JPH0579502U - Multilayer interference filter for gas analyzer - Google Patents

Abstract

(57) [Abstract] [Purpose] A multilayer interference filter for a gas analyzer, which enables a multilayer interference filter that is easy to manufacture and has excellent spectral characteristics to improve the measurement accuracy of measurement components. Get [Structure] The first light source 7a is provided on one side of the first cell 1a and the second cell 1b.
And the second light source 7b, the multilayer interference filter 8 and the main detector 12 and the sub-detector 13 are respectively arranged on the other side, and the sample gas 5 and the reference gas 6 are switched to the first by the switching operation of the four-way switching valve 4. It is configured to be alternately introduced into the first cell 1a and the second cell 1b. Then, the BP surface of the multilayer interference filter 8 is formed by stacking vapor-deposited thin films of Ge and SiO.
The surface is formed by stacking vapor-deposited thin films of Ge and ZnS.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

The present invention relates to a multilayer interference filter used in an infrared gas analyzer for measuring concentrations of NO gas, H ₂ O gas and other measurement components in various exhaust gases.

[0002]

[Prior Art]

 Known examples of infrared gas analyzers for measuring the concentrations of NO gas and other measurement components in various exhaust gases are shown in FIGS. In FIGS. 4 to 5, 21a and 21b are the first cell and the second cell that are configured to transmit infrared rays, and gas inlets 22a and 22b and gas outlets 23a and 23b are provided in these cells. ing. 24 is a sample gas supplied from the gas inlet 22a to the first cell 21a, 25 is a reference gas supplied from the gas inlet 22b to the second cell 21b, and 26a, 26b are one of the first and second cells 21a, 21b. The infrared light emitted from the first and second infrared light sources disposed on the side is incident on the first and second cells 21a and 21b as intermittent light by the chopper 27.

Reference numeral 28 is a multilayer interference filter disposed on the other side of the first and second cells 21a and 21b, 29 is a main detector on which infrared rays transmitted through the multilayer interference filter 27 are incident, and 30 is a main detector. Sub-detectors where infrared light transmitted through 29 is incident, 31a and 31b are pre-amplifiers to which the detection signals of main detector 29 and sub-detector 30 are input, and 32 is a pre-amplifier from the output signal of pre-amplifier 31a. It is a subtracter that subtracts the output signal of the amplifier 31b and outputs a measurement signal.

As shown in FIG. 5, the multilayer interference filter 28 has a bandpass surface 34 (hereinafter referred to as a BP surface) that transmits a wavelength band of infrared rays absorbed by NO gas on one surface of a substrate 33 made of Si. ), A short long cut surface 35 (hereinafter referred to as an SLC surface) for cutting a short wavelength band and a long wavelength band of infrared rays is formed on the other surface in order to reflect noise components other than the wavelength band to be transmitted. It is a thing. The BP surface 34 and the SLC surface 35 are formed by stacking vapor-deposited thin films of Ge, which is a high refractive index material, and ZnS, which is a low refractive index material, respectively, and also constitutes the BP surface 34. Since it is necessary to considerably increase the number of thin film layers forming the SLC plane 35 in comparison with the number of thin film layers, in those thicknesses, the SLC plane 35 is smaller than the BP plane 34. It will be quite thick.

In the infrared gas analyzer, the infrared rays of the first and second light sources 26a and 26b are incident on the first cell and the second cells 21a and 21b as intermittent light by the chopper 27, and the sample gas is input to the first cell 21a. 24 and the reference gas 25 are introduced into the second cell 21b. In this way, when the infrared rays enter the main detector 29 and the sub-detector 30 after passing through each of the first and second cells 21a and 21b and the multilayer interference filter 28, the main detector 29 And the sub-detector 30 input the respective detection signals to the subtractor 32, the subtractor 32 performs subtraction processing on each detection signal, and the signal corresponding to the NO gas concentration compensated for the influence of the interference component. Is output. The NO gas concentration is measured based on the output of the subtractor 32.

