Electromagnetic water meter for measuring the resistance of the sensor to ground

Abstract

The application discloses an electromagnetic water meter for measuring ground insulation resistance of a sensor, comprising a converter and a sensor, wherein the converter is provided with: an insulation resistance test circuit for detecting the insulation resistance RX of the sensor excitation coil to the ground; a DC / DC output circuit for converting voltage and supplying power to the circuit in the converter; an excitation driving circuit for voltage stabilizing control of the output voltage of the DC / DC output circuit; and a sampling control circuit connected with the insulation resistance test circuit, the DC / DC output circuit and the excitation driving circuit respectively for outputting control signals and receiving sampling signals. The application adds the design of the excitation coil ground insulation resistance measurement circuit in the electromagnetic water meter converter, realizes the sensor excitation coil ground insulation resistance measurement, can timely find the sensor fault, prevents the error metering, and can also make the detection of the electromagnetic water meter in the factory assembly, factory inspection and on-site maintenance process more convenient and efficient.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic water meter measuring devices, in particular to an electromagnetic water meter with a measuring sensor ground insulation resistance. BACKGROUND

[0002] The electromagnetic water meter is designed based on the principle of Faraday's law of electromagnetic induction, and is widely used in the flow measurement and control field of conductive liquid due to its high measurement accuracy and no pressure loss. The electromagnetic water meter is composed of a converter and a sensor. The measuring pipe of the electromagnetic water meter sensor is a non-magnetic alloy conduit lined with insulating material. Two electrodes are fixed on the measuring pipe along the pipe diameter direction and pass through the pipe wall. The electrodes are in contact with the measured conductive liquid, and the excitation coil is insulated from the conduit and placed above and below the conduit. In urban pipe networks, most electromagnetic water meters are installed underground, and the sensor is often immersed in water. Due to mechanical damage caused by non-standard installation and other reasons, water may seep into the sensor, causing the excitation coil and measuring electrode of the sensor to have a decreased ground insulation resistance, thereby causing measurement data deviation. Such incorrect measurement results cannot be determined, causing trade disputes between water supply and water users. When there is a serious leakage, the measured flow rate will be greatly different from the usual usage flow rate, and at this time, the electromagnetic water meter failure can be found.

[0003] When the electromagnetic water meter fails or needs to be detected and maintained, it is necessary to check whether the sensor has leaked water. Generally, the method of measuring the ground insulation resistance of the excitation coil or the ground insulation resistance of the measuring electrode is used for judgment. The qualified value of the ground insulation resistance of the excitation coil of the electromagnetic water meter sensor should be greater than 200MΩ during factory inspection. The sensor begins to leak into the sensor interior due to poor sealing, and the process is slow. The excitation coil and measuring electrode in the sensor interior have been subjected to enhanced insulation and sealing treatment. Thus, the ground insulation resistance of the excitation coil and the ground insulation resistance of the electrode will gradually decrease, and the measurement accuracy will also gradually decrease until it cannot be measured. The electrode of the electromagnetic water meter in use is in contact with the measured conductor, and the ground insulation resistance of the electrode cannot be determined. Therefore, the electromagnetic water meter in use can only determine the ground insulation of the sensor by measuring the ground insulation resistance of the excitation coil. During measurement, the converter shell needs to be opened, the sensor coil lead is separated from the electronic components to avoid damage to the electronic components due to high voltage during measurement, and then an insulation resistance meter is used to measure the insulation resistance of the coil to the ground. According to the measured insulation resistance, it is determined whether the sensor has poor ground insulation or has leaked water. In addition, the above measurement method can only determine whether the sensor has leaked water when the excitation coil insulation has been completely destroyed due to water leakage in the sensor interior, and the insulation resistance has decreased to a certain value.

[0004] The electromagnetic water meter and its adaptive excitation circuit disclosed in Chinese patent literature, with publication number CN113494943A and publication date of October 12, 2021, includes a voltage detection circuit, an empty pipe detection circuit, a zero flow detection circuit, a voltage adjustment circuit, a current adjustment circuit, and an excitation drive circuit. The voltage detection circuit detects the voltage across the coil of the excitation drive circuit. The empty pipe detection circuit detects whether the fluid in the pipeline is in an empty pipe state. The zero flow detection circuit detects whether the fluid in the pipeline is in a zero flow state. The voltage adjustment circuit adjusts the supply voltage of the excitation drive circuit. The current adjustment circuit adjusts the supply current of the excitation drive circuit. The excitation drive circuit provides excitation current for the coil. This technology can adjust the supply voltage and excitation current of the excitation drive circuit in time according to different measurement states of the electromagnetic water meter, ensuring the normal measurement accuracy of the electromagnetic water meter, reducing the overall power consumption of the electromagnetic water meter, prolonging the service life of the lithium battery of the electromagnetic water meter, and reducing the replacement workload of the lithium battery of the electromagnetic water meter. However, this technology also requires opening the converter shell to measure the insulation resistance, which is very inconvenient due to the actual installation environment of the electromagnetic water meter. In addition, during factory production and assembly and during factory inspection, the sensor-to-ground insulation resistance needs to be accurately measured, and the sensor coil lead needs to be disconnected from the electronic components during measurement. Therefore, a more convenient and accurate insulation resistance measurement method is needed.

[0005] The fault detection device and method for electromagnetic water meter sensor disclosed in Chinese patent literature, with publication number CN113624306A and publication date of November 9, 2021, includes a coil insulation detection circuit and a coil aging detection circuit. In the coil insulation detection circuit, a 3.3V voltage is applied to the input terminal of the operational amplifier through a series resistor, and the coil-to-ground insulation resistance is connected in parallel with the leakage resistance of the electronic switch and connected to the input terminal of the operational amplifier. The output voltage of the operational amplifier is compared with a preset value to determine the insulation of the coil. However, the coil-to-ground insulation resistance cannot be obtained, and when the sensor starts to leak water and the insulation is not completely damaged, the circuit cannot accurately determine the insulation of the coil and the insulation decline trend, and cannot replace the factory process inspection. SUMMARY

[0006] The present application is to overcome the prior art in the electromagnetic water meter sensor to ground insulation resistance measurement needs to open the converter meter shell for measurement, and in the actual environment of electromagnetic water meter this measurement mode is extremely inconvenient operation problem, a kind of measurement sensor ground insulation resistance electromagnetic water meter, in the electromagnetic water meter converter, excitation coil ground insulation resistance measurement circuit is designed, the on-line accurate measurement of sensor excitation coil ground insulation resistance is realized, so that early detection of sensor failure can be prevented from appearing error measurement, also can make electromagnetic water meter in factory assembly, delivery inspection and on-site maintenance process detection more convenient, accurate, efficient.

