Online calibration system and method for mobile small-flow flowmeter

Abstract

The invention discloses a mobile small-flow flowmeter online calibration system and method, and belongs to the technical field of flow metering calibration. The system comprises a test pipeline, a start-stop valve group connected with a calibrated flowmeter in series, a weighing container, a high-precision electronic balance and a full-automatic control system. The system is characterized by further comprising an automatic emptying system which is kept physically separated from the weighing container during measurement and automatically descends to enter the container to empty liquid after measurement is finished; and the windproof vibration isolation system integrally wraps the high-precision electronic balance and the weighing container and is used for isolating environment airflow and mechanical vibration. Through the non-contact emptying and environment isolation design, the interference of the outside on the weighing precision is fundamentally eliminated, the technical problems of low field calibration precision and poor repeatability of the mobile small-flow flowmeter are solved in combination with the full-automatic control process, and the mobile small-flow flowmeter has the advantages of high calibration precision, high automation degree and high reliability.

Description

Technical Field

[0001] This invention relates to the field of flow meter calibration technology, specifically to an online calibration system and method for mobile small flow meters. Background Technology

[0002] Flow rate, as a crucial process parameter in industrial production and scientific experiments, is directly related to product quality, material balance, energy efficiency, and even production safety through its accurate measurement and control. Especially in high-precision fields such as fine chemicals, biopharmaceuticals, semiconductor manufacturing, and environmental monitoring, extremely stringent requirements are placed on the accurate measurement of minute flow rates. As the core instrument for flow measurement, the flow meter's measurement performance inevitably drifts or degrades during long-term operation due to various factors such as changes in media characteristics, pipeline vibration, and component aging. Therefore, periodic calibration to ensure the accuracy and reliability of its values ​​is essential for maintaining the stability and consistency of the production process.

[0003] Currently, in the field of flow metering, the static mass method is widely recognized as the benchmark method for flow calibration due to its clear measurement principle, good traceability, and high achievable uncertainty level. It is widely used to establish flow standard devices of various levels. Traditional static mass method standard devices are typically large and complex, and are fixedly installed in highly controlled environments such as metrology laboratories. When calibrating flow meters in the field, the common practice is to remove the flow meter from the production line, send it to the laboratory for calibration, and then reinstall it. This offline calibration mode has significant drawbacks: it is not only time-consuming and labor-intensive, increasing the risk of instrument damage during transportation and installation, but more importantly, prolonged downtime for disassembly severely impacts production continuity, causing significant economic losses.

[0004] To overcome the shortcomings of offline calibration, the industry has an urgent need for mobile calibration systems that can be deployed deep into industrial sites and perform online calibration directly on process pipelines. Mobile calibration systems based on the static mass method have emerged in response. However, combining laboratory-level accuracy requirements with the complex and variable environment of the field has revealed many insurmountable technical bottlenecks in practical applications of existing mobile calibration technologies.

[0005] The primary challenge stems from the harsh environmental conditions of industrial sites. Ground vibrations, resonance caused by the start-up and shutdown of large equipment, and personnel movement are all prevalent in these environments and are directly transmitted to the high-precision weighing unit, which serves as the mass reference, through the supporting structure. This causes irregular fluctuations in the readings, severely compromising weighing stability. Simultaneously, unavoidable airflow disturbances in industrial settings, such as those from ventilation systems, air conditioning vents, door and window opening and closing, and even wind generated by personnel movement, exert significant interference on the lightweight weighing containers and the minute mass increments accumulated during calibration, creating noise that drowns out the valid mass signal.

[0006] A deeper problem stems from the compromises made in system structure design by existing technologies to achieve miniaturization and portability of the equipment. For example, to achieve automated emptying, the drain pipes typically need to be physically connected to the weighing container using flexible connections. This continuous connection, regardless of the expensive flexible fittings used, inevitably applies a small but constantly changing additional stress, friction, or torque to the weighing container. This disturbance is directly transmitted to the electronic balance, becoming a source of systemic error that is difficult to eliminate. Throughout the weighing process, this additional stress fluctuates with changes in the liquid level in the container, the gravity of the residual liquid in the pipes, and changes in ambient temperature, directly compromising the accuracy of mass measurement.

