Electromagnetic flowmeter excitation coil independent driving system and calibration and driving method

Abstract

According to the independent driving system for the excitation coils of the electromagnetic flowmeter and the calibration and driving method, the two excitation coils of the electromagnetic flowmeter are each independently provided with a driving power source, and the two excitation coils are driven to generate independent magnetic fields respectively; the DSP controller is used for coordinately controlling the magnitude of the output current of the two driving power supplies, and adjusting the spatial distribution of a resultant magnetic field after the superposition of the two independent magnetic fields in the measuring tube to reach an optimal state, so that a higher signal-to-noise ratio can be obtained under the condition that the excitation coil adopts a smaller driving current, and the measurement accuracy and stability are ensured on the basis of ensuring the measurement accuracy and stability. The power consumption of the electromagnetic flowmeter can be greatly reduced; besides, after the digital power supply is adopted, when the electromagnetic flowmeter is applied on site, the working parameters of the digital power supply can be adjusted according to on-site working conditions, so that the actual use of the electromagnetic flowmeter is very flexible, and the on-site adjustment and maintenance service of the electromagnetic flowmeter is greatly facilitated.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic flowmeter technology, specifically to an independent drive system for the excitation coil of an electromagnetic flowmeter, as well as its calibration and driving method. Background Technology

[0002] Common excitation methods for existing electromagnetic flowmeters include DC, AC at power frequency, low-frequency rectangular wave, and high-frequency rectangular wave. Regardless of the excitation method, the two excitation coils in the electromagnetic flowmeter are connected in series to ensure that the currents in the two coils are completely synchronized and equal. This ensures that the magnetic fields generated by the two excitation coils in the measuring tube are strictly synchronized and have consistent magnetic induction intensity. Furthermore, the magnetic induction intensity is symmetrically distributed on both sides of the plane containing the measuring electrode and the axis of the measuring tube, avoiding the introduction of measurement errors and minimizing interference, thereby improving measurement accuracy and stability. In the article "Development of Multi-Physical Field Digital Twin Model of Typical Industrial Flowmeters and Measurement Systems," a computer simulation was performed on the magnetic field intensity distribution within the measuring tube at several locations along the axial direction of the measuring tube in the region where the excitation coils are located. This simulation vividly displays the ideal spatial distribution of the magnetic field generated by the two excitation coils in the measuring tube as described above (see pages 55 and 56 of "Development of Multi-Physical Field Digital Twin Model of Typical Industrial Flowmeters and Measurement Systems"). Figure 4-7 (Distribution of radial magnetic field intensity inside the pipe at various locations within the excitation coil range). However, in actual production, due to unavoidable assembly errors in the assembly positions of the two excitation coils, the magnetic induction intensity is asymmetrically distributed on both sides of the plane containing the measuring electrode and the axis of the measuring pipe. This problem not only introduces measurement errors but also severely reduces the electromagnetic flowmeter's ability to suppress external electromagnetic interference, seriously affecting measurement accuracy and stability. To improve the problem caused by assembly errors in the assembly positions of the two excitation coils in actual production, the existing solution is to increase the excitation coil drive voltage (DC24V, DC36V, AC220V) and adopt a high-current (125mA-250mA) operating mode to increase the magnetic induction intensity in the measuring tube. The higher magnetic induction intensity increases the output electromotive force of the measuring electrode, thereby improving the signal-to-noise ratio and enhancing measurement accuracy and stability. However, this method results in high power consumption and severe heat generation in the electromagnetic flowmeter, becoming a technical problem that urgently needs to be solved in the electromagnetic flowmeter industry.

[0003] Furthermore, existing electromagnetic flowmeters often use analog circuit constant current sources to drive the excitation coils. These sources have low power conversion efficiency, and the large drive current leads to severe heat generation during operation. This causes the static operating point of the analog circuit constant current source to drift, resulting in a drift in the operating current. Consequently, this affects the measurement accuracy and stability of the electromagnetic flowmeter, leading to lower measurement accuracy. Additionally, because the circuit parameters of the analog circuit constant current source are fixed (determined by the parameters of the circuit components), the operating parameters cannot be adjusted according to actual field conditions. This significantly limits the flexibility of electromagnetic flowmeter applications and causes difficulties in on-site adjustment and maintenance.

[0004] Digital power supply technology has matured significantly. For example, the article "Synchronous Rectification Ruck-Boost Digital Power Supply Based on STM32" (https: / / blog.csdn.net / zeruns / article / details / 139510875) details a digital power supply. Digital power supplies, with their programmability, intelligence, high precision, and flexible adjustment and control, are rapidly replacing traditional analog power supplies and are widely used in many fields. Currently, their main application areas include information and communication, industrial automation and control, consumer electronics, renewable energy and energy storage, transportation, medical equipment, defense and aerospace, and many other industries. However, digital power supplies are not yet used in the electromagnetic flowmeter industry. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention discloses an independent driving system, calibration, and driving method for the excitation coils of an electromagnetic flowmeter. Two excitation coils are independently equipped with driving power supplies, which respectively drive the corresponding excitation coils to generate two independent magnetic fields. These two independent magnetic fields superimpose within the measuring tube to form a composite magnetic field space. A DSP controller coordinates and controls the ratio of the driving currents of the two driving power supplies, adjusting the spatial distribution of the composite magnetic field within the measuring tube to achieve optimal results. This avoids introducing new measurement errors, minimizes interference, and improves measurement accuracy and stability. Simultaneously, it reduces the driving currents of the two driving power supplies, thereby reducing the power consumption of the electromagnetic flowmeter and solving the technical problem of excessively high power consumption commonly found in existing electromagnetic flowmeters.

[0006] To achieve the aforementioned objective, the present invention employs the following technical solution: an independent drive system for excitation coils of an electromagnetic flowmeter, connected to an external power supply, for driving excitation coils located on both sides outside the measuring tube of the electromagnetic flowmeter, and a pair of measuring electrodes are also provided on the measuring tube; the two excitation coils are independently configured with driving power supplies; the two driving power supplies are coordinated and controlled by a DSP controller to drive the two excitation coils to generate independent magnetic fields respectively; the two independent magnetic fields are superimposed to form a composite magnetic field located between the two excitation coils inside the measuring tube.

