An electromagnetic flowmeter

Abstract

This invention relates to the field of flow measurement technology and discloses an electromagnetic flowmeter. The electromagnetic flowmeter includes a pipeline, an excitation coil, a measuring electrode, a power supply module, a grounding electrode, and a signal processing module. The power supply module is used to convert external AC power into DC power suitable for the operation of the excitation coil and output it. The grounding electrode is disposed on the pipeline and is used to connect the fluid in the pipeline to the signal grounding terminal. The signal processing module is connected to the measuring electrode and processes the signal output by the measuring electrode to obtain the flow measurement result. This invention reduces the production cost of the electromagnetic flowmeter by using a grounding electrode instead of a grounding ring.

Description

Technical Field

[0001] This invention relates to the field of flow measurement technology, and more particularly to an electromagnetic flow meter. Background Technology

[0002] An electromagnetic flowmeter is an instrument that uses the principle of electromagnetic induction to measure the flow rate of a conductive fluid based on the electromotive force induced when the fluid passes through an external magnetic field.

[0003] Currently, in electromagnetic flowmeters, the equipotential connection between the measuring reference and the medium is crucial. Different connection methods exist for different measuring pipes. For metal pipes, a direct connection is sufficient to achieve basic equipotential connection. However, for non-metallic pipes such as PVC, the standard approach is to install a grounding ring. The equivalent circuit diagram after grounding with a grounding ring is shown below. Figure 1 As shown.

[0004] While adding a grounding ring can achieve a basic equipotential connection, it also has significant drawbacks. The grounding ring material often needs to match the measuring electrodes. In cases with large measuring diameters and special applications requiring Hastelloy or platinum electrodes, using a grounding ring of the appropriate material increases the cost, consequently raising the overall cost of the electromagnetic flowmeter. Summary of the Invention

[0005] In view of this, the present invention provides an electromagnetic flowmeter to solve or partially solve the technical problem of high cost caused by the use of grounding rings in existing electromagnetic flowmeters.

[0006] The technical solution proposed in this invention is as follows:

[0007] This invention provides an electromagnetic flowmeter, comprising a pipeline, an excitation coil, and a measuring electrode. The flowmeter is characterized by further comprising a power supply module, a grounding electrode, and a signal processing module. The power supply module converts external alternating current into direct current suitable for the operation of the excitation coil and outputs it. The grounding electrode is disposed in the pipeline and connects the fluid within the pipeline to a signal grounding terminal. The signal processing module is connected to the measuring electrode and processes the signal output by the measuring electrode to obtain the flow measurement result.

[0008] In some alternative implementations, the power module includes a transformer and a bridging capacitor. The transformer includes a primary winding and a secondary winding. One end of the primary winding is connected to one end of the bridging capacitor, and the other end of the bridging capacitor is connected to a signal ground terminal. The secondary winding is connected to the excitation coil.

[0009] In some alternative embodiments, the capacitance of the bridging capacitor is 500pF to 1000pF.

[0010] In some alternative embodiments, the power module further includes a rectifier module and a switching power supply chip. The input terminal of the rectifier circuit is connected to an external AC input terminal, the positive output terminal of the rectifier circuit is connected to one end of the first winding, the negative output terminal of the rectifier circuit is connected to the input terminal of the switching power supply chip, and the output terminal of the switching power supply chip is connected to the other end of the primary winding.

[0011] In some alternative embodiments, the power module further includes a filter output circuit, the secondary winding includes a first secondary winding, the input terminal of the filter output circuit is connected to the first secondary winding, and the output terminal of the filter output circuit is connected to the excitation coil.

[0012] In some alternative embodiments, the power module further includes an enable circuit, the secondary winding further includes a second secondary winding, the two input terminals of the enable circuit are respectively connected to the two ends of the first secondary winding, one output terminal of the enable circuit is connected to one end of the second secondary winding, the other output terminal of the enable circuit is connected to the enable terminal of the switching power supply chip, and the other end of the second secondary winding is connected to the input terminal of the switching power supply chip.

[0013] In some alternative implementations, the signal processing module includes an instrumentation amplifier and a processor, with the input of the instrumentation amplifier connected to the measuring electrode and the output of the instrumentation amplifier connected to the processor.