[0007] These problems are amplified dramatically in low-flow-rate calibration scenarios. Low flow rates mean that the accumulated liquid mass within a reasonable sampling time is extremely small. The minute disturbances introduced by environmental and structural defects can be comparable in magnitude to the effective mass increment being measured, leading to a sharp increase in measurement uncertainty and significantly reduced repeatability and reliability of calibration results. Furthermore, many mobile devices, for the sake of simplified design, have low levels of automation, relying on manual operation for starting, stopping, emptying, and data recording. This is not only inefficient but also more prone to introducing random human error, making calibration results difficult to reproduce.

[0008] In summary, how to effectively isolate environmental vibration and airflow interference under harsh conditions of mobile and online operation, fundamentally eliminate additional stress interference caused by system structural design (especially the venting system), and simultaneously achieve a high degree of automation of the entire calibration process to reduce human uncertainty are the technical challenges that urgently need to be solved in the field of mobile low-flow calibration. Summary of the Invention

[0009] The technical problem that this invention aims to solve is that most existing flowmeter calibration devices are fixed platforms, which are bulky and cannot meet the needs of portable and on-site online calibration. Furthermore, for the calibration of small flow rates, especially micro flow rates, the traditional static mass method using commutators will introduce large uncertainties due to factors such as liquid switching disturbances and surface tension. At the same time, high-precision weighing equipment is easily affected by environmental vibrations, airflow, and stress in auxiliary pipelines, leading to a decrease in calibration accuracy and reliability.

[0010] The first aspect of this invention provides a mobile online calibration system for small flow meters, aiming to provide a compact, portable, and high-precision online calibration solution.

[0011] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0012] A mobile online calibration system for small flow meters includes:

[0013] Test piping, used to connect the flow meter to be calibrated in series;

[0014] A start / stop valve assembly is installed on the test pipeline and located downstream of the flow meter being calibrated;

[0015] High-precision electronic balance;

[0016] A weighing container, mounted on the high-precision electronic balance, is used to collect the liquid flowing out from the start-stop valve assembly;

[0017] The control system is connected to the start / stop valve group, the high-precision electronic balance, and the flow meter under calibration. It is used to control the opening and closing of the start / stop valve group and simultaneously collect the mass data of the high-precision electronic balance and the output signal of the flow meter under calibration to achieve the calibration of the flow meter under calibration.

[0018] In a preferred embodiment of the present invention, the control system automates the calibration process through precise timing control. Specifically, at the start of calibration, the initial mass of the high-precision electronic balance is recorded; subsequently, the start-stop valve group is controlled to open and timing is started synchronously; after a preset time is reached, the start-stop valve group is controlled to close and timing is stopped; finally, after the weighing stabilizes, the final mass of the high-precision electronic balance is recorded. This "start-stop method" measurement mode has a simple structure, rapid response, and effectively reduces the uncertainty introduced by the fluid on / off process, making it particularly suitable for precise measurement of small flow rates.

[0019] To further eliminate interference during the weighing process and improve measurement accuracy, the present invention also makes the following improvements:

[0020] The system may also include an automatic emptying system. This automatic emptying system is connected to the weighing container in a non-contact manner to avoid additional stress during weighing. Preferably, the automatic emptying system includes a lifting mechanism and a self-priming pump. After a single measurement, the lifting mechanism moves the drain line into the weighing container and the self-priming pump drains the liquid. During measurement, the drain line is completely separated from the weighing container, fundamentally eliminating interference from the weighing sensor caused by a fixed drain line, and significantly improving the accuracy of minute mass measurements.

[0021] The system may also include a windproof and vibration-isolation system. The high-precision electronic balance is integrally mounted on the windproof and vibration-isolation system. Through physical isolation, the system effectively attenuates mechanical vibrations from the ground and disturbances from airflow in the environment, providing a stable working environment for the high-precision electronic balance and ensuring the reliability of its readings in mobile and field applications.

