JP7629166B2 - Pressure sensor and pressure sensor inspection method - Google Patents

Description

The present invention relates to a pressure sensor, particularly a pressure sensor used as a diaphragm vacuum gauge and an absolute pressure gauge, and to an inspection method for this pressure sensor.

Pressure sensors using thin-film diaphragms are widely used as sensors for measuring the pressure of a fluid or the pressure within a space through which a fluid flows in and out. In these pressure sensors, the pressure of the fluid to be measured (hereinafter referred to as the "measured fluid") or the pressure within a specified space is captured in the form of mechanical displacement through the diaphragm, and this mechanical displacement is detected as an electrical signal, for example a voltage signal, thereby measuring the pressure of the measured fluid or the vacuum state of the space.

For example, the capacitance type and the semiconductor type are widely known as methods for detecting mechanical displacement as an electrical signal. The capacitance type is configured to detect the mechanical displacement of a diaphragm as a change in capacitance between a pair of electrodes, and the semiconductor type is configured to detect the mechanical displacement of the diaphragm as a voltage change through a strain gauge consisting of a Wheatstone bridge circuit formed on a substrate made of a semiconductor material such as Si.

For example, Patent Document 1 describes a capacitance-type pressure sensor (1). This pressure sensor (1) has a diaphragm (32) disposed between two spaces that are isolated from each other and not connected to each other, specifically, a pressure introduction part (10A) that communicates with a space through which the fluid to be measured flows in and out or that is in a vacuum state, and a reference vacuum chamber (10B) that is maintained in a vacuum state. When the pressure in the pressure introduction part (10A) changes, a pressure difference occurs between the pressure introduction part (10A) and the reference vacuum chamber (10B), which causes a mechanical displacement in the diaphragm (32). This mechanical displacement is detected as a change in the capacitance between two electrodes (the pressure-sensing side fixed electrode 110 and the reference side fixed electrode 120).

In a pressure sensor using a diaphragm such as the pressure sensor (1) described above, when surrounding gas (atmosphere, etc.) flows into the reference vacuum chamber, the internal pressure of the reference vacuum chamber changes, which displaces the diaphragm regardless of pressure changes in the measured fluid, etc. For this reason, the flow of gas into the reference vacuum chamber is one of the causes of measurement errors, and therefore, in order to measure the pressure of the measured fluid or the pressure within a specified space with high accuracy using a pressure sensor using a diaphragm, it is necessary to always maintain the reference vacuum chamber in a high vacuum state (hereinafter, this state may be referred to as a "high vacuum state").
Here, the reference vacuum chamber is configured such that a plurality of casing members that define the reference vacuum chamber are joined by welding or the like, and a sealing element is inserted into an opening for evacuation to create a high vacuum inside (hereinafter, the location where the sealing element is inserted may be referred to as the "final vacuum sealing location"). However, poor welding or incomplete sealing of the hole may cause a gap (leakage hole), which may impair the airtightness of the reference vacuum chamber. In preparation for such an impairing of airtightness, for example, a substance that adsorbs the inflowing gas (hereinafter, referred to as a "getter") may be installed in the reference vacuum chamber. However, since there is an upper limit to the amount of gas that the getter can adsorb, if the amount of the inflowing gas exceeds this upper limit, the high vacuum state is not maintained and the internal pressure of the reference vacuum chamber increases. Therefore, even if a getter is installed, it is difficult to always maintain a high vacuum state when the amount of inflowing gas is large. Therefore, in the manufacturing process of a pressure sensor using a diaphragm, regardless of whether or not a getter is used, a step is provided for conducting a leak test (hereinafter, simply referred to as a "leak test" or "test") for the airtightness of the reference vacuum chamber. In this leak test, the presence or absence of a slight leak in the vacuum reference chamber, specifically, the presence or absence of a minute leak of ^{10-7 Pam3} /s or less is checked.

In conventional leak inspections, leaks caused by poor connections such as poor welding are inspected using, for example, methods specified by the Japanese Industrial Standards (JIS), more specifically, the vacuum spray method (spray method) specified in Appendix 1 of JIS Z2331 and the vacuum hood method (vacuum hood method) specified in Appendix 2. In contrast, leaks at the final vacuum sealing point are inspected based on the immersion method (bombing method) specified in Appendix 7 of JIS Z2331 (see Non-Patent Document 1). Note that leaks caused by poor connections such as poor welding and leaks at the final vacuum sealing point may all be inspected using only the immersion method (bombing method), omitting the vacuum spray method (spray method) and the vacuum hood method (vacuum hood method).

In the immersion method (bombing method) of the above leak tests, the first step is to seal helium gas in the test object (reference vacuum chamber equipped with a pressure sensor) using a helium gas bombing device as shown in Figure 6. More specifically, the test object is placed in a bombing tank sealed with pressurized helium gas, and then the test object is left pressurized for a predetermined period of time to seal the helium gas in the test object.

As the second step following the first step, a helium gas leak test is performed using the leak test device shown in Figure 7. More specifically, after the first step is completed, the test specimen is removed from the bombing tank and placed in a vacuum chamber to evacuate the outside of the test specimen.

If there is a gap at the final vacuum sealing point, helium gas will enter the test piece in the first step, and the helium gas that entered will be exhausted to the outside of the test piece in the second step. The exhausted helium gas is measured, and the measured value is compared with the leak value required for the test piece, for example, a preset standard air equivalent leak amount, to distinguish between good and bad products.

JP 2008-107214 A

Japanese Industrial Standards Z2331 Appendix 7

As semiconductors become increasingly dense, it is essential to control environmental parameters in the manufacturing process with high precision, and the demand for higher precision in the pressure sensors (vacuum gauges) used in the manufacturing process is also increasing year by year. To meet this demand, leak testing of the reference vacuum chamber is becoming more important than ever. However, in leak testing of the reference vacuum chamber, particularly the immersion method (bombing method) performed as a leak test for the final vacuum sealing point, it takes a long time to seal helium gas in the reference vacuum chamber, which is the test specimen. This results in extremely poor production efficiency, and there is a problem in that it is difficult to produce pressure sensors that meet the above demands with a short lead time.

The present invention was created in consideration of the above problems, and its purpose is to provide a pressure sensor that can perform a leak test on a reference vacuum chamber in a short time, and to provide an inspection method that can use the pressure sensor to perform a leak test related to the airtightness of the reference vacuum chamber in a short time.

The pressure sensor (10A, 10B) according to the present invention for solving the above problems comprises a diaphragm (12) having a pressure-receiving surface formed on one side, a casing member (upper housing 22 and cover 23) that forms a sealed space (reference vacuum chamber 20W) together with the other side of the diaphragm, and a measuring section (60) that measures the pressure in the space (introduction section 20V) facing the pressure-receiving surface from the deformation of the diaphragm caused by the difference between the pressure applied to the pressure-receiving surface and the internal pressure of the sealed space, and is characterized in that the diaphragm and the casing member are configured to seal the gas (G) to be detected in the inspection of the airtightness of the sealed space in the sealed space.

The pressure sensor may be configured so that the pressure of the gas sealed in the sealed space having a predetermined volume is calculated using at least the lower detection limit of a leak detection device used in the inspection and the allowable inflow amount of the ambient gas that is allowed to flow into the sealed space.

