JP2008196932A - Absolute pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absolute pressure sensor capable of highly accurately measuring pressure without having to correct a resonance frequency of a pressure-sensitive element, which changes according to pressure to be measured, through the use of a complicated correction circuit. <P>SOLUTION: A column 3 is fixed approximately vertically to a major face of a base 2 to a side surface of one end of the base 2 provided for a bottom part in a container 1. An oscillating arm 4 is fixed to an upper end part of the column 3 in such a way as to protrude approximately in parallel with the major face of the base 2. A double-tuning-fork quartz resonator 20 is fixed between the tip side of the oscillating arm 4 protruding from the column 3 and the base 2 in such a way as to be approximately in parallel with the column 3. A bellows 5 is fixed at a location between the column 3 and the double-tuning-fork quartz resonator 20 between the oscillating arm 4 and the base 2. A pressure-receiving part C1 forming a communicating passage between the inside of the bellows 5 and the outside of the container 1 to be an introduction part of pressure to be measured is formed on the side to the bellows 5 that is fixed to the base 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an absolute pressure sensor using a piezoelectric vibrator as a pressure sensitive element.

  Conventionally, it is composed of a bellows for converting the pressure to be measured into force and a swing arm that transmits the force converted by the bellows to the pressure sensitive element. A detection type pressure sensor (absolute pressure sensor) is introduced in, for example, Patent Document 1.

  FIG. 5 is a schematic cross-sectional view for explaining the schematic structure of the absolute pressure sensor described in Patent Document 1. As shown in FIG. 5, the absolute pressure sensor 70 has a column 63 standing on a base 62 fixed to the bottom of the container 61, and the column 63 is integrated with the column 63 via a hinge 66. The swing arm (swing arm) 64 is provided. Further, between the swing arm 64 and the base 62, a pressure sensitive element 80 is fixed on one end side with the support 63 interposed therebetween, and a bellows 65 is fixed on the other end side. A pressure receiving portion (vibration) C3 for introducing fluid pressure through the inside of the bellows 65 and the outside of the container 61 is provided through the portion of the base 62 where the bellows 65 is fixed. In the container 61, the bellows 65 serves as a sealing material that blocks outside air introduced into the bellows 65 from the pressure receiving part C3, and the container 61 is hermetically sealed.

  In the absolute pressure sensor 70 described above, the pressure introduced from the pressure receiving portion C3 and transmitted to the swing arm 64 via the bellows 65 is transmitted to the pressure sensitive element 80 as a moment around the fulcrum between the swing arm 64 and the support 63. Is done. At this time, the pressure introduced from the pressure receiving part C3 is detected by the change in the resistance region or the resonance frequency of the pressure sensitive element 80 according to the received stress.

Japanese Unexamined Patent Publication No. 64-9331

  The inventor investigated the relationship between the direction of the force acting on the pressure sensitive element and the resonance frequency using the double tuning fork crystal resonator as the pressure sensitive element, and obtained the following knowledge. It was. FIG. 4 shows the effect on the pressure-sensitive element when the resonance frequency when no force is applied to the pressure-sensitive element (force = 0) is f0, the negative is when the force is compressed, and the positive is when the force is tensile. It is the graph which showed the relationship between the force to perform and the resonant frequency of a pressure-sensitive element. As shown in FIG. 4, the resonance frequency decreases when the force applied to the pressure sensitive element is in the compression direction, and the resonance frequency increases when the force is tensile. Furthermore, while the relationship between force and frequency change when the force is tension shows a substantially linear proportional relationship, when the force is compression, the amount of change in the resonance frequency decreases slightly as the force in the compression direction increases. It shows a tendency to increase gradually, and the graph shows non-linearity.

  As shown in FIG. 5, in the absolute pressure sensor 70 of Patent Document 1, the pressure introduced from the pressure receiving part C3 is transmitted to the swinging arm 64 through the bellows 65, and further, the swinging with the hinge 66 of the support 63 as a fulcrum. The moving arm 64 transmits the pressure sensing element 80 as a force for compressing the pressure sensing element 80. As described above, the relationship between the force and the change in the resonance frequency when a compressive force is applied to the pressure-sensitive element has non-linearity. For this reason, in order to accurately measure the pressure introduced from the pressure receiving part C3 in the absolute pressure sensor 70, the measured data of the resonance frequency is obtained from the actual pressure value according to the magnitude of the force acting on the pressure sensing element 80. It is necessary to correct (linearize). In particular, in order to perform accurate pressure measurement, there has been a problem that a complicated correction circuit is required for precisely correcting the resonance frequency of the pressure-sensitive element that changes according to pressure.

