High-frequency electromagnetic flowmeter

Abstract

The high-frequency electromagnetic flowmeter comprises an electromagnetic flow converter and an electromagnetic flow sensor, the electromagnetic flow converter is electrically connected with the electromagnetic flow sensor, and the electromagnetic flow converter comprises an A / D analog-to-digital converter, a differential amplifier, a single-chip microcomputer, an electronic switch group and a direct-current constant-current source. The electromagnetic flow sensor comprises a measuring conduit, a measuring electrode, a magnetic conductive piece, a temperature sensor and a magnet exciting coil; according to the electromagnetic flowmeter, the high-frequency three-valued rectangular wave is adopted as excitation current, a flow signal with the sampling frequency one time higher than the excitation frequency is generated through induction, and therefore the noise interference restraining capacity of the electromagnetic flowmeter is improved; by adopting a technical measure which is the same as that of suppressing power frequency interference by low-frequency rectangular waves, the purposes of amplifying flow signals and suppressing power frequency series mode interference and common mode interference are achieved, and the production cost is reduced; the temperature sensor is additionally arranged in the electromagnetic flow sensor, so that the high-frequency electromagnetic flow meter can compensate and correct measurement errors caused by temperature changes.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic flowmeters, in particular to a high-frequency electromagnetic flowmeter. Background Art

[0002] Electromagnetic flowmeter is widely used because its measuring tube is a smooth straight tube without any flow-blocking detection parts and will not be blocked. It can be used to measure liquid-solid two-phase fluids and low-conductivity fluids such as clean water, sewage, mud, pulp, water-coal slurry, etc. In the prior art, most of the electromagnetic flowmeters used are low-frequency rectangular wave excitation electromagnetic flowmeters and dual-frequency electromagnetic flowmeters. Low-frequency rectangular wave excitation electromagnetic flowmeters can only measure the flow of conductive media such as clean water and sewage, and cannot measure the flow of slurry or low-conductivity fluids. Although dual-frequency electromagnetic flowmeters can solve this problem, they still have the following disadvantages: 1. Theory and practice have proved that the magnitude of flow noise interference in slurry measurement is inversely proportional to the frequency of the flow signal. Therefore, in order to reduce the fluctuation of the measurement state, the frequency of the flow signal must be increased as much as possible. The dual-frequency electromagnetic flowmeter uses a high-frequency binary rectangular wave excitation technology solution. If the ability to suppress slurry noise is to be improved, the excitation frequency can only be increased. However, the increase in excitation frequency will cause an increase in eddy current loss of the magnetic conductive parts, causing temperature changes in the magnetic conductive parts, thereby adversely affecting the measurement results. The measurement error caused by this temperature change restricts the increase in the excitation frequency; 2. The dual-frequency electromagnetic flowmeter suppresses the power frequency interference as interference on the high-frequency flow signal, but the two are actually inconsistent (see Figure 2 (c) is the back end), so it is necessary to obtain the high-frequency and low-frequency coefficients through secondary calibration, and the correct flow measurement value can be displayed through the compensation operation of the single-chip microcomputer, and two signal amplification and processing paths are required, thus increasing the production cost; 3. Since the eddy current loss caused by the temperature change of the magnetic conductive parts is proportional to the square of the excitation current frequency, the zero position change caused by temperature change in the low-frequency rectangular wave electromagnetic flowmeter is almost negligible, but in the electromagnetic flowmeter with high-frequency excitation, it will cause a very large change in the instrument zero position, resulting in visible measurement errors. Summary of the invention

[0003] The object of the present invention is to provide a high frequency electromagnetic flowmeter to solve the problems raised in the above background technology.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: a high-frequency electromagnetic flowmeter, including an electromagnetic flow converter and an electromagnetic flow sensor, wherein the electromagnetic flow converter and the electromagnetic flow sensor are electrically connected, the electromagnetic flow converter includes an A / D analog-to-digital converter, a differential amplifier, a single-chip microcomputer, an electronic switch group and a DC constant current source, and the single-chip microcomputer is electrically connected to the A / D analog-to-digital converter and the electronic switch group respectively, the A / D analog-to-digital converter is electrically connected to the differential amplifier, the electronic switch group is electrically connected to the DC constant current source, the electromagnetic flow sensor includes a measuring conduit, measuring electrodes are fixedly connected to the outer walls of both sides of the measuring conduit, and the differential amplifier is electrically connected to the measuring electrodes, a magnetic conductive part is fixedly connected to the measuring conduit, an excitation coil is sleeved on the magnetic conductive part, and the electronic switch group is electrically connected to the excitation coil, a temperature sensor is fixedly connected to the magnetic conductive part, and the temperature sensor is electrically connected to the electromagnetic flow converter.