[0007] In order to achieve the above object, the present application adopts the following technical solutions:

[0008] A kind of measurement sensor ground insulation resistance electromagnetic water meter, including converter and sensor, the converter is provided with:

[0009] Insulation resistance test circuit, for detecting the insulation resistance RX of sensor excitation coil to ground, one end of insulation resistance RX is connected with voltage sampling unit and constant current unit, the other end of insulation resistance RX is connected with mode switching unit and current sampling unit;

[0010] DC / DC output circuit, for converting voltage and powering the circuit in converter;

[0011] Excitation drive circuit, for voltage stabilizing control to the output voltage of DC / DC output circuit;

[0012] Sampling control circuit, insulation resistance test circuit, DC / DC output circuit and excitation drive circuit are connected respectively, for output control signal and receiving sampling signal.

[0013] The present application is based on the original DC / DC output circuit, excitation drive circuit and sampling control circuit of electromagnetic water meter, for the corresponding improvement to these existing circuits, while adding insulation resistance test circuit, can carry out two different modes of flow measurement and insulation resistance measurement respectively, so that the insulation resistance of sensor can be measured without opening the converter shell;The measurement of excitation coil ground insulation resistance in the present application is controlled by electromagnetic water meter button or by remote communication instruction, and can also be set to interval time automatic measurement, and the measured result can be displayed on the display screen of electromagnetic water meter, and the test result is transmitted to the background for staff to view through wireless communication.

[0014] As preferred, the mode switching unit comprises an NMOS tube Q11, the gate of the NMOS tube Q11 is connected with the second control signal end, and the source of the NMOS tube Q11 is connected with the ground through the resistance R14; the drain of the NMOS tube Q11 is connected with the gate of a PMOS tube Q10, one end of the resistance R13 and the gate of an NMOS tube Q9 respectively, the source of the PMOS tube Q10 is connected with the other end of the resistance R13 and the power voltage VBT; the drain of the PMOS tube Q10 is connected with one end of a relay J1 and the negative electrode of a diode D2, the other end of the relay J1 and the positive electrode of the diode D2 are connected and grounded; the source of the NMOS tube Q9 is grounded, and the drain of the NMOS tube Q9 is connected with the other end of the insulation resistance RX and the water meter shell; the current sampling unit's current detection resistance R12 is connected between the source and the drain of the NMOS tube Q9, and the current sampling unit outputs a first sampling voltage RXV1.

[0015] The mode switching unit in the application can switch between the flow measurement mode and the insulation resistance measurement mode, when the second control signal end inputs a low level, the NMOS tube Q11 is turned off, the NMOS tube Q9 is turned on to connect the water meter shell with the ground, at the same time, the PMOS tube Q10 is turned off, and the relay J1 is not attracted, at this time, it is the flow measurement mode; when the second control signal end inputs a high level, the NMOS tube Q11 is turned on, the PMOS tube Q10 is turned on to attract the relay J1, the movable contact is connected with the corresponding normally open contact, at the same time, the NMOS tube Q9 is turned off, and a voltage is generated between the current detection resistance, and the insulation resistance measurement mode is entered; by controlling the micro-power consumption relay J1 to disconnect the excitation coil with the excitation driving circuit H bridge, the test voltage is avoided from damaging the electronic components and generating the leakage current through the excitation driving circuit components, and the insulation resistance measurement accuracy is affected.

[0016] As preferred, the constant current unit comprises a reference chip U5 connected with the second control signal end, the reference voltage output end of the reference chip U5 is connected with the base of a triode Q7 through the resistance R9, the emitter of the triode Q7 is connected with the base and the collector of a triode Q8 through the resistance R10, and the emitter of the triode Q8 is grounded; the collector of the triode Q7 is connected with the base of a triode Q5 and the collector of a triode Q6, the emitter of the triode Q6 is connected with the boost voltage through the resistance R5, the base of the triode Q6 is connected with the emitter of the triode Q5 and the boost voltage through the resistance R4; the collector of the triode Q5 is connected with one end of the insulation resistance RX and the test voltage VHE, and one end of the insulation resistance RX is connected with a voltage sampling unit, and the voltage sampling unit outputs a second sampling voltage RXV2.

[0017] In the application, when not in the insulation resistance measurement mode, the second signal control end outputs low level, the reference chip U5 in the constant current unit has no working voltage, thus no reference voltage REF output, and the transistors Q5, Q6 and Q7 are cut off, so that the test voltage output is turned off, preventing the power consumption caused by the boost voltage through the leakage current; when in the insulation resistance measurement mode, the second control signal end outputs high level, the reference chip U5 has working voltage and outputs reference voltage, so as to control the maximum current flowing through the insulation resistance RX.

[0018] As preferred, the DC / DC output circuit comprises a chip U1, a first voltage output end of the chip U1 outputs the excitation voltage VEE, a feedback input end of the chip U1 inputs the feedback voltage V1, and the chip U1 outputs the boost voltage after boost voltage transformation through the double-coil inductor L1; a voltage input end of the chip U1 and the power supply voltage are connected with a switch unit, and the switch unit controls the connection or disconnection between the power supply voltage and the chip U1 through the signal input by the connected first control signal end.

[0019] In the application, the traditional step-down mode DC / DC conversion circuit is changed into a DC / DC boost-down conversion circuit comprising a boost-down voltage stabilization chip U1, when the excitation current does not reach the constant current value in the insulation resistance measurement mode or the flow test mode, the U1 can automatically work in the boost mode according to the feedback voltage V1 input by the feedback input end, continues to provide constant current drive for the excitation circuit, fully utilizes the battery margin, and avoids early replacement of the battery; the electromagnetic water meter adopts the gap measurement mode to reduce the power consumption, and part of the circuit is in the sleep mode when not measuring, in addition, through the boost-down conversion circuit, the excitation coil can be quickly magnetized, the magnetization time is shortened, the circuit sleep time is relatively prolonged, and the power consumption is reduced.