  The present invention has been made in view of the above problems, and its purpose is to perform high-precision pressure measurement without correcting the resonance frequency of the pressure-sensitive element that changes depending on the pressure to be measured, using a complicated correction circuit. It is an object to provide an absolute pressure sensor capable of performing the following.

  In order to solve the above-mentioned problems, an absolute pressure sensor according to the present invention includes a container capable of hermetically sealing the inside, a column provided substantially vertically on a base in the container, and a beam-like shape on the column. A swing arm supported by the base, a pressure sensitive element composed of a bellows and a piezoelectric vibrating piece fixed between the base and the swing arm, and the inside of the bellows and the outside of the container are communicated with each other. A pressure receiving portion, and the pressure introduced from the pressure receiving portion and transmitted to the swinging arm via the bellows is transmitted to the pressure sensitive element as a moment around the fulcrum between the swinging arm and the support column. An absolute pressure sensor that detects a pressure by a change in a resistance region or a resonance frequency, and is characterized in that a bellows is disposed between a support column and a pressure-sensitive element with respect to the installation direction of the swing arm. .

  According to this configuration, the pressure introduced from the pressure receiving portion is transmitted in the direction of pushing up the swinging arm via the bellows, and this force is transmitted as a force pulling the pressure sensitive element as a moment around the fulcrum between the swinging arm and the support column. Is done. Then, the pressure introduced from the pressure receiving unit is detected by detecting the resistance region or the resonance frequency of the pressure-sensitive element that changes when the force in the pulling direction is applied. The change in the resistance range or the resonance frequency with respect to the force applied to the pressure-sensitive element is closer to a proportional relationship in the tension direction than in the compression direction. As a result, there is no need to correct the detected pressure value with a complicated correction circuit as in the case of a structure in which a force in the compression direction is applied to the pressure-sensitive element.Therefore, without using a correction circuit or with a simple correction circuit, An absolute pressure sensor capable of measuring pressure with high accuracy can be provided.

  In the present invention, the pressure sensitive element is a double tuning fork crystal resonator.

  A double tuning fork crystal resonator having a structure in which two tuning fork type resonators are coupled has a high Q (resonance sharpness), a fast reactivity, and a high magnification at the time of resonance. By using such a double tuning fork crystal resonator as a pressure-sensitive element, it is possible to provide an absolute pressure sensor that is fast in reactivity and capable of highly accurate pressure detection.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view illustrating a schematic structure of an absolute pressure sensor 10 according to the present invention.

  An absolute pressure sensor 10 shown in FIG. 1 includes a container 1, a support column 3 provided substantially vertically on a base 2 provided at the bottom of the container 1, and a swing arm supported in a beam shape on the support column 3. 4. Between the base 2 and the swing arm 4, there are a bellows 5 fixed at a position adjacent to the column 3 and a pressure sensitive element fixed at an end of the swing arm 4 at a position adjacent to the bellows 5. And a double tuning fork crystal resonator 20. A pressure receiving portion C <b> 1 penetrating the inside of the bellows 5 and the outside of the container 1 is provided at a portion of the base 2 to which the bellows 5 is fixed.

  In this embodiment, the container 1 has a substantially cubic shape that can be hermetically sealed by processing a sheet metal material made of metal or an alloy steel in which an element such as carbon is added to a plurality of metals. Is formed. The bottom of the container 1 is provided with a through hole for forming the pressure receiving part C1 and a through hole for planting a vacuum drawing pipe 15 described later.

  In this embodiment, the base 2 provided at the bottom in the container 1 is made of a plate material such as brass, and is bonded and fixed on the container 1 by a method such as brazing. The base 2 has a predetermined thickness and a mechanical force so that the stress when the container 1 is deformed does not affect the support 3, the swing arm 4, the bellows 5, and the double tuning fork crystal resonator 20. It has a strong strength. In addition, a through hole for fixing the bellows 5 and communicating with the pressure receiving portion C1 is provided at a position overlapping the pressure receiving portion C1 of the container 1 in plan view of the base 2.

