Fluid differential pressure measurement device having diaphragms and application thereof

Abstract

A fluid differential pressure measurement device, comprising a plurality of measurement diaphragms, wherein the measurement diaphragms are respectively limited between respective first and second cavities to form a plurality of measurement diaphragm units; a push rod passes through and is connected to the measurement diaphragms; the measurement diaphragm units sense fluid differential pressures and generate corresponding axial acting forces; the axial acting forces jointly act on the push rod; the first and second cavities are provided with through holes; the edges of the holes are connected to the push rod by means of telescopic portions; the holes and the telescopic portions have preset shapes and areas, so that the high-pressure effective sensing areas and the low-pressure effective sensing areas of the corresponding measurement diaphragm units are equal; back pressure spaces of the telescopic portions and back pressure spaces where two ends of the push rod are located are configured to have an equal pressure; the push rod transfers a resultant force of the axial acting forces to a sensor or a mechanical indication mechanism, so as to measure an average value related variable of the corresponding fluid differential pressures of the measurement diaphragm units.

Description

A fluid differential pressure measuring device with a diaphragm and its application Technical Field

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

[0002] In the field of industrial and civil pipeline fluid measurement, various average differential pressure measuring components based on Pitot tubes or averaging pitot tubes are widely used to measure average flow velocity and fluid flow rate. The types of fluids measured include air, industrial gases, industrial fluids, etc. Applications include airflow control valves, portable airflow hoods, fluid measurement and control, etc. The basic measurement principle of average differential pressure measuring components is Bernoulli's equation, which describes the conservation of the sum of kinetic energy, potential energy, and pressure energy of an incompressible fluid flow section. In fluid measurement, neglecting changes in potential energy, the equation describes the conservation of the sum of kinetic energy and pressure energy. Average differential pressure measuring components are simple to manufacture and provide rapid measurement, and are widely used in fluid flow measurement.

[0003] In ideal flow measurement, one of the more accurate methods for measuring underdeveloped flow regimes is to use a Pitot tube to measure the flow point by point after the rectifier and calculate the velocity-related variables at each point, as shown in the following formula.

[0004] ρ: Fluid density (kg / m³) 3 ), where ΔP1......ΔP n The dynamic pressure (Pa) at each measuring point.

[0005] The method can be called the point-by-point calculation method.

[0006] The average differential pressure measuring component can employ a Pitot matrix design for multi-point averaging measurement. By measuring the average total pressure and average static pressure across the cross-section, the average dynamic pressure is calculated, and the average flow velocity is obtained using Bernoulli's equation. Devices as described in US3685355A and US4297900A are designed with a total pressure manifold and multiple static pressure manifolds.

[0007] The average pressure difference measurement component can also use an averaging pitot tube to measure the average flow velocity. Its shape includes square, elliptical, etc., and the averaging pitot tube is arranged perpendicular to the axis of the fluid measurement channel. An averaging pitot tube generally has a high-pressure chamber and a low-pressure chamber forming a single detection tube. The average pressure difference measurement component is composed of one or more averaging pitot tubes. When multiple averaging pitot tubes are used, the high-pressure chambers and low-pressure chambers are connected by pipes. The high-pressure chamber of the averaging pitot tube has multiple total pressure measurement holes on its flow-facing side. Measurements from these multiple total pressure measurement holes achieve the measurement of the average high pressure, which is approximately equal to the average total pressure of the measurement cross-section. The low-pressure chamber has multiple low-pressure measurement holes on its side or rear. When the flow stream passes through the averaging pitot tube, a low-pressure distribution area is formed on its side or rear due to localized velocity enhancement or the appearance of numerous fluid vortices. The average low-pressure value collected by the averaging pitot tube is significantly lower than the average static pressure of the measurement cross-section, and the measured average pressure difference is generally more than 1.5 times greater than the average dynamic pressure at the measurement cross-section.

[0008] In nearly fully developed circular fluid conduits, averaging pitot tubes are typically used for single-tube measurement, such as flute-shaped or Viagra averaging pitot tubes; in some cases, a single low-pressure measuring orifice is also employed. In this case, the velocity distribution exhibits a characteristic of high velocity at the tube center and low velocity near the tube wall, exhibiting axisymmetric properties. A flow coefficient can be derived for more accurate flow measurement.

[0009] The calculation of the average differential pressure measuring component of the averaging pitot tube type can be summarized as follows:

[0010] Where v m Let K be the average flow velocity in the fluid measurement channel, Δp be the average pressure difference, and ρ be the fluid density. Factors affecting the flow coefficient include structural coefficient, blockage coefficient, Reynolds number, and velocity distribution.

[0011] The average differential pressure measuring component formed by the combination of multiple averaging pitot tubes can realize flow measurement in large-sized fluid measurement channels.

