JPS5833499B2 - Reducing gas detection device and its manufacturing method - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a reducing (flammable) material using a metal oxide semiconductor.
The present invention relates to a gas detection device and a manufacturing method thereof.

In recent years, various materials have been studied for detecting reducing gases.

Among these, especially 5n02, Fe 203, ZnO, T
Metal oxide semiconductors in which metal oxides such as iO2 and WO3 are added with platinum-based metals such as pt and Pd, or their oxides as activation catalysts, are attracting attention as sensing element materials.

Devices using these materials for sensing elements have 200 to 500
When heated to a constant temperature suitable for the sensing element at a high temperature of 0°C, various reducing gases such as hydrogen, carbon oxide, methane, propane, alcohol, or ammonia are adsorbed onto the element surface or the element is heated to a certain temperature suitable for the sensing element. This is an application of the phenomenon in which the electrical resistance of metal oxide semiconductors changes due to catalytic combustion on the surface.

In order to reliably and reproducibly quantitatively detect reducing gases as large changes in electrical resistance, these reducing gas detection devices use actual elements such as NiCr, Fe-Cr5Pt-I
Usually, a heating wire such as r, a thermistor, or a metal glaze resistor is integrated into the element as a heating source.

What is important about this configuration is that even when the concentration of the reducing gas is the same, the electrical resistance when detected differs depending on the heating temperature of the element, that is, there is heating temperature dependence. Therefore, the element must always be heated to a predetermined appropriate temperature and maintained under uniform heat distribution.

Therefore, while understanding these problems, we first developed a reducing gas detection device as shown in FIG. 1 as an improved detection device.

This device includes a heating source H formed by covering a coiled metal wire 1 with a heat-resistant insulating material 2, and a pair of electrodes arranged near the center of a hollow part of the coiled metal wire of this heating source. It is characterized by arranging a sensing element S made of a sintered metal oxide semiconductor having dimensions smaller than the coil inner diameter and coil length of the metal wire, in which the wires 4 and 4' are embedded. It is something to do.

The characteristic effect obtained by this device is that the sensing element S
is located inside the cylindrical heating source H and is heated by its radiant heat, so even if the surrounding temperature changes due to changes in airflow, the heating source H has sufficient heat capacity and acts as a barrier. The effect on the sensing element S is extremely small, and the temperature distribution of the sensing element S is very uniform.Furthermore, by using the heating source H vertically, there is a Natural convection toward the top occurs, and this chimney effect effectively sucks in the external atmosphere from the bottom of the heating source H. The reducing gas is also heated and activated by the radiant heat of the heating source H, and the metal oxide of the sensing element S Reacts quickly with the semiconductor 3.

As a result, responsiveness is improved and reducing gases can be rapidly and quantitatively detected.

The present invention further improves this reducing gas detection device,
The aim is to provide a new gas detection device that consumes less power and is highly mass-producible.

The present invention will be explained in detail below. The main point of this invention is that firstly, a coiled metal wire is used as a heating source;
A metal oxide semiconductor reducing gas sensing element having dimensions smaller than the inner diameter and length of the coil of the metal wire, which is formed by burying a pair of electrode wires near the center of the coil hollow part of the coiled metal wire that serves as the heating source. In the device to be placed, the heating source and the electrode extraction part of the sensing element are joined to a frame made in advance from a thin metal plate, the heating source and the sensing element are placed in a predetermined position, and the frame is electrically connected. This feature is characterized in that it is connected to an external connection terminal through the connector.

An embodiment of the present invention is shown in FIG. 2 and will be described in detail.

In FIG. 2, 11 is a metal wire formed into a coil shape.
The heating source HE is partially covered with an insulating layer 12, 12' made of a heat-resistant insulating material so that the wires are not electrically short-circuited.

The state of the insulation is shown in roughly enlarged views in FIGS. 3a and 3b.

This coiled metal wire 11 generates heat when an electric current is passed through it, so its surface has a large specific resistance and is not easily oxidized in normal air. An alloy wire containing Fe-Cr-AI as a main component, for example, a Kanthal alloy wire manufactured by Gabrius, Inc. in the United States, is used.