[0006]

[Problems to be solved by the device]

 As described above, the multilayer interference filter 28 used in the infrared gas analyzer is constructed by stacking the vapor deposition thin films composed of Ge and ZnS on the BP surface 34 and the SLC surface 35, respectively. It was done. Since ZnS has a very unstable sticking coefficient when it is stacked as a thin film on another layer by vacuum deposition, it is difficult to control the deposition environment and achieve the theoretical refractive index and film thickness. Is large, and there is a drawback that the deposition accuracy is reduced. However, even if the deposition accuracy of the ZnS film is lowered, the SLC surface 35 has almost no effect on its function, and even a multi-layered thin film composed of Ge and ZnS causes almost no trouble.

However, when the deposition accuracy of the ZnS thin film decreases, the BP surface 34 acts sensitively and affects the spectral characteristics. Therefore, the conventional multilayer interference filter 28 has a problem that the quality control of the BP surface 34 is quite difficult and the manufacturing cost is increased. Further, the influence of the BP surface 34 on the spectral characteristics affects the measurement accuracy of the infrared gas analyzer. The result of measuring the spectrum of this conventional multilayer interference filter 28 is spectrum B of FIG. 3, which has a high transmittance but the deposition accuracy of the ZnS film constituting the BP plane 34 is lowered, , It is found that the shape is disturbed and the spectral characteristics are affected.

It is also known that the thin film layer of the optical filter is made of Ge and SiO thin films. The vapor-deposited thin films of Ge and SiO have stable bonding properties and can be vapor-deposited with high precision, and therefore have almost no influence on the spectral characteristics of the optical filter. However, since SiO absorbs wavelengths having a transmission center wavelength of 5 μm or more, if SiO is used as each of the constituent materials of the BP surface and the SLC surface, the number of layers increases considerably and the transmittance is greatly reduced. It is known that it is difficult to use SiO as a multilayer film constituent material of an optical filter.

The present invention solves the above problems, and makes it possible to obtain a multilayer interference filter that is easy to manufacture and has excellent spectral characteristics, and to increase the measurement accuracy of the measurement component. It is an object of the present invention to obtain a multilayer film interference filter for a gas analyzer capable of performing the above.

[0010]

[Means for Solving the Problems]

 The multi-layer interference filter for gas analyzer of the present invention is a detector in which a light source for injecting infrared rays into one side of a cell through which a sample gas flows and an infrared ray transmitted through the cell in the other side are detected. In a multilayer interference filter in which the infrared rays can be transmitted between the light source and the detector, the bandpass surface on one side of the substrate forming the multilayer interference filter is Ge and SiO. Of the vapor deposited thin film, and the other short short cut surface is formed of the vapor deposited thin films of Ge and ZnS.

The substrate forming the multilayer interference filter can use any infrared transmitting optical material, and examples thereof include Si, Ge and sapphire. The multilayer interference filter can be arranged either on the downstream side or the upstream side of the cell. The format of the gas analyzer is arbitrary, for example, the format in which the sample gas and the reference gas are alternately introduced into each of the pair of cells, and the sample gas and the reference gas are introduced into one cell. Alternatively, the sample gas may be introduced into one of the pair of cells and the reference gas may be introduced into the other of the pair of cells as shown in the above-mentioned conventional example, and the infrared rays to be incident on each cell are interrupted by a chopper. You can pick up what you want to be light.

[0012]

[Action]

 The multilayer interference filter for a gas analyzer of the present invention is composed of Ge and SiO 2 on the BP surface and Ge and ZnS thin films on the SLC surface, respectively. As described above, SiO, which is a constituent material of the BP surface, absorbs a wavelength having a transmission center wavelength of 5 μm or more and reduces the transmittance. However, the number of layers of each Ge and SiO thin film that composes the BP surface is considerably smaller than that of the SLC surface, so the absorption amount of wavelengths of 5 μm or more by the SiO thin film that composes the BP surface is very large. In addition, the decrease in transmittance due to absorption of SiO can be reduced.

