JP2006119003A - Flow rate detection element for infrared gas analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow rate detection element for an infrared gas analyzer for attaining an improvement of sensing sensitivity and responsiveness without causing complication, large size, and cost increase of a structure. <P>SOLUTION: The flow rate detection element for an infrared gas analyzer includes a substrate 1 having a void part 1a as a gas flow passage, and a heater 4 for applying a constant voltage by being held in a meandering state through an insulation film 2 provided so as to block the void part 1a on the substrate 1. The flow rate detection element forms a plurality of gas flow passage holes 6 on an insulation film part except for a part holding the meandering heater 4, and arranges the meandering heater 4 except for a connection part 4b with an energization electrode 3 to the heater 4 in a region surrounded by a contour OL of the void part 1a on the substrate 1 so that the entire length part is not overlaid on the substrate 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flow rate detecting element for an infrared gas analyzer used as a detector of a non-dispersive infrared gas analyzer (NDIR). Specifically, the gas having the same absorption characteristics as the measurement target gas is filled, and is disposed in a gas passage that connects two gas chambers disposed in series or in parallel to the measurement cell, A substrate having a cavity as a gas flow path, and a heater which is held in a meandering state and is applied with a constant voltage via an insulating film provided on the substrate so as to block the cavity. The present invention relates to a flow rate detection element for an infrared gas analyzer in which a plurality of gas flow holes are formed in an insulating film portion excluding a portion for holding a heater.

  As shown in FIGS. 6 and 7, this type of flow detector for a general infrared gas analyzer includes two heaters 51a and 51b formed in a zigzag meandering manner from a metal foil such as nickel, and the like. It consists of plate materials 52a and 52b made of an insulating material such as glass for arranging and fixing the heaters 51a and 51b opposite to each other, and meandering heaters 51a in openings 53a and 53b formed in these plate materials 52a and 52b. , 51b and a gap between adjacent linear heater portions of the meandering heaters 51a, 51b is formed in the gas flow passage 54.

  Such an infrared gas analyzer flow rate detecting element is used by applying a constant voltage to the heaters 51a and 51b and controlling the temperature so as to be higher than the temperature of the gas filled in the gas chamber by a certain temperature. The And in the non-detection state where infrared rays are not irradiated, the two heaters 51a and 51b exhibit a temperature distribution as indicated by the symbol a in FIG. 7, but in the detection state where one gas chamber is irradiated with infrared rays, The gas filled in the gas chamber expands to generate a gas flow 55 in the gas flow passage 54 toward the other gas chamber. By this gas flow 55, the heater 51a on the upstream side (located on the left side in FIG. 7) is cooled according to the flow rate of the gas, and conversely, the heater 51b on the downstream side (located on the right side in FIG. 7) Then, it is heated by the heat deprived from the heater 51a on the upstream side, and exhibits a temperature distribution as shown by symbol b in FIG. Since the resistance values of the heaters 51a and 51b change due to such a change in temperature distribution, the gas flow rate is detected by outputting the change amount of the resistance value as a voltage value using a Wheatstone bridge circuit. This detected gas flow rate corresponds to the amount of infrared absorption (concentration of the measurement target gas) by the measurement target gas circulated in the measurement cell of the non-dispersion type infrared gas analyzer (not shown because it is well known). Therefore, the concentration of the measurement target gas is measured and analyzed by detecting the gas flow rate.

  By the way, in the flow rate detecting element for a general infrared gas analyzer having the above-described configuration, since the heaters 51a and 51b are simply formed in a meandering shape, when a voltage is applied to the Wheatstone bridge circuit, The temperature of the central part of the heaters 51a and 51b is higher than that of the peripheral part. As a result, when the gas flows, there is a problem that the temperature change in the central part of the heaters 51a and 51b, that is, the difference between the sensitivity and the temperature of the peripheral part occurs, and the resulting sensitivity becomes small.

  In order to solve such a problem, conventionally, only at an internal position surrounded by a heater held in a meandering manner through an insulating film, the gap area sandwiched between adjacent linear heater parts is smaller than the gap area. By forming a gas flow path composed of a plurality of gas flow holes so as to be set to a flow path area, heat transfer between the gas passing through the gas flow path and the heater is performed only in the central portion of the heater. As a result, there has been proposed a device which has obtained a large output due to an increase in efficiency of heat transfer, and has aimed to improve detection sensitivity and responsiveness (see, for example, Patent Document 1).

  Further, by providing auxiliary heating means on the periphery of the meandering heater on the substrate having a hollow portion as a gas flow passage to heat the flow rate detecting element itself, heat transfer from the heater to the substrate, that is, heat dissipation is compensated. In order to improve the detection sensitivity by increasing the average temperature in the cavity region, there has been conventionally proposed (for example, see Patent Document 2).