[0020] As preferred, the excitation drive circuit comprises an excitation coil LC, two ends of the excitation coil are connected with a first moving contact and a second moving contact of a relay J1 respectively, and two normally open contacts of the relay J1 are connected with a test voltage VHE simultaneously; a first normally closed contact of the relay J1 is connected with a source of an NMOS tube Q12 and a drain of an NMOS tube Q14, a second normally closed contact of the relay J1 is connected with a source of an NMOS tube Q13 and a drain of an NMOS tube Q15, and the drain of the NMOS tube Q12 and the drain of the NMOS tube Q13 are connected with the excitation voltage VEE simultaneously; a gate of the NMOS tube Q12, a gate of the NMOS tube Q14, a gate of the NMOS tube Q13 and a gate of the NMOS tube Q15 are connected with a first drive signal end and a second drive signal end through a half-bridge drive circuit; the source of the NMOS tube Q14 and the source of the NMOS tube Q15 are connected as a third sampling voltage IREF output end and are connected with the ground through a resistor R21; the third sampling voltage IREF outputs the feedback voltage V1 through an amplification circuit.

[0021] In the insulation resistance measurement mode of the application, the both ends of the excitation coil LC are switched to the connection test power supply VHE through the relay J1, the MOS tube in the excitation circuit is turned off, no current passes through the sampling resistor in the excitation circuit, so that the feedback voltage V1 is less than the set feedback voltage threshold, the boost voltage output by the chip U1 is continuously increased, and when the boost voltage is increased to the required voltage, the voltage stabilizing tube DZ2 is broken to V1 to increase, and the input of V1 to the chip U1 makes the boost voltage maintain at a stable value; in the flow measurement mode, the both ends of the excitation coil LC are connected with the excitation drive H bridge through the normally closed contact of the relay J1, so that the third sampling voltage IREF is generated on the sampling resistor R21, and the feedback voltage V1 output after amplification of IREF is input into the chip U1 to stabilize the excitation voltage VEE and thus stabilize the excitation current.

[0022] Preferably, the sampling control circuit comprises an analog-to-digital conversion chip U2 and a control chip U3 connected in series, the analog-to-digital conversion chip receives the first sampling voltage RXV1, the second sampling voltage RXV2 and the third sampling voltage IREF; and the control chip U3 outputs control signals through the first control signal end, the second control signal end, the third control signal end, the first drive signal end and the second drive signal end.

[0023] In the application, the relevant data of the excitation coil ground insulation resistance measurement and the relevant data of the flow measurement are input into the same 24-bit analog-to-digital conversion chip U2 for AD conversion, the test voltage VHE is sampled by the voltage sampling unit to obtain the voltage RXV2, and the voltage RXV1 collected on the current sampling unit current detection resistor R12 during insulation resistance measurement is connected to the sampling input end of the chip U2, thereby providing high-precision AD conversion for insulation resistance measurement.

[0024] Preferably, the electromagnetic water meter comprises three working modes:

[0025] The sleep mode, the first control signal end outputs a low level to the DC / DC output circuit, and the DC / DC output circuit does not access the power supply voltage and does not supply power;

[0026] The flow measurement mode, the first control signal end outputs a high level to the DC / DC output circuit, the DC / DC output circuit accesses the power supply voltage to start power supply, the second control signal end outputs a low level to the mode switching unit, the water meter shell is connected with the ground end, the excitation coil is connected with the H bridge, and the flow measurement mode is entered;

[0027] The insulation resistance measurement mode, the first control signal end outputs a high level to the DC / DC output circuit, the DC / DC output circuit accesses the power supply voltage to start power supply, the second control signal end outputs a high level to the mode switching unit, the excitation coil is disconnected from the H bridge and accesses the test voltage, and the water meter shell is connected with the ground end through the current detection resistor, and the insulation resistance measurement mode is entered.

[0028] The electromagnetic water meter has three working modes, enters the flow measurement mode or the insulation resistance measurement mode when measurement is needed, and enters the sleep mode to save energy consumption when measurement is not needed; in addition, the electromagnetic water meter working mode can be controlled by the electromagnetic water meter key control or remote communication instruction control, or can be set to interval time automatic measurement, and the measurement result can be displayed on the display screen of the electromagnetic water meter or transmitted remotely through wireless communication.

[0029] The electromagnetic water meter has the following beneficial effects: the excitation coil ground insulation resistance measurement circuit is added in the electromagnetic water meter converter, the on-line accurate measurement of the sensor excitation coil ground insulation resistance is realized through the boost circuit and the 24-bit test voltage and test current analog-digital conversion, if the measured ground insulation resistance is in the qualified range, but the test data is always in a downward curve, it can be judged that the sensor has started to slowly leak, so that the sensor failure can be found early through the analysis of the measurement data, the error metering can be prevented, and the detection of the electromagnetic water meter in the factory assembly, factory inspection and on-site maintenance process is more convenient, accurate and efficient; the DC / DC step-up and step-down conversion circuit is adopted, when the battery voltage is lower than the required excitation voltage of the constant current drive, the DC / DC step-up and step-down conversion circuit automatically converts to the boost mode to continue to provide the constant current drive for the excitation circuit, and the battery margin is fully utilized; the electromagnetic water meter adopts the gap measurement mode to reduce the power consumption, part of the circuit is in the sleep working mode when measurement is not needed, and through the boost mode, the excitation coil can be quickly magnetized, the magnetizing time is shortened under the condition that the magnetizing energy is unchanged, the sleep time of the related circuit is prolonged, and the power consumption is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the circuit diagram of the DC / DC output circuit in the application;

[0031] Figure 2 is the circuit diagram of the excitation drive circuit in the application;

[0032] Figure 3 is the circuit diagram of the insulation resistance test circuit in the application;

[0033] Figure 4 is the circuit diagram of the sampling control circuit in the application. DETAILED DESCRIPTION

[0034] The application will be further described below in combination with the drawings and specific embodiments.

[0035] An electromagnetic water meter for measuring the ground insulation resistance of a sensor, comprising a converter and a sensor, the converter is provided with: an insulation resistance test circuit for detecting the insulation resistance RX of the sensor excitation coil to the ground, one end of the insulation resistance RX is connected with a voltage sampling unit and a constant current unit, the other end of the insulation resistance RX is connected with a mode switching unit and a current sampling unit; a DC / DC output circuit for converting voltage and powering the circuits in the converter; an excitation driving circuit for voltage stabilizing control of the output voltage of the DC / DC output circuit; a sampling control circuit connected with the insulation resistance test circuit, the DC / DC output circuit and the excitation driving circuit respectively, for outputting control signals and receiving sampling signals.