[0007] Furthermore, the driving power supply is an analog circuit power supply.

[0008] Preferably, the driving power supply is a digital power supply, including a DC / DC conversion circuit, a MOSFET driving circuit, an MCU, a Flash memory chip, a current sampling amplification circuit, and an ADC conversion circuit; The DC / DC conversion circuit is controlled by a PWM signal from the MCU, which steps down (or boosts) the external power supply and outputs it to drive the excitation coil. Among them, the MOSFET drive circuit is used to improve the driving capability of the PWM signal issued by the MCU; Among them, the current sampling amplifier circuit and the ADC conversion circuit are used to collect the current value output by the DC / DC conversion circuit, perform analog-to-digital conversion, and then transmit it to the MCU; Among them, the MCU is the control core of the drive power supply. After calculating the current value collected by the current sampling amplification circuit and ADC conversion circuit, it outputs a PWM signal with a corresponding duty cycle, and controls the stability of the output current of the drive power supply through the feedback control of the MOS transistor drive circuit. The Flash memory chip is used to store the control program of the drive power supply and the parameters of the electromagnetic flowmeter's operating settings.

[0009] Furthermore, the DC / DC conversion circuit is a synchronous BUCK-BOOST power supply circuit.

[0010] Furthermore, it also includes an H-bridge drive circuit; the H-bridge drive circuit is controlled by a DSP controller to convert the constant current mode of the drive power supply output into a rectangular wave mode to drive the excitation coil to work.

[0011] Furthermore, the H-bridge drive circuit has four switching transistors, two of which are connected in parallel on opposite bridge arms and electrically connected to the DSP controller; or all four switching transistors are independently electrically connected to the DSP controller.

[0012] Furthermore, the DSP controller is electrically connected to the measuring electrodes through an ADC conversion circuit and an output voltage sampling amplification circuit; the output voltage sampling amplification circuit is used to acquire and amplify the voltage signal between the two measuring electrodes, and the ADC conversion circuit is used for analog-to-digital conversion of the amplified voltage signal.

[0013] A calibration method for an independent drive system of an electromagnetic flowmeter excitation coil, wherein during calibration, the operating current of one excitation coil is set to the standard operating current Is, and the operating current of the other excitation coil is set to the calibration operating current Id; the standard operating current Is is determined by the design, and the calibration operating current Id is determined during the electromagnetic flowmeter calibration process; the specific steps of the electromagnetic flowmeter calibration method are as follows: S1. The electromagnetic flowmeter is set on the calibration workbench, with tap water as the calibration working medium, and half of the maximum range as the standard test flow rate Qs, which flows continuously through the electromagnetic flowmeter. S2. Set the electromagnetic flowmeter to calibration mode, so that the standard operating current Is flows in opposite directions through the excitation coils located on both sides of the measuring tube; S3. One excitation coil maintains a constant standard operating current Is, while the other excitation coil adjusts its operating current bidirectionally through the DSP controller's power supply. During the bidirectional adjustment of the current in the other excitation coil, the DSP controller detects the potential difference Ui between the two measuring electrodes. When the potential difference Ui = 0, the operating current in the other excitation coil is the calibration operating current Id. Both the standard operating current Is and the calibration operating current Id are stored in the DSP controller. S4. Set the electromagnetic flowmeter to normal operating mode. One excitation coil operates at the standard operating current Is, and the other excitation coil operates at the calibration current Id. The current directions in both coils are the same. The DSP controller switches the current directions of the two excitation coils at a set frequency. Read the measurement results Qm of the electromagnetic flowmeter at three set flow points and calculate the relative error E. Determine whether the electromagnetic flowmeter meets the corresponding accuracy class standard based on the relative error E. The formula for calculating the relative error E is: E = (Qm - Qs) / Qs; Where Qm is the value being calibrated, and Qs is the standard value; If the relative error E of the indicated value meets the corresponding accuracy level standard, the electromagnetic flowmeter is deemed qualified, and the calibration work is completed.

[0014] Furthermore, if the electromagnetic flowmeter is deemed unqualified, the standard operating current Is is increased by 2.5-5% based on the previous calibration, and then the S3-S4 calibration process is repeated; until the increased standard operating current Is reaches 1.5-2.0 times the initial standard operating current Is, if the electromagnetic flowmeter calibration is still unqualified, then the electromagnetic flowmeter assembly is deemed unqualified.

[0015] A driving method for an independent driving system of an electromagnetic flowmeter excitation coil includes a DSP controller that controls two driving power supplies to provide operating current to the corresponding excitation coils with a standard operating current Is and a calibrated operating current Id, respectively, and the current directions in the two excitation coils are the same. The DSP controller controls two H-bridge driving circuits to synchronously change the current direction in the two excitation coils at a set frequency, so that the two excitation coils operate in a synchronous rectangular wave excitation mode. Only when the DSP controller detects that the current direction of the two excitation coils has reversed and the current has stabilized, does it sample the potential difference between the two measuring electrodes at a set sampling frequency.