[0012] For the design and application of Pitot tubes and averaging pitot tubes as average differential pressure measuring components, please refer to "A Modular Flow Measurement Method, Device and Its Application", CN 116295672 A.

[0013] In the field of industrial and civil pipeline fluid measurement, most measurement conditions involve underdeveloped flow regimes, high turbulence, and severe non-uniform velocity distribution. This asymmetry reduces the feasibility and accuracy of average differential pressure measurement devices to varying degrees. In some cases, establishing a mathematical relationship between the measured average velocity and the actual average velocity is often difficult, posing challenges to numerical correction. There are several specific reasons for this.

[0014] First, in some cases, severe uneven flow velocity distribution and asymmetry increase the flow velocity inside the detection tube cavity, resulting in large local pressure loss, the average pressure deviating from its theoretical average value, and the enhanced flow inside the detection tube cavity, which reduces the average performance to varying degrees.

[0015] Second, in some cases, the increased inflow and outflow velocity of the fluid at the measuring hole of the detection tube causes the collected pressure value to deviate too much from the actual total or low pressure value at the measuring hole.

[0016] Third, under some measurement conditions, the static pressure distribution at the measurement cross section is often uneven, and the distribution characteristics change with the total flow rate, which affects the establishment of the mathematical relationship between the measured average flow velocity and the actual average flow velocity, making numerical correction difficult.

[0017] In view of the adverse effects of the above three aspects on measurement and result correction in some measurement conditions of the average differential pressure measuring component, the present invention proposes corresponding solutions. Summary of the Invention

[0018] This invention addresses the characteristics of fluid flow measurement by designing a fluid differential pressure measuring device with diaphragms. The device comprises multiple measuring diaphragms, each positioned between a first and second cavity to form multiple measuring diaphragm units. A push rod passes through and connects to each measuring diaphragm unit. Each measuring diaphragm unit senses the fluid differential pressure and generates a corresponding axial force, which acts collectively on the push rod. The first and second cavities have through-holes, the edges of which connect to the push rod. This connection includes a telescopic section for isolating the pressure measurement spaces of the respective cavities and displacing the push rod. The openings and telescopic sections have predetermined shapes and areas, ensuring that the effective high-pressure sensing area and the effective low-pressure sensing area of ​​the corresponding measuring diaphragm unit are equal. The back pressure space of the telescopic section and the back pressure spaces at both ends of the push rod are configured to have equal pressure. The push rod transmits the resultant force of the axial force to a sensor or mechanical indicating mechanism to measure the average value of the corresponding fluid differential pressure of the measuring diaphragm unit.

[0019] Furthermore, the equal pressure can be ambient air pressure.

[0020] Furthermore, the back pressure space of the telescopic part and the back pressure spaces at both ends of the push rod can be connected through pipes to the same pressure space to achieve the same pressure.

[0021] Furthermore, the measuring device is configured to perform zero-position calibration and measurement with the push rod in a vertical position.

[0022] Furthermore, the measuring device is configured to perform zero-position calibration and measurement when the push rod is in a horizontal state.

[0023] Furthermore, a damping component is provided between the push rod and the sensor to dampen the resultant force; a limit component is provided on the push rod for overpressure protection.

[0024] Furthermore, the push rod is connected to a pull rope for limiting the push rod's position.

[0025] Furthermore, an intermediate diaphragm is provided between the push rod and the sensor. The intermediate diaphragm senses the resultant force and transmits the corresponding pressure to one side of the differential pressure sensitive layer in the sensor through an intermediate medium.

[0026] Furthermore, a semiconductor strain gauge is disposed on the pressure difference sensitive layer, and the semiconductor strain gauge senses the pressure from the intermediate medium through the piezoresistive effect.

[0027] Furthermore, the pressure difference sensitive layer can be a movable electrode of a sensing capacitor.

[0028] This invention enables low-cost measurement of the arithmetic mean of multiple fluid pressure differences, which can significantly improve the stable measurement and monitoring of fluid flow under adverse operating conditions with a certain accuracy, and can significantly reduce manufacturing and maintenance costs, and can be widely applied. Attached Figure Description

[0029] Figure 1 is a cross-sectional view of Example 1 of the fluid differential pressure measuring device.

[0030] Figure 2 is a cross-sectional view of Example 2 of the fluid differential pressure measuring device.

[0031] Figure 3 shows an example of a displacement sensor.

[0032] Figure 4 shows Example 2 of measuring the diaphragm.

[0033] Figure 5 shows an example 2 of a diaphragm measurement unit.

[0034] Figure 6 shows an example 3 of a diaphragm measurement unit.

[0035] Figure 7 shows a three-dimensional view of the diaphragm.

[0036] Figure 8 is a three-dimensional view of the connecting diaphragm.

[0037] Figure 9 is a three-dimensional view of the first cavity.

[0038] Figure 10 shows an example of a measuring diaphragm with a pull rope.