[0014] In some optional embodiments, the signal processing module further includes a first first-order RC filter output circuit and a second first-order RC filter output circuit. The input terminal of the first first-order RC filter output circuit is connected to one of the measurement electrodes, and the output terminal of the first first-order RC filter output circuit is connected to the non-inverting input terminal of the instrumentation amplifier. The input terminal of the second first-order RC filter output circuit is connected to another measurement electrode, and the output terminal of the second first-order RC filter output circuit is connected to the inverting input terminal of the instrumentation amplifier. The output terminal of the instrumentation amplifier is connected to the processor. The cutoff frequency of both the first and second first-order RC filter output circuits is 10kHz to 50kHz.

[0015] In some alternative embodiments, the first first-order RC filter output circuit includes a second resistor and a second capacitor. One end of the second resistor is connected to one of the measurement electrodes, and the other end of the second resistor is connected to the non-inverting input terminal of the instrumentation amplifier. One end of the second capacitor is connected to the non-inverting input terminal of the instrumentation amplifier, and the other end of the second capacitor is connected to the signal ground terminal. The second first-order RC filter output circuit includes a third resistor and a third capacitor. One end of the third resistor is connected to another of the measurement electrodes, and the other end of the third resistor is connected to the inverting input terminal of the instrumentation amplifier. One end of the third capacitor is connected to the inverting input terminal of the instrumentation amplifier, and the other end of the third capacitor is connected to the signal ground terminal.

[0016] In some alternative implementations, the second and third resistors are precision resistors with the same nominal resistance value.

[0017] As can be seen from the above technical solutions, the present invention has the following advantages:

[0018] The present invention provides an electromagnetic flowmeter, including a pipeline, an excitation coil, a measuring electrode, a power supply module, a grounding electrode, and a signal processing module. By using a grounding electrode instead of a grounding ring, the production cost of the electromagnetic flowmeter can be reduced, the installation process of the electromagnetic flowmeter can be simplified, and the risk of pipeline leakage can be effectively reduced.

[0019] By setting a bridging capacitor C1, common-mode interference caused by the introduction of ground electrode 4 can be effectively suppressed, thereby improving the accuracy of flow measurement.

[0020] By controlling the cutoff frequencies of the first-order RC filter output circuit and the second-order RC filter output circuit to between 10kHz and 50kHz, the interference of the power mode can be further suppressed. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a block diagram illustrating the principle of electromagnetic flowmeters in the prior art.

[0023] Figure 2 This is an equivalent circuit diagram of an electromagnetic flowmeter in an embodiment of the present invention;

[0024] Figure 3 This is an equivalent circuit diagram of another electromagnetic flowmeter in an embodiment of the present invention;

[0025] Figure 4 This is a circuit diagram of the electromagnetic flowmeter in an embodiment of the present invention;

[0026] Figure 5 This is a circuit schematic diagram of the power module in an embodiment of the present invention;

[0027] Figure 6 This is a partial circuit schematic diagram of the signal processing module in an embodiment of the present invention;

[0028] Figure 7 The amplitude-frequency response curves of the two RC filter output circuits in this embodiment of the invention are shown when there is a 1% capacitance difference.

[0029] Figure 8 The figures show the amplitude-frequency response curves of the RC filter output circuit at different cutoff frequencies in this embodiment of the invention.

[0030] Figure label:

[0031] 1-Power supply module; 11-Rectifier circuit; 12-Enable circuit; 13-Filter output circuit; 2-Signal processing module; 21-First-order RC filter output circuit; 22-Second-order RC filter output circuit; 23-Instrumentation amplifier; 24-A / D converter; 3-Measuring electrode; 4-Ground electrode; 5-Excitation coil; 6-Pipeline; C1-Bridging capacitor; C2-Second capacitor; C3-Third capacitor; C4-Fourth capacitor; C5-Fifth capacitor; C6-Sixth capacitor; C7-Seventh capacitor; R2-Second resistor; R3-Third resistor; R4-Fourth resistor; R5-Fifth resistor; R6-Sixth resistor; D1-First Zener diode; D2-Second diode; D3-Third diode; D4-Fourth diode; D5-Fifth Zener diode; ra-Primary winding; rb1-First secondary winding; rb2-Second secondary winding; IC1-Switching power supply chip; U1-Optocoupler. Detailed Implementation

[0032] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] This invention provides an electromagnetic flowmeter suitable for flow measurement, especially for electromagnetic flow measurement of non-metallic pipes.

