Pressure sensor and pressure sensor inspection method

Abstract

To provide a pressure sensor capable of performing leak inspection related to airtightness of a reference vacuum chamber in a short time, and a method for inspecting the same.MEANS FOR SOLVING THE PROBLEM: A pressure sensor 10A includes: a diaphragm (a diaphragm 12) having a pressure receiving surface formed on one surface; a casing member (a casing 20) for forming a closed space (a reference vacuum chamber 20W) together with the other surface of the diaphragm; and a measuring unit 60 for measuring pressure in a space (an introducing unit 20V) opposed to the pressure receiving surface from deformation of the diaphragm caused by difference between pressure applied to the pressure receiving surface and internal pressure of the closed space. Gas G to be detected is sealed in the closed space in an inspection of airtightness of the closed space.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pressure sensor, particularly to a pressure sensor used as a diaphragm vacuum gauge and an absolute pressure gauge, and to a method of testing this pressure sensor. [Background technology]

[0002] Pressure sensors using a thin-film diaphragm are widely used as sensors for measuring the pressure of a fluid or the pressure in a space through which a fluid flows in and out. This pressure sensor is configured to capture the pressure of the fluid to be measured (hereinafter referred to as the "measured fluid") or the pressure in a specified space in the form of mechanical displacement through the diaphragm, and detect this mechanical displacement as an electrical signal, for example a voltage signal, to measure the pressure of the measured fluid or the vacuum state of the space.

[0003] As a method for detecting mechanical displacement as an electrical signal, for example, a capacitance type and a semiconductor type are widely known. 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.

[0004] For example, Patent Document 1 describes a capacitance-type pressure sensor (1). This pressure sensor (1) includes a diaphragm (32) disposed between two spaces that are isolated from each other and do not communicate with each other, specifically, a pressure introduction part (10A) that communicates with a space through which a 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 capacitance between two electrodes (a pressure-sensing side fixed electrode 110 and a reference side fixed electrode 120).

[0005] 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 constantly 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 airtightness is maintained by inserting a sealing element 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. To prepare 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 constantly maintain a high vacuum state when the amount of inflowing gas is large. Therefore, in the manufacturing process of pressure sensors using diaphragms, regardless of whether or not they have a getter, a process is provided for performing a leak test (hereinafter, simply referred to as a "leak test" or "test") on 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, -7 Pam 3 The presence or absence of minute leaks of less than / s is checked.

[0006] In conventional leak inspections, leaks caused by poor connections such as poor welding are inspected using, for example, methods defined by the Japanese Industrial Standards (JIS), more specifically, the vacuum spray method (spray method) defined in Appendix 1 of JIS Z2331 and the vacuum hood method (vacuum hood method) defined in Appendix 2. In contrast, leaks at the final vacuum sealing point are inspected based on the immersion method (bombing method) defined 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).

[0007] In the immersion method (bombing method) of the above leak tests, the first step is to fill the test specimen (reference vacuum chamber equipped with a pressure sensor) with helium gas using a helium gas bombing device shown in Fig. 6. More specifically, the test specimen is placed in a bombing tank in which pressurized helium gas is sealed, and then left under pressure for a predetermined period of time to fill the test specimen with helium gas.

[0008] 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 specimen.

[0009] If there is a gap at the final vacuum sealing location, helium gas will enter the test piece in the first step, and the entered helium gas 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 a leak value required for the test piece, for example, a preset standard air equivalent leak amount, to distinguish between a good product and a defective product. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2008-107214 A [Non-patent literature]

[0011] [Non-Patent Document 1] Japanese Industrial Standards Z2331 Appendix 7 Summary of the Invention [Problem to be solved by the invention]

[0012] As semiconductors become more dense, it is essential to control environmental parameters in the manufacturing process with high precision, and the demand for high precision is also increasing year by year for pressure sensors (vacuum gauges) used in the manufacturing process. To meet this demand, leak testing of the reference vacuum chamber is more important than ever. However, in leak testing of the reference vacuum chamber, especially in 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 that it is difficult to produce pressure sensors that meet the above demands with a short lead time.

