JPS62211525A - Temperature sensor - Google Patents

Abstract

PURPOSE:To obtain the high reliability of a sensor even in an atmosphere where oxygen is deficient or little without any working for linking the inside of a casing for protection with the outside air by providing a sealed structure for a thermistor. CONSTITUTION:The thermistor 1 as a thermometric element uses an element consisting of about 20mol% zinc oxide - yttrium oxide and is put in a sealed space 2 formed by laminating unbaked sheet bodies 3, 4, and 5 of alumina ceramics as heat-resisting insulating materials and baking them into one body. This thermistor structure A is supported and fixed to the axis part in a heat- resisting, anticorrosive metallic tube 10 whose one end is sealed by using a heat-resisting adhesive 12. Further, the thermistor 1 is arranged in contact with the sealing end side of the tube 10 and a hollow bolt type temperature sensor fitting 11 is fitted around a metallic tube 10 as a cover for thermistor protection. Then, a coupling pipe 14 and a wiring cord 15 are provided to the open end side of the tube 10. Consequently, the high reliability of the sensor is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a temperature sensor that uses a thermistor as a temperature measuring element, and is particularly suitable for measuring the temperature of combustion exhaust gas discharged from an internal combustion engine or the like.

[Prior Art] As a method of measuring the temperature of combustion exhaust gas from internal combustion engines and various combustion furnaces, a temperature sensor incorporating an oxygen ion-driven or electronic conduction type thermistor as a temperature measuring element is used. The thermistor works as a type of oxygen battery that uses oxygen ions as the charge conduction medium, so it is stable and reliable unless there is a concentration of oxygen higher than a certain concentration (generally 5% or more) in the atmosphere that the thermistor comes into contact with. Unable to obtain measurement results.

The general structure of the temperature sensor is that the thermistor is housed at the sealed end of a heat-resistant metal tube that also serves as a metal fitting and one end is sealed, and the thermistor's protective cover and sensor 9 are mounted on the sealed end. The lead wire is connected to a wiring cord fitted to the open end of the tube.

・ [Problem to be solved by the invention] A temperature sensor with the above-described structure is free from metallurgy during use.
Because the inner wall surface of the 1lI tube combines with the oxygen present in the tube and gradually oxidizes, the oxygen concentration in the atmosphere around the thermistor decreases over time, and the electrical output characteristics of the thermistor decrease accordingly. As a result, the reliability of the temperature sensor decreases over time.

As a countermeasure, it is necessary to make a large number of small holes on the sealed end side of the tube in order to communicate the inner space of the tube with the atmosphere, or to provide a ventilation structure to the glenoid cord.

However, if the inner space of the tube is not communicated with the outside air in this way, it becomes impossible to accurately measure the temperature of combustion exhaust gas, for example, which has an extremely low oxygen concentration.

The present invention relates to a temperature sensor that uses a thermistor as a temperature measuring element and is required to be used in an atmosphere where the oxygen concentration is maintained above a certain level. It is an object of the present invention to provide a temperature sensor that does not require any troublesome processing and can be used with high reliability even in an atmosphere where oxygen is scarce or does not exist at all.

[Means for Solving the Problems] In order to achieve the above object, a temperature sensor according to the present invention includes a thermistor that is surrounded by a heat-resistant insulating material and housed in a closed space in which a gas containing oxygen exists. A configuration was adopted in which the was incorporated as a contact element.

[Operation and Effects of the Invention] In the temperature sensor having the above-mentioned configuration, the temperature sensor used as a temperature measuring element is required to be used in an atmosphere where oxygen exists at a concentration higher than a certain level. It is made of a material and is housed in a sealed space, and since gas containing oxygen is present in this space, unlike conventional temperature sensors using the same type of thermistor, there is no need to introduce outside air into the sensor casing. This eliminates the need for cumbersome machining operations such as drilling numerous small holes.

Furthermore, because thermistors are made of non-metallic materials and are housed in a closed space where oxygen is present, their measurement accuracy may change over time, even for high-temperature gases that contain little oxygen, such as combustion exhaust gas. Highly reliable temperature measurements can be made without any hassle.

[Example] The structure of the present invention will be specifically described below based on the example shown in the attached drawings.