[0005] Preferably, the high-frequency electromagnetic flowmeter uses the same technical solution as the low-frequency electromagnetic flowmeter to suppress the power frequency interference on the high-frequency flow signal and its influence on the measurement.

[0006] Preferably, the excitation current of the electromagnetic flow sensor is a high-frequency three-value rectangular wave.

[0007] Preferably, the flow signal sampling frequency of the electromagnetic flow sensor is twice as high as the excitation frequency.

[0008] Preferably, the A / D analog-to-digital converter is electrically connected to a temperature sensor.

[0009] The high-frequency electromagnetic flowmeter provided by the present invention has the following advantages: the present invention adopts a high-frequency three-value rectangular wave as the excitation current, and induces a flow signal with a sampling frequency twice as high as the excitation frequency, thereby improving the ability of the electromagnetic flowmeter to suppress noise interference; by adopting the same technical measures as the low-frequency rectangular wave to suppress the power frequency interference, the purpose of amplifying the flow signal and suppressing the power frequency series mode interference and common mode interference is achieved, thereby reducing the production cost; by adding a temperature sensor to the electromagnetic flow sensor, the high-frequency electromagnetic flowmeter can compensate and correct the measurement error caused by temperature changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0011] Figure 1 It is the overall structural diagram of the present invention;

[0012] Figure 2 It is a waveform diagram of the excitation current, flow signal, interference signal and sampling control signal of the present invention.

[0013] In the figure: 1. Electromagnetic flow converter; 11. A / D analog-to-digital converter; 12. Differential amplifier; 13. Single chip microcomputer; 14. Electronic switch group; 15. DC constant current source; 2. Electromagnetic flow sensor; 21. Measuring catheter; 22. Measuring electrode; 23. Magnetic conductive part; 24. Temperature sensor; 25. Excitation coil; 3. Converter screen; 4. Button. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] Please refer to the attached Figure 1 -Attached Figure 2The present invention provides an embodiment: a high-frequency electromagnetic flowmeter, comprising an electromagnetic flow converter 1 and an electromagnetic flow sensor 2, wherein the electromagnetic flow converter 1 and the electromagnetic flow sensor 2 are electrically connected, the electromagnetic flow converter 1 comprises an A / D analog-to-digital converter 11, a differential amplifier 12, a single-chip microcomputer 13, an electronic switch group 14 and a DC constant current source 15, and the single-chip microcomputer 13 is electrically connected to the A / D analog-to-digital converter 11 and the electronic switch group 14 respectively, the A / D analog-to-digital converter 11 is electrically connected to the differential amplifier 12, the electronic switch group 14 is electrically connected to the DC The constant current source 15 is electrically connected, the electromagnetic flow sensor 2 includes a measuring conduit 21, measuring electrodes 22 are fixedly connected to the outer walls of both sides of the measuring conduit 21, and the differential amplifier 12 is electrically connected to the measuring electrodes 22, a magnetic conductive part 23 is fixedly connected to the measuring conduit 21, an excitation coil 25 is sleeved on the magnetic conductive part 23, and the electronic switch group 14 is electrically connected to the excitation coil 25, a temperature sensor 24 is fixedly connected to the magnetic conductive part 23, and the temperature sensor 24 is electrically connected to the electromagnetic flow converter 1, and the electromagnetic flow sensor 2 is used to collect Fluid flow data, the electromagnetic flow converter 1 is used to generate high-frequency three-value rectangular wave excitation current and data processing, the measuring catheter 21 is used for fluid circulation, the magnetic conductive member 23 is used to improve the uniformity of magnetic field distribution, the temperature sensor 24 is used to detect temperature, the measuring electrode 22 is used to connect the signal line, the A / D analog-to-digital converter 11 is used for analog-to-digital conversion, the differential amplifier 12 is used to amplify the signal, the single-chip microcomputer 13 is used to complete the frequency multiplication processing of the flow signal sampling frequency, the suppression processing of various interferences and the compensation and correction of the zero position change caused by temperature change, the electronic switch group 14 is used to control the circuit on and off, and the DC constant current source 15 is used to supply power for the excitation current; the high-frequency electromagnetic flowmeter uses the same technical solution as the low-frequency electromagnetic meter to suppress the power frequency interference on the high-frequency flow signal and its influence on the measurement; the excitation current of the electromagnetic flow sensor 2 is a high-frequency three-value rectangular wave, which is used to improve the ability of the electromagnetic flowmeter to suppress noise interference; the flow signal sampling frequency of the electromagnetic flow sensor 2 is twice as high as the excitation frequency; the A / D analog-to-digital converter 11 is electrically connected to the temperature sensor 24, and the temperature sensor 24 inputs the signal into the A / D analog-to-digital converter 11.

