Electromagnetic flowmeter

Abstract

The invention relates to the technical field of flow measurement, and discloses an electromagnetic flowmeter which comprises a pipeline, a magnet exciting coil, a measuring electrode, a power module, a grounding electrode and a signal processing module. The power supply module is used for converting external alternating current into direct current suitable for working of the magnet exciting coil and outputting the direct current; the grounding electrode is arranged on the pipeline and is used for connecting fluid in the pipeline with a signal grounding end; the signal processing module is connected with the measuring electrode and used for processing signals output by the measuring electrode to obtain a flow measuring result, the grounding electrode is adopted for replacing a grounding ring, and the production cost of the electromagnetic flowmeter can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of flow measurement, and in particular to an electromagnetic flowmeter. Background Art

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

[0003] At present, in electromagnetic flowmeters, the equipotential connection between the measurement reference and the medium is very important. There are corresponding connection methods for different measurement pipelines. For metal pipelines, the basic equipotential connection can be achieved by directly connecting the pipeline. For non-metallic pipelines such as PVC, the basic solution is to install a grounding ring. The equivalent circuit diagram after installing a grounding ring is as follows: Figure 1 shown.

[0004] Although basic equipotential connection can be achieved by adding a grounding ring, it also has great disadvantages. Because the material of the grounding ring is often required to be consistent with the measuring electrode, the measuring diameter is large and in some special scenarios, Hastelloy or platinum electrodes are required. If a grounding ring of the corresponding material is used, the cost of the additional grounding ring is high, which in turn leads to an increase in the 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 that the existing electromagnetic flowmeter uses a grounding ring for grounding, which leads to high costs.

[0006] The technical solution proposed by the present invention is as follows:

[0007] The present invention provides an electromagnetic flowmeter, comprising a pipeline, an excitation coil and a measuring electrode, and is characterized in that it also comprises a power module, a grounding electrode and a signal processing module; the power module is used to convert external alternating current into direct current suitable for the operation of the excitation coil and output it; the grounding electrode is arranged 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 a flow measurement result.

[0008] In some optional embodiments, the power module includes a transformer and a jumper capacitor, the transformer includes a primary winding and a secondary winding, one end of the primary winding is connected to one end of the jumper capacitor, the other end of the jumper capacitor is connected to the signal ground terminal, and the secondary winding is connected to the excitation coil.

[0009] In some optional implementations, the capacitance of the jumper capacitor is 500 pF to 1000 pF.

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

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

[0012] In some optional embodiments, the power module also includes an enabling circuit, the secondary winding also includes a second secondary winding, two input ends of the enabling circuit are respectively connected to the two ends of the first secondary winding, one output end of the enabling circuit is connected to one end of the second secondary winding, the other output end of the enabling circuit is connected to the enabling end of the switching power chip, and the other end of the second secondary winding is connected to the input end of the switching power chip.

[0013] In some optional implementations, the signal processing module includes an instrument amplifier and a processor, an input end of the instrument amplifier is connected to the measuring electrode, and an output end of the instrument amplifier is connected to the processor.

[0014] In some optional embodiments, the signal processing module also includes a first first-order RC filter output circuit and a second first-order RC filter output circuit, the input end of the first first-order RC filter output circuit is connected to one of the measuring electrodes, the output end of the first first-order RC filter output circuit is connected to the non-inverting input end of the instrument amplifier, the input end of the second first-order RC filter output circuit is connected to another measuring electrode, the output end of the second first-order RC filter output circuit is connected to the inverting input end of the instrument amplifier, the output end of the instrument amplifier is connected to the processor, and the cutoff frequency of the first first-order RC filter output circuit and the cutoff frequency of the second first-order RC filter output circuit are both 10kHz to 50kHz.

[0015] In some optional 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 measuring electrodes, the other end of the second resistor is connected to the non-inverting input of the instrument amplifier, one end of the second capacitor is connected to the non-inverting input of the instrument amplifier, and the other end of the second capacitor is connected to the signal ground; 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 measuring electrodes, the other end of the third resistor is connected to the inverting input of the instrument amplifier, one end of the third capacitor is connected to the inverting input of the instrument amplifier, and the other end of the third capacitor is connected to the signal ground.

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

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

[0018] An electromagnetic flowmeter provided by the present invention includes a pipeline, an excitation coil, a measuring electrode, a power module, a grounding electrode and a signal processing module. By adopting 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 is simplified, and the risk of pipeline leakage can be effectively reduced.