[0016] Due to the adoption of the technical solution described above, the present invention has the following beneficial effects: The electromagnetic flowmeter excitation coil independent drive system disclosed in this invention has two excitation coils of the electromagnetic flowmeter independently configured with drive power supplies, which drive the two excitation coils to generate independent magnetic fields respectively; by coordinating and controlling the output current of the two drive power supplies through a DSP controller, the spatial distribution of the combined magnetic field after the superposition of the two independent magnetic fields in the measuring tube is adjusted to achieve the optimal state, so that the excitation coils can obtain a high signal-to-noise ratio with a smaller drive current, and the power consumption of the electromagnetic flowmeter can be significantly reduced while ensuring measurement accuracy and stability; in addition, after adopting a digital power supply, the operating parameters of the digital power supply can be adjusted according to the on-site working conditions when the electromagnetic flowmeter is used in the field, making the actual use of the electromagnetic flowmeter very flexible and greatly facilitating the on-site adjustment and maintenance services of the electromagnetic flowmeter. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the electromagnetic flowmeter structure; Figure 2 This is a schematic diagram of the independent drive system for the excitation coil of the electromagnetic flowmeter in Example 1. Figure 3 This is a block diagram of an analog circuit power supply. Figure 4 This is a block diagram of a digital power supply. Figure 5 This is a schematic diagram of the H-bridge drive circuit. Figure 6 This is a schematic diagram of the magnetic field distribution inside the measuring tube under ideal conditions of an electromagnetic flowmeter. Figure 7 This diagram illustrates the distribution of the magnetic field inside the measuring tube under actual conditions of an existing electromagnetic flowmeter. Figure 1 ; Figure 8 This diagram illustrates the distribution of the magnetic field inside the measuring tube under actual conditions of an existing electromagnetic flowmeter. Figure 2 ; Figure 9 This diagram illustrates the distribution of the magnetic field inside the measuring tube under actual conditions of an existing electromagnetic flowmeter. Figure 3 ; Figure 10 This is a schematic diagram of the magnetic field distribution inside the measuring tube of the electromagnetic flowmeter before calibration of the present invention. Figure 11 This is a schematic diagram of the magnetic field distribution inside the measuring tube of the electromagnetic flowmeter after calibration. Figure 12 This is a schematic diagram of the magnetic field distribution inside the measuring tube during calibration under ideal conditions of the present invention; Figure 13 This is a schematic diagram of the magnetic field distribution inside the measuring tube before calibration in the actual state of the present invention; Figure 14 This is a schematic diagram of the magnetic field distribution inside the measuring tube after calibration under actual conditions according to the present invention. Figure 15 This is a table of actual calibration data for a DN65 electromagnetic flowmeter.

[0018] In the diagram: 1. Measuring tube; 2. Excitation coil; 3. H-bridge drive circuit; 4. Drive power supply; 5. External power supply; 6. DSP controller; 7. Measuring electrode. Detailed Implementation

[0019] The present invention will be explained in detail through the following embodiments. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention.

[0020] See the instruction manual appendix Figure 1 The mechanical structure of the electromagnetic flowmeter includes a measuring tube 1, excitation coils 2 arranged parallel to the upper and lower sides of the measuring tube 1, and measuring electrodes 7 symmetrically arranged on the left and right sides of the measuring tube 1. The plane containing the two measuring electrodes 7 and the axis of the measuring tube 1 is called the geometric center plane C of the measuring tube. The plane with symmetrical magnetic induction intensity between the upper and lower excitation electrodes 2 is called the magnetic field intermediate plane M. Ideally, the geometric center plane C of the measuring tube coincides with the magnetic field intermediate plane M. The electromagnetic flowmeter works by establishing a magnetic field in the measuring tube 1 through two parallel excitation coils 2. When a conductive fluid flows through the measuring tube 1, the fluid cuts the magnetic lines of force, generating an induced electromotive force (EMF). The magnitude of this EMF is proportional to the average flow velocity of the conductive fluid. The induced EMF is detected by a pair of measuring electrodes 7, and after conversion and processing, a signal output proportional to the volumetric flow rate is obtained. (See the instruction manual appendix.) Figure 6 This diagram illustrates the magnetic field distribution within the measuring tube of an electromagnetic flowmeter under ideal conditions. Based on the working principle of the electromagnetic flowmeter, ideally, the magnetic induction intensity at the midpoint M between the two excitation coils 2 should be uniform and orthogonal, and the midpoint M should coincide with the geometric center C of the measuring tube. This ideal magnetic field distribution is crucial for achieving high-precision linear measurement (measurement accuracy across the entire flow range). Any abnormality in the magnetic field distribution within the electromagnetic flowmeter will introduce measurement errors and fail to effectively suppress external electromagnetic interference, directly affecting the measurement accuracy and stability of the flowmeter. When the excitation coils 2 are in an ideal assembly position, the two series-connected excitation coils 2 can perfectly achieve the ideal magnetic field distribution within the electromagnetic flowmeter, which is why the excitation coils 2 in existing electromagnetic flowmeters are connected in series. However, unfortunately, the actual assembly position of the excitation coils 2 cannot achieve this ideal state. See the instruction manual appendix Figure 7 , 8The two accompanying figures schematically illustrate that the excitation coil 2 is actually assembled in a non-ideal state, with the excitation coil 2 being offset relative to the measuring tube 1. In this case, with the two excitation coils 2 connected in series in an existing electromagnetic flowmeter and the driving currents being completely synchronized and equal, the offset of the excitation coil 2 relative to the measuring tube 1 causes the intermediate surface M of the magnetic field to separate from the geometric center surface C of the measuring tube. Figure 7 , 8 The images show the distribution of the spatial magnetic field within the electromagnetic flowmeter during the first and second halves of a driving cycle when the excitation coil 2 is driven by a rectangular wave. The magnetic field mid-plane M and the geometric center plane C of the measuring tube are separated in the same direction, but the directions of the magnetic field vectors are different (the different directions of the magnetic field vectors only cause a reversal in the potential difference between the measuring electrodes 7, but do not affect the measurement results). With the two excitation coils 2 connected in series, once the above-mentioned problem occurs in the spatial magnetic field distribution within the electromagnetic flowmeter, there are no technical means to eliminate it, severely affecting the measurement accuracy of the electromagnetic flowmeter, and causing significant variations in measurement error (linearity difference) throughout the entire measurement range. Worse still, the above problems also prevent the electromagnetic flowmeter from effectively suppressing external electromagnetic interference, further exacerbating the problem. To improve measurement accuracy and stability, existing solutions include increasing the excitation coil drive voltage (DC24V, DC36V, AC220V) and adopting a high-current operating mode to increase the magnetic induction intensity in the measuring tube 1 (drive current is generally 125mA-250mA; it should be noted that some low-power products use a drive current of 20-50mA, but this is achieved at the expense of measurement range and response speed). The higher magnetic induction intensity increases the output electromotive force of the measuring electrode 7, thereby improving the signal-to-noise ratio and thus improving the measurement accuracy and stability throughout the entire measurement range. However, this method leads to increased power consumption and severe heat generation in the electromagnetic flowmeter, causing the power supply static operating point to drift and the operating current to drift, which further affects the measurement accuracy and stability of the electromagnetic flowmeter. Furthermore, in addition to the aforementioned issue of misalignment between the excitation coil 2 and the measuring tube 1 during actual assembly, the actual assembly of the excitation coil 2 may also exhibit problems such as non-parallelism and tilting. Please refer to the appendix to the instruction manual. Figure 9When the magnetic coils 2 are not parallel or tilted, there is an angle between the magnetic field mid-plane M (ideal plane) between the two excitation coils 2 and the geometric center plane C of the measuring tube, which cannot be coincident. In this case, during calibration, the thickness of the space between two planes that are a certain distance apart is used to replace the magnetic field mid-plane M. That is, during the calibration process, the electromagnetic flowmeter actually clamps the geometric center plane C of the measuring tube (the area with the same diameter as the measuring tube) located inside the measuring tube 1 in the set space thickness. If the distance between the two planes is too large (i.e., the space thickness is out of tolerance, which means that the non-parallelism and tilt of the two excitation coils 2 are seriously out of tolerance), even after the electromagnetic flowmeter is calibrated, the measurement accuracy and stability still cannot meet the design requirements, and it is necessary to disassemble the two excitation coils 2 and reassemble them. Example 1