[0036] As Figure 1As shown, the DC / DC output circuit includes a chip U1, which is a buck-boost voltage stabilization chip with model number LTC3130. A first voltage output terminal Vout of the chip U1 outputs an excitation voltage VEE, and a feedback input terminal FB of the chip U1 inputs a feedback voltage V1. A Vcc terminal of the chip U1 is connected to one end of a capacitor C6, and an EXT terminal and a GND terminal of the chip U1 are connected to the other end of the capacitor C6 and grounded. The chip U1 outputs a boosted voltage after voltage boosting and transformation through a double-coil inductor L1; the double-coil inductor L1 is formed by a coil L1-1 and a coil L1-2 wound on the same magnetic core, wherein a BST1 terminal of the chip U1 is connected to one end of the coil L1-1 through a capacitor C2 and connected to a SW1 terminal of the chip U1; a BST2 terminal of the chip U1 is connected to the other end of the coil L1-1 through a capacitor C3 and connected to a SW2 terminal of the chip U1; one end of the coil L1-2 is connected to one end of a resistor R0, one end of a capacitor C1, a drain of an NMOS transistor Q3, and a test ground HGND; the other end of the coil L1-2 is connected to an anode of a diode D1, and a cathode of the diode D1 is connected to the other end of the resistor R0, the other end of the capacitor C1, and outputs a boosted voltage; a gate of the NMOS transistor Q3 is connected to a third control signal terminal MCU-3, and a source of the NMOS transistor Q3 is grounded GND. A MPPC terminal, an ILIM terminal, and a MODE terminal of the chip U1 are all grounded. A switching unit is connected between a voltage input terminal of the chip U1 and a power supply voltage, and the switching unit controls the connection or disconnection between the power supply voltage and the chip U1 through a signal input by a connected first control signal terminal. The PVin terminal, the Vin terminal, and the RUN terminal of the chip U1 are connected and connected to one end of a capacitor C4 and a drain of a PMOS transistor Q1, and the other end of the capacitor C4 is grounded; one end of the capacitor C4 is connected to a chip U0, which supplies power to an analog-to-digital conversion chip U2. The source of the PMOS transistor Q1 is connected to one end of a resistor R1 and a power supply voltage VBT, which is supplied by a battery through a fuse F1; the gate of the PMOS transistor Q1 is connected to the other end of the resistor R1 and a drain of an NMOS transistor Q2, the source of the NMOS transistor Q2 is connected to one end of a resistor R2 and grounded, and the gate of the NMOS transistor Q2 is connected to the other end of the resistor R2 and a first control signal terminal MCU-1.

[0037] As Figure 2As shown, the excitation drive circuit includes an excitation coil LC, two ends of the excitation coil are connected with the first movable contact and the second movable contact of the relay J1 respectively, and the two normally open contacts of the relay J1 are connected with the test voltage VHE simultaneously; the first normally closed contact of the relay J1 is connected with the source of the NMOS Q12 and the drain of the NMOS Q14, the second normally closed contact of the relay J1 is connected with the source of the NMOS Q13 and the drain of the NMOS Q15, the drain of the NMOS Q12 and the drain of the NMOS Q13 are connected with the excitation voltage VEE simultaneously; the gate of the NMOS Q12 and the gate of the NMOS Q14 are connected with the first drive signal end EH1 and the second drive signal end EH2 through the half-bridge drive circuit, the gate of the NMOS Q13 and the gate of the NMOS Q15 are connected with the first drive signal end EH1 and the second drive signal end EH2 through the other half-bridge drive circuit; the source of the NMOS Q14 and the source of the NMOS Q15 are connected as the output end of the third sampling voltage IREF, and are connected with the ground through the resistor R21; the third sampling voltage IREF outputs the feedback voltage V1 through the amplification circuit. The positive input end of the amplifier U4 is inputted with the third sampling voltage IREF, one end of the resistor R18 and one end of the resistor R19 are connected with the inverting input end of the amplifier U4, the other end of the resistor R19 is connected with the ground, the other end of the resistor R18 is connected with the output end of the amplifier U4 through the resistor R17, one end of the resistor R20 is connected with the output end of the amplifier U4, the other end of the resistor R20 outputs the feedback voltage V1, one end of the resistor R16, the cathode of the voltage stabilizing tube DZ3 and the anode of the voltage stabilizing tube DZ2 are connected with the other end of the resistor R20, the anode of the voltage stabilizing tube DZ3 is connected with the ground, the other end of the resistor R16 is connected with the ground, and the cathode of the voltage stabilizing tube DZ2 is connected with the boost voltage through the resistor R15.

[0038] As Figure 3As shown, the mode switching unit includes an NMOS transistor Q11. The gate of NMOS transistor Q11 is connected to the second control signal terminal MCU-2, and is connected to the source of NMOS transistor Q11 through resistor R14 and grounded. The drain of NMOS transistor Q11 is connected to the gate of PMOS transistor Q10, one end of resistor R13, and the gate of NMOS transistor Q9. The source of PMOS transistor Q10 is connected to the other end of resistor R13 and connected to the power supply voltage VBT. The drain of PMOS transistor Q10 is connected to one end of relay J1 and the cathode of diode D2. The other end of relay J1 is connected to the positive terminal of diode D2 and grounded; the source of NMOS transistor Q9 is grounded, and the drain of NMOS transistor Q9 is connected to the other end of insulation resistor RX and the water meter casing; the source of NMOS transistor Q9 is connected to one end of bidirectional diode D5, one end of resistor R12, and one end of capacitor C7; the drain of NMOS transistor Q9 is connected to the other end of bidirectional diode D5, the other end of resistor R12, and one end of resistor R11; the other end of resistor R11 is connected to the other end of capacitor C7 and outputs the first sampling voltage RXV1. The model of relay J1 is TXS2SA.

[0039] The constant current unit includes a reference chip U5 connected to the second control signal terminal MCU-2. The reference voltage output terminal REF of the reference chip U5 is connected to the base of transistor Q7 through resistor R9. The emitter of transistor Q7 is connected to the base and collector of transistor Q8 through resistor R10. The emitter of transistor Q8 is grounded. The collector of transistor Q7 is connected to the base of transistor Q5 and the collector of transistor Q6. The emitter of transistor Q6 is connected to the boost voltage through resistor R5. The base of transistor Q6 is connected to the emitter of transistor Q5 and is connected to the boost voltage through resistor R4. The collector of transistor Q5 is connected to one end of the insulation resistor RX and the test voltage VHE. One end of the insulation resistor RX is connected to a voltage sampling unit. One end of the insulation resistor RX is connected to one end of resistor R8 and the cathode of Zener diode DZ1 through resistors R6 and R7 in series. The other end of resistor R8 is connected to the anode of Zener diode DZ1 and grounded. One end of resistor R8 outputs the second sampling voltage RXV2.