  A support column 3 made of metal or the like is fixed to the side surface of one end of the base 2 substantially vertically with the main surface of the base 2 by screws 12 in this embodiment. Further, the swing arm 4 is fixed to the upper end portion of the support column 3 by a screw 14 so as to protrude substantially parallel to the main surface of the base 2 in this embodiment.

  A double tuning fork crystal resonator 20 is fixed between the tip side of the swing arm 4 projecting from the column 3 and the base 2 so as to be substantially parallel to the column 3. A bellows 5 is fixed between the swing arm 4 and the base 2 at a position sandwiched between the support column 3 and the double tuning fork crystal resonator 20. A portion of the bellows 5 fixed to the base 2 is inserted into the through hole of the base 2 and the through hole of the container 1 and exposed to the outside of the container 1, and the inside of the bellows 5 and the outside of the container 1 are connected. A pressure receiving portion C1 serving as a passage is formed. The portion of the bellows 5 protruding from the container 1 and the container 1 are joined so as to be sealed by the brazing material 98, and the outside air introduced into the bellows 5 from the pressure receiving portion C1 is blocked in the container 1. The inside of the container 1 is hermetically sealed.

  As described above, the vacuum pulling pipe 15 made of a relatively soft metal such as copper is inserted into one through hole formed in the bottom of the container 1 so that both end portions protrude to the inside of the container and the outside of the container, respectively. So that it is planted. The evacuation pipe 15 is joined by a joining material such as a brazing material (not shown) so that the inside of the container is sealed.

  Further, lead wires 29a and 29b are connected to and drawn out from electrode terminals (to be described later) of the double tuning fork crystal resonator 20, and the portions covered with the insulating material of the lead wires 29a and 29b are relatively hard materials such as metals. Are inserted together in a sebum tube 16 made of the above material. Further, the sebum tube 16 is inserted into the vacuum drawing pipe 15, and lead wires 29 a and 29 b are drawn out to the outside of the container 1. At this time, the sebum tube 16 in which the lead wires 29a and 29b are inserted is sealed by filling at least a part of the tube with resin or the like.

  Then, the inside of the container 1 is depressurized through the vacuum pipe 15 with the sebum pipe 16 inserted, and when the vacuum state is reached, the outer portion of the container 1 of the vacuum pipe 15 is crushed and completely sealed. The inside of the container 1 is sealed in a vacuum.

  The lead wires 29 a and 29 b drawn out of the container 1 are connected to an oscillation circuit (not shown) for exciting the double tuning fork crystal resonator 20.

(Twin tuning fork crystal resonator)
Next, the structure of a double tuning fork crystal resonator used as a pressure sensitive element in the absolute pressure sensor 10 of this embodiment will be described with reference to the drawings. FIG. 2 is a schematic perspective view illustrating a schematic structure of a double tuning fork crystal resonator.

  As shown in FIG. 2, the double tuning fork crystal resonator 20 is formed by etching a plate-shaped crystal substrate 21 by using a photolithography technique, so that a vibration beam portion 22 located at the center portion and the vibration beam portion 22 are formed. Support portions 23 and 24 formed on both end sides with respect to each other are formed. A substantially rectangular planar through-hole 29 is formed at the approximate center of the vibration beam portion 22.

  Excitation electrodes 25 which are counter electrodes are formed on both main surfaces of the vibration beam portion 22. Further, a lead wiring is drawn out from the excitation electrode 25 and connected to electrode terminals 26 and 27 formed on the support portion 23. The excitation electrode 25, the electrode terminals 26 and 27, and the lead-out wiring are electrode films generally formed by sputtering or vapor deposition of an electrode material. As described above, the double tuning fork crystal resonator 20 has a structure in which the vibration beam portions of two tuning fork resonators are coupled face to face.

Next, the operation of the absolute pressure sensor 10 having the above-described structure will be described.
In the absolute pressure sensor 10 shown in FIG. 1, when a drive voltage is applied to the twin tuning fork crystal resonator 20 from an oscillation circuit (not shown) provided outside the container 1 and excited, the double tuning fork crystal resonator 20 is in a vacuum state. The bending vibration is repeated at the resonance frequency at (resonance frequency f0 in FIG. 4). The bending motion at this time is repeated in the direction of the back side and the near side of the double tuning fork crystal resonator 20 in FIG.

