Profibus-DP ultrasonic flowmeter based on domestic communication chip and flow calculation method

Abstract

The invention discloses a flow calculation method of a Profibus-DP ultrasonic flowmeter based on a domestic communication chip in the technical field of automation instruments. The flow calculation method comprises the following steps that 1, a flow field is divided into three states of laminar flow, turbulent flow and transition flow according to the Reynolds number of fluid; (2) calculating linear velocity distribution of fluid in the pipeline under the laminar flow state and the turbulent flow state based on a fluid mechanics formula, and introducing a correction factor to correct the linear velocity distribution formula under the laminar flow state and the turbulent flow state; for the transition flow state, a linear interpolation method is adopted to deduce a linear velocity calculation formula of the transition flow; and (3) the corrected linear velocity distribution formula is combined with a time difference method, a flow velocity calculation formula is obtained, high-precision flow measurement is achieved, the precision of flow measurement is improved, and the product cost is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of automation instruments, and particularly to an ultrasonic flowmeter and a flow calculation method. Background Art

[0002] Flowmeters are indispensable measurement tools in the industrial field and are widely used in industries such as petroleum, chemical, metallurgy, and heat supply for accurately measuring the flow rate of fluids in pipelines. As a non-invasive flow measurement device, ultrasonic flowmeters have become an important branch in the field of flowmeters due to their significant advantages such as high measurement accuracy and no pressure loss.

[0003] However, traditional ultrasonic flowmeters have limitations in flow velocity detection. Currently, most ultrasonic flowmeters use a single time difference method for flow velocity measurement. This method fails to fully consider the differences in the linear velocity distribution of fluids under different flow field states (such as laminar flow, turbulent flow, and transitional flow), nor does it correct the influence of different working conditions on flow velocity detection. Therefore, the applicable working conditions of traditional ultrasonic flowmeters are relatively single, and the measurement accuracy is difficult to meet the requirements of complex industrial environments.

[0004] In terms of communication technology, imported chips are generally used in traditional industrial sites to achieve Profibus-DP communication, such as products of foreign brands like Siemens. Although these imported chips have reliable performance, their costs are relatively high, which restricts the process of domestic industrial automation upgrading. Although there are domestic related products, there is still much room for improvement in terms of performance and cost control.

[0005] With the continuous growth of domestic industrial automation demand, there is an urgent need for an ultrasonic flowmeter solution that can not only meet the high-precision measurement under complex working conditions but also reduce production costs. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides a Profibus-DP ultrasonic flowmeter based on domestic communication chips and a flow calculation method. Through innovative flow velocity detection algorithms and the application of domestic chips, not only the accuracy of flow measurement is significantly improved, but also the product cost is greatly reduced, providing strong support for domestic industrial automation upgrading.

[0007] The object of the present invention is achieved as follows: A flow calculation method for a Profibus-DP ultrasonic flowmeter based on domestic communication chips includes the following steps:

[0008] Step 1) Divide the flow field into three states: laminar flow, turbulent flow, and transitional flow according to the fluid Reynolds number;

[0009] Step 2) Calculate the linear velocity distribution of the fluid in the pipeline under laminar and turbulent flow states respectively based on the hydrodynamics formula, and introduce a correction factor to correct the linear velocity distribution formula under laminar and turbulent flow states; for the transitional flow state, use the linear interpolation method to derive the linear velocity calculation formula for the transitional flow;

[0010] Step 3) Combine the corrected linear velocity distribution formula with the time difference method to obtain the flow velocity calculation formula, realizing high-precision flow measurement.

[0011] Further, step 1) specifically includes:

[0012] For the classification of flow field characteristics, the Reynolds number division method is adopted. The Reynolds number calculation formula is , u m is the centerline velocity, D is the pipeline diameter, nu is the kinematic viscosity of the fluid. When the Reynolds number is between 0 - 2000, it is in the laminar flow state; when it is between 2000 - 4000, it is usually in the transitional flow state; when it is above 4000, it is in the turbulent flow state.

[0013] Further, step 2) specifically includes:

[0014] After determining the flow field state, calculate the linear velocity at different positions in the pipeline according to the velocity distribution formula:

[0015] The linear velocity distribution formula in laminar flow is ;

[0016] k t is the correction factor for the laminar flow velocity distribution, R is the pipeline radius, and r represents the radial position, that is, the distance from a certain point to the central axis;

[0017] The linear velocity distribution formula in turbulent flow is ;

[0018] k c is the correction factor for the turbulent flow velocity distribution;

[0019] The n parameter is fixed. If the Reynolds number is known, the corresponding n value can be calculated;

[0020] In the transitional flow state, the linear interpolation method is used to process the velocity .

