JPH04160324A - Pyroelectric infrared detector - Google Patents

Abstract

PURPOSE:To improve the detecting capability both for a short distance and for a long distance without changing a crime prevention system by breaking an output balance of elements and making a gap as small as not larger than 1/4 the maximum size of the photodetecting element. CONSTITUTION:It sometimes happens to exceed a trigger level because of an offset of the output balance of inverse polarities of two elements of a dual element type to an object moving with high speeds at a short distance. If the area is made different for the two photodetecting elements thereby to break the output balance, even if the two elements generate outputs simultaneously, the difference can be obtained as an output. An object moving with high speeds at a far distance becomes a small image moving with low speeds on the elements when the object is condensed by an optical system. Therefore, if a gap between the elements is large, it is difficult to obtain a high output of combined waves. As such, the gap is made as small as not larger than 1/4 the maximum size of the photodetecting element. Accordingly, a high output of combined waves can be obtained easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an infrared detector for detecting a human body used in an intruder alarm or the like.

[Prior Art] Pyroelectric infrared detectors, which are currently widely used in intruder alarms, have two light-receiving elements connected in series or parallel with opposite polarity, and housed in a hermetically sealed package. It is a dual element type detector as shown in the figure.

Normally, when using this detector, an optical system such as a Fresnel lens or a concave mirror is used, and the detector is designed to condense light in multiple areas to manage a wide area.

With such a detector, at a medium distance of 3 to 8 m, 1 to 1.5
In order to efficiently amplify signals at a general human body movement speed of m/sec, an amplifier circuit whose frequency characteristic has a peak at about IHz is often used. For this reason, there is almost no false alarm at the normal moving speed of a human body over medium distances, and since it is a balanced differential dual element type, false alarms due to temperature changes are also extremely rare.

A signal from a balanced differential pyroelectric infrared detector is a composite output of outputs obtained from two elements with mutually different polarities. An element that emits a positive signal when infrared rays are incident is a (+) polar element.

The opposite of this is defined as a (-) polar element, and if the image of the object focused on the element moves in the direction of the arrow in Figure 7, that is, from left to right, at normal speed, the (+) polar element The output will be as shown in Figure 8.

The output of the (-) polarity element has the opposite polarity to that in FIG.

In Figure 8, %, N, A shows the moment when the image is reflected on the element, and B shows the moment when the image leaves the element.When the image leaves the element and the temperature of the element decreases,
Since a signal of opposite polarity is obtained, the waveform of negative polarity shown in FIG. 8 is obtained.

When the image of the object moves on the element at an extremely low speed, the output of the (+) polar element and the output of the (-) polar element become as shown in (a) and (b) in Figure 9, respectively. The actual signal will be as shown in FIG. In this case, since the moving speed of the object is extremely slow, the signal of the (+) polar element is generated, and then the signal of the □, (-) polar element is generated, and the signals of each element do not interfere with each other. In addition, when the moving speed of the image is extremely fast, the signals of the two elements are generated almost simultaneously as shown in FIG. 11, and the signals cancel each other out, resulting in almost no output being obtained.

If the image moves at an appropriate speed, as shown in Figure 12, there will be a negative polarity signal when the image emerges from the (+) polarity element, and a (-) polarity signal.
When the image enters the polar element, the signals of negative polarity are reinforced and a high output of negative polarity is obtained. Similarly, if the image moves in the opposite direction on the element, a high output of positive polarity is obtained.

[Problems to be Solved by the Invention] By arbitrarily setting the gap between the elements of the above-mentioned balanced differential pyroelectric infrared detector and the frequency characteristics of the optical system and circuit of the alarm, it is possible to It is possible to configure one that is effective for detecting a high-speed moving object, one that is effective for detecting a general medium-speed moving object over a medium distance, and one that is effective for detecting a long-distance low-speed moving object. However, the detector □, which was designed with emphasis on detecting short-distance, fast-moving objects, was disadvantageous in detecting long-distance, slow-moving objects, and vice versa.

For this reason, in general crime prevention systems, detectors and alarms are designed assuming typical human movement speeds at medium distances, but they still do not detect high-speed moving objects at short distances. Detection of both objects and slow-moving objects at long distances was difficult, and alarms were often missed.
゛The present invention provides protection against both short-distance, high-speed moving objects and long-distance, low-speed moving objects in general security systems.
The object of the present invention is to provide an infrared detector that has the advantage of obtaining a detection capability greater than that of a conventional balanced differential dual element type simply by changing the light-receiving element pattern.

[Means to solve the problem] In order to deal with short-distance, high-speed moving objects, the output balance of the dual element type light-receiving element is disrupted, and in order to deal with long-distance, slow-moving objects, light is received in the gap between the elements. It is characterized by being smaller than the conventional balanced differential dual element type, being less than 71/4 of the maximum dimension of the element.

[Effect] When dealing with a high-speed moving object at a short distance, with a normal dual element type, the outputs of the opposite polarities of the two elements cancel each other out, making it impossible to obtain an output that exceeds the trigger level. In the element pattern according to the invention, since the areas of the light-receiving elements are different between the two elements, even if the two elements emit outputs at the same time, the output difference between the two elements is directly obtained as the output.

When a long-distance, slow-moving object is focused by an optical system, it appears as a very small image moving slowly on the element. In this case, when the light receiving element is normally set at a medium distance, the gap between the elements is too large, making it difficult to obtain a high output from the combined wave of both elements. However, with the element shape according to the present invention, the inter-element gap is very small, one-fourth or less of the maximum dimension of the light-receiving element, so it is possible to easily obtain high output from the composite wave.

