JP2021071391A - Solid electrolyte sensor - Google Patents

Abstract

To provide a solid electrolyte sensor in which a temperature distribution hardly occurs in a sensor element even when the concentration of detection object gas in a measurement atmosphere is high, and which therefor can highly accurately measure the detection object gas, and furthermore can be made compact as a whole.SOLUTION: A solid electrolyte sensor is provided that comprises: a sensor element 10 formed with a solid electrolyte; a first electrode 11 provided on the surface of the sensor element; and a second electrode 12 provided on the surface of the sensor element in a second space S2 partitioned from a first space S1 with which the first electrode is in contact, and further comprises a sensor probe with which an electromotive force generated between the first and second electrodes is measured. A cylindrical heater 50 into which at least a portion of the sensor probe is inserted is constituted in such a manner that: a heating wire 51 is wound in spiral form, so that coils are contiguous; and the heating wire has an electrically insulating coating on its surface and adjacent coils are in close contact with each other.SELECTED DRAWING: Figure 2

Description

The present invention relates to a solid electrolyte sensor provided with a heater.

Various solid electrolyte sensors have been proposed that detect the concentration of gases such as hydrogen gas, oxygen gas, carbon dioxide gas, and water vapor by using a solid electrolyte (ionic conductive ceramics) as a sensor element. I am making a proposal. These solid electrolyte sensors use the principle of a concentration cell in which a potential difference occurs in the solid electrolyte due to the difference in the concentration of the same ion, and when the concentration of the gas to be detected differs between the two spaces sandwiching the sensor element, Measure the electromotive force generated in the sensor element. If the concentration of the gas to be detected in the first space is known among the two spaces, the gas concentration in the second space can be known from the measured electromotive force and the temperature of the sensor element by the Nernst equation. it can. Alternatively, when the gas concentration is unknown by measuring the electromotive force by changing the gas concentration in the second space and creating a calibration curve in advance while the gas concentration in the first space is constant. The gas concentration in the second space can be known from the measured value of the electromotive force of.

Therefore, in such a solid electrolyte sensor, it is necessary that two spaces are partitioned by the sensor element. In the conventional solid electrolyte sensor proposed by the applicant, the sensor element is formed into a bottomed tubular body, or the sensor element is fixed to one end or the middle of the tubular holder via a sealing material to form a holder. The two spaces are partitioned by forming a bottomed tubular body in the shape of the combination of the sensor element and the sensor element.

In the solid electrolyte, the temperature at which the concentration (partial pressure) of the gas to be detected and the electromotive force have a correlation is limited to a predetermined temperature range. That is, the solid electrolyte has a unique temperature range (hereinafter, referred to as "usable temperature range") as a temperature that can be used as a sensor element, and is generally 350 ° C. or higher.

However, the temperature of the measurement atmosphere for which the concentration of the detection target gas is to be detected may be lower than the usable temperature range. Therefore, as a solid electrolyte sensor that can be used even when the temperature of the measurement atmosphere is low, the applicant has previously proposed a solid electrolyte sensor provided with a heater (see, for example, Patent Document 1). In order to keep the temperature of the sensor element within the usable temperature range, the sensor element is heated by a heater.

As shown in FIG. 4A, such a solid electrolyte sensor with a heater is a solid electrolyte sensor 100a (hereinafter, referred to as a solid electrolyte sensor 100a) in which a heater 150 is provided in a first space S1 which is an internal space of a bottomed tubular body 160. As shown in FIG. 4B, the solid electrolyte sensor 100b (hereinafter referred to as “heater internal type”) in which the heater 150 is provided in the second space S2 which is the external space of the bottomed tubular body 160 (hereinafter, “heater interior type”). It can be roughly divided into "heater exterior type"). Generally, the second space S2 is used as the measurement atmosphere, and a reference gas having a known concentration of the detection target gas is introduced into the first space S1.