[0021] See the instruction manual appendix Figure 1 An independent drive system for excitation coils of an electromagnetic flowmeter is provided for driving excitation coils 2 that are parallel to each other on the upper and lower sides of the measuring tube 1 in the electromagnetic flowmeter. Measuring electrodes 7 are symmetrically arranged on the left and right sides of the tube wall of the measuring tube 1. (See attached instruction manual.) Figure 2 The independent drive system for the electromagnetic flowmeter excitation coil includes: excitation coil 2, H-bridge drive circuit 3, drive power supply 4, external power supply 5, and DSP controller 6. Each of the two excitation coils 2 is independently equipped with an H-bridge drive circuit 3 and a drive power supply 4. The input terminal of the drive power supply 4 is electrically connected to the external power supply 5, and its output terminal is electrically connected to the input terminal of the H-bridge drive circuit 3. The output terminal of the H-bridge drive circuit 3 is electrically connected to the corresponding excitation coil 2. The drive power supply 4 and the H-bridge drive circuit 3 are also electrically connected to the DSP controller 6. The DSP controller 6 is electrically connected to the measuring electrode 7 through an ADC conversion circuit and an output voltage sampling amplification circuit (see attached instruction manual). Figure 2 (not shown in the diagram). In this embodiment, the driving power supply 4 is a constant current source for an analog circuit, and its principle block diagram can be found in the appendix of the specification. Figure 3 The external power supply 5 is a 24V or 36V DC power source; the DSP controller 6 is equipped with a display screen and buttons, which are actually the display screen and buttons of the electromagnetic flowmeter; See the instruction manual appendix Figure 5 The H-bridge drive circuit 3 has four MOSFET switches, namely Q1, Q2, Q3, and Q4. The gates of Q1 and Q4 are connected in parallel and electrically connected to the DSP controller 6. The gates of Q2 and Q3 are connected in parallel and electrically connected to the DSP controller 6. The sources of Q1 and Q3 are connected to the positive terminal of the drive power supply 4, and the drains of Q2 and Q4 are connected to the ground of the drive power supply 4. The excitation coil 2 is electrically connected between the two arms of the H-bridge drive circuit 3. Example 2

[0022] See the instruction manual appendix Figure 2The independent drive system for the electromagnetic flowmeter excitation coil includes: excitation coil 2, H-bridge drive circuit 3, drive power supply 4, external power supply 5, and DSP controller 6. Each of the two excitation coils 2 is independently configured with an H-bridge drive circuit 3 and a drive power supply 4. The input terminal of the drive power supply 4 is electrically connected to the external power supply 5, and its output terminal is electrically connected to the input terminal of the H-bridge drive circuit 3. The output terminal of the H-bridge drive circuit 3 is electrically connected to the corresponding excitation coil 2. The drive power supply 4 and the H-bridge drive circuit 3 are also electrically connected to the DSP controller 6. The DSP controller 6 is electrically connected to the measuring electrode 7 through an ADC conversion circuit and an output voltage sampling amplification circuit (see attached instruction manual). Figure 2 (not shown in the figure). In this embodiment, the driving power supply 4 is a digital power supply, and the external power supply 5 it supplies is a 3.6V, 24V or 36V DC source. When the external power supply 5 is 3.6V, it is actually powered by a lithium-ion battery. The DSP controller 6 is equipped with a display screen and buttons, which are actually the display screen and buttons of the electromagnetic flowmeter. See the instruction manual appendix Figure 4The digital power supply includes a DC / DC conversion circuit, a MOSFET driver circuit, an MCU, a Flash memory chip, an output current sampling amplification circuit, and an ADC conversion circuit. The DC / DC conversion circuit is controlled by a PWM signal from the MCU, which steps down or boosts the external power supply 5 to drive the excitation coil 2. The MOSFET driver circuit enhances the driving capability of the PWM signal from the MCU. The current sampling amplification circuit and the ADC conversion circuit collect the current value output by the DC / DC conversion circuit, perform analog-to-digital conversion, and transmit it to the MCU. The MCU is the control core of the digital power supply. Based on the current value collected by the current sampling amplification circuit and the ADC conversion circuit, it calculates and outputs a PWM signal with a corresponding duty cycle to provide feedback control for stabilizing the output current of the drive power supply 4. The Flash memory chip stores the control program of the digital power supply and some operating parameters set by the electromagnetic flowmeter (some operating parameters are set in the DSP controller 6). In this embodiment, the DC / DC conversion circuit is a synchronous BUCK- The BOOST power supply circuit, for its specific circuit schematic, can be found in the main power circuit section of the power board circuit design in the article "Synchronous Rectification Ruck-Boost Digital Power Supply Based on STM32". It can boost or buck the input voltage of 3.6V, 24V, and 36V, thus allowing it to be powered by either a lithium-ion battery or a 24V or 36V DC power supply. In this digital power supply, the input terminal of the DC / DC converter circuit is electrically connected to the external power supply 5, and the output terminal is electrically connected to the H-bridge driver circuit 3. The MCU is electrically connected to the DC / DC converter circuit through a MOSFET driver circuit. The DC / DC converter circuit and the MCU are also electrically connected through an output current sampling amplifier circuit and an ADC conversion circuit. The Flash memory chip is electrically connected to the MCU. The DSP controller 6 is electrically connected to the MCU of the digital power supply and the H-bridge driver circuit 3. The working principle of the digital power supply can be found in "Synchronous Rectification Ruck-Boost Digital Power Supply Based on STM32", and will not be elaborated here. See the instruction manual appendix Figure 5 The H-bridge drive circuit 3 has four MOSFET switches, namely Q1, Q2, Q3, and Q4. The gates of Q1 and Q4 are connected in parallel and electrically connected to the DSP controller 6. The gates of Q2 and Q3 are connected in parallel and electrically connected to the DSP controller 6. The sources of Q1 and Q3 are connected to the positive terminal of the drive power supply 4, and the drains of Q2 and Q4 are connected to the ground of the drive power supply 4. The excitation coil 2 is electrically connected between the two arms of the H-bridge drive circuit 3. Example 3

