JPH0447634Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention relates to a pyroelectric infrared detector used for human body detection, etc. In an anti-series two-element infrared detector, a pair of infrared elements connected in anti-series are used. By setting the viewing angle difference between the light-receiving electrodes in the range of 5° to 10°, it is possible to obtain an infrared detector with high detection accuracy without reducing detection ability and with less noise caused by ambient light. This is what I did.

BACKGROUND ART As infrared detectors, thermopiles, thermistor bolometers, pyroelectric detectors, and the like are conventionally known. Among these, pyroelectric infrared detectors have the highest sensitivity as infrared detectors for human body detection, and have been widely used.

Figure 6 is a sketch of a conventional pyroelectric infrared detector used for human body detection, showing a metal cap 1 and a stem 2 that seals the bottom side of the metal cap 1.
An infrared detection element 4 is placed inside a metal package consisting of an optical window 3 formed on the top side of the metal cap 1.
is stored. Metal package cages are usually TO
It is a small one called -5 with a diameter of about 9 mmφ. The infrared detection element 4 has a pair of light-receiving electrodes 42 and 43 provided on one surface of a thin plate-like pyroelectric element 41, and is arranged on the surface of the support base 5. The support stand 5 is supported at a distance above the stem 2 by a lead terminal 6 which also serves as a support.

FIG. 7 is an electrical circuit diagram of this type of pyroelectric infrared detector, in which a pair of light receiving electrodes 42 and 43 formed on the surface of a pyroelectric element 41 are connected to each other with respective spontaneous polarization characteristics P ₁ ,
Connect so that P ₂ is in anti-series. RL is the load resistance.

In the above-mentioned pyroelectric infrared detector, when infrared rays emitted from a human body act only on the light-receiving electrode 42, the light-receiving electrode 42 generates a signal across the load resistor RL. In this case, the light receiving electrode 43 acts only as a capacitor. Further, when infrared rays act only on the light-receiving electrode 43, a signal with a polarity opposite to that in the case of light reception by the light-receiving electrode 42 is generated at both ends of the load resistor RL. Also in this case, the light receiving electrode 42 acts only as a capacitor.

Furthermore, when the ambient temperature of the infrared detector changes, since the light receiving electrodes 42 and 43 are connected in anti-series so that their spontaneous polarization characteristics have opposite polarities, they generate signals with opposite polarities. and load resistance
No signal appears at either end of RL. For this reason,
The S/N ratio is improved.

Problems that the invention aims to solve However, in conventional pyroelectric infrared detectors, few measures have been taken to eliminate the influence of ambient light from, for example, automobile headlights, and it is difficult to eliminate noise caused by ambient light. There was a problem with this occurring. The disturbance light is transmitted to the light receiving electrodes 42 and 43
There is no problem if the light is applied equally to the light receiving electrodes 42 and 43, but in general, the disturbance light acts unevenly on the light receiving electrodes 42 and 43. Therefore, the light-receiving electrodes 42 and 43 do not cancel out the disturbance light, resulting in noise.

Means for Solving the Problems In order to solve the above-mentioned conventional problems, the present invention provides a pair of light-receiving electrodes on the surface of a pyroelectric element, and divides the pair of light-receiving electrodes into each other according to their respective spontaneous polarization characteristics. In an infrared detector connected in anti-series,
The device is characterized in that the viewing angle difference between the pair of light receiving electrodes in the light receiving front is set in a range of 5° to 10°.

In the infrared detector having the general structure shown in FIG. 6, the parameters that affect the deviation of the viewing angle are the aperture of the optical window 3 formed on the upper surface side of the metal cap 1, and the distance from the light receiving electrodes 42 and 43 to the optical window. 3, the distance between the light receiving electrodes 42 and 43, the electrode width, etc. By appropriately selecting these parameters, the viewing angle deviation is set within the range of 5° to 10°.

Effect As mentioned above, it has been found that when the viewing angle difference between the pair of light-receiving electrodes is set to 10 degrees or less, noise caused by ambient light can be significantly reduced compared to the conventional one. This is presumed to be because when the viewing angle difference between the pair of light-receiving electrodes is set to 10 degrees or less, the irradiation of the disturbance light onto the pair of light-receiving electrodes becomes more uniform than in the conventional case. However, if the viewing angle is too small, although it is effective in preventing noise due to ambient light, the effective light-receiving area of the light-receiving electrode becomes narrow, making it impossible to ensure the necessary detection ability.
It was found that in order to ensure the necessary detection ability and prevent noise caused by ambient light, the viewing angle deviation needs to be set to 5 degrees or more.

Embodiment FIG. 1 shows the structure of an infrared detector according to the present invention,
4 is a diagram showing viewing angles of light receiving electrodes 42 and 43. FIG. In FIG. 1, the support stand 5 and lead terminals 6 are omitted from illustration. The parameters that determine the viewing angle are the window diameter D ₁ of the optical window 3, the distance d ₁ from the light-receiving electrodes 42 and 43 to the optical window 3, and the electrode width of the light-receiving electrodes 42 and 43.
The distance w ₁ and the distance g ₁ between the light receiving electrodes 42-43 were selected as follows.