[0039] Figure 11 is a schematic diagram of the measuring valve assembly in application example 1.

[0040] Figure 12 is a schematic diagram of the measuring valve assembly in application example 2.

[0041] Figure 13 shows application example 1.

[0042] Figure 14 is a partial cross-sectional view of application example 1.

[0043] Figure 15 shows application example 2. Detailed Implementation

[0044] Example 1 of the fluid differential pressure measuring device in this invention is a design of an average value measuring device for air micro differential pressure with a multi-diaphragm structure for the field of HVAC. Figure 1 is a cross-sectional view.

[0045] 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.

[0046] As shown in Figure 9, the first cavity 201 is made of aluminum alloy and is a hollow cylindrical shape with a wall thickness of 1 mm and an inner diameter of 65 mm 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 13. 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.

[0047] 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.

[0048] 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 and driven by it, transmitting force to a sensor or mechanical indicating mechanism. 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 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 causing the pressure-sensitive layer in the MEMS or other differential pressure sensor to sense the change in the resultant force. Various force transmission components can be designed between the push rod and the sensor or mechanical indicating mechanism. These force transmission components sense the axial force of the push rod and transmit it to the sensor or mechanical indicating mechanism. The transmission process may involve changes in the magnitude or direction of the force, and can consist of one or more components. In the example, a pressure plate, intermediate diaphragm, and pressure-conducting tube constitute the force transmission component. The mechanical indicating mechanism is a mechanical transmission structure that transmits, amplifies, or transforms the force transmitted by the push rod, using a mechanical display component to indicate the measured value. Examples include combinations of connecting rods, gears, pointers, and leaf springs, widely used in differential pressure gauges for cleanrooms.

[0049] As shown in Figure 7, in the example 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.

[0050] 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.

[0051] 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.

[0052] The connecting diaphragm 4 connects the measuring diaphragm to the high-pressure or low-pressure chamber. Figure 8 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. It also features a telescopic section 28, made of 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 shown, with the measuring pressure chamber designed as a partially concave shape for 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.

[0053] 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.

[0054] 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, combining a vertical push rod with a horizontal diaphragm setup to achieve excellent centering characteristics. The expansion joint can be made of various types of rubber materials with low elastic modulus and high elasticity.

[0055] Furthermore, the measuring diaphragm can be designed and improved. The measuring diaphragm in Figure 10 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; materials with low elongation 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.

[0056] 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.

[0057] In the example, the septum 3 comprises a rigid intermediate septum portion 301, a telescopic portion 28, and an annular fixing portion 302 connected to the telescopic portion. The annular fixing portion is fixed to the force transmission cavity 206, forming a seal on the intermediate 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 thickness and inner diameter can be adjusted based on the calculation of the additional axial force according to the elastic modulus of the material under different stresses. A soft material that is immiscible with the intermediate medium 8, such as fluorosilicone rubber, can be used. The rigid portion of the intermediate septum 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 septum can adopt a localized overlay 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, a sealant is applied. 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 accommodate 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.

[0058] 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.

[0059] 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 on 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, providing damping 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; the spring can be designed as other damping components such as a rubber spring. The damping component is not essential 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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 boasts a smaller size, 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 13 to prevent dust from causing sensing errors in the measuring diaphragm.

[0065] 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 transmitter 6 has a vent 22 at the bottom so that the pressure on the other side of the sensor is the ambient pressure.

[0066] 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 in the sensor vent, central space, force transmission cavity, and end cap space does not need to be the ambient pressure. It can be connected to other pressure spaces via pipes to obtain an equal pressure, which can be called the reference pressure or back pressure.

[0067] In summary, the spaces of the sensor's vent, the central space, the force transmission cavity, and the end cap in Example 1 can be collectively referred to as the back pressure space. The back pressure space is one or more pressure spaces, characterized in that it is not a measurement pressure space, but its pressure acts on the connecting diaphragm, the cross-section of the push rod, the central diaphragm, or the measuring diaphragm, forming an axial force on the push rod. The pressure of the back pressure space may affect zero-point calibration. In Example 1, the pressure in the central space acts simultaneously on the mounting parts of both the connecting diaphragm and the measuring diaphragm. Since the mounting parts on both sides are fixedly connected to the push rod, it forms a bidirectional axial force on the push rod. If the pressure in the central space is not equal to the ambient pressure, since the four measuring diaphragm units are designed with identical shapes and sizes, the actual impact on zero-point stability is relatively small. Inconsistent pressures in the force transmission cavity, the sensor vent, and the end cap will significantly affect measurement accuracy and zero-point calibration.

[0068] 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.

[0069] Differential pressure sensors can also be resistance strain gauge sensors, which use metal strain gauges as resistance strain gauges and are attached to the differential pressure sensitive layer to form a bridge to output differential pressure signals.

[0070] 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.