The heater-internal type solid electrolyte sensor 100a has an advantage that the whole can be made compact, but there is a problem that accurate measurement cannot be performed when the concentration of the detection target gas becomes high in the measurement atmosphere. This is because when the concentration of the detection target gas becomes high in the measurement atmosphere, heat is easily taken from the sensor element by heat transfer through the gas, so that the sensor element is in contact with the second space S2 which is the measurement atmosphere. It is considered that a temperature difference is likely to occur between the side in contact with the first space S1 in which the heater 150 is provided, that is, a temperature distribution is generated in the sensor element. In particular, hydrogen gas has a high thermal conductivity, so this problem is remarkable.

On the other hand, in the heater exterior type solid electrolyte sensor 100b, since the heater 50 is provided in the second space S2 which is the measurement atmosphere, the temperature of the sensor element changes even if the concentration of the detection target gas becomes high in the measurement atmosphere. Although it is difficult and accurate measurement is possible, there is a problem that the sensor configuration becomes bulky as a whole.

Japanese Unexamined Patent Publication No. 2016-027317

Therefore, in view of the above circumstances, the present invention makes it possible to measure accurately and to make the whole compact because the temperature distribution is unlikely to occur in the sensor element even if the concentration of the detection target gas in the measurement atmosphere is high. It is an object of the present invention to provide a solid electrolyte sensor.

In order to solve the above problems, the solid electrolyte sensor according to the present invention is used.
"The surface of the sensor element in a sensor element formed of a solid electrolyte, a first electrode provided on the surface of the sensor element, and a second space partitioned from the first space in contact with the first electrode. A sensor probe that has a second electrode provided in the above and measures the electromotive force generated between the first electrode and the second electrode.
A tubular heater into which at least a part of the sensor probe is inserted.
The heater has a continuous wire ring by spirally winding the heating wire, and has an electrically insulating film on the surface of the heating wire. "

The solid electrolyte sensor having this configuration is a "heater exterior type" in which at least a part of the sensor probe is inserted into a tubular heater. Therefore, when the space in which the heater is arranged is used as the measurement atmosphere, the temperature distribution is unlikely to occur in the sensor element even if the concentration of the gas to be detected is high, and the gas concentration can be measured accurately.

The heater is formed in a tubular shape by spirally winding a heating wire (a linear electric resistance heating element). Conventionally, when a heating wire is spirally wound to form a heater, a spiral groove is formed in an electrically insulating heater holder in order to prevent a short circuit between adjacent wire rings. By holding the heating wire along the groove, a distance is provided between the adjacent wire rings. Therefore, the entire heater including the heater holder is bulky, and the solid electrolyte sensor provided with such a heater is also bulky.

On the other hand, in this configuration, since the heating wire has an electrically insulating film on its surface, unlike the conventional case, the electrically insulating heater holder does not need to hold the heating wire, but the adjacent wire ring and the wire. There is no short circuit with the ring. Therefore, the heater having this configuration can be made more compact than the conventional heater that uses the heater holder because there is no heater holder and the distance between the adjacent wire rings can be reduced.

The solid electrolyte sensor according to the present invention has, in addition to the above configuration,
"In the heater, the adjacent wire rings are in close contact with each other."

Since the heating wire has an electrically insulating film on its surface, it will not be short-circuited even if the adjacent wire rings are brought into close contact with each other. Therefore, the heater of this configuration can be made more compact because there is no distance between adjacent wire rings.

The solid electrolyte sensor according to the present invention has, in addition to the above configuration,
"The heat of the heater is conducted to the sensor element only through the solid".

In this configuration, since the heat of the heater is conducted only by the solid and transmitted to the sensor element, the sensor element can be heated efficiently. Here, the configuration in which the heat of the heater is "conducted to the sensor element only through the solid" is a configuration in which the heater is in direct contact with the sensor element, or indirectly via another solid such as a holder that supports the sensor element. The heater may be in contact with the sensor element.

