Fluid differential pressure measuring device with push rod

Abstract

A fluid pressure difference measuring device with a push rod, comprising: a measuring diaphragm, a push rod, an intermediate diaphragm, an intermediate medium, a pressure guide cavity, a pressure difference sensitive layer; the measuring diaphragm is limited between a first cavity and a second cavity; one end of the push rod is fixedly connected with the measuring diaphragm, and the other end of the push rod is provided with the intermediate diaphragm; the intermediate diaphragm is arranged on one side of the pressure guide cavity, the other side of the pressure guide cavity is provided with the pressure difference sensitive layer, the pressure guide cavity is a closed structure and is filled with the intermediate medium; the measuring diaphragm has a hard part with a preset area, and a flexible part is fixedly connected at the edge to realize displacement of the hard part; the measuring diaphragm senses a fluid pressure difference and generates an axial force acting on the push rod, the intermediate diaphragm senses the axial force and makes the pressure difference sensitive layer generate deformation through the intermediate medium; the deformation makes an electrical parameter of a related element of the pressure difference sensitive layer change, and the change is used for output of a fluid pressure difference signal by a signal processing circuit.

Description

Technical Field

[0001] This utility model relates to the field of industrial and civil fluid measurement, specifically to a differential pressure measuring device. Background Technology

[0002] In industrial and civil fluid measurement fields, it is often necessary to measure or monitor micro-pressure differences in fluids ranging from 5 to 100 Pa. Examples include pressure differentials in cleanrooms, static pressure in ducts, and flow velocities in ducts within the HVAC system. Mainstream measurement devices include piezoresistive MEMS sensors and capacitive MEMS sensors.

[0003] Piezoresistive MEMS sensors in this range operate by sensing resistance changes generated by semiconductor strain gauges. Due to the low rigidity of the piezoresistive structure, they are sensitive to external interference factors such as packaging stress and temperature fluctuations. When the temperature changes or during long-term continuous use, they often experience zero-point drift of about 1 Pa or more, which significantly affects the measurement. Capacitive MEMS sensors, on the other hand, have relatively smaller zero-point drift, but their manufacturing cost is higher.

[0004] Zero-point drift error of measuring devices is one of the key technical indicators of concern in micro differential pressure measurement in the HVAC field. Therefore, designing and manufacturing low-cost measuring devices with small zero-point drift while meeting measurement accuracy requirements is a problem that needs to be solved. Utility Model Content

[0005] This application provides an optimized design for a fluid differential pressure measurement device. A typical design includes a measuring diaphragm, a push rod, an intermediate diaphragm, an intermediate medium, a pressure-conducting cavity, and a differential pressure sensitive layer. The measuring diaphragm is located between a first cavity and a second cavity, used to sense the fluid differential pressure and generate an axial force acting on the push rod. One end of the push rod is fixedly connected to the measuring diaphragm, and the other end is provided with an intermediate diaphragm, which senses the axial force. The intermediate diaphragm is located on one side of the pressure-conducting cavity, and the differential pressure sensitive layer is located on the other side of the pressure-conducting cavity. The pressure-conducting cavity is a closed structure filled with an intermediate medium, which conducts pressure, causing the differential pressure sensitive layer to deform. The middle portion of the measuring diaphragm and the middle portion of the intermediate diaphragm each include a rigid portion with a preset area. The edges of the rigid portions are fixedly connected to telescopic portions, which are used to realize the displacement of the rigid portions. The differential pressure measurement device also includes related components of the differential pressure sensitive layer. The electrical parameters of these components change during deformation, which is used by the signal processing circuit to output the fluid differential pressure signal.

[0006] Furthermore, the telescopic part is a thin material with a low elastic modulus, used to accommodate the displacement of the rigid part and reduce the corresponding additional axial force.

[0007] Furthermore, the measuring diaphragm is circular.

[0008] Furthermore, the fluid differential pressure measuring device includes multiple pull ropes, one end of which is connected to a push rod to limit the push rod.

[0009] Furthermore, the relevant element is a strain gauge disposed on the differential pressure sensitive layer, and the strain gauge is connected to the signal processing circuit; the strain gauge senses the deformation and generates a resistance change, and the resistance change is used by the signal processing circuit to output the fluid differential pressure signal.

[0010] Furthermore, the strain gauge comprises a semiconductor strain gauge, which generates the resistance change through the piezoresistive effect.

[0011] Furthermore, the relevant element is a fixed electrode plate arranged opposite to the differential pressure sensitive layer, and the differential pressure sensitive layer and the fixed electrode plate form a sensing capacitor, which is connected to the signal processing circuit; the deformation causes the sensing capacitor to change and is used by the signal processing circuit to output the fluid differential pressure signal.