[0037] like Figure 4 As shown, this embodiment of the invention provides an electromagnetic flowmeter, including a pipeline 6, an excitation coil 5, and measuring electrodes 3. Two excitation coils 5 are provided, respectively installed on both symmetrical sides of the pipeline, for applying a magnetic field to the fluid flowing through the pipeline 6. Two measuring electrodes 3 are also provided, fixedly connected to the pipeline 6, to detect the potential difference generated by the fluid flowing through the pipeline 6 under the action of the magnetic field.

[0038] The electromagnetic flowmeter also includes a power supply module 1, a grounding electrode 4, and a signal processing module 2.

[0039] Power module 1 is used to convert external AC power into DC power suitable for the operation of excitation coil 5 and output it.

[0040] Grounding electrode 4 is installed in pipe 6 and is used to connect the fluid in pipe 6 to the signal grounding terminal.

[0041] The signal processing module 2 is connected to the measuring electrode 3 and processes the signal output by the measuring electrode 3 to obtain the flow measurement result.

[0042] Specifically, external AC power is used to provide electrical input for the electromagnetic flowmeter. This input can be of various AC types; in one example, the external AC power is 220V AC mains. Power module 1 has rectification and voltage conversion functions, enabling it to convert the external AC power into DC power suitable for the operation of the excitation coil 5.

[0043] In practical applications, the power chip and corresponding peripheral circuit selected for power module 1 can be determined based on the voltage required for the operation of excitation coil 5 and the actual input of external AC power.

[0044] The grounding electrode 4 is fixedly connected to the conduit 6. Its size is basically the same as that of the measuring electrode 3. It is small in size and independent of the pipe diameter, so the cost can be well controlled. Compared with a large-sized grounding ring, it has virtually no risk of pipe leakage.

[0045] The signal processing module 2 is connected to the measuring electrode 3, thereby acquiring the input signal for measurement. The signal output by the measuring electrode 3 is processed by a specific processor to obtain the flow measurement result.

[0046] The present invention does not limit the selection of processor. The required processor can be determined based on accuracy requirements, cost requirements, and usage environment to analyze the input signal of the measuring electrode 3.

[0047] An embodiment of the present invention provides an electromagnetic flowmeter that reduces production costs and simplifies installation procedures by using a grounding electrode 4 instead of a grounding ring, and effectively reduces the risk of pipeline leakage.

[0048] Since the size of the grounding electrode 4 is basically the same as that of the measuring electrode 3, the grounding electrode 4 is small in size and independent of the pipe diameter, thus helping to reduce the cost of the electromagnetic flowmeter and reducing the risk of pipeline leakage. However, due to the small contact area between the grounding electrode 4 and the fluid to be measured in the pipe, a potential difference exists between the grounding electrode 4 and the measuring electrode 3. This results in both differential-mode voltage (characterizing fluid velocity) and common-mode voltage (VCM) being present in the voltage signals detected by the two measuring electrodes 3. The presence of the common-mode voltage VCM creates a ground loop in the detection circuit. The equivalent circuit of the ground loop is as follows: Figure 2 and Figure 3 As shown, because a common-mode voltage VCM is added to the grounding loop, a common-mode current is also introduced into the electromagnetic flowmeter circuit. The common-mode current will interfere with the detection circuit's processing of the differential-mode signal, thereby affecting the accuracy of the electromagnetic flowmeter's detection.

[0049] In view of this, in some embodiments, such as Figure 5As shown, the power module 1 includes a transformer and a bridging capacitor C1. The transformer includes a primary winding ra and a secondary winding. One end of the primary winding ra is connected to one end of the bridging capacitor C1, and the other end of the bridging capacitor C1 is connected to the signal ground terminal. The secondary winding is connected to the excitation coil 5.