[0023] This embodiment, based on the electromagnetic flowmeter of Embodiment 2, illustrates the calibration method for the independent drive system of the electromagnetic flowmeter's excitation coil. During calibration, one excitation coil 2 operates at a standard operating current Is, and the other excitation coil 2 operates at a calibration current Id. The standard operating current Is is determined by the design; taking a DN65 electromagnetic flowmeter as an example, the current of the excitation coil is currently mainly between 125-250mA. In the technical solution of this patent, the standard operating current Is of the excitation coil 2 is taken as 10mA. The calibration current Id is determined during the electromagnetic flowmeter calibration process. The specific calibration method for the electromagnetic flowmeter is as follows: S1. The electromagnetic flowmeter is set on the calibration workbench, with tap water as the calibration working medium, and half of the maximum range, 15m³ / h, as the standard test flow rate Qs, which flows continuously through the electromagnetic flowmeter. S2. Set the electromagnetic flowmeter to calibration mode using the button; control the drive power supply 4 and H-bridge drive circuit 3 via the DSP controller 6 to make the standard operating current Is (10mA, design value) flow in opposite directions through the excitation coils 2 located on both sides of the measuring tube 1; the specific setting process includes setting the magnitude and direction of the operating current of the excitation coil 2. Refer to the instruction manual for setting the magnitude of the operating current of the excitation coil 2. Figure 2 , 4 To explain, the DSP controller 6 sends control commands to the two digital power supplies. The MCU of the digital power supply calculates the corresponding PWM duty cycle based on the control commands and drives the DC / DC conversion circuit through the MOSFET driver circuit to output the corresponding voltage, driving the corresponding excitation coil 2 to generate a 10mA operating current. The output current sampling amplifier circuit and ADC conversion circuit feed back the operating current of the excitation coil 2 to the MCU. If the operating current of the excitation coil 2 deviates from 10mA, the MCU recalculates the PWM duty cycle based on the feedback current value and drives the DC / DC conversion circuit through the MOSFET driver circuit to output the corresponding voltage, so that the operating current of the excitation coil 2 is stabilized at 10mA. The entire current feedback control process adopts PID control. The direction setting of the operating current of the excitation coil 2 is referenced in the attached instruction manual. Figure 5Explanation: Assuming the operating current of the upper excitation coil 2 needs to be controlled to be counterclockwise and the operating current of the lower excitation coil 2 needs to be controlled to be clockwise, then the DSP controller's control pins 2 and 4 are set to high level, and pins 1 and 2 are set to low level. Switches Q2 and Q3 in the upper H-bridge drive circuit 3 are turned on, and switches Q1 and Q4 are turned off. Similarly, switches Q1 and Q4 in the lower H-bridge drive circuit 3 are turned on, and switches Q2 and Q3 are turned off. The current flow path in the upper circuit is point P, Q3, excitation coil 2, Q2, and GND, with the current direction in excitation coil 2 being counterclockwise. The current flow path in the lower circuit is point P, Q1, excitation coil 2, Q4, and GND, with the current direction in excitation coil 2 being clockwise. This achieves a standard operating current Is of 10mA (design value) flowing in opposite directions through the upper and lower excitation coils 2. (See the attached manual.) Figure 12 Assuming the excitation coil 2 of the electromagnetic flowmeter is in an ideal assembly position, since the currents in the two excitation coils 2 are in opposite directions, the resulting magnetic fields are also in opposite directions. Therefore, the magnetic induction intensity of the mid-surface M of the magnetic field, when superimposed, is zero. Furthermore, since the mid-surface M coincides with the geometric center surface C, even if a working medium (tap water) flows through the electromagnetic flowmeter, the potential difference output between the two measuring electrodes 7 remains zero. (See the attached instruction manual.) Figure 13 In reality, during the assembly process, the excitation coils 2 on both sides often experience assembly deviations. For the sake of discussion, let's assume that the excitation coils 2 are misaligned. In this case, the middle surface M of the magnetic field separates from the geometric center surface C. Therefore, the magnetic induction intensity at the geometric center surface C is not zero. When the working medium (tap water) flows through the measuring tube 1, the potential difference output between the two measuring electrodes 7 is not zero. When the excitation coils 2 are misaligned during assembly, the electromagnetic flowmeter will inevitably exhibit the following behavior during normal operation: as shown in the instruction manual. Figure 7 , 8 The problem shown in 9; S3. Calibration of the operating current of excitation coil 2: To resolve the problem mentioned in S2, the calibration method for an independent drive system of the excitation coil of a DN65 electromagnetic flowmeter is explained below. Please refer to the attached instruction manual. Figure 13 Please note: Keep the standard operating current of the lower excitation coil 2 (Is10mA) constant (or keep the standard operating current of the upper excitation coil 2 (Is10mA) constant and adjust the operating current of the lower excitation coil 2). The operating current of the upper excitation coil 2 is reduced by adjusting the corresponding drive power supply 4 via the buttons on the DSP controller 6 (or the operating current of the lower excitation coil 2 is increased). The control process for reducing the operating current of the upper excitation coil 2 is detailed in the attached instruction manual. Figure 2 , 4The DSP controller 6 sends control commands to the upper digital power supply. The MCU of the digital power supply calculates the corresponding PWM duty cycle based on the control commands and drives the DC / DC converter circuit to output a new voltage through the MOSFET driver circuit. This reduces the operating current of the upper excitation coil 2 to the new set current. The output current sampling amplifier circuit and ADC conversion circuit feed back the new operating current of the upper excitation coil 2 to the MCU. If the new operating current of the excitation coil 2 deviates from the set value, the MCU recalculates the PWM duty cycle based on the feedback current value and drives the DC / DC converter circuit to output the corresponding voltage through the MOSFET driver circuit. To stabilize the operating current of the upper excitation coil 2 at the set value, the entire current feedback control process employs PID control. During the adjustment of the operating current of the upper excitation coil 2, the DSP controller 6 detects the potential difference Ui between the two measuring electrodes 7. When the potential difference Ui = 0, the operating current in the upper excitation coil 2 is the calibration operating current Id, assumed to be 9mA. After the excitation coil operating current calibration is completed, the standard operating current Is (10mA) of the lower excitation coil 2 and the calibration operating current Id (9mA) of the upper excitation coil 2 are both stored in the DSP controller 6. (See the attached instruction manual.) Figure 14 After the operating current of excitation coil 2 is calibrated, the magnetic field of the upper excitation coil 2 decreases, causing the middle surface M of the magnetic field in the electromagnetic flowmeter to move upward and eventually coincide with the geometric center surface C. When the direction of the current in the lower excitation coil 2 is changed (the standard operating current Is10mA remains unchanged), the following will occur as shown in the attached manual. Figure 14 The magnetic field distribution inside the electromagnetic flowmeter shown is ideal, eliminating measurement errors caused by poor magnetic field distribution. It also improves the ability to suppress external electromagnetic interference, allowing the excitation coil 2 to achieve a high signal-to-noise ratio with a small drive current. While ensuring measurement accuracy and stability, it can significantly reduce the power consumption of the electromagnetic flowmeter. S4. Set the electromagnetic flowmeter to normal operating mode using the buttons. Refer to the instruction manual for specific settings. Figure 5Explanation: Pins 2 and 3 of the DSP controller 6 are set to high level, and the Q2 and Q3 switches of the upper and lower H-bridge drive circuits 3 are turned on. At this time, the current flow path of the upper and lower sides is P point, Q3, excitation coil 2, Q2, GND. The current direction of the upper and lower excitation coils 2 is counterclockwise. The working current of the upper excitation coil 2 is the calibration working current Id (9mA), and the working current of the lower excitation coil 2 is the standard working current Is (10mA). Because the magnetic field intermediate surface M and the geometric center surface C have been over-calibrated in step S2, the combined magnetic field distribution after the superposition of the two independent magnetic fields at the geometric center surface C of the electromagnetic flowmeter is in a relatively ideal state of uniform magnetic induction intensity and orthogonal direction. It will not introduce measurement error due to poor magnetic field distribution in the electromagnetic flowmeter. At the same time, it has good linearity throughout the entire flow range and has good suppression capability against external electromagnetic interference. Therefore, it has high measurement accuracy and stability with extremely low power consumption. Using the technical solution of this invention, the DN65 electromagnetic flowmeter has extremely low power consumption (excitation coil working current). Under the premise of a maximum operating current of 10mA, it still meets the 0.5-level accuracy standard. When powered by a lithium-ion battery, the battery life can reach more than 6 years. After the electromagnetic flowmeter is set to normal operating mode, the excitation coil 2 rectangular wave drive frequency is usually set to low-frequency rectangular wave mode, with an operating frequency of 6.25Hz and a measurement sampling frequency of 2.0KHz. For ultra-large diameter electromagnetic flowmeters, such as sewage pipes with a diameter exceeding 500mm, due to the excessive inductance of the excitation coil 2, the drive frequency is set below 1.0Hz. The sampling frequency is also 2.0 kHz. After the electromagnetic flowmeter is set to normal operating mode, the indicated value Qm is measured at flow rates of 6.4, 15.5, and 31.0 m³ / h, respectively. The relative error E is calculated, and the electromagnetic flowmeter is judged to meet the corresponding accuracy class standard based on the relative error E. The formula for calculating the relative error E is: E = (Qm - Qs) / Qs; where Qm is the indicated value being calibrated, and Qs is the standard indicated value. For the actual test results of this DN65 electromagnetic flowmeter, please refer to the appendix of the instruction manual. Figure 15 It fully meets the 0.5 level accuracy standard, is deemed qualified, and the calibration work is completed; If the actual test results of the electromagnetic flowmeter after calibration cannot meet the 0.5 accuracy standard, the standard operating current Is should be increased by 5% based on the previous calibration, i.e., the standard operating current Is should be adjusted to 10.5mA. Then repeat the S3-S4 calibration process until the increased standard operating current Is reaches 2.0 times the initial standard operating current Is (i.e., 20mA). If the electromagnetic flowmeter still fails the test after calibration, it is determined that the electromagnetic flowmeter assembly is unqualified. It needs to be disassembled and reassembled, and then calibrated and tested again. Example 4