Furthermore, in the pressure sensor, the enclosed pressure may be configured to be set to a value larger than the lower limit Pmin calculated from the relational expression Pmin = Qmin/Qα x Pα x ( _MG x Tα/T/M _air ) ^1/2 + Prt, where Pmin is the lower limit of the enclosed pressure, Qmin is the lower detection limit, Qα is the allowable inflow rate, Pα is the ambient pressure at the time of measuring the allowable inflow rate, Tα is the ambient temperature at the time of measuring the allowable inflow rate, M _G is the molecular weight of the gas, M _air : the molecular weight of the ambient gas, T is the ambient temperature at the time of inspection, and Prt is the partial pressure of the gas in the ambient pressure at the time of inspection.

Furthermore, the pressure sensor may be further configured to include a temperature sensor (80) that measures the temperature of the enclosed space, and a correction unit (70) that corrects errors in the pressure measurement caused by changes in the ambient temperature using the value detected by the temperature sensor.

In the pressure sensor, the correction unit may be configured to perform the correction using the value detected by the temperature sensor and the filled pressure (P _O ) and temperature (T _O ) when the gas is filled into the sealed space.

Furthermore, in the pressure sensor, the gas may be configured to be made of a substance that is not occluded by the wall surface that forms the sealed space.

The pressure sensor may also be configured so that the gas is made of a material that is not adsorbed by an adsorbent material (getter 24) disposed in the sealed space to adsorb the ambient gas.

Furthermore, in the pressure sensor, the gas may be configured to consist of a substance other than that contained in air at a ratio of 1% by volume or more.

The method for testing the airtightness of the sealed space provided with the pressure sensor according to the present invention for solving the above problems is characterized by comprising a first step (S1) of placing the pressure sensor inside a specified container, a second step (S2) of creating a vacuum inside the container, a third step (S3) of measuring the amount of gas flowing out of the container using a leak detection device, and a fourth step (S4) of determining the airtightness of the sealed space from the amount of gas flowing out.

In the above explanation, as an example, the names and reference symbols of parts in the drawings that correspond to the components of the invention are given in parentheses.

The present invention provides a pressure sensor that can perform leak testing related to the airtightness of a reference vacuum chamber in a short period of time. In addition, by using this pressure sensor, it is possible to provide an inspection method that can perform leak testing related to airtightness in a short period of time.

FIG. 1 is a cross-sectional view of a pressure sensor according to an embodiment of the present invention. FIG. 2 is a functional block diagram of a pressure sensor according to an embodiment of the present invention. FIG. 3 is a flow diagram showing a method for inspecting a pressure sensor according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a pressure sensor according to another embodiment of the present invention. FIG. 5 is a functional block diagram of a pressure sensor according to another embodiment of the present invention. FIG. 6 is a schematic diagram of a helium gas bombing device used for a leak test carried out in a conventional pressure sensor manufacturing process. FIG. 7 is a schematic diagram of a leak test device used in a leak test carried out in a conventional pressure sensor manufacturing process.

A first and a second embodiment, which are preferred embodiments of the present invention, will be described with reference to Fig. 1 to Fig. 5. Here, components common to each embodiment are given the same reference numerals and repeated explanations will be omitted. Also, each figure is a conceptual diagram, and the contents shown in each figure do not necessarily coincide with an actual pressure sensor.
In the following description, the ambient temperature, the internal temperature of the reference vacuum chamber 20W, and the temperature of the gas G are the same unless otherwise specified (i.e., they are in thermal equilibrium with each other). In addition, among the pressures and temperatures in the description, temperatures and pressures with the same italicized subscripts refer to the temperature and pressure in the same state (at the same time). Furthermore, in the description, the units of pressure, temperature, inflow rate, and leakage rate conform to the SI system of units unless otherwise specified, with the unit of pressure being Pa, the unit of temperature being K, and the units of inflow rate and leakage rate being ^Pam3 /s.

First Embodiment
<Pressure sensor configuration>
First, the configuration of a pressure sensor 10A according to a first embodiment of the present invention will be described with reference to Figures 1 and 2. This pressure sensor 10A is a capacitance type pressure sensor, and is used, for example, as a fluid pressure gauge that measures the pressure of a fluid flowing in a specified pipe, or as a vacuum gauge that measures the vacuum state of a specified space.

As shown in FIG. 1, the pressure sensor 10A is mainly composed of a pressure sensor element 11, a casing 20, a base plate 30 housed in the casing 20, a support diaphragm 40 joined to the base plate 30 and bridged across the casing 20, an electrode lead portion 50 that electrically connects the inside and outside of the casing 20, and a measuring portion 60 that measures pressure based on an electrical signal (e.g., a voltage signal) output from the pressure sensor element 11.

[Pressure sensor element 11]
The pressure sensor element 11 is an element that captures the pressure change of the fluid to be measured or the pressure change in a predetermined space in the form of a mechanical displacement, and detects this mechanical displacement as an electric signal (for example, a voltage signal), and is configured as a capacitance type pressure sensor element as described above. The pressure sensor element 11 has a thin plate shape, for example, approximately 1 cm square in a plan view, and includes a thin plate-like diaphragm 12, a disk-like base 13 that is connected to the diaphragm 12 to form a capacitance chamber C1, a pair of sensor electrodes 14, 14 housed inside the capacitance chamber C1, and a contact pad 15 that is electrically connected to an electrode lead pin 51 described later.

When the fluid to be measured that has flowed into the introduction portion 20V comes into contact with one surface (pressure receiving surface) of the diaphragm 12, the diaphragm 12 deforms, for example so that the center becomes convex toward the top in FIG. 1. This deformation of the diaphragm 12 changes the distance between a pair of sensor electrodes 14, 14 disposed in the capacitance chamber C1, and as a result, the capacitance between these electrodes changes according to the amount of deformation. In this way, the pressure sensor element 11 detects the change in pressure of the fluid to be measured as a change in capacitance. The detected change in capacitance is transmitted to the measurement portion 60 in the form of a voltage signal SV, as shown in FIG. 2.

[Casing 20]
The casing 20 constitutes the outer frame of the pressure sensor 10A, and defines a reference vacuum chamber 20W having a predetermined volume together with a base plate 30 and a support diaphragm 40 described later. It also supports the pressure sensor element 11 inside the reference vacuum chamber 20W via the base plate 30 and the support diaphragm 40, and is an element that defines an introduction section 20V through which the measured fluid flows in and out. The casing 20 is composed of a lower housing 21, an upper housing 22, and a cover 23, and these casing elements are each formed, for example, from Inconel, which is a corrosion-resistant metal. The lower housing 21, the upper housing 22, and the cover 23 are stacked from bottom to top in that order, for example, along the axis CL (the axis of the pipe through which the measured fluid flows in and out), and the respective mating surfaces are formed, for example, on a plane perpendicular to the axis CL, and the opposing parts are joined to each other, for example, by welding.

The lower housing 21 is a cylindrical part formed of a large diameter cylindrical section 21a and a small diameter cylindrical section 21b, with these two sections connected so as to be coaxial. The upper opening end of the large diameter cylindrical section 21a is connected to the lower opening end of the upper housing 22 via a support diaphragm 40. The inner peripheral wall of the small diameter cylindrical section 21b defines an inlet section 20V into which the fluid to be measured flows.