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

[0020] By controlling the cutoff frequencies of the first first-order RC filter output circuit and the second first-order RC filter output circuit to be between 10 kHz and 50 kHz, the industrial mode interference can be further suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly express the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 It is a principle block diagram of an electromagnetic flowmeter in the prior art;

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

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

[0025] Figure 4 1 is a circuit schematic diagram of an electromagnetic flowmeter according to an embodiment of the present invention;

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

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

[0028] Figure 7 The amplitude-frequency characteristic curve when there is a 1% capacitance difference between the capacitances of the two RC filter output circuits in the embodiment of the present invention;

[0029] Figure 8 1 is an amplitude-frequency characteristic curve of the RC filter output circuit at different cut-off frequencies in an embodiment of the present invention.

[0030] Reference numerals:

[0031] 1-power module; 11-rectifier circuit; 12-enable circuit; 13-filter output circuit; 2-signal processing module; 21-first order RC filter output circuit; 22-second first order RC filter output circuit; 23-instrument amplifier; 24-A / D converter; 3-measuring electrode; 4-ground electrode; 5-excitation coil; 6-pipeline; C1-cross-over 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 voltage regulator diode; D2-second diode; D3-third diode; D4-fourth diode; D5-fifth voltage regulator diode; ra-primary winding; rb1-first secondary winding; rb2-second secondary winding; IC1-switching power supply chip; U1-photocoupler. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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.

[0033] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0034] 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, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In addition, 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] An embodiment of the present invention provides an electromagnetic flowmeter suitable for flow measurement, and in particular suitable for electromagnetic flow measurement of non-metallic pipelines.

[0037] like Figure 4 As shown, an embodiment of the present invention provides an electromagnetic flowmeter, including a pipeline 6, an excitation coil 5 and a measuring electrode 3. Two excitation coils 5 are provided, which are respectively installed on both sides of the pipeline symmetrically, and are used to apply a magnetic field to the fluid flowing through the pipeline 6. Two measuring electrodes 3 are also provided, which are 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 further includes a power supply module 1 , a grounding electrode 4 and a signal processing module 2 .

[0039] The power module 1 is used to convert external alternating current into direct current suitable for the operation of the excitation coil 5 and output it.

[0040] The ground electrode 4 is disposed in the pipeline 6 and is used to connect the fluid in the pipeline 6 to the signal ground 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, the external AC power is used to provide power input for the electromagnetic flowmeter, and can be various AC inputs. In one example, the external AC power is 220V AC mains. The power module 1 has rectification and voltage conversion functions, and can 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 the corresponding peripheral circuit selected by the power module 1 can be determined according to the voltage required for the excitation coil 5 to work and the actual input of the external alternating current.

[0044] The grounding electrode 4 is fixedly connected to the pipeline 6, and its size is basically the same as that of the measuring electrode 3, and its volume is small and has nothing to do with the diameter, so the cost can be well controlled. Compared with a large-sized grounding ring, it basically does not have the risk of pipeline leakage.

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

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

[0047] An electromagnetic flowmeter according to an embodiment of the present invention can reduce the production cost of the electromagnetic flowmeter, simplify the installation process of the electromagnetic flowmeter, and effectively reduce the risk of pipeline leakage by adopting the grounding electrode 4 instead of the grounding ring.

[0048] Since the size of the grounding electrode 4 is basically the same as that of the measuring electrode 3, the volume of the grounding electrode 4 is small and has nothing to do with the diameter, which helps to reduce the cost of the electromagnetic flowmeter and reduce 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, there is a potential difference between the grounding electrode 4 and the measuring electrode 3, so that the voltage signals detected by the two measuring electrodes 3 contain both a differential mode voltage that can characterize the fluid flow rate and a common mode voltage VCM (Common mode voltage). Due to the existence of the common mode voltage VCM, a ground loop will be formed in the detection circuit. The equivalent circuit of the ground loop is as follows: Figure 2 and Figure 3 As shown, since the common mode voltage VCM is added to the ground loop, the common mode current is also introduced into the electromagnetic flowmeter circuit. The common mode current interferes with the processing of the differential mode signal by the detection circuit, thereby affecting the accuracy of the electromagnetic flowmeter detection.

[0049] In view of this, in some embodiments, Figure 5As shown, the power module 1 includes a transformer and a jumper 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 jumper capacitor C1, the other end of the jumper capacitor C1 is connected to the signal ground, and the secondary winding is connected to the excitation coil 5.

