Laminar flow differential pressure type high-precision gas mass flow controller

Abstract

This application discloses a laminar flow differential pressure type high-precision gas mass flow controller, comprising: a housing, a laminar flow sensing unit disposed within the housing, a signal acquisition and conditioning module, a digital signal processing and control module, a drive and execution module, and a communication and diagnostic module. The digital signal processing and control module calculates the current mass flow rate based on a built-in Hagen-Poiseuille law modified for gas compressibility, compares the results, and generates a control signal which is output to the drive and execution module. This application effectively addresses the shortcomings of existing laminar flow differential pressure type gas mass flow controllers in terms of measurement linearity, disturbance rejection capability, sensor reliability, and environmental adaptability through structural innovation of the laminar flow sensing unit, cascade feedforward composite control strategy, soft measurement redundancy mechanism, and multivariable real-time compensation, achieving high-precision, high-reliability, and highly environmentally adaptable gas mass flow control.

Description

Technical Field

[0001] This application belongs to the field of flow measurement and control technology, specifically relating to a laminar flow differential pressure type high-precision gas mass flow controller. Background Technology

[0002] With the rapid development of strategic industries such as semiconductor manufacturing, biopharmaceuticals, new energy (such as hydrogen energy), and precision chemicals, precise control of process gas flow has become a key factor affecting product quality, production efficiency, and process safety. As a core component of precision gas flow control, the mass flow controller (MFC) directly impacts product yield and production costs through its accuracy, stability, and reliability. A mass flow controller is a closed-loop controller that can precisely and stably control the gas "quantity" based on setpoints, unaffected by gas pressure or temperature.

[0003] Currently, mainstream MFC technologies are mainly divided into two categories: thermal and laminar flow differential. Thermal MFC achieves flow control by measuring the gas's thermal conductivity characteristics. This technology is relatively mature and widely used, but it suffers from the following problems in practical applications:

[0004] First, it is highly gas-dependent. The measurement results of thermal MFC are highly dependent on the type, composition, and thermal properties (such as specific heat capacity) of the gas, requiring calibration and conversion factor adjustment for each gas. For mixed gases or process gases with fluctuating composition, the measurement basis of thermal MFC will be shaken, leading to zero drift, range changes, and control inaccuracies.

[0005] Secondly, long-term stability is insufficient. The heating element and temperature sensor of the thermal MFC operate at high temperatures for extended periods, posing risks of aging and coating contamination, which can easily lead to measurement drift. Its zero point is also susceptible to changes in ambient and gas temperatures, resulting in significant temperature drift. Furthermore, the heating wire is easily corroded by corrosive gases and affected by impurities in the gas (such as particulate matter and oil), leading to decreased measurement accuracy.

[0006] Third, controlling extremely low flow rates is difficult. In the extremely low flow rate range of milliliters / minute, the measurement signal of thermal MFC is weak, and the accuracy and control performance are often difficult to guarantee.

[0007] In contrast, laminar flow differential pressure MFC is based on the laminar flow phenomenon in fluid mechanics. It calculates the flow rate by measuring the pressure difference across a precision flow channel in laminar flow conditions, following the Hagen-Poiseuille law. This principle makes the pressure difference and mass flow rate inherently linear, offering advantages such as strong gas compatibility, no need to set conversion coefficients for each gas, and the ability to directly measure multiple gases.

[0008] However, existing laminar pressure differential gas mass flow controllers still have the following shortcomings:

[0009] First, the design of the laminar flow sensing element is not reasonable enough, affecting the measurement accuracy. Conventional capillary laminar flow measurement technology suffers from nonlinear problems such as inlet and outlet pressure losses in the laminar flow sensing element structure. The nonlinear pressure loss in the initial stage of laminar flow and the local inlet and outlet losses are difficult to effectively separate from the frictional pressure drop along the flow path in fully developed laminar flow, which interferes with the linear relationship between the differential pressure signal and the mass flow rate, thus affecting the measurement accuracy.

[0010] Second, the ability to withstand upstream pressure disturbances is insufficient. In actual operation, the pressure in the pipeline often fluctuates significantly. When the upstream pressure changes abruptly, traditional control strategies respond with lag, and the accuracy and stability of flow control will decrease significantly. Especially in processes such as semiconductor thin film deposition, which have extremely high requirements for flow accuracy, even a small flow deviation can lead to uneven film thickness and a decrease in chip yield.

[0011] Third, there is a lack of emergency protection mechanisms in case of sensor failure. Differential pressure sensors are the core measuring components of laminar flow mass flow control systems, and their performance significantly impacts the accuracy of the entire system. When the differential pressure sensor becomes inaccurate due to aging, interference, or performance instability, the flow accuracy of the control system also decreases. In applications such as chip manufacturing, where extremely high precision in gas flow control is required, sensor failure will severely affect product quality. Existing products lack effective redundancy and fault-tolerant mechanisms in case of differential pressure sensor malfunction.

[0012] Fourth, the system's self-diagnostic capabilities are insufficient. Existing laminar flow differential pressure MFCs lack systematic health status detection and fault early warning functions, and cannot automatically detect abnormal states such as leaks and sensor zero drift during equipment operation. This makes it difficult for users to promptly identify and eliminate potential faults. Summary of the Invention

[0013] This application provides a laminar flow differential pressure type high-precision gas mass flow controller, which aims to solve the problems of unreasonable laminar flow element structure design in the prior art, which affects measurement accuracy, insufficient resistance to upstream pressure disturbances, lack of emergency protection mechanism when sensor fails, and insufficient system self-diagnosis capability.

[0014] A laminar differential pressure high-precision gas mass flow controller includes: a housing, a laminar flow sensing unit disposed within the housing, a signal acquisition and conditioning module, a digital signal processing and control module, a drive and execution module, and a communication and diagnostic module;

[0015] The laminar flow sensing unit adopts a pressure differential type dual-channel cross-symmetrical structure, including a first branch and a second branch arranged in parallel inside the unit body. The first branch and the second branch have the same channel diameter and are arranged in parallel with each other. The inlet ends of the two branches are connected to the upstream side of the gas channel, and the outlet ends of the two branches are connected to the downstream side of the gas channel.

[0016] A first capillary group and a third capillary group are connected in series along the airflow direction on the first branch, and a second capillary group and a fourth capillary group are connected in series along the airflow direction on the second branch. Each of the first, second, third, and fourth capillary groups is composed of multiple stainless steel capillary tubes of the same inner diameter connected in parallel. The first and fourth capillary groups have the same length, the second and third capillary groups have the same length, and the length of the second capillary group is greater than the length of the first capillary group.

[0017] In the first branch, a first pressure-taking chamber is formed between the first capillary group and the third capillary group; in the second branch, a second pressure-taking chamber is formed between the second capillary group and the fourth capillary group; a first pressure-taking port is provided on the side wall of the first pressure-taking chamber; a second pressure-taking port is provided on the side wall of the second pressure-taking chamber; the first pressure-taking port and the second pressure-taking port are respectively connected to the two sensing ports of the external differential pressure sensor through the pressure-taking channel of the housing.

[0018] The laminar flow sensing unit is specifically configured such that: gas flows sequentially through the first capillary group and the third capillary group via the first branch, and sequentially through the second capillary group and the fourth capillary group via the second branch. Utilizing the cross-symmetry of the two branches, the pressure difference between the first pressure tap and the second pressure tap corresponds to the frictional pressure drop along the path of fully developed laminar flow within the length difference between the second capillary group and the first capillary group, thereby creating a linear relationship between the differential pressure signal and the mass flow rate of the gas flowing through the laminar flow sensing unit.

