JPH0412434Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a pyroelectric infrared detection device used for crime prevention and fire prevention.

A sensor is known in which a pyroelectric infrared detection element is housed in a single package together with an amplifier circuit, etc. to detect a human body, etc., but since this sensor also detects fire, the sensor output can detect human bodies, etc. Unable to distinguish between fires. For this purpose, two methods are used: one that detects a human body for crime prevention and one that detects fire for fire prevention. That is, FIG. 5 shows the infrared spectra of fire (A) and human body (B), and one sensor is used to identify and detect each of these. Therefore, there is a drawback that a large space is required for the infrared detection element itself and the circuit system. These sensors also have a problem in that their output electrical signals change due to changes in ambient temperature and pressure, and such noise output may generate false alarms.

The present invention was developed in view of the above circumstances, and aims to provide a miniaturized pyroelectric infrared detection device that incorporates elements for crime prevention and fire prevention into one package. The present invention will be specifically explained below based on a circuit showing an embodiment thereof.

FIG. 1 is a schematic cross-sectional view of a pyroelectric infrared detection device according to the present invention (hereinafter referred to as the device of the present invention), and 31 is a metal stem for mounting the infrared detection elements 10 and 20; 10,2
0 is in a space hermetically sealed with a metal cap 32. An appropriately sized window 32 is provided on the upper surface of the metal cap 32 (the part facing the stem 31).
A window 32a is opened, and this window 32a is sealed with a window plate 33 made of an infrared transparent material. This window 32a provides access to the metal cap 32 from the monitored space.
This is for injecting infrared rays into the interior, and when this device is installed on the ceiling of a room, the window 32a side will be the lower side, for example. 0.8~ for window board 33
A Si or Ge plate with a thickness of several hundred μm that efficiently transmits infrared light with a wavelength of 15 μm is suitable.

The infrared detecting elements 10 and 20 are formed by forming separate electrode layers on the surface of one half region 411 and the other half region 412 of a pyroelectric thin plate 41 made of LiTaO ₃ (lithium tantalate), respectively, at an appropriate distance apart. 12, 22
In addition, an electrode layer 42 common to both elements is formed on the back surface to a thickness of 500 to 1000 Å using the Ni-Cr vapor deposition method, and the back electrode layer 42 is fixed to the upper surface of the stem 31. For example, a copper support stand 34
It is fixed through an insulating layer 35 made of epoxy resin or the like.

Infrared detection elements 10 and 20 in window plate 33
Optical filters 13 and 23 formed by depositing multiple layers of PbTe, ZnS, etc. are placed above the surface electrode layers 12 and 22, in other words, in the regions facing the surface electrode layers 12 and 22, respectively.
The electrode layer 12, 2 is placed at that position so as to cover the electrode layers 12, 22.
2 and are provided in alignment with each other. These optical filters 13 and 23 have different transmission wavelengths, and the optical filter 13 selectively transmits infrared rays with a wavelength of 5 μm or more for human body detection, and substantially cuts out infrared rays with shorter wavelengths. The low-cut (high-pass) filter or optical filter 23 is a bandpass filter that selectively transmits infrared rays with wavelengths in the range of 0.8 to 7 μm for fire detection, and substantially cuts infrared rays with wavelengths outside this range. Note that it is desirable that the transmission characteristics of these optical filters 13 and 22 be similar to those shown in ○A and ○B in FIG. 5, respectively. The areas and positions of both optical filters 13 and 23 are such that each of the infrared detection elements 10 and 20 selectively captures the infrared rays that have passed through each of the optical filters 13 and 23, and captures as much as possible the infrared rays that have passed only through the window plate 33. It is determined not to be captured.

The surface electrode layers 12, 22 of both the elements 10, 20 are connected to one end of each lead wire 14, 24 made of gold wire or the like. There is a joint type on the stem 31.
A FET (field effect transistor) 36 is provided, and the other end of the lead wire 14 is connected to the gate of the FET 36. Further, the other end of the lead wire 24 is connected to the stem 31. The drain and source of the FET 36 are connected to lead wires 37 and 38 insulated from the stem 31, and the other lead wire 39 is at the same potential as the stem 31. These lead wires are for connection to external circuits.

FIG. 2 is an electrical circuit diagram of the proposed device, in which the stem 31 and lead wire 39 mentioned above are set at the ground level,
A positive potential V _DD is applied to the drain or lead wire 37 of the FET 36, and an output V _put is obtained from its source or lead wire 38. A gate resistor 43 on the order of 10 ⁹ to 10 ¹¹ Ω and a source resistor 44 on the order of 10 KΩ are connected between the gate and source of the FET 36 and the ground level stem 31 or lead wire 39 to apply a self-bias. . Note that the gate resistor 43 is arranged in the cap 32 together with the FET 36, and the source resistor 44 is an external resistor. In the present device, both elements 10 and 20 share the pyroelectric thin plate 41 and also share the back electrode layer 42, so both elements are connected in series so that their polarization directions are opposite. .