[0021] Further, the correction factor is determined through the following steps:

[0022] Under turbulent and laminar flow states, measure the flow velocity of the fluid under specific working conditions by the weighing method respectively. Substitute the measured flow velocity values into the calculation formula containing the correction factor, and solve the correction factors under turbulent and laminar flow states respectively. Use the correction factor to adjust the linear velocity distribution formula.

[0023] Further, the method for obtaining the correction factor specifically includes:

[0024] a) Calculate one flow velocity each under laminar flow and turbulent flow states by the weighing method;

[0025] b) Inverse-deduce the correction factors added in the time difference method based on the flow velocities calculated by weighing; specifically including:

[0026] Obtain one set of experimental data each under laminar flow state and turbulent flow state by the weighing method , where v1 is the flow velocity measured in turbulent flow and v2 is the flow velocity measured in laminar flow. Substitute these two data into and to calculate the correction coefficient and , and then calculate the correction factor k according to c and k t ; c is the speed of sound, is the correction coefficient under laminar flow, is the correction coefficient under turbulent flow.

[0027] 6. A Profibus-DP ultrasonic flowmeter based on a domestic communication chip, used to implement the flow calculation method described in claim 1 or 2, characterized by including:

[0028] A flow acquisition module, which uses a DN20 reflective pipe section and a 1MHz ultrasonic transducer to convert flow data into current pulse signals;

[0029] A time measurement module, which measures the time difference between the ultrasonic wave in the downstream direction and the upstream direction through a TDC-DP22 time measurement chip and transmits the measurement result to the main control module of the flow acquisition;

[0030] A main control module of the flow acquisition, which uses an MSP430 single-chip microcomputer to receive the data transmitted by the time measurement module and calculate the cumulative flow and instantaneous flow data;

[0031] A Profibus-DP communication module, which uses a GD32 single-chip microcomputer as the main control chip to control the domestic communication chip APC3 and transmits Profibus-DP protocol data through a 485 transceiver;

[0032] A display module, which uses an OLED display screen to display the cumulative flow and instantaneous flow data.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The present invention uses a domestic communication chip APC3 to replace the imported chip, and at the same time uses a domestic 485 transceiver CA-IS3092W as the transmission physical layer chip, significantly reducing the cost of the communication module.

[0035] According to the Reynolds number, the present invention classifies the flow field, and uses different linear velocity distribution formulas for different flow field states. Combining with the correction factor and the time difference method, the flowmeter of the present invention can achieve high-precision measurement under various complex working conditions. Compared with the traditional single time difference method or the segmented linearization compensation method, the measurement accuracy is higher and the applicable range is wider.

[0036] The present invention adopts domestic chips and domestic communication modules, which not only reduces the cost, but also improves the autonomy and controllability of the product, meeting the needs of domestic industrial automation upgrading and transformation.

[0037] In summary, through the innovative flow calculation method and optimized hardware design, the present invention solves the problem of insufficient measurement accuracy of traditional ultrasonic flowmeters under complex working conditions, and at the same time realizes the domestic substitution of the communication module, with significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0039] Figure 1 It is the schematic diagram of the ultrasonic flowmeter in the present invention.

[0040] Figure 2 It is the comparison simulation diagram of the linear velocity distribution when the inner diameter of the pipeline of the present invention is 14mm and the Reynolds coefficient is 3480 (i.e., the transitional flow state) and the rest of the flow field states.

[0041] Figure 3 It is the schematic diagram of the solution algorithm of the ultrasonic flowmeter of the present invention for different fluid states.

[0042] Figure 4 It is the overall design structure diagram of the hardware of the present invention.

[0043] Figure 5 It is the hardware structure block diagram of the ultrasonic measurement module of the present invention.

[0044] Figure 6 It is the overall design block diagram of the Profibus communication module of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] Embodiment 1

[0047] As Figure 1 shown, for the principle of the ultrasonic flowmeter and several parameters during speed measurement, it shows that the linear flow velocities of the fluid at different positions in the pipeline are different, and the angle between the propagation direction and the axis is determined.

[0048] A flow calculation method for a Profibus-DP ultrasonic flowmeter based on a domestic communication chip includes the following steps:

[0049] Step 1) Divide the flow field into three states: laminar flow, turbulent flow, and transitional flow according to the fluid Reynolds number;

[0050] As Figure 1 shown, the Reynolds number division method is adopted for the classification of the flow field characteristics. The Reynolds number calculation formula is , u m is the centerline velocity, D is the pipeline diameter, nu is the kinematic viscosity of the fluid. When the Reynolds number is between 0 and 2000, it is in the laminar flow state; when it is between 2000 and 4000, it is usually in the transitional flow state; and when it is above 4000, it is in the turbulent flow state.