[0019] The signal acquisition and conditioning module is electrically connected to the laminar flow sensing unit and the digital signal processing and control module, respectively. It is used to acquire the differential pressure signal output by the laminar flow sensing unit, the absolute pressure signal at the two branch pressure taps, and the temperature signal in the gas flow channel. After amplifying, filtering, and analog-to-digital conversion of the above signals, it generates digital signal data and transmits it to the digital signal processing and control module.

[0020] The digital signal processing and control module receives the digitized signal data, calculates the current mass flow rate according to the built-in Hagen-Poiseuille law with gas compressibility correction, compares the calculated mass flow rate with the externally input flow rate setpoint, and generates a control signal to output to the drive and execution module.

[0021] The drive and execution module receives the control signal, converts it into a drive signal, amplifies the power, and then drives the proportional regulating valve to adjust the gas flow rate.

[0022] The communication and diagnostic module is bidirectionally connected to the digital signal processing and control module, and is used to realize data communication with the host computer and system self-diagnosis.

[0023] Optionally, the lengths of the first capillary group and the fourth capillary group are denoted as... The lengths of the second capillary group and the third capillary group are denoted as . ,and , and The difference ΔL is the effective measurement length;

[0024] The number of capillaries and their inner diameter are the same in each capillary group. The portion of the second capillary group whose length exceeds that of the first capillary group is a fully developed laminar flow section. The pressure difference value corresponds only to the frictional pressure drop along the frictional flow section.

[0025] Optionally, the signal acquisition and conditioning module includes a differential pressure sensor, a first pressure sensor, a second pressure sensor, a temperature sensor, and a signal conditioning unit;

[0026] The high-pressure port of the differential pressure sensor is sealed to the first pressure tapping port through a first pressure tapping pipeline, and the low-pressure port is sealed to the second pressure tapping port through a second pressure tapping pipeline. The differential pressure sensor is used to detect the pressure difference between the first pressure tapping port and the second pressure tapping port and convert it into a first differential voltage signal output.

[0027] The sensing end of the first pressure sensor extends into the first pressure tapping chamber to detect the absolute pressure at the first pressure tapping port and convert it into a second voltage signal output.

[0028] The sensing end of the second pressure sensor extends into the second pressure tapping chamber to detect the absolute pressure at the second pressure tapping port and convert it into a third voltage signal output.

[0029] The probe of the temperature sensor extends into the gas flow channel to detect the real-time temperature of the gas flowing through it and convert it into a fourth resistance signal output.

[0030] The signal conditioning unit receives the first differential voltage signal, the second voltage signal, the third voltage signal, and the fourth resistance signal respectively, and performs amplification, filtering, and analog-to-digital conversion in sequence to generate digitized differential pressure data, first pressure data, second pressure data, and temperature data, which are then transmitted to the digital signal processing and control module.

[0031] Optionally, the digital signal processing and control module includes a flow calculation unit and a multivariable collaborative compensation unit;

[0032] The flow calculation unit receives the differential pressure data, the first pressure data, the second pressure data, and the temperature data output by the signal acquisition and conditioning module, and calculates the current mass flow rate according to the built-in Hagen-Poiseuille law corrected for gas compressibility.

[0033] The multivariable collaborative compensation unit is bidirectionally connected to the flow calculation unit and has a built-in gas property database. The multivariable collaborative compensation unit queries the property database based on the temperature data, the first pressure data, and the second pressure data to calculate the gas density and dynamic viscosity under the current temperature and pressure conditions, and feeds back the calculated dynamic viscosity to the flow calculation unit in real time to replace the viscosity parameter in the calculation model to achieve dynamic compensation for the influence of temperature on gas viscosity.

[0034] The flow calculation unit outputs the calculated current mass flow rate to the deviation calculation unit and the communication interface unit.

[0035] Optionally, the digital signal processing and control module further includes a deviation calculation unit and a cascade control unit;

[0036] The deviation calculation unit receives the current quality flow rate output by the flow calculation unit and the flow rate setting value input by the host computer forwarded by the communication interface unit, calculates the flow rate deviation value by subtracting the flow rate setting value from the current quality flow rate, and outputs it to the main controller of the cascade control unit.

[0037] The cascade control unit is composed of the main controller and the secondary controller connected in series. The main controller takes the flow deviation value as input, generates a pressure setpoint through proportional-integral-derivative control calculation, and outputs it to the secondary controller. The secondary controller takes the difference between the pressure setpoint and the first pressure data as the pressure deviation value, generates a valve opening control quantity through proportional-integral control calculation, and outputs it to the drive and execution module.

[0038] Optionally, the digital signal processing and control module further includes a feedforward compensation unit;

[0039] The feedforward compensation unit receives the first pressure data in real time, performs discrete difference operation on the first pressure data to calculate the upstream pressure change rate, and generates a feedforward compensation amount based on the product of the preset feedforward gain coefficient and the pressure change rate, and outputs it to the feedforward superimposed unit of the cascade control unit.

[0040] The feedforward superimposition unit superimposes the valve opening control quantity and the feedforward compensation quantity to generate a final control signal, which is then output to the drive and execution module.

[0041] When the feedforward compensation unit detects that the upstream pressure change rate exceeds a preset threshold, it immediately generates a corresponding feedforward compensation amount, so that the proportional control valve can perform a pre-adjustment action before the flow deviation is formed.

[0042] Optionally, the drive and execution module is connected in series along the signal flow direction by a digital-to-analog converter, a drive amplifier, and the proportional control valve;

[0043] The digital-to-analog conversion unit receives the final control signal in digital form output by the digital signal processing and control module, converts it into an analog voltage signal or an analog current signal, and outputs it to the drive amplifier unit.

[0044] The drive amplification unit amplifies the analog voltage signal or analog current signal and outputs a drive current to the drive coil of the proportional control valve to drive the valve core of the proportional control valve to generate displacement, thereby changing the flow area of ​​the valve port to achieve proportional regulation of the gas flow rate.

[0045] Optionally, the communication and diagnostic module includes a soft measurement unit and a comparison and selection unit;

[0046] The soft measurement unit receives the first pressure data, the second pressure data, and the temperature data respectively, calculates the theoretical estimate of the differential pressure based on the gas state equation and the impedance characteristics of the laminar flow element, and outputs it to the comparison and selection unit.

[0047] The comparison and selection unit receives the actual differential pressure value and the theoretical differential pressure estimate, respectively, calculates the relative deviation between the two, and when the relative deviation is continuously less than a preset threshold, selects the actual differential pressure value and outputs it to the flow calculation unit; when the relative deviation continuously exceeds the preset threshold and the duration exceeds a preset judgment time, it determines that the differential pressure sensor is abnormal, automatically switches to the theoretical differential pressure estimate as the input of the flow calculation unit, and generates a sensor abnormality flag bit and uploads it to the host computer through the communication interface unit.

[0048] Optionally, the main controller forms a flow loop, the secondary controller forms a pressure loop, the main controller uses the flow deviation as input and outputs a pressure setpoint to the secondary controller, and the secondary controller uses the pressure deviation as input and outputs a valve opening control quantity to the drive and execution module;

[0049] When the upstream pressure changes abruptly, the pressure loop responds quickly and suppresses the pressure disturbance, the flow loop ensures that the flow accurately tracks the set value, and the main controller and the secondary controller work together to form a cascade feedforward composite control.

[0050] Compared with the prior art, this application has at least the following beneficial effects:

[0051] This application employs a laminar flow sensing unit with a pressure differential dual-channel cross-symmetrical structure. The first and second branches have identical structural parameters, differing only in the relative positions of the long and short capillary groups. Through the cross-symmetrical arrangement of the two branches, the pressure difference between the first and second pressure taps effectively offsets local inlet and outlet losses and nonlinear pressure losses in the initial laminar flow section, ensuring that the differential pressure signal corresponds only to the frictional pressure drop along the fully developed laminar flow section. This fully developed laminar flow section satisfies the applicability conditions of the Hagen-Poiseuille law, thus exhibiting an ideal linear relationship between the differential pressure signal and the gas mass flow rate flowing through the laminar flow sensing unit, significantly improving measurement accuracy.

