Excitation circuit and electromagnetic water meter

Abstract

The utility model discloses an excitation circuit and an electromagnetic water meter, and the excitation circuit comprises a filter circuit which is used for being connected with a first PWM signal generation circuit, converting a first PWM signal into a DC voltage signal, and adjusting the voltage value of the DC voltage signal by adjusting the duty ratio of the first PWM signal; the constant current source circuit is connected with the output end of the filter circuit and used for fixing the voltage value of the direct current voltage signal within a preset range; and the driving circuit is connected with the constant current source circuit, inputs the constant current output by the constant current source circuit to the magnet exciting coil, and controls the direction of the current flowing through the magnet exciting coil, so that the magnet exciting coil generates an excitation signal. The excitation current of the electromagnetic water meters with different calibers can be effectively adjusted.

Description

Technical Field

[0001] The utility model relates to the technical field of excitation circuits, in particular to an excitation circuit and an electromagnetic water meter. Background Art

[0002] Electromagnetic water meters are metering instruments designed specifically for the actual requirements of water supply and water use enterprises. They are designed specifically for the water industry and can optimize water supply and water use and ensure accurate water trade measurement and settlement. Electromagnetic water meters generally include converters and sensors, where the sensor contains an excitation coil. The electromagnetic water meter converter outputs a constant current alternating excitation signal to allow the sensor to generate an alternating magnetic field. The stability and reliability of the magnetic field often determine the performance of the electromagnetic water meter.

[0003] However, the current excitation scheme generally outputs a fixed current through a constant current source circuit to control the excitation coil to generate an excitation signal. However, the coil length and number of turns of excitation coils of different calibers are different. The same excitation current generates different intensities of alternating magnetic fields in products of different calibers. A fixed excitation current cannot ensure the best excitation effect for all caliber products.

[0004] Practical content

[0005] In view of this, an embodiment of the utility model provides an excitation circuit and an electromagnetic water meter, which can effectively adjust the excitation current of electromagnetic water meters of different calibers.

[0006] In a first aspect, an embodiment of the present application provides an excitation circuit, comprising:

[0007] a filter circuit, connected to the first PWM signal generating circuit, for converting the first PWM signal into a DC voltage signal, and adjusting a voltage value of the DC voltage signal by adjusting a duty cycle of the first PWM signal;

[0008] A constant current source circuit, connected to the output end of the filter circuit, and used to fix the voltage value of the DC voltage signal within a preset range;

[0009] The driving circuit is connected to the constant current source circuit, inputs the constant current output by the constant current source circuit into the excitation coil, and controls the direction of the current flowing through the excitation coil so that the excitation coil generates an excitation signal.

[0010] In some embodiments of the present application, the filtering circuit includes a digital filtering circuit connected between the microcontroller and the constant current source circuit.

[0011] In some embodiments of the present application, the digital filtering circuit includes a first operational amplifier, a seventh resistor, an eighth resistor, a first capacitor and a second capacitor; the positive input terminal of the first operational amplifier is connected to the first PWM signal via the seventh resistor and the eighth resistor and the first PWM signal generating circuit, and the negative input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier; one end of the first capacitor is connected between the seventh resistor and the eighth resistor, and the other end is connected to the output terminal of the first operational amplifier; one end of the second capacitor is connected to the positive input terminal of the operational amplifier, and the other end is grounded.

[0012] In some embodiments of the present application, the constant current source circuit includes a second operational amplifier, a ninth resistor, a tenth resistor, a twelfth resistor, a thirteenth resistor, and a seventh MOS tube. The positive input terminal of the second operational amplifier is connected to the output terminal of the filter circuit through a voltage divider resistor composed of the ninth resistor and the tenth resistor. The output terminal of the second operational amplifier is connected to the seventh MOS tube through the twelfth resistor. The seventh MOS tube is connected to the driving circuit. The internal resistance of the seventh MOS tube is adjusted to enable the constant current source circuit to output a constant current.

[0013] In some embodiments of the present application, the driving circuit includes an H-bridge circuit consisting of a third MOS tube, a fourth MOS tube, a fifth MOS tube, a sixth MOS tube and an excitation coil, and a first switch circuit and a second switch circuit, the third MOS tube and the fifth MOS tube are located on the first side of the excitation coil, and the fourth MOS tube and the sixth MOS tube are located on the second side of the excitation coil; the third MOS tube and the fourth MOS tube are both connected to a power supply;

[0014] The first switch circuit is used to control the on and off of the third MOS tube and the sixth MOS tube; the second switch is used to control the on and off of the fourth MOS tube and the fifth MOS tube.