On the other hand, the vapor-deposited thin films of Ge and SiO constituting the BP surface have stable bonding properties, etc., and it is easy to control the vapor deposition environment and realize the theoretical refractive index and film thickness. Since it is easy to improve the deposition accuracy of each thin film of Ge and SiO, it is possible to almost eliminate the influence on the spectral characteristics, and it is relatively easy to form a BP surface having excellent spectral characteristics. can do. That is, the decrease in the transmittance due to the absorption of the wavelength of 5 μm or more by the SiO constituting the BP plane was sufficiently compensated by its excellent spectral characteristics while maintaining the high deposition accuracy of each thin film of Ge and SiO. This is what constitutes the BP plane.

In the Ge and ZnS constituting the SLC plane, as described above, it is difficult to maintain the deposition accuracy of the ZnS thin film, but the influence hardly occurs on the SLC plane, and the Ge and ZnS are not affected. And does not absorb light and has no effect on the transmittance. Therefore, the multilayer interference filter of the present invention has a slightly lowered transmittance, but it is sufficiently compensated by the excellent spectral characteristics of the BP surface, which is relatively easy to manufacture, and the infrared gas analyzer measurement It is possible to improve accuracy.

[0015]

【Example】

 An embodiment of the multilayer interference filter for a gas analyzer of the present invention will be described with reference to the NO 2 gas analyzer shown in FIGS. In FIGS. 1 and 2, 1a and 1b are the first cell and the second cell which are arranged in parallel with each other, and these are configured to be capable of transmitting infrared rays, and the gas inlet ports 2a and 2b and the gas outlet port 3a. , 3b are provided. Reference numeral 4 is a four-way switching valve connected to each of the gas inlets 2a and 2b. The sample gas 5 and the comparison gas 6 supplied to this are switched by operating the four-way switching valve 4, and the first and second cells 1a , 1b are alternately introduced.

Reference numerals 7a and 7b are arranged on one side of the first and second cells 1a and 1b, and a first light source and a second light source for injecting infrared rays into them, and 8 is the other side of the first and second cells 1a and 1b. The multi-layered interference filter arranged at is configured to transmit the absorption wavelength range of NO gas, which is the measurement component, and reflect the other wavelength ranges. As shown in FIG. 2, the multilayer interference filter 8 has a BP surface 10 formed by laminating vapor-deposited thin films of Ge and SiO on one surface of a substrate 9 made of Si, and Ge and ZnS on the other surface. The SLC surface 11 is formed by laminating the respective vapor-deposited thin films, and the SLC surface 11 is formed in a number of layers as compared with the BP surface 10.

Reference numeral 12 denotes a pneumatic main detector using a condenser microphone to which the infrared light transmitted through the multilayer interference filter 8 is incident. The main detector 12 is NO gas as a measurement component and CO _{2 as an} interference component. Is configured to be able to detect. Reference numeral 13 is a sub-detector of a pneumatic type in which the infrared ray that has passed through the main detector 12 is incident, and is configured so that CO ₂ can be detected. 14a and 14b are preamplifiers to which the detection signals of the main detector 12 and the sub-detector 13 are input, and 15 subtracts the output signal of the preamplifier 14b from the output signal of the preamplifier 14a and outputs the measurement signal. It is a subtractor.

In the NO gas analyzer configured as described above, the sample gas 5 such as exhaust gas and the reference gas 6 are respectively switched to the first and second cells 1a and 1b by the switching operation of the four-way switching valve 4. The first and second light sources 7a and 7b are alternately introduced into the infrared rays, and the infrared rays are incident on the first and second cells 1a and 1b, respectively. Then, each infrared ray that has passed through the gas introduced into each of the first and second cells 1a and 1b passes through the measurement multilayer interference filter 8 and is incident on the main detector 12, so that the main detector 12 A detection signal corresponding to the incident infrared ray is output, and the signal is input to the subtracter 15 via the preamplifier 14a. Further, since the infrared light incident on the main detector 12 passes through it and is incident on the sub-detector 13, the sub-detector 13 inputs the detection signal to the subtractor 15 via the preamplifier 14b. Therefore, the detection signal of the sub-detector 13 is subtracted from the detection signal of the main detector 12, and the subtractor 15 outputs a measurement signal corresponding to the NO gas concentration in which the influence of the interference component CO ₂ is compensated. The concentration of NO gas is measured based on the output signal of the subtractor 15.

