JPS6266129A - Infrared detector - Google Patents

Abstract

PURPOSE:To set S/N of the output of a detecting body to >=10dB even if a temperature difference of the inside and the outside of a visual field range, by setting an infrared ray which is made incident on an infrared detector, to transmission and non- transmission states alternately, by a pair of vibrating bodies and opposed bodies, and setting the maximum incident angle to <=90 deg.. CONSTITUTION:A position relation of opposed bodies 10, 11 is varied periodically by a periodical vibration in the reverse direction of vibrating bodies 8, 9, and a state that a slit 12 is superposed on each other and opened or closed in repeated. An infrared ray which is made incident on an infrared detecting body 6 from an opening 3 is varied periodically, and a signal corresponding to a difference between a temperature of a part whose temperature is measured and a temperature of the opposed body is outputted. When the maximum incident angle theta is set to <=90 deg., and a temperature of an object to be detected, within a visual field range, and a temperature of the outside of the visual field range are 0 deg.C and 100 deg.C, respectively, an energy ratio of both of them goes to about 9%, and S/N of the output of the detecting body 6 goes to 21dB. Accordingly, even if a temperature difference of a heat source between the inside of the visual field range and the outside of the range is large, the S/N can be set to >=10dB.

Description

[Detailed description of the invention] Industrial application field The present invention relates to an infrared detector.

(b) Prior art Currently, as an infrared detector, US Pat. No. 4,485,305
As disclosed in the above specification, there is a chopper mechanism that is made smaller by forming a piezoelectric body and a pair of opposing bodies. 7 to 9 show such an infrared detector, (1) a sense case consisting of a metal header (2) and a cap (4) having a circular opening (3), (5)
(6) is an infrared transmitting filter fixed to the cap (4) so as to cover the opening (3), and (6) is a pyroelectric filter disposed inside the sensor case (1) facing the window (3). The detector is an infrared detector, and the detector is made of a lithium tantalate (LiTaO) single crystal that generates an electric charge based on the amount of change in incident infrared rays. (7) is a chopper mechanism that changes the infrared rays incident on the detection body, and the chopper mechanism is attached to a pair of piezoelectric vibrating bodies (8) and (9) and to each end of the vibrating bodies (8) and (9). A pair of fixed opposing bodies 10) (11)
The opposing bodies (10) and (11) each have a plurality of slits (12>(12)...) formed in the same shape and size that allow infrared rays to pass through.(13)
) is a shield body that covers the infrared detection body (6),
The shield body is provided with a small hole (14) at a position facing the opposing body (10) (11>).

Therefore, the vibrating bodies (8) and (9) are moved in opposite directions (sixth
(A or B direction in the figure), and as a result, the relative positional relationship of the opposing bodies (10) and (11) changes periodically, and each of the three opposing bodies (10) and (11) A state in which the slits <12) (12) . . . are overlapped and opened and a state in which the slits (12) (12) . Then, in the above-mentioned superimposed state, the infrared rays from the temperature-measuring part are transmitted through the sensor case.
) infrared transmission filter (5), both opposing bodies (10) (1
1) slits (12) (12)... and small holes (14)
), and in the non-overlapping state, only the infrared rays from the opposing bodies (10, 11) pass through the small hole (14) and enter the infrared detector (6).
Therefore, the amount of incident infrared rays changes periodically on the infrared detecting body (6), and the temperature of the temperature measured part and the opposite body (1) change periodically.
0) Outputs a signal according to the temperature difference from the temperature of (11).

In addition, the viewing range of the device that refuses is 1 as shown by diagonal lines in Figure 9.
．． Small hole (14) of shield body (13) and detection body (6)
It is possible to detect only the infrared rays emitted from only the temperature-measuring parts located within the field of view.

(c) Problems to be Solved by the Invention In such a configuration, infrared light emitted from outside the field of view is also diffracted at the slits (12), (12), etc., and the inner wall of the cap (4), the shield body (13) ) The light is reflected by the inner wall and is incident on the infrared detector (6).