[Embodiment 1] Below, along with an embodiment, the differences between the element pattern of a normal dual element type and the present invention and the difference in signal output will be explained in detail.

FIG. 6(b) shows a pattern of a dual-element type light-receiving element, which is most widely used for boat fishing. The size of the light receiving elements is 2×1 mm for both elements, and the gap between the elements is 1 mm. FIG. 1 shows an example of a light-receiving element pattern according to the present invention.The light-receiving element size is 2×1°5mm and 2×0.5mm.
5 mm, and the inter-element gap is 0.2 mm, which is less than the maximum dimension of the 2×1.5 mm elements, ie, 0.625 mm, which is one quarter of the diagonal length. Sign (+)
, (-) indicates the polarity of the signal output.

When a heat source moves at a high speed of 5 m/sec or more over a short distance of 0,5-2 m, with a normal dual element type, the (+) polarity and (-) polarity elements move at the same time and to the same degree. Since signals of opposite polarity are output, the outputs of both elements cancel each other out, making it impossible to obtain sufficient output. However, with the element shape shown in FIG. 1, even if both elements generate signals at the same time, in this case, the (+) polarity element output is superior and a sufficient output can be obtained.

On the other hand, if the heat source is 0.1 to 0.3 m long distance of 20 m or more,
When moving at a slow speed of about /sec, the image of the heat source focused on the element will be very small and will move on the element at a slow speed. Since the (-) polarity element outputs after the output of the element subsides, it was not possible to obtain a composite wave from both elements, and the output itself was at a very low level, so sufficient output could not be obtained. However, if the element shape shown in FIG. 1 according to the present invention is used,
An image enters the (-) polar element at approximately the same time that an image emerges from the (+) polar element, and high output is obtained due to interference of signals from both elements.

In this case, the narrower the gap between elements, the better.

If the (+) polarity output and (-) polarity output of the light-receiving element are unbalanced, it is also possible to divide the element and use it as shown in FIG.

In this case, when the image moves slowly from left to right of the light-receiving element, high output due to signal interference is obtained twice.

[Example 2] Furthermore, as shown in Figure 3, for the element with the smaller output,
It is also possible to provide a temperature compensation element so as not to receive light, and to effectively utilize the cancellation effect against temperature changes. Also, if the output of the light-receiving element is unbalanced and the element gap between both elements is less than a quarter of the maximum dimension of the light-receiving element excluding the connection part,
As shown in FIG. 4, there are no particular restrictions on the shape of the elements or whether they are connected in parallel or in series.

[Embodiment 3] It is also possible to further improve reliability by housing a plurality of elements according to the present invention as shown in FIG. 5, or together with a topographical element pattern in the same package. In this case as well, various wiring methods and signal processing methods can be considered.

[Effects of the invention] Conventional balanced differential dual-element type pyroelectric infrared detectors have a wide detection area, making it difficult to detect objects moving over short or long distances. , by adopting the element pattern of the present invention,
It has become possible to obtain detection capabilities greater than the conventional dual element type at both short and long distances without making any changes to the conventional security system.

[Brief explanation of drawings]

□Figures 1 to 4 show examples of five element patterns according to the present invention, and the + and - symbols indicate the polarity of the elements. The direction of the arrow in FIG. 1 indicates the moving direction of the image focused on the element by the optical system. The range indicated by the dotted line in FIGS. 3 and 4 indicates the light receiving range of the element. Elements outside the dotted line are temperature compensation elements. FIG. 5 shows an example of an element arrangement method when a plurality of elements of the present invention or elements of conventional shapes are used. FIG. 6 shows a dual element type pyroelectric infrared detector of the TO-5 package which is generally widely used, and (a) is a cross-sectional view of its structure. (b) shows the element shape and its arrangement when viewed from directly above. In FIG. 6, at -1, 1, 2-light receiving element electrode. 3-optical filter, 4-can, 5-pyroelectric, 6-pyroelectric support, 7-wiring board, 8-base, 9-terminal. Figure 7 shows the element shape of a general dual element type, and Figure 8 shows the output of the (+) polar element when the image moves at a typical speed in the direction of the arrow in Figure 7. . Figure 9(a) shows the output of the polar element when the image moves at an extremely slow speed in the direction of the arrow in Figure 7.
b) shows the output of the (-) polarity element, and FIG. 10 shows the actual continuous 8-force waveform. FIG. 11 shows a state in which almost no output is obtained when the image moves at an extremely high speed in the direction of the arrow in FIG. This shows a state in which high output is obtained due to interference between elements when moving in the direction of . (a) shows the output originally generated by a (+) polarity element, and (b) shows the output generated by an originally (-) polarity element. (c) shows the combined output of (a) and (b).

Claims (4)

[Claims] (1) A pyroelectric infrared detector characterized in that the output balance of the light-receiving element is disrupted and the gap between the elements is set to 1/4 or less of the maximum dimension of the light-receiving element excluding the connection portion. (2) Regarding the elements described in claim (1),
A pyroelectric infrared detector characterized by adding a temperature compensation element to the element with smaller output. (3) A pyroelectric infrared detector characterized in that a plurality of sets of the elements described in claims (1) and (2) are provided in the same package. (4) A pyroelectric infrared detector characterized in that any number of the elements described in claims (1) and (2) and conventionally shaped elements are housed in the same package.