[0071] 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 of measurement. 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 50 μm, to reduce the impact of intermediate medium expansion on the zero point of 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 can significantly reduce 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.

[0072] 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.

[0073] 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 pore size of 5–10 μm can be used, and the optimal position and configuration of the sintered filter can be determined experimentally.

[0074] 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 interferences 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 using 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 achieve better application results. 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 to 100 Pa while ensuring measurement accuracy.

[0075] 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 inlet 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.

[0076] 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. The differential pressure sensor with a range of 4kpa to 10kpa can be used 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.

[0077] The design of the measuring device 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 part of the measuring diaphragm and the middle part 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 unit 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.

[0078] 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. 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 force transmission cavity is modified accordingly. The positions of the nozzles of the 8 cavities are changed to the mirror image 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 vent 22 of the 3 intermediate cavities, 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.

[0079] 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.

[0080] The three intermediate cavities, the force transmission cavity, and the end cap are connected by pipes to ensure the same back pressure, allowing for zero-point calibration of the sensor. Furthermore, they can be connected to a suitable pressure space. When measuring air pressure difference, 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 difference across the diaphragm, leading to less internal stress in the diaphragm's expansion joint, a lower elastic modulus, and thus better working characteristics.

[0081] 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 intermediate chambers, 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.

[0082] The arrangement of the push rod of the differential pressure measuring device is not limited to vertical or horizontal placement; it can also be placed at an angle for certain measurement accuracies.

[0083] The differential pressure measuring device can also be designed using a displacement sensor to achieve differential pressure measurement, as shown in Figure 3. In this design, the push rod is placed in a horizontal position, and a hard steel ball 503 is provided at the end of the push rod. This ball attracts the magnetic seat 904, which is fixed to the leaf spring 903, thus limiting the push rod. The upper end of the leaf spring is fixed to the force transmission cavity 206. The non-magnetic hard plate 905 is connected and fixed to the magnetic seat 904, and the magnet 901 is fixed to one end of the non-magnetic hard plate. The horizontal position of the magnet 901 changes with the average differential pressure of the fluid being measured. The displacement sensor 902, located inside the circuit cavity 907, senses the positional change of the magnet 901 through the Hall effect and generates an electrical signal that is transmitted to the circuit. The partition 906 isolates the circuit cavity 907 from the force transmission space, ensuring a stable air pressure in the force transmission cavity where the leaf spring is located. A vent 22 is provided on the side of the force transmission cavity 206.

[0084] Differential pressure measuring devices can also employ various force sensors in conjunction with push rods to sense fluid pressure differences. For example, an S-type force sensor with a 10g range can be used, connecting the push rod to the force-receiving end of the sensor to measure force. Alternatively, a leaf spring with attached resistance strain gauges can be used. The strain gauges are attached to specific areas of the leaf spring's surface and connected to form a Wheatstone bridge. When an external force is applied to the force-receiving end through the push rod, the leaf spring undergoes a slight deformation, causing a change in the resistance of the strain gauges. The Wheatstone bridge outputs an electrical signal proportional to the applied force, thus achieving accurate force measurement.

[0085] The structure of the measuring diaphragm unit in Example 1 of the measuring device can be modified to achieve the same function, as shown in Figures 5 and 6. In Example 2 of the measuring diaphragm unit, push rods 5, driven by the measuring diaphragm 1, are located within the high-pressure measuring space 18 and the low-pressure measuring space 19. The characteristic feature is that the end face of the first cavity is connected to the movable cavity 26 via a connecting diaphragm 4, and the movable cavity 26 is fixedly connected to the push rod. Simultaneously, the second cavity has a movable cavity 26 with the same area. This design also ensures that the effective sensing area for high pressure and the effective sensing area for low pressure of the measuring diaphragm unit are equal.

[0086] In this invention, the effective sensing area for high pressure refers to the area corresponding to the axial force exerted by the fluid pressure in the high-pressure space on the push rod, and the effective sensing area for low pressure refers to the area corresponding to the axial force exerted by the fluid pressure in the low-pressure space on the push rod. Essentially, the movable cavity can be considered part of the push rod; its presence reduces either the effective sensing area for high pressure or the effective sensing area for low pressure.

[0087] Furthermore, the design of the measuring diaphragm unit Example 3 is largely the same as that of Example 2, except that the push rod passes completely through the cavity; after designing a fixed bracket for the cavity, this type can also be applied to a differential pressure averaging measuring device with multiple measuring diaphragms.

[0088] A detailed analysis of the design of the measuring diaphragm in Figure 1 reveals several commonalities in the examples. As shown in the detailed diagram, the high-pressure fluid enters the interior of the telescopic section through the measuring gap 1801, exerting a force on the cross-section of the telescopic section. This force causes a loss in the effective high-pressure sensing area, which is approximately half the projected area of ​​the telescopic section on the horizontal plane. By using the same shape and size for both the first and second cavities, and employing telescopic sections of the same shape and area, the effective high-pressure sensing area and the effective low-pressure sensing area of ​​the measuring diaphragm can be made equal. The advantages of the measuring diaphragm in Figure 1 lie in its simple assembly and smaller manufacturing volume.

