JPS6367321B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a thermistor used in cookers and combustors.

Conventional Structures and Problems Thermistors are widely used as temperature detectors, but when used in harsh atmospheres, the temperature sensing element must be protected from such atmospheres.
In other words, when detecting the temperature of the atmosphere inside cooking appliances such as gas ovens and electric ovens, or the exhaust gas atmosphere of combustion appliances such as gas stoves and kerosene stoves, the ambient temperature will be high (up to 300
500℃) as well as steam from soybean oil, oil, water, etc.
The atmosphere contains fine droplets or intermediate decomposition products of fuel generated during combustion. Therefore, when the temperature sensing element is directly exposed to this type of atmosphere, the characteristics are likely to change due to dirt or changes in the material of the temperature sensing element. Therefore, the temperature sensing element is usually isolated from the atmosphere by a glass, metal case, etc. to protect the temperature sensing element.

Conventionally, as shown in FIG. 1, this type of protection method involves taking out an internal lead wire 2 from a metal oxide temperature sensing element 1, connecting this internal lead wire 2 to an external lead wire 3, and then connecting the temperature sensing element 1 with an internal lead wire 2. (1~2)
There is a thermistor sealed in a glass tube 3 having a diameter of φx (2 to 10) mm. Since the temperature sensing element is embedded in such a small volume of glass, a thermistor with quick thermal response can be obtained. However, a drawback of small thermistors is that because the insulation distance between lead wires is short, insulation deterioration due to dirt and the like is likely to occur. This was especially fatal when used in a harsh atmosphere as mentioned above. In order to overcome this drawback, there is also a protection method that includes some lead wires and covers the glass with an insulating material.

However, complete adhesion between the lead wire, glass, and coating insulation depends on the matching of their mutual expansion coefficients, chemical bonding with their mutual interfaces, and coating conditions, such as surface treatment, treatment temperature, treatment time, and coating conditions. This can only be achieved through detailed consideration of factors such as thickness and coating reliability. Therefore, this type of coating not only requires a complicated structure, but also has the disadvantage that it cannot be easily made.

Further, FIG. 2 shows a connection configuration of lead wires when a thin film temperature sensing element is used as the temperature sensing element 1.

The thin film temperature sensing element 5 is constructed by forming an electrode film 7 and a temperature sensitive resistor film 8 on a flat insulating substrate 6, and further, an internal lead wire 2 is connected to the electrode film 7. In this case, the electrode film 7 and the internal lead wire 2 are usually connected by welding or bonding using a highly heat-resistant conductive adhesive. This is because when heat resistance as described above is required, the commonly used soldered connections have poor heat resistance.

A thin wire made of Au, Pt, PtRh, etc. was used for the internal lead wire 2, and both ends of the internal lead wire 2 were connected to the electrode film 7 and the external lead wire 3, respectively. At this time, a thin wire of 0.05 to 0.2φ is selected for the internal lead wire 2, and a thick wire of 0.4 to 1.0φ is selected for the external lead wire 3, so when the internal lead wire 2 is connected to the external lead wire 3 by welding, the welded part The internal lead wire 2 is deformed and becomes "constricted". This "necked" portion has a disadvantage in that it has poor mechanical strength and is prone to wire breakage. This "constriction" is thought to be due to the large difference in heat capacity between the internal lead wire 2 and the external lead wire 3. On the other hand, bonding using a highly heat-resistant conductive adhesive has the disadvantage that the adhesive strength tends to be significantly reduced by a slight stain on the bonding surface, resulting in a lack of bonding reliability.

OBJECTS OF THE INVENTION The present invention provides a thermistor that eliminates these conventional drawbacks, and aims to protect a temperature sensing element with a simple configuration.

Structure of the Invention The thermistor of the present invention includes a thin film temperature-sensitive element composed of a SiC film and an electrode film formed on a flat insulating substrate, an internal lead wire, an external lead wire, and a glass tube. Both ends of the internal lead wire are welded to the external lead wire, the middle part of the internal lead wire is connected to the electrode film, the thin film temperature sensing element is sealed in the glass tube, and The structure is such that an external lead wire is taken out and the length of the glass tube is 1 cm or more.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the lead connection of the present invention is shown in FIG. An electrode film 7 and a temperature-sensitive resistor film 8 were formed on a flat insulating substrate 6 to constitute a thin-film temperature-sensitive element 5.
Next, both sides of the internal lead wire 2 made of a thin wire made of Au, Pt, PtRh, etc. were welded to the external lead wire 3, and the middle part of the internal lead wire 2 was connected to the electrode film 7. Next, the external lead wire 3 was sealed and fixed to a glass tube 4 having a length of 1 cm or more.