[0050] In this embodiment of the invention, after replacing the grounding ring with the grounding electrode 4, a bridging capacitor C1 is added to the power module 1, thereby increasing the circuit impedance and reducing the common-mode current, thus suppressing common-mode interference.

[0051] In some embodiments, the capacitance of the bridging capacitor C1 is 500pF to 1000pF. For example, the capacitance of the bridging capacitor can be 500pF, 750pF, 1000pF, etc.

[0052] By placing a bridging capacitor C1 between the primary winding ra and the secondary winding of the transformer, the impedance of the entire circuit is made equal to the impedance of the bridging capacitor C1 connected in parallel with the parasitic capacitances between the primary and secondary sides of the transformer. Therefore, the impedance can be increased by reducing the capacitance value of the bridging capacitor C1. However, if the capacitance value of the bridging capacitor C1 is too small, it will cause power ripple. When the capacitance value of the bridging capacitor C1 is set in the range of 500pF to 1000pF, the power ripple can be suppressed while increasing the overall circuit impedance of power module 1.

[0053] In some embodiments, the power module 1 further includes a rectifier module and a switching power supply chip IC1. The input terminal of the rectifier circuit 11 is connected to the external AC input terminal, the positive output terminal of the rectifier circuit 11 is connected to one end of the first winding, the negative output terminal of the rectifier circuit 11 is connected to the input terminal of the switching power supply chip IC1, and the output terminal of the switching power supply chip IC1 is connected to the other end of the primary winding ra.

[0054] Specifically, the rectifier circuit 11 includes a rectifier bridge and a seventh capacitor C7. The two output terminals of the rectifier bridge are connected to the two ends of the seventh capacitor C7, respectively. The external AC power is converted into DC power by the rectifier bridge and then output to the primary winding ra of the transformer. After the voltage is converted into the supply voltage by the transformer, it is output to the excitation coil 5 through the secondary winding to supply power to the excitation coil 5.

[0055] The switching power supply chip IC1 acts as a switch to control the power supply, and can be used to control whether the power module 1 supplies power to the outside.

[0056] Specifically, the model number of the switching power supply chip IC1 is TOP254EN.

[0057] The TOP254EN chip integrates a high-voltage, high-power MOSFET. The S pin of the TOP254EN is the source of the MOSFET, the D pin is the drain of the MOSFET, the C pin is the enable pin, the V pin is the voltage monitoring pin, which is connected to the DC high-voltage output terminal of the rectifier circuit 11 through a resistor, the X pin is the external current limiting setting terminal, and the F pin is used to select the chip's operating frequency.

[0058] The D pin of the switching power supply chip IC1 is connected to one end of the primary winding ra after passing through the second diode D2 and the first Zener diode D1 in sequence. The V pin of the switching power supply chip IC1 is connected to one end of the primary winding ra through the fourth resistor R4, and then through one end of the bridging capacitor C1. The other end of the bridging capacitor C1 is grounded.

[0059] In some embodiments, the power module 1 further includes a filter output circuit 13 and an enable circuit 12. The secondary winding includes a first secondary winding rb1. The input terminal of the filter output circuit 13 is connected to the first secondary winding rb1, and the output terminal of the filter output circuit 13 is connected to the excitation coil 5. The secondary winding also includes a second secondary winding rb2. The two input terminals of the enable circuit 12 are respectively connected to the two ends of the first secondary winding rb1. One output terminal of the enable circuit 12 is connected to one end of the second secondary winding rb2. The other output terminal of the enable circuit 12 is connected to the enable terminal of the switching power supply chip IC1, and the other end of the second secondary winding rb2 is connected to the input terminal of the switching power supply chip IC1.