The upper housing 22 is a generally cylindrical part interposed between the lower housing 21 and the cover 23, and its lower open end is connected to the upper open end of the lower housing 21 via the support diaphragm 40 as described above, and its upper open end is connected to the cover 23. The diameter (inner diameter and outer diameter) and axis of the upper housing 22 are generally the same as the diameter (inner diameter and outer diameter) and axis of the large diameter cylindrical part 21a of the lower housing 21. The upper housing 22, together with the cover 23, the pressure sensor element 11, the base plate 30, and the support diaphragm 40, define the reference vacuum chamber 20W inside the casing 20 as described above.

A stopper 22a is provided at a suitable position on the inner peripheral wall surface near the lower open end of the upper housing 22. The provision of the stopper 22a prevents the base plate 30 from moving excessively due to a sudden increase in pressure of the fluid to be measured.

Furthermore, the upper housing 22 has a hole 22b formed, for example, in its side wall. This hole 22b is used to exhaust gas (e.g., the atmosphere) remaining inside the reference vacuum chamber 20W during the manufacturing process and to seal in the gas G, which will be described later. After the above-mentioned exhaust operation and the operation of sealing in the gas G are performed, the reference vacuum chamber 20W has its internal pressure maintained at a sealing pressure, which will be described later, by inserting a sealing element 25 into the hole 22b.
Furthermore, hole 22b need only be located in a position where the above-mentioned exhaust and sealing operations can be performed from the outside of pressure sensor 10A, that is, in a position that can connect the outside of pressure sensor 10A to the reference vacuum chamber 20W, and therefore may open not in the side wall of upper housing 22, but, for example, in the cover 23 that defines the reference vacuum chamber 20W.
Furthermore, in cases where the above-mentioned exhaust operation and/or sealing operation can be performed without providing the hole 22b, the hole 22b and the sealing element 25 can be omitted. For example, in a case where the manufacturing process is configured so that the casing 20 is assembled inside a vacuum chamber, the operation of sealing the gas G can be performed without the hole 22b and the sealing element 25 by sealing a specified amount of the gas G inside the reference vacuum chamber 20W and then joining the mating surfaces of the casing members (the upper housing 22 and the cover 23) that define the reference vacuum chamber 20W by welding or the like. In this way, there are various methods for sealing the gas G in the reference vacuum chamber 20W, and the method is not limited to a specific one.

Gas G is sealed inside the reference vacuum chamber 20W through the above-mentioned operations. This gas G is a substance that can leak out of the reference vacuum chamber 20W and is detected by the leak detection device during a leak test related to the airtightness of the reference vacuum chamber 20W, which will be described later.
A getter 24 made of a gas adsorbent material may be disposed in the reference vacuum chamber 20W to maintain a desired degree of vacuum. The getter 24 is made of zirconium (Zr), vanadium (V), iron (Fe), etc., to adsorb oxygen, nitrogen, etc., which constitute air. The getter 24 is disposed, for example, at a position where it contacts the inner peripheral side surface of the upper housing 22 and the lower surface of the cover 23. However, the position where the getter 24 is disposed is not limited to this position.

When a getter 24 is provided, from the viewpoint of ensuring the effectiveness of the leak inspection and a given measurement accuracy, it is preferable that the gas G be made of a substance that is not adsorbed to the getter 24. For example, the gas G is a noble gas having stable nuclides such as helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe) and having poor reactivity, or is made of methane ( _CH4 ) or the like. From the viewpoint of improving the accuracy of leak testing, it is preferable that the gas be a gas other than the main components, such as nitrogen (N2) and oxygen (O2), contained at a ratio of 1% by volume or more, from among the components that make up air, specifically, nitrogen (approximately 78% by volume), oxygen (approximately 21% by volume), argon (approximately 0.9% by volume), carbon dioxide (approximately 300 ppm), neon (approximately 18 ppm), helium (approximately 5.2 ppm), methane (approximately 1.5 ppm), krypton (approximately 1 _ppm ), and sulfur dioxide (approximately _{1 ppm} ).
Furthermore, from the viewpoint of ensuring the effectiveness of the leak test and a given accuracy, it is desirable that the gas G is a material that is not occluded by the members constituting the wall surfaces defining the reference vacuum chamber 20W, i.e., the inner wall surface of the casing 20 (more specifically, the upper housing 22 and the cover 23), the outer surface of the pressure sensor element 11, the outer surface of the base plate 30 (more specifically, the first base plate 31), the outer surface of the support diaphragm 40, and the outer surface of the hermetic seal 57 described below. For example, since helium gas (He ₂ ) is occluded by glass, it is desirable to use a material other than helium gas for the gas G when the hermetic seal 57 is made of glass.

In order to ensure the effectiveness of the test, it is preferable that the gas G is sealed in the reference vacuum chamber 20W at a predetermined temperature and a sealed pressure equal to or greater than a certain value. The lower limit of this sealed pressure will be described in detail in the section "Regarding the sealed pressure of gas G" below. In order to reduce measurement errors, an upper limit may be set for the sealed pressure. This upper limit of the sealed pressure will also be described in detail in the section "Regarding the sealed pressure of gas G".

The cover 23 is made of a roughly disk-shaped plate, and has an electrode lead insertion hole 23a formed at a predetermined position. The electrode lead portion 50 is embedded in this electrode lead insertion hole 23a via a hermetic seal 57, thereby ensuring a predetermined electrical seal. The hermetic seal 57 is made of, for example, glass (silicon dioxide).

In this way, the casing 20 has a lower housing 21, an upper housing 22, and a cover 23 stacked along the axis CL, and has the external shape of two connected cylinders of different diameters with the axis CL.

[Base plate 30]
The base plate 30 is a component that supports the pressure sensor element 11, and is composed of a first base plate 31 and a second base plate 32. The base plate 30 is supported so as to be bridged to the casing 20 via a support diaphragm 40 described later.

The first base plate 31 and the second base plate 32 are made of, for example, sapphire, which is a single crystal of aluminum oxide. Both the first base plate 31 and the second base plate 32 are located away from the inner surface of the casing 20, with the former bonded to the upper surface of the support diaphragm 40 and the latter bonded to the lower surface of the support diaphragm 40. Here, the first and second base plates 31, 32 are sufficiently thick compared to the thickness of the support diaphragm 40, which prevents the base plate 30 from warping due to thermal stress caused by the difference between the thermal expansion coefficients of the base plate 30 and the support diaphragm 40.

The first base plate 31 and the second base plate 32 have an introduction hole 31a and an introduction hole 32a opened at approximately the center thereof to communicate the space C2, which faces the pressure receiving surface of the diaphragm 12 of the pressure sensor element 11, with the introduction section 20V into which the measured fluid flows. In addition, the pressure sensor element 11 is bonded to the underside of the second base plate 32 via an aluminum oxide-based bonding material so that the introduction hole 32a and the space C2 are in communication. The first base plate 31 and the pressure sensor element 11 are bonded by a well-known method.