[0024] Based on the DN65 electromagnetic flowmeter calibrated in Example 3, the driving method of the independent drive system for the electromagnetic flowmeter excitation coil is specifically described: The calibrated operating current Id (9.0mA) of the upper excitation coil 2 and the standard operating current Is (10mA) of the lower excitation coil 2 of the calibrated electromagnetic flowmeter are stored in the DSP controller 6. Before the electromagnetic flowmeter operates, during initialization, the DSP controller 6 automatically loads Is (10mA) and Id (9.0mA) into the MCU of the digital power supply. The MCU controls the current output value of the corresponding DC / DC conversion circuit, making the operating current of the excitation coil 2 located above the measuring tube 1 9.0mA and the operating current of the excitation coil 2 located below the measuring tube 1 10.0mA. When the electromagnetic flowmeter operates, the DSP controller 6 sends a PWM control signal at a frequency of 6.25Hz (with a period of 160ms) (changing the level of control pins 1, 2, 3, and 4 of the DSP controller 6), driving the H-bridge drive circuit 3 to flip the current direction in the excitation coil 2 once. For the specific driving process, please refer to the attached instruction manual. Figure 5To clarify: During the first half of a driving cycle of excitation coil 2, control pins 2 and 3 of DSP controller 6 are set to high level, and control pins 1 and 4 are set to low level. At this time, the current direction of both upper and lower excitation coils 2 is counterclockwise. During the second half of the driving cycle, control pins 1 and 4 of DSP controller 6 are set to high level, and control pins 2 and 3 are set to low level. At this time, the current direction of both upper and lower excitation coils 2 is clockwise. This process continues, with DSP controller 6 controlling the two excitation coils 2 to operate in a rectangular wave mode. When the two excitation coils 2 operate in a rectangular wave mode, the MCU of the digital power supply continuously provides feedback control of the output current of the DC / DC conversion circuit, meaning the MCU always... The output current of the DC / DC conversion circuit can be detected, and the DSP controller 6 and MCU can always detect the operating current of the two excitation coils 2 through communication. When the DSP controller 6 detects that the operating current of the two excitation coils 2 has completed its reversal and reached a stable state, it then collects the potential difference between the two measuring electrodes 7 at a set frequency of 2.0KHz. This eliminates the differential high-frequency interference caused by the reversal of the current direction of the excitation coils 2, and improves the detection accuracy and stability of the electromagnetic flowmeter. The following describes the process of collecting the potential difference between the measuring electrodes 7: At the beginning of the first half of the driving cycle of the excitation coils 2, the currents of the upper and lower excitation coils 2 rise synchronously. When the DSP controller 6 detects that the operating current of the two excitation coils 2 has completed its reversal and reached a stable state, it collects the potential difference between the two measuring electrodes 7 at a set frequency of 2.0KHz. After both currents reach their preset values ​​(10mA and 9.0mA respectively), a 2.0ms delay is set, and the DSP controller 6 begins to acquire the potential difference Ui between the two measuring electrodes 7 at a frequency of 2.0kHz. 2.0ms before the end of the first half-cycle, the DSP controller 6 stops acquiring the potential difference between the two measuring electrodes 7, thus avoiding high-frequency differential interference caused by the current reversal in the excitation coil 2. At the beginning of the second half-cycle of one driving cycle of the excitation coil 2, the currents of the upper and lower excitation coils 2 synchronously commutate and rise. After the DSP controller 6 detects that both currents have reached their preset values ​​(10mA and 9.0mA respectively), a 2.0ms delay is set, and the DSP controller 6 starts... The potential difference Ui between the two measuring electrodes 7 is initially acquired at a frequency of 2.0 kHz. 2.0 ms before the end of the second half-cycle, the DSP controller 6 stops acquiring the potential difference between the two measuring electrodes 7, thus avoiding high-frequency interference caused by the reversal of the current direction of the excitation coil 2. Therefore, in one driving cycle of the excitation coil 2, flow data can actually be acquired twice, that is, the actual sampling frequency of the flow data is 12.5 Hz. In half a driving cycle of the excitation coil 2, the actual time for acquiring Ui data is about 64 ms (80% of the half-cycle duration), and a total of 128 flow data points can be acquired. These 128 flow data points are filtered and averaged to obtain the final flow data.