The solid electrolyte sensor according to the present invention has the above configuration.
"The heater is
A heater having the electrically insulating coating of aluminum oxide on the surface of the heating wire, which is an alloy wire containing iron, chromium, and aluminum.
A heater having the electrically insulating coating of chromium oxide on the surface of the heating wire which is an alloy wire containing nickel and chromium, and
It can be selected from a heater having the electrically insulating coating of silicon oxide on the surface of the heating wire which is an alloy wire containing nickel, chromium and silicon. "

When an alloy wire containing iron, chromium, and aluminum is heated to a high temperature in an oxidizing atmosphere, aluminum, which is a component of the alloy, is oxidized and a film of aluminum oxide is formed on the surface of the alloy wire. Further, when an alloy wire containing nickel and chromium is heated to a high temperature in an oxidizing atmosphere, chromium, which is a component of the alloy, is oxidized and a chromium oxide film is formed on the surface of the alloy wire. Alternatively, when an alloy wire containing nickel, chromium, and silicon is heated to a high temperature in an oxidizing atmosphere, silicon, which is a component of the alloy, is oxidized and a silicon oxide film is formed on the surface of the alloy wire. Aluminum oxide, chromium oxide, and silicon oxide are all electrically insulating. The film formed by such an oxidation reaction has an advantage that it is denser and less likely to be peeled off as compared with a film formed by coating the surface of a heating wire with an electrically insulating material. Further, there is an advantage that an electrically insulating film can be easily formed only by heating the heating wire at a high temperature in an oxidizing atmosphere.

The above alloy wire may contain other components in addition to the components listed respectively. For example, alloy wires containing iron, chromium, and aluminum may contain cobalt. Further, the alloy wire containing nickel and chromium and the alloy wire containing nickel, chromium and silicon may contain manganese and iron.

As described above, according to the present invention, even if the concentration of the detection target gas in the measurement atmosphere is high, the temperature distribution is unlikely to occur in the sensor element, accurate measurement can be performed, and the whole can be made compact. A solid electrolyte sensor can be provided.

FIG. 1 (a) is a side view of a heater having a configuration of a solid electrolyte sensor according to the first embodiment of the present invention, and FIG. 1 (b) is a vertical cross-sectional view of the heater of FIG. 1 (a) as a conventional heater. 1 (c) is a vertical cross-sectional view of a heater holder of a conventional heater. FIG. 2 is a vertical cross-sectional view of the solid electrolyte sensor according to the first embodiment of the present invention. FIG. 3A is a vertical cross-sectional view of the solid electrolyte sensor of the second embodiment, and FIG. 3B is a vertical cross-sectional view of the solid electrolyte sensor of the modified example. FIG. 4A is a schematic configuration diagram of a heater internal type solid electrolyte sensor, and FIG. 4B is a schematic configuration diagram of a heater exterior type solid electrolyte sensor.

Hereinafter, the solid electrolyte sensor 1 according to the first embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 2, the solid electrolyte sensor 1 has a shape in which the holder 20 and the sensor element 10 are combined by fixing the sensor element 10 to one end of the tubular holder 20 via a sealing material 29. A bottomed tubular body is formed, and a first space S1 which is an internal space of the bottomed tubular body and a second space S2 which is an external space are partitioned. The holder 20 is made of a material having electrical insulation and heat resistance, such as alumina ceramics and mullite ceramics.

In the sensor element 10, the first electrode 11 is provided on the surface in contact with the first space S1, and the second electrode 12 is provided on the surface in contact with the second space S2. By connecting 32 to an electrometer (not shown), the electromotive force generated between the first electrode 11 and the second electrode 12 is detected. Further, a thermocouple 41 for detecting the temperature of the sensor element 10 is inserted in the first space S1. Then, the second space S2 is used as the measurement atmosphere, and the reference gas having a known concentration of the detection target gas is introduced into the internal space S1 via the introduction pipe 42.

