Double-metering automatic switching circuit of flow metering instrument

Abstract

The utility model relates to a double-metering automatic switching circuit of a flow metering device. Comprising a main control module, a reed pipe metering power supply module, a Hall metering power supply module, a reed pipe metering module and a Hall metering module. According to the circuit, a main control module outputs a control signal to switch the starting states of a reed switch and a Hall sensor, negative feedback is formed on the control signal through output signals of two metering modules, abnormity (such as Hall magnetic interference and reed switch mechanical faults) is detected in real time, and metering source switching is automatically triggered; therefore, the problems that a single sensor is insufficient in reliability and low power consumption and continuous metering are difficult to consider at the same time are solved, the operation reliability of the system in a complex environment is remarkably improved, the overall power consumption is optimized, and the metering adaptability and accuracy are enhanced.

Description

Technical Field

[0001] This utility model relates to a dual-metering automatic switching circuit for a flow meter. Background Technology

[0002] In recent years, the smart gas meter industry has developed rapidly, and the situation continues to improve. The industry has increasingly higher requirements for the safety and accuracy of meter readings, especially in terms of anti-interference, reduced power consumption, reduced failure rate, improved reliability, and reduced manufacturing costs. Pulse metering, with its real-time and direct reflection of gas consumption (each pulse corresponds to a fixed, minute gas volume), has become key to achieving accurate billing in smart gas meters. Its core advantages lie in its ultra-low power consumption potential, simple interface, and controllable cost.

[0003] Currently, the mainstream metering sampling sensors are reed switches, which offer zero power consumption and low cost, and Hall effect sensors, which are contactless, long-lasting, highly resistant to interference, and exhibit no signal jitter. However, reed switches have inherent problems such as limited mechanical lifespan, inaccurate metering due to contact jitter, and weak resistance to magnetic interference; while Hall effect sensors struggle to meet the ultra-low power consumption requirements due to continuous static current. In the context of the technological iteration of smart gas meters, single-pulse metering modes (such as using reed switches or Hall effect sensors independently) are no longer sufficient to meet the balance between high accuracy and low power consumption. The accumulation of these problems leads to serious consequences such as energy waste, unfair billing and resource allocation, and decreased user trust. A breakthrough is urgently needed by combining the advantages of both reed switch metering and Hall effect metering. Utility Model Content

[0004] In view of the problems existing in the prior art, the purpose of this utility model is to provide a technical solution for a dual-metering automatic switching circuit for flow metering instruments.

[0005] The aforementioned automatic switching circuit for dual metering in a flow meter is characterized by comprising:

[0006] Main control module: Used to output control signals and process metering signals;

[0007] Reed switch metering power supply module: Receives control signals from the main control module and supplies power to the reed switch metering module;

[0008] Hall effect metering power supply module: Receives control signals from the main control module and supplies power to the Hall effect metering module;

[0009] Reed switch metering module: Connects to the reed switch metering power supply module, including at least two reed switches in parallel and a current-limiting resistor, and outputs a metering signal;

[0010] Hall effect metering module: Connects to the Hall effect metering power supply module, including metering carry Hall sensor U1, metering half-turn Hall sensor U2, and external interference Hall sensor U3. Metering carry Hall sensor U1 and metering half-turn Hall sensor U2 cooperate to measure and output the same metering signal; external interference Hall sensor U3 shares an output terminal with metering carry Hall sensor U1. When external interference occurs, external interference Hall sensor U3 outputs a different signal than metering half-turn Hall sensor U2.

[0011] The main control module switches the power supply status of the reed switch metering module and the Hall metering module through control signals, and switches between Hall metering and reed switch metering based on the abnormal signal characteristics output by the reed switch metering module and the Hall metering module.