[0089] Essentially, in this example, the push rod and the pressure chamber wall are sealed together, achieving isolation of the pressure measurement space within the corresponding chamber and displacement of the push rod. The connection can be made solely through a telescopic section, or it can be a combination of the telescopic section and other components. The telescopic section achieves isolation of the pressure measurement space and displacement of the push rod, including axial and radial displacement. In summary, the aforementioned high-pressure and low-pressure chambers have through openings, the edges of which are connected to the push rod. This connection includes a telescopic section for isolating the pressure measurement space of the corresponding measuring diaphragm unit and displacing the push rod. The opening and the telescopic section have a predetermined shape and area such that the effective sensing area for high pressure and the effective sensing area for low pressure of the corresponding measuring diaphragm unit are equal.

[0090] 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.

[0091] Meanwhile, the design of multiple measuring diaphragms described above has wide applications in engineering. It achieves complete isolation between the measured fluid and the force transmission components, enabling accurate measurement; it allows for accurate measurement of low-range fluids using high-range differential pressure sensors; and it enables low-cost measurement of the arithmetic mean of multiple fluid differential pressures, significantly reducing manufacturing and maintenance costs.

[0092] Its typical design can be summarized as follows: a fluid differential pressure measuring device, characterized by comprising multiple measuring diaphragms, each diaphragm being confined between its respective first and second cavities to form multiple measuring diaphragm units. A push rod passes through and connects to the measuring diaphragms. The measuring diaphragm units sense the fluid differential pressure and generate a corresponding axial force, which acts collectively on the push rod. The first and second cavities have through openings, the edges of which are connected to the push rod. The connecting structure includes a telescopic part for isolating the measuring pressure space of the corresponding cavities and displacing the push rod. The openings and telescopic parts have preset shapes and areas, such that the effective sensing area for high pressure and the effective sensing area for low pressure of the corresponding measuring diaphragm units are equal. The push rod transmits the resultant force of the axial force to a sensor or mechanical indicating mechanism to measure the average value of the corresponding fluid differential pressure of the measuring diaphragm unit. The design can be simplified by replacing multiple measuring diaphragms with a single measuring diaphragm to measure a single fluid differential pressure value, while keeping other design elements unchanged. In this case, a high-range differential pressure sensor can be used to achieve accurate measurement of a low-range value.

[0093] One of the conditions for the above measurement is that the back pressure spaces at both ends of the push rod are configured to have equal pressure, so that the pressure at both ends of the push rod will not cause interference from axial force during the test; the two ends include the push rod near the end face of the measuring pressure chamber at the beginning and end, for example, near the end face of the second chamber at the bottom in device example 1.

[0094] Furthermore, the back space of the telescopic part and the spaces at both ends of the push rod can be configured to have equal pressure to ensure zero-position stability; furthermore, the back pressure space of the telescopic part and the back pressure spaces at both ends of the push rod can be connected through pipes to the same pressure space to achieve the same pressure.

[0095] The differential pressure measuring device can be configured to perform zero-point calibration and measurement when the push rod is in a vertical position; the differential pressure measuring device can also be configured to perform zero-point calibration and measurement when the push rod is in a horizontal position. Various damping components can be provided between the push rod and the sensor to dampen the force exerted by the push rod on the sensor; various limiting components can be designed.

[0096] In the design, an intermediate diaphragm and wet sensing design can be adopted to enhance the flexibility of use and the performance against external force disturbances. An intermediate diaphragm can be set between the push rod and the sensor. The intermediate diaphragm senses the resultant force and transmits the corresponding pressure to one side of the differential pressure sensitive layer in the sensor through the intermediate medium. A semiconductor strain gauge can be set on the differential pressure sensitive layer. The semiconductor strain gauge senses the pressure from the intermediate medium through the piezoresistive effect. The differential pressure sensitive layer can be the movable plate of a sensing capacitor.

[0097] The design of multiple diaphragms has wide applications in the HVAC field, as illustrated in Figures 11-15. The meaning and definition of the average differential pressure measuring component in this invention are consistent with those in "A Modular Flow Measurement Method, Device and Its Application," CN 116295672 A. Please refer to this publication for details. The definitions of parameters such as measuring sub-channels, interval components, measuring sub-regions, regional differential pressure, detection tubes, average flow velocity related variables, structural coefficients, theoretical flow coefficients, and measurement flow coefficients are consistent with this publication.

