JPH03211448A - Infrared gas sensor - Google Patents

Abstract

PURPOSE:To suppress the entry of a noise and to improve the detection accuracy by fitting an infrared detector to a circuit board where other electric components are fitted and fixing the circuit board to a support member. CONSTITUTION:The infrared detector 1 is fitted to the printed board where other electric components 1 are fitted and the printed board 8 is fixed to the support member 9. Consequently, the distance between the infrared detector 1 and other electric components 11 can be shortened extremely and the entry of noises from the gap between them is suppressed to improve the detection accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to an infrared gas sensor that measures the concentration of gas by utilizing the property that infrared rays emitted from a light source are absorbed and attenuated by gas.

(b) Conventional technology Infrared gas sensors are used in gas concentration meters, etc. that measure gas concentration without contact by detecting the amount of infrared rays that reach the gas to be measured without being absorbed. The elements used for this are generally differential input type, and a pyroelectric element is a typical example.

A conventional infrared gas sensor 100 is shown in FIG. The sensor 100 is composed of an infrared detection section S made of a pyroelectric element, a chopper 104 made of a metal disk 103 having a notch 101 and rotated by a motor 102, and a position detector 105 of the metal disk 103. An output corresponding to the amount of infrared rays is generated as an alternating current signal of the same frequency as that at which the metal disk 103 interrupts 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 1
The above-mentioned infrared detection section S is housed in a shield box 2, and a chopper C consisting of 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. Further, the entire body is covered with a case 6 in which through holes 5 are formed at corresponding positions. As shown in FIG. 2, the slit member 4 is constructed by attaching two plates with slits formed in an overlapping relationship, and the piezoelectric bimorph vibrator 3 is generated at the same frequency as the frequency of the drive voltage input to the 7-bar C. The slit is opened and closed by vibration, and the infrared ray U that enters through the through hole 5 and reaches the infrared detection section S is intermittent, and an output corresponding to the amount of infrared rays is generated as an alternating current signal with the same frequency as the input frequency of the chopper C. do.

(c) Problems to be Solved by the Invention In any of the above detectors, the AC signal obtained from the infrared detection section S is weak and appears as a ripple in the DC component. Therefore, the AC component in this cannot be used unless it is amplified. However, since the infrared detection section S and the amplifier circuit section were conventionally separated, noise entered from the signal line between them, hindering good detection.

The present invention aims to solve this problem.

(d) Means for Solving the Problems The present invention provides a modulation type infrared detector incorporating a light source that generates infrared rays, a gas cell for circulating a gas to be measured, a piezoelectric bimorph chopper, and this infrared detector. In an infrared type gas sensor which obtains an output by making the infrared rays that have passed through the gas to be measured enter the infrared detector, the infrared detector is attached to a circuit to which other electrical parts are attached. By attaching the circuit board to the substrate and fixing the circuit board to the support member, the infrared detector is provided at a predetermined position within the support member.

(E) Function According to the present invention, by extremely shortening the distance between the infrared detector of the infrared gas sensor and other electrical components, it is possible to reduce the intrusion of noise from there.

(f) Example Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a longitudinal sectional view of an infrared gas sensor A of the present invention, and FIG. 2 shows a perspective view thereof. Furthermore, FIG. 3 shows an exploded perspective view of a so-called modulation type pyroelectric infrared detector 1 developed in recent years. The infrared detector 1 houses the above-mentioned infrared detection section S in a shield box 2, and has a chopper consisting of a slit member 4 driven by a piezoelectric bimorph vibrator 3 at a position corresponding to a through hole (not shown) formed in the shield box 2. The entire body is covered by a case 6 in which a hole 5 is provided and a through hole 5 is formed at a corresponding position, and these parts are built into the case 6. The slit member 4 is constructed by attaching two plates with slits formed in an overlapping relationship as shown in FIG. The slit is opened and closed, and the infrared ray U that enters through the through hole 5 and reaches the infrared detection section S is intermittent, 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.

Moreover, such a configuration allows the infrared detector l to be very small in size, and has a size that allows it to be mounted on a printed circuit board.

The infrared gas sensor A is used, for example, to measure carbon dioxide gas concentration, and has a through hole 5 fitted with a sapphire glass window 7 that transmits infrared rays.

Next, in FIGS. 1 and 2, 8 is a printed circuit board for mounting the infrared detector 1, and 9 is a support member for supporting the circuit board 8.

The support member 9 is formed into a box shape from a thin stainless steel plate of approximately TO08 size, and is open downward and has an insertion hole 10 bored in the upper surface. Further, other electrical components (generally referred to as 11) to which the infrared detector 1 is electrically connected are also attached to the same side of the circuit board 8 as the infrared detector tiSl is attached.

Reference numeral 12 denotes a gas cell formed into a rectangular shape using brass or machined aluminum, inside which passages 13 are formed on the left and right sides through which carbon dioxide gas, which is the gas to be measured, flows; Through-holes 14 are formed in the upper and lower portions thereof, and the upper and lower portions are sealed with sapphire glasses 15 and 15.

Further, 16 and 17 are gas inlets and outlets to which tubes (not shown) for introducing gas are connected.

Reference numeral 18 is a light source plate formed into a rectangular shape by machining brass or aluminum, and is hollow inside, with a through hole 19 communicating with the top surface.

