Differential pressure sensor

Abstract

To accurately detect excessive differential pressure.SOLUTION: A differential pressure sensor 10 comprises: a diaphragm 12H deformed by receiving pressure HP of a fluid on a high-pressure side; a diaphragm 12L deformed by receiving pressure LP of the fluid on a low-pressure side; and a conversion circuit 15 that converts respective deformations of the diaphragms 12H and 12L into electric signals EH and EL respectively. The differential pressure sensor 10 comprises: a support member 11 that supports the diaphragms 12H and 12L and is filled with interlocking oil O interlocking with the respective deformations of the diaphragms 12H and 12L; and a processing circuit 16 that derives differential pressure between the pressure HP and the pressure LP on the basis of the electric signals EH and EL. The processing circuit 16 determines that the differential pressure between the pressure HP and the pressure LP is excessive differential pressure when the deformation of the diaphragm 12L indicated by the electric signal EL is a deformation to be convex to a side opposite to the support member side 11 and is a deformation with a deformation degree larger than a predetermined reference.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a differential pressure sensor.

Background Art

[0002] A differential pressure sensor is known that includes a first diaphragm that is deformed by receiving a first pressure on the high-pressure side of a fluid and a second diaphragm that is deformed by receiving a second pressure on the low-pressure side of the fluid, and derives a differential pressure between the first pressure and the second pressure (Patent Document 1).

[0003] When the differential pressure becomes excessive, the first diaphragm abuts against the stopper surface of the diaphragm chamber, so that its deformation stops and the differential pressure reaches a saturated state. By detecting that the differential pressure has reached the saturated state, an excessive differential pressure can be detected.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when an excessive differential pressure greater than the differential pressure required for the first diaphragm to hit the stopper surface (for example, a differential pressure 10 times or more the differential pressure) occurs, the first diaphragm is pressed against the stopper surface and distorted. This distortion may include distortion due to compression of the first diaphragm, as well as distortion due to the presence of a strain gauge provided on the first diaphragm and / or irregularities on the stopper surface. Due to such distortion, the differential pressure to be monitored may exhibit behavior as if no excessive differential pressure has occurred. And due to this behavior, an excessive differential pressure may not be detected even though an excessive differential pressure actually has occurred.

[0006] An object of the present invention is to accurately detect an excessive differential pressure. [Means for solving the problem]

[0007] To solve the above problems, the differential pressure sensor according to the present invention comprises: a first diaphragm that deforms upon receiving a first pressure on the high-pressure side of a fluid; a second diaphragm that deforms upon receiving a second pressure on the low-pressure side of the fluid; a conversion circuit that converts the deformation of the first diaphragm into a first electrical signal and the deformation of the second diaphragm into a second electrical signal; a support member that supports the first diaphragm and the second diaphragm, and is filled with an interlocking fluid that interlocks the deformation of the first diaphragm and the deformation of the second diaphragm; and a processing circuit that derives the differential pressure between the first pressure and the second pressure based on the first electrical signal and the second electrical signal, wherein the processing circuit determines that the differential pressure between the first pressure and the second pressure is excessive when the deformation of the second diaphragm indicated by the second electrical signal is a deformation that is convex on the opposite side from the support member and is a deformation greater than a predetermined standard.

[0008] As an example, the conversion circuit comprises two first strain gauges connected in series via a first node that convert the deformation of the first diaphragm into the first electrical signal, and two second strain gauges connected in series via a second node that convert the deformation of the second diaphragm into the second electrical signal, with the first electrical signal output from the first node and the second electrical signal output from the second node.

[0009] As an example, the conversion circuit includes a first full-bridge circuit comprising a plurality of bridge-connected third strain gauges that converts the deformation of the first diaphragm into the first electrical signal, and a second full-bridge circuit comprising a plurality of bridge-connected fourth strain gauges that converts the deformation of the second diaphragm into the second electrical signal.

