JPS6412329B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a capacitive pressure sensor that detects displacement of a diaphragm due to pressure as a change in capacitance. The so-called capacitive pressure sensor, which detects the displacement of a diaphragm due to pressure as a change in capacitance through opposing electrodes, has excellent durability due to its fundamental stability and the stability of the materials used. ing. For this reason, it is widely used as a pressure sensor for automobiles, which have particularly severe usage conditions. FIG. 1 is a sectional view showing the structure of such a conventional capacitive pressure sensor. In the figure, 1 is an insulating ceramic substrate, 2 is a diaphragm, and 3 and 4 are the substrate 1 and diaphragm 2, respectively. An electrode for detecting capacitance formed on the inner surface, 5 a glass layer for providing a predetermined gap between the diaphragm 2 and the substrate 1 and maintaining airtightness from the outside world, and 6 a glass layer for detecting capacitance changes. A circuit section 7 converts into an electrical signal (generally a DC voltage) and further processes the signal as required; 7 is a capsule section 8 and a circuit section 6
It is a housing that accommodates. The capsule part 8 is
It is electrically connected to the circuit section 6 by a lead wire 9, and is kept airtight with external pressure by a ring 10, so that pressure can be applied to the diaphragm 2 through the pressure inlet 11 of the housing 7. It is configured. The conventional capacitive pressure sensor described above does not directly detect pressure changes as electrical signals.
After converting pressure to capacity, this is converted to voltage (DC voltage corresponding to pressure) and detected. What is the capsule part 8 that converts pressure to capacity and the circuit part 6 that converts capacity to voltage? independently assembled,
In the end, it is common to combine the two. In other words, in terms of manufacturing, the capacity of the capsule section 8 alone is measured, a certain degree of selection is made at this stage, and then it is assembled into a housing together with the circuit section 6. Furthermore, the function of the circuit section 6 is modified, which is a relatively complicated process. I had to step on it. In particular, since the capacitance variation range of this pressure sensor is extremely small at several tens of pF,
It is sensitive to the effects of stray capacitance when measuring capsule capacity and stray capacitance when assembling the housing. For these reasons, in the conventional pressure sensor, a pressure sensor that satisfies the specifications could only be obtained through complicated selection and adjustment of the capsule portion 8 and the circuit portion 6. In addition, when looking at the above-mentioned conventional pressure sensor structurally, as shown in FIG. , it had some problems. For example, the airtightness of the measured pressure is easily lost due to misalignment with the O-ring when the capsule 8 is assembled, or due to deterioration of the O-ring. There was also a risk that the circuit would deteriorate due to the contaminated atmosphere (gasoline vapor, humidity) at the measurement pressure. As described above, conventional pressure sensors currently have major problems in terms of manufacturing and structure. The present invention provides a pressure sensor that is easy to adjust, suitable for mass production, and highly reliable, by casing the capsule side surface separately from the housing, thereby eliminating the above-mentioned conventional drawbacks. . Hereinafter, one embodiment of the present invention will be described in detail using the drawings. FIG. 2 shows a sectional view of the pressure sensor according to an embodiment of the present invention after it is assembled into a housing. Components having the same functions as those in FIG. 1 are given the same reference numerals. Example 1 The manufacturing process of the capsule portion of this pressure sensor will be specifically explained below. One side of the 96% alumina substrate 1 with a diameter of 30 mm and a thickness of 2 mm, and one side with a diameter of 30 mm and a thickness of 0.5 mm.
Circular thin film electrodes 3 and 4 are provided on one side of an alumina substrate 2 having the same size of mm, respectively, and a glass layer 5 for providing a predetermined gap around one electrode side.
was printed, and the two were combined and sealed. Here, the glass layer 5 may be printed on both sides. The glass sealing temperature at this time varies depending on the substrate material and glass material used, but the temperature is 10 to 30℃ at a temperature of 400 to 700℃.
It is best to do this in about a minute. After forming the capsule portion 8 in this manner, a lead wire 9 for electrical connection to the electrode is provided. Next, the rubber rings 12 and 1 are covered with an aluminum case 14 via the silicone rubber rings 12 and 13.
3 was caulked mechanically. Furthermore, the case 14 was assembled together with the circuit section 6 into the housing 7 so that the pressure introduction port 11 was located in the opening 15 of the housing 7, thereby obtaining a pressure sensor. Embodiment 2 FIG. 3 is a sectional view of a capsule portion of a pressure sensor according to another embodiment of the present invention, and the capsule portion of the pressure sensor shown in FIG. 3 will be specifically explained below according to the manufacturing process. In the same manner as in Example 1, circular electrodes 3 and 4 were provided on one side of the substrate 1 and the diaphragm 2, respectively, and then a Pt-based thick film baked layer 16 was formed around the other side of the substrate 1 and the diaphragm 2, respectively. It was printed in a ring shape with a width of 2 mm, dried, and baked at 850°C for 10 minutes. Further, in the same manner as in Example 1, a sealing glass layer 5 was provided, a capsule portion 8 was obtained, and a lead wire 9 was provided. Next, thick film baking layer 1 on both sides of the capsule.
Print solder paste on 6 and make copper case 17.
Then cover with a thick film baking layer 16 by melting the solder.
was soldered to case 17. Furthermore, it was assembled into the housing 7 in the same manner as in Example 1 to obtain a pressure sensor. In the pressure sensor of the present invention described above, since the capsule portion is shielded in advance with a metal case, it is less susceptible to the influence of stray capacitance of the measurement system.
The table below shows the difference (ΔC) between the capacity of the capsule alone and the capacity when assembled into the housing.

[Table] From this table, it can be seen that the capsule part of the pressure sensor of the present invention is not easily affected by stray capacitance between the capsule and the housing when the circuit is installed, since only the capsule part is shielded. Therefore, characteristic adjustment becomes even easier. In other words, the capsule section can be handled as if it were a component with a complete change in capacity, which facilitates management during production. In addition, due to the structure of the present invention, the airtightness of the capsule portion is independent, that is, the airtightness of the measurement pressure is double-layered, so the durability of the sensor is greatly improved. In addition, since the capsule part with the metal case part can be freely handled as one component,
The structure of the housing can also be designed to be simple. As described above, since the capacitive pressure sensor of the present invention has a capsule part cased in advance, the stray capacitance of the capsule part can be reduced and the durability of the structure can be improved. Compared to sensors, it is easier to mass produce and has more stable performance.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional pressure sensor, and FIGS. 2 and 3 are sectional views of an example of a pressure sensor according to an embodiment of the present invention. 1...Porcelain substrate, 2...Diaphragm, 3, 4
... Electrode, 5 ... Sealing glass layer, 6 ... Circuit section,
7...Housing, 8...Capsule portion, 9...Lead wire, 11...Pressure inlet, 13...Rubber ring, 14, 17...Metal case, 15...Opening, 16...Thick film baking layer.

Claims (1)

[Claims] 1. A ceramic substrate, a diaphragm made of an insulating thin plate disposed on one surface of the ceramic substrate with a predetermined gap, and a displacement due to pressure of the diaphragm caused by the relative displacement between the ceramic substrate and the diaphragm. a circuit section that detects a change in capacitance between opposing electrodes provided on a surface; a metal case having a pressure introduction port and maintaining airtightness of the side surface of the ceramic substrate and the diaphragm; A capacitive pressure sensor comprising: a housing that holds the metal case inside so that the mouth is located at the opening, and houses the circuit section.