The configuration including the sensor element 10, the first electrode 11, the second electrode 12, and the holder 20 corresponds to the “sensor probe” of the present invention.

The solid electrolyte sensor 1 is a heater exterior type. The heater 50 has a cylindrical shape, and at least a portion of the sensor probe in which the sensor element 10 is present is inserted into the heater 50.

The heater 50 has a coil shape in which a wire ring is continuous by winding the heating wire 51 in a spiral shape. The heating wire 51 of the present embodiment is an alloy wire containing iron, chromium, and aluminum, and an electrically insulating film of aluminum oxide is formed on the surface thereof. Such an electrically insulating film is formed by heating the heating wire 51, which is an alloy wire containing iron, chromium, and aluminum, to a high temperature in an oxidizing atmosphere to oxidize aluminum, which is a component of the alloy. To.

As shown in FIGS. 1A and 1B, the heating wire 51 is wound so that adjacent wire rings are in close contact with each other. Since the heating wire 51 has an electrically insulating film on its surface, even if adjacent wire rings are brought into close contact with each other, there is no short circuit between the wire rings.

In the conventional heater 150 in which the heating wire 151 is spirally wound, as shown in FIGS. 1 (c) and 1 (b), a spiral groove 165 is formed in the electrically insulating heater holder 160. By holding the heating wire 151 along the groove 165, a distance is provided between the adjacent wire rings, and a short circuit between the adjacent wire rings is prevented. Therefore, the entire heater 150 including the heater holder 160 becomes bulky, and the solid electrolyte sensor provided with such a heater 150 also has to be bulky.

On the other hand, since the spiral heating wire 51 is wound around the heater 50 so that the adjacent wire rings are in close contact with each other, the length of the heater 50 is shorter than that of the conventional heater 150 when compared with the same number of turns. Further, since the heater 50 does not require the heater holder 160, the cylindrical outer diameter is smaller than that of the conventional heater 150. Therefore, the heater 50 can obtain the same amount of heat generation while being more compact than the conventional heater 150.

Further, when the sensor probe is inserted into the conventional heater 150, the heat generated by energizing the heating wire 151 is transferred to the sensor probe via the heater holder 160, resulting in poor thermal efficiency. On the other hand, in the solid electrolyte sensor 1 of the present embodiment including the heater 50, the heat generated by energizing the heating wire 51 is transferred to the sensor probe without passing through another object such as a heater holder, so that the thermal efficiency is high. The sensor element 10 can be heated well. Further, since the heater 50 and the sensor probe can be brought closer to each other because there is no heater holder, the thermal efficiency of heating the sensor element 10 is good in this respect as well.

Since the solid electrolyte sensor 1 of the present embodiment is an exterior type in which the heater 50 is arranged in the second space S2 which is the measurement atmosphere, the sensor even when the concentration of the detection target gas is high in the measurement atmosphere. The temperature distribution is unlikely to occur in the element, and the concentration of the detection target gas can be measured accurately.

Next, the solid electrolyte sensor 2 of the second embodiment will be described. The same components as those of the solid electrolyte sensor 1 of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The difference between the solid electrolyte sensor 2 of the second embodiment and the solid electrolyte sensor 1 is that the heat of the heater 50 is conducted to the sensor element 10 only through the solid without passing through the air layer. Specifically, as shown in FIG. 3A, the coiled heater 50 is wound around the holder 20. The heating wire 51 of the heater 50 has an electrically insulating coating on the surface, but the electrically insulating film 35 is used as a heater in case of a short circuit between the second electrode 12 and the lead wire 32. It may be interposed between the 50 and the holder 20. As the electrically insulating film 35, a mica (mica) film having excellent electrical insulation and high heat resistance can be used. Since the mica film has flexibility, it is easy to wind it around the holder 20 so that a gap is not formed between the heater 50 and the holder 20.