[0022] In another embodiment of the invention, the start-stop valve assembly may include at least two sets of start-stop pipes connected in parallel. The control system automatically selects the optimal set of start-stop pipes for operation based on a set calibration flow point. This design broadens the effective calibration range of the system, ensuring stable flow fields and precise control at flow points of different magnitudes.

[0023] To ensure the accuracy of the calibration results, the control system performs air buoyancy correction during data processing. It calculates the standard mass m using the collected initial and final masses, along with environmental parameters (such as temperature and pressure), through the following formula. S :

[0024]

[0025] Where, m end For the final mass, m start For the initial mass, ρ a ρ is the air density. w To calibrate the density of the standard weights used in the high-precision electronic balance, ρ f The density of the fluid used for calibration is under the current operating conditions.

[0026] Simultaneously, the control system performs corresponding data processing based on the signal type of the flow meter being calibrated. For example, when the flow meter being calibrated is a pulse output type, it records the cumulative number of pulses N over a preset time period. p and the instrument coefficient K of the flow meter being calibrated f The measured mass m of the flow meter being calibrated is calculated. MUT The calculation formula is as follows:

[0027]

[0028] Finally, the control system compares the measurement quality m of the flow meter being calibrated. MUT Compared with standard mass m S The relative error E of the flow meter being calibrated is calculated.

[0029] A second aspect of the present invention provides an online calibration method for a mobile small-flow meter, which utilizes the aforementioned system and is characterized by comprising the following steps:

[0030] s1: Provide a calibration system, which includes a test pipeline connected in series with the flow meter being calibrated, a start-stop valve group connected to the test pipeline, a high-precision electronic balance placed downstream of the start-stop valve group, and a weighing container set on the high-precision electronic balance.

[0031] s2: Through a control system, the start-stop valve group is controlled to open and then close within a preset time, so that the fluid flows into the weighing container after passing through the flow meter being calibrated and the start-stop valve group;

[0032] s3: The control system synchronously collects the mass change data of the high-precision electronic balance and the output signal of the flow meter being calibrated within the preset time period, and calculates the measurement error of the flow meter being calibrated based on the mass change data and the output signal.

[0033] This invention provides a mobile online calibration system and method for small flow meters. It offers the following advantages:

[0034] 1. It greatly improves the accuracy of calibration.

[0035] The core advantage of this invention lies in its innovative non-contact automatic emptying system. Through a lifting mechanism, the drain pipe only contacts the weighing container during emptying, remaining completely separated during the critical mass measurement stage. This design fundamentally eliminates the additional stress, vibration transmission, and torque interference caused by pipe connections in traditional moving devices, ensuring the purity and accuracy of high-precision electronic balance readings, especially effective in measurements involving minute mass accumulations.

[0036] 2. It has excellent measurement repeatability and reliability.

[0037] This is thanks to its unique windproof and vibration isolation system. The vibration isolation platform effectively filters out mechanical vibrations from the ground, while the fully enclosed windproof cover isolates the system from airflow disturbances in the environment. By creating a stable and interference-free "microenvironment" for the high-precision weighing unit, the system can withstand the influence of complex industrial environments, ensuring that every measurement is performed under consistent conditions, thereby obtaining highly consistent calibration results.

[0038] 3. It achieves a high degree of automation in the entire calibration process, significantly reducing human error.

[0039] This invention integrates a complete control system. From parameter setting, flow field stabilization, start-stop sampling, data acquisition, purging and resetting to final calculation and report generation, all steps are executed automatically by the program. This not only significantly improves calibration efficiency, but more importantly, it avoids random errors introduced by inconsistencies in manual timing, reading, and operation, ensuring the standardization and objectivity of the entire calibration process.

[0040] 4. It possesses strong on-site online calibration capabilities, resulting in significant economic benefits.

[0041] The mobile design of this invention, combined with efficient environmental isolation technology, enables it to adapt to complex industrial environments. The equipment can be easily moved to the production line to directly calibrate operating flow meters without interrupting the production process. This saves companies significant downtime and disassembly / reassembly costs, enables rapid response to instrument performance issues and preventative maintenance, and ensures production continuity.