The BP surface 10 of the multilayer interference filter 8 is a vapor-deposited thin film of Ge and SiO, and the number of stacked layers is smaller than that of the SLC surface 11. The thin film is vapor-deposited with high accuracy, and the SLC surface 11 is formed of vapor-deposited thin films of Ge and ZnS. The measurement result of the spectral spectrum of the multilayer interference filter 8 is the spectral spectrum A of FIG. 3, and the transmittance is slightly lower than the spectral spectrum B of the conventional multilayer interference filter. However, it is clear that the multilayer film interference filter 8 has excellent spectral characteristics in its form, with almost no disturbance as in the above-mentioned spectral distribution B. That is, it is clear that the decrease in the transmittance due to the use of the SiO 2 thin film on the BP surface 10 is sufficiently compensated by the excellent spectral characteristics. Therefore, since the multilayer interference filter 8 transmits the infrared wavelength band absorbed by the measurement component of the sample gas with high accuracy, the measurement component can be measured with high accuracy.

[0020]

[Effect of the device]

 As described above, the multilayer interference filter for a gas analyzer of the present invention has a band-pass surface formed on one surface of the substrate of Ge and SiO vapor-deposited thin films, and a short-long cut surface on the other surface of Ge and ZnS. The bandpass surface is formed by each vapor-deposited thin film, and the number of thin film layers forming the bandpass surface is considerably smaller than the number of thin film layers forming the short long cut surface. Therefore, although the thin film constituent material SiO of the bandpass surface absorbs a wavelength having a transmission center wavelength of 5 μm or more, since the number of layers is relatively small, it is possible to reduce the decrease in the transmittance due to the absorption of SiO. is there. And, since Ge and SiO that compose this bandpass surface have stable bonding properties of the respective vapor-deposited thin films and can be vapor-deposited with high precision, a bandpass surface having excellent spectral characteristics should be used. It is possible to configure the structure, and the excellent light distribution characteristic can sufficiently compensate for the decrease in the transmittance. Moreover, the quality control of the bandpass surface is easy, and the cost can be reduced.

In addition, since the deposition coefficient of ZnS vapor deposition thin film constituting the short long cut surface is rather unstable, the vapor deposition accuracy is slightly lowered, but it has almost no effect on the function of the short long cut surface. , The short long cut surface efficiently cuts the short wavelength band and long wavelength band of infrared rays that do not require transmission. Therefore, the multilayer interference filter for a gas analyzer accurately transmits the absorption wavelength region of the measurement component in the sample gas and makes it incident on the detector, thereby improving the measurement precision of the measurement component.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a gas analyzer according to an embodiment.

FIG. 2 is an enlarged view of a multilayer interference filter according to an embodiment.

FIG. 3 is a spectral spectrum diagram of a multilayer interference filter.

FIG. 4 is a configuration diagram of a conventional gas analyzer.

FIG. 5 is an enlarged view of a conventional multilayer interference filter.

[Explanation of symbols]

1a and 1b: first and second cells, 7a and 7b: first and second light sources, 8:
Multilayer interference filter, 9: substrate, 10: BP surface, 11: SL
C side.

Claims (1)

[Scope of utility model registration request] 1. A light source for injecting infrared rays into the cell is arranged on one side of a cell through which a sample gas flows, and a detector for detecting infrared rays transmitted through the cell is arranged on the other side thereof, and the light source and the detection are performed. In the multilayer interference filter arranged so that infrared rays can pass therethrough, the bandpass surface on one side of the substrate forming the multilayer interference filter is formed of vapor-deposited thin films of Ge and SiO, and A multilayer interference filter for a gas analyzer, characterized in that a short long cut surface is formed of vapor deposited thin films of Ge and ZnS.