[0060] The enabling circuit 12 includes an optocoupler U1, which comprises a light-emitting diode (LED) and a phototransistor. The two ends of the LED are the two input terminals of the optocoupler U1. The positive terminal of the LED is connected in series with a sixth resistor R6 and a fifth Zener diode D5, and then connected to one end of the first secondary winding rb1. The negative terminal of the LED is connected to the other end of the first secondary winding rb1. The two ends of the phototransistor are the output terminals of the optocoupler U1. One end of the phototransistor is connected through a fourth diode D4 and one end of the second secondary winding rb2, and simultaneously through a fifth capacitor C5 and the other end of the second secondary winding rb2. The other end of the phototransistor is connected in series with a sixth capacitor C6 and a fifth resistor R5, and then connected to the X pin of the TOP254EN chip. The F pin of the TOP254EN chip is connected to the series junction between the fifth resistor R5 and the sixth capacitor C6. When the rectifier circuit 11 outputs DC power, the C pin receives an enable signal through the optocoupler U1, and the S pin and D pin are connected.

[0061] The filter output circuit 13 is used to filter out high-frequency noise components in the output voltage.

[0062] The filter output circuit 13 mainly consists of a third diode D3 and a fourth capacitor C4. The positive terminal of the third diode D3 is connected to one end of the second secondary winding rb2, and the negative terminal is grounded after passing through the fourth capacitor C4. The negative terminal of the fifth Zener diode D5 is connected to the negative terminal of the third diode D3, and the positive terminal of the fifth Zener diode D5 is connected to the positive terminal of the light-emitting diode after passing through the sixth resistor R6.

[0063] In some embodiments, the signal processing module 2 includes an instrumentation amplifier and a processor, with the input terminal of the instrumentation amplifier connected to the measuring electrode 3 and the output terminal of the instrumentation amplifier connected to the processor.

[0064] The processor can be a central processing unit, a network processor, or a combination thereof. The processor may further include hardware chips. These hardware chips can be application-specific integrated circuits (ASICs), programmable logic devices (PLDs), or combinations thereof. The programmable logic devices can be complex programmable logic devices (CLPs), field-programmable gate arrays (FPGAs), general-purpose array logic (GDAs), or any combination thereof.

[0065] The flow measurement result is obtained by processing the signal output by measuring electrode 3 through a specific processor.

[0066] In one example, the instrumentation amplifier consists of two voltage followers and an instrumentation amplifier 23. By configuring the instrumentation amplifier, common-mode interference can be further reduced.

[0067] In some embodiments, such as Figure 6 As shown, the instrumentation amplifier also includes a first-order RC filter output circuit 21 and a second-order RC filter output circuit 22. The input terminal of the first-order RC filter output circuit 21 is connected to a measurement electrode 3, and the output terminal of the first-order RC filter output circuit 21 is connected to the non-inverting input terminal of the instrumentation amplifier 23. The input terminal of the second-order RC filter output circuit 22 is connected to another measurement electrode 3, and the output terminal of the second-order RC filter output circuit 22 is connected to the inverting input terminal of the instrumentation amplifier 23. The output terminal of the instrumentation amplifier 23 is connected to the processor. The cutoff frequencies of the first-order RC filter output circuit 21 and the second-order RC filter output circuit 22 are both between 10kHz and 50kHz.

[0068] Specifically, the first-order RC filter output circuit 21 includes a second resistor R2 and a second capacitor C2. One end of the second resistor R2 is connected to a measurement electrode 3, and the other end of the second resistor R2 is connected to the non-inverting input terminal of the instrumentation amplifier 23. One end of the second capacitor C2 is connected to the non-inverting input terminal of the instrumentation amplifier 23, and the other end of the second capacitor C2 is connected to the signal ground terminal.

[0069] The second first-order RC filter output circuit 22 includes a third resistor R3 and a third capacitor C3. One end of the third resistor R3 is connected to another measuring electrode 3, and the other end of the third resistor R3 is connected to the inverting input terminal of the instrumentation amplifier 23. One end of the third capacitor C3 is connected to the inverting input terminal of the instrumentation amplifier 23, and the other end of the third capacitor C3 is connected to the signal ground terminal.

[0070] A typical instrumentation amplifier usually consists of two voltage followers and one instrumentation amplifier 23. However, in actual operation, the RC filter output circuit 13 connected to the two voltage followers cannot be completely identical. Taking the capacitor in the filter output circuit 13 as an example, if there is a 1% capacitance difference between the capacitors of the RC filter output circuit 13 connected to the two voltage followers, its amplitude-frequency response curve will be as follows: Figure 7 As shown.