[0015] In some embodiments of the present application, the first switch circuit includes a first MOS tube, and the second switch circuit includes a second MOS tube;

[0016] The first MOS tube, the second MOS tube, the fifth MOS tube and the sixth MOS tube are all connected to the microcontroller of the excitation circuit, the first MOS tube and the sixth MOS tube are connected to the third PWM signal output by the microcontroller, and the second MOS tube and the fifth MOS tube are connected to the second PWM signal output by the microcontroller.

[0017] In some embodiments of the present application, the first MOS tube, the second MOS tube, the fifth MOS tube and the sixth MOS tube are NMOS tubes, and the third MOS tube and the fourth MOS tube are PMOS tubes.

[0018] In some embodiments of the present application, a feedback circuit connected to the voltage sampling end of the constant current source circuit is also included, and the feedback circuit is used to connect to the excitation circuit controller to detect the sampled voltage value of the constant current source circuit in real time, so that the excitation circuit controller calculates the current value of the constant current source circuit according to the sampled voltage value.

[0019] In some embodiments of the present application, the feedback circuit includes a third amplifier, the positive input terminal of the third amplifier is connected to the voltage sampling terminal of the constant current source circuit through a fourteenth resistor, the negative input terminal of the third amplifier is grounded through a fifteenth resistor, the negative input terminal of the third amplifier is connected to the output terminal of the third amplifier through a sixteenth resistor, and the output terminal is used to be connected to the excitation circuit controller.

[0020] In a second aspect, an embodiment of the present application provides an electromagnetic water meter, comprising the excitation circuit according to the first aspect of claim

[0021] The technical solution provided in the embodiments of the present application has at least the following technical effects or advantages:

[0022] An excitation circuit provided in an embodiment of the present application converts a received PWM wave into a DC voltage through a filter circuit 1, and the DC voltage is input into a constant current source circuit 2, and then the constant current source circuit 2 outputs a constant current to a drive circuit 3, and the drive circuit 3 generates an excitation signal of an excitation coil according to the constant current, that is, an excitation current, and the product parameters of the excitation coil (such as the coil length and the number of turns of the excitation coil) are different, then the excitation current required by the excitation coil is also different, and the excitation current is determined according to the constant current output by the constant current source circuit 2, and the constant current is determined according to the constant current output by the filter circuit 1. The DC voltage is positively correlated, and the voltage value of the DC voltage is related to the duty cycle of the PWM wave. Therefore, by adjusting the duty cycle of the PWM wave, the excitation current is adjusted, and the PWM wave can be generated by a PWM wave generating device (such as an MCU processor). In principle, the PWM wave can be generated by a mature software program, that is, the excitation circuit of this embodiment does not need to change the hardware circuit structure of the excitation circuit, but only needs to adjust the duty cycle of the PWM wave received by the filter circuit 1, so as to provide a more accurate excitation current (excitation signal) for the excitation coil of different product parameters, and the PWM wave adjustment is also relatively convenient and low-cost to implement.

[0023] The above description is only an overview of the technical solution of the embodiment of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiment of the present application more obvious and easy to understand, the specific implementation method of the present application is listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0025] Figure 1 A schematic diagram of the framework structure of the excitation circuit provided in some embodiments of the utility model;

[0026] Figure 2 It is a schematic diagram of the structure of the filter circuit in some embodiments of the utility model;

[0027] Figure 3 It is a structural schematic diagram of a constant current source circuit in some embodiments of the utility model;

[0028] Figure 4 It is a schematic diagram of the structure of the driving circuit in some embodiments of the utility model;

[0029] Figure 5 A schematic diagram of the framework structure of another excitation circuit provided in some embodiments of the utility model;

[0030] Figure 6 It is a schematic diagram of the structure of the feedback circuit in some embodiments of the utility model;

[0031] Figure 7 A schematic diagram of the specific structure of the excitation circuit provided in some embodiments of the utility model. DETAILED DESCRIPTION

[0032] The following embodiments of the technical solution of the present application 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 present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of the embodiments of the present application; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application; the terms "including" and "having" in the specification and claims of the present application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0034] In the description of the embodiments of the present application, “plurality” means more than two, unless otherwise clearly and specifically defined.

[0035] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0036] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship. In the description of the embodiments of the present application, the term "plurality" refers to more than two (including two).