[0012] The aforementioned flow meter dual-metering automatic switching circuit is characterized in that the Hall metering power supply module includes a MOSFET Q1, current-limiting resistors R11, R10, R22, R23, R12, R13, filter capacitors C5 and C6; the control signal of the main control module is connected to the gate of the MOSFET Q1 via the current-limiting resistor R11, and the power supply VDD is connected to the source of the MOSFET Q1 and connected to the gate of the MOSFET Q1 via the current-limiting resistor R10; the drain of the MOSFET Q1... The current-limiting resistor R22 and filter capacitor C5 are grounded. The drain of MOSFET Q1 is grounded via current-limiting resistor R23 and filter capacitor C6. The drain of MOSFET Q1 is also grounded via resistor R5. One end of current-limiting resistor R12 is connected between current-limiting resistor R22 and filter capacitor C5. The other end of current-limiting resistor R12 is at node CT_A. One end of current-limiting resistor R13 is connected between current-limiting resistor R23 and filter capacitor C6. The other end of current-limiting resistor R13 is at node CT_B. When MOSFET Q1 is on, it supplies power to the Hall effect metering module; when it is off, it disconnects power.

[0013] The aforementioned flow meter dual-metering automatic switching circuit is characterized in that the reed switch metering power supply module includes MOSFETs Q2 and Q3, current-limiting resistors R8, R16, R17, R24, R25, R14, R15, filter capacitors C7 and C8; the control signal of the main control module is connected to the gate of MOSFET Q3 via current-limiting resistor R8 and grounded via current-limiting resistor R17; the source of MOSFET Q3 is grounded; the drain of MOSFET Q3 is connected to the gate of MOSFET Q2; the drain of MOSFET Q3 is connected to power supply VDD via current-limiting resistor R16; and power supply VDD... Connect the source of MOSFET Q2. The drain of MOSFET Q2 is grounded via current-limiting resistor R24 ​​and filter capacitor C7. The drain of MOSFET Q2 is also grounded via current-limiting resistor R25 and filter capacitor C8. One end of current-limiting resistor R14 is connected between current-limiting resistor R24 ​​and filter capacitor C7, with the other end of current-limiting resistor R14 being the Reed_A node. One end of current-limiting resistor R15 is connected between current-limiting resistor R25 and filter capacitor C8, with the other end of current-limiting resistor R15 being the Reed_B node. When the control signal is high, MOSFETs Q3 and Q2 are turned on, supplying power to the reed switch metering module. When the control signal is low, MOSFETs Q3 and Q2 are turned off.

[0014] The aforementioned flow meter dual-metering automatic switching circuit is characterized in that, in the Hall metering module, the power supply terminals of the metering carry Hall sensor U1, the metering half-turn Hall sensor U2, and the external interference Hall sensor U3 are all connected to the drain of MOSFET Q2. The drain of MOSFET Q2 is connected to the ground terminal of the external interference Hall sensor U3 via a filter capacitor C3. The drain of MOSFET Q2 is connected to the ground terminal of the metering carry Hall sensor U1 via a filter capacitor C1. The drain of MOSFET Q2 is connected to the metering half-turn Hall sensor via a filter capacitor C2. The ground terminals of U2, the metering carry Hall sensor U1, the metering half-turn Hall sensor U2, and the external interference Hall sensor U3 are all grounded; the output terminal of the metering carry Hall sensor U1 is grounded through the voltage divider resistor R1 and the current limiting resistor R3; the output terminal of the metering half-turn Hall sensor U2 is grounded through the voltage divider resistor R4 and the current limiting resistor R2; the voltage divider resistor R1 and the current limiting resistor R3 form the CT_B node; the voltage divider resistor R4 and the current limiting resistor R2 form the CT_A node; and the output terminal of the external interference Hall sensor U3 is connected to the CT_B node.

[0015] The aforementioned flow meter dual metering automatic switching circuit is characterized in that the reed switch metering module includes reed switch A, reed switch B, current limiting resistor 20 and current limiting resistor 21, one end of reed switch A is connected to the Reed_A node, and the other end of reed switch A is grounded, one end of reed switch B is connected to the Reed_B node, and the other end of reed switch B is grounded.

