JP2855841B2 - Infrared analyzer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to miniaturization of an analyzer using infrared rays.

<Prior Art> FIG. 5 is a diagram for explaining the principle of a conventional infrared spectrometer for measuring the concentration of a measurement gas from the difference in the amount of infrared absorption between a standard gas and a measurement gas. The light emitted from the infrared light source 1 is turned into an intermittent light by an optical sector 3 rotated by a synchronous motor 2 and then split into two light beams by a distribution cell 4 to enter a standard cell 5 and a measurement cell 6, respectively. The standard cell 5 is usually filled with an inert gas (such as N ₂ ) as a standard gas, and the incident infrared rays do not undergo characteristic absorption in this cell. on the other hand,
In the measurement cell 6, light is absorbed in a specific wavelength band according to the components and concentrations in the measurement gas. By detecting the difference in intensity between the two light beams, the concentration of the measurement gas component can be measured. The gas-filled detector 7 is composed of a room filled with a certain concentration of the measurement component gas and a microflow sensor 8 connected to the room. When intermittent light enters the room filled with the gas, it is sealed in the light beam. Only the light having the characteristic absorption wavelength of the gas is absorbed, and the gas in the closed room expands intermittently. The magnitude of the expansion force depends on the amount of light in the characteristic wavelength region of the measurement gas component incident on the room. In this case, the pressure difference between the two chambers is detected by the micro flow sensor 8 as a change in gas flow rate. After the electric output of the micro flow sensor 8 is amplified by the amplifier 9, the electric output is synchronously rectified by the synchronous rectification circuit 10 in synchronization with the rotation cycle of the rotating sector 3, and the density signal is output through the smoothing circuit 11 and the DC amplification circuit 12.

<Problems to be solved by the invention> However, the device having the above configuration is composed of a plurality of mechanical units and electric circuits, and as a whole, constitutes one system. In comparison, there are drawbacks in that the dimensions are very large and the amount of sample gas required for measurement is large. On the other hand, a gas sensor or the like having an element size has a problem that accuracy and sensitivity are very poor.

<Object of the Invention> The present invention has been made to solve the above-mentioned problems, and has as its object to realize an infrared analyzer having high accuracy, high sensitivity, and an element size.

<Means for Solving the Problems> The present invention relates to an infrared spectrometer that measures the concentration of a measurement gas from the difference in the amount of infrared absorption between a standard gas and a measurement gas. A standard cell, a measurement cell through which a measurement gas flows, a microvalve that introduces or discharges each gas into these cells, a micro light source that emits infrared light into each cell, and infrared light that has passed through each cell. An intermittent optical chopper, and a microminiature infrared sensor that detects infrared light transmitted through the optical chopper,
The point is that it is formed on a substrate using a micromachining technique.

<Effect> Since a very small measuring cell is used, the concentration can be measured with a small amount of measuring gas, and since the detection is performed with a very small infrared sensor, measurement can be performed with high sensitivity and high accuracy.

<Example> FIG. 1 is an exploded perspective view showing an infrared spectrometer according to the present invention. The measurement principle of this apparatus is to measure the concentration of the measurement gas from the difference in the amount of infrared absorption between the standard gas and the measurement gas, as in the case of FIG.

In the figure, 21 is an upper silicon substrate, 22 is an intermediate glass substrate, and 23 is a lower silicon substrate. The substrates 21 to 23 form a sandwich structure, are very firmly adhered to each other by electrostatic bonding, and are configured so that gas flowing inside does not leak to the outside. Reference numerals 24 and 25 are formed on the substrate 21. Micro valves for sampling for introducing a standard gas and a measurement gas into the cell, 26 and 27 are valve actuators for driving these micro valves 24 and 25, respectively. 29 is formed on the substrate 22, and through-holes for passing the standard gas and the measurement gas downward in the figure, 30, 31 respectively.
Are standard cells and measurement cells respectively formed on the substrate 23 by anisotropic etching of silicon, 32 and 33 are formed on the substrate 22, respectively, through holes for passing the standard gas and the measurement gas upward in the figure, 34 And 35 are formed on the substrate 21 and are microvalves for discharging a standard gas and a measurement gas from the cell, respectively, and 36 and 37 are valve actuators for driving the microvalves 34 and 35, respectively.