[0040] like Figure 4 As shown, the sampling control circuit includes a connected analog-to-digital converter chip U2 and a control chip U3. U2 is an ADS1224 digital-to-analog converter chip, and U3 is an STM32 control chip. The analog-to-digital converter chip U2 receives a first sampling voltage RXV1, a second sampling voltage RXV2, a third sampling voltage IREF, and a flow signal. The control chip U3 outputs control signals through a first control signal terminal MCU-1, a second control signal terminal MCU-2, a third control signal terminal MCU-3, a first drive signal terminal EH1, and a second drive signal terminal EH2. The digital-to-analog converter chip U2 is powered by chip U0.

[0041] The electromagnetic water meter comprises three working modes:

[0042] The hibernation mode, the first control signal end outputs low level to the DC / DC output circuit, the DC / DC output circuit is not connected with the power supply voltage of the AD sampling circuit and is not powered;

[0043] The flow measurement mode, the first control signal end outputs high level to the DC / DC output circuit, the DC / DC output circuit is connected with the power supply voltage of the AD sampling circuit and starts to be powered, the second control signal end outputs low level to the mode switching unit, the water meter shell is short-circuited with the ground end, the excitation coil is connected with the H bridge, and the flow measurement mode is entered;

[0044] The insulation resistance measurement mode, the first control signal end outputs high level to the DC / DC output circuit, the DC / DC output circuit is connected with the power supply voltage of the AD sampling circuit and starts to be powered, the second control signal end outputs high level to the mode switching unit, the excitation coil is disconnected with the H bridge and is connected with the test voltage, the water meter shell is connected with the ground end through the current detection resistance, and the insulation resistance measurement mode is entered.

[0045] The original DC / DC output circuit, excitation driving circuit and sampling control circuit of the electromagnetic water meter are improved, the insulation resistance test circuit is added, the flow measurement and the insulation resistance measurement can be performed in two different modes, the insulation resistance of the sensor can be measured without opening the converter shell, the measurement of the insulation resistance of the excitation coil to the ground is controlled by the electromagnetic water meter button or the remote communication instruction, the measurement result can be displayed on the display screen of the electromagnetic water meter and transmitted to the background through wireless communication for the staff to check.

[0046] The mode switching unit can switch between the flow measurement mode and the insulation resistance measurement mode, when the second control signal end inputs low level, the NMOS tube Q11 is turned off, the NMOS tube Q9 is turned on to connect the water meter shell with the ground end, the PMOS tube Q10 is turned off, and the relay J1 is in the normally closed state, so that the flow measurement mode is realized; when the second control signal end inputs high level, the NMOS tube Q11 is turned on, the PMOS tube Q10 is turned on to make the relay J1 be attracted, the moving contact is connected with the corresponding normally open contact, the NMOS tube Q9 is turned off, and the voltage is generated between the current detection resistance, so that the insulation resistance measurement mode is realized; the connection between the excitation coil and the excitation driving circuit H bridge is disconnected through the control of the micro-power consumption relay J1, so as to avoid that the test voltage damages the electronic components and the leakage current is generated through the excitation driving circuit components, and the insulation resistance measurement accuracy is affected.

[0047] In the application, when not in the insulation resistance measurement mode, the second signal control end outputs low level, the reference chip U5 in the constant current unit has no working voltage, thus no reference voltage REF output, the transistors Q5, Q6 and Q7 are cut off, thereby the test voltage output is turned off, and the power consumption generated by the boost voltage through the leakage current is prevented; when in the insulation resistance measurement mode, the second control signal end outputs high level, the reference chip U5 has working voltage and outputs reference voltage, thereby the maximum current flowing through the insulation resistance RX is controlled.

[0048] In the application, the traditional step-down mode DC / DC conversion circuit is changed into a DC / DC step-up and step-down conversion circuit containing a step-up and step-down voltage stabilizing chip U1; when the circuit is in the insulation resistance measurement mode or the excitation current does not reach the constant current value in the flow test mode, U1 can automatically work in the step-up mode according to the feedback voltage V1 input from the feedback input end, and continue to provide constant current drive for the excitation circuit, so that the battery margin is fully utilized, and the battery is prevented from being replaced in advance; the electromagnetic water meter adopts a gap measurement mode to reduce power consumption, and part of the circuit is in a sleep mode when not measuring, in addition, through the step-up and step-down conversion circuit, the excitation coil can be quickly magnetized, the magnetizing time is shortened, the circuit sleep time is relatively prolonged, and the power consumption is reduced.

[0049] In the application, the test voltage of the insulation resistance to ground comes from the boost voltage, the boost voltage is obtained by coupling the primary side inductor coil L1-1 and the secondary side inductor coil L1-2 in the DC / DC output circuit, and the required boost voltage is obtained at the L1-2 end, and the test ground HGND of the boost voltage is connected with the GND of the circuit board through the NMOS tube Q3. When the electromagnetic water meter works in the flow measurement mode, the output end MCU-3 of the chip U3 outputs low level to control Q3 to be turned off, and no current passes through HGND and GND, so that the insulation resistance test circuit is prevented from generating additional power consumption in the flow measurement mode, and when the electromagnetic water meter works in the insulation resistance measurement mode, MCU-3 outputs high level, so that Q3 is turned on, HGND and GND are turned on, and a current loop is provided for the insulation resistance measurement.

[0050] In the application, in the insulation resistance measurement mode, the two ends of the excitation coil LC are switched to the connection test power VHE through the relay J1, the MOS tube in the excitation circuit is turned off, and no current passes through the sampling resistor in the excitation circuit, so that the feedback voltage V1 is less than the set feedback voltage threshold value, and the boost voltage output by the chip U1 is continuously increased, and when the boost voltage is increased to the required voltage, the zener DZ2 is broken down to V1, the feedback voltage V1 input to the chip U1 makes the boost voltage remain at a stable value; in the flow measurement mode, the two ends of the excitation coil LC are connected with the excitation drive H bridge through the normally closed contact of the relay J1, so that the third sampling voltage IREF is generated on the sampling resistor R21, and the feedback voltage V1 output after IREF is amplified is input to the chip U1 to stabilize the excitation voltage VEE and thus stabilize the excitation current.