[0013] The present invention was created in consideration of the above-mentioned problems, and its object is to provide a pressure sensor that can perform leak testing of a reference vacuum chamber in a short period of time, and to provide an inspection method that can use the pressure sensor to perform leak testing related to the airtightness of the reference vacuum chamber in a short period of time. [Means for solving the problem]

[0014] The pressure sensor (10A, 10B) of 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) which forms a sealed space (reference vacuum chamber 20W) together with the other side of the diaphragm, and a measurement unit (60) which measures the pressure in a space (introduction portion 20V) facing the pressure-receiving surface from 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 a gas (G) to be detected in an inspection of the airtightness of the sealed space in the sealed space.

[0015] In the pressure sensor, the filling pressure of the gas sealed in the sealed space having a predetermined volume may be 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.

[0016] In the pressure sensor, the filled pressure is expressed by the relation Pmin=Qmin / Qα×Pα×(M G ×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 where T is the ambient temperature at the time of the inspection, and Prt is the partial pressure of the gas in the ambient pressure at the time of the inspection.

[0017] Furthermore, the pressure sensor may be further configured to include a temperature sensor (80) that measures the temperature of the sealed space, and a correction unit (70) that corrects an error in the measurement value related to the pressure caused by a change in the ambient temperature, using the value detected by the temperature sensor.

[0018] In the pressure sensor, the correction unit is configured to correct the value detected by the temperature sensor and the filled pressure (P O ) and temperature (T O ) may be used to perform the correction.

[0019] Furthermore, in the pressure sensor, the gas may be made of a substance that is not occluded by a wall surface that defines the sealed space.

[0020] In the pressure sensor, the gas may be made of a substance that is not adsorbed by an adsorbent substance (getter 24) disposed in the sealed space for adsorbing the ambient gas.

[0021] Furthermore, in the pressure sensor, the gas may be made of a substance other than the substance contained in air at a rate of 1% by volume or more.

[0022] In addition, in order to solve the above-mentioned problems, the method for inspecting the airtightness of the sealed space provided with the pressure sensor of the present invention is characterized by comprising a first step (S1) of placing the pressure sensor inside a specified container, a second step (S2) of evacuating the inside of 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.

[0023] In the above description, as an example, the names and reference characters of parts in the drawings that correspond to components of the invention are given in parentheses. Effect of the Invention

[0024] According to the present invention, it is possible to provide a pressure sensor that can perform a leak test related to the airtightness of a reference vacuum chamber in a short time. Also, by using the pressure sensor, it is possible to provide an inspection method that can perform a leak test related to the airtightness in a short time. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a cross-sectional view of a pressure sensor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a functional block diagram of a pressure sensor according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a flow diagram illustrating the method for inspecting a pressure sensor according to the embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of a pressure sensor according to another embodiment of the present invention. [Diagram 5] FIG. 5 is a functional block diagram of a pressure sensor according to another embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram of a helium gas bombing device used for leak testing performed in a conventional pressure sensor manufacturing process. [Figure 7] 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] A first and second preferred embodiment 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 match the 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 a state of 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 and leakage are in accordance with 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 and leakage being Pam. 3 / s.

[0027] 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.

[0028] 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 within 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 measurement portion 60 that measures pressure based on an electrical signal (e.g., a voltage signal) output from the pressure sensor element 11.

[0029] [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 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.

[0030] When the fluid to be measured that has flowed into the introduction section 20V comes into contact with one surface (pressure receiving surface) of the diaphragm 12, the diaphragm 12 deforms, for example so that the center portion becomes convex toward the upper side 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 section 60 in the form of a voltage signal SV, as shown in FIG. 2.

[0031] [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 an 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 opposing portions are joined together, for example, by welding.

[0032] The lower housing 21 is a cylindrical portion formed of a large diameter cylindrical portion 21a and a small diameter cylindrical portion 21b, and these two portions are connected so as to be coaxial. The upper opening end of the large diameter cylindrical portion 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 portion 21b defines an introduction portion 20V into which the fluid to be measured flows.

