) representative of the entire spectral range.
9. A passive infra-red detector as claimed in claim 7, characterised in that the base signal (A0) already comes from the multi-spectral sensor (3) which produces it from an infra-red signal representative of the total wavelength range.
10. A passive infra-red detector as claimed in one of the preceding claims (7 to 9), characterised in that the logic unit (6) uses the mean value of the voltage amplitude of the total wavelength range as a basic value for the comparison with a respective value coming from the memory (8) and considers the amplitude ratio of said two values in the overall evaluation.
11. A passive infra-red detector as claimed in claim 5, characterised in that in addition to the signals (A0 to A4) for the individual spectral channels at least one special signal (AS) is provided which supplies the logic unit (6) with at least one special information which facilitates the identification of the radiation object (9) or influences the type of its output to the output unit (8).
12. A passive infra-red detector as claimed in one of the preceding claims, characterised in that the multi-spectral sensor (3) is provided with an aperture (30) which is approximately disposed in the focal plane of the focussing optical system (1).
13. A passive infra-red detector as claimed in claim 12, characterised in that the total radiation (14) entering the interior of the multi-spectral sensor (3) by way of the aperture (30) is dispersed at first spatially and then spectrally and thereafter reaches optoelectric transducer elements (38).
14. A passive infra-red detector as claimed in claim 13, characterised in that in the path of the rays behind the aperture (30) there is arranged a separating optical system (34) in the multi-spectral sensor (3) which is used for spatial separation of the total radiation (14) and at least one selectively acting bandpass element is arranged between the same and the transducer elements (38) in each of the thus formed partial path of the rays, which bandpass elements allows the passage of only a relatively narrow wavelength range.
15. A passive infra-red detector as claimed in claim 14, characterised in that the bandpass element is a selectively reflecting mirror (34), an optical filter (35) or a selectively acting transducer element (38).
16. A passive infra-red detector as claimed in one of the preceding claims, characterised in that the evaluation circuit (4 to 8) comprises electric bandpass filters (4) which allow the passage only of signals (A1 to A4) of a specific spectrum.

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