[0016] This invention uses a main control module to output a control signal to switch the activation status of the reed switch and the Hall sensor, and uses the output signals of the two metering modules to form negative feedback on the control signal to detect abnormalities in real time (such as magnetic interference to the Hall sensor or mechanical failure of the reed switch) and automatically trigger the switching of the metering source. This solves the problems of insufficient reliability of a single sensor and the difficulty in balancing low power consumption and continuous metering, significantly improves the operational reliability of the system in complex environments, optimizes overall power consumption, and enhances metering adaptability and accuracy.

[0017] Advantages of this utility model:

[0018] 1. Power consumption optimization: Under normal circumstances, only low-power reed switches are used or Hall sensors are activated on demand to reduce the average power consumption of the system;

[0019] 2. Reliability redundancy: Dual sensors serve as backups for each other, enabling seamless switching in case of failure and reducing downtime;

[0020] 3. Enhanced anti-interference: Real-time monitoring of magnetic field interference via external interference Hall sensor U3 ensures high switching accuracy;

[0021] 4. Cost control: Eliminating the need for additional anti-interference components reduces maintenance costs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall circuit structure of this utility model;

[0023] Figure 2 This is a schematic diagram of the switching circuit structure of this utility model;

[0024] Figure 3 This is a schematic diagram of the peripheral circuit structure of the main control module of this utility model;

[0025] Figure 4 This is a block diagram of the modules of this utility model. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings:

[0027] This invention comprises a main control module, a reed switch metering power supply module, a Hall effect metering power supply module, a reed switch metering module, and a Hall effect metering module. The main control module adjusts the input levels of the reed switch metering power supply module and the Hall effect metering power supply module via input control signals, thereby controlling their on / off states. The reed switch metering power supply module provides a stable voltage to the reed switch metering module, and the Hall effect metering power supply module outputs a stable voltage to the Hall effect metering module, ensuring the normal operation of both types of metering modules. They operate independently and complement each other in various application scenarios. The main control module uses the signals from the output terminals of the reed switch metering module and the Hall effect metering module to determine if interference has occurred, and selects different control signals to output based on environmental conditions for power supply control, thereby controlling the on / off states of the reed switch metering and Hall effect metering. Through the coordinated power supply and independent operation design of the reed switch and Hall effect sensor, the application range is expanded while ensuring system stability.

[0028] The main control module outputs a control signal, which is divided into two channels to simultaneously control the reed switch metering power supply module and the Hall metering power supply module.

[0029] The input control signal is connected to the Hall effect metering power supply module, which consists of current-limiting resistors R11, R10, R22, R23, R12, and R13, capacitors C5 and C6, and MOSFET Q1. The control signal is connected to the gate of MOSFET Q1 through current-limiting resistor R11, and the power supply VDD is connected to the source of MOSFET Q1 to provide the operating voltage for the circuit. The current-limiting resistor limits the current flowing into the gate of MOSFET Q1, protecting MOSFET Q1 from damage caused by excessive current.

[0030] One drain path of MOSFET Q1 is connected to current-limiting resistor R22, then to current-limiting resistor R12 and capacitor C5, forming an RC filter network. The other drain path of MOSFET Q1 is connected to current-limiting resistor R23, then to current-limiting resistor R13 and capacitor C6, forming another RC filter network. Capacitors C5 and C6 are used to eliminate power supply noise or stabilize voltage. Resistors and capacitors in the circuit perform current limiting, voltage division, and filtering functions, ensuring the stability and reliability of the circuit.

[0031] When the control signal is low, the gate voltage of MOSFET Q1 is also low, turning on MOSFET Q1. Once on, a low-impedance path is formed between the source and drain of MOSFET Q1, allowing current to flow from VDD to the Hall effect metering module. When the control signal is high, the gate voltage of MOSFET Q1 increases, turning off MOSFET Q1 and preventing current flow, thus de-energizing the Hall effect metering module. This circuit controls the gate voltage of MOSFET Q1 via a control signal, thereby achieving on / off control of the Hall effect metering module.