[0037] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "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, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0038] The main function of the excitation coil in the electromagnetic device is to generate an alternating magnetic field through the excitation current. Taking the electromagnetic water meter as an example, the flow rate of the fluid flowing in the measuring tube is measured based on the electromotive force generated between the detection electrodes when the fluid flows in the magnetic field generated by the excitation coil. It can be seen that accurate excitation current is crucial to the accuracy of the electromagnetic device.

[0039] This embodiment provides an excitation circuit, such as Figure 1As shown, the excitation circuit may include a filter circuit 1, a constant current source circuit 2 connected to the output end of the filter circuit 1, and a drive circuit 3 connected to the output end of the constant current source circuit 2. The filter circuit 1 is connected to the first PWM signal generating circuit, receives the first PWM signal, converts the first PWM signal into a DC voltage signal, and adjusts the voltage value of the DC voltage signal by adjusting the duty cycle of the first PWM signal. The constant current source circuit 2 is connected to the output end of the filter circuit 1, and is used to fix the voltage value of the DC voltage signal within a preset range. The drive circuit 3 is respectively connected to the microcontroller and the constant current source circuit 2, and the constant current output from the constant current source circuit 2 is input to the excitation coil, and based on the second PWM signal and the third PWM signal output by the microcontroller, controls the different current directions flowing through the excitation coil, so that the excitation coil generates an excitation signal.

[0040] The excitation circuit provided in this embodiment converts the received PWM wave into a DC voltage through a filter circuit 1. The DC voltage is input to a constant current source circuit 2, and then the constant current source circuit 2 outputs a constant current to a drive circuit 3. The drive circuit 3 generates an excitation signal, i.e., an excitation current, for an excitation coil according to the constant current. Different product parameters of the excitation coil (such as the length of the excitation coil and the number of turns of the coil) will result in different excitation currents required by the excitation coil. The excitation current is determined based on the constant current output by the constant current source circuit 2, and the constant current is related to the DC output by the filter circuit 1. The voltage is positively correlated, and the voltage value of the DC voltage is related to the duty cycle of the PWM wave. Therefore, by adjusting the duty cycle of the PWM wave, the excitation current is adjusted, and the PWM wave can be generated by a PWM wave generating device (such as an MCU processor). In principle, the PWM wave can be generated by a mature software program, that is, the excitation circuit of this embodiment does not need to change the hardware circuit structure of the excitation circuit, but only needs to adjust the duty cycle of the PWM wave received by the filter circuit 1, so as to provide a more accurate excitation current (excitation signal) for the excitation coil of different product parameters, and the PWM wave adjustment is also relatively convenient and low-cost to implement.

[0041] The filter circuit 1 may include a digital filter circuit 1 connected between the microcontroller and the constant current source circuit 2. The digital filter circuit 1 has a simple and reasonable structure and is easy to implement.

[0042] Specifically, if Figure 2As shown, the digital filter circuit 1 may include a first operational amplifier U1, a seventh resistor R7, an eighth resistor R8, a first capacitor C1 and a second capacitor C2; the positive input terminal of the first operational amplifier U1 is connected to the first PWM signal generating circuit via the seventh resistor R7 and the eighth resistor R8, and the first PWM signal is connected, and the negative input terminal of the first operational amplifier U1 is connected to the output terminal of the first operational amplifier U1; one end of the first capacitor C1 is connected between the seventh resistor R7 and the eighth resistor R8, and the other end is connected to the output terminal of the first operational amplifier U1; one end of the second capacitor C2 is connected to the positive input terminal of the first operational amplifier, and the other end is grounded.

[0043] In this embodiment, by providing the seventh resistor R7, the eighth resistor R8, the first capacitor C1 and the second capacitor C2, an RC filter circuit 1 is implemented, which can effectively filter the first PWM signal and convert the first PWM signal into a DC voltage signal.

[0044] In some embodiments, Figure 3 As shown, the constant current source circuit 2 may include a second operational amplifier U2, a ninth resistor R9, a tenth resistor R10, a twelfth resistor R12, a thirteenth resistor R13, and a seventh MOSFET Q7. The positive input terminal of the second operational amplifier U2 is connected to the output terminal of the filter circuit 1 through a voltage divider resistor composed of a ninth resistor R9 and a tenth resistor R10. The output terminal of the second operational amplifier U2 is connected to the seventh MOSFET Q7 through the twelfth resistor R12. The seventh MOSFET Q7 is connected to the drive circuit 3. The internal resistance of the seventh MOSFET Q7 is adjusted to enable the constant current source circuit 2 to output a constant current.