[0025] It should be noted that in Examples 3 and 4, only one set of standard operating parameters for the electromagnetic flowmeter of the present invention is illustrated, including a standard operating current Is (10mA), a 6.25Hz rectangular wave drive for the excitation coil, and a sampling period of 2.0KHz. In actual field applications, the operating parameters of the electromagnetic flowmeter can be flexibly set according to the specific conditions. For example, if the factory-set accuracy of the electromagnetic flowmeter is 0.5%, but high-precision flow information acquisition is required in the pharmaceutical field, the standard operating current Is can be set to 125mA or 250mA via the buttons on the flowmeter. Online calibration can improve the accuracy of electromagnetic flowmeters to 0.3 or 0.2 class. When used for flow measurement of complex fluids such as slurry and concrete, the excitation coil rectangular wave drive frequency can be set to 25Hz via buttons on the electromagnetic flowmeter, combined with a 2.0KHz sampling frequency to enhance the suppression of fluid noise. For applications where the flow rate of the detected medium fluctuates greatly, the excitation coil rectangular wave drive frequency can be adjusted to 200Hz. After the drive current stabilizes during the positive and negative half-cycles of one drive cycle, only 1-2 flow data points need to be collected to achieve an actual flow sampling frequency of 400Hz.

[0026] To further clarify, the calibration and driving methods of the electromagnetic flowmeter using analog circuit power supply in Example 1 are the same as those of the electromagnetic flowmeter using digital power supply in Example 2. The difference is that, since the current adjustment of the analog circuit power supply is affected by the inherent parameters of the circuit electrical components, the adjustable range is smaller. In practical applications, the adjustable range and flexibility of its working parameters are significantly different from those of the electromagnetic flowmeter using digital power supply.

[0027] The parts of this invention not described in detail are prior art.

Claims

1. An independent drive system for the excitation coil of an electromagnetic flowmeter, connected to an external power supply (5), for driving the excitation coils (2) arranged on both sides outside the measuring tube (1) of the electromagnetic flowmeter, wherein a pair of measuring electrodes (7) are also provided on the measuring tube (1); characterized in that: Two excitation coils (2) are independently equipped with driving power supplies (4); the two driving power supplies (4) are coordinated and controlled by a DSP controller (6) to drive the two excitation coils (2) to generate independent magnetic fields respectively; the two independent magnetic fields are superimposed to form a composite magnetic field located between the two excitation coils (2) in the measuring tube (1).

