JPH01313735A - Infrared-ray gas detector - Google Patents

Abstract

PURPOSE:To measure many kinds of gas concentration by one kind of optical filter by providing an optical filter having a band pass characteristic being variable electro-optically. CONSTITUTION:A two-dimensional image sensor 2 is placed on a base 1, and a pyroelectric thin plate 3 is provided on its upper part, by which an infrared- ray image sensor is constituted. On its upper part, an optical filter 10 having a three-layer structure in which an electro-optical element 5 of PLZT, etc., is pinched between two pieces of polarizers 4, 4 is provided. On the upper face of a case 6, an infrared-ray transmission window 7 is provided and from the bottom face, a lead wire 8 is drawn out. In the electro-optical element 5, groove- shaped electrodes 5a, 5b are provided on the lower face side, and that which has superposed an AC modulation voltage on a DC bias is applied through the lead wire 8. Transmissivity of the optical filter 10 depends on an applied voltage, therefore, by selecting a suitable voltage, the optical filter having a passing band in the absorption wavelength of gas to be detected or its vicinity is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an infrared gas detection device, and more specifically,
The present invention relates to an infrared gas detection device that can measure the concentration of a gas by detecting the amount of infrared rays transmitted through the gas using its infrared absorption characteristics.

[Conventional technology]

FIG. 6 is a schematic perspective view of a conventional infrared gas detection device.

In FIG. 6, a CCD (Charge Coupled Device) is equipped with pixels 21 arranged in a two-dimensional matrix.
The electrodes of each pixel 21 are formed by vapor deposition on the surface of an image sensor 22 using a semiconductor device.

A pyroelectric thin plate 23, which is an infrared detector, is provided on the front surface of the pyroelectric thin plate 23, and electrodes are deposited on the back surface of the pyroelectric thin plate 23 in a matrix pattern corresponding to the electrodes of each pixel 21 of the image sensor 22. ) the bumper is deposited,
It is crimped to the electrode of each pixel 21.

The surface of the pyroelectric thin plate 23 is covered with an optical filter 24 having a certain bandpass characteristic. In the infrared gas detection device having the above configuration, the infrared ray A having a certain wavelength band and filtered by the optical filter 24 generates thermal distortion on the pyroelectric thin plate 23. In the distorted pyroelectric thin plate 23, an electromotive force is generated due to the piezoelectric effect, and charges are accumulated in each pixel 21 of the image sensor 22.

The amount of accumulated charge in each pixel 21 has a value corresponding to the amount of infrared ray A that has passed through the pyroelectric thin plate 23. The accumulated charges are sequentially transferred within the image sensor 22 and taken out from the video signal output terminal 25.

By the way, gases generally absorb infrared rays at specific wavelengths,
Furthermore, it has the property of absorbing infrared rays in an amount that corresponds to the concentration of the gas. Therefore, if the optical filter 24 having the characteristic of transmitting the infrared absorption wavelength of the gas to be detected is used in the above-mentioned infrared gas detection device, only the infrared rays of that wavelength will be transmitted, and the amount of infrared rays absorbed by the gas to be detected will be transmitted. can be measured, so the concentration of the gas to be detected can be determined from the absorbed amount.

Since the infrared gas detection device described above is equipped with a two-dimensional image sensor, it is also possible to detect a two-dimensional concentration distribution of the gas to be detected.

[Problem to be solved by the invention]

In the conventional infrared gas detection device described above, the optical filter 24
Since the infrared transmission band wavelength of is constant for one type of filter, only one type of gas concentration can be measured.

Therefore, in order to detect the concentration distribution of several types of gases, there is a problem in that it is necessary to use multiple detection devices depending on the infrared absorption wavelength of each gas, or to replace and use multiple optical filters. .

In view of the above circumstances, it is an object of the present invention to provide an infrared gas detection device capable of measuring the concentration of many types of gases with one type of optical filter using a filtering means having an electro-optically variable transmission characteristic. With the goal.

[Means to solve the problem]

An infrared gas detection device according to the present invention includes a filtering means having a pass band in the infrared region, and an infrared detection means for detecting an amount of infrared rays filtered by the filtering means, wherein the filtering means is , which is characterized by having a characteristic that the passband is electro-optically variable.

[Effect]

By providing a filtering means having a characteristic of electro-optically variable pass band, the value of the wavelength of infrared rays passing through the filtering means can be electrically controlled and set to an arbitrary value.

Therefore, by setting the infrared passband of the filtering means according to the value of the infrared absorption wavelength of the gas to be detected,
It is possible to measure the concentration of many types of gases.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to drawings showing embodiments thereof.

FIG. 1 is a structural diagram of an infrared gas detection device according to the present invention.

A two-dimensional image sensor 2 made of, for example, a CCD is arranged on a base 1, and on the top thereof, for example, LiTa0z
A pyroelectric thin plate 3 made of the following is provided, and infrared detection means, that is, an infrared image sensor, is constructed with the same structure as the conventional one.

There are two polarizers 4, 4 on the top of the infrared image sensor.
An optical filter 10 having a three-layer structure in which an electro-optical element 5 such as PLZT is sandwiched is provided.

The optical filter 10, which is the filtering means described above, has electro-optically variable transmission characteristics. The infrared image sensor and optical filter 10 configured as described above are housed in a case 6.

An infrared transmitting window 7 made of silicon, for example, is provided on the top surface of the case 6 to allow infrared rays P to enter, and from the bottom surface of the case 6, leads connected to the image sensor 2, the electro-optical element 5, etc. are provided. Line 8 is drawn out.

FIG. 2 is a perspective view of the optical filter 10 from below, and FIG. 3 is a schematic structural diagram of the optical filter 0. As shown in FIG.