[0033] 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.

[0034] 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 being excessively displaced due to a sudden increase in pressure of the fluid to be measured.

[0035] Furthermore, the upper housing 22 has a hole 22b opening, for example, in its side wall. This hole 22b is used when exhausting gas (e.g., the atmosphere) remaining inside the reference vacuum chamber 20W during the manufacturing process and when sealing 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 outside pressure sensor 10A, that is, in a position that can connect the outside of pressure sensor 10A to reference vacuum chamber 20W, and therefore may open not in the side wall of upper housing 22, but, for example, in cover 23 that defines reference vacuum chamber 20W. Furthermore, in cases where the above-mentioned exhaust work and / or filling work 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 filling work of the gas G can be performed without the hole 22b and the sealing element 25 by joining the mating surfaces of the casing members (upper housing 22 and cover 23) that define the reference vacuum chamber 20W by welding or the like after filling the reference vacuum chamber 20W with a specified amount of the gas G. 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.

[0036] 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 a leak detection device during a leak test for 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.

[0037] 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 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 rate of 1% or more by volume, 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 substance that is not occluded by the members constituting the walls 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 later. For example, since helium gas (He2) is occluded by glass, it is desirable to use a substance other than helium gas for the gas G when the hermetic seal 57 is made of glass.

[0038] Moreover, in order to reliably guarantee the effectiveness of the test, it is preferable that the gas G is sealed in the reference vacuum chamber 20W at a certain level of sealed pressure or more at a predetermined temperature. The lower limit of this sealed pressure will be described in detail in the section "Regarding the sealed pressure of gas G" below. Also, in order to reduce measurement errors, an upper limit may be set for the sealed pressure. The upper limit of this sealed pressure will also be described in detail in the section "Regarding the sealed pressure of gas G".

[0039] The cover 23 is made of a substantially 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).

[0040] Thus, the casing 20 is formed by stacking the lower housing 21, the upper housing 22 and the cover 23 along the axis CL, and has an outer shape in which two cylinders of different diameters are connected together and share the axis CL.

[0041] [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, which will be described later.

[0042] 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. The first base plate 31 and the second base plate 32 are both located at positions spaced apart 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 thicker than the thickness of the support diaphragm 40, thereby preventing the base plate 30 from warping due to thermal stress caused by the difference between the thermal expansion coefficients of the base plate 31 and the support diaphragm 40.

[0043] 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 for communicating the space C2, which faces the pressure receiving surface of the diaphragm 12 of the pressure sensor element 11, with the introduction part 20V into which the measured fluid flows. The pressure sensor element 11 is bonded to the lower surface of the second base plate 32 via an aluminum oxide-based bonding material so that the introduction hole 32a and the space C2 communicate with each other. The first base plate 31 and the pressure sensor element 11 are bonded to each other by a well-known method.

[0044] [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 shape of the lower opening end of the upper housing 22 and the upper opening end of the lower housing 21. The support diaphragm 40 has the first base plate 31 joined to its upper surface and the second base plate 32 joined to its lower surface, and its outer peripheral portion (peripheral edge portion) 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 section 20V into which the measured fluid flows.

[0045] [Electrode lead part 50] The electrode lead portion 50 includes an electrode lead pin 51 and a metallic shield 52. The electrode lead pin 51 is embedded at its center in the metallic 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. The other end of the electrode lead pin 51 is connected to conductive contact springs 55 and 56.

[0046] The contact springs 55, 56 are elastic elements that are provided to absorb any displacement of the pressure sensor element 11 caused by a sudden increase in pressure resulting from the sudden inflow of the fluid to be measured from the inlet portion 20V (more specifically, when the pressure increase causes the base plate 30 bridged to the casing 20 via the support diaphragm 40 to displace, thereby displacing the pressure sensor element 11 supported thereby), thereby preventing this displacement from affecting the measurement accuracy of the pressure sensor element 11.