[Support diaphragm 40]
As described above, the support diaphragm 40 is a component provided to bridge the base plate 30 through the casing 20, and is made of a thin Inconel plate. Its shape matches the outer peripheral edge shape of the casing 20, specifically, the outer peripheral edge shapes of the lower opening end of the upper housing 22 and the upper opening end of the lower housing 21. With the first base plate 31 joined to the upper surface of the support diaphragm 40 and the second base plate 32 joined to the lower surface, the outer peripheral portion (peripheral edge portion) of the support diaphragm 40 is sandwiched between the lower opening end of the upper housing 22 and the upper opening end of the lower housing 21 and joined by welding or the like. Note that the thickness of the support diaphragm 40 is, for example, several tens of microns in this embodiment, which is sufficiently thinner than the first and second base plates 31 and 32. In addition, in the center of the support diaphragm 40, along with the introduction holes 31a and 32a, an introduction hole 40a is opened to connect the space C2 facing the pressure-receiving surface of the diaphragm 12 to the introduction portion 20V into which the measured fluid flows.

[Electrode lead part 50]
The electrode lead portion 50 includes an electrode lead pin 51 and a metal shield 52, and the center portion of the electrode lead pin 51 is embedded in the metal shield 52 by a hermetic seal 53 made of an insulating material such as glass, and an airtight state is maintained between both ends of the electrode lead pin 51. One end of the electrode lead pin 51 and the shield 52 protrudes from the upper surface of the cover 23 to the outside along the axis CL, and an electric signal (for example, a voltage signal SV) output from the pressure sensor element 11 is transmitted to an amplifier (amplifier) and a signal processing unit arranged outside (the amplifier (amplifier) is included in an analog detection circuit AC described later, and the signal processing unit is a functional unit equivalent to the measurement unit 60). As described above, the hermetic seal 53 is also interposed between the shield 52 and the cover 23. In addition, conductive contact springs 55 and 56 are connected to the other end of the electrode lead pin 51.

The contact springs 55 and 56 are elastic elements that are provided to absorb displacement of the pressure sensor element 11 caused by a sudden pressure rise resulting from the sudden inflow of the fluid to be measured from the inlet 20V (more specifically, when the pressure rise causes displacement of the base plate 30 bridged to the casing 20 via the support diaphragm 40, causing displacement of the pressure sensor element 11 supported thereby), so as not to affect the measurement accuracy of the pressure sensor element 11.

[Measurement unit 60]
As shown in FIG. 2, the measurement unit 60 is a functional unit that receives the voltage signal SV output from the pressure sensor element 11 and measures the value of the pressure inside the introduction portion 20V from the voltage value related to the pressure contained in this voltage signal SV (hereinafter referred to as the "measured pressure value." This measured pressure value corresponds to the "pressure" value and the "measurement value" described in the claims), and is mainly composed of an interface 61, a central processing unit (CPU) 62, and a memory 63.

The central processing unit (CPU) 62 is a device that acquires a voltage value related to the pressure output from the pressure sensor element 11 through the voltage signal SV, and calculates a measured pressure value using this voltage value, a calculation program stored in the memory 63, and various information, etc., and is composed of a microprocessor, etc.
The memory 63 is a device that stores the above-mentioned calculation program executed through the central processing unit (CPU) 62, and information used in this calculation program, such as information related to the correlation (calibration curve) between the voltage value and the measured pressure value, and is composed of, for example, a non-volatile memory.
The interface 61 is an element for electrically communicating with an external device, etc., and can take the form of various existing standards. The measured pressure value calculated by the central processing unit (CPU) 62 is transmitted to the external device 100 electrically communicating via the interface 61 in the form of, for example, an electrical signal S.

<Regarding the pressure of gas G>
In the technical field to which the pressure sensor using a diaphragm belongs, it is technical common sense to maintain the reference vacuum chamber in a high vacuum state from the viewpoint of measurement accuracy. However, the present invention is characterized by changing the technical idea seen in this technical common sense and sealing the gas G in the reference vacuum chamber in order to solve the above problem. Therefore, in order to achieve the object of the present invention while maintaining a given measurement accuracy, it is desirable to properly manage the filling pressure of the gas G. Specifically, as described above, from the viewpoint of reliably ensuring the effectiveness of the inspection, it is desirable to set a lower limit value for the filling pressure of the gas G sealed in the reference vacuum chamber 20W. Also, from the viewpoint of reducing measurement errors, it is preferable to set an upper limit value for the filling pressure of the gas G sealed in the reference vacuum chamber 20W. Below, the lower limit value and the upper limit value of the filling pressure will be described in detail.

[Lower limit of charging pressure]
In the reference vacuum chamber 20W, a very small gap (leak hole) communicating with the outside (atmosphere) may be formed on the mating surfaces of the parts that define the reference vacuum chamber 20W due to poor joints caused by poor welding or the like, and a gap may also be formed due to insufficient sealing. Specifically, gaps may be formed on the mating surfaces of the upper housing 22, the cover 23, and the support diaphragm 40 that face the outside (atmosphere), as well as on the mating surface between the electrode lead insertion hole 23a that opens into the cover 23 and the electrode lead portion 50 that is embedded in this hole via a hermetic seal 57, and a gap may also be formed between the hole 22b and the sealing element 25. For this reason, during use of the pressure sensor 10A, the surrounding gas (atmosphere) under atmospheric pressure may flow into the reference vacuum chamber 20W. As described in the background art, this inflow of the surrounding gas is a cause of measurement errors. Therefore, in order to provide a pressure sensor 10A with high measurement accuracy, it is necessary to maintain the reference vacuum chamber 20W in a high vacuum state, i.e., to suppress the inflow of the surrounding gas to a specified value or less (hereinafter, this specified value will be referred to as the "allowable inflow amount Qα"). The allowable inflow amount Qα is set, for example, based on the measurement accuracy and quality assurance period required for the pressure sensor 10A, and also, if a getter 24 is provided, is set in consideration of its adsorption capacity (capacity).

Here, whether the reference vacuum chamber 20W is maintained in a high vacuum state is determined through a leak test for the airtightness of the reference vacuum chamber, as described above. Conventional tests are performed, for example, by the immersion method (bombing method) consisting of a bombing process and a leak detection process, as described above. In this immersion method (bombing method), in the bombing process, gas (e.g., helium gas) flows from the surroundings in a high-pressure state toward the reference vacuum chamber in a nearly vacuum state through, for example, the leak hole, and in the leak detection process, the surroundings of the vacuum reference chamber are evacuated to a vacuum, causing the gas that flowed into the reference vacuum chamber to leak out of the chamber. The inspection device measures the amount of this leaked gas, and for example, compares the amount of leak with a predetermined allowable value to determine whether the airtightness is good or bad. Here, in the immersion method (bombing method), the bombing process is performed for a sufficiently long time so that the amount of leaked gas is within the range of the leak detection capability of the inspection device (so that it is greater than the lower limit of leak detection). In other words, the effectiveness of the inspection is ensured by carrying out a sufficiently long bombing process.

In contrast, in the pressure sensor 10A according to the present invention, which enables leak testing related to airtightness without requiring a bombing process, the effectiveness of the test cannot be guaranteed throughout the duration of the bombing process. Therefore, from the perspective of increasing the effectiveness of the leak test (ensuring effectiveness under any conditions), the inventors came up with the idea of sealing gas G at a certain or higher enclosed pressure P at a predetermined temperature in the reference vacuum chamber 20W, as described above, that is, setting a lower limit (lower enclosed pressure Pmin) for the enclosed pressure P.