The broken line arrow in the figure represents infrared rays P. As shown in FIG. 3, the electro-optical element 5 is provided with groove-shaped electrodes 5a, 5a on the lower surface thereof, with a groove load of 1.0 and an interval of d between the inner ends of the two grooves.

The image sensor 2 is located below the portion between the two groove-shaped electrodes 5a, 5a.

A voltage is applied from a power source through a lead wire 8 between the two groove-shaped electrodes 5a, 5a.

Next, the operating principle of the optical filter 10 will be explained.

For example, in FIG. 3, when no voltage is applied to the electro-optical element 5, the electro-optical element 5 is an optically isotropic medium, so the infrared rays P transmitted through the upper polarizer are transmitted through the electro-optical element 5. Even after that, the polarization direction does not change.

Therefore, the infrared rays P are transmitted in orthogonal polarization directions (polarizer 4 in the figure,
It cannot pass between the two polarizers 4°4 having the arrow mark in 4). On the other hand, when a voltage is applied to the electro-optic element 5, the infrared rays P undergo a phase change due to the electro-optic effect. Therefore, the infrared ray P is a component that coincides with the polarization axis of the polarizer (analyzer) 4 on the side of the pyroelectric thin plate 3 (see the solid line arrow in the figure).
Only people will be able to pass through.

The amplitude E when the infrared ray P exits the polarizer 4 on the pyroelectric thin plate 3 side
0 is the amplitude of the infrared rays P incident on the electro-optical element 5, and Eo" = E4" 5in2 (Δψ/2) - (
1).

Therefore the wavelength λ. The outgoing intensity I of the infrared rays P relative to the incident intensity K of the optical filter 10 is expressed by equation (2).

However, in the above formula li There is a relationship.

Here, Δψ: Phase change V that polarized infrared rays P undergoes in the crystal of electro-optical element 5: Voltage applied to the lead wire 8 of the infrared gas detection device Vλ/2: Half-wave voltage no: Ordinary refractive index n, : extraordinary refractive index rc + +33 + '13' electro-optic constant.

Polarized wavelength λ. The phase change Δψ that the electro-optical element 5 undergoes in the crystal of the infrared ray P is expressed by the following equation.

λ.

(no go r +3 no" r :+*)
E) ・”(6) where E is the strength of the electric field in the crystal.

(6) +31. (4), (5) and E=V
Substituting /d gives π V .

The voltage V applied to the lead wire 8 of the infrared gas detection device
is the DC bias V, the AC modulation voltage V, sinω,
Add the superimposed t. Then...(8) becomes.

Here, if we select ■5 so that θ+πVb/VA/2=0, we get the following.

Here, the AC modulation voltage Vm sinωm j =V,!
/2, the transmittance (1/K) of infrared rays P is maximum.

From the above, it can be seen that the transmittance of the optical filter is controlled by the applied voltage V. Also, this transmittance is V,! , □, but as is clear from equation (3), λ. and V27□ have a unique correspondence relationship. Therefore the wavelength λ. It is possible to determine the voltage (2) that exhibits the maximum transmittance for infrared rays. Figure 5 shows PLZT λ=3.3μm (C
It is a graph showing the relationship between the applied voltage V and the transmittance at the absorption wavelength of Ha, which takes the maximum value at 172V.

This characteristic expresses equations (2) or (9), and since the functions of these equations are cos functions, they have periodic peaks, and the peaks in the necessary infrared 'm' pH range can be used. .

Since the transmittance thus depends on the applied voltage V, selecting an appropriate voltage makes it possible to obtain an optical filter having a passband at or near the absorption wavelength of the gas to be detected.

Note that it is also possible to configure an optical filter with a narrow passband by using a plurality of electro-optical elements and combining their respective passbands.

In the apparatus of the present invention as described above, the applied voltage is set to a predetermined value depending on the gas to be detected. Then, the absorbed amount of the gas will be detected by the pyroelectric thin plate 3 and the image sensor 2. If the same thing is done by changing the voltage, it becomes possible to detect multiple gases.

Note that in the above embodiment, since a two-dimensional image sensor is used, a two-dimensional gas concentration distribution can also be measured. It goes without saying that the present invention can also be used when a plurality of detection gases are mixed.

Furthermore, the present invention can also be applied to a device in which infrared rays are detected by a single photoelectric conversion element without using a two-dimensional image sensor.

〔Effect of the invention〕

As described in detail above, the infrared gas detection device of the present invention is equipped with an optical filter having an electro-optically variable band-pass characteristic, so that a plurality of detection devices corresponding to the infrared absorption wavelength of each gas can be used. There is no need to use a filter or replace multiple optical filters.
Since the concentration of many types of gases can be measured with one type of optical filter, it is possible to improve measurement efficiency and reduce costs.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of an infrared gas detection device according to the present invention, Fig. 2 is a perspective view of an optical filter, Fig. 3 is a structural diagram of an optical filter, and Fig. 4 shows the wavelength of transmitted infrared rays of the optical filter. A graph showing the relationship with the half-wavelength voltage, FIG. 5 is a voltage-transmittance characteristic diagram, and Part 6 is a perspective view of a conventional infrared gas detection device. 2... Image sensor 3... Infrared detector 4...
・Polarizer 5... Electro-optical element 5a... Groove electrode
10... Optical filter patent Applicant Sanyo Electric Co., Ltd. Agent Patent attorney Noboru Kono P Figure 2 P Kakatsu Figure 3 % 4 Figure vJ6 Application chamber fL (v) % 5 Figure

Claims (1)

[Scope of Claims] 1. An infrared gas detection device comprising a filtering means having a passband in the infrared region and an infrared detecting means for detecting the amount of infrared rays filtered by the filtering means, wherein the filtering means is electrically An infrared gas detection device characterized by having an optically variable passband characteristic.