41 is a micro lamp (micro lamp) that emits light containing infrared rays, 42 and 43 are infrared transmitting films that transmit only infrared rays out of the light emitted from the micro lamp 41, and 44 and 45.
Are high-precision mirrors formed by depositing gold or the like on the inner walls of the standard cell 30 and the measurement cell 31, respectively, and reflecting films 46 and 43, which reflect light passing through the infrared transmitting films 42 and 43, respectively.
47 is a filter for selecting a wavelength on which the infrared light reflected by the mirrors 44 and 45 is incident, respectively, and 48 is a rotating type super movable by electrostatic force or the like in which the light transmitted through the filters 46 and 47 is periodically intermittent. A small optical chopper (micro chopper), 49 is an ultra-small infrared sensor such as a pyroelectric type or HgCdTe that detects infrared light transmitted through the optical chopper 48, and 50 is formed on the substrate 21 and output from the infrared sensor 49 This is a signal processing circuit that converts a signal into measurement data. Each of the above components is formed on each substrate by using a microfabrication technology for IC manufacturing or a microfabrication technology equivalent thereto.

The operation of the apparatus having the above configuration will be described below with reference to FIGS. 2 and 3. The same parts as those in FIG. 1 are denoted by the same symbols. The light emitted from the micro lamp 41 passes through the infrared transmitting films 42 and 43, so that only the infrared light enters the standard cell 30 and the measuring cell 31, respectively. Standard cell 30, measurement cell
The infrared lights 62 and 63 incident on 31 are reflected by mirrors 44 and 45, respectively, pass through the standard gas and the measurement gas, respectively, are again guided to filters 46 and 47 by mirrors 44 and 45, respectively, and Intermittent. The light that has passed through the optical chopper 48 is detected by the infrared sensor 49, and the signal processing circuit 50 calculates the concentration of the measurement gas based on the difference in the amount of transmitted light between the standard cell 30 and the measurement cell 31. In FIG. 2, reference numeral 61 denotes a seal ring used together with the microvalve 25. Third
In the figure, reference numeral 81 denotes an extraction electrode from the infrared sensor 49.

FIG. 4 shows the micro lamp shown in FIGS. 1 and 2.
41 is a cross-sectional view of a main part showing details of 41. FIG. 1 and 2 are denoted by the same reference numerals and description thereof is omitted.
Reference numeral 72 denotes a vacuum chamber formed by micromachining technology near one surface of the substrate 21 (hereinafter referred to as a lamp forming surface).
Is a filament formed so as to be supported by the substrate 21 in a cantilever manner inside the vacuum chamber 72 and coated with an infrared radiator. 74 is a lamp forming surface of the substrate 21 and the vacuum chamber.
A reflective heat-dissipating film 75 formed so as to cover a structural portion 77 (described later) on the 72 is arranged adjacent to the vacuum chamber 72 so that the thickness thereof is reduced on the other surface (hereinafter referred to as a light emitting surface) of the substrate 21. A light emitting portion composed of a processed portion, 76 is a reflective film formed around the light emitting portion 75 on the light emitting surface of the substrate 21, and 77 is a structural portion covering the upper portion to seal the vacuum chamber 72. . As the reflection heat dissipation film 74 and the reflection film 76, a metal film such as Au can be used. The length of the left and right sides of the substrates 21 to 23 in FIG. 1 can be, for example, 10 mm.

The operation of the apparatus having the above configuration will be described below. filament
The light emitted upward in FIG. 4 by the light emission of 73 is reflected downward by the reflective heat dissipation film 74, and is emitted outside from the light emitting section 75 together with the light emitted directly downward from the filament 73. In the light emitting portion 75, since the substrate 21 is thin, light absorption and attenuation are small. The reflecting film 76 on the lower side of the figure is a light emitting section 75
Since the light emitted obliquely from the substrate and the reflected light from the components on the lower side of the figure are reflected without entering the substrate 21, the efficiency can be increased. When a part of the radiation emitted upward in the drawing is absorbed by the substrate 21 and the temperature of the substrate 21 rises due to heat conduction from the filament 73, this heat is radiated with high efficiency by the reflective heat radiation film 74. Therefore, the substrate 21
Temperature rise can be suppressed. In order to reduce light absorption, a structure 77 for sealing the vacuum chamber 72 is formed to have a small thickness. Further, by forming the light emitting portion on the side opposite to the lamp forming surface, since no convex portion exists on the light emitting surface, it is easy to form a sophisticated structure for utilizing the emitted light. Here, since the microlamp 41 uses silicon as a substrate, it absorbs at a light wavelength of 1.1 μm or less and transmits at a wavelength longer than that, so that an infrared lamp can be constituted as it is. In addition, if any ceramic is formed in the light emitting part, not only silicon,
An infrared lamp that efficiently emits infrared light can be configured. In FIG. 4, on the light emitting surface of the substrate 21,
Although the concave portion is formed by the micro-processing technique to reduce the thickness of the light emitting section 75, this processing becomes unnecessary if the entire substrate 21 is thinned.