[0098] Figure 13 shows application example 1, and Figure 14 is a partial cross-sectional view of it. The device in Figure 13 modifies the averaging pitot tube to form a novel rhomboid averaging pitot tube. The example includes a first total pressure measuring hole 01h, a second total pressure measuring hole 02h, a third total pressure measuring hole 03h, a fourth total pressure measuring hole 04h, and a first low pressure measuring hole 01l, a second low pressure measuring hole 02l, a third low pressure measuring hole 03l, and a fourth low pressure measuring hole 04l. The space near the first total pressure measuring hole is enclosed by the cavity partition plate 16, the high and low pressure partition plate 14, and the averaging pitot tube wall 15, forming a high-pressure measuring cavity. The other three total pressure measuring holes, using the same design, have corresponding high-pressure measuring cavities, and the four low-pressure measuring holes have corresponding low-pressure measuring cavities. The first total pressure measuring hole, the first low-pressure measuring hole, and the corresponding measuring pressure cavities constitute a measuring module. Similarly, the other total pressure measuring holes and low-pressure measuring holes constitute three other measuring modules.

[0099] The internal pressure in the four high-pressure chambers is led out by the internal measuring tube 17 and connected to the four first chambers through the measuring tube. Similarly, the internal pressure in the four low-pressure chambers is led out by the internal measuring tube 17 and connected to the four second chambers through the measuring tube. The novel averaging pitot tube has a first high-pressure nozzle 1201h, a second high-pressure nozzle 1202h, a third high-pressure nozzle 1203h, a fourth high-pressure nozzle 1204h, a first low-pressure nozzle 1201l, a second low-pressure nozzle 1202l, a third low-pressure nozzle 1203l, and a fourth low-pressure nozzle 1204l. In the design, each pair of tested modules is connected to the corresponding diaphragm measuring unit.

[0100] Figure 11 is a schematic diagram of the measuring valve assembly in Application Example 1. Each measured nozzle and each measuring pressure chamber is connected via measuring tube 13. Individual differential pressure and differential pressure averaging measurements are achieved by controlling the measuring switching valve, thus realizing high-precision flow measurement. The measuring tube can take various forms and, together with the internal measuring tube, can be collectively referred to as the pressure measuring channel.

[0101] Specifically, when the eight unified switching valves v0 are open, the following valves are closed: the first high-pressure measuring valve v01ha, the second high-pressure measuring valve v02ha, the third high-pressure measuring valve v03ha, the fourth high-pressure measuring valve v04ha, the first low-pressure measuring valve v01la, the second low-pressure measuring valve v02la, the third low-pressure measuring valve v03la, the fourth low-pressure measuring valve v04la, the second unified high-pressure measuring valve v02hb, the third unified high-pressure measuring valve v03hb, the fourth unified high-pressure measuring valve v04hb, the second unified low-pressure measuring valve v02lb, the third unified low-pressure measuring valve v03lb, and the fourth unified low-pressure measuring valve v04lb; and the first unified high-pressure measuring valve v01hb and the first unified low-pressure measuring valve v01lb. This valve operation enables individual measurement of the regional differential pressure of the first measured module. This operation uniformly performs the same differential pressure measurement on all measuring diaphragm units, and can be referred to as unified differential pressure measurement.

[0102] The aforementioned unified switching valve, high-pressure measuring valve, low-pressure measuring valve, and the following balanced switching valve can be collectively referred to as measuring switching valves.

[0103] Then, the same actions are performed on the second, third, and fourth tested modules and their corresponding measurement switching valves to measure the regional pressure difference corresponding to the second, third, and fourth tested modules. The calculation circuit calculates the average flow velocity of the fluid measurement channel when the area weights of the tested modules are equal; the formula is as follows:

[0104] ΔP1, ΔP2, ΔP3, and ΔP4 represent the regional pressure differences corresponding to each measured module, and ρ represents the fluid density.

[0105] k1, k2, k3, and k4 are the theoretical flow coefficients of the four measured modules at different flow velocities. In this invention, the theoretical flow coefficient refers to the flow coefficient of the measurement sub-channel containing the measured module when placed in a straight uniform flow field, with a preset flow velocity corresponding to the corresponding pressure difference; when there are no spacers between the measured modules, the measurement sub-channel is the fluid measurement channel; the local measurement area corresponding to the measured module is called the measurement sub-region. The above measurement and calculation achieve a relatively accurate measurement of the total flow rate of the fluid measurement channel.

[0106] Then, eight unified switching valves (v0, v01hb, v01lb, v02hb, v02lb, v03hb, v03lb, v04hb, and v04lb) were closed. The following valves were then opened: the first high-pressure valve (v01ha), the second high-pressure valve (v02ha), the third high-pressure valve (v03ha), the fourth high-pressure valve (v04ha), the first low-pressure valve (v01la), the second low-pressure valve (v02la), the third low-pressure valve (v03la), and the fourth low-pressure valve (v04la). The average pressure difference Δp of the four regions was measured. a The calculation can be simplified; the simplified formula is:

[0107] K a For the entire averaging tube at ΔP a The corresponding theoretical flow coefficient.