[0047] [Measurement section 60] As shown in FIG. 2, the measurement unit 60 is a functional unit that receives a voltage signal SV output from the pressure sensor element 11 and measures the value of the pressure inside the introduction section 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.

[0048] 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.

[0049] <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 converting 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.

[0050] [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 joining due to poor welding or the like, and a gap may also be formed due to insufficient sealing. Specifically, a gap 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), and on the mating surface between the electrode lead insertion hole 23a that opens in the cover 23 and the electrode lead portion 50 embedded in this hole via the 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 below a specified value (hereinafter, this specified value is 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).

[0051] Here, whether the reference vacuum chamber 20W is maintained in a high vacuum state or not is judged through a leak inspection related to the airtightness of the reference vacuum chamber, as described above. As described above, the conventional inspection is performed, for example, by the immersion method (bombing method) consisting of a bombing process and a leak detection process. 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 substantially 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 judges whether the airtightness is good or bad by, for example, comparing the amount of leak with a predetermined allowable value. 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 the bombing process for a sufficiently long time.

[0052] 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 time of the bombing process. Therefore, from the viewpoint of increasing the effectiveness of the leak test (ensuring effectiveness under any conditions), the inventors have come up with the idea of ​​sealing the gas G with a filled pressure P equal to or greater than a certain value at a predetermined temperature in the reference vacuum chamber 20W, as described above, that is, of setting a lower limit (lower limit filled pressure Pmin) for the filled pressure P.

[0053] 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 with 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 the inside of 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 filled pressure Pmin of the gas G, is set so that the amount of this leakage is higher than the lower limit of leakage detection of the inspection device, the effectiveness of the inspection can be reliably guaranteed.

[0054] In order to set the lower limit of the filled pressure Pmin, the amount of gas G that can leak from the reference vacuum chamber 20W at the time of inspection (hereinafter referred to as the leakage amount Q T It is necessary to consider the leakage amount Q T is, for example, the pressure P of the gas G at the time of leak testing. T At the same time, the partial pressure of the gas G contained in the gas remaining in the inspection device (around the reference vacuum chamber 20W) is Pr T In this case, it can be calculated by the following formula (1).

[0055]

number

[0056] C in the above formula (1) G (Hereinafter, the gas conductance C G ") is a value that indicates the degree (leakability) of leakage of gas G 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, hole diameter, etc.) and the physical properties of gas G (molecular weight, etc.), but can be calculated as follows.

[0057] That is, when the pressure sensor 10A is in use, it is assumed that the gas present around it (atmosphere in normal use) flows into the reference vacuum chamber 20W by the allowable inflow amount Qα through the gap formed in the casing 20. Here, the allowable inflow amount Qα is, for example, the inflow amount [Pam 3 / s], and the ambient pressure Pα and the internal pressure P of the reference vacuum chamber 20W in that state W20 It is calculated by the following formula (2) which includes α as a parameter.

[0058]

number

[0059] Cair in formula (2) (hereinafter referred to as "conductance of air Cair") 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.). The conductance of air Cair is expressed as Pα>>P 20W Considering that α, it can be approximately calculated as Qα / Pα.

[0060] Here, the phenomenon in which the gas G leaks from the reference vacuum chamber 20W to the outside and the phenomenon in which the surrounding gas (e.g., the atmosphere) flows from the outside to the reference vacuum chamber 20W both occur through the same path (i.e., the above-mentioned gap). G and the atmospheric conductance Cair are related by a relational expression that includes the gas's physical properties (such as molecular weight and viscosity coefficient) and temperature as parameters. For example, if the flow of gas G in the leak path (the above gap) and the flow of the surrounding gas (e.g., the atmosphere) in the inflow path (the above gap) are assumed to be molecular flows, the gas conductance C G can be expressed by the following equation (3) using the atmospheric conductance Cair.

[0061]

number

[0062] As mentioned above, the atmospheric conductance Cair can be approximately calculated as Qα / Pα. Therefore, the gas conductance C G can be approximately calculated from the following formula (4).

[0063]

number

[0064] Therefore, the leakage amount Q T can be calculated from the following formula (5).