[0045] In this embodiment, the DC voltage signal output by the filter is divided by the ninth resistor R9 and the tenth resistor R10, and then input into the positive input terminal of the second operational amplifier U2. The voltage value generated after the voltage division generates a current on the thirteenth resistor R13 on the negative input terminal of the operational amplifier, which is the current value of the constant current source circuit 2. The constant current source circuit 2 composed of the ninth resistor R9, the tenth resistor R10, the twelfth resistor R12, the thirteenth resistor R13, and the seventh MOS tube Q7 adjusts the internal resistance of the seventh MOS tube Q7 to achieve that the current value does not change with the change of the load within a reasonable load range and remains constant.

[0046] In some embodiments, Figure 4As shown, the driving circuit 3 includes an H-bridge circuit composed of a third MOSFET Q3, a fourth MOSFET Q4, a fifth MOSFET Q5, a sixth MOSFET Q6 and an excitation coil, as well as a first switch circuit and a second switch circuit. The third MOSFET Q3 and the fifth MOSFET Q5 are located on a first side of the excitation coil, and the fourth MOSFET Q4 and the sixth MOSFET Q6 are located on a second side of the excitation coil; the third MOSFET Q3 and the fourth MOSFET Q4 are both connected to a power supply; the first switch circuit is used to control the on and off of the third MOSFET Q3 and the sixth MOSFET Q6; and the second switch is used to control the on and off of the fourth MOSFET Q4 and the fifth MOSFET Q5.

[0047] In this embodiment, an H-bridge circuit consisting of a third MOSFET Q3, a fourth MOSFET Q4, a fifth MOSFET Q5, a sixth MOSFET Q6 and an excitation coil is provided. The H-bridge circuit can generate an alternating excitation current by changing the current direction on the excitation coil, thereby realizing positive and negative excitation. The on-off of the third MOSFET Q3 and the sixth MOSFET Q6 is controlled by the first switch circuit, and the on-off of the fourth MOSFET Q4 and the fifth MOSFET Q5 is controlled by the second switch, thereby controlling the generation of an alternating excitation current on the excitation coil and the frequency of the alternating excitation current.

[0048] Specifically, the first switching circuit may include a first MOSFET Q1, and the second switching circuit may include a second MOSFET Q2; the first MOSFET Q1, the second MOSFET Q2, the fifth MOSFET Q5 and the sixth MOSFET Q6 are all connected to the microcontroller of the excitation circuit, the first MOSFET Q1 and the sixth MOSFET Q6 are connected to the third PWM signal output by the microcontroller, and the second MOSFET Q2 and the fifth MOSFET Q5 are connected to the second PWM signal output by the microcontroller.

[0049] In this embodiment, the second MOSFET Q2 and the fifth MOSFET Q5 are controlled by the second PWM signal output by the microcontroller, and the first MOSFET Q1 and the sixth MOSFET Q6 are controlled by the third PWM signal output by the microcontroller, thereby controlling the conduction direction of the H-bridge circuit and the direction of the excitation current. Moreover, multiple complex control processes can be controlled by the output signal of the microcontroller, making the overall structure simpler and more reliable.

[0050] Further, the first MOS transistor Q1, the second MOS transistor Q2, the fifth MOS transistor Q5 and the sixth MOS transistor Q6 are NMOS transistors, and the third MOS transistor Q3 and the fourth MOS transistor Q4 are PMOS transistors.

[0051] In other embodiments, Figure 5As shown, the excitation circuit may also include a feedback circuit 4 connected to the voltage sampling end of the constant current source circuit 2, and the feedback circuit 4 is used to be connected to the excitation circuit controller to detect the sampled voltage value of the constant current source circuit 2 in real time, so that the excitation circuit controller calculates the current value of the constant current source circuit 2 according to the sampled voltage value.

[0052] In this embodiment, the cross-current output by the constant current source circuit 2 to the drive circuit 3 is monitored in real time by the feedback circuit 4, and the magnitude of the cross-current can directly affect the magnitude of the excitation current. By detecting the cross-current, it is possible to detect whether the excitation current of the excitation coil is in a normal state, and then the working state of the excitation coil can be judged based on the excitation current. In this way, once there is a problem with the excitation current of the excitation coil (such as a large deviation from the normal value), it can be discovered in time and a warning can be issued.