[0012] Furthermore, the push rod is provided with a limit component for overpressure protection. Attached Figure Description

[0013] Figure 1 is a cross-sectional view of Example 1 of the fluid differential pressure measuring device.

[0014] Figure 2 is a cross-sectional view of Example 2 of the fluid differential pressure measuring device.

[0015] Figure 3 shows a three-dimensional view of the diaphragm.

[0016] Figure 4 shows Example 2 of measuring the diaphragm.

[0017] Figure 5 shows a three-dimensional view of the connecting diaphragm.

[0018] Figure 6 is a three-dimensional view of the first cavity.

[0019] Figure 7 shows an example of a measuring diaphragm with a pull rope. Detailed Implementation

[0020] Example 1 of the fluid differential pressure measuring device in this utility model is a design of an average value measuring device for air micro differential pressure with a multi-diaphragm structure for the HVAC field. Figure 1 is a cross-sectional view.

[0021] The diagram shows four measuring diaphragm units; a first cavity 201, a second cavity 202, and a measuring diaphragm 1 located between them constitute a measuring diaphragm unit. The first cavity and the second cavity can be collectively referred to as the measuring pressure cavity; the measuring pressure cavity and the measuring diaphragm together constitute a high-pressure measuring space 18 and a low-pressure measuring space 19; the high-pressure measuring space 18 and the low-pressure measuring space 19 can be collectively referred to as the measuring pressure space. The first cavity and the second cavity are fastened together using mounting bolts 24.

[0022] As shown in Figure 6, the first cavity 201 is made of aluminum alloy and is a hollow cylindrical shape with a wall thickness of 1mm and an inner diameter of 65mm at the diaphragm mounting location. It has 6 through holes 25 for connecting with the second cavity 202, and 6 screw holes 27 on the inner edge for connecting and fixing the diaphragm. The outer edge is designed with an annular groove 30 for sealing and limiting the measuring diaphragm. The inner edge is designed with an annular groove 30 for sealing and limiting the connecting diaphragm 4. The upper part of the cavity is designed with a strip groove 23 for connecting the space between the cavities to the external environment, so that the pressure in the middle space 20 or the end cap 205 is the same as the air pressure in the external environment. The side of the cavity is designed with a cavity nozzle 21 for connecting the measuring tube. The central space 20 is located between the two pressure measuring chambers and is separated from the measured air by a connecting diaphragm. In the example, there are 3 central spaces. After adopting the design of the strip groove 23, their pressure is the same as the ambient pressure. Since the pressure inside the end cap 205, the pressure inside the force transmission chamber 206, and the pressure sensed by the sensor vent are also the ambient pressure, the resultant force of the axial force of the external environment on the push rod is basically zero.

[0023] The space outside the first cavity 201 at the top of the diagram is protected by an end cap. The space inside the end cap has the same pressure as the environment due to the effect of the strip groove. The force transmission cavity and the second cavity 202 at the bottom are connected by screws 31 to protect the corresponding space. A vent 22 is provided on the outside of the force transmission cavity to ensure that the pressure inside the cavity is the same as the environment.

[0024] The measuring diaphragm refers to the diaphragm used to drive the push rod. It has a high-pressure measuring space 18 and a low-pressure measuring space 19 on its two sides. The measuring diaphragm is a key component for sensing fluid pressure differences. In this example, it is connected and fixed to the push rod 5 via a set screw or other components. The push rod 5 is a rigid component connected to the measuring diaphragm, driven by the diaphragm, and transmits force to the sensor. This force changes with the fluid pressure difference. It can generally be designed as a circular shaft. Multiple rods can be connected to the measuring diaphragm separately and then combined. In this example, a solid PVC cylinder with a diameter of 4mm is used, but it can be optimized as a hollow cylinder. In this example, four measuring diaphragm units sense the fluid pressure difference and generate corresponding axial forces. These axial forces act together on the push rod, and the middle diaphragm is subjected to the resultant force of multiple axial forces applied by the push rod. The middle diaphragm senses this resultant force and then transmits the corresponding pressure through the intermediate medium 8 in the pressure-conducting tube 11, thereby enabling the pressure-sensitive layer in a differential pressure sensor such as a MEMS to sense the change in the resultant force. Various force transmission components can be designed between the push rod and the sensor; the force transmission component senses the axial force of the push rod and transmits the force to the sensor. The transmission process may include changes in the magnitude or direction of the force, and it can be composed of one or more components; in the example, the pressure plate, the intermediate diaphragm, the pressure guide tube, etc. constitute the force transmission component.

