JPH04282446A - Method, element and apparatus for detecting concentration of gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for detecting an organic gas or vapor (hereinafter referred to as gas), a gas detection element used therein, and a gas detection apparatus using such a gas detection element. It is especially used to detect gases such as organic solvents and fuel oil.

0002

[Prior Art] Gas detection elements conventionally used in this type of gas detection device include catalytic combustion type gas detection elements;
There are semiconductor type gas detection elements using metal oxides, thermal conduction type gas detection elements that utilize differences in thermal conductivity of gases, etc.

[0003] Also, Special Publication No. 43-6836, Utility Publication No. 54
- As disclosed in Publication No. 15672, conductive powder is dispersed and mixed into a polymeric material such as natural rubber or silicone rubber whose outer surface tends to undergo swelling deformation or volume change when exposed to organic gas. There are sensing elements that use film resistors.

0004

[Problems to be Solved by the Invention] Therefore, in the conventional gas detection method and device of this type, the above-mentioned catalytic combustion type, semiconductor type, thermal conduction type, etc. gas detection elements all have temperatures of 100 to 500°C. During measurement, depending on the concentration of the gas, it may become a source of ignition and even cause an explosion. Therefore, these gas detection elements must be made to have an explosion-proof structure, resulting in a problem that the structure is complicated, large in size, and expensive. In addition, gas detection elements using such film resistors do not require a heating mechanism and can be used at room temperature, so there is no risk of ignition or explosion, and they have the advantage of being explosion-proof themselves. It has the drawbacks of low gas detection sensitivity in a low concentration range and high temperature dependence of gas detection sensitivity.

Therefore, in order to solve the problems of the conventional gas detection element using a film resistor, the present invention maintains the detection element itself at a specific low temperature. A gas detection method with improved gas detection sensitivity,
The object of the present invention is to provide a gas detection element for use therein.

[0006]

[Means for Solving the Problems] The structure of the method, gas detection element, and gas detection device of the present invention to achieve the object will be explained using FIGS. 1 to 8 corresponding to each embodiment. In the first invention, as shown in FIGS. 1 to 3, the concentration of the gas is detected by measuring the electrical resistance value of the film resistor (1a), which changes when the outer surface is exposed to and comes into contact with the gas to be detected. The gas detection method is characterized in that the film resistor (1a) is maintained at a specific temperature lower than the temperature of the detection gas atmosphere, and the electrical resistance value is measured.

In the second invention, in FIGS. 1 to 6, the lower surface (1b) of the film resistor (1a) is provided with a refrigerant (3a) inside.
This gas detection element is formed and bonded to the side surface of the pipe body (3) through which the gas flows.

A third aspect of the invention is that in FIGS. 1 to 7, the film resistor (1a) is connected to the cold contact surface (4) of the thermocouple element (4).
c) is a gas detection element having a structure in which the gas detection element is bonded with an electrically insulating layer (2) interposed therebetween.

[0009] In a fourth aspect of the present invention, in FIGS. 1 to 8, the upper surface of the film resistor (1a) is exposed to the gas to be detected, and the lower surface (1b) is on the inner surface of the gas distribution pipe (13) to be detected. and is attached to the surface of a thermal conductor (6) connected to a cooling member (7) provided on the outside of the gas distribution pipe (13) to be detected, via an electrically insulating layer (2). This is a gas detection device equipped with a gas detection element (10).

0010

[Operation] Since the present invention has such a configuration and structure, the method of the present invention is such that the polymer member constituting the coating material absorbs the gas that comes into contact with the outer surface and swells, thereby forming a carbon conductor. Bonds and contacts between particles are relaxed, increasing electrical resistance, and the degree of swelling depends on the concentration of the gas to be detected, and even at the same concentration, the lower the temperature of the film resistor, the more it swells. This is based on the principle that it becomes easier to do. Therefore, by maintaining the film resistor at a temperature lower than the detection atmosphere temperature, low concentration gas can be detected with high sensitivity.