The operation of the present device having such a configuration is as follows. That is, when infrared rays (5 μm or more as shown in FIG. 5) emitted by the human body enter the device through the window plate 33, most of this infrared rays is transmitted only through the filter 13 and is absorbed by the surface electrode layer of the element 10. Negative charge is generated on the 12 side, and the output V _put is lower than the normal level. Also, when a fire occurs, for example, infrared rays from the flames (as shown in Figure 5, the peak is about 2 μm)
When the infrared rays (distributed around 0.8 to 7 μm) enter the device through the window plate 33, most of this infrared rays are passed through the filter 23.
The negative charge is generated on the surface electrode layer 22 side of the element 20, and as a result, the output V _put rises from the normal level. Of course, such level changes can be used to provide remote notification or operate an alarm.

Therefore, when the ambient temperature changes due to heating or the like, both regions 411 and 412 of the pyroelectric thin plate 41
Both exhibit the pyroelectric effect due to their influence, but in the device of the present invention, the polarization directions of the two are reversed and the elements containing each are connected in series, and since both have the same area, the inside of this series circuit This cancels out the charging effect, and there is almost no change in the FET output. Pyroelectric materials also exhibit a piezoelectric effect as is well known, so if the door of a well-tight room in which this device is installed is suddenly closed, a piezoelectric effect will appear in both elements 10 and 20. Since the polarization directions are also opposite, they are canceled out in the same way as above and there is no effect. Note that the light-receiving areas of both elements do not have to be strictly equal, and a difference in the light-receiving areas within a range that does not adversely affect the circuit operation is acceptable.

FIG. 3 shows another embodiment of the invention. Support bases 34', 34' made of a conductive material are fixed on the metal stem 31, and infrared detection elements 10', 20' are mounted on the support bases 34', 34' using a conductive adhesive. 35', 35'. The infrared detecting elements 10', 20' each consist of a front electrode layer 12, 22, a pyroelectric thin plate 11, 21, and a back electrode layer 15, 25.
25 to support stands 34', 3 with adhesive 35', 35'.
It is glued to 4'. The difference from the embodiment shown in FIG. 1 is that the polarization directions of the pyroelectric thin plates 11 and 21 are reversed as schematically shown in FIG. 14' and connected to the gate of FET36. The back electrode layers 15 and 25 are made of adhesive 3
5', 35' and support stands 34', 34', they are collectively connected to the stem 31 and connected to an external circuit by a lead wire 39. FIG. 4 shows the electric circuit of this embodiment, and as is clear from this figure, both elements 10' and 20' are connected in parallel so that their polarization directions are opposite.

Optical filters 13 and 23 having the same transmission wavelength range as before are adhered to the portions of the window plate 33 facing the surface electrode layers 12 and 22. Other parts similar to those in FIGS. 1 and 2 are given the same reference numerals.

In the case of this embodiment as well, infrared rays emitted by the human body enter the interior through the window plate 33 and most of it passes through the filter 13.
The light passes only through the light and is projected onto the surface electrode layer of the element 10'. As a result, a negative charge is generated on the surface electrode layer 12 side, and the output _Vput is lowered from the normal level as in the previous embodiment. On the other hand, when a fire occurs, the infrared rays are transmitted only through the filter 23, and a negative charge is generated on the back electrode layer 25 side of the element 20', resulting in the output V _put being higher than the normal level.

In this case as well, the effects of ambient temperature and pressure are canceled out. As described above, the pyroelectric infrared detection device according to the present invention has two infrared detection elements using pyroelectric materials housed in one package having a window through which infrared rays from a subject are incident. Optical filters with different transmission wavelength ranges are deposited on the window in alignment with the positions of each infrared detection element, and the two infrared detection elements are connected so that their polarization directions are opposite. Because it is crime prevention,
A device that also serves as fire protection can be configured to be extremely compact, and a system that can distinguish and detect a human body from a fire can be easily realized. Furthermore, an optical filter for distinguishing between a human body and a fire is placed on the window plate that seals the window in the cap, making assembly easy. Furthermore, the present invention has excellent effects such as no noise output due to changes in ambient temperature and pressure.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a schematic cross-sectional structural diagram thereof, Fig. 2 is an electric circuit diagram, Fig. 3 is a schematic structural diagram of another embodiment, and Fig. 4. is its electrical circuit diagram, and Figure 5 is the infrared spectrum of fire and human body, respectively. 10,20...Infrared detection element, 11,21,
41,...Pyroelectric thin plate, 12,22...Surface electrode layer, 13,23...Optical filter, 15,25,
42... Back electrode layer, 36... FET.

Claims (1)

[Claims for Utility Model Registration] A package having a window through which infrared rays from a subject are incident; and a package housed within the package, connected to each other so as to have opposite polarization directions and to output detection signals to a common line. Two infrared detection elements using a pyroelectric material, and an optical filter having different transmission wavelength ranges and formed on the window and aligned with each infrared detection element storage position, the two infrared detection elements The pyroelectric infrared detection device is characterized in that it outputs different detection signals to the common line depending on the wavelength of incident infrared rays.