[0032] The input control signal is connected to the reed switch metering power supply module, which consists of current-limiting resistors R8, R16, R17, R24, R25, R14, and R15, filter capacitors C7 and C8, and MOSFETs Q2 and Q3. The input control signal is connected to the gate of MOSFET Q3 through current-limiting resistor R8, which limits the current flowing into the gate of MOSFET Q3 to prevent excessive gate voltage. The gate of MOSFET Q3 is connected to one end of pull-down resistor R17, and the other end of pull-down resistor R17 is grounded. The source of MOSFET Q3 is directly grounded, and one drain of MOSFET Q3 is directly connected to the gate of MOSFET Q2. The other drain of MOSFET Q3 is connected to the source of MOSFET Q2 through current-limiting resistor R16. The power supply voltage VDD is directly connected to the source of MOSFET Q2.

[0033] In contrast to the Hall effect metering power supply module, when the control signal is high, the gate voltage of MOSFET Q3 increases, MOSFET Q3 is turned on, and the drain of MOSFET Q3 is pulled low to ground. Then, the gate voltage of MOSFET Q2, which is connected to the drain of MOSFET Q3, becomes low. The voltage difference between the source and gate of MOSFET Q2 is large, MOSFET Q2 is turned on, allowing current to flow from the source to the drain of MOSFET Q2, which can power the reed switch metering module.

[0034] When the control signal is low, the gate voltage of Q3 decreases, and MOSFET Q3 is turned off. The gate of MOSFET Q2 is connected to the current-limiting resistor R16 and pulled up to VDD high. Therefore, the voltage difference between the gate voltage and the source voltage of MOSFET Q2 is small, and MOSFET Q2 is turned off. Current is not allowed to flow from the source to the drain of MOSFET Q2, and the reed switch metering module is not powered.

[0035] When MOSFET Q2 is turned on to power the reed switches, one output signal from the drain of MOSFET Q2 passes through current-limiting resistors R24 and R14 and is output to the Reed_A terminal of the reed switch metering module; the other output signal passes through current-limiting resistors R25 and R15 and is output to the Reed_B terminal of the reed switch metering module, powering both reed switches respectively. Both signals are connected to ground via filter capacitors C7 and C8, respectively, limiting rapid signal changes within a short period and protecting the circuit.

[0036] The Hall effect metering module consists of three Hall sensors: a carry-in Hall sensor U1, a half-turn Hall sensor U2, and an external interference Hall sensor U3. It is also equipped with current-limiting resistors R3 and R2, voltage-dividing resistors R1 and R4, and filter capacitors C1, C2, and C3. The voltage output from the Hall effect metering power supply module is connected to the power supply terminals of the carry-in Hall sensor U1, the half-turn Hall sensor U2, and the external interference Hall sensor U3 to power the Hall sensors. The ground terminals of all three sensors are directly grounded.

[0037] The input voltage LH_POW of the metering carry Hall sensor U1 is directly grounded through capacitor C1. The output terminal OUT of the metering carry Hall sensor U1 is connected to the output terminal OUT of the external interference Hall sensor U3 through voltage divider resistor R1, and the signal at this point is CT_B. The voltage node after the output terminal OUT of the metering half-turn Hall sensor U2 is CT_A through voltage divider resistor R4, and voltage divider resistor R4 is directly grounded through current limiting resistor R2. The metering carry Hall sensor U1 and the metering half-turn Hall sensor U2 are placed at the upper and lower ends of the counting wheel of the metering instrument, respectively. A magnet is set on the counting wheel. The two Hall sensors (metering carry Hall sensor U1 and metering half-turn Hall sensor U2) only output a high level when the counting wheel rotates and drives the magnet to rotate (when electromagnetic induction is generated), and the main control module will only count when both output signals CT_A and CT_B output the same high level signal.

[0038] For the external interference Hall sensor U3, the input voltage LH_POW is grounded through an RC filter network consisting of a filter capacitor C3 and a resistor R5 connected in parallel. The output terminal OUT of the external interference Hall sensor U3 is grounded through a current-limiting resistor R3. Similar to the metering carry Hall sensor U1 and the metering half-turn Hall sensor U2, the external interference Hall sensor U3 outputs a high-level signal through the OUT terminal when there is external magnetic interference.