[0025] As shown in Figure 3, in the example of the measuring device, the measuring diaphragm is circular. Its push rod mounting part 101 is made of rigid material, including a mounting hole 101a for the push rod, a screw hole 27 for fixing the push rod, and a limiting groove 30 for connecting and limiting the diaphragm 4. The push rod mounting part is fixedly connected to a rigid diaphragm 102 with a thickness of 1 mm. The mounting part and the rigid diaphragm can be made of PVC or other lightweight materials, and can be integrally molded using a mold, with reinforcing ribs designed locally. The rigid diaphragm is connected to the soft diaphragm 104 at the junction 103 using an adhesive bonding process. The soft diaphragm body is 1 mm thick and has a telescopic part 28 and limiting ribs 29; the soft diaphragm is made of silicone. The telescopic part is designed with a thin wall, combining the low elastic modulus and super-elasticity of silicone to adapt to the displacement of the rigid part and reduce the corresponding additional axial force. The flexible diaphragm can be manufactured and connected to the rigid diaphragm using a partial overmolding process. In the manufacturing process, the interface of the rigid diaphragm is first cleaned and pre-treated, then a special adhesive is applied, and liquid silicone is used to vulcanize and mold the diaphragm around its perimeter to obtain the measuring diaphragm. In actual manufacturing, the push rod mounting part of the measuring diaphragm and the rigid diaphragm can be designed as separate parts. After the rigid and flexible diaphragms are connected and molded, the push rod mounting part and the rigid diaphragm are then bonded or welded together for fixation.

[0026] The rigid portion of the measuring diaphragm can be flexibly designed, as shown in Example 2 of Figure 4; it modifies the measuring diaphragm design of Example 1 of the measuring device. In this example, the soft diaphragm 104 is directly connected to the mounting portion, and a rigid annular thin plate 39 replaces the rigid diaphragm. The rigid annular thin plate and the soft diaphragm are bonded together to form a rigid composite layer. Furthermore, by controlling the inner diameter of the rigid annular thin plate, a soft gap can be left near the mounting portion to dampen axial forces.

[0027] The radial cross-section of the telescopic part can be a semi-circular ring as shown in the example; it can be designed with a thickness of approximately 50 μm, and the inner radius of the ring can be designed to be 1~2 mm. The thickness or inner diameter can be adjusted based on the elastic modulus of the silicone under different stresses to calculate the additional axial force, or by referring to the tensile strength of the silicone. The calculation of the additional axial force can be based on the maximum displacement of the push rod, combined with the elastic modulus and dimensions. The telescopic part can be designed in other different shapes.

[0028] The connecting diaphragm 4 connects the measuring diaphragm to the high-pressure or low-pressure chamber. Figure 5 shows a three-dimensional view of the connecting diaphragm. The connecting diaphragm is fixed to the chamber by screws 31 passing through an annular gasket 32 ​​and through-hole 25, forming a sealed space between the high-pressure or low-pressure chamber. A telescopic section 28 is also designed, using a thin material with low elastic modulus to accommodate the displacement of the push rod and reduce the corresponding additional axial force. The center of the annular gasket 32 ​​is located on the push rod axis and can be made of various rigid materials; other connection methods such as bonding can also be used to achieve a seal between the connecting diaphragm and the chamber. In the example, the connection between the connecting diaphragm and the measuring diaphragm is designed with a partially concave shape in the measuring pressure chamber to facilitate convenient and accurate installation positioning. The connecting diaphragm can be made of silicone and injection molded. The shape and size of the telescopic section can be consistent with the telescopic section of the measuring diaphragm, or the thickness or inner diameter of the telescopic section can be adjusted based on the calculation of the additional axial force according to the elastic modulus corresponding to different stresses.

[0029] The connection between the aforementioned connecting diaphragm and the measuring diaphragm essentially achieves a flexible connection between the measuring pressure chamber and the push rod. In practical designs, the measuring pressure chamber can be directly connected to the push rod via the connecting diaphragm. In this case, the measuring diaphragm can be connected to the push rod using a push rod mounting part of other shapes.

[0030] During measurement, the pressure difference between the two sides of the measuring diaphragm, connecting diaphragm, and intermediate diaphragm increases, leading to increased internal stress. This increases the radial force exerted by the diaphragm on the centrally located push rod. The annular design of the expansion joint allows the diaphragm to center the push rod; the centering performance improves with increasing pressure difference. Example 1 fully utilizes the inherent centering function of the measuring diaphragm, connecting diaphragm, and intermediate diaphragm. The combination of a vertical push rod and a horizontal diaphragm achieves excellent centering characteristics. The expansion joint can be made of various types of rubber materials with low elastic modulus and high elasticity.

