JPH071203B2 - Infrared detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an infrared detecting device for detecting the amount of infrared rays, or for detecting the gas concentration or temperature by the amount of transmitted infrared rays.

(B) Conventional technology Infrared detectors are used in non-contact thermometers that measure the temperature of objects, and gas concentration meters that measure the gas temperature by detecting the amount of infrared light that reaches without being absorbed by gas. The element used for detecting infrared rays is generally a differential input type, and a pyroelectric element is a typical one.

A conventional infrared detector 100 is shown in FIG. The detector 100 is a chopper composed of an infrared detector S composed of a pyroelectric element, a metal disk 103 having a cutout 101 and rotated by a motor 102.
104 and a position detector 105 of the metal disk 103, and generates an output corresponding to the amount of infrared rays as an alternating current signal having the same frequency as the metal disk 103 interrupts the incident infrared rays U. .

Further, in recent years, a so-called modulation type pyroelectric infrared detector 1 as shown in FIG. 1 has also been developed. Detector 1
Stores the above-mentioned infrared detecting section S in the shield box 2, and provides a chopper C composed of a slit member 4 driven by the piezoelectric bimorph vibrator 3 at a position corresponding to a through hole (not shown) formed in the shield box 2. Further, a case 6 having a through hole 5 formed at a position corresponding thereto covers the entire structure. The slit member 4 is constructed by attaching two plates having slits as shown in FIG. 2 in a superposition relationship, and the piezoelectric bimorph vibrator 3 vibrates at the same frequency as the frequency of the drive voltage input to the chopper C. The slit is opened and closed to interrupt the infrared ray U which is incident from the through hole 5 and reaches the infrared detecting section S, and an output corresponding to the infrared ray amount is generated as an AC signal having the same frequency as the input frequency of the chopper C.

(C) Problem to be Solved by the Invention FIG. 6 shows a block diagram of a detection electric circuit when used as a carbon dioxide gas detector, for example. The infrared detector S of the modulation type pyroelectric infrared detector 1 is 1
The driving circuit 7 applies a driving voltage of, for example, 4 HZ to the chopper C because it has a good sensitivity to an infrared input of 10 to 10 HZ. As a result, intermittent infrared rays of 4HZ enter the infrared detector S.

The output of the infrared detector S has a frequency of 4HZ, which is the same as the frequency of the input voltage of the chopper C, but its value is very small.
Since it is mixed with the DC component, only the AC component is amplified by the AC amplifier 8. 9 is a filter for noise removal, 10
Is an oscillator for the drive circuit 7 for driving the chopper C. Reference numeral 11 is an infrared source connected to the power supply 12. Since the amount of infrared rays emitted from here and reaching the infrared detecting section S is absorbed by the gas in the meantime, the output of the infrared detecting section S changes depending on the gas concentration.

Here, since the output of the infrared detector S is an AC signal,
Cannot input to A / D converter or linearization circuit. Therefore, the full-wave rectifier circuit 13 and the smoothing circuit 14 are converted into a DC signal to obtain an output based on the gas concentration.

However, since the output signal frequency of the infrared detector S is as low as 4HZ, unless a large-capacity capacitor is set in the smoothing circuit 14, the ripple component causes a decrease in resolution and fluctuation in the gas concentration display value. As a result, the response of the detector becomes slow, and generally 95% response takes about 60 seconds. Therefore, when used in a device that controls the environmental conditions to a constant gas concentration, there is a problem that the overshoot becomes large.

The present invention aims to solve such problems.

(D) Means for Solving the Problems The present invention provides an infrared detection device for obtaining an AC output by intermittently irradiating an infrared detection section with infrared rays by a chopper.
Full-wave rectify the AC output that changes depending on the amount of infrared rays with a full-wave rectifier circuit, and an A / D converter that captures this output at the point where the waveforms of the full-wave rectified output voltage can be compared with the chopper and the arithmetic unit It is synchronized.