In addition, heat-resistant insulating materials include glass with a high melting point and 5i0
2. Inorganic cement mainly composed of Al2O3, ZrO2, etc. is applied and sintered to form the insulating layers 12, 12'.

In FIG. 2, sE is a gas detection element made of a metal oxide semiconductor, and its size can be accommodated in the hollow part of the heat source HE as described above.

It consists of a sensitive body 13 and electrode wires 14, 14' which are smaller than the inner diameter and length of the coiled metal wire 11, which has enough margin to avoid direct contact with the metal wire 11 of the heating source HE.

This sensitive body 13 is made of 5n02, Fe20a, Zn
O.

It is made by molding and firing powder of metal oxides such as TiO2 and wD3, or composite metal oxides containing other metal elements.

During this molding, PT, ph, Ir with a thickness of 50 to 200μ
, Pt, or its alloy wire is buried in the electrode wire 14.
, 14'.

Now, the end 11 of the coiled metal wire 11 which becomes the heating source HE
A, 11A' and the dead wire 14 buried in the semiconductor element
, 14' are the ends 15A, 15A', 1 of the frame 15, which are made in advance by chemical etching or mechanical punching of a metal plate, respectively.
5B and 15B'.

Of course, in this case, the semiconductor gas detection element sE is arranged in the center of the hollow part of the heating source HF, as shown in FIG.

This frame 15 is Fe-Ni-C. A metal plate with low thermal conductivity such as alloy (Kovar) or Fe-Cr alloy (stainless steel) is used.

This is important in order to keep the heat losses dissipated by conduction through the heating source HE and the sensing element SEO frame as small as possible and to keep the temperature of the heating source HE and sensing element sE constant at low power.

The other end portions 15a, 15 of this frame 15
15b, 15b' are ends 17a of metal lead pins 17, which are four external connection terminals embedded in an electrically insulating base (header) 16 made of heat-resistant synthetic resin, glass, or ceramic material. , 17a'.

17b and 17b'.

Note that this frame is 15a s 15a', 1 sb
j The part 15b' was first connected in a series as shown by the dotted line pltp2, that is, it was a deformed comb-shaped frame, and after the frame was joined to one end of the pin, the dotted line part was cut and removed individually. It is characterized by following the steps described below.

Finally, the mount constructed in the above order is surrounded by a protector 18.

This protector 18 is made of a metal net of about 100 meshes or a sintered metal having continuous pores, and is caulked with a metal belt 19 in the shape of a cap, and is used when detecting reducing gases that are potentially flammable and explosive. This is to provide an explosion-proof function and to prevent the detection element from being contaminated by dust, oil smoke, etc., thereby completing the reducing gas detection device according to the present invention.

Now, as a main point of the present invention, it has been explained that the heating source and the sensing element are fixed in appropriate corresponding positions using the frame and electrically connected to the external connection terminal via the frame.
The use of this frame plays an important role in achieving mass production effects for this detection device.

As a specific example, FIG. 4 shows a rough assembly process diagram during mass production.

First, in FIG. 4a, as explained in the embodiment of FIG. 2, the deformed comb-shaped frame 15 is semi-endless.

The plurality of frames 15 are integrated by the base.

The sensing element SE has already been joined to one end of the frame 15 in FIG.
1 is joined.

At this time, an insulating layer partially covered with a heat-resistant material has already been formed to insulate the coiled metal wires, thereby configuring the heating source HE.

Next, in FIG. 4d, this frame 15 is joined to external connection terminals (lead pins) 17 embedded in the header 16 in advance.

After all the connections are completed in FIG. 4e, unnecessary frames are cut and removed, and finally, the protective cap 18 is placed on the frame in FIG. 4f, completing the reductive vaporization detection device of the present invention.

As described above, in the embodiment of the present invention, the external connection terminals are arranged in parallel in a straight line, and the joints of the coiled metal wire serving as a heating source and the frame, the sensing element and the frame, and the frame and the external connection terminal are are arranged on almost the same plane, and the detection device can be assembled on the same plane.
It has characteristics that lead to extremely low manufacturing costs.

On the other hand, in terms of characteristics, it has the following improved features.

First, in conventional coiled metal wires in which the entire surface is covered with an insulating layer, the inflow of gas from the outside relies on a method that strongly generates natural convection due to the chimney effect.