Furthermore, in the gas detection element and detection device of the present invention, the substrate on which the film resistor is bonded is tubular and a refrigerant is circulated inside to cool the substrate, or the cold junction surface of the thermoelectric element is cooled. The film resistor can be maintained at a low specific temperature and can be read and measured accurately and easily on a large scale as a high value electrical resistance.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. In the figure, FIGS. 1 to 3 are 1 to 3 of the first method of the present invention.
1 is a diagram showing a configuration of an apparatus according to an embodiment of the method of the present invention, and FIG. 3 is a sectional view showing the structure of a gas detection element. That is, the detection device for carrying out the method of the present invention has a configuration as shown in FIG.
2) to the measurement container (13).
), the measurement container (
13) The film resistor (1a) of the gas detection element (1) described below is installed so as to cross orthogonally within the gas detection element (1).
While touching the outer surface of the gas, it is guided from the outlet (15) at the other end to the flow meter (16), and then sucked in by the pump (17) to control the constant flow of gas throughout the device. .

The structure of the gas sensing element (1) of the present invention is shown in FIG.
- In FIG. 6, as shown in the external view shown in FIG. 2 and the cross-sectional view shown in FIG. 3, a pair of electrodes ( 5a,
5a) and lead wires (5b, 5b), and according to the conventional example described above, a polymeric material such as natural rubber or silicone rubber with carbon powder uniformly dispersed therein is used to obtain a predetermined resistance value. , to form a film by coating both electrodes (5a, 5a) to form a film resistor (1a). Cooling water (3a) is passed through the duct hole (3b) of the glass tube (3) of the film resistor (1a).

Further, in the gas detection device of the present invention, as shown in FIG. 8, the upper surface of the film resistor (1a) is exposed to the gas to be detected, and the lower surface (1b) is connected to the gas distribution pipe (1a) to be detected.
13) and connected to the cooling member (7) provided outside the gas distribution tube (13) to be detected, through an electrically insulating layer (2). This is a gas detection device equipped with a gas detection element (10) bonded to the gas detection element (10).

The operating procedure of the method of the present invention is as follows: Using the apparatus outlined above, first, fresh air is flowed into the measuring container (13), and the glass tube (3) to which the film resistor (1a) is attached is heated. Water at a predetermined temperature (3
a) Water is passed through and the internal temperature is set to 1℃, 21℃, and 50℃, respectively.
The base value is measured while maintaining the temperature at a predetermined temperature of °C. Next, add toluene vapor to the gas bag (11) at 0.25v each.
ol%, 0.50vol%, 0.75vol%, 1.0
Sample gas is prepared to maintain gas concentrations of 0 vol% and 1.25 vol%. Next, the film resistor (1a) is maintained at a temperature of 1° C., 21° C., and 50° C., respectively, and the inside of the measuring container (13) is replaced with the above-mentioned toluene-containing air. The gas flow rate during measurement is 50 ml/min.
Next, read the value when the resistance value of the gas detection element (1) becomes stable.

In the method of the present invention, an example was shown in which a gas detection element using a glass tube, which is an electrical insulator, was used.
Using a gas detection device with a film resistor provided on the cold junction surface of a metal tube or thermoelectric element with good thermal conductivity through an electrical insulating layer, or a gas detection device with a heat dissipation fin as a member to cool the film resistor. It's okay. The key is to keep the film resistor constant at a specific temperature lower than the atmosphere of the gas to be detected so that the gas to be detected uniformly contacts the gas sensing element.

[0017] The results measured using the above procedure are shown in Figure 9 (A
1, A2, A3), gas detection element (1)
It can be seen that by lowering the temperature, the degree of change in resistance increases with respect to the same concentration of toluene-containing air, resulting in higher sensitivity. Furthermore, when the temperature of the gas detection element (1) changes, the resistance value changes greatly for gases of the same concentration, indicating that the resistance value is highly dependent on temperature, and according to the method of the present invention,
The temperature of the gas detection element (1) can be specified and kept constant, and highly reliable measurement results can be obtained.

Furthermore, benzene was measured in the same manner as in the case of toluene, and for comparison, when the temperature of the gas detection element (1) was 21°C, the dotted line (A) in FIG.
2. In B2), also increase the temperature of the gas detection element (1) by 1°C.
When lowered to
The difference between 1 and B1 is much larger. That is, boiling point 1
Toluene (A1, A2) with a boiling point of 10°C has a greater temperature dependence than benzene (B1, B2) with a boiling point of 80°C. That is, by keeping the gas sensing element (1) at a low temperature, gas selectivity can be significantly improved. Conversely, by selecting the temperature of the gas detection element (1), it is also possible to provide selectivity of the gas to be measured.