[0065]

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[0066] Here, in order to reliably guarantee the effectiveness of the inspection, as described above, the leakage amount Q of the gas G T Therefore, the pressure P of the gas G at the time of inspection should be set to be equal to or greater than the lower limit Qmin of leak detection by the inspection device. T may be set so as to satisfy the following formula (6).

[0067]

number

[0068] Therefore, the lower limit charged pressure Pmin is calculated based on the following formula (7).

[0069]

number

[0070] The condition when the allowable inflow amount Qα is measured is not limited to the standard condition of the ambient pressure Pα=100 [kPa] and the ambient temperature Tα=298.15 [K], but may be any condition. In addition, the temperature when the lower limit filled pressure Pmin is set is the ambient temperature T T is not limited to and may be any value (partial pressure Pr T (The partial pressure at any temperature may be the partial pressure at any temperature.) Therefore, the ambient temperature Tα and the ambient temperature T T The measurement state of the allowable inflow Qα and the temperature that defines the lower limit of the enclosed pressure Pmin may be set so that the values ​​of the allowable inflow Qα and the lower limit of the enclosed pressure Pmin are the same. T Considering that is extremely small, the lower limit charged pressure Pmin depends solely on the leak detection lower limit value Qmin and the allowable inflow amount Qα.

[0071] As an example of the lower limit of the enclosed pressure Pmin, the lower limit of the enclosed pressure Pmin at the standard condition, i.e., the ambient temperature Tα = 298.15 [K] and the ambient pressure Pα = 100 [kPa], is calculated as follows: G is 4, and the molecular weight of the surrounding gas (air) is M air is 29, and the allowable inflow Qα is 1E-9 [Pam 3 / s], ambient temperature during inspection T T is 298.15 [K], which is the same as the ambient temperature Tα, and the leak detection lower limit Qmin is 1E-15 [Pam 3 / s], partial pressure Pr T If is set to 0 [Pa], it becomes 0.0371 [Pa].

[0072] In the above discussion, the flow of the gas G in the gap is assumed to be a molecular flow and the lower limit filling pressure Pmin is calculated and set, but the flow of the gas G in the gap may be assumed to be an intermediate flow or a laminar flow and the lower limit filling pressure Pmin may be calculated and set. For example, when an intermediate flow is assumed, the gas conductance C G can be expressed by the following equation (8) using the atmospheric conductance Cair. G The enclosed pressure P is calculated by substituting T The lower limit charged pressure Pmin may be calculated and set based on the above.

[0073]

number

[0074] [Upper limit of charging pressure] When the temperature inside the reference vacuum chamber 20W changes while 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 this 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 of pressure change for which temperature correction is possible, the effect of the inclusion of gas G on the measurement accuracy can be substantially suppressed. Here, if the pressure change at the limit of temperature compensation is ΔPr, the maximum ambient temperature in the environment in which pressure sensor 10A is expected to be used is T1, the internal pressure of reference vacuum chamber 20W at this time is P1, the ambient temperature at the time gas G is charged is T, and the charged pressure at the same time is P, then the charged pressure P should be set to satisfy the condition P1 - P = (T1 / T-1) × P ≦ ΔPr. Therefore, the upper limit charged pressure Pmax should be set to a value calculated from the following formula (9).

[0075]

number

[0076] <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 performed 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.

[0077] First, the pressure sensor 10A, which is 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.

[0078] Next, the inside of the container is evacuated using an exhaust device provided in the inspection device to create a vacuum, and the vacuum state is maintained for a predetermined time (step S2).

[0079] 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 description thereof will be omitted.

[0080] 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 good, 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.

[0081] <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 the production efficiency (the pressure sensor can be manufactured with a short lead time).

[0082] Furthermore, by setting a lower limit for the charged pressure of 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 charged pressure of gas G, it is possible to suppress measurement errors in pressure changes of the fluid to be measured within an acceptable range, thereby providing the desirable effect of 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, thereby making it possible to produce high-quality, high-measurement-accuracy pressure sensors with short lead times.