[0052] The digital signal processing and control module of this application adopts a cascaded feedforward composite control strategy. The main controller forms a flow loop (outer loop), using the flow deviation as the input and output pressure setpoints; the secondary controller forms a pressure loop (inner loop), using the pressure deviation as the input and output valve opening control quantity; the feedforward compensation unit detects the upstream pressure change rate in real time and generates the feedforward compensation quantity. When the upstream pressure changes abruptly, the inner loop (pressure loop) can respond quickly and suppress pressure disturbances, while the outer loop (flow loop) ensures that the flow accurately tracks the setpoint. Based on this, the feedforward compensation enables the regulating valve to make pre-adjustment actions before the flow deviation is formed. The three work together to effectively avoid the problem of inaccurate flow accuracy in the control system caused by sudden changes in fluid pressure.

[0053] The communication and diagnostic module of this application includes a soft-sensing unit and a comparison and selection unit. The soft-sensing unit calculates the theoretical estimate of the differential pressure in real time based on the gas state equation and the impedance characteristics of the laminar flow elements; the comparison and selection unit continuously compares the deviation between the actual differential pressure value and the theoretical estimate. When the deviation continuously exceeds a preset threshold, the differential pressure sensor is automatically identified as malfunctioning, and the system switches to the soft-sensing output value as the input for flow calculation. This mechanism avoids the problem of decreased flow accuracy in the control system caused by deterioration in the performance of the differential pressure sensor, significantly improving the system's reliability and fault tolerance.

[0054] The communication and diagnostic module of this application includes a self-diagnostic unit that can automatically perform system health status checks at preset diagnostic time points. After the proportional control valve enters a fully closed state, it monitors the pressure decay curve to calculate the system leakage rate and detects zero drift of the differential pressure sensor when the valve is closed. The self-diagnostic unit summarizes the detection results, generates a diagnostic report, and uploads it to the host computer or stores it locally, enabling users to promptly detect abnormal states such as leaks and sensor zero drift, facilitating preventative maintenance and troubleshooting.

[0055] The multivariable collaborative compensation unit of this application incorporates a physical property database containing density-temperature-pressure and viscosity-temperature relationship tables for various common gases. This unit receives temperature and pressure data in real time, queries the physical property database, and uses interpolation methods to calculate the gas density and dynamic viscosity under the current conditions. The calculated dynamic viscosity is then fed back to the flow calculation unit in real time to replace the viscosity parameters in the model. This mechanism achieves dynamic compensation for the influence of temperature changes on gas viscosity, effectively suppressing the impact of ambient temperature fluctuations on measurement accuracy.

[0056] This application is based on the laminar pressure differential measurement principle of Hagen-Poiseuille's law, where the linear relationship between differential pressure and mass flow rate is independent of the gas type. Users only need to select the current gas to be measured through the gas type selection interface, and the multivariate collaborative compensation unit will then call the corresponding physical property parameters for compensation calculation. Compared to thermal MFCs, which require calibration and conversion coefficient adjustment for each gas, this application significantly reduces the user's operational complexity and operating costs.

[0057] This application effectively addresses the shortcomings of existing laminar differential pressure gas mass flow controllers in terms of measurement linearity, anti-disturbance capability, sensor reliability, and environmental adaptability through structural innovation of laminar flow sensing units, cascade feedforward composite control strategy, soft measurement redundancy mechanism, and multivariable real-time compensation. It achieves high-precision, high-reliability, and strong environmental adaptability gas mass flow control. Attached Figure Description

[0058] Figure 1 A schematic diagram of module connections for a laminar flow differential pressure type high-precision gas mass flow controller provided in one embodiment of this application;

[0059] Figure 2 This is a planar schematic diagram of the laminar flow sensing unit of a laminar flow differential pressure type high-precision gas mass flow controller provided in one embodiment of this application. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0061] This application provides a laminar flow differential pressure type high-precision gas mass flow controller, such as... Figure 1 As shown, it includes: a housing, a laminar flow sensing unit disposed within the housing, a signal acquisition and conditioning module, a digital signal processing and control module, a drive and execution module, and a communication and diagnostic module;

[0062] The housing has a hollow cylindrical structure, integrally formed from stainless steel, and is divided into an inlet section, a sensing section, and an outlet section along its length. The inlet section has an airflow inlet, and the outlet section has an airflow outlet. Both the inlet and outlet are standard pipe thread interfaces for sealing connections with external air supply and exhaust pipes. The sensing section contains an axially continuous gas flow channel with an inner diameter larger than the inlet and outlet diameters. This allows the airflow to expand and slow down upon entering the housing, reducing flow disturbance at the inlet.

[0063] The gas flow channel is arranged sequentially along the airflow direction with mounting positions for rectifier elements, laminar flow sensing units, and regulating valves, with each mounting position separated by a smoothly transitioned stepped surface or a sealing end face. Several pressure tapping channels are provided on the sidewall of the sensing section of the housing, each extending radially into the gas flow channel for mounting the sensing ends of differential pressure sensors and pressure sensors.

[0064] The outlet section sidewall of the housing has a sensor interface for installing a temperature sensor. The probe of the temperature sensor extends into the gas flow channel to detect the temperature of the gas flowing through it.

[0065] The exterior of the housing has several mounting bosses and threaded connection holes for fixing and mounting the circuit board assemblies of the signal acquisition and conditioning module, digital signal processing and control module, and communication and diagnostic module. Both ends of the housing also have sealing grooves, in which O-rings are embedded to form a sealing fit with the external pipe joint on the airflow inlet side and the regulating valve assembly on the airflow outlet side, respectively.

[0066] like Figure 2 As shown, the laminar flow sensing unit has an overall columnar structure and is fixedly installed in the gas flow channel of the sensing section of the housing. The laminar flow sensing unit adopts a pressure difference type dual-channel cross-symmetrical structure, including a first branch and a second branch arranged in parallel inside the unit body. The flow channels of the first branch and the second branch have the same diameter and are connected in parallel. The inlet ends of the two branches are connected to the upstream side of the gas flow channel, and the outlet ends of the two branches are connected to the downstream side of the gas flow channel, so that the gas entering the laminar flow sensing unit is evenly distributed to flow in the two branches.

[0067] On the first branch, a first capillary group and a third capillary group are connected in series along the airflow direction. On the second branch, a second capillary group and a fourth capillary group are connected in series along the airflow direction. Each of the first, second, third, and fourth capillary groups consists of multiple stainless steel capillary tubes of the same inner diameter connected in parallel. The number of capillary tubes and their inner diameter are the same in each capillary group. The first and fourth capillary groups have the same length, denoted as _____. The second capillary group and the third capillary group have the same length, denoted as... ,and The difference in length between the two That is, the effective measurement length;

[0068] The capillary assemblies are arranged in a symmetrical manner in the two branches: the first capillary assembly in the first branch (length...) Upstream, the third capillary group (length) Downstream; in the second branch, the second capillary group (length) Upstream, fourth capillary group (length) Downstream. Thus, the two branches have identical structural parameters except for the relative positions of the long and short capillary groups, resulting in identical flow resistance characteristics. Both ends of each capillary group are fixed to the branch flow channel via tube sheets, forming pressure-tapping chambers between adjacent capillary groups;

[0069] A first pressure tap is provided on the side wall of the pressure tapping chamber between the first and third capillary groups in the first branch, and a second pressure tap is provided on the side wall of the pressure tapping chamber between the second and fourth capillary groups in the second branch. The first and second pressure taps are respectively connected to the two sensing ports of an external differential pressure sensor through the pressure tapping channel of the housing. The pressure at the first pressure tap is denoted as... The pressure at the second pressure tap is recorded as The difference between the two This is the pressure difference value.

