JP2000283919A - Infrared gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive infrared gas analyzer mass productive and having a uniform detection performance between lots. SOLUTION: A piezo-resistance type semiconductor pressure sensor composed by forming a diaphragm (pressure receiving face) 2 by thinning a silicon single crystal substrate 1 from the back face by etching or the like, and by forming a piezo-resistance (gauge resistance) thereon by diffusion or ion implantation, is used as a gas concentration detecting part of this infrared gas analyzer. Thus, the inexpensive infrared gas analyzer capable of mass production, and having a uniform detection performance between lots, high sensitivity and high reliability, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared gas analyzer for measuring the concentration of a specific gas species by utilizing the gas pressure fluctuation accompanying the infrared spectrum absorption of a component gas to be measured.

[0002]

2. Description of the Related Art Many heteronuclear molecules consisting of two or more different atoms are irradiated with infrared light having a wavelength of 1 to 20 μm, and the transition of vibrational and rotational kinetic energy levels specific to the chemical species occurs. Absorbs certain infrared spectra and causes thermodynamic changes, such as an increase in internal energy, volume, or pressure. A non-dispersive infrared spectrometer is a device that measures the concentration of a gas component by utilizing such characteristics of the gas component.

FIG. 8 shows the configuration of a single-beam infrared gas analyzer. As shown in the figure, an infrared gas analyzer generally comprises a light source section 42 for generating infrared light, a cell section 44 into which a sample is introduced, and a detector section 46 for measuring the intensity of infrared light passing through the cell section. And the sample gas concentration is measured.

A light source section 42 generates an infrared light, and a chopper 50 for intermittently intermitting the infrared light with a heater 48 as a generation source to enter a cell section 44 and a detector section 46.
Consists of The cell portion 44 is a portion into which the sample is introduced, and the front and rear of the pipe are sealed with a window 54 made of infrared-transmissive glass or CaF2 capable of transmitting infrared rays in a wide spectral range. A gas inlet / outlet 56 is provided to allow gas to flow to the other end, and the inner surface thereof is mirror-finished or coated with gold or the like in order to efficiently reflect infrared light.

FIG. 9 shows a detailed view of the detector section 46. The detector part is divided into two front and rear chambers 24 and 26,
At least the front of the front room 24 and the front room 24 and the rear room 26
The partition between them is separated by a window 28 that transmits infrared light, and these two chambers have a structure connected by a bypass 30 that allows a small flow of gas. In addition, in order to measure the pressure difference between the front and rear chambers, it is connected to the pressure detection unit 34 via the partition walls of these two chambers or the introduction pipe 32. As the pressure detecting unit 34, an electric diaphragm or the like of a capacitance measuring type called a membrane capacitor is used. This utilizes a phenomenon in which one side of two electrodes is a diaphragm, the diaphragm bends when pressure is applied, and the capacitance changes due to a change in the distance between the electrodes. Furthermore, these two chambers contain, for example, CO
It is filled with only a chemical species such as 2 or a gas obtained by diluting the chemical species with an inert gas such as Ar, He, or N2.

[0006] The infrared light emitted from the light source passes through the cell unit 44 and enters the detector unit 46. At this time, if the component to be measured is present in the cell, a part of the incident infrared light is absorbed by the gas in the cell according to the gas concentration in the cell. The remaining infrared light is incident on the detector. The infrared light incident from the front of the detector front chamber is absorbed by the front chamber 24 and the rear chamber 26, and due to the pressure difference between the front and rear chambers caused by the energy absorption, the infrared light intensity before incidence on the detector, that is, the measured light intensity The component concentration can be measured.

[0007]

In such a detector for infrared analysis, a membrane capacitor which has been used for measuring a pressure difference between the front and rear chambers has a high sensitivity, but the manufacturing thereof requires a skilled technique by hand. , The productivity was inferior, the unit price was inevitably increased, and the lot-to-lot variation was large. The present invention has been made to solve the above problems, and has as its object to provide an infrared analyzer that can be mass-produced, is inexpensive, and has uniform performance between lots.

[0008]

In order to solve the above problems, an infrared spectrometer according to the present invention is provided with a light source for irradiating an infrared measuring light to a measuring cell at one end of the measuring cell.
At the other end of the measurement cell, two light receiving chambers are arranged in series in the optical axis direction of the measurement light at a position for receiving the measurement light transmitted through the measurement cell, and the two light reception chambers have a small bypass. A piezoresistive semiconductor pressure sensor as the detector, wherein the infrared spectrometer comprises a front and rear chamber type detector which communicates via a unit and converts a pressure difference between two light receiving chambers into an electric signal. Is used. As the piezoresistive semiconductor sensor, a differential pressure measurement type, an absolute pressure measurement type, a gauge pressure measurement type, or the like is used.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows a detector portion for detecting a gas concentration of an infrared gas analyzer of the present invention, and is an outline of a piezoresistive electronic diaphragm type pressure sensor (hereinafter, piezo pressure sensor). The piezo pressure sensor has a diaphragm (pressure receiving surface) 2 formed by thinning a silicon single crystal substrate 1 from the back surface by etching or the like, and a piezo resistor (gauge resistor) 3 formed thereon by diffusion or ion implantation.

FIG. 2 explains the operation principle of the piezo pressure sensor. First, the basic piezoresistive effect. When stress is applied to the piezoresistor, a crystal lattice is distorted, and the number of carriers in the semiconductor and the mobility change, so that the electrical conductivity, that is, the electrical resistance changes. It is a phenomenon.