JP 2003-57087 A Japanese Patent Laid-Open No. 9-229853

  However, in all of the conventional examples described above, a part of the meandering heater is surrounded by the outline of the hollow portion of the substrate, that is, protrudes outside the gas flow path and overlaps with the substrate to contact the substrate from the heater. As a result, there is a problem that the temperature distribution of the gas flow path is not uniform, and the detection sensitivity and responsiveness cannot be sufficiently improved.

  In particular, when an auxiliary heating means such as that disclosed in Patent Document 2 is provided, not only does the structure of the flow rate detecting element itself become complicated and large, and the manufacturing cost increases, but also auxiliary heating in addition to the heat dissipation loss to the substrate. Therefore, there is a problem that the power consumption is very large and the running cost is inevitably increased.

  The present invention has been made in view of the above-described circumstances, and an object thereof is an infrared gas analyzer capable of improving detection sensitivity and responsiveness without causing a complicated structure, an increase in size, and an increase in cost. An object of the present invention is to provide a flow rate detecting element.

  In order to achieve the above object, the flow rate detecting element for an infrared gas analyzer according to the present invention is disposed in a gas passage that connects two gas chambers filled with a gas having the same absorption characteristics as the gas to be measured. A flow rate detecting element for an infrared gas analyzer, which is held in a meandering state via a substrate having a cavity as a gas flow path and an insulating film provided on the substrate so as to block the cavity. In a flow rate detecting element for an infrared gas analyzer, in which a plurality of gas flow holes are formed in an insulating film portion excluding a portion holding the meandering heater. The meandering heater excluding the connection portion with the electrode is arranged in a region surrounded by the outline of the hollow portion of the substrate so that the full length portion does not overlap the substrate.

  According to the present invention having the above-described configuration, the entire length of the meandering heater to which a constant voltage is applied is disposed in a region that does not contact the substrate. Since the temperature distribution near the circulation part can be made uniform, the detection sensitivity and the response can be improved. In addition, heat dissipation loss to the substrate can be suppressed only by the arrangement of the heater, and it is not necessary to install auxiliary heating means to suppress the heat dissipation, so the structure of the flow rate detection element itself is simplified and downsized In addition, the power consumption can be reduced.

  In particular, as described in claim 2, the meandering heater excluding the connection portion with the electrode for energization to the heater includes a portion located on the outermost periphery of the full length portion and a contour line of the cavity portion in the substrate. The heat dissipation loss to the substrate can be further reduced and the total length of the heater can be shortened, and the same resistance value can be obtained by centrally arranging the cavity in the vicinity of the center so that an annular insulating film portion exists between When the detection element is formed, the heater width can be narrowed and the sensors can be arranged at a higher density to further improve the detection sensitivity.

  Further, in the flow rate detecting element for an infrared gas analyzer according to the present invention, as described in claim 3, the meandering heater excluding the connection portion with the energization electrode to the heater is surrounded by the meandering heater. In order to increase the resistance, the heater wire width at both sides close to the energizing electrode part is set at a constant heater wire interval over the entire length so that the temperature of the region is uniform. By forming it narrower than the width, or by forming the heater line interval on both sides close to the energizing electrode part smaller than the heater line interval in the central part under a constant heater line width over its entire length, It becomes possible to make the temperature distribution in the central part and the peripheral part near the gas circulation part uniform, and the detection sensitivity can be further improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view of a flow rate detecting element (hereinafter simply referred to as a flow rate detecting element) A for an infrared gas analyzer according to the present invention, FIG. 2 is a longitudinal sectional view taken along line XX of FIG. It is a longitudinal cross-sectional view along the YY line of FIG. This flow rate detection element A is similar to the general flow rate detection element shown in FIGS. 6 and 7 in a gas passage that connects two gas chambers filled with a gas having the same absorption characteristics as the measurement target gas. The two detection element units A1 and A1 having the same shape and the same structure are arranged in two layers so as to be orthogonal to the gas passage.

  The detection element unit A1 of the flow rate detection element A meanders through a substrate 1 having a cavity 1a as a gas flow path and an insulating film 2 provided on the substrate 1 so as to block the cavity 1a. And a heater 4 to which a constant voltage is applied by the energizing electrodes 3 and 3, and a linear heater portion 4a adjacent to the insulating film 2 portion excluding the portion holding the meandering heater 4 , 4a, a plurality of oval gas flow holes 6 are formed in a state of being connected to the cavity 1a.

Here, an example of a manufacturing method of the detection element unit A1 will be briefly described. The substrate 1 is formed of amorphous glass or a crystalline material such as Si or MgO. A material having a high temperature coefficient such as Pt, Ni or NiCr is deposited in a meandering manner with a thickness of 0.1 to 0.5 μm, for example, by sputtering, and is exposed to form a heater 4 having a predetermined pattern. A photosensitive polyimide, an epoxy-based organic insulating thin film, or an inorganic insulating thin film such as SiO ₂ is deposited to a thickness of 0.5 to 3 μm on the top, and the heater 4 having the meandering pattern is formed from above by exposing it. The insulating film 2 to be held is formed, and then the substrate 1 is etched from the back side thereof to form a cavity 1a as a gas flow path.