[0053] Specifically, if Figure 6 As shown, the feedback circuit 4 includes a third amplifier, the positive input terminal of the third amplifier is connected to the voltage sampling terminal of the constant current source circuit 2 through a fourteenth resistor R14, the negative input terminal of the third amplifier is grounded through a fifteenth resistor R15, and the negative input terminal of the third amplifier is connected to the output terminal of the third amplifier through a sixteenth resistor R16, and the output terminal is used to be connected to the excitation circuit controller.

[0054] In this embodiment, the output voltage of the constant current source circuit 2 is input to an amplifier module composed of a third amplifier, a fifteenth resistor R15, and a sixteenth resistor R16. The amplifier module can amplify the output voltage of the current source circuit to a suitable ratio, and then output the sampled voltage amplified at a suitable ratio to the MCU controller of the excitation circuit for voltage analysis. Exemplarily, the sampled voltage is input to the MCU controller through the ADC conversion unit of the MCU controller. Since the sampled voltage is an amplified voltage, it is convenient to calculate the current value on the cross-current source, so as to facilitate the subsequent judgment of the usage scenario and the working condition of the excitation module.

[0055] In another embodiment, Figure 7 The excitation circuit shown is described in detail as follows:

[0056] Figure 7 The 1 in the figure represents the filter circuit module. The PWM wave output by the MCU is controlled to pass through a second-order low-pass filter circuit composed of a resistor R7, a capacitor C1, a resistor R8, a capacitor C2, and an operational amplifier U1. By adjusting the duty cycle of the PWM wave, the DC voltage value output by the second-order low-pass filter circuit can be controlled. The resistor R7 is connected to the resistor R8 and the capacitor C1. The resistor R8 is connected to the positive input terminal of the operational amplifier U1 after passing through the capacitor C2. One end of the capacitor C1 is connected between the resistor R7 and the resistor R8, and the other end is connected to the output terminal of the operational amplifier U1.

[0057] like Figure 1 As shown, Figure 7 The 2 in the figure represents the constant current source circuit module. The DC voltage value generated by the filter circuit is input to the positive input terminal of the operational amplifier U2 after voltage division by resistors R9 and R10. The voltage value generated after voltage division generates a current on the resistor R13 at the negative input terminal of the operational amplifier, which is the current value of the constant current source circuit. The constant current source circuit composed of resistors R9, R10, R12, R13, and MOS tube Q7 adjusts the internal resistance of MOS tube Q7 through the feedback circuit to achieve a reasonable load range. The current value does not change with the change of load and remains constant.

[0058] like Figure 1 As shown, Figure 7 The 3 in the figure represents the drive circuit module. When PWM2 outputs a high level and PWM3 outputs a low level, R1 is at a low level and Q1 is turned off. At this time, the gate of Q3 is at a high level and Q3 is turned off. R6 is at a low level and Q6 is turned off. R5 is at a high level and Q5 is turned on. R2 is at a high level and Q2 is turned on. At this time, the gate of Q4 is at a low level and Q4 is turned on. VCC flows through the excitation coil through Q4 and flows to the constant current source circuit through Q5, driving the constant current source circuit to work. At this time, the current in the excitation coil flows from right to left. When PWM2 outputs a low level and PWM3 outputs a high level, R1 is at a high level, Q1 is turned on, and the gate of Q3 is at a low level, Q3 is turned on, R6 is at a high level, Q6 is turned on, R5 is at a low level, Q5 is turned off, R2 is at a low level, Q2 is turned off, and the gate of Q4 is at a high level, Q4 is turned off, VCC flows through the excitation coil through Q3, and flows to the constant current source circuit through Q6, driving the constant current source circuit to work, and the current flow direction of the excitation coil is from left to right. Therefore, the H-bridge circuit composed of MOS tube Q3, MOS tube Q4, MOS tube Q5, MOS tube Q6 and the excitation coil generates an alternating excitation current by changing the current direction of the excitation coil, thereby realizing positive and negative excitation.

[0059] like Figure 1 As shown, Figure 7 The 4 in the figure represents the feedback circuit module. The voltage at the negative end of the constant current source is connected to the positive input end of the operational amplifier U3 through R14. The input voltage is amplified to a suitable ratio through the amplifier circuit composed of resistors R15, R16 and operational amplifier U3, and input to the ADC pin of the MCU to collect the voltage. The current value on the constant current source is calculated through the collected voltage, so as to judge the usage scenario and the working condition of the excitation module.

[0060] To achieve the above-mentioned purpose, an embodiment of the utility model further provides an excitation water meter, comprising the above-mentioned excitation circuit.