[0031] Furthermore, the measuring diaphragm can be designed and improved. The measuring diaphragm in Figure 7 is an improvement on the measuring diaphragm of Example 1 of the measuring device, with the addition of 6 pull ropes 38. The annular portion containing limiting ribs near the through hole is made of rigid PVC material, and the pull ropes 38 are located between the junction and the aforementioned annular portion. The pull ropes have a preset length and a certain tensile strength; they can be made of lightweight materials such as polypropylene fiber or glass fiber; low-elongation materials are preferred. When the push rod is in the centered state, the pull ropes are in a slack state. When the push rod is displaced due to device vibration or external force, the pull ropes can extend and straighten to limit the push rod mounting part, preventing excessive displacement that could damage the telescopic part and cause significant disturbance to the differential pressure measurement value. The diameter and number of pull ropes can be determined based on the ultimate tensile force calculation and experiment. In the design of the measuring device, the position of the pull ropes can be flexibly set, not limited to the diaphragm, but can be set between the push rod and the side wall of the cavity; at the same time, pull ropes with the same function can also be set inside the intermediate diaphragm and the connecting diaphragm for limiting.

[0032] The installation of the pull rope can be achieved through a drilling and glue-filling process. First, drill holes of a certain depth in the relevant areas, clean the inside of the holes, apply special adhesive to the inside of the holes, place the pull rope in the holes, and use precision glue-filling equipment to fill the holes with special glue, allowing the glue to stand and cure.

[0033] The diaphragm 3 in the example comprises a rigid intermediate diaphragm portion 301, a telescopic portion 28, and an annular fixing portion 302 connected to the telescopic portion. The annular fixing portion is connected and fixed to the force transmission cavity 206, forming a seal against the pressure-conducting cavity. The force transmission cavity is made of stainless steel. The telescopic portion 28 is annular, with a cross-sectional shape consistent with the telescopic portion of the measuring diaphragm. It is made of a thin material with a low elastic modulus, and can be designed to be approximately 50 μm thick. The inner radius of the annulus can be designed to be 1-2 mm. The additional axial force can be calculated based on the elastic modulus of the material under different stresses, and the thickness and inner diameter can be adjusted accordingly. A soft material that is immiscible with the intermediate medium 8, such as fluorosilicone rubber, can be used. The rigid portion of the intermediate diaphragm can be made of lightweight materials, such as Teflon or PVC; or it can be made of stainless steel sheet. The annular fixing portion can be made of stainless steel. The forming and connection process of the telescopic portion of the intermediate diaphragm can adopt a local encapsulation forming process similar to that of the measuring diaphragm. The connection and fixation between the intermediate septum and the force transmission cavity can be achieved by welding. A limiting step can be machined into relevant parts of the force transmission cavity, and the intermediate septum can be placed on it. Pulse laser welding is then performed under the pressure of the heat dissipation fixture. After welding, sealant is applied for sealing. Alternatively, the connection and fixation between the intermediate septum and the force transmission cavity can refer to the gasket design in CN 202580374 U "Compression-type Pipe Fittings" for compression and fixation of the intermediate septum. Internal installation threads can be machined into relevant parts of the force transmission cavity. Grooves can be machined into relevant parts of the force transmission cavity to place O-rings, and the intermediate septum is placed on top of the O-rings. A gasket with external threads is machined, and mounting bosses and other mounting parts are machined on the gasket. Using a clamp, the gasket is screwed into the force transmission cavity, and the O-ring is compressed to form a seal on the intermediate septum.

[0034] The measuring diaphragm, intermediate diaphragm, and soft parts connecting the diaphragm can be manufactured using mold compression molding or injection molding processes. During the manufacturing process, the control of vulcanization temperature can be optimized or secondary vulcanization can be implemented to improve molding accuracy.

[0035] In the example, the push rod end is designed with a boss 34 for limiting the cylindrical helical spring 33; the other end of the cylindrical helical spring 33 is limited to the lower pressure plate 35 with a boss. A retaining ring 502 and a locking sleeve 501 with a set screw are used to limit the push rod 5 to prevent overpressure of the sensor; the limiting plate 10 is connected by a screw on the side and a force transmission cavity, used to limit the push rod, and its position can be adjusted vertically. The spring 33 is located between the push rod and the pressure plate, and can dampen the force between the push rod and the sensor. The spring, as a damping component, works in conjunction with the limiting component to achieve good overpressure protection performance; the spring can be designed as other damping components such as a rubber spring. The damping component is not a necessary component in this invention and can be designed as needed. In the design, the pressure plate can be connected and fixed using adhesive and an intermediate septum; the pressure plate and the intermediate septum may also not be connected.

[0036] A gap is left between the push rod and the limiting plate, so that there is no resistance to the push rod at this point, and at the same time, the back pressure above the diaphragm in the middle is the ambient pressure; through holes can be further provided on the limiting plate to balance the air pressure.