Here, at the time of the above-mentioned inspection, the pressure inside the reference vacuum chamber 20W is set to be higher than the ambient pressure. Therefore, in the reference vacuum chamber 20W, which has low airtightness, an amount of gas G that is approximately proportional to the difference between the internal pressure of the reference vacuum chamber 20W and the ambient pressure leaks out from inside the reference vacuum chamber 20W to the outside. Therefore, if the lower limit of the pressure inside the reference vacuum chamber 20W, i.e., the lower limit sealed pressure Pmin of gas G, is set so that this leakage amount is greater than the lower limit of leakage detection of the inspection device, the effectiveness of the inspection can be reliably guaranteed.

In order to set the lower limit filled pressure Pmin, it is necessary to consider the amount of gas G that may leak from the reference vacuum chamber 20W at the time of inspection (hereinafter referred to as the "leakage amount _QT "). This leakage amount _QT can be calculated, for example, by the following formula ( ₁ ) when the filled pressure of gas G at the time of leakage inspection _{is PT} and the partial pressure of gas G contained in the gas remaining in the inspection device (around the reference vacuum chamber 20W) at the same time is PrT.

C _G in the above formula (1) (hereinafter referred to as "gas conductance C _G ") is a numerical value that represents the degree (leakability) of gas G leaking from the reference vacuum chamber 20W to the outside through the gap that may be formed due to processing accuracy, etc., and depends on the dimensions of the gap (length, pore diameter, etc.) and the physical properties of gas G (molecular weight, etc.), but can be calculated as follows.

That is, it is assumed that when pressure sensor 10A is used, the gas present in the surroundings (atmosphere in normal use) flows into reference vacuum chamber 20W by the above-mentioned allowable inflow amount Qα through the above-mentioned gap formed in casing 20. Here, allowable inflow amount Qα is defined as the inflow amount [Pam3/s] measured when the surrounding conditions surrounding pressure sensor 10A are in standard conditions (ambient pressure Pα=100 [kPa], ambient temperature Tα=298.15 [K]), and is calculated by the following formula ( ² ) including ambient pressure Pα and internal pressure _PW20α of reference vacuum chamber 20W in said conditions as parameters.

C in formula (2) (hereinafter referred to as "conductance C of air") is a value that represents the degree (ease of flow) of air flowing from the outside into the reference vacuum chamber 20W through the gap that may be formed due to processing accuracy, etc., and is a value that depends on the dimensions of the gap (length, hole diameter, etc.) and the physical properties of the air (gas composition, molecular weight, etc.). Considering that Pα>> _P20Wα , the conductance C of air can be approximately calculated as Qα/Pα.

Here, both the event of gas G leaking from the reference vacuum chamber 20W to the outside and the event of surrounding gas (e.g., air) flowing from the outside to the reference vacuum chamber 20W occur through the same path (i.e., the above gap). Therefore, the gas conductance C _G and the air conductance C air are related by a relational expression that includes the gas's physical properties (molecular weight, viscosity coefficient, etc.) and temperature as parameters. For example, if the flow of gas G in the leakage path (the above gap) and the flow of surrounding gas (e.g., air) in the inflow path (the above gap) are assumed to be molecular flows, the gas conductance C _G can be expressed by the following formula (3) using the air conductance C air.

ここで、Ｍ_Ｇは気体Ｇの分子量を表し、Ｍ_ａｉｒは周囲の気体（空気）の実効的な分子量（通常Ｍ_ａｉｒ＝２９）を表し、Ｔ_Ｔ〔Ｋ〕は検査時点の周囲温度を表す。

Here, M _G represents the molecular weight of gas G, M _air represents the effective molecular weight of the surrounding gas (air) (usually M _air =29), and T _T [K] represents the ambient temperature at the time of inspection.

As described above, the atmospheric conductance C can be approximately calculated as Qα/Pα. Therefore, the gas conductance _C can be approximately calculated from the following formula (4).

Therefore, the leakage amount _QT can be calculated from the following formula (5).

In order to reliably guarantee the effectiveness of the inspection, as described above, the leakage amount _QT of the gas G should be set to be equal to or greater than the lower leakage detection limit Qmin of the inspection device. Therefore, the charged pressure _PT of the gas G at the time of inspection should be set to satisfy the following formula (6).

Therefore, the lower limit pressure Pmin is calculated based on the following formula (7):

The state when the allowable inflow Qα is measured is not limited to the standard state of the ambient pressure Pα=100 [kPa] and the ambient temperature Tα=298.15 [K], but may be any state. The temperature when the lower limit filled pressure Pmin is set is not limited to the ambient temperature T _T at the time of inspection, but may be any state (the partial pressure Pr _T may also be a partial pressure at this any temperature). Therefore, the measurement state of the allowable inflow Qα and the temperature defining the lower limit filled pressure Pmin may be set so that the ambient temperature Tα and the ambient temperature T _T in the formula (8), which are distinguished for convenience of explanation, are the same value. Considering this fact and the fact that the ambient pressure Pα is approximately constant and the partial pressure Pr _T is extremely small under normal use, the lower limit filled pressure Pmin depends solely on the leak detection lower limit Qmin and the allowable inflow Qα.

As an example of the lower limit filled pressure Pmin, under standard conditions, i.e., ambient temperature Tα = 298.15 [K] and ambient pressure Pα = 100 [kPa], the lower limit filled pressure Pmin is 0.0371 [Pa] when the gas G is helium gas with a molecular weight M _G of 4, the molecular weight M _air of the surrounding gas (air) is 29, the allowable inflow rate Qα is 1E-9 [ ^Pam3 /s], the ambient temperature T _T during inspection is 298.15 [K], which is the same as the ambient temperature Tα, the leak detection lower limit Qmin is 1E-15 [ ^Pam3 /s], and the partial pressure Pr _T is 0 [Pa].

In the above discussion, the lower limit filled pressure Pmin was calculated and set assuming that the flow of the gas G in the gap is a molecular flow, but the lower limit filled pressure Pmin may be calculated and set assuming that the flow of the gas G in the gap is an intermediate flow or a laminar flow. For example, when an intermediate flow is assumed, the gas conductance C _G can be expressed by the following formula (8) using the atmospheric conductance C air. The lower limit filled pressure Pmin may be calculated and set based on the filled pressure P _T calculated by substituting this gas conductance C _G into the above formula (5).

ここで、ｄは漏れ孔の径を表し、は上流圧力と下流圧力の平均値を表し、Ｒは気体定数を表し、η_Ｇは気体Ｇの粘性係数を表し、η_ａｉｒは周囲の気体（空気）の粘性係数を表し、Ｗは通過確率を表す。

Here, d represents the diameter of the leak hole, represents the average value of the upstream and downstream pressures, R represents the gas constant, η _G represents the viscosity coefficient of gas G, η _air represents the viscosity coefficient of the surrounding gas (air), and W represents the passage probability.

[Upper limit of charging pressure]
When the temperature inside the reference vacuum chamber 20W changes while the gas G is sealed in the reference vacuum chamber 20W, the pressure inside the chamber also changes in proportion to the temperature change. If the pressure change caused by the temperature change is large, the measured pressure value is corrected using the temperature change (such correction is sometimes called "temperature correction"). Therefore, if the upper limit filled pressure Pmax of the gas G is set so that the pressure change is smaller than the limit pressure change at which temperature correction is possible, the effect of the filled gas G on the measurement accuracy can be substantially suppressed.
Here, if the limit pressure change for temperature correction is ΔPr, the maximum ambient temperature in the environment in which the pressure sensor 10A is expected to be used is T1, the internal pressure of the reference vacuum chamber 20W at this time is P1, the ambient temperature at the time when the gas G is enclosed is T, and the enclosed pressure at the same time is P, then the enclosed pressure P should be set so as to satisfy the condition P1 - P = (T1/T-1) x P ≦ ΔPr. Therefore, the upper limit enclosed pressure Pmax should be set to a value calculated from the following formula (9).