[0016] Working principle: In the present invention, the polarization voltage generated by the measuring electrode 22 during operation will generate noise interference, resulting in large fluctuations in output when measuring two-phase fluid or low conductivity fluid. However, due to the use of high-frequency three-value rectangular wave excitation current, the frequency of the flow signal generated by induction is twice as high as the flow signal frequency generated by high-frequency binary wave excitation induction, thereby doubling the ability of the electromagnetic flowmeter to suppress noise interference. Specifically, Figure 2 As shown, Figure 2 (a) shows the continuous 50Hz sine wave power frequency interference waveform. Figure 2(b) is a high-frequency three-value rectangular wave, indicating that the period of the 1Hz excitation frequency is 5ms, so the excitation frequency is 200Hz, and the sampling frequency of the flow signal is 400Hz. The power consumption of the 200Hz excitation frequency achieves the same effect of suppressing slurry noise and flow noise as the flow signal with a sampling frequency of 400Hz. Figure 2 (c) is the power frequency interference waveform at zero flow, indicating the "local" power frequency interference sampled by the flow signal conversion at zero flow. Figure 2 (d) is the normal high-frequency flow signal Ea sampled by the first sampling signal a and the corresponding power frequency interference "local" sa, Figure 2 (e) is the negative flow signal Eb sampled by the second sampling signal b and the corresponding power frequency interference "local" sb, from Figure 2 (d) and Figure 2 (e) It can be seen that the flow signal is sampled twice in the 5ms cycle time, one is the positive flow signal Ea, and the other is the negative flow signal Eb. Figure 2 (f) is the flow signal waveform after being amplified by the differential amplifier 12. Figure 2 (g) is the first sampling timing a, Figure 2(h) is the second sampling sequence b; the principle of suppressing power frequency interference and amplifying flow signal is: when a1, a2, a3, a4 in the first sampling sequence sample the normal flow signals Ea1, Ea2, Ea3, Ea4, the power frequency interference local sa1, sa2, sa3, sa4 are also sampled and become string mode interference; when it is input from the A terminal to the differential amplifier 12, a summation operation is realized; as can be seen in the figure, sa1+sa2=-(sa3+sa4), which are equal in size but opposite in direction, so the output terminal Vo=0; the string mode interference input from the A terminal is effectively suppressed; similarly, the string mode power frequency interference input from the B terminal of the differential amplifier 12 sb1, sb2, sb3, and sb4 are also effectively suppressed; the process is repeated to eliminate the influence of the power frequency cross-mode on the measurement; in the positive half cycle (10ms) of the power frequency interference, the power frequency interference input from the A end of the differential amplifier 12 is locally sa1 and sa2, and the power frequency interference input from the B end is sb1 and sb2, and sa1+sa2=sb1+sb2, forming a common mode interference of equal magnitude and direction, and the differential amplifier 12 performs a subtraction operation, and the output value Vo=0 at the output end; similarly, in the negative half cycle (10ms) of the power frequency interference, the power frequency interference input from the A end is locally -sa3 and -sa4, and the power frequency interference input from the B end is The power frequency interference is -sb3, -sb4, and -(sa3+sa4)=-(Sb3+sb4), which becomes common mode interference of equal magnitude and direction. After the subtraction operation of the differential amplifier 12, the power frequency common mode value Vo=0 outputted from the output end, and the power frequency common mode interference input to the differential amplifier end is effectively suppressed. The process is repeated to eliminate the influence of the power frequency common mode interference on the measurement. When the flow rate of the measured fluid is stable (including zero flow) and the amplifier gain factor is K, after the normal flow signal Ea1 is input to the A end and Eb1 is input to the B end, the differential amplifier 12 performs a subtraction operation: Vo=K[Ea1-(-Eb1)]=2KE; zero flow When measuring, Vo=0; the flow signal is stably amplified; the technical measures to compensate for the measurement error caused by temperature change are: installing a temperature sensor 24 on the magnetic conductive part 23 in the electromagnetic flow sensor 2; after the flow meter obtains the sensor coefficient through calibration, the zero position of multiple temperature points can be added; the method of setting the zero point is as follows: after the electromagnetic flow sensor 2 is installed and the flow is passed, select several temperature points as needed, when the selected temperature point is displayed on the converter screen 3, close the valve, the display screen will display the zero position of the temperature point, and by operating the button 4, set the selected temperature point and its zero position to the corresponding position in the menu, and the flow meter will enter the normal working state after the flow is passed;This operation is repeated several times, for example, a zero position is set at 20°C, 25°C, 30°C, and 35°C, and a three-segment zero position broken line is formed in the temperature compensation calculation. At this time, the zero position of the flow meter is no longer the zero position during flow calibration, but a continuous dynamic zero position from 20°C to 35°C. The more zero positions are set, the smaller the measurement error. In this way, although the flow meter has a zero position change due to temperature changes, the sensor coefficient of the flow meter is still the factory calibration value, so the flow value displayed and output by the flow meter after the zero position is corrected is a correct value; wherein, the electronic switch group 14 is used to control the circuit conduction, the DC constant current source 15 is used to supply power for the excitation current, the measuring conduit 21 is used for fluid circulation, the A / D analog-to-digital converter 11 is used for analog-to-digital conversion, and the excitation coil 25 is used to detect the flow rate of the fluid. ;