[0070] When the laminar flow sensing unit is working, the gas enters from upstream and splits into two paths, flowing through the first branch and the second branch respectively. In the first branch, the gas flows sequentially through a length of... The first capillary group and its length are The third capillary group; in the second branch, the gas flows sequentially through a length of The second capillary group and its length are The fourth capillary group. Due to the cross-symmetry in the structure of the two branches, the local inlet and outlet losses and nonlinear pressure losses in the laminar flow initiation section of the first capillary group in the first branch are similar to those in the first half of the second capillary group in the second branch (length is...). The corresponding losses of the first capillary group in the first branch are completely equal to those of the first half of the second capillary group in the second branch.

[0071] Therefore, the pressure at the first pressure tap Pressure at the second pressure tap After subtraction, the equal pressure losses mentioned above cancel each other out, and the pressure potential difference ΔP corresponds only to the latter half of the second capillary group (length is...). The laminar flow frictional pressure drop is fully developed within the laminar flow sensing unit. The flow in this latter half is completely free from the influence of the inlet section, satisfying the applicable conditions of the Hagen-Poiseuille law, thus resulting in an ideal linear relationship between the differential pressure signal and the gas mass flow rate flowing through the laminar flow sensing unit.

[0072] The signal acquisition and conditioning module is fixedly installed in the circuit board mounting cavity on one side of the housing. It is electrically connected to the first pressure tap and the second pressure tap of the laminar flow sensing unit, as well as the temperature sensor interface in the gas flow channel, via flexible ribbon cables or shielded cables. This module is used to acquire the differential pressure signal output by the laminar flow sensing unit, the absolute pressure signals at the two branch pressure taps, and the temperature signal in the gas flow channel in real time. It then amplifies, filters, and performs analog-to-digital conversion on the raw electrical signals output by the sensors from each branch, generating digital signal data that can be directly read and processed by the digital signal processing and control module.

[0073] The signal acquisition and conditioning module mainly consists of a differential pressure sensor, a first pressure sensor, a second pressure and temperature sensor, and a signal conditioning unit.

[0074] The differential pressure sensor employs a piezoresistive differential pressure sensing chip. Its high-pressure port is sealed and connected to a first pressure tapping port via a first pressure tapping pipeline, and its low-pressure port is sealed and connected to a second pressure tapping port via a second pressure tapping pipeline. The differential pressure sensor detects the pressure difference between the first and second pressure tapping ports and converts it into a first differential voltage signal output.

[0075] To avoid gas stagnation or pressure transmission lag in the pressure tapping lines, the inner diameter of both the first and second pressure tapping lines is not less than 2 mm, and the length of the lines is controlled within 50 mm. A microporous damping element is provided at the connection between the pressure tapping lines and the pressure tapping ports to suppress the interference of airflow pulsation on the differential pressure measurement value.

[0076] The first pressure sensor is fixedly installed on the side wall of the housing near the first pressure tapping port. Its sensing end extends through the pressure tapping channel of the housing side wall into the first pressure tapping chamber where the first pressure tapping port is located. It is used to detect the absolute pressure at the pressure tapping chamber downstream of the first capillary group in the first branch and convert the pressure value into a second voltage signal output.

[0077] The second pressure sensor is fixedly installed on the side wall of the housing near the second pressure port. Its sensing end extends through the pressure tapping channel on the side wall of the housing into the second pressure tapping chamber where the second pressure tapping port is located. It is used to detect the absolute pressure at the pressure tapping chamber downstream of the second capillary group in the second branch and convert the pressure value into a third voltage signal output.

[0078] Both the first and second pressure sensors are absolute pressure piezoresistive sensors with a range of 0–200 kPa (absolute pressure) and an accuracy of no less than ±0.1%FS, to ensure the accuracy of pressure data under low-pressure gas measurement conditions. The first and second pressure sensors are set independently, used for density and viscosity correction in flow calculations, and also to provide pressure feedback signals for the secondary control loop in cascade control.

[0079] The temperature sensor employs a platinum resistance temperature sensing element, fixedly installed within the sensor interface located on the side wall of the housing's outlet section. Its probe extends into the gas flow channel and is positioned downstream of the laminar flow sensing unit and upstream of the proportional control valve. This installation position avoids interference from the complex flow field within the laminar flow sensing unit on the temperature measurement while ensuring that the measured temperature accurately reflects the temperature of the gas flowing through the unit. The temperature sensor detects the real-time temperature of the flowing gas and converts it into a fourth resistance signal output that varies with temperature.

[0080] The signal conditioning unit is integrated on a printed circuit board, which includes an instrumentation amplifier, an active filter, and an analog-to-digital converter. The instrumentation amplifier is a differential input precision instrumentation amplifier, whose differential input terminals are connected to the differential voltage output terminals of the differential pressure sensor. It is used to amplify the first differential voltage signal output by the differential pressure sensor in a differential mode to suppress common-mode interference.

[0081] The instrumentation amplifier also features three independent single-ended input channels, connected to the signal outputs of the first pressure sensor, the second pressure sensor, and the temperature sensor, respectively, for amplifying the second voltage signal, the third voltage signal, and the fourth resistance signal. The gain of the instrumentation amplifier is programmable and set by the digital signal processing and control module via a serial interface to adapt to signal amplitude variations within different measurement ranges.

[0082] The active filter is a fourth-order Butterworth low-pass filter, whose input is connected to the output of the instrumentation amplifier. Its cutoff frequency is set to 10Hz to filter out high-frequency noise and power frequency interference in the sensor signal. The analog-to-digital converter (ADC) is a 24-bit Σ-Δ type, whose input is connected to the output of the active filter. It synchronously samples and converts the amplified and filtered analog signals at a sampling rate of not less than 1kHz.

[0083] The analog-to-digital converter (ADC) incorporates a programmable gain amplifier and a reference voltage source. The reference voltage source is high-precision, low-drift, with a temperature coefficient not exceeding 5 ppm / ℃ to minimize the impact of ambient temperature variations on conversion accuracy. The ADC converts each analog signal into digitized differential pressure data ΔP and first pressure data. Second pressure data and temperature data T, and via SPI or I 2The C-series data is transmitted to the digital signal processing and control module via the serial data bus.

[0084] The signal conditioning unit is also equipped with an electromagnetic shielding cover, which covers the entire signal conditioning circuit board and is reliably connected to the housing through a grounding terminal to reduce the impact of external electromagnetic interference on weak sensor signals. The power supply for the signal conditioning unit is provided by the power management unit of the digital signal processing and control module. Each sensor and signal conditioning circuit is equipped with an independent low-dropout linear regulator to ensure the stability and purity of the power supply voltage.

[0085] The digital signal processing and control module is fixedly installed in the adjacent cavity of the circuit board mounting cavity where the signal acquisition and conditioning module is located, and is electrically connected to the output terminal of the signal conditioning unit through a board-to-board connector or a flexible ribbon cable.

[0086] This module uses a digital signal processor or high-performance microcontroller as its core computing unit. It integrates a floating-point unit and a hardware multiplier to receive the digitized differential pressure data ΔP and the first pressure data output from the signal acquisition and conditioning module. Second pressure data Based on the temperature data T, the current mass flow rate is calculated according to the built-in Hagen-Poiseuille law with gas compressibility correction. The calculated mass flow rate is compared with the externally input flow rate setpoint, and a control signal is generated and output to the drive and execution module.

[0087] The digital signal processing and control module is internally divided into a flow calculation unit, a multivariable collaborative compensation unit, a deviation calculation unit, a feedforward compensation unit, and a cascade control unit. The units exchange data with each other through an internal data bus.