[0010] As an example, the support member includes a stopper surface that restricts excessive deformation of the first diaphragm toward the support member. [Effects of the Invention]

[0011] According to the present invention, excessive differential pressure can be detected with high accuracy. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic plan view of a differential pressure sensor according to an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view of AA in Figure 1. [Figure 3] Figure 3 is a schematic plan view of a differential pressure sensor according to a modified example. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments of the present invention and their modifications will be described with reference to the drawings.

[0014] (Embodiment) As shown in Figures 1 and 2, a differential pressure sensor 10 according to one embodiment of the present invention comprises a support member 11, a diaphragm layer 12, a sealing member 13, a pressure sensing member 14, a conversion circuit 15, and a processing circuit 16. The differential pressure sensor 10 is configured to detect the differential pressure between the high-pressure side pressure HP and the low-pressure side pressure LP of a fluid to be measured (for example, a fluid flowing through a predetermined pipe). The differential pressure sensor 10 is configured, for example, as the differential pressure detection unit of a differential pressure transmitter.

[0015] The support member 11 supports the diaphragm layer 12. The support member 11 has a laminated structure in which a first layer 11A and a second layer 11B are stacked. The first layer 11A is provided with a through hole 11D that penetrates in the vertical direction. The lower surface of the second layer 11B is provided with diaphragm chambers 11H and 11L, which are recesses. A connecting passage 11E is provided from the first layer 11A to the second layer 11B, connecting the diaphragm chambers 11H and 11L to each other. The through hole 11D and the connecting passage 11E are connected. The upper part of the through hole 11D is sealed with a sealing member 13.

[0016] The diaphragm layer 12 is fixed to the lower surface of the second layer 11B. The diaphragm layer 12 covers and seals the diaphragm chambers 11H and 11L of the second layer 11B. The portion of the diaphragm layer 12 that covers the diaphragm chamber 11H is also called diaphragm 12H. Diaphragm 12H is supported by the support member 11 and deforms when subjected to pressure HP. The portion of the diaphragm layer 12 that covers the diaphragm chamber 11L is also called diaphragm 12L. Diaphragm 12L is supported by the support member 11 and deforms when subjected to pressure LP.

[0017] The through-hole 11D, communication passage 11E, diaphragm chambers 11H and 11L, which are sealed by the diaphragm layer 12 and the sealing member 13, are filled with interlocking oil O, which acts as an interlocking fluid to synchronize the deformation of the diaphragms 12H and 12L.

[0018] The pressure sensing member 14 is fixed to the lower surface of the diaphragm layer 12 and has pressure sensing paths 14H and 14L consisting of through holes extending in the vertical direction. Pressure sensing path 14L guides the low-pressure side pressure LP to the diaphragm 12L. Pressure sensing path 14H guides the high-pressure side pressure HP to the diaphragm 12H.

[0019] In this embodiment, the high-pressure side pressure HP causes the diaphragm 12H to deform convexly toward the support member 11 side (upwards) (see the dashed line in Figure 2). This deformation of the diaphragm 12H is transmitted to the diaphragm 12L via the interlocking oil O, causing the diaphragm 12L to deform convexly toward the opposite side (downwards) from the support member 11 side (see the dashed line in Figure 2). The low-pressure side pressure LP is applied to the diaphragm 12L, but due to the relationship pressure HP > pressure LP, the diaphragm 12L deforms convexly toward the opposite side from the support member 11 side. Thus, when a differential pressure occurs, which is the difference between pressure HP and pressure LP, the diaphragms 12H and 12L deform convexly toward different sides (in this case, opposite directions up and down).

[0020] The inner surface of the diaphragm chamber 11H becomes a stopper surface 11HA (also called an overpressure protection mechanism) that abuts against the diaphragm 12H (see the dashed line in FIG. 2) when the diaphragm 12H is greatly deformed convexly toward the support member 11 side, restricting further deformation of the diaphragm 12H. Similarly, the inner surface of the diaphragm chamber 11L also serves as a stopper surface 11LA that restricts excessive deformation of the diaphragm 12L. The stopper surfaces 11HA and 11LA are formed in a curved surface shape, for example, an aspherical shape.