D ₁ = 6 mmφ d ₁ = 1.5 mm w ₁ = 0.5 mm g ₁ = 0.5 mm As a result, the viewing angle ω ₁₁ when looking from the inner edge of the light receiving electrode 42 to the inner peripheral edge 101 of the metal cap 1 is as follows.
The viewing angle ω ₁₂ from the outer edge to the inner peripheral edge 101 of the metal cap 1 was about 70°, which was about 63° with respect to the surface normal n of the infrared detecting element 4. Also in the light receiving electrode 43, the viewing angle ω ₂₁ seen from the inner edge is about 63°, and the viewing angle ω ₂₂ seen from the outer edge is about 70°. Therefore, the viewing angle difference Δω between the light receiving electrodes 42 and 43 with respect to the light receiving front is Δω=ω ₂₂ −ω ₁₁ =7° or Δω=ω ₁₂ −ω ₂₁ =7°, which means that the viewing angle of about 7° A deviation Δω has occurred.

Comparative Example FIG. 2 is a diagram showing viewing angles of light receiving electrodes 42 and 43 in a conventional infrared detector. The window diameter D ₁ of the optical window 3, the distance d ₁ from the light-receiving electrodes 42, 43 to the optical window 3, the electrode width w ₁ of the light-receiving electrodes 42, 43, and the interval g ₁ between the light-receiving electrodes 42-43 are as follows. Selected.

D ₁ = 6 mmφ d ₁ = 1.5 mm w ₁ = 1 mm g ₁ = 1 mm In this comparative example, the viewing angle ω ₁₁ when looking from the inner edge of the light receiving electrode 42 to the inner peripheral edge 101 of the metal cap 1 is approximately 60°. The viewing angle ω ₁₂ when viewing the inner circumferential edge 101 of the metal cap 1 from the outer edge was approximately 72°. Even for the light-receiving electrode 43, the viewing angle ω ₂₁ when viewed from the inner edge
is approximately 60°, and the viewing angle ω ₂₂ when looking from the outer edge is approximately 72°.
It was hot. Therefore, the viewing angle deviation Δω between the light receiving electrodes 42 and 43 is Δω=ω ₂₂ −ω ₁₁ =12° or Δω=ω ₁₂ −ω ₂₁ =12°, and the viewing angle deviation Δω of 12° or more is It is occurring. Due to such a large viewing angle deviation Δω, conventional infrared detectors cause noise due to disturbance light.

Next, each of the infrared detectors shown in the example shown in Fig. 1 and the comparative example shown in Fig. 2 was incorporated into a normal intruder alarm, and a disturbance light on/off test was conducted under the conditions shown in Fig. 3. . In FIG. 3, 7 is a disturbance light source of a 100W white lamp, 8 is an infrared detector, and 9 is an intrusion alarm, which has a low frequency amplifier with an amplification factor of 10,000 times.

FIG. 4 shows the data of the infrared detector according to the present invention obtained under the measurement conditions shown in FIG. 3, and FIG. 5 shows the data of the conventional infrared detector. As shown in FIG. 5, in the conventional infrared detector, extremely large noise appears when the disturbance light source 7 is turned on and off, but in the infrared detector according to the present invention, the disturbance light source 7
It can be seen that almost no noise is generated even when the light is turned on and off, and that an extremely large effect can be obtained in preventing noise caused by ambient light.

Effects of the invention As described above, the present invention provides an infrared ray that includes a pair of light-receiving electrodes on the surface of a pyroelectric element, and connects the pair of light-receiving electrodes so that their respective spontaneous polarization characteristics are in anti-series. In the detector, the viewing angle difference between the pair of light-receiving electrodes in front of the light-receiving surface is set to 5° to 10°.
, it is possible to provide an infrared detector with high detection accuracy and less noise caused by ambient light without reducing the detection ability.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the structure of an infrared detector according to the present invention and the viewing angle of the light receiving electrode, Figure 2 is a diagram showing the structure of a conventional infrared detector and the viewing angle of the light receiving electrode, and Figure 3 is a diagram showing the structure of a conventional infrared detector and the viewing angle of the light receiving electrode.
The figure shows the noise measurement conditions for the disturbance light of each infrared detector shown in Figures 1 and 2, and Figure 4 shows the conditions for measuring noise in the disturbance light of each infrared detector shown in Figures 1 and 2.
The data of the infrared detector according to the present invention obtained under the measurement conditions shown in the figure, Figure 5 is the data of the conventional infrared detector, Figure 6 is the sketch of the conventional infrared detector, and Figure 7 is the same symbol. It is a diagram. DESCRIPTION OF SYMBOLS 1... Metal cap, 2... Stem, 3... Optical window, 4... Infrared detection element, 42, 43... Light receiving electrode, _ω11 , _ω12 , _ω21 , _ω22 ... Viewing angle.

Claims (1)

[Scope of utility model registration request] In an infrared detector in which a pair of light-receiving electrodes are provided on the surface of a pyroelectric element, and the pair of light-receiving electrodes are connected so that their respective spontaneous polarization characteristics are in anti-series, the distance between the pair of light-receiving electrodes at the front of the light-receiving element is An infrared detector characterized in that the viewing angle deviation is set in the range of 5° to 10°.