[0037] When the four pressure measuring chambers are connected to the same pressure, zero-point calibration can be performed via the circuit. During measurement, the push rod is pushed downward slightly by the corresponding measuring diaphragm, and a greater pressure is applied to the pressure plate 35 by the spring. After transmission through the intermediate diaphragm, the pressure of the intermediate medium increases, and the sensor transmits a signal to the calculation circuit, which can calculate the arithmetic mean of each pressure difference. When the air pressure difference is too large, the push rod will be blocked by the limiting plate for overpressure protection. During the measurement process, the pressure of an individual first chamber may be less than the pressure of the corresponding second chamber, causing the corresponding measuring diaphragm to exert an upward axial force on the push rod.

[0038] Furthermore, when the four sets of pressure measuring chambers are connected to the same air pressure difference, the force exerted by each measuring diaphragm on the push rod is the same, and the calculation circuit can obtain the air pressure difference value.

[0039] In Example 1, the actual forces acting on the intermediate septum include the axial force exerted by the diaphragm unit on the push rod, the back pressure, and the pressure generated by the weight of the push rod and diaphragm components. In this invention, the axial force refers to the axial force generated by the pressure of the fluid being measured in the pressure measurement space on the push rod, excluding the axial force generated by the diaphragm's own weight. The resultant force of these axial forces acts on the intermediate septum with a corresponding pressure, which can be positive or negative depending on the direction. In practical design, the first chamber can be connected to the low-pressure side of the fluid, and the second chamber can be connected to the high-pressure side of the fluid. The axial force acting on the push rod is upward, and the pressure sensed during the differential pressure sensing layer test is less than the pressure at zero. This design is also feasible.

[0040] Compared to traditional single-diaphragm designs, the design of multiple diaphragm measuring units achieves the arithmetic mean of multiple pressure differences at a lower cost, making it widely applicable in fluid flow measurement. It also offers a smaller footprint, facilitating industrial applications. Furthermore, with appropriate design, the displacement of the measuring diaphragm during measurement is minimal, or even negligible after eliminating damping, reducing the breathing effect of the measuring chamber. Various precision filters can be installed at suitable locations on the measuring tube to prevent dust from causing sensing errors in the measuring diaphragm.

[0041] The intermediate medium that works in conjunction with the intermediate diaphragm, as a liquid medium for transmitting pressure, can be an electrically insulating liquid with a small coefficient of expansion, such as silicone oil, or a liquid medium such as natural or synthetic grease; the rigid pressure-conducting tube 11 is connected to the sensor nozzle 601, and silicone oil fills the space between them up to the differential pressure sensitive layer; the differential pressure sensor transmitter 6 has a vent 22 at the bottom so that the pressure on the other side of the sensor is the ambient pressure.

[0042] The differential pressure sensor can employ existing wet-type semiconductor strain gauge MEMS sensors. The strain gauges change resistance through the piezoresistive effect. The core structure of the sensor is fabricated using a series of mature micro-nano fabrication processes, such as silicon etching, bonding, and sacrificial layer release, ensuring good reliability. Typically, four semiconductor strain gauges are integrated onto the sensitive membrane. These strain gauges are usually formed through selective doping, such as boron diffusion. They are arranged in different strain regions of the membrane and connected to form a Wheatstone bridge circuit. When a differential pressure exists, the deformation of the sensitive membrane causes the resistance of each strain gauge to change in opposite directions, resulting in a differential voltage signal output by the bridge that is proportional to the differential pressure. This sensitive membrane acts as the differential pressure sensing layer, sensing the pressure from the silicone oil on one side and the ambient pressure on the other. With zero fluid pressure differences in the four measuring diaphragm units, the differential pressure sensor can achieve zero-point calibration. The pressure at the sensor vent, the central space, the force transmission cavity, and the space inside the end cap does not need to be the ambient pressure. These pressures can be obtained by connecting to other pressure spaces through pipes; this pressure can be called the reference pressure or back pressure.

[0043] The differential pressure sensor can also utilize existing technology, employing a capacitive MEMS differential pressure sensor filled with silicone oil and featuring a wet channel, achieving measurement in conjunction with an intermediate diaphragm. The core structure consists of a pair of parallel opposing plates, with a movable plate fixed to a fixed plate via a suspended support structure, forming a sensing capacitor. When the sensor is subjected to external pressure, the intermediate medium applies pressure to the movable plate, causing elastic deformation and altering the distance between the two plates, resulting in a change in the capacitance value of the sensing capacitor. The movable plate uses an insulating material as the contact diaphragm, such as alumina ceramic coated with a metal film or a single-crystal silicon diaphragm. These materials not only possess excellent mechanical strength and overload resistance, but their insulating properties also help reduce leakage current and improve signal stability, making them suitable for differential pressure monitoring under complex operating conditions. The sensing capacitor is connected to a signal processing circuit; its changes are processed by the circuit and accurately converted into an electrical signal output proportional to the differential pressure, achieving high-precision pressure measurement.