[0039] The reed switch metering module consists of reed switch A, reed switch B, current-limiting resistor R20, and current-limiting resistor R21. The signal output from the Reed_A node of the reed switch metering power supply module is grounded after being connected to the parallel circuit of current-limiting resistor R20 and reed switch A; the signal output from the Reed_B node is grounded after being connected to the parallel circuit of current-limiting resistor R21 and reed switch B. When the counting wheel of the metering instrument rotates, it causes the reed switch to engage, and the reed switch conduction is equivalent to a short circuit. Since the reed switch is connected in parallel with the current-limiting resistor, the Reed_A and Reed_B signals generated when the reed switch is conducting are both connected to the main control module for metering.

[0040] The main control module acquires input signals from the reed switch metering channel (Reed_A / Reed_B) and the Hall effect metering channel (CT_A / CT_B). The initial metering method (reed switch or Hall effect) can be freely customized, while the other sensor serves as a high-reliability backup. If the working metering circuit uses Hall effect metering, the output signal of CT_B consists of the metering carry Hall effect sensor U1 and the external interference Hall effect sensor U3. Due to the presence of the voltage divider resistor R1, the output voltage of the metering carry Hall effect sensor U1 is lower than the output voltage of the external interference Hall effect sensor U3. Therefore, when there is no interference, the external interference Hall effect sensor U3 does not work, and the output voltage of the external interference Hall effect sensor U3 is the same as the output voltage of the metering half-turn Hall effect sensor U2. Once the Hall effect metering is affected by external magnetic interference, the voltage signal at CT_B will be higher than that at CT_A. The main control module will identify the abnormal voltage characteristics and automatically switch to the low-power reed switch metering. Conversely, if some reed switch meters fail due to mechanical wear, the output signal of the reed switch metering channel (Reed_A / Reed_B) will become abnormal. Once the main control module detects the abnormal voltage characteristics, it will consider that the reliability of the reed switch metering has decreased and will switch to high-precision, anti-interference Hall metering.

[0041] This design significantly improves the operational reliability of gas metering in complex environments (such as strong magnetic fields and extreme temperatures). At the same time, by providing power on demand (normal operation is low-power Hall pulse metering, and only reed switches are used in the interference state), the overall power consumption and cost of the system are effectively optimized, ensuring the real-time performance and accuracy of the settlement data.

[0042] The core point of this utility model:

[0043] Main control module: outputs control signals to the power supply module and receives Reed_A / Reed_B (reed switch) and CT_A / CT_B (Hall effect) signals;

[0044] Dual power supply module (reed switch metering power supply module, Hall effect metering power supply module): adopts MOS transistor switching structure, turns the power supply of reed switch / Hall effect on and off according to the control signal;

[0045] The main control module determines abnormalities based on voltage characteristics: when Hall metering is in operation, if the output voltage of the metering carry Hall sensor U1 is lower than the output voltage of the external interference Hall sensor U3, it is determined to be subject to magnetic interference; when reed switch metering is in operation, if the Reed_A / Reed_B signals are continuously abnormal, it is determined to be a mechanical fault.

[0046] The switching logic of the main control module is as follows: the initial metering mode is configurable, and the backup metering module monitors in real time; when an abnormality is detected in the working metering module, it automatically switches to the backup metering module and cuts off the original power supply.

[0047] The core operating procedure of this utility model is as follows:

[0048] Initial state: Taking Hall metering (configured with HL41F metering carry Hall sensor U1 and metering half-turn Hall sensor U2) as the default mode as an example, MOSFET Q1 is turned on (control signal is equal to low level), and MOSFET Q2 / MOSFET Q3 are turned off;

[0049] Magnetic interference detection: External interference Hall sensor U3 (e.g., model H43F) monitors the external magnetic field. When the voltage of CT_B (output of metering carry Hall sensor U1) is less than the output of external interference Hall sensor U3, the main control module (in this embodiment, an STM32F070 microcontroller is used) outputs a high-level control signal, MOSFET Q1 is turned off (Hall power off), and then MOSFET Q2 / MOSFET Q3 is turned on (reed switch power supply). In this embodiment, the LIT TELFUSE MDSR_10 reed switch is used.