In this case, it was necessary to provide directionality to the equipment set in order to make the heating source vertical.

However, in the embodiment of the present invention, the insulation between the lines is only partially provided, and gas can freely flow in and out between the lines, and the device set has almost no directionality, and the detection Reducing gases also tend to be thermally activated by a heating source, resulting in improved responsiveness.

Of course, there is no particular problem with the insulating layer covering the entire surface between the metal wires as in the conventional case, but when there is a change in the airflow around the detection device, that is, when the ambient temperature is likely to change, it is necessary to cover the entire surface with the insulation layer. The insulating layer between the metal wires should be partially covered or completely covered because it acts as a barrier and makes the temperature distribution of the sensing element very uniform, which has the effect of maintaining and improving quantitative detection accuracy. There is almost no difference in the effects of the present invention no matter which one is adopted.

Second, by using a frame with low thermal conductivity, as mentioned above, the heat loss dissipated to the outside through the frame is small and power consumption is reduced, and the heating source and sensing element are sufficient to withstand sudden changes in airflow. The heat capacity can be maintained and the temperature distribution is uniform, which are factors that improve detection accuracy.

Third, by bonding the heating source and the sensing element to the frame, the mechanical strength that cannot normally be maintained with the metal wire of the heating source and the lead wire of the sensing element is improved, and the sensing element is directly attached to the metal wire that is the heating source. It can be placed and fixed so that there is no contact, and the structure is strong against drops and vibrations as a detection device.

As is clear from the above description, according to the present invention, since the detection element and the coiled metal wire are connected to the external connection terminal through the frame made of a thin metal plate, less heat is dissipated through the frame and power consumption is reduced. Finish.

Further, since the frame is integrated by the base portion during manufacture, it is easy to manufacture and is highly suitable for mass production.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway perspective view of a reducing gas detection device conceived prior to the present invention, Fig. 2 is a partially cutaway perspective view of a reducing gas detection device in an embodiment of the present invention, and Fig. 3a. ,b
are a plan view and a side view of a part of the same device, Figures 4a and b
ye, d, e, and f are diagrams showing the manufacturing process of the same device. 11... Coiled metal wire, 11A, 11B・■
. End, 14, 14'...Lead wire, 14Bt
14B'... End, 15... Frame, 15A, 15A'. 15Bt15B'... End, sE...
Semiconductor gas detection element, HF, ... heating source, 12, 1
2'...Insulating layer, 13...Sensor, 1
6... Header, 17... Metal lead bin, 18... Protector, 20... Base.

Claims (1)

[Scope of Claims] 1. A coiled metal wire is used as a heating source, and a semiconductor sensing element that reacts with reducing gas in a heated state is housed in a hollow part of the coiled metal wire, and this semiconductor sensing element The electrode wire connected to the coiled metal wire is pulled out from the hollow part of the coiled metal wire, and the end of the pulled out electrode wire and the terminal of the metal wire are electrically connected to one end of a plurality of frames made of thin metal plates, respectively. and the other ends of the plurality of frames are respectively connected to a plurality of external connection terminals. 2 A plurality of external connection terminals are arranged in parallel on substantially the same plane, and a connection terminal for a coiled metal wire serving as a heating source and a connection terminal for a semiconductor sensing element are arranged on the same side of these external connection terminals, and 2. The reducing gas detection device according to claim 1, wherein the coiled metal wire and the connection terminal of the semiconductor detection element are connected to the external connection terminal via a frame. 3. The reducing gas detection device according to claim 1 or 2, wherein a plurality of lead pins implanted in an electrically insulating base are used as the plurality of external connection terminals. 4. The reducing gas detection device according to claim 1 or 2, wherein a metal with low thermal conductivity is used as the material of the frame. 5. A thin metal plate having a shape in which a plurality of frames are connected at the base thereof is prepared, and a terminal of a metal wire formed in a coil shape is attached to the end of the plurality of frames, and a hollow part of the coiled metal wire is provided. After connecting the electrode wires of a semiconductor sensing element that reacts to reducing gas in a heated state inserted into the base, and connecting a plurality of external connection terminals to the base facing each frame, the need for the base is removed. A method of manufacturing a reducing gas detection device, characterized by cutting parts to make each frame independent.