(E) Action According to the present invention, stable detection can be performed without lowering the resolution even if the output voltage contains a large amount of ripples. Furthermore,
The smoothing circuit is unnecessary and the response is extremely good.

(F) Example Next, an example of the present invention will be described with reference to the drawings. FIG. 3 shows a block diagram of an electric circuit when the infrared detector of the present invention is used as a carbon dioxide gas detector, for example. still,
In the figure, the same reference numerals as those in the conventional example are the same, and the detector portion uses the so-called modulation type pyroelectric infrared detector 1 as shown in FIG. Reference numeral 16 is a micro computer, which generates a predetermined frequency voltage for driving the chopper C by the software of the program and inputs it to the drive circuit 7. 17 is an A / D converter,
It is configured to take in the output signal of the full-wave rectifier circuit 13 at the timing controlled by the microcomputer 16.

The timing chart shown in FIG. 4 shows the input voltage of the chopper C, the output voltage of the full-wave rectifier circuit 13, and the A / D converter 17
3 shows a start signal that determines the conversion timing of the.
The microcomputer 16 generates a driving voltage for the chopper C at a frequency of 4HZ, for example, and A
Generates a start signal to the / D converter 17. At this timing, the A / D converter 17 takes in the output voltage of the full-wave rectifier circuit 13, performs A / D conversion, and outputs the carbon dioxide gas concentration as a digital value to the microcomputer 16. The microcomputer 16 displays and controls the gas concentration based on this data.

With this configuration, the A / D converter 17 operates at the same ripple position each time as shown in FIG. 4, and since this value is compared, a smoothing circuit is not required. In addition, deterioration of resolution due to ripple and display fluctuation can be ignored in principle. In particular, the timing at which the A / D converter 17 captures the output of the full-wave rectifier circuit 13 is created by the same microcomputer 16, so there is no synchronization deviation,
High accuracy.

Here, the start signal of the A / D converter 17 is the chopper C.
It does not necessarily have to be the same as the driving cycle of the above, and it is sufficient to determine the same point that can be compared in the AC waveform that changes with the amount of infrared rays. It does not matter if the cycle is twice as long. Further, in the case of full-wave rectification as in the embodiment, different waves may be compared at positions of the same phase across 90 degrees. Furthermore, although the present invention is applied to the detection of the carbon dioxide gas concentration in the embodiments, the present invention is not limited to this and may be applied to the detection of other gas or temperature.

(G) Effect of the Invention According to the infrared detection device of the present invention, the output voltage at the point at the same position subjected to full-wave rectification can be detected without lowering the resolution, and stable infrared detection can be performed, thereby displaying It is possible to prevent fluctuation of the image and deterioration of resolution. In particular, since a smoothing circuit is not required, excellent effects such as an extremely improved response can be obtained.

[Brief description of drawings]

1 to 4 show an embodiment of the present invention, FIG. 1 is an exploded perspective view of a modulation type pyroelectric infrared detector, FIG. 2 is a perspective view of a slit member, and FIG. 3 is an electric circuit. Fig. 4 is a timing chart showing the input voltage of the chopper, the output voltage of the full-wave rectifier circuit and the conversion start signal of the A / D converter. Fig. 5 is a perspective view of a conventional infrared detector. FIG. 6 shows the same electric circuit. 1 ... Infrared detector, 13 ... Full-wave rectifier circuit, 16 ... Microcomputer, 17 ... A / D converter, C ... Chopper, S ... Infrared detector.

Claims (1)

[Claims] 1. An infrared detecting device for intermittently irradiating an infrared detecting section with an infrared ray by a chopper to obtain an AC output, wherein the AC output varying with the amount of the infrared rays is full-wave rectified by a full-wave rectifying circuit, An infrared detecting device characterized in that an A / D converter for taking in this output is synchronized with the chopper by a computing device in that the waveforms of the output voltage subjected to the full-wave rectification can be compared.