<Leakage inspection for airtightness of reference vacuum chamber>
Next, a leak test for checking the airtightness of the pressure sensor 10A according to the first embodiment of the present invention will be described with reference to Fig. 3. This leak test is carried out at a predetermined point in the manufacturing process of the pressure sensor 10A, specifically, after the pressure sensor 10A is assembled to such an extent that the reference vacuum chamber 20W is formed.

First, the pressure sensor 10A, which has been assembled until the reference vacuum chamber 20W is formed,
The sample is placed in a predetermined container (pellicle) (step S1). At this time, as described above, gas G is sealed in the reference vacuum chamber 20W so that a pressure equal to or higher than the lower limit enclosed pressure Pmin is maintained at a predetermined temperature.

Next, the container is evacuated using an exhaust device provided in the inspection device to create a vacuum inside the container, and the vacuum state is maintained for a predetermined period of time (step S2).

After a predetermined time has elapsed, the amount of gas G in the container is measured using a leak detector provided in the inspection device (step S3). Note that the specific method for measuring the amount of gas G follows a conventional method, and detailed explanation will be omitted.

The airtightness of the reference vacuum chamber 20W is judged based on the measured value (step S4). For example, if the measured value is equal to or less than an allowable value in terms of product quality, the product is judged to be a good product, and if the measured value is greater than the allowable value, the product is judged to be defective.
The specific method for determining the measured value will follow conventional methods, and detailed explanation will be omitted.

<Effects of the pressure sensor 10A>
According to the pressure sensor 10A having the above configuration, the bombardment process can be omitted in the leak test for the airtightness of the reference vacuum chamber 20W. This makes it possible to shorten the time required for manufacturing and improve production efficiency (pressure sensors can be manufactured with a short lead time).

In addition, by setting a lower limit for the pressure of the gas G, it is possible to ensure the effectiveness of tests that require high leak detection accuracy, and by setting an upper limit for the pressure of the gas G, it is possible to achieve the desirable effect of suppressing measurement errors in pressure changes of the fluid to be measured within an acceptable range, thereby avoiding a decrease in measurement accuracy. This effect makes it possible to simultaneously satisfy, at a high level, the difficult-to-achieve requirements of shortening the time required for leak testing of the reference vacuum chamber 20W and achieving high testing accuracy and measurement accuracy, making it possible to produce high-quality, high-measurement-accuracy pressure sensors with short lead times.

Second Embodiment
Next, a pressure sensor 10B according to a second embodiment of the present invention will be described with reference to Fig. 4 and Fig. 5. This pressure sensor 10B is characterized in that it is provided with a correction unit 70 for correcting the effect (error) on the measured pressure value caused by the gas G being sealed in the reference vacuum chamber 20W at a predetermined sealing pressure, and in that it is provided with a temperature sensor 80 for measuring the temperature T10B around the pressure sensor 10B in order to carry out the correction. Other than the configuration related to these characteristics, the pressure sensor 10B is the same as the pressure sensor 10A. The configuration related to these characteristics will be described below.

[Correction unit 70]
The correction unit 70 is a functional unit provided to correct errors in the measured pressure value that may arise due to the gas G being sealed inside the reference vacuum chamber 20W, i.e., when the internal temperature of the reference vacuum chamber 20W changes, the internal pressure of the reference vacuum chamber 20W in which gas G is sealed also changes proportionally to this, and is configured to include a part of the measurement unit 60, more specifically, a central processing unit (CPU) 62 and a memory 63 provided in the measurement unit 60, as shown in Figure 5.
The central processing unit (CPU) 62 constituting the correction unit 70 performs correction calculations based on a predetermined correction calculation program and various predetermined data, and calculates a corrected measured pressure value.
The memory 63 constituting the correction unit 70 stores the above-mentioned correction calculation program executed through the central processing unit (CPU) 62, and various data required to execute this correction calculation program, such as the voltage value V ₀ related to temperature from the pressure sensor element 11 and the voltage value V _T related to temperature from the temperature sensor 80, which are obtained during inspection (adjustment) performed before product shipment, and correction coefficients (correction coefficients a _ij , as well as correction coefficients a0, a1, b0, and b1, which will be described later) calculated using these values.
A specific example of the above correction calculation will be explained in detail in the "Correction Method" section below.

[Temperature sensor 80]
The temperature sensor 80 for measuring the temperature around the pressure sensor 10B is made of, for example, a platinum resistance thermometer, and is disposed in approximately the middle of the outer surface of the casing 20, as shown in Fig. 4. However, the position where the temperature sensor 80 is disposed is not limited to this position, and may be, for example, inside the reference vacuum chamber 20W.

<Correction method>
The above correction calculation (correction method) is executed to correct an error in the measured pressure value that may occur due to the gas G sealed inside the reference vacuum chamber 20W, that is, an error in the measured pressure value caused by a change in the pressure of the gas G that occurs with a change in the ambient temperature of the pressure sensor 10B and a change in the internal pressure of the reference vacuum chamber 20W. Specific examples of the correction calculation (correction method) include the "first correction method", "second correction method", and "third correction method" shown below.

[First correction method]
The first correction method is a method of performing a correction calculation using the following formula (10). This formula (10) corresponds to a calibration curve that specifies the relationship between the voltage value detected by the sensor and the measured pressure value, and includes a voltage value V _O related to pressure and a voltage value V _t related to temperature as measurement parameters, and also includes a correction coefficient a _ij (i=0 to m, j=0 to n) that is a constant. The correction coefficient a _ij is calculated in advance by substituting values related to pressure and temperature measured by applying a predetermined pressure to the pressure sensor 10B at a predetermined ambient temperature in an inspection process (adjustment process) before product shipment, specifically, the voltage value V _O related to pressure and the voltage value V _t related to temperature outputted from the pressure sensor element 11 and the temperature sensor 80 included in the pressure sensor 10B, into formula (10) (the time point at which the voltage values V _O and V _t related to pressure and temperature are measured in the inspection process is referred to as the "inspection measurement point"). These correction coefficients _aij are calculated by a central processing unit (CPU) 62 and then stored in a memory 63 as product characteristic values.
During actual use, the calculated correction coefficient _aij , the voltage value _V0 related to the pressure successively detected through the pressure sensor element 11, and the voltage value _Vt related to the temperature successively detected through the temperature sensor 80 are substituted into equation (10) to successively calculate a measured pressure value in which the error caused by the sealing of the gas G has been corrected.