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

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

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

[0053] In some embodiments, the power module 1 also includes a rectifier module and a switching power chip IC1, the input end of the rectifier circuit 11 is connected to the external AC input end, the positive output end of the rectifier circuit 11 is connected to one end of the first winding, the negative output end of the rectifier circuit 11 is connected to the input end of the switching power chip IC1, and the output end of the switching power 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, and the two output ends of the rectifier bridge are respectively connected to the two ends of the seventh capacitor C7, and 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 power 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 switch power chip IC1 is used as a switch for controlling power supply. Whether the power module 1 supplies power to the outside can be controlled by the switch power chip IC1.

[0056] Specifically, the model 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, and is connected to the DC high-voltage output terminal of the rectifier circuit 11 through a resistor. The X pin is the external current limit setting terminal, and the F pin is used to select the chip operating frequency.

[0058] The D pin of the switching power chip IC1 is connected to one end of the primary winding ra through the second diode D2 and the first voltage regulator diode D1 in sequence, and the V pin of the switching power chip IC1 is connected to one end of the primary winding ra through the fourth resistor R4, and then connected through one end of the jumper capacitor C1, and the other end of the jumper 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 end of the filter output circuit 13 is connected to the first secondary winding rb1, and the output end of the filter output circuit 13 is connected to the excitation coil 5. The secondary winding also includes a second secondary winding rb2, two input ends of the enable circuit 12 are respectively connected to the two ends of the first secondary winding rb1, one output end of the enable circuit 12 is connected to one end of the second secondary winding rb2, the other output end of the enable circuit 12 is connected to the enable end of the switch power chip IC1, and the other end of the second secondary winding rb2 is connected to the input end of the switch power chip IC1.

[0060] The enabling circuit 12 includes a photocoupler U1, which includes a light emitting diode and a phototransistor. The two ends of the light emitting diode are the two input ends of the photocoupler U1. The positive electrode of the light emitting diode is connected in series with the sixth resistor R6 and the fifth voltage stabilizing diode D5 in sequence and then connected to one end of the first secondary winding rb1. The negative electrode of the light emitting diode is connected to the other end of the first secondary winding rb1. The two ends of the phototransistor are the output ends of the photocoupler U1. One end of the phototransistor is connected to one end of the second secondary winding rb2 through the fourth diode D4, and is connected to the other end of the second secondary winding rb2 through the fifth capacitor C5. The other end of the phototransistor is connected in series with the sixth capacitor C6 and the fifth resistor R5 in sequence and then connected to the X pin of the TOP254EN chip. The F pin of the TOP254EN chip is connected to the series connection point between the fifth resistor R5 and the sixth capacitor C6. When the rectifier circuit 11 outputs direct current, the C pin inputs an enabling signal through the photocoupler U1, and the S pin is connected to the D pin.

[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 is mainly composed of a third diode D3 and a fourth capacitor C4. The anode of the third diode D3 is connected to one end of the second secondary winding rb2, and the cathode is grounded after passing through the fourth capacitor C4. The cathode of the fifth voltage zener diode D5 is connected to the cathode of the third diode D3, and the anode of the fifth voltage zener diode D5 is connected to the anode of the light emitting diode after passing through the sixth resistor R6.

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

[0064] The processor may be a central processing unit, a network processor or a combination thereof. The processor may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0065] The signal output by the measuring electrode 3 is processed by a specific processor to obtain the flow measurement result.

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

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

[0068] Specifically, the first 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 measuring electrode 3, the other end of the second resistor R2 is connected to the non-inverting input terminal of the instrument amplifier 23, one end of the second capacitor C2 is connected to the non-inverting input terminal of the instrument 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, the other end of the third resistor R3 is connected to the inverting input terminal of the instrument amplifier 23, one end of the third capacitor C3 is connected to the inverting input terminal of the instrument amplifier 23, and the other end of the third capacitor C3 is connected to the signal ground terminal.

[0070] The commonly used instrumentation amplifier is usually composed of two voltage followers and an instrumentation amplifier 23. However, in actual working conditions, the RC filter output circuit 13 connected to the two voltage followers cannot be completely consistent. 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, the amplitude-frequency characteristic curve is as follows: Figure 7 shown.

[0071] from Figure 7 It can be seen that 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 to the front end of the instrumentation amplifier, which also reduces the overall common mode rejection ratio of the circuit to 66dB. At this time, it can be considered that the instrumentation amplifier basically loses its power frequency suppression function.