[0044] With the intermediate diaphragm and the measuring diaphragm unit structure clearly defined, the average value of the pressure difference measured by the aforementioned differential pressure sensor and the pressure difference of the measured air can be used for calculation of the calculation circuit based on structural parameters such as the effective sensing area of ​​the diaphragm or by establishing a linear relationship through experiments.

[0045] In the example, the height of the intermediate septum is lower than the height of the differential pressure sensor. This height difference reduces the stress on the differential pressure sensing layer when it is at the zero-point measurement position. The pressure-conducting tube can be a pipe with a smaller inner diameter, such as a stainless steel capillary tube with an inner diameter of 50µm, to reduce the impact of intermediate medium expansion on the zero-point measurement. After being sealed on both sides by the intermediate septum and the pressure-sensitive layer, the pressure-conducting tube becomes a closed space, which can be called a pressure-conducting cavity. Its form can be simplified; the differential pressure sensor can be placed below the intermediate septum, shortening the length of the pressure-conducting cavity. Using a thinner or shorter pressure-conducting cavity significantly reduces the additional pressure effect caused by the volume change of silicone oil at different temperatures, avoiding a significant impact on measurement accuracy and zero-point calibration.

[0046] The liquid column filled with silicone oil below the intermediate diaphragm expands or contracts with temperature changes, causing its height to change accordingly. The density of the silicone oil changes accordingly, ensuring that the pressure exerted by the liquid column on the differential pressure sensitive layer remains essentially unchanged with temperature. This characteristic, combined with the optimized design of the pressure-conducting cavity, results in minimal zero-point drift of the measuring device; if necessary, temperature measurement can also be used to compensate for and correct the zero point.

[0047] Furthermore, microporous components can be incorporated into the conduction channels of the intermediate medium to prevent liquid hammer from affecting the sensor. Alternatively, a sintered filter can be placed in front of the differential pressure sensing layer to reduce the impact of the intermediate medium's inertia, thereby minimizing its adverse effects on sensor measurements. A filter gap of 5-10 μm can be used, and the optimal position and configuration of the sintered filter can be determined experimentally.

[0048] The intermediate septum can be configured with a smaller area to further amplify the pressure value. Micro-differential pressure measurement can be achieved using a higher range and more economical differential pressure sensor, with measurement accuracy and stability exceeding that of some small-range differential pressure sensors. For example, a typical piezoresistive 2000 Pa MEMS sensor, compared to a piezoresistive 100 Pa MEMS sensor, has a larger or thicker differential pressure sensing layer under the same structure. The pressure-sensitive structure often has higher rigidity, and its sensitivity to external interference such as encapsulation stress and temperature fluctuations is often significantly reduced, exhibiting better overall stability. Specifically, this includes lower full-scale temperature drift, lower zero-point temperature drift, lower zero-point temperature rise drift, and lower long-term zero-point drift. When a measurement device is designed with a 2000 Pa sensor and an intermediate septum, it can have lower zero-point drift compared to a 100 Pa sensor with the same structure. In micro-differential pressure measurement in the HVAC field, zero-point drift error is one of the main technical indicators that needs to be guaranteed. The combination of a measuring diaphragm, an intermediate septum, and a higher range sensor can lead to better applications. The design of the measuring device example 1 can use a piezoresistive MEMS differential pressure sensor with a higher range, which can achieve low zero-point drift measurement of differential pressure of 5~100pa while ensuring measurement accuracy.

[0049] When the measuring device example 1 measures only a single air pressure difference, only a pair of first and second chambers can be designed. Further, the structure can be simplified by having the force sensing chamber directly serve as the second chamber, eliminating the air vent and adding a chamber nozzle to connect the force sensing chamber to the low-pressure side of the measured air, allowing the pressure of the force sensing chamber to act directly on one side of the measuring diaphragm; eliminating the diaphragm connection allows the high-pressure fluid to act on the entire other side of the measuring diaphragm, including the middle section, as in the diaphragm structure of the Magnesense series sensors from Dwyer, USA; in this case, the back pressure of the differential pressure sensor's differential pressure sensing part needs to be kept consistent with the measured low pressure.