The principle of the present invention will be explained in more detail. The swelling action of the coating material (1a) of the gas detection element (1) due to the gas is a kind of dissolution phenomenon, and the swelling rate is determined by the SP value (Solubility Parameter) of the gas molecules.
meter). The closer the SP value of a substance is to that of the polymer membrane, the higher the solubility in the outer surface film (1a), the better the substance swells, and the higher the detection sensitivity of the gas detection element (1). The rate of swelling by this gas also depends on the relative vapor concentration of the substance at that temperature (vapor concentration/saturated vapor concentration at that temperature). In other words, it depends on the degree of wetting of the film due to steam (equilibrium content). The film (1a), which is moist to some extent, reaches equilibrium when the relative concentration of vapor generated from itself matches the relative concentration of the gas phase. Therefore, even if the vapor concentration in the gas phase is constant, the higher the temperature, the lower the relative vapor concentration, the easier it is to dry, and the film (1a) is less likely to get wet. Furthermore, the lower the boiling point of a substance, the lower the relative vapor concentration at a constant temperature and constant concentration, and the difference in boiling point depending on the type of gas causes a significant difference in detection sensitivity. In other words, as mentioned above, toluene with a boiling point of 110°C has a higher detection sensitivity than benzene with a boiling point of 80°C.

From the above, film resistor (1a
) By maintaining the film temperature at a constant temperature lower than the temperature of the detection atmosphere, low concentration gases can be detected with high accuracy and sensitivity without the need for a heating mechanism. In this way, the film resistor (1
Until now, there has been no gas detection element (1) based on the principle of operation by cooling a).

Next, an example of the gas detection element (1) will be described. The gas sensing element (1) shown in the sectional view showing the configuration of the device in FIG. 1, the enlarged sectional view of the same part in FIG. 3, the external view of the element in FIG. 2, and the sectional view in FIG. 3) flat strip-shaped electrode plates (5a, 5a) are arranged at intervals, and are connected to a resistance meter (18) with lead wires (5b, 5b). (1a) is the electrode (5
This is a film resistor formed to cover parts a and 5a). The ceramic base (3) is provided with a duct (3b) that serves as a passage for a refrigerant (3a) such as air or water for cooling.

The above is the basic structure, and as an application example, in order to maintain good heat conduction and enhance the cooling effect,
When the base body is a metal tube (3), Figs. 4 and 6
As shown in the cross-sectional view, electrode plates (5a, 5a) are formed on the surface with an insulating layer (2) interposed therebetween. In addition, when using the electronic cooling element (4) of the thermoelectric element, as shown in the cross section of FIG. (5a, 5a) and film resistor (
1a), then a thermoelectric element (
A power source (4) and lead wires (4b, 4b) to connect to it are required; a refrigerant and its flow path are not required. In that case,
As shown by the dotted line, it may be attached to the inner wall surface of the gas distribution pipe (13), or it may be used by being suspended inside the pipe (13).

Furthermore, in the gas detection device of the present invention shown in FIG. 8, the upper surface of the film resistor (1a) is exposed to the gas to be detected, and the lower surface (1b) is exposed to the gas distribution pipe (13). arranged on the inner surface of the gas flow pipe (
13) A cooling member such as a cooling fin provided on the outside of the
This gas detection device is equipped with a gas detection element (10) that is bonded to the metal surface of a thermal conductor (6) connected to a heat conductor (6) via an electrically insulating layer (2).

Although the embodiments considered to be representative of the present invention have been described above, the present invention is not necessarily limited to the structures of these embodiments, and the present invention is not necessarily limited to the structures of these embodiments. The present invention can be modified and implemented as appropriate within the scope of achieving the purpose of the present invention and having the following effects.

[0025]

Effects of the Invention As is already clear from the above description, the method of the present invention maintains the film resistor (1a) at a temperature lower than the temperature of the detection gas atmosphere, thereby allowing a low concentration gas to be used in the process compared to conventional elements. This gas detection method has remarkable effects that cannot be expected from conventional methods, such as high precision and high sensitivity detection without the need for a heating mechanism.

