JPH05215685A - Infrared gas analyzer - Google Patents

Abstract

PURPOSE:To provide an infrared gas analyzer constituted so as to enhance the analytical accuracy of component gas by preventing the thermal effect on the sensor attaching block of a detection part and suppressing the oblique incidence of light on a band-pass filter. CONSTITUTION:In an absorbancy type infrared gas analyzer wherein an infrared ray source is arranged on the incident side of a measuring cell 1 filled with sample gas and a detection part 4 having an infrared sensor 6 and a band-pass filter 7 incorporated therein is arranged on the emitting side of said cell 1, a heat insulating shield spacer 9 having the light pervious hole 9a communicating with the infrared sensor opened thereto is interposed between the end surface on the emitting side of the measuring cell and the detection part not only to suppress the improper heating and temp. rise of the sensor attaching block by the beam transmitted through the measuring cell but also to prevent the incidence of light on the band-pass filter in an oblique direction to prevent the generation of a side band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an absorption type infrared gas analyzer for qualitatively and quantitatively analyzing various component gases contained in a sample gas.

[0002]

2. Description of the Related Art The absorption type infrared gas analyzer mentioned above is
Qualitative and quantitative analysis of the sample gas is performed from the amount of infrared absorption by the measurement component gas contained in the sample gas. This method generally has good selectivity and high measurement sensitivity, so it is used in various fields as a gas analyzer. Widely used.

Next, the structure of a conventional single-beam absorption type infrared gas analyzer and its operating principle will be described with reference to FIG. In the figure, 1 is a measuring cell through which a sample gas flows, 2 is an infrared light source provided on the incident side of the measuring cell 1, 3 is a rotary chopper that intermittently interrupts the luminous flux emitted from the infrared light source 2, and 4 is the emitting side of the measuring cell 1. Is a detector installed on the sensor mounting block 5
A plurality of infrared sensors 6 corresponding to various measurement component gases contained in the sample gas are bandpass filters (multilayer film interference filters for giving infrared sensors wavelength selectivity).
It is installed as a pair with 7. The infrared sensor 6
Is a solid-state sensor such as a pyroelectric sensor or a semiconductor sensor.

With this structure, the infrared light emitted from the light source 2 is contained in the sample gas in the process of entering the measurement cell 1 as a light beam 8 which is intermittently cut by the chopper 3 at a constant period and is transmitted through the measurement cell 1. Infrared wavelengths peculiar to various measurement component gases are absorbed according to the concentration of the components. Further, a part of the light flux transmitted through the measurement cell 1 is received by each infrared sensor 6 through the bandpass filter 7 through the opening window of the sensor mounting block 5, and the detection signal corresponding to the amount of the light is converted into an electric signal to the outside. Taken out.

[0005]

By the way, the following problems remain in the structure in which the detecting portion 4 is arranged directly opposite to the emission side end surface of the measuring cell 1 as described above. That is, among the luminous fluxes 8 that have passed through the measurement cell 1, reference numerals 8a,
A part of the light flux represented by 8b reaches the infrared sensor 7 through the bandpass filter 6, but the other light flux 8c irradiates the sensor mounting block 5 (for example, made of aluminum) to heat the block. For this reason, the temperature of the sensor mounting block 5 rises and heat is transferred to the infrared sensor 6, which causes a drift with respect to the sensor detection signal. Therefore,
Conventionally, a temperature compensating element is incorporated in the sensor mounting block 5 together with the infrared sensor, and means for compensating the temperature of the sensor detection signal due to a change in ambient temperature is taken.
Even with this method, if a different temperature change is applied between the infrared sensor and the temperature compensating element due to the uneven temperature distribution of the sensor mounting block 5, a drift may occur and the S / N ratio may be lowered.

As another problem, a bandpass filter (multilayer interference filter) combined with the infrared sensor 6 is provided.
7 is basically designed to exhibit a predetermined wavelength selection characteristic under the condition that a light ray is incident parallel to the optical axis,
When the light beam 8b shown in the figure passes through the measurement cell 1 and is totally reflected on the wall surface and light is incident on the bandpass filter 7 from an oblique direction, sidebands appear and the wavelength selectivity to the infrared sensor is increased. There is a problem that it adversely affects the.

The present invention has been made in view of the above points, and an object of the present invention is to solve the above-mentioned problems by preventing thermal influence on a sensor mounting block of a detection unit and oblique incidence of light on a bandpass filter. An object of the present invention is to provide an infrared gas analyzer capable of suppressing the component gas to improve the accuracy of analysis.

[0008]

In order to achieve the above object, in the infrared gas analyzer of the present invention, a light transmitting hole communicating with the infrared sensor is opened between the emitting side end face of the measuring cell and the detecting portion. Then, a heat-insulating light-shielding spacer that covers the front surface of the sensor mounting block is provided and configured.