[0042] 5. It broadens the effective calibration range and improves the efficiency of multi-point calibration.

[0043] Its start / stop valve assembly adopts a parallel structure, including dedicated piping for different flow ranges. The control system can automatically select the optimal fluid channel according to the set calibration point, ensuring accurate start / stop control from low to high flow rates. Combined with a fully automated process, the system can quickly and continuously complete calibration tasks at multiple flow points without manual intervention, greatly reducing the time required to complete a full calibration report. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the overall system structure according to an embodiment of the present invention;

[0045] Figure 2 This is a flowchart of the calibration method according to an embodiment of the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of this invention.

[0047] refer to Figures 1 to 2 This invention provides a compact, mobile online calibration system for small flow meters that enables on-site calibration. Based on the static mass start-stop method, this system, through integrated design, solves the technical problems of traditional calibration devices being bulky, inconvenient to move, and lacking calibration accuracy at low flow rates.

[0048] The calibration system primarily consists of a control system and several functional components that connect to it for signal and control communication. These components together form a complete fluid measurement and calibration loop. Fluid enters the test pipeline from an external liquid source, flows sequentially through the flow meter to be calibrated, an on / off valve assembly, and finally into a weighing container mounted on a high-precision electronic balance. The entire weighing unit is protected by a windproof and vibration-damping system, and the weighing container is also equipped with an independent automatic evacuation system. The operating conditions in the pipeline are monitored in real time by pressure and temperature transmitters.

[0049] The control system is the central hub of the entire calibration device. Its hardware consists of an industrial control computer (the host computer) and a programmable logic controller (PLC) (the slave computer). The industrial control computer is responsible for the human-machine interface, setting the calibration process, performing complex data calculations, and generating and storing the final report. The PLC is responsible for executing instructions from the host computer in real time, directly controlling the actions of field equipment, and acquiring various sensor signals at high speed. Internally, it integrates a high-precision timer, input / output modules for signal conversion, and analog-to-digital and digital-to-analog converters.

[0050] The start-stop valve assembly is the key actuator for implementing the static mass start-stop method, directly determining the accuracy of the sampling process. This assembly is located downstream of the flow meter being calibrated and consists of at least one high-speed pneumatic diaphragm valve or high-speed pneumatic ball valve. The valve's rapid response characteristics ensure the instantaneous start and stop times of the fluid flow, thereby precisely defining the time window for mass accumulation. In a specific embodiment, the start-stop valve assembly may include multiple parallel pipelines of different diameters, such as one DN1 pipeline and one DN6 pipeline. The control system 1 can automatically select the appropriate pipeline and valve based on the currently calibrated flow point to ensure optimal control accuracy and flow field stability over a wide flow range.

[0051] One of the core innovations of this invention lies in its highly integrated weighing unit, which provides a reliable guarantee for high-precision measurement. This weighing unit specifically includes a high-precision electronic balance, a weighing container, a windproof and vibration-damping system, and an automatic emptying system. The high-precision electronic balance serves as the system's mass benchmark, and its selection ensures that the resolution and measuring range fully cover calibration requirements. The weighing container is preferably made of stainless steel or acrylic, and its internal baffle structure effectively suppresses fluctuations generated during liquid injection, accelerating the stabilization of the weighing reading.

[0052] To eliminate interference from the environment during the weighing process, the windproof and vibration-isolation system completely encloses the high-precision electronic balance and its weighing container. The system has vibration-damping elements at the bottom to absorb mechanical vibrations from the ground, and a transparent windproof cover on the outside to isolate ambient airflow. This design is crucial for ensuring the measurement stability of the device during on-site mobile calibration under various working conditions.

[0053] This system empties the liquid from the weighing container after each measurement, designed to fundamentally eliminate stress interference caused by traditional fixed drain lines during weighing. The automatic emptying system includes a lifting mechanism, a self-priming pump, and a drain line. Throughout the weighing process, the lifting mechanism raises the drain line to a position completely out of contact with the weighing container. After a measurement is completed and data is recorded, the control system commands the lifting mechanism to descend, allowing the end of the drain line to re-enter the liquid in the weighing container, and then activates the self-priming pump to drain the liquid. This "non-contact" emptying method ensures that there are no additional mechanical connections other than the liquid during high-precision electronic balance mass readings, thus guaranteeing the accuracy of measurements even for minute mass changes.