[0088] The flow calculation unit communicates via SPI or I 2 The C-series data bus is connected to the output of the analog-to-digital converter of the signal conditioning unit, and is used to synchronously receive differential pressure data ΔP and first pressure data. Second pressure data And temperature data T. The flow calculation unit contains a Hagen-Poiseuille law calculation model modified for gas compressibility, whose mathematical expression is:

[0089]

[0090] in, The final output mass flow rate, in kg / h; ΔL is the flow correction coefficient, determined by factory calibration experiments; n is the number of capillaries in a single capillary group; d is the inner diameter of the capillary, in meters; μ(T) is the gas dynamic viscosity at temperature T, obtained by the "multivariable collaborative compensation unit" by querying the physical property database based on temperature T and feeding it back to this formula, in Pa·s; ΔL is the difference in length between long and short capillaries, in meters; ΔP is the pressure potential difference, in Pa. and These are the absolute pressures at the first and second pressure taps, respectively, in Pa. For the current gas at average pressure The real-time density at temperature T is calculated and output in real time by the "multi-variable collaborative compensation unit" calling the gas state equation; This is the gas expansion correction factor; The range of is strictly within the interval (0,1), mathematically it never diverges, and physically it accurately characterizes the effect of relative pressure drop on compressibility;

[0091] The flow calculation unit updates the calculated current mass flow rate at a rate of no less than 100Hz. The results are output to the deviation calculation unit and the communication interface unit, respectively.

[0092] The multivariable collaborative compensation unit is bidirectionally connected to the flow calculation unit and has an electrically erasable programmable read-only memory built in as the storage medium for the gas property database. The database pre-stores density-temperature-pressure relationship tables and viscosity-temperature relationship tables for various common gases (including but not limited to air, nitrogen, argon, carbon dioxide, methane, helium, and hydrogen) in different temperature ranges (-20℃ to +80℃) and different pressure ranges (0 to 1MPa).

[0093] The multivariable collaborative compensation unit receives temperature data T and first pressure data output by the signal conditioning unit in real time. Second pressure data Based on the currently detected gas type identification code, the system queries the physical property database and calculates the gas density ρ(T,P) and dynamic viscosity μ(T) under the current temperature and pressure conditions using linear interpolation or cubic spline interpolation methods. The calculated dynamic viscosity μ(T) is fed back to the flow calculation unit in real time via the internal data bus, replacing the viscosity parameters in the calculation model, thereby achieving dynamic compensation for the influence of temperature changes on gas viscosity.

[0094] The multivariable collaborative compensation unit is also equipped with a gas type selection interface. Users can select the gas type currently being measured through the host computer command of the communication interface unit or the local DIP switch. The multivariable collaborative compensation unit then calls the corresponding physical property parameters to perform compensation calculations.

[0095] The deviation calculation unit is connected to the flow calculation unit and the communication interface unit via an internal data bus, and is used to receive the current quality flow rate output by the flow calculation unit. The flow rate setting value input from the host computer is forwarded by the communication interface unit. The deviation calculation unit contains a subtractor to calculate the flow rate setpoint. Compared with current mass flow rate Difference, calculate the deviation value The deviation value is then output to the main controller of the cascade control unit at an update rate of not less than 100Hz.

[0096] The feedforward compensation unit is connected to the digital output terminal of the first pressure sensor via an internal data bus, and is used to receive the first pressure data in real time. The feedforward compensation unit contains a differentiator to process the first pressure data. Perform discrete difference calculations to determine the rate of change of upstream pressure. , where k is the current sampling time, k-1 is the previous sampling time, and Δt is the sampling interval;

[0097] The feedforward compensation unit calculates the feedforward gain coefficient based on the preset feedforward gain coefficient. With pressure change rate The product generates the feedforward compensation amount. It is then output to the feedforward superimposed unit of the cascade control unit via the internal data bus. Feedforward gain coefficient. After being calibrated at the factory, the settings are stored in the module's non-volatile memory. When the feedforward compensation unit detects that the upstream pressure change rate exceeds the preset threshold, it immediately generates the corresponding feedforward compensation amount, enabling the regulating valve to pre-adjust before the flow deviation is formed, thereby effectively suppressing the disturbance effect of sudden changes in upstream pressure on downstream flow.

[0098] The cascade control unit consists of three parts: a main controller, a secondary controller, and a feedforward superimposed unit, which are connected in series via an internal data bus. The input terminal of the main controller is connected to the output terminal of the deviation calculation unit to receive the flow deviation value. ;

[0099] The main controller employs a digital proportional-integral-derivative (DI-DE) control algorithm to perform proportional, integral, and derivative operations on the deviation value e to generate the pressure setpoint. The proportional gain of the main controller Integral coefficient and differential coefficients After being pre-configured at the factory, the parameters are stored in the module's non-volatile memory. Users can adjust these parameters online via host computer commands through the communication interface unit. The first input terminal of the secondary controller is connected to the output terminal of the primary controller, receiving the pressure setpoint generated by the primary controller. The second input terminal of the secondary controller is connected to the digital output terminal of the first pressure sensor via an internal data bus to receive the actual pressure value. ;

[0100] The secondary controller has a subtractor inside to adjust the pressure setpoint. Compared with actual pressure value Calculate the pressure deviation value by taking the difference. The secondary controller employs a digital proportional-integral control algorithm to control pressure deviation values. Perform proportional and integral calculations to generate the valve opening control quantity. The proportional and integral coefficients of the secondary controller are set at the factory and stored in the module's non-volatile memory;

[0101] The first input of the feedforward accumulator is connected to the output of the secondary controller to receive the valve opening control quantity. The second input terminal of the feedforward superimposed unit is connected to the output terminal of the feedforward compensation unit to receive the feedforward compensation amount. The feedforward accumulator contains an adder to convert the valve opening control quantity... With feedforward compensation Superimposed to generate the final control signal It is then output to the analog-to-digital conversion unit of the drive and execution module via the internal data bus;

[0102] In the aforementioned cascade control unit, the main controller forms the outer loop (flow loop), which takes the flow deviation as input and outputs the pressure setpoint; the secondary controller forms the inner loop (pressure loop), which takes the pressure deviation as input and outputs the valve opening control value.

[0103] When upstream pressure changes abruptly, the inner loop (pressure loop) can respond quickly and suppress pressure disturbances, while the outer loop (flow loop) ensures that the flow rate accurately tracks the setpoint. The feedforward compensation unit, combined with feedforward control, further improves the system's response speed to sudden changes in upstream pressure. These three elements work together to form a cascaded feedforward composite control strategy.

[0104] The digital signal processing and control module also includes a power management unit, which is connected to an external DC power supply. It integrates multiple low-dropout linear regulators and DC-DC converters to provide stable power supplies of different voltage levels to the digital signal processor, various functional units, sensors and signal conditioning circuits.

[0105] The power management unit also includes a power-on reset circuit and a voltage monitoring circuit. When the supply voltage falls below a preset threshold, a reset signal is automatically generated to ensure reliable module reset in case of voltage abnormalities. All computational and control logic of the digital signal processing and control module is driven by embedded firmware stored in the internal flash memory. This firmware supports online upgrades; users can download updated firmware to the module's flash memory via commands from the host computer through the communication interface unit to complete the upgrade.

[0106] The drive and actuation module is fixedly mounted on a mounting bracket on the outside of the housing outlet section and electrically connected to the output terminal of the cascade control unit of the digital signal processing and control module via a shielded cable. This module is used to receive the final digital control signal output by the cascade control unit, convert it into an analog drive signal, amplify its power, and then drive the proportional regulating valve to actuate, thereby precisely regulating the gas flow rate through the housing.

[0107] The drive and execution module consists of three parts in sequence along the signal flow direction: a digital-to-analog conversion unit, a drive amplification unit, and a proportional control valve. The three parts are connected in series through printed wires or shielded cables on the circuit board.