[0061] It can be understood that the excitation water meter provided in this embodiment includes the above-mentioned excitation circuit, so it can at least achieve the beneficial effects that can be achieved by the above-mentioned excitation circuit, which will not be described in detail here.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application 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; and 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 present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. An excitation circuit, characterized in that: include: a filter circuit, connected to the first PWM signal generating circuit, for converting the first PWM signal into a DC voltage signal, and adjusting a voltage value of the DC voltage signal by adjusting a duty cycle of the first PWM signal; A constant current source circuit, connected to the output end of the filter circuit, and used to fix the voltage value of the DC voltage signal within a preset range; The driving circuit is connected to the constant current source circuit, inputs the constant current output by the constant current source circuit into the excitation coil, and controls the direction of the current flowing through the excitation coil so that the excitation coil generates an excitation signal.

2. The excitation circuit according to claim 1, characterized in that: The filter circuit includes a digital filter circuit connected between the microcontroller of the excitation circuit and the constant current source circuit.

3. The excitation circuit according to claim 2, characterized in that: The digital filtering circuit includes a first operational amplifier, a seventh resistor, an eighth resistor, a first capacitor and a second capacitor; the positive input terminal of the first operational amplifier is connected to the first PWM signal via the seventh resistor and the eighth resistor and the first PWM signal generating circuit, and the negative input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier; one end of the first capacitor is connected between the seventh resistor and the eighth resistor, and the other end is connected to the output terminal of the first operational amplifier; one end of the second capacitor is connected to the positive input terminal of the first operational amplifier, and the other end is grounded.

4. The excitation circuit according to claim 1, characterized in that: The constant current source circuit includes a second operational amplifier, a ninth resistor, a tenth resistor, a twelfth resistor, a thirteenth resistor, and a seventh MOS tube. The positive input end of the second operational amplifier is connected to the output end of the filter circuit through a voltage divider resistor composed of the ninth resistor and the tenth resistor. The output end of the second operational amplifier is connected to the seventh MOS tube through the twelfth resistor. The seventh MOS tube is connected to the drive circuit. The internal resistance of the seventh MOS tube is adjusted so that the constant current source circuit outputs a constant current.

5. The excitation circuit according to claim 1, characterized in that: The driving circuit includes an H-bridge circuit composed of a third MOS tube, a fourth MOS tube, a fifth MOS tube, a sixth MOS tube and an excitation coil, and a first switch circuit and a second switch circuit. The third MOS tube and the fifth MOS tube are located on a first side of the excitation coil, and the fourth MOS tube and the sixth MOS tube are located on a second side of the excitation coil; the third MOS tube and the fourth MOS tube are both connected to a power supply; The first switch circuit is used to control the on and off of the third MOS tube and the sixth MOS tube; the second switch is used to control the on and off of the fourth MOS tube and the fifth MOS tube.

6. The excitation circuit according to claim 5, characterized in that: The first switch circuit includes a first MOS tube, and the second switch circuit includes a second MOS tube; The first MOS tube, the second MOS tube, the fifth MOS tube and the sixth MOS tube are all connected to the microcontroller of the excitation circuit, the first MOS tube and the sixth MOS tube are connected to the third PWM signal output by the microcontroller, and the second MOS tube and the fifth MOS tube are connected to the second PWM signal output by the microcontroller.

7. The excitation circuit according to claim 6, characterized in that: The first MOS tube, the second MOS tube, the fifth MOS tube and the sixth MOS tube are NMOS tubes, and the third MOS tube and the fourth MOS tube are PMOS tubes.

8. The excitation circuit according to claim 5, characterized in that: It also includes a feedback circuit connected to the voltage sampling end of the constant current source circuit, and the feedback circuit is used to connect to the excitation circuit controller to detect the sampled voltage value of the constant current source circuit in real time so that the excitation circuit controller calculates the current value of the constant current source circuit according to the sampled voltage value.

9. The excitation circuit according to claim 8, characterized in that: The feedback circuit includes a third amplifier, a positive input terminal of the third amplifier is connected to the voltage sampling terminal of the constant current source circuit through a fourteenth resistor, a negative input terminal of the third amplifier is grounded through a fifteenth resistor, and a negative input terminal of the third amplifier is connected to the output terminal of the third amplifier through a sixteenth resistor, and the output terminal is used to be connected to the excitation circuit controller.

10. An electromagnetic water meter, characterized in that: The invention comprises the excitation circuit as described in any one of claims 1 to 9.

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