Figures 1 and 2 show an example of a thermistor sealing structure for sealing a negative temperature coefficient thermistor as a temperature measuring element incorporated in a temperature sensor according to the present invention in a space surrounded by a heat-resistant insulating material. FIG. 2 is a side sectional view shown and an explanatory diagram of a method of forming this sealed structure.

The thermistor 1 as a temperature measuring element uses 20 mol% of zinc oxide to yttrium oxide, and unfired sheets 3.4 and 5 of alumina porcelain as heat-resistant insulating materials.
Sealed medium 1I12 formed by laminating and integrally firing
It is stored inside.

The method for forming this sealed space 2 will be explained with reference to FIG. 2. First, three alumina Ia material plates 3.4 and 5, which are formed into unfired extremely thin sheet-like rectangular shapes, are prepared. do. The widths of these three 11♂ material plates are the same, and the width is slightly longer than that of the bottom layer, the porcelain material plate 3. These three porcelain material plates are stacked and fired to form a sintered body, but prior to firing, the porcelain material plate 4, which is the middle layer of the laminated structure, has one end in its longitudinal direction. A hollow hole 4a of a square, circular or other appropriate shape is provided, and an electrode 6 for taking out the output of the thermistor 1 is provided on the upper surface of the somewhat long ceramic material plate 3, which is the lowest layer.
and 7 are formed by a printing method using a conductive paste composition. One end sides of the two electric bridges 6 and 1 formed by the printing method are positioned to face each other in the hollowed hole 4a.

After that, when the middle layer porcelain material plate 4 is placed on the bottom layer porcelain material plate 3 on which the pair of electrodes are printed, the hollowed-out hole 48 becomes a depression, so a thermistor as a semiconductor porcelain is placed in this depression. Fill the unfired material of No. 1 in an amount insufficient to completely fill the cavity. Finally, Mogami WJT! By stacking the single material plates 5 on top of each other and placing them in a firing furnace and heating them in a conventional manner, three layers of
1V! The A material plates 3.4 and 5 are sintered together to form an integral structure, and the cutout hole 48 portion is a hermetic seal cut off from the outside world, as shown in FIG. 1, which is a side sectional view of the thermistor sealed structure. Create space 2.

During the firing process of the porcelain material board, the unfired material of the thermistor 1, which is filled with enough particles to completely fill the sealed space 2 formed as described above, is also fired at the same time. will be done. Since the electrodes 6 and 7 for taking out the output of the thermistor 1 are printed in advance on the bottom surface of the sealed space 2, the lead wires are connected to the thermistor 1 at the same time in the firing process. 20 indicates a container made of thermistor material.

In the upper layer of the hermetic gap 2 of the thermistor sealed structure formed in this way, there is air trapped within the gap during the firing process, so it can be used as a temperature measuring element! A requirement for use of conductive or electronically conductive thermistors is that they must be placed in an atmosphere containing a certain concentration of oxygen (generally 5% or more).

Since the porcelain material plates 3 to 5 and the thermistor material 1 use pure aluminum oxide and zinc oxide to yttrium oxide, impurity gas as a reaction product enters the sealed gap 2 during the firing process. There will be no inconvenience caused by occupying the space.

Furthermore, since the constituent material of the hermetically sealed gap 2, which seals the thermistor 1 in a state where it is completely isolated from the outside air, is pure alumina porcelain, the temperature sensor can be used for long periods of time in environments where temperatures reach over 1000 degrees Celsius. Even after being used for many years, the alumina porcelain does not react with the oxygen present in the closed gap to reduce the oxygen content in the gap.

FIG. 3 shows, as an axial sectional view, an example of the structure of a temperature sensor for measuring the combustion exhaust gas temperature of an internal combustion engine, which incorporates the thermistor sealed structure shown in the above embodiment.

The thermistor closed structure A is supported and fixed using a heat-resistant adhesive 12 to a shaft core within a heat-resistant and corrosion-resistant metal duplex 10 whose one end is sealed. Thermistor 1 is duplex 10
is placed in contact with the sealed end side of the A metal fitting 11 is fitted onto the metal tube 10 as an integral part of the thermistor protective cover, and a metal fitting 11 is fitted onto the hollow bolt-shaped temperature sensor, and a wiring cord 15 is fitted onto the tM discharging end side of the tube 1o. The joint pipe 14 is fitted.

