JPH03209150A - Infrared type gas sensor - Google Patents

Abstract

PURPOSE:To miniaturize the gas sensor by housing an IR light source into a light source block and fixing the light source to a gas cell and a supporting member of an IR detecting part. CONSTITUTION:A gas to be measured enters a gas inlet 16 and after dust is removed by an air filter, the gas flows in the gas cell 12 and is emitted from a gas outlet 17. The light source 20 causes the front end of an electric heater to generate heat and to radiate IR rays. The IR rays are absorbed in the process when the gas to be measured passes and are attenuated. The remaining IR rays arrive at an IR detector 1. A chopper C of the IR detector 1 opens and closes a slit member 4 by a piezoelectric vibrator 3 and intermits the incident IR rays from a through-hole 5. The IR detecting part s housed in a sealing box 2 generates an AC signal and detects the gas concn. by the change thereof. The detector 1 is mounted to a printed circuit board 8 and is hermetically supported in a supporting member 9. The detector is fixed by the gas cell 12 together with a light source block 18, by which the entire part is miniaturized.

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 the 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 chotsuba 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.

(c) Problems to be Solved by the Invention According to the above structure, since the motor 102 and the metal disc l03 are included, the entire device becomes large and a very large installation volume is required. There is a problem in that the design of the entire device to which it is attached is severely restricted.

Therefore, in recent years, a so-called modulation type pyroelectric infrared detector using a piezoelectric bimorph oscillator has been developed. Although this reduces the overall size of the sensor, it reduces the distance between the light source and the infrared detection part. Therefore, there was a problem that the infrared detection section was damaged by the heat from the light source.

The present invention aims to solve this problem.

(2) Means for Solving the Problems The present invention provides an infrared gas sensor that obtains an output by irradiating infrared rays that have passed through a gas to be measured onto an infrared detecting section, and in which a light source for generating infrared rays is housed. A light source block made of a thermally conductive material has an infrared light passing section through which infrared light from The gas cell is fixed to one surface of the light source block on the infrared passing section side, and the supporting member is attached to the gas cell with the infrared detection section sealed. The light source block is located and fixed on the opposite side of the light source block, and a mounting hole is formed on the other surface of the light source block.

(E) Function According to the present invention, the overall size of the infrared gas sensor can be extremely miniaturized, and the positioning of the light source, gas cell, and infrared detection section can be easily performed. Meanwhile, heat generated from the light source is dissipated during the process of being conducted through the support member. Furthermore, the heat of the light source block is conducted through the member attached to the attachment hole and dissipated.

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

FIG. 1 is an exploded perspective view of an infrared gas sensor A of the present invention, FIG. 2 is a perspective view of the assembled state, FIG. The figure shows a longitudinal cross-sectional view in a plane perpendicular to FIG. 3, and FIG. 5 shows a bottom view of the same. Further, FIG. 7 shows an exploded perspective view of a so-called modulation type pyroelectric infrared detector 1 to be housed within the support plate 9. As shown in FIG.

The detection 51 houses the above-mentioned infrared detection unit S in the shield box 2, and a chopper C is inserted into the shield box 2 from 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. established,
Further, the entire body is covered with a case 6 having a through hole 5 formed at a corresponding position. The slit member 4 is made by attaching two plates each having a slit in an overlapping relationship as shown in FIG.
The slit is opened and closed by the vibration, and the infrared ray U that enters through the through hole 5 and reaches the infrared detection part S is interrupted.
An output corresponding to the amount of infrared rays is generated as an AC signal of the same frequency as the input frequency of chopper C.

With this structure, the infrared detector 1 can be made very small and can be mounted on a printed circuit board. After the signal from the infrared detector 1 is rectified and A/D converted, it is input to a microcomputer (not shown) and is subjected to arithmetic processing as data for controlling and displaying the gas concentration.

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 plate for supporting the board 8. The support plate 9 is made of a thin stainless steel plate having a diameter of about 8 and is shaped like a box, and is open downward and has an insertion hole 10 formed in its upper surface. Also,
Other electronic components 11 to which the infrared detector 1 is electrically connected are also attached to the substrate 8.

12 is a gas cell formed into a rectangular shape by cutting out brass or 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; A through hole l4 as an infrared transmitting portion is formed above and below through the passage 13, and transparent glass 15, 15
The top and bottom are sealed. Further, 16 and 17 are gas inlets and outlets for introducing and discharging gas.

Reference numeral 18 is a light source block made of brass or machined aluminum and shaped into a rectangular shape, and the inside is hollow, and furthermore, there is a through hole 19 as an infrared passage part that communicates the hollow part with the upper surface. It is well-formed.

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.

Next, the assembly procedure of each part will be explained with reference to FIG.

The light source 20 is housed inside the light source block 18, and its tip portion is positioned in correspondence with the through hole 19 and is shielded by a closing plate 2l. Next, the gas cell 12 is placed on the light source block 18 as shown by the solid line arrow in the figure, and with the transparent glass l5 corresponding to the through hole l9, the screw hole 22b is passed through the screw hole 22a formed through the gas cell l2 from the upper surface of the gas cell l2. , 22b and screws 22, 22 to fix the gas cell 12 to the light source block l8. Furthermore, a support plate 9 is placed over the gas cell 12 as indicated by the broken line arrow in the figure, and screw holes 23a formed in the side surfaces of the support plate 9 and the gas cell l2 are inserted. The support plate 9 is fixed to the gas cell 12 with screws 23, 23 at 23a, 23b, 23b. At this time, the support plate 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 thereof. The depth of the notch 25 is such that the deepest part thereof is the gas inlet l6.
Alternatively, the screw holes 23a and 23 are in contact with the outlet 17.
Positioning becomes very easy by placing them in a relationship where b coincides with each other.