[0051] The relevant data of the excitation coil ground insulation resistance measurement and the relevant data of the flow measurement are input into the same 24-bit analog-digital conversion chip U2 for AD conversion. The test voltage VHE, the voltage RXV2 sampled by the voltage sampling unit, and the voltage RXV1 collected on the current sampling unit's current detection resistor R12 during insulation resistance measurement are respectively connected to the sampling input end of the chip U2 to provide high-precision AD conversion for insulation resistance measurement.

[0052] The electromagnetic water meter has three working modes. When measurement is needed, the flow measurement mode or the insulation resistance measurement mode is entered, and when measurement is not needed, the sleep mode is entered to save energy. In addition, the control of the electromagnetic water meter working mode can be realized by the electromagnetic water meter key control or remote communication instruction control, or can be set as interval automatic measurement. The measurement result can be displayed on the display screen of the electromagnetic water meter or can be transmitted remotely through wireless communication.

[0053] In the embodiment of the present application, when the electromagnetic water meter enters the flow measurement mode or the excitation coil ground insulation resistance measurement mode from the sleep mode, Figure 4 The control end MCU-1 of the middle chip U3 outputs a 3.0V voltage to the gate of the PMOS transistor Q1. Figure 1 The drain of the NMOS transistor Q2 is connected with the gate of the PMOS transistor Q1. Since Q2 is turned on, the gate of Q1 is pulled to the ground, the source of Q1 is connected with the positive pole of the 3.6V battery through the power supply voltage VBT, and thus Q1 is turned on. The 3.6V battery voltage is transmitted through VBT end→Q1 source→Q1 drain→the power supply input end of the chip U1 to make the chip U1 work, and the chip U1 outputs the excitation voltage VEE for the excitation driving circuit to work. Similarly, the input end of the chip U0 is connected with the drain of Q1. After the chip U0 is powered on, it outputs a 2.8V voltage to supply the Figure 4 The analog-digital conversion chip U2 works.

[0054] When the electromagnetic water meter works in the flow measurement mode, Figure 4 The control end MCU-2 of the middle chip U3 outputs a low level, which is connected with the gate of the NMOS transistor Q11. Figure 3 The gate of Q11 is not supplied with voltage and thus is turned off. Since Q11 is turned off, the 3.6V voltage of the power supply voltage VBT is supplied to the gate of Q9 through the resistor R13, the gate of Q9 has a 3.6V voltage with respect to the ground end GND, and thus Q9 is turned on to connect the ground end GND with the water meter shell, i.e. the instrument shell, to provide a reference level for the flow measurement mode. In addition, since Q11 is turned off, the potential difference between the two ends of the resistor R13 is zero, and thus the gate and the source of the PMOS transistor Q10 are not supplied with a conduction voltage, and thus Q10 is turned off. The micro-power consumption relay J1 is not supplied with a working voltage and thus is released and is in a normally closed state. Since the relay J1 is released,Figure 2 The A end of the excitation coil LC on the sensor is connected through the 2nd movable contact of the change-over switch J1-S1 of the relay J1, the 3rd normally closed contact of J1-S1, and the source of Q12. The B end of the excitation coil LC on the sensor is connected through the 2nd movable contact of the change-over switch J1-S2 of the relay J1, the 3rd normally closed contact of J1-S2, and the source of Q13. Thus, the excitation coil LC is connected with the H-bridge circuit composed of Q12, Q13, Q14, and Q15. Figure 4 The driving signals EH1 and EH2 output by the chip U3 control the half-bridge driving circuit, so that the H-bridge circuit is cross-conducting and cut-off according to the set excitation mode, and the required excitation current is generated in the excitation coil LC. The magnitude of the excitation current is determined by the excitation voltage VEE output by the chip U1 in the DC / DC output circuit. The excitation current is connected to the ground terminal GND through the H-bridge circuit, the excitation coil, and the current sampling resistor R21. The excitation current flows through the sampling resistor R21, and a voltage IREF is generated on the resistor R21. The signal of the voltage IREF is transmitted to the analog-to-digital conversion chip U2 for AD conversion, so that the control chip U3 can monitor the excitation current. Meanwhile, the voltage IREF is also connected to the non-inverting input terminal of the operational amplifier U4. The amplified circuit composed of the amplifier U4, the resistors R17, R18, R19, and R20 amplifies and outputs the feedback voltage V1. The feedback voltage V1 is input to the feedback terminal FB of the chip U1. The chip U1 controls the output voltage VEE by judging the feedback voltage input to the FB terminal. When the feedback voltage V1 is greater than the preset feedback voltage threshold, the output excitation voltage VEE is reduced to reduce the excitation current. When the feedback voltage V1 is less than the feedback voltage threshold, the output excitation voltage VEE is increased to increase the excitation current, so as to achieve the purpose of controlling the excitation current by the feedback voltage V1. By designing the resistance value of the resistor R21 and changing the amplification factor of the chip U4, the feedback voltage V1 can be changed, and then the required excitation current is obtained, so as to realize constant-current excitation. In this flow measurement mode, due to the control of the feedback voltage V1 after amplification of the voltage IREF on the feedback terminal FB of the chip U1, the induced voltage of the inductor L1-2 is less than 10V after rectification and filtering by the diode D1 and the capacitor C1, so as to reduce the charging loss of the capacitor C1 in the flow measurement mode.

[0055] When the electromagnetic water meter works in the insulation resistance measurement mode, the control end MCU-2 of the chip U3 outputs a 3.0V voltage to the gate of the NMOS tube Q11 to make Q11 conduct, the gate of the PMOS tube Q10 is pulled to the ground, Q10 is turned on, and the 3.6V power supply voltage is applied to the two ends of the coil of the relay J1 through the VBT end and the PMOS tube Q10, so that the relay J1 is attracted. Because the relay J1 is attracted, the A end of the excitation coil LC is connected through the 2nd moving contact of the change-over switch J1-S1 of the relay J1, the normally open contact of the 1st end of J1-S1, and the test voltage VHE, the B end of the excitation coil LC is connected through the 2nd moving contact of the change-over switch J1-S2 of the relay J1, the normally open contact of the 1st end of J1-S2, and the test voltage VHE, the A and B ends of the excitation coil LC are disconnected from the H-bridge circuit, and the A and B ends of the excitation coil LC are connected to the test voltage VHE. In the insulation resistance measurement mode, the driving signals EH1 and EH2 output by the chip U3 control the half-bridge drive circuit to make Q12, Q13, Q14, and Q15 turn off, no current flows through the sampling resistor R21, the voltage IREF across the resistor R21 is 0, and the feedback voltage V1 output after being amplified by the amplifier U4 is less than the feedback voltage threshold in the chip U1, so that the voltage output by the chip U1 is increased. Because the voltage IREF is continuously 0, the voltage output by the chip U1 is continuously increased.