According to the infrared analyzer with this configuration, sensors with low accuracy and sensitivity are integrated and miniaturized like an IC, thereby realizing a high-sensitivity, high-accuracy, ultra-compact, high-performance infrared analyzer. can do. That is, for example, when the pyroelectric type is used as the infrared sensor 49, the heat capacity is small because it is very small, and the temperature easily rises even with a small amount of light, so that the sensitivity is improved. In addition, since an ultra-small measurement cell is used, the sample amount of the measurement gas can be small. As a result, an epoch-making infrared analyzer having a size equal to or smaller than that of the conventional gas sensor and having sensitivity and accuracy equal to or higher than that of the conventional infrared analyzer can be realized.

Also, by using the microfabrication technology of IC manufacturing to integrate itself into a small sensor component, mass production and low cost can be realized.

In the above embodiment, the optical chopper 48 is not limited to the one using the piezoelectric actuator or the electrostatic actuator, but may be an optical one such as an electro-optical element.

As the standard gas, any inert gas having no infrared absorption such as N ₂ can be used.

By selecting the filters 46 and 47, 1 μm to 1
Absorption at any wavelength between 0 μm can be used for measurement.

Further, the micro lamp 41 is not limited to the configuration shown in FIG. 4, and any light source that emits light including infrared rays and can be realized by using micro processing technology can be used.

Alternatively, a thermal sensor may be used as an infrared sensor to detect thermal expansion as in the related art using a pressure sensor or the like formed by a micromachining technique.

Further, by adopting a structure in which the optical path in the cell is reflected multiple times by the reflection film, the amount of infrared absorption can be increased and the S / N ratio can be improved.

In addition, by forming a plurality of measurement cells on the same substrate and incorporating different wavelength filters and optical sensors for each measurement cell, a multi-component analysis such as gas chromatography can be performed in real time.

<Effect of the Invention> As described above, according to the present invention, an infrared spectrometer with a high accuracy and high sensitivity and an element size can be realized.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing one embodiment of an infrared spectrometer according to the present invention, FIGS. 2 and 3 are cross-sectional views showing the operation of the apparatus shown in FIG. 1, and FIG. FIG. 2 is a sectional view of a main part showing details of a micro lamp 41 in FIG. 2 and FIG.
FIG. 5 is an explanatory view of the principle showing a conventional infrared analyzer. 21,22,23 …… Substrate, 24,25,34,35 …… Micro valve, 3
0: Standard cell, 31: Measurement cell, 41: Ultra-small light source, 4
8 …… Optical chopper, 49 …… Microminiature infrared sensor, 62,63 ……
Infrared.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Ishii 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation (56) References JP-A-1-97841 (JP, A) JP-A Sho 61-186804 (JP, A) JP-A-63-98548 (JP, A) JP-A-62-261036 (JP, A) JP-A 64-13439 (JP, A) JP-A-3-197846 (JP, A) A) International Publication No. 91/10122 (WO, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 21/00-21/01, 21/17-21/6 1

Claims (1)

(57) [Claims] An infrared spectrometer for measuring the concentration of a measurement gas from the difference in the amount of infrared absorption between a standard gas and a measurement gas, comprising: a standard cell for flowing a standard gas; a measurement cell for flowing a measurement gas; A micro-valve for introducing or discharging each of the gases, a microminiature light source for emitting infrared light into each of the cells, an optical chopper for intermittently transmitting infrared light transmitted through each of the cells, and detecting infrared light transmitted through the optical chopper. An infrared spectrometer characterized in that an ultra-small infrared sensor is formed on a substrate using micromachining technology.