JPH07120318A - Pyroelectric type infrared detector - Google Patents

Abstract

PURPOSE:To provide an inexpensive pyroelectric type infrared detector which achieves higher detection accuracy and reliability with a simple structure. CONSTITUTION:A pyroelectric type sensor element 10 is arranged, an infrared radiation element 12 is provided near the sensor element 10 to radiate infrared rays cyclically and a drive circuit 14 to heat the infrared radiation element 12 cyclically. A level comparator 20 is provided to compare an output level of the sensor element 10 with a specified level and a cycle comparator 22 to compare the cycle of an output waveform of the sensor element 10 with a specified cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric infrared detecting device for converting infrared rays into electric signals by utilizing the pyroelectric effect.

[0002]

2. Description of the Related Art Conventionally, so-called pyroelectric infrared sensors are
Since it cannot detect stationary infrared radiation,
The sensor is moved, or an optical chopper that blocks the incident light at a predetermined end is arranged in front of the sensor to convert the incident light into an alternating current so that it can be detected. The optical chopper includes a mechanical type that uses a rotating disk having gaps formed at predetermined intervals, a mechanical type that moves a mirror, and a PLZT or liquid crystal type. Further, there is also proposed a pyroelectric sensor element in which a heater material is formed so that an abnormality of the sensor can be detected.

[0003]

However, when the above-mentioned conventional sensor itself is moved, the background noise is large, the SN ratio is deteriorated, and malfunctions are likely to occur. Further, the mechanical type optical chopper needs a mechanical driving device such as a motor and a bimorph element, and has a moving part, so that it has a drawback of low reliability. Further, although the one using PLZT or liquid crystal has no movable part and the SN ratio is relatively good, it has a drawback of high cost.
Further, the heater element formed on the sensor element itself is for detecting an abnormality and does not make it possible to detect a stationary infrared radiator.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide an inexpensive pyroelectric infrared detector having a simple structure, high detection accuracy and high reliability. To do.

[0005]

According to the present invention, there is provided an infrared radiating element having a pyroelectric type sensor element, which radiates infrared rays periodically in the vicinity of the sensor element, and the infrared radiating element is periodically heated. And a drive circuit for driving the sensor element, and a level comparator for comparing the output level of the sensor element with a predetermined level, and a cycle comparator for comparing the cycle of the output waveform of the sensor element with a predetermined period. It is an infrared detector. The infrared emitting element is a heating element arranged behind the sensor element in the sensor package.

[0006]

In the pyroelectric infrared detector of the present invention, the sensor element is irradiated with infrared rays of a predetermined cycle, and based on the output of the infrared rays of the predetermined cycle and the output of the infrared radiator, its output level and Both the moving object and the stationary object can be detected by the cycle of the output signal.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 show a first embodiment of the present invention. The pyroelectric infrared detection device of this embodiment is shown in FIG.
As shown in FIG. 2, a heating element 12, which is an infrared radiation element such as a heater, is arranged in front of the field of view of the pyroelectric infrared sensor element 10, and a chopper circuit for causing the heating element 12 to generate heat at a predetermined cycle 14 is provided. Sensor element 1
As shown in FIG. 2, 0 is accommodated in the sensor package 16, and a condenser lens and the like (not shown) are arranged on the front side of the sensor package 16. In addition, the heating element 12
Is an infrared ray having a wavelength close to the infrared ray emitted by the detection target, which is smaller than the calorific value of the detection target,
Any element capable of electrically generating heat, such as one using a heat wire heater or a resistor element, or one using a semiconductor element such as an LED, may be used.

In the detection circuit of the pyroelectric infrared detector of this embodiment, as shown in FIG. 1, the output of the sensor element 10 is
The output signal of the sensor element 10 output from the level comparison circuit 20 is input to the level comparison circuit 20 that compares the output levels, and is input to the period comparison circuit 22.
Further, a signal of a predetermined cycle by the chopper circuit 14 is also input to the cycle comparison circuit 22 as a comparison target.

The operation of the pyroelectric infrared detector of this embodiment is as follows. First, when there is no infrared radiator within the field of view of the sensor element 10, as shown by the rectangular wave in FIG.
As the output signal of 0, a signal of a predetermined cycle is output by the chopper circuit 14 which is a drive circuit. Then, as shown in FIG. 2, when an infrared radiator such as a human enters the field of view 30 of the sensor element 10, a large output is obtained in the plus direction as shown in FIG. When the infrared radiator goes out of the field of view, an output in the minus direction is obtained from the time when it comes out of the field of view 30 as shown in FIG. Therefore, the output of the sensor element 10 is set with predetermined comparison values L1 and L2 and compared by the level comparator 20, and when the output of the comparison value L2 or more is obtained, the infrared radiator enters the visual field 30. Is detected,
When the output of the comparison value L1 or less is obtained, it can be detected that the infrared radiator has gone out of the visual field.