[0021] The conversion circuit 15 is configured to convert each deformation (here, the degree and direction of deformation) of the diaphragms 12H and 12L into electrical signals EH and EL. The processing circuit 16 includes strain gauges S1 and S2 provided on the diaphragm 12H and connected in series, and strain gauges S3 and S4 provided on the diaphragm 12L and connected in series. Each of the strain gauges S1 to S4 is composed of a piezoresistive element formed by introducing boron, which is a p-type impurity, into a diaphragm layer 12 made of, for example, n-type single-crystal silicon.

[0022] The resistance values of the strain gauges S1 and S2 change due to the deformation of the diaphragm 12H. The resistance values of the strain gauges S3 and S4 change due to the deformation of the diaphragm 12L. A driving voltage V from a DC power supply VS is applied to both ends of each of the sets of the strain gauges S1 and S2 and the sets of the strain gauges S3 and S4. The negative terminal of the DC power supply VS is connected to the reference potential.

[0023] An electrical signal EH indicating a voltage VH (also referred to as a potential VH with the reference potential set to 0V) obtained by dividing the driving voltage V according to the resistance values of the strain gauges S1 and S2 is output from a node N1 connecting the two strain gauges S1 and S2. The voltage VH changes according to the deformation of the diaphragm 12H. That is, the deformation of the diaphragm 12H is converted into the voltage VH. This point will be described in detail below.

[0024] Strain gauges S1 and S2 have the same shape and the same resistance value when the diaphragm 12H is undeformed (flat). Strain gauge S1 extends along the radial direction of the diaphragm 12H, and strain gauge S2 extends along the tangential direction in the circumferential direction of the diaphragm 12H. As a result, when the diaphragm 12H is deformed, strain gauges S1 and S2 deform into different shapes, and consequently, their respective resistance values ​​change to different values. Therefore, the voltage VH changes according to the degree of deformation of the diaphragm 12H.

[0025] Furthermore, strain gauges S1 and S2 are thinner than the diaphragm layer 12, i.e., the diaphragm 12H, and are unevenly distributed on either the upper or lower surface side of the diaphragm layer 12. As a result, the deformation patterns of strain gauges S1 and S2 differ depending on whether the diaphragm 12H deforms convexly toward the support member 11 or convexly toward the opposite side. Therefore, the voltage VH changes in the opposite direction of the deformation of the diaphragm 12H, relative to the voltage value when the diaphragm 12H is not deformed. Here, strain gauges S1 and S2 are configured such that when the diaphragm 12H deforms convexly toward the support member 11, the voltage VH increases and approaches the drive voltage V. When the diaphragm 12H deforms convexly toward the opposite side, the voltage VH decreases and approaches 0V, that is, the potential VH approaches the reference potential.

[0026] Node N2, which connects the two strain gauges S3 and S4, outputs an electrical signal EL that represents a voltage VL (also called a potential VL with a reference potential of 0V) obtained by dividing the drive voltage V by the respective resistance values ​​of strain gauges S3 and S4. The voltage VL changes in accordance with the deformation of the diaphragm 12L. In other words, the deformation of the diaphragm 12L is converted into a voltage VL. The principle of the change in voltage VL is the same as the change in voltage VH. The explanation of strain gauge S3 follows the explanation of strain gauge S1, and the explanation of strain gauge S4 follows the explanation of strain gauge S2. The voltage VL, like the voltage VH, increases and approaches the drive voltage V when the diaphragm 12L deforms convexly toward the support member 11.

[0027] The electrical signals EH and EL from nodes N1 and N2 are input to the processing circuit 16 via terminals T1 and T2, which consist of bonding pads and the like. The processing circuit 16 is composed of a processor such as a microcontroller.