20 is a light source consisting of an electric heater that emits infrared rays;
The tip generates heat of approximately 600°C and emits infrared rays. This light source 20 is housed inside the light source holder 18, and its tip is positioned and shielded by a closing plate 21 so as to correspond to the through hole 19. Next, the gas cell 12 is connected to the light source block 18.
The transparent glass 15 is placed on top of the gas cell 12 and fixed to the light source block 18 with screws 22 and 22 from the top surface of the gas cell 12, with the transparent glass 15 corresponding to the through hole 19. Furthermore, cover the support member 9 from above the gas cell 12 and attach the gas cell 1 with screws 23 and 23 from both sides.
Fixed at 2. At this time, the support member 9 contains the gas cell 12, and only the gas port 16 and the outlet 17 are exposed to the outside from the notch 25.

The infrared detector 1 is soldered to the circuit board 8 in advance. The circuit board 8 is mounted on the support member 9 with the screws 26 while the infrared detector 1 is inserted into the support member 9 through the insertion hole 10.
．． Fix at 26. At this time, both screw holes are formed in such a positional relationship that the through hole 5 of the infrared detection 51 corresponds to the transparent glass 15. Further, the electrical component 11 is positioned on the side of the support member 9.

Next, FIG. 5 shows an electric circuit diagram of the infrared detector 1 and electric components 11 installed on the circuit board 8. The corresponding parts are indicated by broken lines. DC is a DC power source, Pl is an output terminal, and P2 is a ground terminal. 27 is an FET that amplifies the output of the infrared detection S1. 28 is an operational amplifier for AC amplification that amplifies the output of FET 27;
9 is a power supply for FET. The resistor 31 is used to adjust the amplification gain of the operational amplifier 28, thereby reducing variations in the gas sensor and making the device compatible. The output of the operational amplifier 28 is a rectifier circuit (not shown),
The data is connected to a circuit board to which an A/D conversion circuit and a microcomputer are attached, is inputted to the microcomputer, and is subjected to arithmetic processing as data for controlling and displaying gas concentration.

The infrared rays emitted from the light source 20 enter the passage 1 of the gas cell 12.
It is absorbed and attenuated in the process of passing through the gas to be measured flowing through the detector 1, and the remainder reaches the infrared detection section S of the detector 1. Since the amount of infrared rays absorbed by this gas changes depending on the concentration of the gas, the gas concentration can be captured as a change in the above-mentioned AC output and used as information for display or concentration control.

Here, the output of the FET is connected to the electrical component 11 at a connecting portion 30 on the circuit board 8.

Conventionally, the electrical component 11 was provided on a circuit board that was equipped with the rectifier circuit, etc., which was separate from the infrared detector 1, so this connection part 30 became a long lead wire, and noise could enter from there. Although there was a problem that the control became unstable, as in the present invention, the infrared detector 1 and the electric component 11 are placed on the same circuit board 8, and the minute output line and the power supply line are shortened, thereby suppressing the intrusion of noise. Furthermore, in the embodiment, the electrical component 11 is located outside the support member 9, so it is not affected by the heat from the light source 20.

Next, FIG. 6 shows another embodiment of the infrared detector 1, in which the electric component 11 is the infrared detector 1 on the circuit board 8.
It is attached to the side opposite to the one on which it is attached. This allows the distance of the connecting portion 30 to be further shortened, and the overall size of the infrared gas sensor A can be made even more compact.

In addition, although the sensor of the present invention was applied to detect carbon dioxide gas in the embodiment, the sensor is not limited thereto and can be applied to other types of gas. In that case, the material of the window 7 should be changed depending on the type of gas.

(g) Effects of the Invention According to the present invention, by extremely shortening the distance between the infrared detector of the infrared gas sensor and other electrical components, it is possible to suppress the intrusion of noise from there. As a result, the detection accuracy can be improved, and the overall size of the infrared gas sensor can be made extremely small, so that design constraints are eliminated, especially in small-sized devices.

[Brief explanation of drawings]

1 to 6 show embodiments of the present invention, FIG. 1 is a longitudinal sectional view of an infrared gas sensor, FIG. 2 is a perspective view of the same, and FIG. 3 is a modulation type pyroelectric infrared detector. 4 is a perspective view of the slit member, FIG. 5 is an electric circuit diagram of the infrared gas sensor, and FIG. 6 is a diagram showing another embodiment of the infrared gas sensor. 7
The figure is a perspective view of a conventional infrared detector. 1... Infrared detector, 8... Printed circuit board, 9
... Supporting member, 11... Electrical component, 12... Gas cell, 18... Light source block, 20... Light source, A.
...Infrared gas sensor S...Infrared detection section. Figure 1 Figure 6 Figure 2 0 1 8 71!1 Figure 3

Claims (1)

[Claims] 1) Consisting of a light source that generates infrared rays, a gas cell for circulating a gas to be measured, a modulation type infrared detector with a built-in piezoelectric bimorph chopper, and a support member for containing the infrared detector, In a device that obtains an output by making the infrared rays that have passed through the gas to be measured enter the infrared detector, the infrared detector is attached to a circuit board to which other electrical components are attached, and the circuit board is attached to the support member. An infrared gas sensor, wherein the infrared detector is fixed at a predetermined position within the support member.