Further, in the light-shielding spacer having the above structure, it is preferable that the inner peripheral wall surface of the light-transmitting hole opened in the spacer is formed as a light-absorbing surface having a low light reflectance.

[0010]

With the above construction, the light flux transmitted through the measuring cell is shielded by the light-shielding spacer except the light-transmitting hole of the light-shielding spacer, so that the sensor mounting block is not directly irradiated with infrared rays and heated. In addition, the light-shielding spacer itself is made of a heat insulating material such as rubber and has almost no heat transfer to the sensor mounting block side, and the influence of thermal drift on the detection signal of the infrared sensor is reduced.

Further, by largely selecting the thickness of the light-shielding spacer in advance, most of the light entering the light-transmitting hole of the spacer from the front oblique direction is mostly transmitted through the light-transmitting hole before reaching the bandpass filter. Hit the inner wall. Here, by setting the inner peripheral wall surface of the light transmitting hole as a light absorbing surface having a low light reflectance, only the light entering the light transmitting hole of the light shielding spacer from an oblique direction is absorbed and cut by the wall surface. Therefore, the ratio of the incident light from the oblique direction to the bandpass filter in the latter stage is minimized, and the adverse effect of the wavelength selectivity on the infrared sensor such as the side band caused by the oblique incident light hardly appears.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, in which the same members corresponding to those in FIG. 2 are designated by the same reference numerals. In the illustrated embodiment, the emitting end face of the measuring cell 1 and the detector 4
A light-shielding spacer 9 made of a heat insulating material having a low light reflectance, such as rubber, is newly interposed between and.
The light-shielding spacer 9 has a light-transmitting hole 9a at a position corresponding to the infrared sensor 6 incorporated in the sensor mounting block 5 of the detection unit 4. When the material of the light-shielding spacer itself reflects light well, at least the inner peripheral wall surface of the light-transmitting hole 9a is roughened or light-absorbing material is coated to reflect the light. It is better to lower the rate.

With this configuration, of the light flux 8 emitted from the infrared light source (see FIG. 2) and transmitted through the measurement cell 1,
Light fluxes 8a and 8b entering the light transmitting hole 9a of the light shielding spacer 9
The light beam 8c except for is shielded by the light shielding spacer 9 and is not directly irradiated to the sensor mounting block 5 at the rear portion. In addition, since the light-shielding spacer itself has a heat insulating property, there is almost no heat transfer to the detecting portion 4, so that improper heating and uneven temperature of the sensor mounting block 5 can be prevented.

Of the light beams 8a and 8b entering the light transmitting hole 9a of the light-shielding spacer 9, a light beam 8a parallel to the optical axis.
Is transmitted through the transparent hole 9a as it is, and the bandpass filter 7
On the other hand, most of the light beam 8b incident from the oblique direction hits the inner peripheral wall surface of the light transmitting hole and is absorbed and cut in the process of passing through the light transmitting hole 9a. Therefore, the proportion of light obliquely incident on the bandpass filter 7 in the subsequent stage is extremely small, and the influence on the measurement and analysis result due to the sideband is significantly reduced.

[0015]

As described above, according to the structure of the present invention, the sensor mounting block of the detecting portion is measured by the function of the heat insulating light-shielding spacer interposed between the emitting end face of the measuring cell and the detecting portion. It is possible to effectively prevent undesired heating and temperature rise due to direct irradiation of the light flux transmitted through the cell. As a result, undue heating and temperature fluctuations around the infrared sensor incorporated in the sensor mounting block are reduced, so that stable temperature compensation can be performed in the detection unit. further,
By interposing the light-shielding spacer, it is possible to significantly reduce the measurement and analysis accuracy of the infrared gas analyzer, such as reducing the ratio of incident light from the diagonal direction with respect to the bandpass filter and suppressing the generation of a cissade band.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the main configuration of an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of a conventional single-beam infrared gas analyzer

[Explanation of symbols]

 1 Measuring Cell 2 Infrared Light Source 4 Detecting Section 5 Sensor Mounting Block 6 Infrared Sensor 7 Band Pass Filter 8 Luminous Flux 9 Light Shielding Spacer 9a Transparent Hole

Claims (2)

[Claims] 1. An infrared ray of absorption type in which an infrared light source is provided on the incident side of a measuring cell filled with a sample gas and an infrared sensor is provided on the emitting side together with a bandpass filter in a sensor mounting block. In the gas analyzer, a heat-insulating light-shielding spacer that covers the front surface of the sensor mounting block by opening a light-transmitting hole that communicates with the infrared sensor is provided between the emission end surface of the measurement cell and the detection unit. Infrared gas analyzer. 2. The infrared gas analyzer according to claim 1, wherein an inner peripheral wall surface of the light transmitting hole opened in the light shielding spacer is a light absorbing surface having a low light reflectance.