DE2903610A1 - Monitor with radiation source and detector - has evaluation circuit with reference with inbuilt thermal elements and projection via lens - Google Patents

Abstract

A monitoring system consists of a radiation source and a radiation detector followed by an evaluation circuit. It reduces the chances of triggering the fault alarm unnecessarily. The radiation source is designed as a reference surface which is kept at a given temp. value relative to ambient temp. by heating or cooling. The radiation detector is an opto-electrical radiation detector, which is sensitive to a given wavelength at a given temp. The reference surface contains a built-in thermal element which will measure the temp. There is a good thermal element which measures the ambient temp. It is kept in a medium or in the ground if the monitoring system is out of doors. The reference surface is projected onto the detector via a lens.

Description

"Monitoring order"

The invention relates to a monitoring arrangement with a radiation source, a radiation detector on which the radiation source is imaged and an evaluation circuit which is connected downstream of the radiation detector.

Monitoring systems of this type are e.g. in the form of light barriers known for a long time. The attachments usually contain one in the visible - or infrared light source, a photocell or photodiode as a radiation detector as well as an evaluation circuit connected downstream of the radiation detector9 which triggers an alarm when the light path between the light source and Radiation detector is interrupted i.e. if, for example, the monitored Area being crossed by an intruder. To the background radiation behind Turning off the light source are usually optical means, such as lenses provided in the light path so that only the light stai from the light source is infinite is fed to the radiation detector In addition, filters are usually provided9 which z, B, the radiation component of the light source lying in the visible range absorb. Such an arrangement is e.g. from the publication Elektro-Technik, No. 12, 1964, "Photoelectric anti-theft protection" by K. H. Schröter.

Now, however, a number of possibilities are conceivable by which a flour alarm can be triggered or the monitoring can be bypassed. For example if small light sources or narrow bundles of light are used, a false alarm will be triggered be triggered by small objects, such as birds When using large ones Radiation sources, on the other hand, can influence environmental influences, such as changing solar radiation make disturbing noticeable.

3 for systems with radiation detectors, which in one of the intrinsic temperature are sensitive to a wavelength range corresponding to a human body, can finally be monitored by using a screen with bypass temperature be bypassed.

The invention was therefore based on the object of a monitoring arrangement of the type mentioned at the beginning to indicate which one works casually and the ones mentioned Disadvantages with regard to the triggering of false positives and the bypassability of the monitoring largely avoids.

The object is achieved according to the invention in that the radiation source is designed as a reference surface, which by heating and / or cooling devices kept at a temperature T z Sa + #T which differs from the ambient temperature Ta and that the radiation detector is an optoelectronic radiation detector, of at least one wavelength k corresponding to the temperature T is sensitive to radiation is.

The: Difference #T between the ambient temperature Ta and the one to be observed Temperature 2 should be low, preferably not significantly higher than + 30 ° C. On the one hand, this has the advantage that the energy consumption for heating and / or cooling the reference area can be kept very small.

On the other hand, the radiation emanating from the reference surface is due to des compared to the ambient temperature Da only slightly shifted Radiation maximum very difficult to locate, so that the entire arrangement in its effect is approximately comparable to a passive monitoring arrangement for heating For example, resistance elements can be used for the reference surface, while the cooling can take place, for example, using Peltier elements the reference surface temperature sensors are built in to control the stimulus and / or cooling elements are used. To avoid false alarms from smaller objects , it is advisable to design the reference surface over a large area.

Optical means, such as lenses, are used to remove the surface The emitted radiation is then focused on a radiation detector, which is preferably used Sensitive to radiation in the wavelength range # 2 #### 1 with # 1 <15 µm and # 2> 4 µm is.

A photodiode is preferably used as the radiation detector, a phototransistor or photoresistor, if necessary with an upstream filter in Question. Between the reference surface and the 3rd photodiode, one or more in the infrared permeable filters are arranged, which only for a small Part of the spectrum emitted by the reference surface is radiolucent are.