[0028] The processing circuit 16 detects the differential pressure that deforms the diaphragms 12H and 12L convexly to opposite sides (the support member 11 side and the opposite side), respectively, based on the electrical signals EH and EL. As described above, the direction of deformation of the diaphragm 12H when the voltage VH increases is the same as the direction of deformation of the diaphragm 12L when the voltage VL increases. Therefore, the processing circuit 16 can detect the differential pressure based on the difference between the voltage VH indicated by the electrical signal EH and the voltage VL indicated by the electrical signal EL. As an example, the processing circuit 16 detects the differential pressure by calculating the difference obtained by subtracting the voltage VL from the voltage VH. The processing circuit 16 may also detect the differential pressure by deriving the actual value of the differential pressure based on the value obtained by subtracting the voltage VL from the voltage VH and a predetermined calculation formula and / or table.

[0029] The processing circuit 16 further determines that the differential pressure between pressure HP and pressure LP is excessive when the deformation of the diaphragm 12L indicated by the electrical signal EL is convex on the opposite side from the support member 11, and the degree of deformation is greater than a predetermined standard. When the processing circuit 16 determines that the differential pressure is excessive, it outputs this information to an external device of the differential pressure sensor 10. For example, the processing circuit 16 determines whether the value of the voltage VL indicated by the electrical signal EL is smaller than a predetermined threshold. If the determination result is positive, the processing circuit 16 determines that the differential pressure between pressure HP and pressure LP is excessive and outputs this information to an external device of the differential pressure sensor 10. As a result, the differential pressure fluctuations due to the distortion of the diaphragm 12H pressed against the stopper surface 11HA by the excessive differential pressure, as described above, are ignored, and the excessive differential pressure is detected with high accuracy.

[0030] Furthermore, in this embodiment, the differential pressure can be derived and excessive differential pressure can be detected by a simple circuit configuration consisting of two strain gauges S1 and S2 connected in series via node N1 for diaphragm 12H, and two strain gauges S3 and S4 connected in series via node N2 for diaphragm 12L.

[0031] The conversion circuit 15 may be configured such that the direction of deformation of the diaphragm 12H when the voltage VH increases and the direction of deformation of the diaphragm 12L when the voltage VL increases are on different sides. In this case, the processing circuit 16 detects the differential pressure based on the sum of the voltages VH and VL.

[0032] The conversion circuit 15 may be configured such that the voltage VL increases when the diaphragm 12L deforms convexly toward the side opposite to the support member 11. In such a case, when the voltage VL becomes greater than a predetermined threshold, the conversion circuit 15 may detect an excessive differential pressure by determining that the deformation of the diaphragm 12L indicated by the electrical signal EL is a deformation that is convex toward the side opposite to the support member 11, and that the degree of deformation is greater than a predetermined standard.

[0033] (Variation 1) The differential pressure sensor 20 in this modified example has a full-bridge conversion circuit 25, as shown in Figure 3, instead of the conversion circuit 15. The configuration of the differential pressure sensor 20 will be described below, focusing on the differences from the differential pressure sensor 10. Any explanations not mentioned below are the same as those for the differential pressure sensor 10.

[0034] The conversion circuit 25 includes a full-bridge circuit B1 that converts the deformation of the diaphragm 12H into an electrical signal EH, and a full-bridge circuit B2 that converts the deformation of the diaphragm 12L into an electrical signal EL.

[0035] The full-bridge circuit B1 comprises a bridge-connected set of four strain gauges S11 to S14. Strain gauges S11 and S12 are connected in series, and strain gauges S13 and S14 are connected in series. The pair of strain gauges S11 and S12 and the pair of strain gauges S13 and S14 are connected in parallel. Strain gauges S11 and S14 extend along the radial direction of the diaphragm 12H, while strain gauges S12 and S13 extend along the tangential direction in the circumferential direction of the diaphragm 12H. The full-bridge circuit B1 inputs an electrical signal EH, which represents the voltage VH between node N11 connecting strain gauges S11 and S12 and node N12 connecting strain gauges S13 and S14, to the processing circuit 16 via terminals T11 and T12. The full-bridge circuit B1, i.e., strain gauges S11 to S14, is configured such that the voltage VH is 0V when the diaphragm 12H is not deformed. Furthermore, the full-bridge circuit B1 is configured such that the voltage VH increases as the diaphragm 12H deforms convexly toward the support member 11, and decreases (becomes negative) as the diaphragm 12H deforms convexly toward the opposite side of the support member 11.