Each piezoresistor (gauge resistor) 3 has two locations parallel to the center of the diaphragm 2 and 2 opposed to the circumference.
When the diaphragm 2 is distorted by applying pressure, a stress corresponding to the amount of distortion is generated in each piezoresistor, and the piezoresistors R1 to R4 change in proportion to the stress. When a Wheatstone bridge is formed by these four gauge resistors as shown in FIG. 3 and a voltage or current is applied, an output potential difference proportional to pressure is obtained. Now, let the resistance around the circumference be R
The potential difference V0 at the time of constant current drive with 1, R3 and the resistance of the central part being R2, R4 can be obtained by the following equation. V0 = (R1R3−R2R4) / (R1 + R2 + R3 + R4) * I FIG. 4 is a structural diagram of a differential pressure detection type sensor. Room 4, rear room 5
A pressure tube 14a for introducing a gas pressure is formed in each of the chambers, and detects a pressure difference between gases introduced into each chamber.

FIG. 5 shows an example in which a differential pressure type piezo pressure sensor is applied to a single beam type infrared gas analyzer. The detector section has an infrared-transparent CaF2 window 12 bonded to an aluminum body 9 having concentric holes of different diameters.
The detector is divided into two front and rear chambers 10 and 11. On the back of the detector, a black back plate 15 was arranged to prevent infrared light from entering from outside. In addition, a bypass 13 is provided between the two chambers as needed, which allows a very small flow of gas. When measuring CO2,
Both chambers are filled with CO2 gas diluted with the same concentration of an inert gas such as Ar or N2. Gas inlet pipes 14b are installed in both chambers.
Is connected. As the piezo pressure sensor 16, a sensor having a full scale of ± 1 kPa to ± 5 kPa was used. Since the piezo pressure sensor unit incorporates an electronic circuit 8 for performing arithmetic processing, an output signal can be obtained at a predetermined full scale by applying a necessary voltage thereto.

Most of the infrared light incident from the front of the detector is absorbed by the front chamber 10 and the rest is absorbed by the rear chamber 11. Since the front and rear chambers of the detector section are thermodynamically almost constant-volume systems, as a result, the pressure increases in each room, and a pressure difference occurs between the two chambers. This is connected to the piezo pressure sensor 16.
By functioning as a detector, it functions as a detector for infrared gas analyzers.

FIG. 6 shows an example in which the mechanism using the differential pressure sensor described in FIG. 5 is implemented by two gauge pressure or absolute pressure type piezo pressure sensors 17. By arranging a plurality of sensors in this manner, an effect equivalent to that of a differential pressure sensor can be obtained. FIG. 7 shows an example in which the present invention is applied to a tandem cell type using two conventional cells for sample and reference. In the figure, S indicates the position of a sample (sample gas) cell, and R indicates the position of a reference (comparison gas) cell. A sample light chamber 19a having a reference light chamber 18 and a reference light chamber 19b are provided. The difference between the gas pressure of the sample light chamber 19a and the gas pressure of the reference light chamber 19b is determined by the pressure sensor 21.
Is detected by

[0015]

According to the present invention, an infrared gas analyzer which can be mass-produced, is inexpensive, has uniform detection performance between lots, has high sensitivity, and has high reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a sensor part of an infrared gas analyzer of the present invention.

FIG. 2 is an operation diagram of a sensor unit of the infrared gas analyzer of the present invention.

FIG. 3 is an equivalent circuit diagram of a sensor unit of the infrared gas analyzer of the present invention.

FIG. 4 is a configuration diagram of a differential pressure detection type sensor of the infrared gas analyzer of the present invention.

FIG. 5 is a configuration diagram of a detector section of the infrared gas analyzer of the present invention.

FIG. 6 is another embodiment of the detector section of the infrared gas analyzer of the present invention.

FIG. 7 is another embodiment of the detector section of the infrared gas analyzer of the present invention.

FIG. 8 is a configuration diagram of a general infrared gas analyzer.

FIG. 9 is a configuration diagram of a detector section of a conventional infrared gas analyzer.

Claims (4)

[Claims] 1. A light source for irradiating an infrared measuring light to a measuring cell is disposed at one end of the measuring cell, and the measuring light transmitted through the measuring cell is received at the other end of the measuring cell. At the position, two light receiving chambers are arranged in series or in parallel with respect to the optical axis direction of the measurement light, and the two light receiving chambers communicate with each other via a small bypass portion, and a pressure difference between the two light receiving chambers is reduced. An infrared gas analyzer comprising a front-rear or left-right chamber type detector which is converted into an electric signal, wherein a piezoresistive semiconductor pressure sensor is used as the detector. 2. The infrared sensor according to claim 1, wherein at least one or more differential pressure measuring piezoresistive semiconductor pressure sensors are used as pressure detectors to measure the differential pressure between the front chamber and the rear chamber. Gas analyzer. 3. The method according to claim 1, wherein at least two or more absolute pressure measuring piezoresistive semiconductor pressure sensors are used as pressure detectors to individually measure the pressures in the front chamber and the rear chamber. Infrared gas analyzer. 4. The method according to claim 1, wherein at least two or more gauge pressure measuring piezoresistive semiconductor pressure sensors are used as pressure detectors to individually measure the pressures in the front chamber and the rear chamber. The infrared gas analyzer according to claim 1, wherein