The temperature sensitive resistor film 8 includes an oxide film of Fe, Ni, Co, Mn, etc., or a film of Ge, Si, SiC, etc. Among these various temperature-sensitive resistor films 8, SiC films are particularly suitable for use in cookers, combustors, and the like as described above. This type of application requires a heat resistance of 350 to 400℃, while SiC
This is because the film can sufficiently satisfy this heat resistance.

In the thermistor of the present invention, the external lead wires 3 are taken out from both ends of the glass tube 4, and the length of the glass tube 4 is 1.
A sufficiently long insulation distance of cm or more can be obtained. Therefore, the insulation properties do not deteriorate even when used in the harsh atmosphere described above. In fact, a thermistor with a length of glass tube 4 of 1 cm and 2.5 cm was left in a gas oven, soybean oil or salad oil was dropped into the oven at a rate of (0.5 to 2.0 cc) per minute, and the temperature inside the oven was adjusted to (300 to 2.0 cc). The samples were kept at 330)°C and changes in insulation resistance were observed over time.
As a result, even after the elapse of time (1000 to 3000), both were the same as the initial value (insulation resistance 1000 MΩ or more when DC 1000 V was applied). 1φ×5mm under similar conditions
When testing the thermistor with a temperature-sensitive element embedded in the glass and the lead wire taken out, the insulation resistance was lower than the initial value (1000MΩ or more as above).
It was 10 to 200MΩ.

Further, in the thermistor of the present invention, both ends of the internal lead wire 2 are welded to the external lead wire 3, and the internal lead wire 2 is welded to the external lead wire 3.
is connected to the thin film temperature sensing element 5 at the middle part thereof. The internal lead wire 2 and external lead wire 3 are welded at two places.
Since it is connected, the mechanical strength of the connected portion can be improved. In fact, when the drop test was repeated in cases where the connection between the internal lead wire 2 and the external lead wire 3 was in one place and in two cases, the former was found to be 1 to 20% lower after 30 to 50 tests. A disconnection occurred at the connection. On the other hand, in the latter case, no disconnection occurred even after 50 tests. In addition, the drop test
The thermistor of the present invention was allowed to fall naturally onto concrete from a height of 1.5 m once, and this was repeated multiple times.

Note that the glass tube 4 and the external lead wire 3 must have similar coefficients of thermal expansion. In this way, there are several known combinations of glass and metal (usually a metal with high electrical conductivity is selected for the external lead wire 3), in which the mutual coefficients of thermal expansion are similar. . Among these, the combination of selecting Kovar glass for the glass tube 4 and Kovar alloy wire for the external lead wire 3 is excellent. This means that the Kovar glass and Kovar alloy wire are 420 to 450
This is due to the fact that their thermal expansion coefficients are similar up to a high temperature of °C.

Effects of the invention (1) The thermistor of the present invention has external lead wires taken out from both ends of the glass tube, and the length of the glass tube is 1 cm.
The above structure has the effect that the insulation properties do not deteriorate even when used in a harsh atmosphere.

(2) Since the thermistor of the present invention has both ends of the internal lead wire welded to the external lead wire, the internal lead wire and the external lead wire are connected at two places. Therefore, the mechanical strength of the connection portion can be improved.

[Brief explanation of drawings]

Figure 1 is a sectional view showing a conventional thermistor, Figure 2
This figure is a sectional view showing the lead wire connection of a conventional thin film thermistor, and FIG. 3 is a plan view showing the lead wire connection of a thermistor according to an embodiment of the present invention. 2... Internal lead wire, 3... External lead wire, 5
. . . Thin film thermosensitive element, 7 . . . Electrode film, 8 . . . Temperature sensitive resistor.

Claims (1)

[Claims] 1. A thin film temperature sensing element consisting of a SiC film and an electrode film formed on a flat insulating substrate, an internal lead wire, an external lead wire and a glass tube,
Both ends of the internal lead wire are welded to the external lead wire, the middle part of the internal lead wire is connected to the electrode film, the thin film temperature sensing element is sealed in the glass tube, and A thermistor in which an external lead wire is taken out and the length of the glass tube is 1 cm or more.