Figure 10 shows the results of measuring the visual field characteristics (equal sensitivity distribution characteristics) in this type of conventional device.Such measurements were performed when a point heat source was placed on the center line of the visual field (dotted chain line C in Figure 9). The output generated from the infrared detector (6) is the reference value (100%
), the relationship between the heat source position centered on the center line C and the output of the infrared detector (6>) was measured when the point heat source was moved on a spherical surface centered on the fulcrum O. ,
The directions shown in the figure are up, down, left and right, but these directions correspond to the directions shown by arrows in FIG.

Further, FIG. 11 shows the average relative output of each heat source position equiangular from the center line C.

Now, if the viewing angle θ' is 24 degrees, the viewing range in Figure 10 is within the 12" line. Also, the 0.2% output line indicating the output of 0.2% of the reference value is the 10th As is clear from the figure, it spreads up to 30 degrees in the left and right direction,
Moreover, it also extends downward by more than 20 degrees.

Next, using the average relative output shown in FIG.
Find the ratio V+/V+ with l.

The sum of the sums Vl and Vt is equivalent to the volume of the solid formed by rotating the graph in FIG. It is equivalent to the volume. Total sum again! is equivalent to the volume obtained by subtracting the total Vl from the volume of the solid created by the above rotation.

Therefore, from the graph shown in FIG. 11, the above V 1 / V
+ is about 13%, and the SN ratio is 201og
(V I / V r )--(1) Calculated from Tou's formula and becomes 18 dB.

As described above, when a heat source of the same temperature exists inside and outside the viewing range, the S/N ratio of the output of the infrared detector (6) is 10 dB or more, which poses no practical problem.

However, if the heat source (non-sensing object) within the visual range is OoC and the entire area outside the visual range is 100°C, the relative output outside the visual range will be 5 times that of the relative output within the visual range. Therefore, V I/V 1 increases to 75%, and along with this, the S/N ratio becomes extremely poor at 2.5 dB.

(2) Means for Solving the Problems The present invention has been made in view of the above points, and its structural features include an infrared detecting body that generates a charge according to the amount of change in incident infrared light, and an infrared rays directed to the detecting body. first and second opposing bodies disposed in the incident area and having both an infrared transmitting part and an infrared non-transmitting part;
A state in which the infrared transmitting part and the infrared non-transmitting part of the first opposing body overlap with the infrared non-transmitting part and the infrared transmitting part of the second opposing body, and the infrared transmitting part of the first and second opposing body and In order to repeat the state in which the non-infrared transmitting parts overlap each other, first and second vibrating bodies that respectively vibrate the first and second opposing bodies, and the respective components are housed, and the infrared detection The device includes a case having an opening for infrared rays incident at a position facing the body, and the maximum incident angle θ when looking at the infrared transmitting portion from the opening is 90° C. or less.

(E) Effect With this configuration, even if there is an object to be detected at O''C within the field of view and a heat source at 100℃ outside the above range, measurement can be performed with an accuracy of 10 dB or more in S/N ratio. be.

(f) Example FIGS. 1 and 2 show the results of experiments conducted by the present inventors.

Figure 1 shows the visual field characteristics in which the position of the output line of 0.2% of the reference output is separated from the visual field (hereinafter referred to as the extrusion angle), and there is an f8 source at 0°C within the visual field.
The relationship between the output of the infrared detector and the S/N ratio was investigated when the temperature of the entire area outside the visual field was 100°C.

As is clear from FIG. 1, it was found that when the protrusion angle of the 0.2% output line was 7'' or less, the S/N ratio of the output of the infrared detector was 10 dB.

Furthermore, as shown in FIG. 9, FIG. 2 shows the half-value angle 0/2 of the maximum incident angle θ of the opposing body (11) into the slit (12) seen from the aperture (3) and the protrusion of the above 0.2% output line. The results of investigating the relationship with angle are shown.

As is clear from FIG. 2, it has been found that in order to make the protrusion angle of the 0.2% output line 71 or less, it is necessary to satisfy θ/2≦45°, that is, θ≦90@.

FIG. 3 shows an embodiment of the present invention constructed based on the above results. Note that the same parts in FIG. 3 as in FIG. 9 are denoted by the same numerals, and a description thereof will be omitted.

In the device of this embodiment, the viewing range is defined by the infrared detector (6) and the aperture (3), and the viewing angle θ' is approximately 24°. Further, the maximum angle of incidence θ to the slit (12) as seen from the aperture (3>) is 62°.