[0108] Under conditions of insufficiently developed flow, and when the flow velocities of the four measured modules are not significantly different, the above simplified calculation formula has a certain degree of accuracy.

[0109] Traditional averaging pitot tubes connect the total pressure measurement orifice and the low-pressure measurement orifice for measurement. The high-pressure average and low-pressure average differ from the arithmetic mean. Under fully developed flow conditions, the accuracy is high when calculated using the flow coefficient. However, in some underdeveloped flow conditions, measurement accuracy is lost. Severe non-uniform velocity distribution and asymmetry increase the flow velocity inside the detection tube cavity, causing large local pressure losses, deviations of the average pressure from the designed theoretical average, and enhanced flow within the detection tube cavity, leading to varying degrees of reduced averaging performance. In some cases, increased fluid inflow and outflow velocities at the measurement orifices cause the collected pressure values ​​to deviate significantly from the actual total or low pressure values ​​at the measurement orifices. Under certain measurement conditions, the static pressure difference at the measurement cross-section is too large, and the distribution characteristics may change with the total flow rate. The principle of average measurement dictates that static pressure distribution differences affect measurement accuracy and further impact the establishment of the mathematical relationship between the measured average velocity and the actual average velocity, posing difficulties for numerical correction in some cases.

[0110] By adopting the solution of this invention, fluid flow between the tested modules is completely eliminated, and fluid inflow and outflow at the measuring orifice of the detection tube are largely eliminated. Furthermore, its measurement principle determines that the uneven distribution of static pressure in the fluid measurement channel has virtually no impact on measurement accuracy. Under certain operating conditions, the simplified calculation formula described above significantly improves measurement accuracy compared to traditional averaging pitot tube measurements, and can already meet the accuracy requirements of some engineering measurements. Simultaneously, adopting the solution of this invention greatly reduces the risk of dust accumulation inside the detection tube.

[0111] Furthermore, v0 and ΔP can be recorded for the same total flow rate. a The total flow rate can be continuously changed to measure and calculate different values ​​of v0 and ΔP. a The values ​​form a sample database, which can then be used to establish a ΔP-value database through interpolation or fitting. a The function v0 = f(ΔP) is the independent variable and the function value is the function v0 = f(ΔP). a It can be applied to measurements. Experiments can also be conducted under different ρ and viscosity coefficient ν conditions to obtain functions of multiple independent variables for measurement.

[0112] Since this invention measures the arithmetic mean, under the condition that the flow field distribution characteristics of the fluid measurement channel remain unchanged under the same total flow rate, the function v0=f(ΔP) a This will enable rapid and accurate measurements. In practical engineering, in most cases, the flow field distribution characteristics of large-sized ducts and fluid pipelines remain unchanged when the total flow rate is constant. Therefore, this function can achieve rapid and accurate measurement and monitoring, and has significant application value.

[0113] Before measurement, the measuring device can open eight unified switching valves, close all high-pressure measuring valves and low-pressure measuring valves, and open the balance switching valve to make the pressure in each first chamber and second chamber equal, thereby performing zero-point calibration before measurement.

[0114] Obviously, by using multiple L-shaped Pitot tubes or multiple S-shaped Pitot tubes, and optimizing the structural design, and then using the same switching valve assembly, the above measurements will achieve a significant improvement in measurement accuracy. The same design applies to Fechheimer type Pitot tubes and other types of averaging pitot tubes.

[0115] Figure 12 is a schematic diagram of the measuring valve assembly in Application Example 2, which is a flow measurement system composed of four diamond-shaped averaging pitot tubes. Each measured module composed of one diamond-shaped averaging pitot tube has four total pressure measuring ports 00h and four low pressure measuring ports 00l. The four average differential pressure measuring components respectively have the following: the fifth measured high pressure nozzle 1205h and the fifth measured low pressure nozzle 1205l; the sixth measured high pressure nozzle 1206h and the sixth measured low pressure nozzle 1206l; the seventh measured high pressure nozzle 1207h and the seventh measured low pressure nozzle 1207l; and the eighth measured high pressure nozzle 1208h and the eighth measured low pressure nozzle 1208l.

[0116] Figure 12 is a schematic diagram of the measuring valve group in Application Example 2. The measurement principle is the same as that of the new averaging pitot tube. After measuring the arithmetic mean of the switching valve's action, a simple flow rate calculation can be achieved. Furthermore, under the same operating steps, after achieving a unified differential pressure measurement, a more accurate flow rate measurement can be obtained by calculating the regional differential pressure corresponding to the four measured modules, thus obtaining the function v0 = f(ΔP). a It is used in measurement.