[0072] By adjusting the cutoff frequency of the first-order RC filter output circuit (including the first first-order RC filter output circuit 21 and the second first-order RC filter output circuit 22) at the front end of the instrument amplifier 23, the common mode rejection ratio of the instrument amplifier can be improved. Figure 8 The following are the amplitude-frequency characteristic curves at different cutoff frequencies assuming that the capacitance value in the first-order RC filter output circuit differs 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, respectively, the suppression ratios of the power frequency noise 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, the present application selects a first-order RC filter output circuit with a cutoff frequency between 10kHz-50kHz. At this time, the common mode rejection ratio can reach 86dB, which has a more ideal suppression effect on the power frequency noise caused by component errors.

[0074] The cut-off frequency calculation formula of the first-order RC filter output circuit is f=1 / (2πRC), and the resistance value and capacitance value of the first-order RC filter output circuit can be determined according to the cut-off frequency.

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

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

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

[0078] The embodiment of the present invention can ideally suppress power frequency noise caused by capacitance component errors and effectively suppress common mode interference by introducing a first order RC filter output circuit 21 and a second first order RC filter output circuit 22 with cutoff frequencies of 10kHz to 50kHz.

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

[0080] The A / D converter 24 is provided to convert the analog signal output by the instrument amplifier 23 into a digital signal, so that the processor can process and analyze the input signal.

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

[0082] 1. The grounding ring is replaced by the grounding electrode 4, which reduces the production cost of the electromagnetic flowmeter and simplifies the installation process of the electromagnetic flowmeter.

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

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

[0085] Although example embodiments and their advantages have been described in detail, those skilled in the art may make various changes, substitutions and modifications to these embodiments without departing from the spirit and defined scope of the present invention, and such modifications and variations are all within the defined scope.

Claims

1. An electromagnetic flowmeter, comprising a pipeline, an excitation coil and a measuring electrode, characterized in that: Also includes a power module, a ground electrode and a signal processing module; The power supply module is used to convert external alternating current into direct current 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.

2. The electromagnetic flowmeter according to claim 1, characterized in that: The power module includes a transformer and a jumper capacitor. The transformer includes a primary winding and a secondary winding. One end of the primary winding is connected to one end of the jumper capacitor, the other end of the jumper capacitor is connected to a signal ground terminal, and the secondary winding is connected to the excitation coil.

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

4. The electromagnetic flowmeter according to claim 2, characterized in that: The power module also includes a rectifier module and a switching power chip, the input end of the rectifier circuit is connected to the external AC input end, the positive output end of the rectifier circuit is connected to one end of the first winding, the negative output end of the rectifier circuit is connected to the input end of the switching power chip, and the output end of the switching power chip is connected to the other end of the primary winding.

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

6. The electromagnetic flowmeter according to claim 5, characterized in that: The power module also includes an enabling circuit, and the secondary winding also includes a second secondary winding. Two input ends of the enabling circuit are respectively connected to two ends of the first secondary winding, an output end of the enabling circuit is connected to one end of the second secondary winding, another output end of the enabling circuit is connected to the enabling end of the switching power chip, and the other end of the second secondary winding is connected to the input end of the switching power chip.

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

8. The electromagnetic flowmeter according to claim 7, characterized in that: The signal processing module also includes a first first-order RC filter output circuit and a second first-order RC filter output circuit, the input end of the first first-order RC filter output circuit is connected to one of the measuring electrodes, the output end of the first first-order RC filter output circuit is connected to the non-inverting input end of the instrument amplifier, the input end of the second first-order RC filter output circuit is connected to another measuring electrode, the output end of the second first-order RC filter output circuit is connected to the inverting input end of the instrument amplifier, the output end of the instrument amplifier is connected to the processor, and the cutoff frequency of the first first-order RC filter output circuit and the cutoff frequency of the second first-order RC filter output circuit are both 10kHz to 50kHz.

9. The electromagnetic flowmeter according to claim 8, characterized in that: The first first-order RC filter output circuit comprises a second resistor and a second capacitor, one end of the second resistor is connected to one of the measuring electrodes, the other end of the second resistor is connected to the non-inverting input terminal of the instrument amplifier, one end of the second capacitor is connected to the non-inverting input terminal of the instrument 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 the other measuring electrode, the other end of the third resistor is connected to the inverting input terminal of the instrument amplifier, one end of the third capacitor is connected to the inverting input terminal of the instrument amplifier, and the other end of the third capacitor is connected to the signal ground terminal.

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

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