[0051] Step 2) Calculate the linear velocity distribution of the fluid in the pipeline in the laminar flow and turbulent flow states respectively based on the fluid mechanics formula, and introduce a correction factor to correct the linear velocity distribution formula in the laminar flow and turbulent flow states; for the transitional flow state, use the linear interpolation method to derive the linear velocity calculation formula of the transitional flow; specifically:

[0052] After determining the flow field state, calculate the linear flow velocity at different positions in the pipeline according to the velocity distribution formula:

[0053] The linear velocity distribution formula in laminar flow is ;

[0054] k t is the correction factor of the laminar flow velocity distribution, R is the pipeline radius, and r represents the radial position, that is, the distance from a certain point to the central axis;

[0055] The linear velocity distribution formula in turbulent flow is ;

[0056] k c is the correction factor of the turbulent flow velocity distribution;

[0057] With the n parameter fixed, if the Reynolds number is known (the value of the Reynolds number can be obtained by querying the relevant geometric parameters of the fluid and the pipe from Nikuradse's experimental data), the corresponding n value can be calculated.

[0058] The velocity is processed by linear interpolation in the transitional flow regime. 。

[0059] Furthermore, the correction factor is determined through the following steps:

[0060] Under turbulent and laminar flow regimes, the flow velocity of the fluid under specific working conditions is measured by the weighing method respectively. The measured flow velocity values are substituted into the calculation formula containing the correction factor to solve the correction factors under turbulent and laminar flow regimes respectively, and the linear velocity distribution formula is adjusted with the correction factor.

[0061] Specifically, the specific method for obtaining the correction factor is as follows:

[0062] a) Calculate one flow velocity under laminar and turbulent flow regimes respectively by the weighing method;

[0063] b) Inverse-deduce the correction factor added in the time difference method in combination with the flow velocity calculated by weighing;

[0064] Calculate the laminar flow velocity , where c is the speed of sound, is the correction coefficient under laminar flow;

[0065] Calculate the turbulent flow velocity , is the correction coefficient under turbulent flow;

[0066] When the fluid is in laminar flow, u = u c， , when in turbulent flow, u = u t , Substitute into the following time difference method calculation formula: The laminar flow time difference calculation formula can be obtained: , simplify , since , therefore So it can be obtained that , at this time , since errors will occur in the coefficient part during the formula simplification process, the correction coefficient Finally, it can be obtained that The turbulent flow time difference calculation formula is: Where , since So it can be obtained that Where , at this time , since errors will occur in the coefficient part during the formula simplification process, the correction coefficient , so the flow velocity in the turbulent state , so the coefficients α and β can be corrected using the correction factors k c and k t for correction;

[0067] For the calculation of the correction coefficients, one experimental data each in the laminar state and the turbulent state can be obtained by the weighing method , v1 is the flow velocity measured in the turbulent flow, v2 is the flow velocity measured in the laminar flow, and the two data are substituted into and to calculate the correction coefficients α and β. Also, because the coefficients and are related to the correction factors k c and k t , the correction factors k c and k t can be obtained;

[0068] After calculation according to the above method, the correction factors and coefficient values can be obtained.

[0069] Step 3) Substitute the correction factors k c , k t , α, and β into the streamline velocity distribution formulas for turbulent flow, laminar flow, and transitional flow , , Combined with the time difference , when it is turbulent, u = u t when it is laminar, u = u c when it is transitional flow, u = u. After obtaining the time differences in different states and substituting them into the formula the flow velocity can be obtained, achieving high-precision flow measurement.

[0070] Embodiment 2

[0071] As Figure 4 shown, the Profibus-DP ultrasonic flowmeter based on domestic communication chips of the present invention mainly consists of three parts; namely, the ultrasonic measurement module part, the Profibus-DP communication module part, and the display part; among them, after the ultrasonic measurement module obtains the flow data through the ultrasonic measurement pipe section, it sends the data to the Profibus-DP communication module using the serial port, and displays the data on the OLED display screen in the way of I 2 C. After receiving the data, the Profibus-DP communication module converts the received data into the Profibus-DP format and transmits it to the Profibus-DP bus through the 485 bus.

[0072] As Figure 5As shown in the figure, the hardware part of the ultrasonic metering module mainly includes an LDO voltage stabilization module, a time metering module, an OLED display module, an MCU module, a peripheral expansion interface, and an ultrasonic transducer. Among them, the ultrasonic metering module is connected to the Profibus-DP communication module through the peripheral expansion interface.