[0117] The above process can be summarized as follows: A measurement switching valve is used to switch between unified differential pressure measurement and arithmetic mean measurement of differential pressure in each region; unified differential pressure measurement enables individual measurement of differential pressure in each region; the calculation circuit calculates the average flow velocity related variables of the measurement sub-region based on the differential pressure in each region, thereby obtaining the average flow velocity related variables of the measurement region; a functional relationship is established between the average flow velocity related variables and the arithmetic mean of the measurement region; and this functional relationship is applied to the calculation of the average flow velocity related variables of the measurement region. The average flow velocity related variables include the average flow velocity related variables corresponding to the regional differential pressure of the measured module with only one total pressure measurement point; the average flow velocity related variables include the regional differential pressure.

[0118] In this invention, signal transmission includes transmission via wired or wireless communication; circuitry includes circuitry of devices such as remote computers and PLCs.

[0119] The valve assembly and measuring tube components of the aforementioned average differential pressure measuring device, including the measuring tube 13, can utilize a thinner measuring tube, allowing for modular design and the creation of a miniaturized switching module for ease of use. Furthermore, the measuring switching valve is not limited to an electric valve; a manual valve can be used for switching, saving costs. Additionally, a mechanical indicating mechanism can be employed to achieve simple monitoring and display of average flow velocity-related variables.

[0120] The module under test can be designed with spaced components to form a measurement sub-channel, as shown in Figure 5 of CN 116295672 A, to further improve measurement accuracy; furthermore, setting a rectifier component in front of the module under test will improve measurement accuracy and stability.

[0121] The flow measurement device can use any differential pressure measuring device of the above form to measure the arithmetic mean of multiple fluid differential pressures. Specifically, it can be summarized as follows: the device includes multiple measured modules and a differential pressure measuring device. The measured modules are set in the measurement area and connected to the differential pressure measuring device through a pressure measurement channel to measure the regional differential pressure. The flow measurement device calculates or displays the average flow velocity related variables of the measurement area based on the regional differential pressure. Its characteristic is that the flow measurement device includes the measurement of the arithmetic mean of at least some regional differential pressures and applies it to the calculation or display of the average flow velocity related variables.

[0122] Furthermore, the measuring diaphragm units in the aforementioned fluid differential pressure measuring device can employ different pressure sensing areas to achieve different weighted arithmetic mean measurements.

[0123] 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.

[0124] In the description of this invention, it should be understood that the terms "upper", "lower", "horizontal", "middle", "center", "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 limiting the invention.

[0125] 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 invention should be included within the protection scope of this invention.

Claims

1. A fluid differential pressure measurement device, characterized by The measurement device comprises a plurality of measurement diaphragms, each of which is located between a first cavity and a second cavity to form a plurality of measurement diaphragm units, and a push rod penetrating and connecting the measurement diaphragms, the measurement diaphragm units sensing fluid pressure difference and generating corresponding axial forces, the axial forces acting on the push rod together; the first cavity and the second cavity have a through hole, the edge of the through hole is connected with the push rod, and the connection structure comprises an expansion part for realizing isolation of the measurement pressure space of the corresponding cavity and displacement of the push rod; the through hole and the expansion part have a preset shape and area, so that the high-pressure effective sensing area and the low-pressure effective sensing area of the corresponding measurement diaphragm unit are equal; the back pressure space of the expansion part and the back pressure space at both ends of the push rod are configured to have equal pressure; the push rod conducts the resultant force of the axial forces to a sensor or a mechanical indicating mechanism, for realizing measurement of a variable related to the average value of the corresponding fluid pressure difference of the measurement diaphragm units.

2. The measuring device of claim 1, wherein, The equal pressure is the ambient air pressure.

3. The measuring device of claim 1, wherein, The back pressure space of the expansion part and the back pressure space at both ends of the push rod are connected through a pipeline and connected to the same pressure space, realizing the same pressure.

4. The measuring device of claim 1, wherein, The measurement device is configured to perform zero calibration and measurement when the push rod is in a vertical state.

5. The measuring device of claim 1, wherein, The measurement device is configured to perform zero calibration and measurement when the push rod is in a horizontal state.

6. The measuring device of claim 1, wherein, A damping part is arranged between the push rod and the sensor for damping the resultant force; a limiting part is arranged on the push rod for overpressure protection.

7. The measuring device of claim 1, wherein, A pull rope is connected to the push rod for limiting the push rod.

8. The measuring device of claim 1, wherein, An intermediate diaphragm is arranged between the push rod and the sensor, the intermediate diaphragm senses the resultant force and transmits the corresponding pressure to one side of a pressure difference sensitive layer in the sensor through an intermediate medium.

9. The measuring device of claim 8, wherein, A semiconductor strain gauge is arranged on the pressure difference sensitive layer, the semiconductor strain gauge senses the pressure from the intermediate medium through piezoresistive effect.

10. The measuring device of claim 8, wherein, The pressure difference sensitive layer is a movable electrode plate of a sensing capacitor.

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