[0083] 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 sealing the gas G 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 perform 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.

[0084] [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 arithmetic processing unit (CPU) 62, and various data necessary for executing this correction calculation program, such as a voltage value V0 related to temperature from the pressure sensor element 11 acquired during an inspection (adjustment) performed before product shipment, and a voltage value V1 related to temperature from the temperature sensor 80. T , and a correction coefficient calculated using these values ​​(correction coefficient a ij , as well as the correction coefficients a0, a1, b0, b1). A specific example of the above correction calculation will be explained in detail in the "Correction Method" section below.

[0085] [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.

[0086] <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 changes in the pressure of the gas G that occur with changes in the ambient temperature of the pressure sensor 10B and 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.

[0087] [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 defines the relationship between the voltage value detected by the sensor and the measured pressure value, and the voltage value V related to the pressure O and the voltage value V t as a measurement parameter, and a constant correction coefficient a ij (i=0~m, j=0~n) Correction coefficient a ij are 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, voltage values ​​V related to pressure outputted from the pressure sensor element 11 and the temperature sensor 80 of the pressure sensor 10B. O and the voltage value V t is calculated in advance by substituting into equation (10) (the voltage value V related to pressure and temperature in the above inspection process) O , V t The time when the correction coefficient a is measured is called the "inspection measurement point." ij is calculated by a central processing unit (CPU) 62 and then stored in a memory 63 as a product characteristic value. During actual use, the calculated correction factor a ij and a voltage value V related to the pressure successively detected through the pressure sensor element 11. O and a voltage value V related to the temperature successively detected by the temperature sensor 80. t By substituting into equation (10), the measured pressure value in which the error caused by the sealed gas G is corrected is calculated successively.

[0088]

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[0089] Correction coefficient a through a central processing unit (CPU) 62 ij The calculation of is performed, for example, as follows. That is, the value that determines the order of the equation (10), more specifically, the maximum value of the index i of the voltage value V0 related to the pressure in the equation (10) and the voltage value V related to the temperature are calculated as follows. t The maximum value of the exponent j is set to a predetermined value, for example, taking into consideration the measurement accuracy (correction accuracy) and the processing capacity of the central processing unit (CPU) 62. ij and the correction factor a ij The number of inspection measurement points required to obtain ij (equal to the number of For example, the maximum value of the index i of the voltage value V0 related to pressure and the voltage value V related to temperature t In the case where the correction calculation is performed using the equation (10) in which the maximum value of the exponent j is set to 1, that is, the quadratic equation (10), the four correction coefficients a ij (i=0~1, j=0~1) will be calculated. And these four correction coefficients a ij In order to calculate (i=0-1, j=0-1), at least four test measurement points are set, and an arbitrary value of applied pressure P is applied at each ambient temperature Tu (u=1-4). in A voltage value V0u (u=1 to 4) related to the pressure is applied to the pressure sensor 10B using a predetermined device. At this time, a voltage value V0u (u=1 to 4) related to the pressure is measured through the pressure sensor element 11, and a voltage value V related to the temperature is measured through the temperature sensor 80. t These measured values ​​are sent to a central processing unit (CPU) 62 via an analog detection circuit AC and an A / D converter AD. The central processing unit (CPU) 62 calculates the applied pressure P in u (u = 1 to 4), voltage value V0 related to pressure, and voltage value V related to temperature t By substituting u (u = 1 to 4) into equation (10), the correction coefficient a ijCalculate (i=0~1, j=0~1).

[0090] In Table 1 below, the ambient temperatures Tu (u=1 to 4) at the four inspection and measurement points are T1=23 [°C], T2=23 [°C], T3=200 [°C], and T4=200 [°C], and the applied pressure P applied at each inspection and measurement point is in u (u=1~4) is P in 1=0 [Pa], P in 2=100 [Pa], P in 3=0 [Pa] and P in Voltage value V0u (u=1 to 4) related to pressure and voltage value V related to temperature when 4=100 [Pa] t According to Table 1, the voltage values ​​V0u (u = 1 to 4) and V t u (u = 1 to 4) is (V01, V t 1)=(1.1 [v], 2.1 [v]), (V02, V t 2)=(4.3 [v], 2.1 [v]), (V03, V t 3)=(1.2 [v], 3.1 [v]), (V04, V t 4)=(4.2〔v〕, 3.1〔v〕).