The average visual field characteristics of the device of this embodiment configured in this way are shown in FIG. 4. This FIG. 4 is similar to FIG.
indicates the average relative output of each heat source position equiangular from
At this time, as is clear from FIG. 4, the protrusion angle of the 0.2% output line is 4 degrees.

In addition, if there is a heat source that has the same temperature both inside and outside the viewing range, the outside of the viewing range (the 4th
The ratio of the relative output total Vl in the shaded area H) in the figure is V
l/Vl is about 1.8%, so the infrared detector (6
) is approximately 32 dB. Further, assuming that the temperature of the object to be detected within the visual field is 0°C and the temperature of the entire area outside the visual field is 100°C, the above energy ratio V +
/V+ is approximately 9%, and along with this, the S/N ratio is 21
dB.

As a second example, when the maximum incident angle θ is 62°, 0
．． Based on the result of the first embodiment that the protrusion angle of 2% becomes about 4%, the geometric viewing angle θ' defined by the infrared detector (6) and the aperture (3) is set to 16". It is something.

The visual field characteristics of the apparatus of this embodiment constructed in this manner are shown in FIGS. 5 and 6.

Incidentally, FIG. 6 shows the average relative output of each heat source position equiangular from the center line C in the equal sensitivity distribution shown in FIG.

As is clear from the 5th fsA, a substantially uniform equal sensitivity distribution is shown with respect to the center line C, and the 0.2% output line substantially overlaps with the 12° position line. In addition, if heat sources of the same temperature are placed around the center line C, the area 1 within 12@line
(See Figure 6) relative output total V1 of the area layer outside the 12° line (clearly indicated by diagonal lines in Figure 6)
The ratio of l is approximately 1.0%, and therefore, if the field of view is an area where the half-value angle is 12'' centered on the center line C, the S/N ratio of the output of the infrared detector ← 6) is approximately 40 dB. Become.

Further, the above energy ratio V x / V when there is a detected object at 0°C within the viewing range within the half-value angle of 12° and the temperature of the entire area outside the viewing range is 100°C.
+ is 5%, and accordingly the S/N ratio is approximately 28 dB.

In this way, the geometric field of view defined by the infrared detector (6) and the aperture (3) is set to 0, which corresponds to the maximum angle of incidence.
By narrowing down in advance by the protrusion angle of 2% output, more accurate measurement becomes possible.

(G) Effects of the Invention According to the present invention, even if the temperature difference between the heat source within the viewing range and that outside the viewing range is large, the S/N ratio of the output of the infrared detector can be reduced to 10.
It can be more than dB.

[Brief explanation of drawings]

Figures 1 and 2 are graphs showing the experimental results that formed the basis of the present invention, Figure 3 is a sectional view showing the first embodiment of the present invention, and Figure 4 is the equal sensitivity of the first embodiment. FIGS. 5 and 6 are characteristic diagrams showing the distribution of equal sensitivity according to the second embodiment of the present invention, FIGS. 7 to 11 show the conventional example, and FIGS.
The figure and FIG. 9 are cross-sectional views, No. sr5! J is a partially enlarged plan view, and FIGS. 10 and 11 are equal sensitivity distribution characteristic diagrams. (1)...Case, (3)...Opening, (6)...
Infrared detection body, (10) (11)... Opposing body, (12
)...Slit (infrared transmitting part), θ...Maximum incident angle.

Claims (1)

[Claims] (1) An infrared detecting body that generates a charge according to the amount of change in incident infrared rays, first and second opposing bodies that are arranged in the infrared incident area to the detecting body and have both an infrared transmitting part and an infrared non-transmitting part; The state in which the infrared transmitting part and the infrared non-transmitting part of the first opposing body overlap with the infrared non-transmitting part and the infrared transmitting part of the second opposing body, and the infrared transmitting part and the infrared non-transmitting part of the first and second opposing bodies overlap, respectively. In order to alternately repeat the state in which the transparent parts overlap each other, first and second vibrating bodies that vibrate the first and second opposing bodies, respectively, house the respective components and face the infrared detecting body. An infrared detector, comprising: a case having an opening for infrared incidence at a position where the infrared rays enter, and a maximum incidence angle θ when looking at the infrared transmitting portion from the opening is 90° or less.