[0054] In addition, the pressure and temperature transmitters in the system are used to monitor the pressure and temperature of the fluid in the test pipeline in real time. This data is used to determine whether the current flow field is stable, and the collected temperature data is used to accurately calculate the fluid density ρ. f and air density ρ a These density values ​​form the basis of the calculations, and are key parameters necessary for subsequent calculations to correct for air buoyancy.

[0055] In one specific embodiment of the present invention, an online calibration method for a mobile small flow meter is provided. This method is executed through the aforementioned calibration system. Its core is based on the static quality start-stop method and combined with a fully automated control process to ensure the high efficiency and high accuracy of calibration.

[0056] The entire calibration process is centrally scheduled by the control system, requiring no manual intervention. Before calibration begins, the operator inputs relevant information about the flowmeter to be calibrated, such as model, serial number, and instrument coefficient K, through the human-machine interface on the industrial control computer. f (For pulse output flow meters), and set one or more flow points to be calibrated.

[0057] The first step in the calibration process is system preparation and reset. The control system first adjusts the variable frequency pump or control valve in the liquid source system using a PID algorithm based on the set target flow point to establish a stable flow field within the test pipeline. At this time, the start / stop valve assembly is closed, and the fluid circulates in the main loop but does not enter the weighing container. The system continuously monitors the readings of the pressure and temperature transmitters. After the flow field stabilizes, it collects the readings of a high-precision electronic balance until the value fluctuates within a set small range. The mass value recorded at this point is the initial mass m. start At the same time, the control system clears the internal accumulated value of the flow meter being calibrated through the signal interface and resets its internal high-precision timer.

[0058] Once preparation is complete, the system automatically enters the measurement and sampling phase. The control system sends a precise digital signal via the PLC to instantly open the start-stop valve assembly, allowing fluid to begin flowing into the weighing container. Simultaneously with valve opening, a high-precision timer within the PLC begins timing and synchronously acquires the output signal of the flowmeter being calibrated, for example, counting pulse signals. After the preset sampling time t is reached, the control system immediately sends a signal to close the start-stop valve assembly, thus precisely cutting off the fluid flowing into the weighing container. Timing and signal acquisition also cease synchronously.

[0059] After fluid injection is complete, the system waits for the liquid level in the weighing container to return to normal and for the reading of the high-precision electronic balance to stabilize completely. Once the reading stabilizes, the control system automatically records the mass value at that moment as the final mass m. end This completes the data acquisition process for a single-point measurement.

[0060] Next, the system enters the data processing and calculation phase. First, to obtain the true fluid mass unaffected by air buoyancy, the control system needs to correct the balance's weighing results. Standard mass m S The calculation formula is as follows:

[0061]

[0062] In this formula, m end For the final quality of the record, m start For the initial mass recorded, ρ a ρ represents the air density of the ambient environment, a value that can be calculated by the control system based on real-time collected data of ambient temperature, atmospheric pressure, and humidity. w The density of the standard weights used to calibrate this high-precision electronic balance is a known constant, typically 8000 kg / m³. 3 . ρ f To calibrate the density of the medium at the current operating temperature, this value is calculated from the real-time temperature measured by the temperature transmitter using a lookup table or a fitted formula.

[0063] At the same time, the control system calculates the cumulative mass reading m of the flowmeter being calibrated in this measurement based on the output signal collected. MUT Taking a pulse output flow meter as an example, its calculation formula is:

[0064]

[0065] Where, N p K is the total number of pulses output by the flowmeter being calibrated, collected by the system within the sampling time t. f This is the preset instrument coefficient of the flow meter, expressed in pulses per kilogram.