[0026] In the second invention, a pair of electrodes (5a, 5a) and lead wires (5b, 5b) are arranged at intervals on the outer surface of the tube (3), and the carbon powder is uniformly spread. A polymeric material dispersed in the gas detection element (
Due to the structure of the film resistor (1a) in 1), by passing the refrigerant (3a) through the duct hole (3b) of the tube body (3), the film resistor (1a) can be easily and reliably brought to a low temperature. This gas detection element has an effect that can be maintained.

Further, the third invention provides a film resistor (1a
) is attached to the cold junction surface (4c) of the thermocouple element (4) via the electrically insulating layer (2) with good thermal conductivity, so it can be easily and easily cooled without flowing a refrigerant. This gas detection element has the effect of reliably maintaining the film resistor (1a) at a low temperature. Furthermore, the gas detection element (10) used in the gas detection device of the fourth invention is
This method skillfully utilizes the principle of the present invention, and is particularly effective when the temperature of the gas to be detected is higher than the outside temperature (room temperature) and the difference is large. Further, in the gas detection device of the fourth invention, when the temperature of the gas to be detected is particularly high,
Gas detection element (10) without cooling member (7)
) can also be arranged inside the gas flow pipe (13).

As described above, a gas detection element using a film resistor has an inherently explosion-proof structure and can be applied to a low power consumption type gas alarm. By selecting the SP value of the material, detection sensitivity and selectivity can be improved. Another advantage is that the thickness of the film resistor and the spacing between the electrodes can be freely selected to adjust the detection sensitivity and response speed. Further, as an additional effect, by stopping the cooling, the temperature can be increased, promoting the desorption of the adsorbed gas, and shortening the return time to the zero point.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway cross-sectional explanatory diagram showing the configuration of an apparatus according to an embodiment of the method of the present invention.

FIG. 2 is an external view of a gas detection element used in the method of the present invention.

FIG. 3 is a sectional view taken along line III-III of an embodiment of the gas detection element used in the method of the present invention shown in FIG.

FIG. 4 is a partial cross-sectional view of another embodiment of the gas sensing element of the present invention.

FIG. 5 is a partially cutaway sectional view of another embodiment of the gas sensing element of the present invention.

FIG. 6 is a sectional view of another embodiment of the gas sensing element of the present invention.

FIG. 7 is a cross-sectional explanatory diagram of an embodiment of the present invention to which a thermoelectric element is applied.

FIG. 8 is a sectional view showing the structure of the gas detection device of the present invention.

FIG. 9 is a diagram showing changes in the resistance value of the gas sensing element at various temperatures at various concentrations of toluene gas in the method of the present invention.

FIG. 10 is a diagram showing the difference in the change in resistance value due to the temperature difference between the gas detection elements for toluene gas and benzene gas between the method of the present invention and an example of a conventional method.

[Explanation of symbols]

(1) Gas detection element (1a) Film resistor (1b) Bottom surface of film resistor (2) Electrical insulation layer (3) Pipe body (3a) Refrigerant (3b) Refrigerant flow path (4) Thermocouple element (4c) Cold contact surface (6) Thermal conductor (7) Cooling member (10) Gas detection element (13) Gas flow pipe

Claims (4)

[Claims] 1. A gas detection method for detecting the gas concentration by measuring the electrical resistance value of the film resistor (1a), which changes when the outer surface is exposed to and comes into contact with the gas to be detected, comprising: A gas detection method characterized in that the film resistor (1a) is maintained at a specific temperature lower than the temperature of the detection gas atmosphere and the electrical resistance value is measured. 2. The film resistor (1a) according to claim 1.
A gas detection element characterized in that a lower surface (1b) of the element is formed and adhered to an outer surface of a tube (3) through which a refrigerant (3a) flows. 3. The film resistor (1a) according to claim 1.
A gas sensing element characterized in that: is formed by adhering to a cold contact surface (4c) of a thermocouple element (4) via an electrically insulating layer (2). 4. The film resistor (1a) according to claim 1.
The upper surface of is exposed to the gas to be detected, and the lower surface (1b) is
On the surface of a thermal conductor (6) arranged on the inner surface of the gas distribution tube to be detected (13) and connected to the cooling member (7) provided on the outside of the gas distribution tube to be detected (13), Gas sensing element (10) adhered via electrical insulating layer (2)
) A gas detection device characterized by comprising: