Signal processing circuit and electromagnetic flowmeter

Abstract

The utility model discloses a signal processing circuit and an electromagnetic flowmeter, the signal processing circuit comprises a filtering preprocessing circuit, a primary signal amplification circuit, a voltage following circuit, a secondary signal amplification circuit and an A / D sampling circuit which are connected in sequence, the filtering preprocessing circuit is provided with two signal input ends and two signal output ends, a first signal input end of the filtering preprocessing circuit is connected with a signal output positive electrode end of the electromagnetic flow sensor, a second signal input end of the filtering preprocessing circuit is connected with a signal output negative electrode end of the electromagnetic flow sensor, and the primary signal amplification circuit is a double-input single-output feedback amplification circuit. The first signal input end of the first-stage signal amplification circuit is connected with the first signal output end of the filtering preprocessing circuit, and the second signal input end of the first-stage signal amplification circuit is connected with the second signal output end of the filtering preprocessing circuit. The accuracy of the detection result of the electromagnetic flowmeter can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of flow detection, in particular to a signal processing circuit and an electromagnetic flowmeter. Background Art

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

[0003] The electromagnetic flowmeter detects the flow signal of the conductive fluid in the target pipeline through an electromagnetic flow sensor. The flow signal is processed by signal processing methods such as analog-to-digital conversion and output to the processor for flow conversion and analysis.

[0004] Since the flow detection signal output by the electromagnetic flow sensor is a weak alternating signal of microvolt to millivolt level, and the internal impedance of the signal is very high, the amplitude of the noise signal is much larger than the flow detection signal output by the electromagnetic flow sensor. Therefore, the electromagnetic flowmeter is very susceptible to electromagnetic interference at the work site, and the electromagnetic interference noise signal will be superimposed on the signal electromotive force obtained from the sensor, causing the flow velocity signal measured by the electromagnetic flowmeter to fluctuate, thereby affecting the accuracy of the electromagnetic flowmeter detection results.

[0005] Therefore, how to improve the accuracy of electromagnetic flowmeter detection results is a problem that needs to be solved urgently. Utility Model Content

[0006] In view of the defects in the prior art, the utility model aims to provide a signal processing circuit and an electromagnetic flowmeter which can improve the accuracy of the detection result.

[0007] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0008] According to a first aspect of the utility model, the utility model provides a signal processing circuit, which is applied to an electromagnetic flowmeter, wherein the electromagnetic flowmeter comprises an electromagnetic flow sensor for converting a flow velocity signal of a measured fluid into a corresponding alternating electrical signal according to a preset function relationship.

[0009] The signal processing circuit includes a filter preprocessing circuit, a primary signal amplification circuit, a voltage follower circuit, a secondary signal amplification circuit and an A / D sampling circuit, wherein:

[0010] The filter preprocessing circuit has two signal input terminals and two signal output terminals. The first signal input terminal of the filter preprocessing circuit is connected to the positive terminal of the signal output of the electromagnetic flow sensor, and the second signal input terminal of the filter preprocessing circuit is connected to the negative terminal of the signal output of the electromagnetic flow sensor.

[0011] The first-stage signal amplifier circuit is a dual-input single-output feedback amplifier circuit, wherein the first signal input terminal of the first-stage signal amplifier circuit is connected to the first signal output terminal of the filter preprocessing circuit, and the second signal input terminal of the first-stage signal amplifier circuit is connected to the second signal output terminal of the filter preprocessing circuit.

[0012] The output end of the first-stage signal amplifying circuit, the voltage follower circuit, the second-stage signal amplifying circuit and the A / D sampling circuit are connected in sequence.

[0013] Preferably, the first-stage signal amplification circuit includes a differential amplification circuit, an integral feedback circuit and a reference voltage output circuit, wherein:

[0014] The output end of the differential amplifier circuit is connected to the first input end of the integral feedback circuit and the input end of the voltage follower circuit, the first signal input end of the differential amplifier circuit is connected to the first signal output end of the filter preprocessing circuit, the second signal input end of the differential amplifier circuit is connected to the second signal output end of the filter preprocessing circuit, the second input end of the integral feedback circuit is connected to the output end of the reference voltage output circuit, the differential amplifier circuit also has a feedback signal input end, and the output end of the integral feedback circuit is connected to the feedback signal input end of the differential amplifier circuit.

[0015] Preferably, the differential amplifier circuit comprises a first operational amplifier, a second operational amplifier, a first resistor, a second resistor, a third resistor and a fourth resistor, wherein:

[0016] The non-inverting input terminal of the first operational amplifier is connected to the first signal output terminal of the filter preprocessing circuit, the inverting input terminal of the first operational amplifier is connected to the first resistor and one end of the second resistor, the other end of the first resistor is connected to the output terminal of the first operational amplifier and the input terminal of the voltage follower circuit, the other end of the second resistor is connected to the output terminal of the second operational amplifier and one end of the third resistor, the other end of the third resistor is connected to the inverting input terminal of the second operational amplifier and one end of the fourth resistor, the other end of the fourth resistor is connected to the output terminal of the integral feedback circuit as the feedback signal input terminal of the differential amplifier circuit, and the non-inverting input terminal of the second operational amplifier is connected to the second signal output terminal of the filter preprocessing circuit.

[0017] Preferably, the first operational amplifier and the second operational amplifier are both TLV2211 operational amplifiers.

[0018] Preferably, the first resistor, the second resistor, the third resistor and the fourth resistor are precision resistors with the same resistance value.

[0019] Preferably, the integral feedback circuit comprises a third operational amplifier, a fifth resistor and a first capacitor, wherein:

[0020] The non-inverting input terminal of the third operational amplifier is connected to the output terminal of the reference voltage output circuit as the second input terminal of the integral feedback circuit, the inverting input terminal of the third operational amplifier is connected to the first capacitor and one end of the fifth resistor, the other end of the fifth resistor is connected to the output terminal of the differential amplifier circuit as the first input terminal of the integral feedback circuit, and the output terminal of the third operational amplifier is connected to the other end of the first capacitor and the feedback signal input terminal of the differential amplifier circuit.

[0021] Preferably, the reference voltage output circuit comprises a voltage reference chip, and the voltage reference chip is a chip of model REF3312.

[0022] Preferably, the A / D sampling circuit includes an A / D converter, and the A / D converter is a low-noise analog-to-digital converter of model AD7193.

[0023] Preferably, the filter preprocessing circuit includes a sixth resistor, a seventh resistor, a second capacitor, a third capacitor and a fourth capacitor, wherein:

[0024] One end of the sixth resistor is connected to the positive terminal of the signal output of the electromagnetic flow sensor, the other end of the sixth resistor is connected to one end of the second capacitor, one end of the third capacitor and the first signal input terminal of the first-level signal amplification circuit, the other end of the second capacitor is grounded, one end of the seventh resistor is connected to the negative terminal of the signal output of the electromagnetic flow sensor, the other end of the seventh resistor is connected to one end of the fourth capacitor, the other end of the third capacitor and the second signal input terminal of the first-level signal amplification circuit, and the other end of the fourth capacitor is grounded.

[0025] According to a second aspect of the utility model, the present application provides an electromagnetic flowmeter, comprising the signal processing circuit described in any one of the above-mentioned first aspects.

[0026] Beneficial effects of the utility model:

[0027] The utility model sets a filtering preprocessing circuit, a primary signal amplifying circuit, a voltage following circuit, a secondary signal amplifying circuit and an A / D sampling circuit. The filtering preprocessing circuit filters out high-frequency, i.e., spurious and useless interference signals, in the flow detection signal output by the electromagnetic flow sensor, and performs multi-stage amplification on the filtered weak flow detection signal through the primary signal amplifying circuit and the secondary signal amplifying circuit, so that the weak flow detection signal is converted into a stable analog voltage signal and output to the A / D sampling circuit, which is converted into a digital signal recognizable by the processor of the electromagnetic flowmeter after analog-to-digital conversion and output for subsequent flow analysis and processing. In addition, a voltage following circuit is set between the primary signal amplifying circuit and the secondary signal amplifying circuit. The higher input resistance of the voltage following circuit can reduce the influence of the secondary signal amplifying circuit on the primary signal amplifying circuit, while the lower output resistance of the voltage following circuit can reduce the influence of the output end of the primary signal amplifying circuit on the secondary signal amplifying circuit, thereby improving the stability of the signal. Therefore, the utility model can effectively improve the accuracy of the detection result of the electromagnetic flowmeter.

[0028] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific implementation of the utility model or the technical solution in the prior art, the following is a brief introduction to the drawings required for the specific implementation or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0030] Figure 1 It is a circuit principle block diagram of a signal processing circuit in one embodiment of the utility model;

[0031] Figure 2 It is a circuit schematic diagram of a first-stage signal amplification circuit in one embodiment of the utility model;

[0032] Figure 3 It is a circuit schematic diagram of a filter preprocessing circuit in one embodiment of the utility model. DETAILED DESCRIPTION

[0033] The following embodiments of the technical solution of the utility model are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the utility model, and are therefore only used as examples, and cannot be used to limit the protection scope of the utility model.

[0034] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by technicians in the field to which the utility model belongs.

[0035] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0036] In addition, the terms "first", "second", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0037] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like 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 an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this utility model can be understood according to specific circumstances.

[0038] In the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being “above”, “above”, and “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, and “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0039] like Figure 1-3 As shown, the embodiment of the utility model provides a signal processing circuit, which is applied to an electromagnetic flowmeter, the electromagnetic flowmeter includes an electromagnetic flow sensor 100 for converting a flow velocity signal of a measured fluid into a corresponding alternating electrical signal according to a preset function relationship,

[0040] The signal processing circuit includes a filter preprocessing circuit 1, a primary signal amplifying circuit 2, a voltage follower circuit 3, a secondary signal amplifying circuit 4 and an A / D sampling circuit 5, wherein:

[0041] The filter preprocessing circuit 1 has two signal input terminals and two signal output terminals. The first signal input terminal of the filter preprocessing circuit 1 is connected to the positive terminal of the signal output of the electromagnetic flow sensor 100, and the second signal input terminal of the filter preprocessing circuit 1 is connected to the negative terminal of the signal output of the electromagnetic flow sensor 100.

[0042] The first-stage signal amplifier circuit 2 is a dual-input single-output feedback amplifier circuit. The first signal input terminal of the first-stage signal amplifier circuit 2 is connected to the first signal output terminal of the filter preprocessing circuit 1, and the second signal input terminal of the first-stage signal amplifier circuit 2 is connected to the second signal output terminal of the filter preprocessing circuit 1.

[0043] The output end of the primary signal amplifying circuit 2, the voltage follower circuit 3, the secondary signal amplifying circuit 4 and the A / D sampling circuit 5 are connected in sequence.

[0044] The signal processing circuit of this embodiment is provided with a filter preprocessing circuit 1, a primary signal amplifying circuit 2, a voltage follower circuit 3, a secondary signal amplifying circuit 4 and an A / D sampling circuit 5. The filter preprocessing circuit 1 filters out the high frequency, i.e., the stray useless interference signal, in the flow detection signal output by the electromagnetic flow sensor 100, and the primary signal amplifying circuit 2 and the secondary signal amplifying circuit 4 perform multi-stage amplification on the filtered weak flow detection signal, so that the weak flow detection signal is converted into a stable analog voltage signal and output to the A / D sampling circuit 5. After analog-to-digital conversion, it is converted into a digital signal recognizable by the processor 200 of the electromagnetic flowmeter and output for subsequent flow analysis and processing. In addition, a voltage follower circuit 3 is provided between the primary signal amplifying circuit 2 and the secondary signal amplifying circuit 4. Its higher input resistance can reduce the influence of the secondary signal amplifying circuit 4 on the primary signal amplifying circuit 2, and its lower output resistance can reduce the influence of the output end of the primary signal amplifying circuit 2 on the secondary signal amplifying circuit 4, thereby improving the stability of the signal. Therefore, the utility model can effectively improve the accuracy of the detection result of the electromagnetic flowmeter.

[0045] like Figure 1 As shown, in one embodiment, the first-stage signal amplification circuit 2 includes a differential amplification circuit 21, an integral feedback circuit 22 and a reference voltage output circuit 23, wherein:

[0046] The output end of the differential amplifier circuit 21 is connected to the first input end of the integral feedback circuit 22 and the input end of the voltage follower circuit 3, the first signal input end of the differential amplifier circuit 21 is connected to the first signal output end of the filter preprocessing circuit 1, the second signal input end is connected to the second signal output end of the filter preprocessing circuit 1, the second input end of the integral feedback circuit 22 is connected to the output end of the reference voltage output circuit 23, the differential amplifier circuit 21 also has a feedback signal input end, and the output end of the integral feedback circuit 22 is connected to the feedback signal input end of the differential amplifier circuit 21.

[0047] In the first-stage signal amplification circuit 2 of this embodiment, the differential amplifier circuit 21 can suppress the interference signal, and the integral feedback circuit 22 can play a role in DC offset feedback compensation for the output signal of the differential amplifier circuit 21, thereby improving the stability of the signal after the first-stage amplification, and the reference voltage output circuit 23 is mainly used to provide a reference voltage to the integral feedback circuit 22.

[0048] like Figure 3 As shown, in one embodiment, the differential amplifier circuit 21 includes a first operational amplifier U1, a second operational amplifier U2, a first resistor R1, a second resistor R2, a third resistor R3 and a fourth resistor R4, wherein:

[0049] The non-inverting input terminal of the first operational amplifier U1 is connected to the first signal output terminal of the filter preprocessing circuit 1, the inverting input terminal of the first operational amplifier U1 is connected to the first resistor R1 and one end of the second resistor R2, the other end of the first resistor is connected to the output terminal of the first operational amplifier U1 and the input terminal of the voltage follower circuit 3, the other end of the second resistor is connected to the output terminal of the second operational amplifier U2 and one end of the third resistor R3, the other end of the third resistor R3 is connected to the inverting input terminal of the second operational amplifier U2 and one end of the fourth resistor R4, the other end of the fourth resistor R4 is connected to the output terminal of the integral feedback circuit 22 as the feedback signal input terminal of the differential amplifier circuit 21, and the non-inverting input terminal of the second operational amplifier U2 is connected to the second signal output terminal of the filter preprocessing circuit 1.

[0050] In this embodiment, the first operational amplifier U1 and the second operational amplifier U2 form a series-type dual operational amplifier common-phase input high common-mode rejection ratio differential amplifier circuit 21, so that the common-phase interference signal is suppressed.

[0051] Specifically, in this embodiment, the first operational amplifier U1 and the second operational amplifier U2 are both operational amplifiers of model TLV2211. In the first-stage signal amplification circuit 2, a dual operational amplifier common-phase input high common-mode rejection ratio differential amplifier circuit 21 composed of two micro-power single operational amplifiers TLV2211 is selected, which can well suppress the common-phase interference signal.

[0052] Specifically, in one embodiment, the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 are precision resistors with the same resistance value. The first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 use precision resistors with the same resistance value to ensure accurate matching of the circuit. These four precision resistors have a small temperature drift coefficient and good consistency, and can have a very high suppression ability for common mode signals. At the same time, since the signal is input from the in-phase terminal of the operational amplifier, the circuit has a very high input impedance. Specifically, the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 use precision resistors with an accuracy of 0.1%.

[0053] like Figure 3 As shown, in one embodiment, the integral feedback circuit 22 includes a third operational amplifier U3, a fifth resistor R5 and a first capacitor C1, wherein:

[0054] The non-inverting input terminal of the third operational amplifier U3 is connected to the output terminal of the reference voltage output circuit 23 as the second input terminal of the integral feedback circuit 22, the inverting input terminal of the third operational amplifier U3 is connected to the first capacitor C1 and one end of the fifth resistor R5, the other end of the fifth resistor R5 is connected to the output terminal of the differential amplifier circuit 21 as the first input terminal of the integral feedback circuit 22, and the output terminal of the third operational amplifier U3 is connected to the other end of the first capacitor C1 and the feedback signal input terminal of the differential amplifier circuit 21.

[0055] In this embodiment, the integral feedback circuit 22 feeds back the voltage signal output by the differential amplifier circuit 21 to the feedback signal input terminal of the differential amplifier circuit 21 for comparison with the input signal, and uses the effective input signal obtained by comparison to control the output, thereby playing a role in DC offset feedback compensation for the output signal, making the output result more stable and accurate.

[0056] Specifically, in this embodiment, the third operational amplifier U3 is an operational amplifier of model ADA4638.

[0057] like Figure 3 As shown, specifically, in one embodiment, the reference voltage output circuit 23 includes a voltage reference chip U4, and the voltage reference chip U4 is a chip of model REF3312.

[0058] In one embodiment, the A / D sampling circuit 5 includes an A / D converter, and the A / D converter uses a low-noise analog-to-digital converter of model AD7193. The AD7193 analog-to-digital converter is suitable for high-precision measurement and has low noise. It has a built-in PGA (programmable gain amplifier) ​​that can directly input small signals, so that the analog signal amplification factor of only about 200 can meet all measurement requirements.

[0059] like Figure 2As shown, in one embodiment, the filtering preprocessing circuit 1 includes a sixth resistor R6, a seventh resistor R7, a second capacitor C2, a third capacitor C3 and a fourth capacitor C4, wherein:

[0060] One end of the sixth resistor R6 is connected to the positive terminal of the signal output of the electromagnetic flow sensor 100, the other end of the sixth resistor R6 is connected to one end of the second capacitor C2, one end of the third capacitor C3 and the first signal input terminal of the first-level signal amplification circuit 2, the other end of the second capacitor C2 is grounded, one end of the seventh resistor R7 is connected to the negative terminal of the signal output of the electromagnetic flow sensor 100, the other end of the seventh resistor R7 is connected to one end of the fourth capacitor C4, the other end of the third capacitor C3 and the second signal input terminal of the first-level signal amplification circuit 2, and the other end of the fourth capacitor C4 is grounded.

[0061] In this embodiment, the sixth resistor R6 and the second capacitor C2 as well as the seventh resistor R7 and the fourth capacitor C4 respectively form low-pass filter circuits for filtering out high-frequency and stray useless interference signals in the measurement signal output by the electromagnetic flow sensor 100 .

[0062] Specifically, in one embodiment, the secondary signal amplification circuit 4 is a signal amplification circuit constructed using a low-drift, low-power operational amplifier of model AD620AN.

[0063] According to the second aspect of the utility model, the present application provides an electromagnetic flowmeter, comprising the signal processing circuit of any one of the above-mentioned first aspects.

[0064] It should be noted that, since the electromagnetic flowmeter includes the signal processing circuit in the above embodiment, the electromagnetic flowmeter has the same technical effect as the signal processing circuit in the above embodiment, which will not be described in detail here.

[0065] In the specification of the present utility model, a lot of specific details are described. However, it is understood that the embodiments of the present utility model can be practiced without these specific details. In some examples, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this specification.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model 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 replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the utility model, and they should all be included in the scope of the claims and specification of the utility model.

Claims

1. A signal processing circuit, applied to an electromagnetic flowmeter, the electromagnetic flowmeter comprising an electromagnetic flow sensor for converting a flow velocity signal of a measured fluid into a corresponding alternating electrical signal according to a preset function relationship, characterized in that: The signal processing circuit includes a filter preprocessing circuit, a primary signal amplification circuit, a voltage follower circuit, a secondary signal amplification circuit and an A / D sampling circuit, wherein: The filter preprocessing circuit has two signal input terminals and two signal output terminals. The first signal input terminal of the filter preprocessing circuit is connected to the positive terminal of the signal output of the electromagnetic flow sensor, and the second signal input terminal of the filter preprocessing circuit is connected to the negative terminal of the signal output of the electromagnetic flow sensor. The first-stage signal amplifier circuit is a dual-input single-output feedback amplifier circuit, wherein the first signal input terminal of the first-stage signal amplifier circuit is connected to the first signal output terminal of the filter preprocessing circuit, and the second signal input terminal of the first-stage signal amplifier circuit is connected to the second signal output terminal of the filter preprocessing circuit. The output end of the first-stage signal amplifying circuit, the voltage follower circuit, the second-stage signal amplifying circuit and the A / D sampling circuit are connected in sequence.