[0036] The full-bridge circuit B2 comprises a bridge-connected set of four strain gauges S21 to S24. Strain gauges S21 and S22 are connected in series, and strain gauges S23 and S24 are connected in series. The pair of strain gauges S21 and S22 and the pair of strain gauges S23 and S24 are connected in parallel. Strain gauges S21 and S24 extend along the radial direction of the diaphragm 12L, while strain gauges S22 and S23 extend along the tangential direction in the circumferential direction of the diaphragm 12L. The full-bridge circuit B2 inputs an electrical signal EL, which represents the voltage VL between node N21 connecting strain gauges S21 and S22 and node N22 connecting strain gauges S23 and S24, to the processing circuit 16 via terminals T21 and T22. The full-bridge circuit B2, i.e., strain gauges S21 to S24, is configured such that the voltage VH is 0V when the diaphragm 12L is not deformed. Furthermore, the full-bridge circuit B2 is configured such that the voltage VL increases as the diaphragm 12L deforms convexly toward the support member 11, and decreases (becomes negative) as the diaphragm 12L deforms convexly toward the opposite side of the support member 11.

[0037] The processing circuit 16 derives the differential pressure between pressure HP and pressure LP based on the electrical signals EH and EL, similar to the embodiment described above. When the conversion circuit 16 is configured such that the direction of deformation of the diaphragm 12H when the voltage VH increases and the direction of deformation of the diaphragm 12L when the voltage VL increases are on different sides, that is, one side is on the support member 11 side and the other side is on the opposite side, the processing circuit 16 detects the differential pressure based on the sum of voltage VH and voltage VL.

[0038] The processing circuit 16 may determine that the differential pressure between pressure HP and pressure LP is excessive when the deformation of the diaphragm 12L indicated by the electrical signal EL is a deformation that is convex on the opposite side from the support member 11, and the degree of deformation is greater than a predetermined standard, and in such cases, it may determine whether the voltage VL is smaller than a predetermined threshold. The processing circuit 16 may perform the above determination by determining whether the potential VL+ is greater than a predetermined threshold or whether VL- is smaller than a predetermined threshold, with the voltage VL being the difference between the voltage VL+ from node N21 and the voltage VL- from node N22.

[0039] Although the full-bridge circuit complicates the circuit configuration, it allows for higher voltages VH and VL than in the above embodiment. This improves the sensitivity of the differential pressure sensor 20 based on voltages VH and VL.

[0040] (Modification 2) The configuration of the conversion circuit is arbitrary. For example, in addition to the strain gauges described above, or in place of some of the strain gauges, a temperature-compensating strain gauge may be provided. Alternatively, some of the strain gauges may be replaced with resistors whose resistance value does not change even when the diaphragm deforms. Such resistors may be provided outside the diaphragm. Elements other than piezoresistive elements (such as load cells) may be used as strain gauges.

[0041] (Variation 3) In the above, differential pressure and excessive differential pressure are detected based on the voltage indicated by the electrical signal. However, differential pressure and excessive differential pressure may also be detected based on the electrical signal indicating the change in current caused by the deformation of the diaphragm.

[0042] (Modification 4) The processing circuit 16 may be configured to determine that the differential pressure between pressure HP and pressure LP is excessive when the deformation of the diaphragm 12H indicated by the electrical signal EH is a convex deformation on the opposite side from the support member 11, and the degree of deformation is greater than a predetermined standard. This excessive differential pressure is the result of the pressure on the lower pressure side of the fluid being measured being mistakenly applied to the diaphragm 12H.