[0108] The digital-to-analog converter (DAC) unit is integrated on the printed circuit board of the drive and execution module. Its digital input terminal is connected to the output terminal of the feedforward superimposed unit of the cascade control unit via a serial peripheral interface (SPI) to receive the final control signal U in digital form. The DAC unit uses a high-precision, low-drift multiplicative DAC chip with a resolution of 16 bits and a setup time of no more than 10 microseconds to ensure fast response and high control resolution of the control signal.

[0109] The digital-to-analog converter (DAC) integrates a high-precision bandgap reference voltage source with a temperature coefficient not exceeding 5 ppm / ℃, providing a stable reference voltage for the analog-to-digital conversion process. The DAC converts the received 16-bit digital control signal into a 0–10V DC analog voltage signal or a 4–20mA DC analog current signal, and outputs it to the drive amplifier unit via its analog output terminal. The output mode of the DAC is configured by the digital signal processing and control module through a mode selection pin. Users can select either voltage or current output mode via host computer commands, based on the input requirements of the subsequent drive amplifier unit and proportional control valve.

[0110] The drive amplification unit is located on the output side of the digital-to-analog converter unit. Its signal input terminal is connected to the analog output terminal of the digital-to-analog converter unit. It is used to receive the analog voltage or current signal output by the digital-to-analog converter unit and amplify the signal to provide sufficient drive power to drive the proportional control valve. The drive amplification unit adopts a voltage-controlled constant current source drive circuit topology, which is mainly composed of an operational amplifier, a power field-effect transistor (MOSFET), and a precision sampling resistor.

[0111] The operational amplifier is configured as a voltage-to-current converter. Its non-inverting input receives the analog voltage signal output by the digital-to-analog converter, its inverting input is connected to the voltage feedback terminal of the precision sampling resistor, and its output is connected to the gate of the power MOSFET.

[0112] The drain of the power MOSFET is connected in series with the drive coil of the proportional control valve and then connected to the power supply. The source is grounded through a precision sampling resistor. The voltage across the precision sampling resistor is fed back to the inverting input of the operational amplifier through a feedback network to form a closed-loop current control.

[0113] When the input voltage changes, the operational amplifier adjusts the conduction level of the power MOSFET to ensure that the current flowing through the proportional control valve drive coil is precisely proportional to the input voltage, thereby achieving linear voltage-to-current conversion and power amplification. The precision sampling resistor has a resistance of 0.1Ω to 0.5Ω and is wound with a low-temperature coefficient manganese-copper alloy. The voltage across its terminals is amplified by a differential amplifier and fed back to the operational amplifier, forming a high-precision current closed-loop control.

[0114] The power supply for the drive amplifier unit is provided by the power management unit of the digital signal processing and control module. The power supply voltage is DC 24V, and the maximum output current is not less than 500mA, which is sufficient to drive conventional piezoelectric or electromagnetic proportional control valves.

[0115] The drive amplifier unit also includes a freewheeling diode, connected in reverse parallel across the proportional control valve drive coil. This diode absorbs the reverse induced electromotive force generated by the drive coil when the power MOSFET is turned off, protecting the power switching devices from overvoltage breakdown. The output of the drive amplifier unit is connected to the two ends of the proportional control valve drive coil via two shielded wires, delivering the amplified drive current to the proportional control valve.

[0116] The proportional control valve is located upstream of the outlet section of the gas flow channel inside the housing and downstream of the temperature sensor. It is fixedly installed on the valve seat inside the outlet section of the housing using a flange or threaded connection. A sealing gasket is provided between the valve seat and the housing to ensure airtightness. The proportional control valve is normally closed (the valve is completely closed when not energized) and uses either a piezoelectric or electromagnetic actuation method.

[0117] When a piezoelectric proportional control valve is used, its core driving element is a piezoelectric stack actuator. When no driving voltage is applied, the actuator is in a naturally extended state and the valve is completely closed. When the driving current output by the drive amplifier unit is converted into a driving voltage by the drive coil of the proportional control valve and applied to both ends of the piezoelectric stack, the piezoelectric stack generates a mechanical displacement proportional to the magnitude of the driving voltage according to the inverse piezoelectric effect. This displacement is converted into the lifting displacement of the valve core through the valve core transmission mechanism, thereby changing the flow area of ​​the valve orifice and realizing the proportional regulation of the gas flow rate.

[0118] When an electromagnetic proportional control valve is used, its core driving element is a proportional electromagnet. When the armature of the electromagnet is not energized, it is in the closed position under the action of the return spring. When the driving current output by the drive amplifier unit flows through the drive coil of the proportional electromagnet, the electromagnet generates an electromagnetic attraction force proportional to the magnitude of the driving current, which overcomes the elastic force of the return spring and drives the armature to produce a displacement. This displacement is converted into the lifting displacement of the valve core through the valve core transmission mechanism, thereby changing the flow area of ​​the valve port and realizing the proportional regulation of the gas flow rate.

[0119] The proportional control valve's valve core and seat are both precision-machined from stainless steel, and the sealing surfaces between them are ground. The leakage rate in the closed state is no higher than 0.5% of the full-scale flow rate. The proportional control valve's response time is no more than 100 milliseconds, enabling it to complete the stroke from fully closed to fully open within 100 milliseconds after the digital signal processing and control module issues a control command, ensuring rapid tracking of upstream pressure fluctuations and changes in the flow setpoint.

[0120] The flow regulation characteristics of the proportional control valve are tested and calibrated one by one before leaving the factory. The relationship curve between its control current and output flow is stored in the non-volatile memory of the digital signal processing and control module, which is used as a reference by the cascade control unit when generating control signals.

[0121] The external terminals of the proportional control valve are led out through the lead hole in the side wall of the housing via a sealed lead wire and connected to the output terminal of the drive amplifier unit. The lead hole is sealed with epoxy resin to ensure that the gas pressure inside the housing does not leak out.

[0122] The communication and diagnostic module is fixedly installed in an adjacent cavity to the circuit board mounting cavity of the digital signal processing and control module. It is bidirectionally connected to the digital signal processing and control module via a parallel data bus or a serial peripheral interface. This module is used to realize data communication between the controller and the host computer, local display and parameter storage of system operating status, and sensor redundancy verification and system self-diagnosis functions based on soft measurement technology.

[0123] The communication and diagnostic module is internally divided into a communication interface unit, a soft measurement unit, a comparison and selection unit, a self-diagnosis unit, a display unit, and a storage unit. The units exchange data and work together through an internal data bus and a control bus.

[0124] The communication interface unit integrates three hardware communication interfaces: Universal Asynchronous Receiver / Transmitter (UART), Controller Area Network (CAN) bus, and Ethernet Media Access Control (MAC) controller, which correspond to three communication protocols: RS485 serial communication, Modbus industrial fieldbus, and EtherCAT industrial Ethernet, respectively.

[0125] The digital signal input terminal of the communication interface unit is connected to the flow calculation unit, multivariate collaborative compensation unit, and self-diagnosis unit of the digital signal processing and control module via an internal data bus to obtain the current quality flow rate. Current pressure and Data such as current temperature T, gas type identification code, valve opening feedback value, and system diagnostic report;

[0126] The communication interface unit encapsulates the above data into data frames according to the communication protocol format preset by the user, and sends them to the host computer through its communication port;

[0127] The communication interface unit also includes a communication parameter register for storing parameters such as communication baud rate, data bit length, number of stop bits, parity check mode, and slave address. These parameters can be modified online by the user via host computer commands and written to non-volatile memory for storage. The communication interface unit is also used to receive flow rate settings from the host computer. The system receives gas type switching commands, PID control parameter adjustment commands, diagnostic trigger commands, and firmware upgrade data packets, and forwards the received data to the corresponding functional units via the internal data bus.