  The pressure that is the measurement target introduced from the pressure receiving part C <b> 1 is converted into a force corresponding to the effective area of the bellows 5. This force is transmitted as a force in the pulling direction to the double tuning fork crystal resonator 20 as a moment around the fulcrum between the swing arm 4 and the support column 3 by the swing arm 4. The resonance frequency f0 of the double tuning fork crystal resonator 20 to which a force in the pulling direction is applied changes in a direction in which the resonance frequency increases as shown in FIG. The amount of change in the resonance frequency at this time is converted into a pressure by a microcomputer provided in the oscillation circuit, thereby outputting a pressure (absolute pressure) value applied to the pressure receiving unit C1.

  The effects of the above embodiment will be described below.

  (1) In the absolute pressure sensor 10 of the above embodiment, the base 2 is fixed to the bottom of the container 1 sealed in a vacuum state, and the side surface of one end of the base 2 is substantially perpendicular to the main surface of the base 2. The column 3 was fixed as follows. The swing arm 4 is fixed to the upper end portion of the column 3 so as to protrude substantially parallel to the main surface of the base 2. A double tuning fork crystal resonator 20 was fixed between the tip end of the swing arm 4 projecting from the support 3 and the base 2 so as to be substantially parallel to the support 3. Then, the bellows 5 is fixed at a position between the swing arm 4 and the base 2 between the support column 3 and the double tuning fork crystal resonator 20, and the pressure receiving pressure that communicates the inside of the bellows 5 with the outside of the container 1. Part C1 was provided.

  According to this configuration, the pressure to be measured introduced from the pressure receiving part C <b> 1 is transmitted as a force for pushing up the swing arm 4 by the bellows 5, and this force is a moment around the fulcrum between the swing arm 4 and the column 3. It is transmitted as a force pulling the double tuning fork crystal resonator 20. As described above, the change in the resonance frequency with respect to the force applied to the double tuning fork crystal resonator 20 is more linear when the direction of the force applied to the double tuning fork crystal resonator 20 is the tension direction than when the direction is the compression direction. A proportional relationship with As a result, there is no need to correct the detected pressure value with a complex correction circuit as in the case of a structure in which a force in the compression direction is applied to the double tuning fork crystal resonator 20, so that the correction circuit can be used without using a correction circuit or simple correction. The circuit makes it possible to measure pressure with high accuracy.

  (2) In the above embodiment, the double tuning fork crystal resonator 20 is used as the pressure sensitive element.

  According to this configuration, the double tuning fork crystal resonator 20 has a high Q (resonance sharpness) and has a fast reactivity and a high magnification at the time of resonance. A possible absolute pressure sensor 10 can be provided.

  (3) In the above embodiment, the support column 3 is fixed to the base 2 with the screw 12, and the swing arm 4 is fixed to the support column 3 with the screw 14.

  According to this structure, since the support | pillar 3 and the rocking | fluctuation arm 4 can be fixed reliably by the simple method by screwing, it serves for manufacturing the absolute pressure sensor 10 at low cost.

  The present invention is not limited to the above-described embodiment, and the following modified examples can also be implemented.

  (Modification) In the above-described embodiment, the support 3 and the swing arm 4 which are separate parts are fixed by the screw 14, but the present invention is not limited thereto. The support and the swing arm may be formed by integral processing. FIG. 3 is a schematic cross-sectional view for explaining an absolute pressure sensor 40 in which a support column and a swing arm are integrally formed. In this modification, the same components as those in the above embodiment are denoted by the same reference numerals and description thereof is omitted.

  An absolute pressure sensor 40 shown in FIG. 3 includes a container 1, a support column 33 provided substantially perpendicularly on a base 2 provided at the bottom of the container 1, and bent from the support column 33 at a substantially right angle with respect to the base 32. The swinging arm 34 extending in parallel is integrally formed. In the present embodiment, a half-etched portion 39 is formed at a bent portion that becomes a boundary between the support column 33 and the swing arm 34. Between the base 2 and the swing arm 34, a bellows 5 fixed at a position adjacent to the support 33 and a double tuning fork crystal vibration fixed at an end of the swing arm 34 at a position adjacent to the bellows 5. And a child 20. A pressure receiving portion C <b> 1 penetrating the inside of the bellows 5 and the outside of the container 1 is provided at a portion of the base 2 to which the bellows 5 is fixed.