[0050] Based on the measurement device example 1, when only a pair of first and second chambers are designed, the diameter of the intermediate septum can be designed to be in the range of 6mm to 10mm to achieve a 40 to 100 times amplification of the measured pressure. A differential pressure sensor with a range of 4kpa to 10kpa can be designed to achieve an air pressure differential measurement range of 100pa. A larger inner diameter of the measuring pressure chamber can be designed to increase the diameter of the intermediate septum.

[0051] The design of the measuring device in Example 1 is suitable for differential pressure measurement of various gaseous fluids. When applied to liquid differential pressure, after the measured medium enters the measuring diaphragm, an exhaust pipe and exhaust device can be connected to an appropriate location in the pressure chamber to expel air, achieving a certain level of measurement accuracy. For liquid differential pressure measurement, a diaphragm similar to an intermediate diaphragm can also be added to the pressure measuring channel, allowing the measuring diaphragm to remain filled with air; one side of the added diaphragm is air, and the other side is the fluid being measured. This design can also achieve a certain level of measurement accuracy. A typical design with an intermediate diaphragm and intermediate medium can be summarized as a fluid differential pressure measuring device with an intermediate medium, characterized by comprising a measuring diaphragm, a push rod, an intermediate diaphragm, an intermediate medium, a pressure-conducting cavity, and a differential pressure sensitive layer; the measuring diaphragm is located between a first cavity and a second cavity; one end of the push rod is fixedly connected to the measuring diaphragm, and the other end of the push rod is provided with the intermediate diaphragm; the intermediate diaphragm is disposed on one side of the pressure-conducting cavity, and the differential pressure sensitive layer is disposed on the other side of the pressure-conducting cavity, the pressure-conducting cavity being a closed structure filled with the intermediate medium; the middle portion of the measuring diaphragm and the middle portion of the intermediate diaphragm each include a rigid portion with a predetermined area, the edges of the rigid portions being fixedly connected to telescopic portions, the telescopic portions being used to realize the displacement of the rigid portions; the measuring diaphragm senses the fluid differential pressure and generates an axial force acting on the push rod, the intermediate diaphragm senses the axial force and causes the differential pressure sensitive layer to deform through the intermediate medium; the deformation causes changes in the electrical parameters of the relevant components of the differential pressure sensitive layer, the changes being used by the signal processing circuit to output the fluid differential pressure signal. The preferred design prioritizes a horizontally positioned diaphragm. This horizontal positioning fully utilizes the diaphragm's centering characteristics, ensuring that horizontal interference forces or vibrations do not significantly affect the measurement structure, thus providing horizontal anti-interference capabilities. In this design, since the intermediate medium transmits fluid pressure, the position and orientation of the differential pressure sensitive layer can be flexibly set; for example, the differential pressure sensitive layer can be adjacent to the intermediate diaphragm, forming a compact structural design.

[0052] The differential pressure measuring device can also adopt a vertical placement design for the diaphragm, as shown in Example 2 of the fluid differential pressure measuring device in Figure 2. Its design is mostly the same as that of Example 1 of the fluid differential pressure measuring device. After the push rod is placed horizontally, the corresponding measuring diaphragm unit is placed vertically. The intermediate diaphragm is designed to be smaller in size than that in Example 1, and the local parts of the force transmission cavity are modified accordingly. The positions of the nozzles of the 8 cavities are changed to the mirror positions of Example 1. The strip grooves on the 4 first cavities are removed, and the original strip grooves are designed as planes. A back pressure pipe 37 is added and connected to the vents 22 of the 3 central spaces, the force transmission cavity, the end cap, and the sensor. The back pressure pipe can be made of various hard or soft materials. An elastic rope 36 is added in the force transmission cavity and the end cap to suspend the push rod and center it.

[0053] The small size of the intermediate diaphragm amplifies the pressure sensed by the sensor, facilitating measurement and reducing zero-point drift caused by the push rod in a horizontal position. Furthermore, the pressure plate connected to the intermediate diaphragm can be made of a thin, lightweight material; a rubber-type damping component can replace the spring to optimize the force on the intermediate diaphragm; alternatively, the damping component can be eliminated, with the push rod acting directly on the intermediate diaphragm. In this case, a limiting component can be designed on the left side of the intermediate diaphragm or inside the sensor. Under the suspension of the elastic rope, the push rod can be centered at zero position through position adjustment; the elastic rope, as an auxiliary centering component, reduces additional errors caused by misalignment during measurement. The design of the elastic rope can be combined with the aforementioned pull rope design for limiting, forming protection for the telescopic part. The elastic rope can be made of silicone or other rubber materials, and the optimal diameter and design length can be determined experimentally. Alternatively, the design can omit the elastic rope, utilizing the tension generated by the telescopic part of the diaphragm to suspend the push rod while optimizing its weight; in this case, centering is not a necessary measurement condition.