[0128] The soft measurement unit is connected to the first pressure data output terminal, the second pressure data output terminal, and the temperature data output terminal of the signal acquisition and conditioning module via an internal data bus, respectively, for receiving the first pressure data in real time. Second pressure data and temperature data T;

[0129] The soft-sensor unit contains a differential pressure calculation model based on the gas state equation and the impedance characteristics of laminar flow elements. This model first uses initial pressure data... Second pressure data Given the temperature data T, the gas property database in the multivariable collaborative compensation unit is called to calculate the gas density ρ(T,P) and dynamic viscosity μ(T) under the current state.

[0130] Then, based on the geometric parameters of the capillaries in the laminar flow sensing unit (inner diameter d, length difference ΔL, number of capillaries n) and the Hagen-Poiseuille law, the theoretical estimate of the pressure potential difference under the current flow conditions is derived. The soft-sensor unit continuously outputs theoretical estimates of the differential pressure at the same sampling rate as the differential pressure sensor. To the comparison and selection unit;

[0131] The comparison and selection unit is connected to the digital output terminal of the differential pressure sensor and the output terminal of the soft measurement unit, respectively, and is used to receive the actual differential pressure value ΔP and the theoretical estimate of the differential pressure in real time. The comparison and selection unit contains a comparator and a threshold register. The threshold register stores the deviation threshold (usually 5% of the full-scale differential pressure) that is factory-calibrated or user-set.

[0132] The comparator continuously calculates the relative deviation between the actual differential pressure value and the theoretical estimate. ,in This is the full-scale value of the differential pressure sensor;

[0133] When relative deviation When the pressure remains below the preset threshold, the comparison and selection unit selects the actual differential pressure value ΔP as the output and transmits it to the flow calculation unit.

[0134] When relative deviation If the differential pressure sensor continuously exceeds a preset threshold for a duration exceeding a preset judgment time (typically 3 to 5 sampling cycles), the comparison and selection unit determines that the differential pressure sensor has experienced performance degradation, aging, or malfunction, and automatically switches to the output value of the soft measurement unit. As input to the flow calculation unit, it also generates sensor anomaly flags and uploads them to the host computer via the communication interface unit;

[0135] The output of the comparison and selection unit is also equipped with a signal holding circuit to maintain the continuity of the output signal during switching, and to avoid sudden changes in flow calculation and control output caused by signal jumps.

[0136] The self-diagnostic unit is connected to the proportional control valve drive end, the digital output end of the first pressure sensor and the second pressure sensor of the drive and execution module respectively through the internal data bus, and is used to automatically perform system health status detection at a preset diagnostic time point.

[0137] The self-diagnostic unit has an internal timer. Users can write the desired self-diagnostic time into the timer's register via instructions from the host computer. When the timer reaches the preset diagnostic trigger time, the self-diagnostic unit first sends a valve closing command to the drive and execution module, controlling the proportional control valve to enter a fully closed state.

[0138] Then, the pressure decay curves of the first and second pressure sensors are continuously monitored, and the pressure drop within a preset time period (usually 5 to 30 seconds) after shutdown is recorded. The self-diagnostic unit calculates the overall leakage rate of the system based on the pressure decay rate and the volume of the gas flow channel inside the housing. When the leakage rate exceeds a preset threshold, a leakage alarm is generated.

[0139] The self-diagnostic unit is also equipped with a zero drift detection subunit, which continuously collects the output value of the differential pressure sensor when the valve is closed, calculates the deviation between the output value and the factory zero value, and generates a sensor zero drift alarm when the deviation exceeds a preset threshold.

[0140] The self-diagnostic unit summarizes the above test results to generate a diagnostic report. The report includes the diagnostic time, leakage rate, zero drift value, current output values ​​of each sensor, valve closure status feedback value, and pass / alarm flags for each test. The diagnostic report is uploaded to the host computer via the communication interface unit and stored in the storage unit for later retrieval.

[0141] The display unit uses an organic light-emitting diode (OLED) display or a liquid crystal display, and is fixedly installed on the display window outside the housing. It is connected to the display driver interface of the communication and diagnostic module via a flexible ribbon cable. The display unit is used to display the current mass flow rate locally in real time. Cumulative traffic, primary pressure Second pressure The display unit displays information including pressure difference ΔP, gas temperature T, valve opening percentage, current operating status (normal / abnormal), and a summary of diagnostic results. It also features a backlight control circuit that automatically adjusts the screen brightness according to ambient light or allows manual adjustment by the user via buttons. The display unit has a refresh rate of at least 1Hz to ensure real-time data display.

[0142] The storage unit uses ferroelectric RAM (FRAM) or flash memory and is connected to the communication and diagnostic module through a serial peripheral interface;

[0143] The storage unit is used to store critical data during device operation, including but not limited to: historical flow setpoints, real-time snapshots of current mass flow rate and differential pressure, calibration parameters of the multivariable co-compensation unit, and flow correction coefficients. Updated version of the gas property database; PID control parameters (proportional coefficient) Integral coefficient Differential coefficients and feedforward gain coefficient The storage unit includes communication parameter configuration, diagnostic logs, and firmware program images. The total storage capacity of the storage unit is no less than 2MB, with diagnostic logs stored cyclically in chronological order, capable of storing at least the most recent 1000 diagnostic records. The storage unit supports data reading and exporting via host computer commands from the communication interface unit. Users can view historical data curves and diagnostic records through host computer software, facilitating trend analysis and preventative maintenance.

[0144] All logical functions of the communication and diagnostic module are driven by an embedded firmware program stored in the internal flash memory of its microcontroller. This firmware program runs independently of the main control program of the digital signal processing and control module, and the two exchange data and synchronize status through an internal data bus.

[0145] The firmware of the communication and diagnostic module supports online upgrades. Users can download the updated firmware to the module's flash memory via commands from the host computer on the communication interface unit. The upgrade process does not affect the normal flow control function of the digital signal processing and control module. The power supply for the communication and diagnostic module is provided by the power management unit of the digital signal processing and control module. The module has an independent low-dropout linear regulator and power isolation circuit inside, ensuring electrical isolation between the communication interface and the internal control circuit, and preventing interference introduced by external communication lines from affecting the normal operation of the controller.