  According to this configuration, since the support 33 and the swing arm 34 are integrally formed by bending the same material, it is not necessary to join the support and the swing arm, and the manufacturing process can be simplified. Become. Further, since a half-etched portion 39 is formed at the bent portion of the support column 33 and the swing arm 34, the bending process is facilitated while ensuring the mechanical strength of the respective portions of the support column 33 and the swing arm 34. be able to. Furthermore, the support structure of the support column 33 and the swing arm 34 can be formed only by forming the half-etched portion 39 by batch processing and bending. Thus, high-precision cutting is not required unlike the support 63 and the swing arm 64 of the absolute pressure sensor 70 described in Patent Document 1 described above, and low-cost manufacturing can be performed by a relatively simple process.

  The embodiment of the present invention made by the inventor has been specifically described above, but the present invention is not limited to the above-described embodiment, and various modifications are made without departing from the scope of the present invention. Is possible.

  For example, in the above embodiment, the base 2 is installed at the bottom of the container 1, but if the bottom plate portion of the container has the required mechanical strength, the bottom plate portion of the container itself can be used as a base. Can be configured.

  Moreover, in the said embodiment, although the cylindrical outer edge used the bellows 5 which has a bellows shape, it is not restricted to this. The bellows 5 is displaced according to the pressure taken in from the pressure receiving portion C1, thereby transmitting the pressure as a force to the swinging arm 4 (34) and having a shape restoring property as the pressure is attenuated. For example, a bellows having an elliptical cross section may be used.

  In the above embodiment, the base 2 and the support column 3 (33) and the support column 3 and the swing arm 4 are connected by the screws 12 and 14, but the present invention is not limited thereto. . Other joining methods such as brazing, welding, or a method of bonding using an adhesive may be used.

  Moreover, in the said embodiment, although the pressure receiving part C1 used as the introduction part of the pressure which communicates and measures the bellows 5 and the exterior of the container 1 was provided in the baseplate part of the container 1 directly under the pressure introduction part of the bellows 5. However, the present invention is not limited to this, and a configuration in which the pressure receiving portion is provided on the side surface of the container is also possible. Similarly, the evacuation pipe 15 may be provided on the side surface or the upper surface of the container 1, and the container 1 is sealed not only by the method using the evacuation pipe 15 but also by a brazing material or a sealing resin. It is good also as a structure.

1 is a schematic cross-sectional view illustrating a schematic structure of an embodiment of an absolute pressure sensor according to the present invention. The perspective view which shows typically the double tuning fork crystal resonator as a pressure sensitive element. The schematic cross section explaining the modification of an absolute pressure sensor. The graph which showed the relationship between the force which acts on a pressure sensitive element, and the resonant frequency of a pressure sensitive element. The schematic cross section explaining the schematic structure of the conventional absolute pressure sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,61 ... Container, 2,62 ... Base, 3, 33, 63 ... Post, 4, 34, 64 ... Swing arm, 5, 65 ... Bellows, 10, 40, 70 ... Absolute pressure sensor, 20 ... Pressure sensitive A double tuning fork crystal resonator as an element, 80... Pressure sensitive element, C1, C3.

Claims (2)

A container capable of hermetically sealing the inside, a support provided substantially vertically on the base in the container, a swing arm supported in a beam-like manner on the support, the base and the swing A pressure sensing element comprising a bellows and a piezoelectric vibrating piece fixed between the arm and a pressure receiving portion penetrating so as to communicate the inside of the bellows and the outside of the container; The pressure introduced to the swing arm via the bellows is transmitted to the pressure sensitive element as a moment around the fulcrum of the swing arm and the column, and the resistance region or resonance of the pressure sensitive element is transmitted. An absolute pressure sensor that detects the pressure by a change in frequency,
The absolute pressure sensor, wherein the bellows is disposed between the support column and the pressure sensitive element with respect to the installation direction of the swing arm. The absolute pressure sensor according to claim 1,
An absolute pressure sensor, wherein the pressure sensitive element is a double tuning fork crystal resonator.

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