JPH03186723A - Infrared detector - Google Patents

Abstract

PURPOSE:To remarkably reduce the cost of the whole device by providing an integration circuit for smoothing the waveform of an AC output varied due to the infrared-ray quantity, and fetching the output of this circuit to an A/D converter at a comparable point. CONSTITUTION:A microcomputer 16 generates a driving voltage to a chopper C, and also, generates a start signal to an A/D converter 17 at the time T1 by the same period as its generation. The converter 17 fetches the output voltage of an integration circuit 20 by this timing, applies it to A/D conversion 17, ends a converting operation at the time T2 and outputs carbon dioxide gas concentration as a digital value to the computer 16. The computer 16 executes the display and the control of gas concentration, based on this data. In such a state, the variation of a half-wave rectifying circuit 13 is slow by the circuit 20, therefore, the variation of a voltage value between the time T1 and T2 becomes smaller. Therefore, the conversion accuracy is improved and an error caused by the conversion time of the converter 17 can be made small. On the other hand, since a delay by the circuit 20 is also small, responsiveness of the detector is quickened.

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. Detector 10
0 indicates an infrared detection section S made of a pyroelectric element, a chopper 104 having a notch 101 and cut out from a metal disk 103 rotated by a motor 102, and a position detector 1 for the metal disk 103.
05, 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 l as shown in FIG. 1 has been developed. Detection 51
The above-mentioned infrared detection section S is housed in a shield box 2, and a chopper C cut out from a slit member 4 driven by a piezoelectric bimorph vibrator 3 is provided at a position corresponding to a through hole (not shown) formed in the shield box 2. 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. 7 shows a block diagram of a detection electric circuit when used, for example, as a carbon dioxide gas detector.

Since the infrared detecting 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
A driving voltage of is applied to chopper C. With this, 4H
2 intermittent infrared rays are incident on the infrared detection section S.

The output of the infrared detection section S has a frequency of 4 Hz, 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. 11 is an infrared source connected to a power source 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 half-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 4H2.
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.

Therefore, the applicant previously proposed that the voltage be taken into the A/D converter in synchronization with the cycle of the AC signal obtained from the infrared detection section S, thereby eliminating the smoothing circuit 14, but the In order to detect the Even with the above, a high-speed successive approximation type A/D converter with a conversion time of 25 μsec or less must be used, resulting in an expensive problem.

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. An integrating circuit is provided for smoothing within a range that does not impair the signal, and the output of this integrating circuit is input to the A/D converter at a point where it can be compared.

(E) Function According to the present invention, sufficient processing time for the A/D converter can be secured, so there is no need to use an expensive high-speed processing type converter, and responsiveness is not impaired.

(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. In the figure, the same reference numerals as in the conventional example are the same, and the infrared detector section uses a so-called modulation type pyroelectric infrared detector 1 as shown in FIG. A microcomputer 16 generates a predetermined frequency voltage for driving the chopper C according to software and inputs it to the drive circuit 7. 20 is an integrating circuit for smoothing the output of the half-wave rectifier circuit 13. Further, 17 is an A/D converter, which is configured to take in the output signal of the integrating circuit 20 at a timing controlled by the microcomputer 16.

Figure 4 shows an AC amplifier 8, a filter 9 for noise removal,
An example of an actual analog circuit of the half-wave rectifier circuit 13 and the integration circuit 20 is shown. Since it is not necessary for the integrating circuit 20 to completely remove ripples in the output of the half-wave rectifying circuit 13, the capacitor 21 used therein may be small.

Next, the timing chart shown in FIG. 5 shows the input voltage of the chopper C, the output voltage of the integrating circuit 20, and the conversion timing of the A/D converter 17. Note that the half-sine waveform indicated by the broken line in the figure indicates the output voltage of the half-wave rectifier circuit 13.

Microcomputer 16 measures 4H2 on chopper C.
A drive voltage is generated at a frequency of , and a start signal is generated to the A/D converter 17 at time T1 at the same frequency. The A/D converter 17 takes in the output voltage of the integrating circuit 20 at this timing, performs A/D conversion, completes the conversion operation at time T2, and outputs the carbon dioxide gas concentration to the microcomputer 16 as a digital value. The microcomputer 16 displays and controls the gas concentration based on this data.

Since the change in the output voltage of the half-wave rectifier circuit 13 is made slow by the integrating circuit 20, the change in the voltage value between time T1 and time T2 is small. Therefore, the conversion accuracy is improved and the error due to the conversion time of the A/D converter 17 can be reduced by 5 to 10 times or more. On the other hand, the integrating circuit 20
Since there is little delay due to
% response time is approximately 15 seconds, which is faster than conventional methods.

In addition, due to the groove bottom as shown in Figure 5 (A/D converter 17 operates at the same ripple position every time, and these values are compared, it is possible to completely eliminate ripples as in the conventional case). There is no need for a smoothing circuit with a large capacity.Furthermore, the reduction in resolution due to ripples and display fluctuations can be ignored in principle.In particular, the timing at which the A/D converter 17 takes in the output of the integrating circuit 13 is Since they are produced by the same microcomputer 16, there is no synchronization difference, resulting in high precision.

Here, the start signal of the A/D converter 17 does not necessarily have to be the same as the drive cycle of the chopper C. 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, and it is an integral multiple of that point. There is no problem even if the cycle is Further, in the embodiment, the present invention is 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, temperature, etc.

(G) Effects of the Invention According to the infrared detection device of the present invention, detection with sufficient accuracy is possible even with an integral type A/D converter having a slow processing speed.

This allows the use of an inexpensive A/D converter, resulting in a significant cost reduction of the entire device. Furthermore, since it is not necessary to completely remove ripples in the detection voltage, sufficient responsiveness can be ensured.

[Brief explanation of drawings]

1 to 5 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. 4 is an electric circuit diagram showing an example of an actual analog circuit, and FIG. 5 is a timing chart showing the input voltage of the chopper, the output voltage of the half-wave rectifier circuit, and the conversion timing of the A/D converter. , FIG. 6 is a perspective view of a conventional infrared detector, and FIG. 7 is an electric circuit thereof. 1... Infrared detector, 13... Half-wave rectifier circuit, 16
...Microcomputer, 17...A/D converter, 20...Integrator circuit, C...Chopper S...
・Infrared detection section.

Claims (1)

[Claims] 1) In a device that obtains an AC output by intermittently irradiating an infrared detection section with infrared rays, an integrating circuit is provided to smooth the waveform of the AC output, which changes depending on the amount of infrared rays, within a range that does not impair responsiveness. An infrared detection device characterized in that the output of the integrating circuit is configured to be input into an A/D converter so that the output can be compared.