The output extraction electrodes 6 and 7 of the thermistor 1 are formed on the lower WJ porcelain material plate 3 by a printing method.
Lead wires 8 are soldered to each of them, one electrode of which is soldered to the core wire 9 of the wiring cord 15, and the other electrode electrically connected to the mounting bracket 11 of the temperature sensor.

, b is a soldering part, 14a is a caulking part of the joint pipe 14, and 17 is a wiring connector.

FIG. 4 shows the temperature measuring side end of a temperature sensor as a second embodiment. The difference from the first embodiment is that there is a communication hole 10 at the end of the protective metal tube 10 of the thermistor 1 on the side vortex side.
This is due to the establishment of group a.

As mentioned at the beginning, one of the features of the temperature sensor according to the present invention is that it eliminates the need for the troublesome drilling process to provide an oxygen supply communication hole to the thermistor in the protective tube of the thermistor as a temperature measuring element. is doing. However, by sealing the thermistor inside a metal tube, direct contact between the thermistor and the gas being measured is prevented, so it takes some time before accurate temperature measurement results are displayed. It turns out. Therefore, when responsiveness to temperature changes in the gas to be measured and rapid measurement are particularly required, it is desirable to provide the thermistor protective metal duplex 10 with a communication hole 10a communicating with the outside air.

If the gas to be measured is, for example, combustion exhaust gas from various combustion furnaces or internal combustion engines, a conventional temperature sensor of the same type would lose its sensor function because the oxygen concentration is too low, but this example sensor uses a thermistor. 1 is completely covered by a cover made of alumina porcelain and is placed in the presence of oxygen at the required concentration, so it can fulfill its role without causing any trouble. Further, the thermistor 1 is prevented from being adversely affected by the chemically active exhaust gas.

FIG. 5 shows a conventional type temperature sensor that incorporates the temperature sensor of the present invention having the structure shown in FIG. 4 and a conventional thermistor without a sealed structure in place of the thermistor sealed structure A of this temperature sensor. The graph shows experimental data comparing the output characteristics of each sensor.

The experiment was conducted when the oxygen concentration in the area where the temperature sensor was placed was 5.
The oxygen concentration was changed in a so-called oxidizing atmosphere where the oxygen concentration was 5% or more and in a reducing atmosphere where the oxygen concentration was 5% or less.

When graphs of electrical resistance (IoaR) versus ambient temperature were obtained for both sensors, the sensor of the present invention drew the same graph (A) regardless of whether it was in an oxidizing atmosphere or a reducing atmosphere. On the other hand, the conventional sensor showed the same curve as graph (a) in an oxidizing atmosphere, but a completely different graph (b) in a reducing atmosphere.

In other words, as a result of experiments, it was found that while the measured value of the conventional humidity sensor fluctuates significantly depending on the concentration of oxygen present in the temperature measurement area, the one of the present invention shows no dependence on oxygen at 81 degrees Celsius. It was confirmed.

[Brief explanation of drawings]

Figure 1 shows the thermistor mounted in the sensor of the present invention in a side cross-sectional view of the structure, Figure 2 shows the mounting in an explanatory diagram of the manufacturing process of the structure, and Figure 3 shows the mounting of the thermistor in Figure 1 in the structure. FIG. 4 is a partial sectional view of a temperature sensor as a second embodiment, and FIG. 5 is a comparative data graph of the output characteristics of the sensor of the present invention and a conventional sensor.

Claims (1)

[Scope of Claims] 1) A temperature sensor incorporating as a temperature measuring element a thermistor surrounded by a heat-resistant insulating material and housed in a closed space in which a gas containing oxygen exists. 2) The temperature sensor according to claim 1, wherein the thermistor is a magnetic semiconductor made of stabilized zirconia, and the heat-resistant insulating material is alumina porcelain. 3) The sealed space is formed by stacking a plurality of unfired porcelain material plates and firing them integrally. temperature sensor. 4) A pattern of conductive paste for forming the electrodes of the thermistor is printed on the unfired porcelain material plate, and a conductive paste is printed on the unfired porcelain material plate in a sufficient amount to fill the closed space before firing. 4. The temperature sensor according to any one of claims 1 to 3, wherein an amount of unfired raw material for the thermistor is stored. 5) The temperature sensor according to any one of claims 1 to 4, wherein the temperature sensor is a sensor for measuring the temperature of combustion exhaust gas of fuel.