Further, when the infrared radiator is stationary within the visual field 30 of the sensor element 10 or is moving only within the visual field, as shown in FIG. It is buried by the infrared rays of the infrared radiator inside, and a constant infrared ray is incident on the sensor element 10, and a constant output is obtained. As a result, when a constant output equal to or more than a half wavelength of the signal of the chopper circuit 14 is obtained, it is detected that the infrared radiator is stationary within the field of view or moving within the field of view.

The level comparator 20 and the period comparator 22 are combined to output L1 or more and then output L1.
When the following output is obtained, it means that the infrared radiator has passed, and when the constant output is obtained after the output of L2 or more, the infrared radiator is staying in the visual field 30, and thereafter. When the output of L1 or less is obtained, it is detected that the infrared radiator within the field of view has gone out.

According to the pyroelectric infrared detector of this embodiment, the stationary infrared radiation within the visual field 30 can be obtained by simply disposing the heating element 12 within the visual field 30 of the infrared sensor element 10 and driving it at a predetermined frequency. It is possible to detect the body, has no mechanical moving parts, is highly reliable, and is inexpensive.

Next, a second embodiment of the present invention will be described with reference to FIG. Here, the same members as those in the above-described embodiment are designated by the same reference numerals, and the description thereof will be omitted. In the pyroelectric infrared detection device of this embodiment, L, which is a heating element as an infrared radiation element, is provided on the back side of the sensor element 10 in the sensor package 16.
The ED 32 is arranged. The output wavelength of the LED 32 is, for example, 9.4 μm, which is close to the infrared wavelength emitted by humans.
It emits near wavelengths.

The pyroelectric infrared detection device of this embodiment is provided with the LED 32 which is a heating element in the sensor package 16, the device is miniaturized, the drive is easy, and the reliability is high.

The pyroelectric infrared detection device of the present invention is not limited to the above-mentioned embodiment. For example, the number of sensor elements is plural, and the infrared radiator is caused by the deviation of the timing of infrared rays detected by each sensor element. The moving direction of the may be detected. Further, the type of the infrared radiating element can be appropriately selected, and for example, a resistor element such as a PTC thermistor may be arranged inside the sensor package.

[0016]

EFFECT OF THE INVENTION The pyroelectric infrared detector of the present invention is capable of detecting an infrared radiator remaining in the field of view with a simple structure, has no mechanical moving parts, has high sensitivity and high reliability. And the price can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a pyroelectric infrared detection device according to a first embodiment of the present invention.

FIG. 2 is a schematic view showing a usage state of the pyroelectric infrared detection device of this embodiment.

FIG. 3 is a time chart showing an operating state of the pyroelectric infrared detection device of this embodiment.

FIG. 4 is a schematic vertical sectional view of a pyroelectric infrared detection device according to a second embodiment of the present invention.

[Explanation of symbols]

 10 sensor element 12 heating element 14 chopper circuit 20 level comparator 22 period comparator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaya Nomura 3158 Shimookubo, Osawano-cho, Kamishinagawa-gun, Toyama Prefecture Hokuriku Electric Industry Co., Ltd.

Claims (4)

[Claims] 1. A pyroelectric infrared detection device comprising a pyroelectric sensor element, and an infrared radiation element which periodically radiates infrared radiation is provided in the vicinity of the sensor element. 2. A pyroelectric sensor element, an infrared radiating element which is provided in the vicinity of the sensor element and which radiates infrared rays periodically, a drive circuit which periodically heats the infrared radiating element, and the sensor element. 2. A pyroelectric infrared detection device, comprising: a level comparator for comparing the output level of 1 to a predetermined level; and a period comparator for comparing the period of the output waveform of the sensor element with a predetermined period. 3. The infrared radiating element is a heating element arranged in front of or behind the sensor element, and a drive circuit for periodically heating the heating element is provided. The described pyroelectric infrared detection device. 4. The pyroelectric infrared detection device according to claim 1, wherein the infrared radiation element is a heating element arranged behind the sensor element in the sensor package.