[0050] Reed switch fault response: When the Reed_A / Reed_B signal is abnormal, the main control module outputs a low-level control signal.

[0051] MOSFETs Q2 and Q3 are turned off, but this will cause MOSFET Q1 to turn on, switching back to Hall effect metering.

[0052] Similarly, when a reed switch is selected in the initial state, if the system detects that the metering signal of the reed switch metering port Reed_A or Reed_B is abnormal due to the damage of the reed switch device, it can automatically switch to Hall metering to ensure the normal operation of the system.

[0053] This invention only requires the use of the I / O ports of the main control module chip, and the control part can be completed using existing technology. In the embodiment, Reed_A is connected to the chip's PC0 pin, Reed_B is connected to the chip's PC1 pin, CT_A is connected to the chip's PC2 pin, CT_B is connected to the chip's PC3 pin, and the control signal is the chip's PC6 pin.

[0054] This utility model has the following beneficial effects:

[0055] 1. Flexibility: It can select reed switches or Hall sensors for measurement based on signal strength, response speed and anti-interference capability; it can automatically switch to the most suitable sensor mode in different working environments (such as strong magnetic fields), which can not only meet the usage requirements of two types of sensors, but also ensure measurement accuracy in different scenarios; it can flexibly adapt to different sensors and pulse measurement equipment by selecting different devices through the output control signal of the main control module.

[0056] 2. Improved metrological reliability: By combining the magnetic field anti-interference capability of the reed switch with the mechanical vibration resistance of the Hall sensor, the sensor can be selected for metrology based on the type of environmental interference; dual metrology switching effectively suppresses signal distortion caused by environmental interference, ensuring long-term metrological accuracy under complex working conditions; the two metrology systems avoid the paralysis of the entire metrology system due to the failure of a single sensor, thus enhancing the reliability of the system.

[0057] 3. Reduced Costs: The dual sensors are redundant, and when one sensor fails, it can seamlessly switch to the other to maintain operation, significantly reducing downtime and providing a buffer period for maintenance, thus reducing emergency repair costs. Through collaborative work, the equipment can fully leverage the advantages of both sensors, reducing the performance limitations of a single sensor. The automatic switching function allows the circuit to flexibly respond to different application requirements without the need to replace additional sensors. While improving operating efficiency, it reduces the overall maintenance frequency, achieving dual optimization of reliability and cost control.

Claims

1. A dual-metering automatic switching circuit for a flow meter, characterized in that... include: Main control module: Used to output control signals and process metering signals; Reed switch metering power supply module: Receives control signals from the main control module and supplies power to the reed switch metering module; Hall effect metering power supply module: Receives control signals from the main control module and supplies power to the Hall effect metering module; Reed switch metering module: Connects to the reed switch metering power supply module, including at least two reed switches in parallel and a current-limiting resistor, and outputs a metering signal; Hall effect metering module: Connects to the Hall effect metering power supply module, including metering carry Hall sensor U1, metering half-turn Hall sensor U2, and external interference Hall sensor U3. Metering carry Hall sensor U1 and metering half-turn Hall sensor U2 cooperate to measure and output the same metering signal; external interference Hall sensor U3 shares an output terminal with metering carry Hall sensor U1. When external interference occurs, external interference Hall sensor U3 outputs a different signal than metering half-turn Hall sensor U2. The main control module switches the power supply status of the reed switch metering module and the Hall metering module through control signals, and switches between Hall metering and reed switch metering based on the abnormal signal characteristics output by the reed switch metering module and the Hall metering module.