2. The signal processing circuit according to claim 1, characterized in that: The first-stage signal amplification circuit includes a differential amplification circuit, an integral feedback circuit and a reference voltage output circuit, wherein: The output end of the differential amplifier circuit is connected to the first input end of the integral feedback circuit and the input end of the voltage follower circuit, the first signal input end of the differential amplifier circuit is connected to the first signal output end of the filter preprocessing circuit, the second signal input end of the differential amplifier circuit is connected to the second signal output end of the filter preprocessing circuit, the second input end of the integral feedback circuit is connected to the output end of the reference voltage output circuit, the differential amplifier circuit also has a feedback signal input end, and the output end of the integral feedback circuit is connected to the feedback signal input end of the differential amplifier circuit.

3. The signal processing circuit according to claim 2, characterized in that: The differential amplifier circuit includes a first operational amplifier, a second operational amplifier, a first resistor, a second resistor, a third resistor and a fourth resistor, wherein: The non-inverting input terminal of the first operational amplifier is connected to the first signal output terminal of the filter preprocessing circuit, the inverting input terminal of the first operational amplifier is connected to the first resistor and one end of the second resistor, the other end of the first resistor is connected to the output terminal of the first operational amplifier and the input terminal of the voltage follower circuit, the other end of the second resistor is connected to the output terminal of the second operational amplifier and one end of the third resistor, the other end of the third resistor is connected to the inverting input terminal of the second operational amplifier and one end of the fourth resistor, the other end of the fourth resistor is connected to the output terminal of the integral feedback circuit as the feedback signal input terminal of the differential amplifier circuit, and the non-inverting input terminal of the second operational amplifier is connected to the second signal output terminal of the filter preprocessing circuit.

4. The signal processing circuit according to claim 3, characterized in that: The first operational amplifier and the second operational amplifier are both TLV2211 operational amplifiers.

5. The signal processing circuit according to claim 3, characterized in that: The first resistor, the second resistor, the third resistor and the fourth resistor are precision resistors with the same resistance.

6. The signal processing circuit according to claim 2, characterized in that: The integral feedback circuit includes a third operational amplifier, a fifth resistor and a first capacitor, wherein: The non-inverting input terminal of the third operational amplifier is connected to the output terminal of the reference voltage output circuit as the second input terminal of the integral feedback circuit, the inverting input terminal of the third operational amplifier is connected to the first capacitor and one end of the fifth resistor, the other end of the fifth resistor is connected to the output terminal of the differential amplifier circuit as the first input terminal of the integral feedback circuit, and the output terminal of the third operational amplifier is connected to the other end of the first capacitor and the feedback signal input terminal of the differential amplifier circuit.

7. The signal processing circuit according to claim 2, characterized in that: The reference voltage output circuit includes a voltage reference chip, and the voltage reference chip is a chip of model REF3312.

8. The signal processing circuit according to claim 1, characterized in that: The A / D sampling circuit includes an A / D converter, and the A / D converter adopts a low-noise analog-to-digital converter of model AD7193.

9. The signal processing circuit according to any one of claims 1 to 8, characterized in that: The filter preprocessing circuit includes a sixth resistor, a seventh resistor, a second capacitor, a third capacitor and a fourth capacitor, wherein: One end of the sixth resistor is connected to the positive terminal of the signal output of the electromagnetic flow sensor, the other end of the sixth resistor is connected to one end of the second capacitor, one end of the third capacitor and the first signal input terminal of the first-level signal amplification circuit, the other end of the second capacitor is grounded, one end of the seventh resistor is connected to the negative terminal of the signal output of the electromagnetic flow sensor, the other end of the seventh resistor is connected to one end of the fourth capacitor, the other end of the third capacitor and the second signal input terminal of the first-level signal amplification circuit, and the other end of the fourth capacitor is grounded.

10. An electromagnetic flowmeter, characterized in that: The signal processing circuit comprises the signal processing circuit according to any one of claims 1 to 9.

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