The calculation of the correction coefficients _aij through the CPU 62 is performed, for example, as follows. That is, the value that defines the order of the formula (10), more specifically, the maximum value of the exponent i of the voltage value _V0 related to the pressure in the formula (10) and the maximum value of the exponent j of the voltage value _Vt related to the temperature are set to predetermined values, for example, taking into consideration the measurement accuracy (correction accuracy) and the processing capacity of the CPU 62. This determines the number of correction coefficients _aij to be calculated and the number of inspection measurement points required to obtain the correction coefficients _aij (usually the same value as the number of correction coefficients _aij ).
For example, in a case where the correction calculation is performed using equation (10) in which the maximum value of the index i of the voltage value _V0 related to pressure and the maximum value of the index j of the voltage value _Vt related to temperature are both set to 1, that is, quadratic equation (10), four correction coefficients _aij (i=0 to 1, j=0 to 1) are calculated. In order to calculate these four correction coefficients _aij (i=0 to 1, j=0 to 1), at least four inspection measurement points are set, and an arbitrary value of applied pressure _Pin u (u=1 to 4) is applied to the pressure sensor 10B using a predetermined device under each ambient temperature Tu (u=1 to 4). At this time, the voltage value _V0u (u=1 to 4) related to pressure is measured through the pressure sensor element 11, and the voltage value _Vtu (u=1 to 4) related to temperature is measured through the temperature sensor 80. These measured values are transmitted to the arithmetic processing unit (CPU) 62 through the analog detection circuit AC and the A/D converter AD. The central processing unit (CPU) 62 calculates the correction coefficient a ij (i = 0 to 1, j = 0 to 1) by substituting the applied pressure _{P in} u (u = 1 to 4), the voltage value V ₀ u (u = 1 to 4) related to the pressure, and the voltage value V _t u (u = 1 to 4) related to the temperature into equation (10).

Table 1 below lists the measured values of the voltage values V 0 u (u = 1 to 4) related to pressure and the voltage values V _t u (u = 1 to 4) related to temperature when the ambient temperatures Tu (u = 1 to 4) at the four inspection measurement points are T1 = 23 [°C], T2 = 23 [°C], _T3 = 200 [°C] and T4 = 200 [°C], and the applied pressures P _in u (u = 1 to 4) applied at each inspection measurement point are P _in 1 = ₀ [Pa], P _in 2 = 100 [Pa], P in 3 = ₀ [Pa] and P in 4 = 100 [Pa]. According to Table 1, the voltage values V ₀ u (u = 1 to 4) and voltage values V _t u (u = 1 to 4) at each inspection measurement point are (V ₀ 1, V _t 1) = (1.1 [v], 2.1 [v]), (V ₀ 2, V _t 2) = (4.3 [v], 2.1 [v]), (V ₀ 3, V _t 3) = (1.2 [v], 3.1 [v]), (V ₀ 4, V _t 4) = (4.2 [v], 3.1 [v]).

By substituting the values of the applied pressure P _in u (u = 1 to 4) and the data (V ₀ u, V _t u) (u = 1 to 4) at the above four inspection measurement points, i.e., (P _in 1, V ₀ 1, V _t 1) = (0 [Pa], 1.1 [V], 2.1 [V]), (P _in 2, V ₀ 2, V _t 2) = (100 [Pa], 4.3 [V], 2.1 [V]), (P _in 3, V ₀ 3, V _t 3) = (0 [Pa], 1.2 [V], 3.1 [V]), (P _in 4, V ₀ 4, V _t 4) = (100 [Pa], 4.2 [V], 3.1 [V]) into equation (10), four equations are obtained. The central processing unit (CPU) 62 constituting the correction unit 70 uses these four equations to determine the correction coefficients a ₀₀ , a ₁₀ , a ₀₁ , and a _11. In this example, a ₀₀ =-22.5625, a ₁₀ =26.8750, a ₀₁ =-5.62500, and a ₁₁ =2.08333.

In order to perform a correction with higher accuracy (high-order correction), that is, to set at least one of the maximum value of the index i of the voltage value _V0 related to the pressure and the maximum value of the index j of the voltage value _Vt related to the temperature in the formula (10) to 2 or more, the number of measurement points during the inspection may be appropriately increased. For example, in order to perform correction using the formula (10) in which the maximum value of the index i is set to 2 and the maximum value of the index j is set to 1, that is, the third-order formula (10), six inspection measurement points may be set. In addition, with respect to the measurement points during the inspection, the temperature and pressure may be changed in a plurality of sections, and the above correction coefficient _aij may be obtained for each section (temperature correction may be performed using a table method in which each section has a correction coefficient _aij ).

[Second correction method]
The second correction method is a method of performing a correction calculation using the following formula (11). Like formula (10), this formula (11) corresponds to a calibration curve that specifies the relationship between the voltage value detected by the sensor and the measured pressure value, and includes the voltage value V _O related to pressure and the voltage value V _t related to temperature as measurement parameters, and also includes correction coefficients a0, a1, b0, and b1, which are constants. The correction coefficients a0, a1, b0, and b1 are calculated in advance by substituting into formula (11) the values related to pressure and temperature obtained by applying a predetermined pressure to the pressure sensor 10B at a predetermined ambient temperature in an inspection process (adjustment process) before product shipment, specifically, the voltage value V _O related to pressure and the voltage value V _t related to temperature outputted from the pressure sensor element 11 and the temperature sensor 80 included in the pressure sensor 10B. This calculation process is executed through the central processing unit (CPU) 62.

Among the above correction coefficients, the correction coefficients a0 and a1 are values that depend on pressure and are calculated as follows. That is, the pressure (applied pressure Pin) applied to the pressure sensor 10B is changed with the temperature kept constant (fixed to the reference temperature), and the output of the pressure sensor 10B, more specifically, the voltage value _V0 related to the pressure output from the pressure sensor element 11 included in the pressure sensor 10B, is acquired at a predetermined sampling rate through the analog detection circuit AC and the A/D converter AD. Here, the relationship between the applied pressure _Pin and the voltage value _V0 is defined as, for example, a linear function _Pin = a0 + a1 × _V0 , and the correction coefficients a0 and a1 are calculated from the data α related to the applied pressure _Pin and the voltage value _V0 .

Among the above correction coefficients, the correction coefficients b0 and b1 are values that depend on temperature and are calculated as follows. That is, the temperature around the pressure sensor 10B is changed in a state where no pressure is applied, and the values output from the pressure sensor 10B, more specifically, the voltage value _V0 related to the pressure output from the pressure sensor element 11 included in the pressure sensor 10B and the voltage value _Vt related to the temperature output from the temperature sensor 80 are acquired at a predetermined sampling rate through the analog detection circuit AC and the A/D converter AD. The data β related to the obtained voltage value _V0 and voltage value _Vt are added to the above data α, and the values of these data (data α and data β) are substituted into the formula (11) to calculate the correction coefficients b0 and b1.

The correction coefficients a0, a1, b0, and b1 obtained in the above process are stored in memory 63 as product characteristic values.

During actual use, the voltage value _V0 related to pressure sequentially output from the pressure sensor element 11 of the pressure sensor 10B, the voltage value _Vt related to temperature sequentially output from the temperature sensor 80, and the correction coefficients a0, a1, b0, and b1 stored in the memory 63 are substituted into the above equation (11) to sequentially calculate the corrected measured pressure value (P in the above equation (11)).
This second correction method is useful when the sensitivity of the pressure sensor 10B (sensitivity of the pressure sensor element 11) to temperature changes is small.

In the above example, the formula (11) defines the corrected measured pressure value as a linear function of the voltage value _V0 related to pressure output from the pressure sensor element 11 and the voltage value _Vt related to temperature output from the temperature sensor 80, but this may be defined as a higher-order function. Also, for the measurement point during the inspection, the temperature and pressure may be changed in a plurality of sections, and the correction coefficient may be obtained for each section (temperature correction may be performed using a table method having a correction coefficient for each section).