2. A dual metering automatic switching circuit for a flow metering instrument according to claim 1, characterized in that The Hall effect metering power supply module includes a MOSFET Q1, current-limiting resistors R11, R10, R22, R23, R12, R13, filter capacitors C5 and C6. The control signal from the main control module is connected to the gate of MOSFET Q1 via current-limiting resistor R11. The power supply VDD is connected to the source of MOSFET Q1 and then to the gate of MOSFET Q1 via current-limiting resistor R10. The drain of MOSFET Q1 is connected to the gate of MOSFET Q1 via current-limiting resistor R22 and filter capacitor C6. C5 is grounded. The drain of MOSFET Q1 is grounded via current-limiting resistor R23 and filter capacitor C6. The drain of MOSFET Q1 is also grounded via resistor R5. One end of current-limiting resistor R12 is connected between current-limiting resistor R22 and filter capacitor C5, with the other end of current-limiting resistor R12 at node CT_A. One end of current-limiting resistor R13 is connected between current-limiting resistor R23 and filter capacitor C6, with the other end of current-limiting resistor R13 at node CT_B. When MOSFET Q1 is on, it supplies power to the Hall effect metering module; when it is off, it disconnects power.

3. A dual metering automatic switching circuit for a flow metering instrument according to claim 2, characterized in that The reed switch metering power supply module includes MOSFETs Q2 and Q3, current-limiting resistors R8, R16, R17, R24, R25, R14, R15, filter capacitors C7 and C8. The control signal of the main control module is connected to the gate of MOSFET Q3 via current-limiting resistor R8 and grounded via current-limiting resistor R17. The source of MOSFET Q3 is grounded, and the drain of MOSFET Q3 is connected to the gate of MOSFET Q2. The drain of MOSFET Q3 is connected to the power supply VDD via current-limiting resistor R16. The power supply VDD is connected to the source of MOSFET Q2. The drain of S-channel MOSFET Q2 is grounded via current-limiting resistor R24 ​​and filter capacitor C7. The drain of MOSFET Q2 is grounded via current-limiting resistor R25 and filter capacitor C8. One end of current-limiting resistor R14 is connected between current-limiting resistor R24 ​​and filter capacitor C7, with the other end of current-limiting resistor R14 being the Reed_A node. One end of current-limiting resistor R15 is connected between current-limiting resistor R25 and filter capacitor C8, with the other end of current-limiting resistor R15 being the Reed_B node. When the control signal is high, MOSFETs Q3 and Q2 are turned on, supplying power to the reed switch metering module. When the control signal is low, MOSFETs Q3 and Q2 are turned off.

4. A dual metering automatic switching circuit for a flow metering instrument according to claim 3, characterized in that In the Hall effect metering module, the power supply terminals of the metering carry Hall sensor U1, the metering half-turn Hall sensor U2, and the external interference Hall sensor U3 are all connected to the drain of MOSFET Q2. The drain of MOSFET Q2 is connected to the ground terminal of the external interference Hall sensor U3 via filter capacitor C3. The drain of MOSFET Q2 is connected to the ground terminal of the metering carry Hall sensor U1 via filter capacitor C1. The drain of MOSFET Q2 is connected to the ground terminal of the metering half-turn Hall sensor U2 via filter capacitor C2. The ground terminals of the metering carry Hall sensor U1, the metering half-turn Hall sensor U2, and the external interference Hall sensor U3 are all grounded. The output terminal of the metering carry Hall sensor U1 is grounded via voltage divider resistor R1 and current limiting resistor R3. The output terminal of the metering half-turn Hall sensor U2 is grounded via voltage divider resistor R4 and current limiting resistor R2. The voltage divider resistor R1 and the current limiting resistor R3 form a CT_B node, and the voltage divider resistor R4 and the current limiting resistor R2 form a CT_A node. The output terminal of the external interference Hall sensor U3 is connected to the CT_B node.

5. A dual metering automatic switching circuit for a flow metering instrument according to claim 4, characterized in that The reed switch metering module includes reed switch A, reed switch B, current limiting resistor R20 and current limiting resistor R21. One end of reed switch A is connected to the Reed_A node, and the other end of reed switch A is grounded. One end of reed switch B is connected to the Reed_B node, and the other end of reed switch B is grounded.

Images