[0054] The three central spaces, force transmission chamber, and end caps are connected by pipes to ensure identical back pressure, allowing for zero-point calibration of the sensor. Furthermore, they can be connected to a suitable pressure space. When measuring air pressure differentials, if the low-pressure value is high, such as when measuring the flow velocity in a high static pressure duct, the back pressure pipe interface 3701 can be connected to the static pressure sampling port in the duct to achieve a higher back pressure. A higher back pressure results in a lower pressure differential across the diaphragm, leading to lower internal stress in the diaphragm's expansion joint, a lower elastic modulus, and thus better working characteristics.

[0055] The horizontally positioned push rod design allows the measuring device to accurately measure minute pressure differences in liquids. After installing a venting device on the back pressure connector and venting measures are taken on the back pressure connector connected to the sensor, most of the gas in the three central spaces, the force transmission chamber, the end cap, and the sensor can be expelled. Further venting by connecting the nozzle to the pressure measuring chamber with a venting device allows most of the gas in the measuring device to be expelled, thus enabling accurate measurement of liquid pressure differences. When measuring liquid pressure differences, a sensor with a vertically positioned pressure-sensitive layer can be used for easy venting.

[0056] The telescopic part can be made of a thin material with a suitable elastic modulus so as not to significantly affect the measurement accuracy of the differential pressure sensor. The telescopic part should not be limited to components made of materials such as rubber. Under some operating conditions, the deformation of the differential pressure sensitive layer is minimal. When no damping component is installed, the axial displacement of the push rod is minimal. This should not be interpreted as the push rod having no displacement; in this case, a metal material with a high elastic modulus can be used.

[0057] The terms “first,” “second,” and “third” used in this article are for descriptive purposes only and should not be interpreted as indicating or implying relative importance.

[0058] In the description of this utility model, it should be understood that the terms "upper", "lower", "horizontal", "middle", "intermediate", "one side", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0059] Finally, it should be noted that the embodiments described in this article have been described in detail. For those skilled in the art, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A fluid differential pressure measuring device with a push rod, characterized in that... It includes a measuring diaphragm, a push rod, an intermediate diaphragm, an intermediate medium, a pressure-conducting cavity, and a differential pressure-sensitive layer; the measuring diaphragm is located between the first cavity and the second cavity, and is used to sense the fluid pressure difference and generate an axial force acting on the push rod; one end of the push rod is fixedly connected to the measuring diaphragm, and the other end is provided with an intermediate diaphragm, which senses the axial force; The intermediate diaphragm is disposed on one side of the pressure-conducting cavity, and the differential pressure sensitive layer is disposed on the other side of the pressure-conducting cavity. The pressure-conducting cavity is a closed structure filled with an intermediate medium, which conducts pressure, causing the differential pressure sensitive layer to deform. The middle part of the measuring diaphragm and the middle part of the intermediate diaphragm each include a rigid portion with a preset area. The edges of the rigid portions are fixedly connected to telescopic portions, which are used to realize the displacement of the rigid portions. The differential pressure measuring device also includes related components of the differential pressure sensitive layer. The electrical parameters of the related components change during deformation, which is used by the signal processing circuit to output the fluid differential pressure signal.

2. The fluid differential pressure measuring device according to claim 1, characterized in that, The telescopic part is a thin material with a low elastic modulus, used to accommodate the displacement of the rigid part and reduce the corresponding additional axial force.

3. The fluid differential pressure measuring device according to claim 1, characterized in that, The measuring diaphragm is circular.

4. The fluid differential pressure measuring device according to claim 1, characterized in that, The fluid differential pressure measuring device includes multiple pull ropes, one end of which is connected to a push rod to limit the push rod.

5. The fluid differential pressure measuring device according to claim 1, characterized in that, The relevant element is a strain gauge disposed on the pressure difference sensitive layer, and the strain gauge is connected to the signal processing circuit; the strain gauge senses the deformation and generates a resistance change, and the resistance change is used by the signal processing circuit to output the fluid pressure difference signal.

6. The fluid differential pressure measuring device according to claim 5, characterized in that, The strain gauge comprises a semiconductor strain gauge, which generates the resistance change through the piezoresistive effect.

7. The fluid differential pressure measuring device according to claim 1, characterized in that, The relevant element is a fixed electrode plate arranged opposite to the differential pressure sensitive layer. The differential pressure sensitive layer and the fixed electrode plate form a sensing capacitor, which is connected to the signal processing circuit. The deformation causes the sensing capacitor to change and is used by the signal processing circuit to output the fluid differential pressure signal.

8. The fluid differential pressure measuring device according to claim 1, characterized in that, The push rod is equipped with a limit component for overpressure protection.

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