  In each detection element unit A1 in the flow rate detection element A manufactured by the manufacturing method as in the above example, the meandering heater 4 has a full-length portion excluding the connection portions 4b and 4b with the electrodes 3 and 3 for energization. The substrate 1 is disposed in a region surrounded by the outline OL of the cavity 1 a so as not to overlap with the substrate 1. More specifically, the portion located on the outermost part of the full length portion of the meandering heater 4, that is, the folded heater portions 4 c that connect the adjacent linear heater portions 4 a and 4 a and the energizing electrodes 3 and 3, respectively. The annular insulating film portion 2a exists between the linear heater portions 4d, 4d connected to the connecting portions 4b, 4b and the outer line OL of the cavity portion 1a of the substrate 1, and is concentrated near the center of the cavity portion 1a. Has been placed.

  According to the flow rate detecting element A configured as described above, the meandering heater 4 is arranged in a concentrated manner in the vicinity of the central portion of the hollow portion 1a as a gas flow path in a region where the meandering heater 4 does not overlap the substrate 1. Therefore, a heat dissipation loss due to heat conduction from the heater 4 to the substrate 1 is suppressed, and the temperature in the vicinity of the gas circulation part (the cavity part 1a and the gas circulation hole 6) can be uniformly increased to obtain a large output. Further, it is possible to suppress the heat dissipation loss to the substrate 1 only by arranging the heater 4, and it is not necessary to install auxiliary heating means for suppressing the heat dissipation loss. Therefore, the structure of the flow rate detection element A itself is simplified. In addition to reducing the size and manufacturing cost, the overall power consumption is significantly reduced due to the fact that there is no extra power consumption for auxiliary heating and the heat dissipation loss to the substrate 1 is suppressed. It is possible to improve detection sensitivity and responsiveness.

  In the above embodiment, the meandering heater 4 is shown as having a constant heater line width over its entire length. However, as shown in FIG. The heater line width at both sides close to the energizing electrodes 3 and 3 is made narrower than the heater line width at the center part, or as shown in FIG. In addition, the heater wire spacing at both sides close to the energizing electrodes 3 and 3 is made smaller than the heater wire spacing at the central portion, and the Joule heat at the peripheral portion of the gas circulation portion is made. Can be made larger than the Joule heat in the central part, and the temperature distribution in the central part and the peripheral part in the vicinity of the gas circulation part can be made uniform or almost uniform. The voltage value output as the average value Kikushi, it is possible to further improve the detection sensitivity.

It is a top view of the flow volume detection element for infrared gas analyzers concerning the present invention. It is a longitudinal cross-sectional view along the XX line of FIG. It is a longitudinal cross-sectional view along the YY line of FIG. It is a top view of the principal part which shows the modification of the meandering heater in a flow volume detection element. It is a top view of the principal part which shows the other modification of the meandering heater in a flow volume detection element. It is a top view which shows the conventional thermal type flow volume detection element. It is the VV sectional view taken on the line of FIG.

Explanation of symbols

A Flow detection element for infrared gas analyzer 1 Substrate 1a Cavity part 2 Insulating film 3 Electrode for energization 4 Meandering heater 4a Linear heater part 4b Connection part with electrode for energization 6 Gas flow hole OL Outline of cavity part

Claims (3)

A flow rate detection element for an infrared gas analyzer disposed in a gas passage that connects two gas chambers filled with a gas having the same absorption characteristics as the measurement target gas, and a substrate having a cavity as a gas flow passage And a heater that is held in a meandering state and is applied with a constant voltage via an insulating film provided on the substrate so as to block the cavity, and an insulating film excluding a portion that holds the meandering heater In the flow detection element for an infrared gas analyzer formed by forming a plurality of gas flow holes in the part,
The meandering heater excluding the connection portion with the energization electrode to the heater is arranged in a region surrounded by the outline of the hollow portion of the substrate so that the full length portion does not overlap the substrate. A flow rate detecting element for an infrared gas analyzer.   The serpentine heater, excluding the connection portion with the electrode for energization to the heater, has an annular insulating film portion between the outermost portion of the full length portion and the outline of the hollow portion of the substrate. The flow rate detecting element for an infrared gas analyzer according to claim 1, wherein the flow rate detecting element is centrally arranged near the center of the cavity so as to exist.   The meandering heater, excluding the connection portion with the energizing electrode to the heater, has a uniform heater line interval over its entire length so that the temperature of the region surrounded by the meandering heater is uniform. The heater line width on both sides close to the energizing electrode part is formed narrower than the heater line width on the center part, or both sides close to the energizing electrode part with a constant heater line width over its entire length The flow rate detection element for an infrared gas analyzer according to claim 1 or 2, wherein the heater wire interval of the portion is formed smaller than the heater wire interval of the central portion.

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