JPH03186722A - Infrared detector - Google Patents

Abstract

PURPOSE:To stably detect infrared rays without deteriorating the resolution by fetching an AC output at a point comparable of the waveform of AC outputs with each other varied by the infrared-ray quantity. CONSTITUTION:A microcomputer 16 generates a driving voltage to a chopper C, and also, generates a start signal to an A/D converter 17 by a period of 1/2 thereof. The converter 17 fetches the output voltage of a full-wave rectifying circuit 13 by this timing, brings it to A/D conversion, and outputs carbon dioxide gas concentration as the digital value to the computer 16. The computer 16 executes the display and the control of gas concentration, based on this data. Also, the converter 17 operates in the same position of a ripple every time, and compares this value, therefore, a smoothing circuit becomes unnecessary. Especially, the timing by which the converter 17 inputs the output of the circuit 13 is made by the computer 16, therefore, there is no shift of synchronization, and high accuracy is obtained.

Description

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

(b) Conventional technology Infrared detection devices are used in thermometers that measure the temperature of objects without contact, and gas concentration meters that measure gas concentration by detecting the amount of infrared rays that reach the gas without being absorbed. The elements used to detect infrared rays are generally differential input type, and a pyroelectric element is a typical example.

A conventional infrared detector 100 is shown in FIG. detection 510
0 indicates an infrared detection section S that is detected from a pyroelectric element, a chopper 104 that has a notch 101 and is cut out from a metal disk 103 rotated by a motor 102, and a position detector 1 for the metal disk 103.
The groove bottom is made from 05, and output according to the amount of infrared rays,
It is generated as an alternating current signal of the same frequency as the metal disk 103 interrupting the incident infrared rays U.

Furthermore, in recent years, a so-called modulation type pyroelectric infrared detector 1 as shown in FIG. 1 has been developed. detector l
The above-mentioned infrared detection section S is housed in a shield box 2, and a chopper C is provided at a position corresponding to a through hole (not shown) formed in the shield box 2, which is connected to a slit member 4 driven by a piezoelectric bimorph vibrator 3. Furthermore, the entire body is covered with a case 6 in which through holes 5 are formed at corresponding positions. The slit member 4 is formed by attaching two plates with slits in an overlapping relationship as shown in FIG. By opening and closing the slit, the infrared rays U entering through the through hole 5 and reaching the infrared detecting section S are interrupted, and an output corresponding to the amount of infrared rays is generated as an alternating current signal of the same frequency as the input frequency of the chopper C.

(c) Problems to be Solved by the Invention FIG. 6 shows a diagram of a detection electric circuit when used, for example, as a carbon dioxide gas detector.

Since the infrared detection section S of the modulation type pyroelectric infrared detector 1 has good sensitivity to infrared input of 1 to 10H2, the drive circuit 7 can detect, for example, 4H2
Apply Z drive voltage to chopper C. This results in 4
The intermittent infrared rays of H2 are incident on the infrared detection section S.

The output of the infrared detection section S has a frequency of 4H2, which is the same as the frequency of the input voltage of the chopper C, but the value is very small and 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. II 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 therebetween, the output of the infrared detecting section S changes depending on the gas concentration.

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

However, the output signal frequency of the infrared detector S is 4H.
Since Z is low, if a capacitor with a large capacity is not set in the smoothing circuit 14, the ripple component will cause a decrease in resolution and fluctuations in the gas concentration display value. Therefore, the response as a detector becomes slow, and generally a 95% response takes about 60 seconds. Therefore, when used in a device that controls environmental conditions to a constant gas concentration, there is a problem that overshoot becomes large.

The present invention aims to solve this problem.

(d) Means for Solving the Problems The present invention provides an infrared detection device that obtains an AC output by intermittently irradiating an infrared detection section with infrared rays. It is configured to take in AC output.

(E) Effect According to the present invention, even if the output voltage contains a large amount of ripple, stable detection can be performed without reducing the resolution. Furthermore,
No smoothing circuit is required, resulting in extremely high responsiveness.

(f) Embodiments Next, embodiments of the present invention will be explained with reference to the drawings. FIG. 3 shows a block diagram of an electric circuit when the infrared detection device of the present invention is used, for example, as a carbon dioxide gas detection device. still,
In the figure, the same reference numerals as in the conventional example are the same, and the detector section uses a so-called modulation type pyroelectric infrared detector l as shown in FIG. 16 is a microcomputer, which generates a predetermined frequency voltage for driving the chopper C according to the software program;
Input to the drive circuit 7. Further, 17 is an A/D converter, which is configured to take in the output signal of the full-wave rectifier circuit 13 at a 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 a start signal that determines the conversion timing of the A/D converter 17. The microcomputer 16 generates a drive voltage for the chopper C at a frequency of, for example, 4H2, and also
A start signal is generated to the A/D converter 17 at a period of . The A/D converter 17 takes in the output voltage of the full-wave rectifier circuit 13 at this timing, performs A/D conversion, and outputs the carbon dioxide gas concentration to the microcomputer 16 as a digital value. microcomputer 16
displays and controls the gas concentration based on this data.

Due to this groove bottom, as shown in Fig. 4, the A/D converter 17 operates at the same ripple position every time, and the values are compared, so a smoothing circuit is not required.
Null so that resolution degradation and display fluctuation due to ripple can be ignored in principle. In particular, since the timing at which the A/D converter 17 takes in the output of the full-wave rectifier circuit 13 is created by the same microcomputer 16, there is no synchronization shift, resulting in high precision.

Here, the start signal of the A/D converter 17 does not necessarily have to be the same as the driving cycle of the chopper C, and it is sufficient to determine the same point that can be compared in the AC waveform that changes depending on the amount of infrared rays. It may be a period of % of that, or a period of an integral multiple of that. 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. Further, in the embodiment, the present invention was applied to detecting the concentration of carbon dioxide gas, but the present invention is not limited thereto, and may be applied to detecting other gases or temperatures.

(G) Effects of the Invention According to the infrared detection device of the present invention, stable infrared detection is possible without reducing resolution, thereby preventing display fluctuations and resolution degradation. especially,
Since a smoothing circuit is not required, excellent effects such as extremely improved responsiveness can be achieved.

[Brief explanation of drawings]

1 to 4 show embodiments 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 Chizutsuba, the output voltage of the full-wave rectifier circuit, and the conversion start signal of the A/D converter, and Fig. 5 is a perspective view of a conventional infrared detector. Figure 6 shows the same electric circuit. 1... Infrared detector, 13... Full wave rectifier circuit, 16
...Microcomputer, 17...A/D Nian/<-Yu, C...Chiyo Tsuba S...Infrared detection unit.

Claims (1)

[Claims] 1) In the device that obtains an AC output by intermittently irradiating an infrared detection section with infrared rays, the AC output is configured to be taken in at a point where the waveform of the AC output that changes depending on the amount of infrared rays can be compared. Infrared detection device.