[0056] The external inductance of the SW1 end and the SW2 end of the chip U1 is wound by the double coils L1-1 and L1-2 of the same magnetic core. The L1-1 winding provides freewheeling and energy storage for voltage conversion, and the number of turns of the L1-2 winding is greater than that of the L1-1 winding. Because the voltage output by the chip U1 is continuously increased, the boost voltage output after the voltage induced to the L1-2 winding via the L1-1 winding is rectified by the diode D1 and filtered by the capacitor C1 is also continuously increased.

[0057] When the electromagnetic water meter works in the insulation resistance measurement mode, the control end MCU-3 of the chip U3 outputs a high level, controls the NMOS tube Q3 to be turned on, connects HGND and GND, and thus the voltage on the capacitor C1→ the resistance R15→ the stabilizing tube DZ2→ the stabilizing tube DZ3→ the ground end GND→ the NMOS tube Q3→ HGND forms a current loop. Since the stabilizing value of the stabilizing tube DZ2 is 120V, when the voltage on C1 exceeds 125V, the stabilizing tube DZ2 is Zener broken, so that the current flows through the resistance R16, the feedback voltage V1 on the resistance R16 is greater than the preset feedback voltage threshold, thereby the output voltage is reduced, indirectly reducing the boost voltage, and thus the output boost voltage is stabilized at 125V. In the insulation resistance test circuit, the resistance R4, the resistance R5, the resistance R9, the resistance R10, the triode Q5, the triode Q6, the triode Q7 and the triode Q8 form a constant current unit. When the electromagnetic water meter works in the insulation resistance measurement mode, the control end MCU-2 of the chip U3 outputs a 3V voltage to supply power to the reference chip U5, and the reference chip U4 outputs a reference voltage REF to control the output current of the triode Q5. In this embodiment, the designed constant current is 0.5mA, and when the measured magnetizing coil ground insulation resistance RX is 0Ω, the test voltage VHE controlled by the constant current unit makes the maximum current flowing through the insulation resistance RX be 0.5mA.

[0058] The present application calculates the magnetizing coil ground insulation resistance RX by the test voltage VHE applied when sampling the magnetizing coil ground insulation resistance and the current I flowing through the measured insulation resistance RX. When the electromagnetic water meter works in the insulation resistance flow measurement mode, the control end MCU-2 of the chip U3 outputs a 3.0V voltage to the gate of the NMOS tube Q11, Q11 is turned on, the gate of the NMOS tube Q9 is pulled to the ground through the drain of Q11, the NMOS tube Q9 connected in parallel between the current detection resistance R12 is turned off, and thus the test current flows from the test voltage VHE→ the measured insulation resistance RX→ the current detection resistance R12→ the ground end GND, and a voltage is generated between the resistance R12. In this embodiment, the resistance R12 has a resistance value of 4KΩ, and the current I flowing through the measured insulation resistance RX generates a voltage of I*4KΩ between the resistance R12. After the voltage is filtered by the resistance R11 and the capacitor C11, the output voltage is RXV1. The first sampling voltage RXV1 is input into the analog-to-digital conversion chip U2. Since the input impedance of the chip U2 is very high, the voltage drop generated when the voltage on the resistance R12 passes through the resistance R11 can be ignored, and thus RXV1=I*4KΩ. When the magnetizing coil ground insulation resistance is 0, RXV1 is the maximum value, and in this embodiment, the maximum value of RXV1 is 0.5mA*4KΩ=2V; when the magnetizing coil ground insulation resistance is infinite, RXV1 tends to be 0V.

[0059] The test voltage VHE is divided by the resistor R6, the resistor R7 and the resistor R8 to generate a voltage RXV2 at both ends of R8, RXV2=VHE*R8 / (R6+R7+R8), in the embodiment, the resistance of R6 and R7 is selected as 10MΩ, the resistance of R8 is selected as 330KΩ, when the excitation coil has an infinite ground insulation resistance, the maximum voltage of the second sampling voltage RXV2 is less than 2.1V, the second sampling voltage RXV2 is input into the analog-digital conversion chip U2. Through the sampling and conversion of the chip U2, the chip U3 obtains the voltage values of RVX1 and RXV2, and RX=(VHE-RXV1) / I=(VHE-RXV1)*R12 / RXV1=(R6+R7+R8)*RXV2 / R8-RXV1)*R12 / RXV1 can be obtained according to VHE=(R6+R7+R8)*RXV2 / R8 and RXV1=I*R12. The voltage RXV1 and the voltage RXV2 are sampled by 24-bit high-precision sampling, so that the resolution of the insulation resistance test can reach the mΩ level. In view of the actual measurement requirements of the electromagnetic water meter, the measurement results of the embodiment are displayed in three sections, which are 1 MΩ-10MΩ, the display scale is 1KΩ, the measurement accuracy is 0.2%; 10MΩ-100MΩ, the display scale is 10KΩ, the measurement accuracy is 0.2%; 100MΩ-1000MΩ, the display scale is 100KΩ, the measurement accuracy is 2%.

[0060] In the embodiment, the measurement of the excitation coil ground insulation resistance of the electromagnetic water meter can be instructed by the electromagnetic water meter operation button, the electromagnetic water meter infrared communication interface, the electromagnetic water meter wireless transmission communication interface or the set timing measurement mode of the electromagnetic water meter. The micro-power measurement mode is used during measurement, the maximum test voltage is preferably 125V, the test current is 0.5mA, when the excitation coil ground insulation resistance is greater than 1MΩ, the battery working current is less than 30mA, the measurement time is less than 50ms, which is less than the power consumption of one excitation cycle of the electromagnetic water meter, and the online automatic measurement is generally set to 6 hours of measurement once. The measurement results of the embodiment can be displayed on the display interface of the electromagnetic water meter, when the measured excitation coil ground insulation resistance of the electromagnetic water meter continuously decreases or is less than the alarm setting value, the electromagnetic water meter will display an alarm on the display interface, and the test results and the alarm signal are wirelessly transmitted.