[0043] (Variation 5) The configuration of the differential pressure sensor 10 is arbitrary; for example, at least a part of the processing circuit 16 and the other parts 11-15 may be housed in separate enclosures and positioned at a distance from each other. For example, the processor constituting the processing circuit 16 may be provided outside the pressure sensor 10. The processing circuit 16 may also be provided as part of another device. The processing circuit 16 may include an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The differential pressure sensor 10 may also include a temperature sensor for detecting the temperature of the interlocking fluid O. The detected temperature is used to correct the voltages VH, VL, etc., to cancel out the deformation of the diaphragms 12H and 12L caused by the contraction due to the temperature of the interlocking fluid O.

[0044] (Scope of the present invention) Although the present invention has been described above with reference to embodiments and modifications, the present invention is not limited to the above embodiments and modifications. For example, the present invention includes various modifications to the above embodiments and modifications that can be understood by those skilled in the art within the scope of the technical concept of the present invention. The configurations listed in the above embodiments and modifications can be combined as appropriate to the extent that they do not contradict each other. [Explanation of symbols]

[0045] 10...Differential pressure sensor, 11...Support member, 11A...First layer, 11B...Second layer, 11D...Through hole, 11E...Communication passage, 11H...Diaphragm chamber, 11HA...Stopper surface, 11L...Diaphragm chamber, 11LA...Stopper surface, 12...Diaphragm layer, 12H...Diaphragm, 12L...Diaphragm, 13...Sealing member, 14...Pressure sensing member, 14H...Pressure sensing path, 14L...Pressure sensing path, 15...Conversion circuit, 16...Processing circuit, 20...Differential pressure sensor N...Conversion circuit, B1...Full bridge circuit, B2...Full bridge circuit, HP...Pressure, LP...Pressure, N1...Node, N2...Node, N11...Node, N12...Node, N21...Node, N22...Node, O...Interlocking oil, S1~S4, S11~S14, S21~S24...Strain gauge, T1...Terminal, T2...Terminal, T11...Terminal, T12...Terminal, T21...Terminal, T22...Terminal, VS...DC power supply, V...Drive voltage.

Claims

1. A first diaphragm that deforms under the first pressure on the high-pressure side of the fluid, A second diaphragm that deforms upon receiving a second pressure on the low-pressure side of the fluid, A conversion circuit that converts the deformation of the first diaphragm into a first electrical signal and the deformation of the second diaphragm into a second electrical signal, A support member that supports the first diaphragm and the second diaphragm, the support member being filled with a fluid that links the deformation of the first diaphragm and the deformation of the second diaphragm, The system includes a processing circuit that derives the differential pressure between the first pressure and the second pressure based on the first electrical signal and the second electrical signal, The processing circuit determines that the differential pressure between the first pressure and the second pressure is excessive when the deformation of the second diaphragm indicated by the second electrical signal is a deformation that is convex on the side opposite to the support member, and the degree of deformation is greater than a predetermined standard. Differential pressure sensor.

2. The aforementioned conversion circuit is Two first strain gauges connected in series via a first node convert the deformation of the first diaphragm into the first electrical signal, The device comprises two second strain gauges connected in series via a second node, which convert the deformation of the second diaphragm into the second electrical signal, The first node outputs the first electrical signal, The second node outputs the second electrical signal. The differential pressure sensor according to claim 1.

3. The aforementioned conversion circuit is A first full-bridge circuit comprising a plurality of bridged third strain gauges, which converts the deformation of the first diaphragm into a first electrical signal, A second full-bridge circuit comprising a plurality of bridged fourth strain gauges, which converts the deformation of the second diaphragm into the second electrical signal, The differential pressure sensor according to claim 1.

4. The support member is provided with a stopper surface that restricts excessive deformation of the first diaphragm toward the support member. A differential pressure sensor according to any one of claims 1 to 3.

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