Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1984-09-17
1987-02-03
Rowland, James L.
Communications: electrical
Condition responsive indicating system
Specific condition
340600, G08B 1318
Patent
active
046411348
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention is related to an alarm detector for the detection of e.g. unauthorized entry by detecting the radiation given off by the intruder.
BACKGROUND OF THE INVENTION
It has long been known in the art to detect the presence of human beings and animals by detecting the heat radiation that they emit. The devices that have generally been used for the purpose contain an infrared-sensitive detector of some kind, generally one of the types pyroelectric, thermopile detector, certain semiconductor detectors such as lead sulphide detectors, or similar. These detectors are either insensitive, expensive, require cooling, or draw continuous current during their use.
An alarm detector which functions in such a manner that it draws very little or no current when it does not sense any signal, which does not require cooling, has low inherent noise, and is inexpensive, would find wide application. One consequence of these properties is that it need not necessarily be connected to the mains even if it operates for years.
SUMMARY OF THE INVENTION
The purpose of the present invention is therefore to provide a device for the detection of unauthorized entry by detecting the heat radiation given off by the intruder. Such device shall be cheap and simple to manufacture, draw very little current when not sending an alarm signal, and have high sensitivity.
The device of the invention, allows detecting moving bodies that are warmer or cooler than a static environment, contains an infrared-sensitive detector that is connected to a preamplifier and a signal processing unit arranged to emit electrical signals to an output means. According to the invention, the detector consists of a Peltier element with one hot side and one cold side and a current supply terminal. One of the hot or cold sides of the Peltier element is placed in good thermal contact with a heat sink of high heat capacity and the other side is arranged to serve as the radiation-sensitive detector surface of the detector, and the current supply terminal of the Peltier element is connected with the input to a band-pass filter whose output is connected to the input of the preamplifier.
It is moreover appropriate, according to the invention, for the preamplifier and the signal processing unit both to be based on C/MOS technology and for the signal processing unit to be arranged not only to initiate current supply to the output but also to send an alarm signal to the output when an alarm situation arises.
It is also advantageous for the side of the Peltier element that serves as the radiation-sensitive detector surface to be provided with a heat-absorbing layer.
The invention is described more particularly below with reference to the attached FIGS. 1 through 3, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the general structure of a Peltier element as known in the art.
FIG. 2 shows the construction of the detector unit according to the present invention.
FIG. 3 shows the electronic circuitry of a device according to the invention in the form of a block diagram.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the typical structure of a Peltier element. Such elements are normally used for heating or cooling objects, such as a component requiring to be cooled. Detectors, too, are often cooled by means of Peltier elements, often cascaded. Thus the Peltier element is not designed to be used as a detector. However, it is cheap, has low internal impedance, is strong, and has large surface area compared to most detectors. Moreover, it does not require any current supply, but actually produces current when there is a temperature difference between the hot side 6 and the cold side 7. The Peltier element consists of a number of p-n junctions connected in series between two current supply terminals 10, 12.
FIG. 2 shows the construction of the detector unit 1 of the device according to the invention. The Peltier element 5 is arranged with its hot side 6 to the heat sink 8, which is preferably a block of metal with high therm
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Rowland James L.
Tumm Brian R.
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