2. The independent drive system for the excitation coil of the electromagnetic flowmeter according to claim 1, characterized in that: The driving power supply (4) is an analog circuit power supply.

3. The independent drive system for the excitation coil of the electromagnetic flowmeter according to claim 1, characterized in that: The driving power supply (4) is a digital power supply, including a DC / DC conversion circuit, a MOS transistor driving circuit, an MCU, a Flash memory chip, a current sampling amplifier circuit, and an ADC conversion circuit; Among them, the DC / DC conversion circuit is controlled by the PWM signal issued by the MCU, which steps down (or boosts) the external power supply (5) and outputs it to drive the excitation coil (2) to work. Among them, the MOSFET drive circuit is used to improve the driving capability of the PWM signal issued by the MCU; Among them, the current sampling amplifier circuit and the ADC conversion circuit are used to collect the current value output by the DC / DC conversion circuit, perform analog-to-digital conversion, and then transmit it to the MCU; Among them, the MCU is the control core of the drive power supply (4). After calculating the current value collected by the current sampling amplifier circuit and the ADC conversion circuit, it outputs the PWM signal with the corresponding duty cycle, and controls the stability of the output current of the drive power supply (4) through the feedback control of the MOS tube drive circuit. The Flash memory chip is used to store the control program of the drive power supply (4) and the parameters of the electromagnetic flowmeter operation settings.

4. The independent drive system for the excitation coil of the electromagnetic flowmeter according to claim 3, characterized in that: The DC / DC conversion circuit is a synchronous BUCK-BOOST power supply circuit.

5. The independent drive system for the excitation coil of the electromagnetic flowmeter according to claim 2 or 4, characterized in that: It also includes an H-bridge drive circuit (3); the H-bridge drive circuit (3) is controlled by a DSP controller (6) to convert the constant current mode output by the drive power supply (4) into a rectangular wave mode to drive the excitation coil (2) to work.

6. The independent drive system for the excitation coil of the electromagnetic flowmeter according to claim 5, characterized in that: The H-bridge drive circuit (3) is equipped with four switching transistors, of which two switching transistors on opposite bridge arms are connected in parallel and electrically connected to the DSP controller (6); or all four switching transistors are independently electrically connected to the DSP controller (6).

7. The independent drive system for the excitation coil of the electromagnetic flowmeter according to claim 6, characterized in that: The DSP controller (6) is electrically connected to the measuring electrode (7) through the ADC conversion circuit and the output voltage sampling amplification circuit; the output voltage sampling amplification circuit is used to collect and amplify the voltage signal between the two measuring electrodes (7), and the ADC conversion circuit is used for the analog-to-digital conversion of the amplified voltage signal.

8. A calibration method based on the independent drive system of the electromagnetic flowmeter excitation coil as described in claim 7, characterized in that: During calibration, the operating current of one excitation coil (2) is set to the standard operating current Is, and the operating current of the other excitation coil (2) is set to the calibration operating current Id; the standard operating current Is is determined by the design, and the calibration operating current Id is determined during the calibration of the electromagnetic flowmeter; the specific steps of the electromagnetic flowmeter calibration method are as follows: S1. The electromagnetic flowmeter is set on the calibration workbench, with tap water as the calibration working medium, and half of the maximum range as the standard test flow rate Qs, which flows continuously through the electromagnetic flowmeter. S2. Set the electromagnetic flowmeter to calibration mode, so that the standard working current Is flows in opposite directions through the excitation coils (2) located on both sides of the measuring tube (1); S3. One of the excitation coils (2) keeps the standard working current Is constant, while the other excitation coil (2) adjusts the driving power supply (4) through the DSP controller (6) to bidirectionally adjust the working current. During the bidirectional adjustment of the current in the other excitation coil (2), the DSP controller (6) detects the potential difference Ui between the two measuring electrodes (7). When the potential difference Ui between the two measuring electrodes (7) is 0, the working current in the other excitation coil (2) is the calibration working current Id. The standard working current Is and the calibration working current Id are both stored in the DSP controller (6). S4. Set the electromagnetic flowmeter to normal operating mode. The operating current of one excitation coil (2) is the standard operating current Is, and the operating current of the other excitation coil (2) is the calibration operating current Id. The current directions in the two coils are the same. The DSP controller (6) switches the operating current directions of the two excitation coils (2) at a set frequency. Read the measurement results Qm of the electromagnetic flowmeter at three set flow points and calculate the relative error E of the indication. Determine whether the electromagnetic flowmeter meets the corresponding accuracy level standard based on the relative error E of the indication. The formula for calculating the relative error E of the indication is: E = (Qm - Qs) / Qs; Where Qm is the value being calibrated, and Qs is the standard value; If the relative error E of the indicated value meets the corresponding accuracy level standard, the electromagnetic flowmeter is deemed qualified, and the calibration work is completed.

9. The calibration method for the independent drive system of the electromagnetic flowmeter excitation coil according to claim 8, characterized in that: If the electromagnetic flowmeter is deemed unqualified, adjust the standard operating current Is by increasing it by 2.5-5% based on the previous calibration, and then repeat the S3-S4 calibration process. Continue until the increased standard operating current Is reaches 1.5-2.0 times the initial standard operating current Is. If the electromagnetic flowmeter calibration is still unqualified, then the electromagnetic flowmeter assembly is deemed unqualified.

10. A driving method based on the independent driving system of the electromagnetic flowmeter excitation coil as described in claim 8, characterized in that: The DSP controller (6) controls two drive power supplies (4) to provide working current to the corresponding excitation coils (2) with standard working current Is and calibration working current Id respectively, and the current direction in the two excitation coils (2) is the same; the DSP controller (6) controls two H-bridge drive circuits (3) to synchronously change the current direction in the two excitation coils (2) at a set frequency, so that the two excitation coils (2) work in a synchronous rectangular wave excitation mode; when the DSP controller (6) detects that the current direction of the two excitation coils (2) is reversed and the current is stable, it samples the potential difference between the two measuring electrodes (7) at a set sampling frequency.

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