[0017] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0018] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0019] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high frequency electromagnetic flowmeter, comprising an electromagnetic flow converter (1) and an electromagnetic flow sensor (2), characterized in that: The electromagnetic flow converter (1) and the electromagnetic flow sensor (2) are electrically connected. The electromagnetic flow converter (1) comprises an A / D analog-to-digital converter (11), a differential amplifier (12), a single-chip microcomputer (13), an electronic switch group (14) and a direct current constant current source (15). The single-chip microcomputer (13) is electrically connected to the A / D analog-to-digital converter (11) and the electronic switch group (14), respectively. The A / D analog-to-digital converter (11) is electrically connected to the differential amplifier (12), the electronic switch group (14) is electrically connected to the direct current constant current source (15), and the electromagnetic flow sensor (2) is electrically connected to the electromagnetic flow converter (1). The flow sensor (2) comprises a measuring conduit (21), measuring electrodes (22) are fixedly connected to the outer walls of both sides of the measuring conduit (21), and a differential amplifier (12) is electrically connected to the measuring electrodes (22); a magnetic conductive part (23) is fixedly connected to the measuring conduit (21), an excitation coil (25) is sleeved on the magnetic conductive part (23), and an electronic switch group (14) is electrically connected to the excitation coil (25); a temperature sensor (24) is fixedly connected to the magnetic conductive part (23), and the temperature sensor (24) is electrically connected to the electromagnetic flow converter (1).

2. The high frequency electromagnetic flowmeter according to claim 1, characterized in that: The same technical solution as the low-frequency electromagnetic flow meter is used to suppress the power frequency interference on the high-frequency flow signal and its influence on the measurement.

3. The high frequency electromagnetic flowmeter according to claim 1, characterized in that: The excitation current of the electromagnetic flow sensor (2) is a high-frequency three-value rectangular wave.

4. The high frequency electromagnetic flowmeter according to claim 3, characterized in that: The flow signal sampling frequency of the electromagnetic flow sensor (2) is twice as high as the excitation frequency.

5. The high frequency electromagnetic flowmeter according to claim 1, characterized in that: The A / D analog-to-digital converter (11) is electrically connected to the temperature sensor (24).

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