[0071] from Figure 7 As can be seen, when there is a 1% capacitance error in the circuit, the suppression of power frequency noise (50Hz) is about -66dB. At this time, a differential power frequency interference signal of about 52dB will be introduced at the front end of the instrumentation amplifier, which will also reduce the overall common mode rejection ratio of the circuit to 66dB. At this time, it can be considered that the instrumentation amplifier has basically lost its power frequency suppression function.

[0072] The common-mode rejection ratio of the instrumentation amplifier can be improved by adjusting the cutoff frequency of the first-order RC filter output circuit (including the first-order RC filter output circuit 21 and the second-order RC filter output circuit 22) at the front end of the instrumentation amplifier 23. Figure 8 The amplitude-frequency response curves at different cutoff frequencies are given when the capacitance values ​​in the first-order RC filter output circuit differ by 1%.

[0073] Depend on Figure 8 It can be seen that when the cutoff frequencies of the first-order RC filter output circuit are 100Hz, 1kHz, 10kHz and 100kHz, the power frequency noise suppression ratios are -48dB, -66dB, -86dB and -106dB, respectively. That is, the common-mode rejection ratios of the entire circuit are 48dB, 66dB, 86dB and 106dB, respectively. Therefore, this application selects a first-order RC filter output circuit with a cutoff frequency between 10kHz and 50kHz. At this time, the common-mode rejection ratio can reach 86dB, which plays a relatively ideal role in suppressing power frequency noise caused by component errors.

[0074] The cutoff frequency of a first-order RC filter output circuit can be calculated using the formula f = 1 / (2πRC). The resistance and capacitance values ​​of the first-order RC filter output circuit can be determined based on the cutoff frequency.

[0075] By setting the parameter relationship between the second capacitor C2, the second resistor R2, the third capacitor C3, and the third resistor R3, the cutoff frequency is made to satisfy 10kHz < f < 50kHz, thereby suppressing power frequency noise.

[0076] Specifically, the second resistor R2 and the third resistor R3 are precision resistors with the same nominal resistance value. By using precision resistors with the same nominal resistance value, it can be ensured that the cutoff frequency of the first-order RC filter output circuit 21 and the second-order RC filter output circuit 22 meets the requirement of 10kHz < f < 50kHz, thus avoiding the increase of power frequency noise due to resistance value error.

[0077] In one example, to ensure that the cutoff frequencies of the first-order RC filter output circuit 21 and the second-order RC filter output circuit 22 are both between 10kHz and 50kHz, the resistance of the second resistor R2 is 20KΩ, the capacitance of the second capacitor C2 is 100pF, the resistance of the third resistor R3 is 20KΩ, and the capacitance of the third capacitor C3 is 100pF.

[0078] The embodiments of the present invention introduce a first-order RC filter output circuit 21 and a second-order RC filter output circuit 22, both with cutoff frequencies ranging from 10kHz to 50kHz, which can effectively suppress power frequency noise caused by capacitor component errors and effectively suppress common-mode interference.

[0079] In some embodiments, the output terminal of the instrumentation amplifier 23 is further provided with an A / D converter 24, which is used to convert the signal output by the instrumentation amplifier 23 into a digital signal.

[0080] By setting up A / D converter 24 to convert the analog signal output by instrumentation amplifier 23 into a digital signal, the processor can easily process and analyze the input signal.

[0081] An electromagnetic flowmeter according to an embodiment of the present invention has the following effects:

[0082] 1. Replacing the grounding ring with grounding electrode 4 reduces the production cost of the electromagnetic flowmeter and simplifies the installation process.

[0083] 2. By setting a bridging capacitor C1, the common-mode interference caused by the introduction of ground electrode 4 can be effectively suppressed, thereby improving the accuracy of flow measurement.

[0084] 3. By controlling the cutoff frequencies of the first-order RC filter output circuit 21 and the second-order RC filter output circuit 22 to between 10kHz and 50kHz, the interference of the working mode can be further suppressed.

[0085] While exemplary embodiments and their advantages have been described in detail, those skilled in the art can make various changes, substitutions and modifications to these embodiments without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined herein.