[0146] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A laminar flow differential pressure type high-precision gas mass flow controller, characterized in that, include: The housing, a laminar flow sensing unit disposed within the housing, a signal acquisition and conditioning module, a digital signal processing and control module, a drive and execution module, and a communication and diagnostic module; The laminar flow sensing unit adopts a pressure differential type dual-channel cross-symmetrical structure, including a first branch and a second branch arranged in parallel inside the unit body. The first branch and the second branch have the same channel diameter and are arranged in parallel with each other. The inlet ends of the two branches are connected to the upstream side of the gas channel, and the outlet ends of the two branches are connected to the downstream side of the gas channel. A first capillary group and a third capillary group are connected in series along the airflow direction on the first branch, and a second capillary group and a fourth capillary group are connected in series along the airflow direction on the second branch. Each of the first, second, third, and fourth capillary groups is composed of multiple stainless steel capillary tubes of the same inner diameter connected in parallel. The first and fourth capillary groups have the same length, the second and third capillary groups have the same length, and the length of the second capillary group is greater than the length of the first capillary group. In the first branch, a first pressure-taking chamber is formed between the first capillary group and the third capillary group; in the second branch, a second pressure-taking chamber is formed between the second capillary group and the fourth capillary group; a first pressure-taking port is provided on the side wall of the first pressure-taking chamber; a second pressure-taking port is provided on the side wall of the second pressure-taking chamber; the first pressure-taking port and the second pressure-taking port are respectively connected to the two sensing ports of the external differential pressure sensor through the pressure-taking channel of the housing. The laminar flow sensing unit is specifically configured such that: gas flows sequentially through the first capillary group and the third capillary group via the first branch, and sequentially through the second capillary group and the fourth capillary group via the second branch. Utilizing the cross-symmetry of the two branches, the pressure difference between the first pressure tap and the second pressure tap corresponds to the frictional pressure drop along the path of fully developed laminar flow within the length difference between the second capillary group and the first capillary group, thereby creating a linear relationship between the differential pressure signal and the mass flow rate of the gas flowing through the laminar flow sensing unit. The signal acquisition and conditioning module is electrically connected to the laminar flow sensing unit and the digital signal processing and control module, respectively. It is used to acquire the differential pressure signal output by the laminar flow sensing unit, the absolute pressure signal at the two branch pressure taps, and the temperature signal in the gas flow channel. After amplifying, filtering, and analog-to-digital conversion of the above signals, it generates digital signal data and transmits it to the digital signal processing and control module. The digital signal processing and control module receives the digitized signal data, calculates the current mass flow rate according to the built-in Hagen-Poiseuille law with gas compressibility correction, compares the calculated mass flow rate with the externally input flow rate setpoint, and generates a control signal to output to the drive and execution module. The drive and execution module receives the control signal, converts it into a drive signal, amplifies the power, and then drives the proportional regulating valve to adjust the gas flow rate. The communication and diagnostic module is bidirectionally connected to the digital signal processing and control module, and is used to realize data communication with the host computer and system self-diagnosis.

2. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 1, characterized in that, The lengths of the first capillary group and the fourth capillary group are denoted as follows: The lengths of the second capillary group and the third capillary group are denoted as . ,and , and The difference ΔL is the effective measurement length; The number of capillaries and their inner diameter are the same in each capillary group. The portion of the second capillary group whose length exceeds that of the first capillary group is a fully developed laminar flow section. The pressure difference value corresponds only to the frictional pressure drop along the frictional flow section.

3. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 1, characterized in that, The signal acquisition and conditioning module includes a differential pressure sensor, a first pressure sensor, a second pressure sensor, a temperature sensor, and a signal conditioning unit; The high-pressure port of the differential pressure sensor is sealed to the first pressure tapping port through a first pressure tapping pipeline, and the low-pressure port is sealed to the second pressure tapping port through a second pressure tapping pipeline. The differential pressure sensor is used to detect the pressure difference between the first pressure tapping port and the second pressure tapping port and convert it into a first differential voltage signal output. The sensing end of the first pressure sensor extends into the first pressure tapping chamber to detect the absolute pressure at the first pressure tapping port and convert it into a second voltage signal output. The sensing end of the second pressure sensor extends into the second pressure tapping chamber to detect the absolute pressure at the second pressure tapping port and convert it into a third voltage signal output. The probe of the temperature sensor extends into the gas flow channel to detect the real-time temperature of the gas flowing through it and convert it into a fourth resistance signal output. The signal conditioning unit receives the first differential voltage signal, the second voltage signal, the third voltage signal, and the fourth resistance signal respectively, and performs amplification, filtering, and analog-to-digital conversion in sequence to generate digitized differential pressure data, first pressure data, second pressure data, and temperature data, which are then transmitted to the digital signal processing and control module.

4. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 3, characterized in that, The digital signal processing and control module includes a flow calculation unit and a multivariable collaborative compensation unit; The flow calculation unit receives the differential pressure data, the first pressure data, the second pressure data, and the temperature data output by the signal acquisition and conditioning module, and calculates the current mass flow rate according to the built-in Hagen-Poiseuille law corrected for gas compressibility. The multivariable collaborative compensation unit is bidirectionally connected to the flow calculation unit and has a built-in gas property database. The multivariable collaborative compensation unit queries the property database based on the temperature data, the first pressure data, and the second pressure data to calculate the gas density and dynamic viscosity under the current temperature and pressure conditions, and feeds back the calculated dynamic viscosity to the flow calculation unit in real time to replace the viscosity parameter in the calculation model to achieve dynamic compensation for the influence of temperature on gas viscosity. The flow calculation unit outputs the calculated current mass flow rate to the deviation calculation unit and the communication interface unit.

5. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 4, characterized in that, The digital signal processing and control module also includes a deviation calculation unit and a cascade control unit; The deviation calculation unit receives the current quality flow rate output by the flow calculation unit and the flow rate setting value input by the host computer forwarded by the communication interface unit, calculates the flow rate deviation value by subtracting the flow rate setting value from the current quality flow rate, and outputs it to the main controller of the cascade control unit. The cascade control unit is composed of the main controller and the secondary controller connected in series. The main controller takes the flow deviation value as input, generates a pressure setpoint through proportional-integral-derivative control calculation, and outputs it to the secondary controller. The secondary controller takes the difference between the pressure setpoint and the first pressure data as the pressure deviation value, generates a valve opening control quantity through proportional-integral control calculation, and outputs it to the drive and execution module.

6. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 5, characterized in that, The digital signal processing and control module also includes a feedforward compensation unit; The feedforward compensation unit receives the first pressure data in real time, performs discrete difference operation on the first pressure data to calculate the upstream pressure change rate, and generates a feedforward compensation amount based on the product of the preset feedforward gain coefficient and the upstream pressure change rate, and outputs it to the feedforward superimposed unit of the cascade control unit. The feedforward superimposition unit superimposes the valve opening control quantity and the feedforward compensation quantity to generate a final control signal, which is then output to the drive and execution module. When the feedforward compensation unit detects that the upstream pressure change rate exceeds a preset threshold, it immediately generates a corresponding feedforward compensation amount, so that the proportional control valve can perform a pre-adjustment action before the flow deviation is formed.

7. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 1, characterized in that, The drive and execution module consists of a digital-to-analog converter, a drive amplifier, and a proportional control valve connected in series along the signal flow direction. The digital-to-analog conversion unit receives the final control signal in digital form output by the digital signal processing and control module, converts it into an analog voltage signal or an analog current signal, and outputs it to the drive amplifier unit. The drive amplification unit amplifies the analog voltage signal or analog current signal and outputs a drive current to the drive coil of the proportional control valve to drive the valve core of the proportional control valve to generate displacement, thereby changing the flow area of ​​the valve port to achieve proportional regulation of the gas flow rate.

8. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 5, characterized in that, The communication and diagnostic module includes a soft measurement unit and a comparison and selection unit; The soft measurement unit receives the first pressure data, the second pressure data, and the temperature data respectively, calculates the theoretical estimate of the differential pressure based on the gas state equation and the impedance characteristics of the laminar flow element, and outputs it to the comparison and selection unit. The comparison and selection unit receives the actual differential pressure value and the theoretical differential pressure estimate, respectively, calculates the relative deviation between the two, and when the relative deviation is continuously less than a preset threshold, selects the actual differential pressure value and outputs it to the flow calculation unit; when the relative deviation continuously exceeds the preset threshold and the duration exceeds a preset judgment time, it determines that the differential pressure sensor is abnormal, automatically switches to the theoretical differential pressure estimate as the input of the flow calculation unit, and generates a sensor abnormality flag bit and uploads it to the host computer through the communication interface unit.

9. The laminar flow differential pressure type high-precision gas mass flow controller according to claim 5, characterized in that, The main controller forms a flow loop, and the secondary controller forms a pressure loop. The main controller uses the flow deviation as input and outputs a pressure setpoint to the secondary controller. The secondary controller uses the pressure deviation as input and outputs a valve opening control value to the drive and execution module. When the upstream pressure changes abruptly, the pressure loop responds quickly and suppresses the pressure disturbance, the flow loop ensures that the flow accurately tracks the set value, and the main controller and the secondary controller work together to form a cascade feedforward composite control.

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