The infrared detection 51 is soldered to the board 8 in advance. The substrate 8 is then fixed to the support plate 9 with screws 26, with the detector 1 inserted into the support plate 9 through the insertion hole 10. At this time, both screw holes 26a, 26a, 26b, and 26b are set in such a positional relationship that the through hole 5 of the infrared detector 1 corresponds to the transparent glass 15. Further, the substrate 8 closes the insertion hole 10. On the other hand, a screw hole 28 is provided on the bottom surface of the light source block 18.
a, 28a is clearly visible.

By assembling the light source block 18, gas cell 12, and support plate 9 together with the gas cell 12 interposed between the light source block l8 and the infrared detector 1 in this manner, the entire infrared gas sensor A can be miniaturized. At the same time, the light source 20, the through holes 15, 15, and the infrared detector 1 can be positioned in a straight line very easily. As a result, the light source 20 and the infrared detector 1 come close to each other,
There is a concern that the infrared detection section S will be stressed by the heat from the light source 20, but since the support plate 9 is made of a thin plate with good heat dissipation, the heat emitted from the light source 20 will be transferred to the support plate 9.
Since the infrared rays are dissipated in the process of being conducted, it is possible to prevent the infrared detection section S from deteriorating due to heat. Furthermore, the support plate 9 and the substrate 8 are shaped to seal the area around the infrared detector 1, thereby preventing dust and light from entering from the outside, and preventing changes in the amount of infrared rays incident on the infrared detector S. We ensure that detection is performed in good conditions.

Next, FIG. 6 shows the state in which the infrared gas sensor A is attached to the equipment. The infrared gas sensor A is attached and fixed to the exterior plate 29 of the device using screws 28, 28 through the screw holes 28a, 28a on the lower surface of the light source block 18. As a result, the heat generated from the light source 20 is transferred to the light source block 18.
Since the infrared rays are conducted from the infrared rays to the exterior plate 29 and radiated from there, deterioration of the infrared detecting section S due to heat is even better prevented. In addition, each screw 26, 23, 22 can be removed as shown in Figure 6, so parts can be replaced while still attached to the device.
Maintenance work becomes easier.

A tube 32 for introducing a gas to be measured with an air filter 31 interposed therebetween is connected to the gas port 16, and a tube 33 for discharging gas is connected to the gas outlet 17, and the entire body is covered with a cover 34.

The infrared rays emitted from the light source 20 pass through the tube 16, remove dust from the air filter 31, and enter the gas inlet 1.
6 towards the gas outlet 17 of the gas cell 12 passage 13
It is absorbed and attenuated during the process of passing through the gas to be measured, and the remainder reaches the infrared detection section S of the detector 1.

The amount of infrared rays absorbed by this gas changes depending on the concentration of the gas. In other words, the higher the concentration, the less the amount of infrared rays that reaches the gas, and the lower the concentration, the more. It can be captured and used as information for display and concentration control.

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, the overall size of the infrared gas sensor can be extremely reduced, so that design constraints are eliminated, especially in small-sized devices. In addition, since the light source, the gas to be measured, and the infrared detector are located very close to each other, it is easy to position the three, and defects caused by misalignment can be eliminated. This is prevented by heat radiation from the support plate and the equipment to which it is attached. Furthermore, since the infrared gas sensor of the present invention can be disassembled while still attached to the device, maintenance work is extremely easy.

[Brief explanation of drawings]

1 to 8 show embodiments of the present invention. FIG. 1 is an exploded perspective view of an infrared gas sensor, FIG. 2 is a perspective view of the same assembled state, and FIG. 3 shows a gas inlet and an outlet. FIG. 4 is a vertical cross-sectional view of the infrared gas sensor in a plane perpendicular to FIG. 3, FIG. 5 is a bottom view of the infrared gas sensor, and FIG. 7 is an exploded perspective view of a modulation type pyroelectric infrared detector, FIG. 8 is a perspective view of a slit member, and FIG. 9 is a conventional one. FIG. 2 is a perspective view of an infrared detector. 1... Infrared detector, 8... Printed circuit board, 9
...Support plate, l2...Gas cell, l4...Through hole (
Infrared transmitting section), 16... Gas inlet, 17... Gas outlet, l8... Light source block, 19... Through hole (infrared passing section), 20... Light source, 28a... Screw hole ,A
...Infrared gas sensor S...Infrared detection section.

Claims (1)

[Claims] 1) In a device that obtains an output by irradiating an infrared detection section with infrared rays that have passed through the gas to be measured, a thermal detector that houses the light source for generating infrared rays and has an infrared passing section through which the infrared rays from the light source passes. a light source block made of a conductive material; a gas cell having an infrared transmitting section through which the gas to be measured flows; and a box-shaped box made of a thin thermally conductive material, with the infrared detecting section attached therein. The gas cell is fixed to one surface of the light source block on the infrared passing section side, and the support member is located on the opposite side of the gas cell from the light source block while sealing the infrared detection section. An infrared gas sensor, characterized in that the light source block is fixed to the light source block, and a mounting hole is formed on the other surface of the light source block.