An evaluation circuit is connected downstream of the radiation detector, which e.g. can be designed in such a way that it responds to rapid changes in a detector signal ID responds.

Such a circuit preferably contains an amplifier and a differentiating element. An alarm can then be triggered, for example, if the differentiated detector signal is too large, or if so where AD is any selectable value> 0.

Should the monitoring arrangement to secure a room used in which there is a substantially constant temperature Ta is sufficient it also keeps the temperature T of the reference surface at a constant temperature T = Ta # #T to hold.

On the other hand, an outdoor area with changing temperature Ta should be secured there is also a corresponding change in the temperature U of the reference surface required so that the desired temperature difference #T can be maintained.

Such a monitoring arrangement should be based on an example under With the help of Figures 1 and 2 will be described in more detail.

Fig. 1 shows the entire arrangement with its most important components. R is the reference area which is created by the cooling and / or heating devices KH is kept at the desired temperature T. In the reference area R is at least a thermocouple Thi installed, which is used to measure the temperature 2. Farther at least one thermocouple Th2 is provided, which is used to measure the ambient temperature Ta serves. If the monitoring arrangement is in the open air, this is useful Bringing thermocouple Th2 into a medium, e.g. in the ground, so that rapid Temperature changes, which can lead to the automatic triggering of the alarm, are avoided will.

Both thermocouples Th1 and Th2 act on a device which the heating and / or cooling devices KH controls.

The reference surface R is then applied to the radiation detector by means of a lens L D pictured. Downstream of the radiation detector D is a signal processing device SV (for processing the detector signal ID) as well as the alarm device controlled by SV A.

Some typical values for dimensioning the arrangement according to the invention are to be found in the following list in summary: distance (L-R): 5m distance (L-D): 4cm diameter (R) 25cm diameter (D): 2mm temperature (R): 1000 PbSe detector alarm triggering: AD = 0.04 s -1 In Qig. 2 is an advantageous one Embodiment of the reference surface shown in cross section The reference surface R consists of a metal plate with a glass cover or a glass plst Metal (M: metal, G: glass, KH: cooling and / or heating device, Th1: thermocouple in the reference area R). A reference surface embodied in this way has a small one Sensitivity to disturbing solar radiation, because e.g. the visible Part of the sunlight (around v = 0.6 / um) is absorbed by the metal - there is heating at the metal / glass interface - and infrared radiation (IR approximately in the range v = 10Xum) is emitted by the glass (glass absorbs IR).

Because of the poor thermal conductivity of glass, the Glass surface only slowly. There is no alarm triggering, even if the cooling elements are not very efficient Blank page

Claims (1)

Claims 1. Monitoring arrangement with a radiation source, a radiation detector on which the radiation source is imaged, as well as an evaluation circuit, which is connected downstream of the radiation detector, thereby characterized in that the radiation source is designed as a reference surface, which by heating and / or boiling devices to one of the ambient temperature Ta different temperature @ = Ta # #T is maintained and that de @ radiation detector is an optoelectric radiation detector, which is at least one temperature T corresponding wavelength k is sensitive to radiation. ? Monitoring arrangement according to Claim 1, characterized in that that when using the monitoring arrangement in an environment with essentially constant temperature Ta a reference surface kept at a constant temperature T. is provided. 3. Monitoring arrangement according to claim 1, characterized in that that when using the monitoring arrangement in a Environment with Changes in the temperature Ta a device for controlling the stimulation and / or cooling devices it is provided such that the temperature 2 of the reference surface corresponds to the ambient temperature Ta is tracked by a predetermined distance AT. 4. Monitoring arrangement according to claims 1 to 3, characterized in that that the difference AT between ambient temperature Ta and the temperature to be maintained T is not selected to be significantly greater than # 30 ° C. 5. Monitoring arrangement according to claims 1 to 4, characterized in that that the radiation detector at least in the wavelength range between # 2 #### 1 with # 1 <15 µm and # 2> 4 µm is radiation sensitive.