[0073] As Figure 6 shown in the figure, after the linear voltage stabilization circuit converts the 5V power supply into 3.3V, it supplies power to the three chips of the single-chip microcomputer, communication ASIC, and 485 transceiver. At the same time, since the 485 transceiver requires both 3.3V and 5V power supplies, an additional auxiliary power supply circuit is designed to provide 5V power supply. The single-chip microcomputer uses the domestic single-chip microcomputer GD32F103RBT6 as the local slave user, and the communication ASIC uses the model APC3 as the FDL controller, which is controlled by the single-chip microcomputer. At the same time, it controls the 485 transceiver CA-IS3092 as the physical layer chip, which is responsible for connecting the Profibus-DP cable.

[0074] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A flow calculation method for a Profibus-DP ultrasonic flowmeter based on domestic communication chips, characterized in that, Including the following steps: Step 1) Divide the flow field into three states: laminar flow, turbulent flow, and transitional flow according to the fluid Reynolds number; Step 2) Calculate the linear velocity distribution of the fluid in the pipeline in laminar flow and turbulent flow states respectively based on the fluid mechanics formula, and introduce a correction factor to correct the linear velocity distribution formula in laminar flow and turbulent flow states; for the transitional flow state, use the linear interpolation method to derive the linear velocity calculation formula for transitional flow; Step 3) Combine the corrected linear velocity distribution formula with the time difference method to obtain the flow velocity calculation formula, realizing high-precision flow measurement.

2. The flow calculation method of the Profibus-DP ultrasonic flowmeter based on domestic communication chips according to claim 1, characterized in that Step 1) Specifically includes: For the classification of flow field characteristics, the Reynolds number division method is adopted. The Reynolds number calculation formula is , u m is the centerline velocity, D is the pipe diameter, nu is the kinematic viscosity of the fluid. When the Reynolds number is between 0 and 2000, it is in the laminar flow state. When it is between 2000 and 4000, it is usually in the transitional flow state. When it is above 4000, it is in the turbulent flow state.

3. The flow calculation method of the Profibus-DP ultrasonic flowmeter based on domestic communication chips according to claim 2, characterized in that, Step 2) Specifically includes: After determining the flow field state, calculate the linear velocity at different positions in the pipeline according to the velocity distribution formula: The formula for the linear velocity distribution in laminar flow is ; k t is the correction factor for the laminar flow velocity distribution, R is the pipe radius, and r represents the radial position, that is, the distance from a certain point to the central axis; The formula for the linear velocity distribution during turbulence is ; k c is the correction factor for the turbulent flow velocity distribution; When the n parameter is fixed, if the Reynolds number is known, the corresponding n value can be calculated; The velocity is processed by linear interpolation in the transitional flow regime .

4. The flow calculation method of the Profibus-DP ultrasonic flowmeter based on domestic communication chips according to claim 3, characterized in that, The correction factor is determined through the following steps: In the turbulent flow and laminar flow states, measure the flow velocity of the fluid under specific working conditions by the weighing method respectively, substitute the measured flow velocity values into the calculation formula containing the correction factor, solve the correction factors in the turbulent flow and laminar flow states respectively, and adjust the linear velocity distribution formula with the correction factor.

5. The flow calculation method of the Profibus-DP ultrasonic flowmeter based on domestic communication chips according to claim 4, characterized in that, The specific method for obtaining the correction factor includes: a) Calculate one flow velocity in the laminar flow and turbulent flow states respectively by the weighing method; b) Combine the flow velocities calculated by weighing to inversely deduce the correction factor added in the time difference method; specifically includes: Obtain one set of experimental data each under laminar flow state and turbulent flow state by the weighing method , where v1 is the flow velocity measured in turbulent flow and v2 is the flow velocity measured in laminar flow. Substitute the two data into and to calculate the correction coefficient and , and then calculate the correction factor k according to c and k t ; c is the speed of sound, is the correction coefficient under laminar flow, is the correction coefficient under turbulent flow.

6. A Profibus-DP ultrasonic flowmeter based on domestic communication chips for implementing the flow calculation method according to claim 1 or 2, characterized in that Including: A flow rate acquisition module, which uses a DN20 reflective pipe section and a 1MHz ultrasonic transducer to convert flow rate data into current pulse signals; A time measurement module, which measures the time difference between the ultrasonic wave flowing in the forward direction and the reverse direction through a TDC-DP22 time measurement chip and transmits the measurement result to the flow rate acquisition main control module; A flow rate acquisition main control module, which uses an MSP430 single-chip microcomputer to receive the data transmitted by the time measurement module and calculate the cumulative flow rate and instantaneous flow rate data; A Profibus-DP communication module, which uses a GD32 single-chip microcomputer as the main control chip to control the domestic communication chip APC3 and transmit Profibus-DP protocol data through a 485 transceiver; A display module, which uses an OLED display screen to display the cumulative flow rate and instantaneous flow rate data.

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