[Third correction method]
The third correction method is a method of calculating a corrected measured pressure value Py for a measured pressure value Px (measured pressure value Px before correction) calculated by a central processing unit (CPU) 62 constituting the measurement unit 60, using the following formula (12) including as parameters the internal pressure P _O (charged pressure P _O of gas G) and internal temperature T _O (ambient temperature T _O ) of the reference vacuum chamber 20W at the time when the gas G is sealed in the reference vacuum chamber 20W, and the ambient temperature Tx at the time of measurement. Here, data stored in advance in a memory 63 constituting the correction unit 70 (data stored during the operation of charging gas G) is used for the internal pressure P _O (charged pressure P _O of gas G) and internal temperature T _O (ambient temperature T _O ) of the reference vacuum chamber 20W at the time when the fluid G is charged. Furthermore, for the measured pressure value Px before correction and the temperature Tx of the fluid G at the time when this measured pressure value Px is measured (the internal temperature Tx of the reference vacuum chamber 20W), values calculated sequentially by the central processing unit (CPU) 62 based on the voltage value _V0 and the voltage value _Vt detected through the pressure sensor element 11 and the temperature sensor 80 are used.

<Effects of the pressure sensor 10B>
The pressure sensor 10B having the above configuration can correct an error in the measured pressure value that occurs when the gas G is sealed inside the reference pressure chamber 20W. Therefore, it is possible to provide a pressure sensor that combines the above-mentioned effects achieved by the pressure sensor 10A according to the first embodiment of the present invention with higher measurement accuracy.

The preferred embodiments of the present invention have been described above through the pressure sensor 10A according to the first embodiment and the pressure sensor 10B according to the second embodiment, but the present invention is not limited to these embodiments and various modifications are possible without departing from the gist of the present invention. Furthermore, even if a configuration is not directly described in the specification and drawings, it is within the scope of the technical idea of the present invention as long as it achieves the functions and effects of the present invention. Furthermore, the embodiments described above and shown in each figure can be combined with each other as long as there is no contradiction in their purpose and configuration, etc.

For example, from the viewpoint of extending the product life, a leak test related to the airtightness of the reference vacuum chamber 20W may be configured to be performed on a pressure sensor disposed in a production facility or the like through regular maintenance, etc. In this case, the pressure sensors 10A and 10B may be provided with a mechanism that allows them to be easily attached and detached from the production facility, etc.
In addition, it is assumed that the internal pressure of the reference vacuum chamber 20W will differ between when the product is shipped and when regular maintenance is performed due to the inflow of surrounding gas (atmosphere, etc.) during use. For this reason, the correction unit 70 may be configured so that the calculation of the correction coefficient used in the above correction calculation can be performed every time regular maintenance is performed.

10A...pressure sensor, 10B...pressure sensor, 11...pressure sensor element, 12...diaphragm, 20...casing, 20W...reference vacuum chamber, 21...lower housing, 22...upper housing, 22b...hole, 23...cover, 23a...electrode lead insertion hole, 24...getter, 25...sealing element, 30...base plate 30, 40...support diaphragm, 50...electrode lead portion, 57...hermetic seal, 60...measuring portion, 61...interface (I/O), 62...processing unit (CPU), 63...memory, 70...correction portion, 80...temperature sensor, G...gas.

Claims (9)

A diaphragm having a pressure receiving surface formed on one surface thereof;
a casing member forming a sealed space together with another surface of the diaphragm;
a measuring unit that measures the pressure in the space facing the pressure-receiving surface from a deformation of the diaphragm caused by a difference between the pressure applied to the pressure-receiving surface and the internal pressure of the sealed space,
the diaphragm and the casing member are configured to seal in the sealed space a gas that is to be detected in an inspection of the airtightness of the sealed space ,
A pressure sensor in which the filling pressure of the gas sealed in the sealed space having a predetermined volume is set to a value greater than a lower limit value calculated using at least the lower detection limit value of a leak detection device used in the inspection and the allowable inflow amount of ambient gas allowed to flow into the sealed space, and is set to a value less than an upper limit value calculated using at least the maximum ambient temperature in the environment in which the pressure sensor is expected to be used and the minimum value of pressure change that depends on temperature change of the gas and can be corrected using the value of the temperature change . A diaphragm having a pressure receiving surface formed on one surface thereof;
a casing member forming a sealed space together with another surface of the diaphragm;
The pressure difference between the pressure applied to the pressure receiving surface and the internal pressure of the sealed space causes the separation
a measuring unit that measures the pressure in a space facing the pressure-receiving surface based on the deformation of the membrane,
The diaphragm and the casing member are detection objects in the inspection of the airtightness of the sealed space.
The gas is sealed in the sealed space,
The pressure sensor sets the pressure of the gas sealed in the sealed space having a predetermined volume to a value greater than at least a lower limit (Pmin) calculated from the lower detection limit (Qmin) of a leak detection device used in the inspection, the allowable inflow rate (Qα) of the ambient gas allowed to flow into the sealed space, the ambient pressure (Pα) at the time of measuring the allowable inflow rate, the ambient temperature (Tα) at the time of measuring the allowable inflow rate, the molecular weight (MG) of the gas _, the molecular weight (Mair) of the ambient gas _, the ambient temperature ( _TT ) at the time of the inspection , and the partial pressure ( _PrT ) of the gas in the ambient pressure at the time of the inspection . 3. The pressure sensor according to claim 2,
The filling pressure is

Pmin: lower limit of the enclosed pressure, Qmin: the lower detection limit, Qα: the allowable inflow rate, Pα: ambient pressure at the time of measuring the allowable inflow rate, Tα: ambient temperature at the time of measuring the allowable inflow rate, M _G : molecular weight of the gas, M _air : molecular weight of the ambient gas, T _T : ambient temperature at the time of inspection, Pr _T : pressure sensor set to a value greater than the lower limit calculated from the partial pressure of the gas in the ambient pressure at the time of inspection. The pressure sensor according to any one of claims 1 to 3,
A temperature sensor for measuring a temperature of the enclosed space;
a correction unit that corrects an error in the pressure measurement value caused by a change in ambient temperature using a value detected by the temperature sensor. 5. The pressure sensor according to claim 4,
The correction unit is a pressure sensor that performs the correction using a value detected by the temperature sensor and an enclosed pressure and temperature when the gas is enclosed in the sealed space. The pressure sensor according to any one of claims 1 to 5,
The gas is a pressure sensor made of a substance that is not occluded by the wall surface that forms the sealed space. The pressure sensor according to any one of claims 1 to 6,
The gas pressure sensor comprises a material that is not adsorbed by an adsorbent material disposed in the sealed space for adsorbing ambient gas. The pressure sensor according to any one of claims 1 to 7,
The gas is a pressure sensor made of a substance other than a substance contained in air at a ratio of 1% by volume or more. A method for inspecting the airtightness of the sealed space provided in the pressure sensor according to any one of claims 1 to 8, comprising the steps of:
A first step of placing a pressure sensor inside a predetermined container;
a second step of creating a vacuum inside the container;
a third step of measuring the rate at which the gas leaves the container using a leak detection device;
a fourth step of determining airtightness of the sealed space based on the amount of gas flowing out;
An inspection method consisting of:

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