In the solid electrolyte sensor 2 having such a configuration, the heat of the heater 50 has a heat conduction path which is conducted to the sensor element 10 only through the solid material of the film 35, the holder 20, and the sealing material 29. The sensor element 10 can be heated efficiently, and the temperature of the sensor element 10 can be easily controlled.

Further, as shown in FIG. 3B, when the sensor probe is inserted into the tubular protective tube 70 to protect the sensor probe, the electrically insulating film 36 is wound from the outside of the heater 50. You can also. With such a configuration, even when the protective tube 70 is made of an electrically conductive material such as metal, it is possible to avoid a short circuit between the heater 50 and the protective tube 70. As the film 36, a mica film can be used in the same manner as the film 35. By winding the film 36 from the outside of the heater 50 in this way, there is also an advantage that the heat of the heater 50 can be easily conducted to the sensor probe without escaping to the outside.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to the above embodiments, and as shown below, various improvements are made without departing from the gist of the present invention. And the design can be changed.

For example, in the above embodiment, the case where the first space S1 and the second space S2 are partitioned by fixing the sensor element 10 to one end of the holder 20 is illustrated, but the sensor element itself is a bottomed cylinder. By forming the body, it is possible to partition the first space, which is the internal space of the bottomed tubular body, and the second space, which is the external space. In this case, when the heat of the heater is conducted to the sensor element only through the solid as in the second embodiment, the heater is wound directly around the sensor element or wound around the sensor element via an electrically insulating film.

Further, in the above, the case where the bottomed tubular sensor element 10 opens in the internal space S1 has been illustrated, but the bottomed tubular sensor element may be fixed to the holder 20 so as to open in the external space S2. .. Further, in the above, the case where the shape of the sensor element 10 is a bottomed cylinder is illustrated, but the shape of the sensor element is not limited to the bottomed cylinder, and may be a flat plate or a columnar shape.

Further, in the above, the case where the bottomed tubular body is formed as a whole by fixing the sensor element 10 to one end of the holder 20 is illustrated, but the sensor element is located in the middle of the inner peripheral surface of the holder. It may be fixed via a sealing material. In this case, since the holder and the sensor element have a combined shape and have two bottomed tubular parts, the concept of distinguishing the internal space and the external space does not occur, but one of them is set as the first space. The other is the second space. In this case, the shape of the sensor element fixed in the middle of the inner peripheral surface of the holder can be a bottomed cylinder, a flat plate, or a columnar shape.

1 Solid electrolyte sensor 10 Sensor element 11 First electrode 12 Second electrode 20 Holder 50 Heater 51 Heating wire S1 First space S2 Second space

Claims (4)

On the surface of the sensor element in a sensor element formed of a solid electrolyte, a first electrode provided on the surface of the sensor element, and a second space partitioned from the first space in contact with the first electrode. A sensor probe having a provided second electrode and measuring the electromotive force generated between the first electrode and the second electrode.
A tubular heater into which at least a part of the sensor probe is inserted.
The heater is a solid electrolyte sensor in which a wire ring is continuous by spirally winding a heating wire, and has an electrically insulating coating on the surface of the heating wire. The solid electrolyte sensor according to claim 1, wherein in the heater, the adjacent wire rings are in close contact with each other. The solid electrolyte sensor according to claim 1 or 2, wherein the heat of the heater is conducted to the sensor element only through the solid. The heater is
A heater having the electrically insulating coating of aluminum oxide on the surface of the heating wire, which is an alloy wire containing iron, chromium, and aluminum.
A heater having the electrically insulating coating of chromium oxide on the surface of the heating wire which is an alloy wire containing nickel and chromium, and
Any one of claims 1 to 3, wherein the heater is selected from a heater having the electrically insulating coating of silicon oxide on the surface of the heating wire which is an alloy wire containing nickel, chromium and silicon. The solid electrolyte sensor described in.

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