[0066] Finally, control system 1 compares the two calculation results to evaluate the metering performance of the flowmeter under calibration at that flow point. The formula for calculating the relative error E is:

[0067]

[0068] To assess the repeatability of the flowmeter being calibrated, the entire process described above, from measurement and control sampling to data processing, is automatically repeated multiple times (e.g., 3 to 5 times) at the same flow point. After completing all repeatability tests at a flow point, the control system activates the automatic evacuation system to empty the weighing container. Subsequently, the system automatically adjusts the flow field to the next set calibration flow point and begins a new calibration cycle until all preset points have been calibrated. Finally, the system integrates all calibration data and calculation results to automatically generate a calibration report that conforms to the specifications.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A mobile online calibration system for small flow meters, characterized in that, include: Test piping, used to connect the flow meter to be calibrated in series; The start / stop valve assembly is installed on the test pipeline and located downstream of the flow meter being calibrated; High-precision electronic balance; The weighing container, mounted on a high-precision electronic balance, is used to collect liquids flowing out from the start-stop valve assembly. The control system is connected to the start / stop valve group, the high-precision electronic balance, and the flow meter being calibrated. It is used to control the opening and closing of the start / stop valve group and simultaneously collect the mass data of the high-precision electronic balance and the output signal of the flow meter being calibrated in order to calibrate the flow meter being calibrated.

2. The system according to claim 1, characterized in that, The control system is specifically used to: record the initial mass of the high-precision electronic balance at the start of calibration; control the start / stop valve group to open and synchronously start timing; control the start / stop valve group to close and stop timing after the preset time is reached; and record the final mass of the high-precision electronic balance after the reading stabilizes.

3. The system according to claim 1, characterized in that, It also includes an automatic emptying system, which is connected to the weighing container in a non-contact manner. The automatic emptying system includes a lifting mechanism and a self-priming pump. The lifting mechanism is used to move the drain pipe into the weighing container after a single measurement and to drain the liquid in the weighing container by the self-priming pump, so as to avoid interference with the weighing caused by fixing the drain pipe.

4. The system according to claim 1, characterized in that, It also includes a windproof and vibration isolation system, on which the high-precision electronic balance is mounted. The windproof and vibration isolation system is used to isolate the influence of environmental airflow and mechanical vibration on the weighing stability of the high-precision electronic balance.

5. The system according to claim 1, characterized in that, The start-stop valve assembly includes at least two sets of start-stop pipelines connected in parallel. The control system selects one set of start-stop pipelines to operate according to the set calibration flow point, so as to adapt to the calibration requirements of different flow ranges.

6. The system according to claim 2, characterized in that, The control system is also used to calculate the standard mass m based on the collected initial mass and final mass using the following formula and in combination with environmental parameters. S : Where, m end For the final mass, m s tart is the initial mass, ρ a ρ is the air density. w ρ is the density of the standard weight. f Fluid density for calibration.

7. The system according to claim 1, characterized in that, When the flow meter being calibrated is a pulse output type, the control system records the cumulative number of pulses N within a preset time period. p and the instrument coefficient K of the flow meter being calibrated f The measured mass m of the flow meter being calibrated is calculated. MUT The calculation formula is as follows:

8. The system according to claim 6, characterized in that, The control system further measures the mass m of the flow meter being calibrated. MUT With the standard mass m S By comparing the results, the relative error E of the flowmeter being calibrated is calculated.

9. The system according to claim 1, characterized in that, The start / stop valve assembly consists of a high-speed pneumatic diaphragm valve or a high-speed pneumatic ball valve to ensure the speed and repeatability of fluid cut-off and opening.

10. A method for online calibration of a mobile small-flow meter, characterized in that, Includes the following steps: s1: Provide a calibration system, which includes a test pipeline connected in series with the flow meter being calibrated, a start-stop valve group connected to the test pipeline, a high-precision electronic balance placed downstream of the start-stop valve group, and a weighing container set on the high-precision electronic balance. s2: Through a control system, the start-stop valve group is controlled to open and then close within a preset time, so that the fluid flows into the weighing container after passing through the flow meter being calibrated and the start-stop valve group; s3: The control system synchronously collects the mass change data of the high-precision electronic balance and the output signal of the flow meter being calibrated within the preset time period, and calculates the measurement error of the flow meter being calibrated based on the mass change data and the output signal.

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