Claims

1. An electromagnetic flowmeter, comprising a pipeline, an excitation coil, and measuring electrodes, characterized in that, It also includes a power supply module, a grounding electrode, and a signal processing module; The power module is used to convert external AC power into DC power suitable for the operation of the excitation coil and output it. The grounding electrode is disposed in the pipeline and is used to connect the fluid in the pipeline to the signal grounding terminal; The signal processing module is connected to the measuring electrode and processes the signal output by the measuring electrode to obtain the flow measurement result; The power module includes a transformer and a bridging capacitor. The transformer includes a primary winding and a secondary winding. One end of the primary winding is connected to one end of the bridging capacitor, and the other end of the bridging capacitor is connected to a signal ground terminal. The other end of the bridging capacitor is connected to one end of the secondary winding. The bridging capacitor is connected between one end of the primary winding and the signal ground terminal.

2. The electromagnetic flowmeter according to claim 1, characterized in that, The capacitance of the bridging capacitor is 500pF to 1000pF.

3. The electromagnetic flowmeter according to claim 1, characterized in that, The power module also includes a rectifier circuit and a switching power supply chip. The input terminal of the rectifier circuit is connected to the external AC input terminal, the positive output terminal of the rectifier circuit is connected to one end of the primary winding, the negative output terminal of the rectifier circuit is connected to the input terminal of the switching power supply chip, and the output terminal of the switching power supply chip is connected to the other end of the primary winding.

4. The electromagnetic flowmeter according to claim 3, characterized in that, The power module further includes a filter output circuit, the secondary winding includes a first secondary winding, the input terminal of the filter output circuit is connected to the first secondary winding, and the output terminal of the filter output circuit is connected to the excitation coil.

5. The electromagnetic flowmeter according to claim 4, characterized in that, The power module further includes an enable circuit, and the secondary winding further includes a second secondary winding. The two input terminals of the enable circuit are respectively connected to the two ends of the first secondary winding. One output terminal of the enable circuit is connected to one end of the second secondary winding. The other output terminal of the enable circuit is connected to the enable terminal of the switching power supply chip. The other end of the second secondary winding is connected to the input terminal of the switching power supply chip.

6. The electromagnetic flowmeter according to claim 1, characterized in that, The signal processing module includes an instrumentation amplifier and a processor. The input terminal of the instrumentation amplifier is connected to the measuring electrode, and the output terminal of the instrumentation amplifier is connected to the processor.

7. The electromagnetic flowmeter according to claim 6, characterized in that, The signal processing module further includes a first-order RC filter output circuit and a second-order RC filter output circuit. The input terminal of the first-order RC filter output circuit is connected to one of the measurement electrodes, and the output terminal of the first-order RC filter output circuit is connected to the non-inverting input terminal of the instrumentation amplifier. The input terminal of the second-order RC filter output circuit is connected to another measurement electrode, and the output terminal of the second-order RC filter output circuit is connected to the inverting input terminal of the instrumentation amplifier. The output terminal of the instrumentation amplifier is connected to the processor. The cutoff frequencies of both the first-order RC filter output circuit and the second-order RC filter output circuit are 10kHz to 50kHz.

8. The electromagnetic flowmeter according to claim 7, characterized in that, The first-order RC filter output circuit includes a second resistor and a second capacitor. One end of the second resistor is connected to one of the measurement electrodes, and the other end of the second resistor is connected to the non-inverting input terminal of the instrumentation amplifier. One end of the second capacitor is connected to the non-inverting input terminal of the instrumentation amplifier, and the other end of the second capacitor is connected to the signal ground terminal. The second first-order RC filter output circuit includes a third resistor and a third capacitor. One end of the third resistor is connected to another of the measurement electrodes, and the other end of the third resistor is connected to the inverting input terminal of the instrumentation amplifier. One end of the third capacitor is connected to the inverting input terminal of the instrumentation amplifier, and the other end of the third capacitor is connected to the signal ground terminal.

9. The electromagnetic flowmeter according to claim 8, characterized in that, The second and third resistors are precision resistors with the same nominal resistance value.

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