[0091] [Table 1]

[0092] The applied pressure P at the above four test measurement points in u (u = 1 to 4) and data (V0u, V t u) (u=1 to 4), that is, (P in 1, V01, V t 1)=(0[Pa], 1.1[v], 2.1[v]), (P in 2, V02, V t 2)=(100[Pa], 4.3[v], 2.1[v]), (P in 3, V03, V t 3)=(0[Pa], 1.2[v], 3.1[v]), (P in 4, V04, V t4) = (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 obtain the correction coefficient a 00 , a 10 , a 01 , a 11 In this example, a 00 =-22.5625, a 10 =26.8750, a 01 =-5.62500, a 11 =2.08333.

[0093] In order to perform a higher accuracy correction (higher order correction), that is, the maximum value of the index i of the voltage value V0 related to the pressure in the formula (10) and the voltage value V related to the temperature are t The number of measurement points during inspection may be appropriately increased so that at least one of the maximum values ​​of the index j is set to 2 or more. For example, six inspection measurement points may be set in order to perform correction using equation (10) in which the maximum value of index i is set to 2 and the maximum value of index j is set to 1, i.e., third-order equation (10). In addition, for the measurement points during inspection, the temperature and pressure may be changed in a number of sections, and the above correction coefficient a may be applied to each section. ij It may be configured to calculate the correction coefficient a for each section. ij (It may be configured to perform temperature correction using a table method that has

[0094] [Second correction method] The second correction method is a method of performing a correction calculation using the following formula (11). Like formula (10), formula (11) corresponds to a calibration curve that defines the relationship between the voltage value detected by the sensor and the measured pressure value, and the voltage value V O and the voltage value V tas measurement parameters, and also include correction coefficients a0, a1, b0, and b1, which are constants. The correction coefficients a0, a1, b0, and b1 are obtained by applying a predetermined pressure to the pressure sensor 10B under a predetermined ambient temperature in an inspection process (adjustment process) before product shipment, and are expressed as pressure and temperature-related values, specifically, pressure-related voltage values ​​V output from the pressure sensor element 11 and temperature sensor 80 of the pressure sensor 10B. O and the voltage value V t This calculation process is executed by the central processing unit (CPU) 62.

[0095]

number

[0096] Of 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 a 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 an analog detection circuit AC and an A / D converter AD. Here, the applied pressure P in The relationship between and the voltage value V0 is expressed as a linear function P in = a0 + a1 × V o The applied pressure P is defined as in And from the data α relating to the voltage value V0, the correction coefficients a0 and a1 are calculated.

[0097] 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 pressure output from the pressure sensor element 11 included in the pressure sensor 10B and the voltage value V related to temperature output from the temperature sensor 80 are calculated as follows. tare obtained at a predetermined sampling rate through an analog detection circuit AC and an A / D converter AD. t The data β relating to is added to the above data α, and the values ​​of these data (data α and data β) are substituted into equation (11) to calculate the correction coefficients b0 and b1.

[0098] The correction coefficients a0, a1, b0, and b1 obtained in the above process are stored in the memory 63 as product characteristic values.

[0099] During actual use, the pressure sensor element 11 of the pressure sensor 10B sequentially outputs a voltage value V0 related to pressure, and the temperature sensor 80 sequentially outputs a voltage value V t By substituting the correction coefficients a0, a1, b0, and b1 stored in the memory 63 into the above equation (11), the corrected measured pressure value (P in the above equation (11)) is calculated successively. This second correction method is useful when the sensitivity of the pressure sensor 10B (the sensitivity of the pressure sensor element 11) to temperature changes is small.