[0061] The above embodiments are further elaborated and described to facilitate understanding, and are not any limitation of the present application, any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electromagnetic water meter for measuring the insulation resistance of a sensor to ground, comprising a converter and a sensor, characterized in that, The converter is equipped with: The insulation resistance test circuit is used to detect the insulation resistance RX of the sensor excitation coil to ground. One end of the insulation resistance RX is connected to a voltage sampling unit and a constant current unit, and the other end of the insulation resistance RX is connected to a mode switching unit and a current sampling unit. DC / DC output circuit, used to convert voltage and power the circuitry within the converter; The excitation drive circuit is used to regulate and control the output voltage of the DC / DC output circuit. The sampling control circuit is connected to the insulation resistance test circuit, the DC / DC output circuit, and the excitation drive circuit, respectively, and is used to output control signals and receive sampling signals. The mode switching unit includes an NMOS transistor Q11. The gate of Q11 is connected to the second control signal terminal and is connected to the source of Q11 through a resistor R14 and grounded. The drain of Q11 is connected to the gate of a PMOS transistor Q10, one end of a resistor R13, and the gate of an NMOS transistor Q9. The source of Q10 is connected to the other end of R13 and connected to a voltage VBT. The drain of Q10 is grounded through a relay J1. The source of Q9 is grounded, and the drain of Q9 is connected to the other end of an insulation resistor RX and the water meter casing. A current sensing resistor R12 of a current sampling unit is connected between the source and drain of Q9, and the current sampling unit outputs a first sampling voltage RXV1. In insulation resistance measurement mode, the second control signal terminal outputs a high level, the water meter casing is grounded through R12, and the two ends of the excitation coil are switched to the test power supply VHE through J1. In flow measurement mode, the second control signal terminal outputs a low level, the water meter casing is grounded, and the two ends of the excitation coil are switched to the H-bridge of the excitation drive circuit via J1.

2. An electromagnetic water meter for measuring the insulation resistance of a sensor to ground according to claim 1, characterized in that, In the mode switching unit, the drain of Q10 is connected to the negative terminal of diode D2, and the positive terminal of D2 is grounded. In the current sampling unit, one end of R12 connected to the instrument housing is connected to resistor R11, the other end of R12 is connected to one end of capacitor C7 and grounded, and the other end of resistor R11 and the other end of capacitor C7 are connected to output the first sampling voltage RXV1.

3. An electromagnetic water meter for measuring the insulation resistance of a sensor to ground according to claim 1 or 2, characterized in that, The constant current unit includes a reference chip U5 connected to the second control signal terminal. The reference voltage output terminal of the reference chip U5 is connected to the base of transistor Q7 through resistor R9. The emitter of transistor Q7 is connected to the base and collector of transistor Q8 through resistor R10. The emitter of transistor Q8 is grounded. The collector of transistor Q7 is connected to the base of transistor Q5 and the collector of transistor Q6. The emitter of transistor Q6 is connected to a boost voltage through resistor R5. The base of transistor Q6 is connected to the emitter of transistor Q5 and connected to a boost voltage through resistor R4. The collector of transistor Q5 is connected to one end of the insulation resistor RX and the test voltage VHE. One end of the insulation resistor RX is connected to a voltage sampling unit, which outputs a second sampling voltage RXV2.

4. An electromagnetic water meter for measuring the insulation resistance of a sensor to ground according to claim 1, characterized in that, The DC / DC output circuit includes a chip U1. The first voltage output terminal of the chip U1 outputs an excitation voltage VEE, and the feedback input terminal of the chip U1 receives a feedback voltage V1. The chip U1 outputs a boost voltage after being boosted by a dual-coil inductor L1. A switching unit is connected between the voltage input terminal of the chip U1 and the power supply voltage. The switching unit controls the connection or disconnection between the power supply voltage and the chip U1 by a signal input from the connected first control signal terminal.

5. An electromagnetic water meter for measuring the insulation resistance of a sensor to ground according to claim 1, 2, or 4, characterized in that, The excitation drive circuit includes an excitation coil LC. The two ends of the excitation coil are connected to the first moving contact and the second moving contact of relay J1, respectively. The two normally open contacts of relay J1 are simultaneously connected to the test voltage VHE. The first normally closed contact of relay J1 is connected to the source of NMOS transistor Q12 and the drain of NMOS transistor Q14. The second normally closed contact of relay J1 is connected to the source of NMOS transistor Q13 and the drain of NMOS transistor Q15. The drains of NMOS transistors Q12 and Q13 are simultaneously connected to the excitation voltage VEE. The gates of NMOS transistors Q12, Q14, Q13, and Q15 are connected to the first drive signal terminal and the second drive signal terminal through a half-bridge drive circuit. The sources of NMOS transistors Q14 and Q15 are connected as the output terminal of the third sampling voltage IREF and grounded through resistor R21. The third sampling voltage IREF is amplified to output the feedback voltage V1.

6. An electromagnetic water meter for measuring the insulation resistance of a sensor to ground according to claim 1, characterized in that, The sampling control circuit includes an analog-to-digital converter chip U2 and a control chip U3 connected to each other. The analog-to-digital converter chip receives a first sampling voltage RXV1, a second sampling voltage RXV2 and a third sampling voltage IREF. The control chip U3 outputs control signals through a first control signal terminal, a second control signal terminal, a third control signal terminal, a first drive signal terminal and a second drive signal terminal.

7. An electromagnetic water meter for measuring the insulation resistance of a sensor to ground according to claim 1, 2, 4, or 6, characterized in that, The electromagnetic water meter includes three operating modes: In sleep mode, the first control signal terminal outputs a low level to the DC / DC output circuit, and the DC / DC output circuit is not connected to the power supply voltage and is not powered. In flow measurement mode, the first control signal terminal outputs a high level to the DC / DC output circuit, the DC / DC output circuit is connected to the power supply voltage and begins to supply power, the second control signal terminal outputs a low level to the mode switching unit, the water meter casing is connected to the ground terminal, and the flow measurement mode is entered. In insulation resistance measurement mode, the first control signal terminal outputs a high level to the DC / DC output circuit, the DC / DC output circuit is connected to the power supply voltage and begins to supply power, the second control signal terminal outputs a high level to the mode switching unit, and the water meter casing is connected to the ground terminal through the current sensing resistor, thus entering the insulation resistance measurement mode.

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