[0100] In addition, the formula (11) used in the above example is such that the measured pressure value after correction is a voltage value V0 related to pressure output from the pressure sensor element 11 and a voltage value V related to temperature output from the temperature sensor 80. t However, it may be defined as a higher-order function. Also, the temperature and pressure of the measurement points during the inspection may be changed in a number of sections, and the above correction coefficient may be calculated for each section (temperature correction may be performed using a table method that has a correction coefficient for each section).

[0101] [Third correction method] The third correction method is to correct the internal pressure P of the reference vacuum chamber 20W at the time when the gas G is sealed in the reference vacuum chamber 20W, by subtracting the internal pressure P of the reference vacuum chamber 20W from the measured pressure value Px (measured pressure value Px before correction) calculated by the central processing unit (CPU) 62 constituting the measurement unit 60. O (The pressure P of gas G O) and the internal temperature T O (Ambient temperature T O ) and the ambient temperature Tx at the time of measurement as parameters, the following formula (12) is used to calculate the corrected measured pressure value Py. Here, the internal pressure P O (The pressure of gas G is P O ) and the internal temperature T O (Ambient temperature T O ) is data stored in advance in the memory 63 constituting the correction unit 70 (data stored during the work of sealing in the gas G). In addition, 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) are calculated using the voltage value V detected through the pressure sensor element 11 and the temperature sensor 80. O and the voltage value V t The values ​​successively calculated by the central processing unit (CPU) 62 based on the above are used.

[0102]

number

[0103] <Effects of pressure sensor 10B> According to the pressure sensor 10B having the above configuration, it is possible to correct an error in the measured pressure value caused by the gas G being sealed inside the reference pressure chamber 20W. Therefore, it is possible to provide a pressure sensor which combines the above-mentioned effects achieved by the pressure sensor 10A according to the first embodiment of the present invention with higher measurement accuracy.

[0104] Although 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, 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 the drawings can be combined with each other as long as there is no contradiction in their purpose, configuration, etc.

[0105] 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, a mechanism that allows the pressure sensors 10A and 10B to be easily attached and detached from the production facility or the like may be provided. 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. [Explanation of symbols]

[0106] 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...measurement portion, 61...interface (I / O), 62...processing unit (CPU), 63...memory, 70...compensation portion, 80...temperature sensor, G...gas.

Claims

1. 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, 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.

2. 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 objects to be detected 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. 3. The pressure sensor according to claim 2, The filling pressure is [0010] Pmin: the lower limit of the enclosed pressure, Qmin: the lower detection limit, Qα: the allowable inflow rate, Pα: the ambient pressure at the time of measuring the allowable inflow rate, Tα: the ambient temperature at the time of measuring the allowable inflow rate, M Ｇ : molecular weight of the gas, M ａｉｒ : molecular weight of the surrounding gas, T Ｔ : Ambient temperature at the time of the inspection, Pr Ｔ : partial pressure of the gas in the ambient pressure at the time of the test The pressure sensor is set to a value greater than the lower limit value calculated from the above.

4. The pressure sensor according to any one of claims 1 to 3, A temperature sensor for measuring a temperature of the enclosed space; The temperature sensor detects errors in the pressure measurement caused by changes in ambient temperature. and a correction unit that performs correction using the output value.

5. 5. The pressure sensor according to claim 4, The correction unit is configured to calculate a temperature difference between the value detected by the temperature sensor and the temperature of the gas sealed in the sealed space. The pressure sensor performs the compensation using the filled pressure and temperature.

6. 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.

7. The pressure sensor according to any one of claims 1 to 6, The gas is adsorbed by an adsorbent material disposed in the sealed space for adsorbing ambient gas. A pressure sensor made of non-magnetic material.

8. The pressure sensor according to any one of claims 1 to 7, The gas is a pressure sensor made of a substance other than the substance contained in air at a ratio of 1% by volume or more. 。

9. The pressure sensor according to any one of claims 1 to 8 has a sealed space with high airtightness. A testing method comprising: 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 amount of gas flowing out of the container using a leak detection device. and, 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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