An ultralow power consumption flowmeter

Abstract

This invention relates to the field of fluid measurement technology and discloses an ultra-low power flow meter, comprising a differential pressure sensor core, an instrumentation amplifier, a microcontroller, an LCD display, a constant current source, a voltage regulator, a power input terminal, and an alarm circuit. The differential pressure sensor core converts the fluid differential pressure into a differential voltage signal, which is amplified by the instrumentation amplifier and then processed by the analog-to-digital converter of the microcontroller. The voltage regulator provides a reference voltage for the sensor and the instrumentation amplifier, and the constant current source provides a stable excitation current to the sensor. The alarm circuit consists of an electronic switch and a current-limiting adjustment network connected in parallel between the power input terminal and ground. In case of an abnormality, the electronic switch conducts, drawing additional current to generate a switching signal. This invention, through the selection of low-power devices throughout the entire chain and a periodic wake-up working mode, controls the normal operating current of the entire device to within 100 microamps, meeting intrinsically safe explosion-proof requirements, and avoids full-scale output saturation error through a dynamic margin calibration algorithm.

Description

Technical Field

[0001] This invention relates to the field of fluid measurement technology, and in particular to an ultra-low power flow meter. Background Technology

[0002] In the field of industrial flow measurement, applications in remote pumping stations, deep-sea wellheads, underground coal mine gas, and petrochemical industries place extremely stringent requirements on the power consumption of flow detection instruments. These high-risk or difficult-to-maintain locations typically require instruments with intrinsically safe explosion-proof performance, meaning that the electrical energy generated by the circuit under normal operation and fault conditions is insufficient to ignite flammable gases or dust in the specific environment. While current low-power flow transmitters on the market have reduced power consumption compared to traditional equipment, their typical overall operating current is still around 0.16 mA. In some scenarios with strict explosion-proof requirements, there is still a risk of excessive circuit energy, making it difficult to perfectly meet the stringent voltage and current limits of intrinsically safe equipment without adding costly additional protective measures such as safety barriers. The high power consumption also limits the battery life in battery-powered scenarios. The increased frequency of operation and the increased safety risks due to battery maintenance and replacement in remote or high-risk environments cannot be ignored. In addition, when existing equipment is calibrated near full scale, the output of the amplifier circuit or microcontroller is prone to approach its saturation limit, resulting in nonlinear errors and affecting the accuracy of high-end measurements. Furthermore, the sensor core is also affected by power supply voltage fluctuations during operation, which can introduce additional measurement drift and weaken the long-term stability of the instrument. Summary of the Invention

[0003] In view of this, the present invention addresses the technical problems of existing low-power flow meters having relatively high power consumption, making it difficult to fully meet the strict energy limits of intrinsically safe explosion-proof equipment in high-risk environments, as well as the deficiency of insufficient calibration accuracy near full scale, by providing an ultra-low power flow meter.

[0004] This invention provides an ultra-low power flow meter, comprising a differential pressure sensor core, an instrumentation amplifier, a microcontroller, an LCD screen, a constant current source, a voltage regulator, a power input terminal, and an alarm circuit. The differential pressure sensor core converts fluid differential pressure into a differential voltage signal. The non-inverting and inverting input terminals of the instrumentation amplifier are connected to the positive and negative output terminals of the differential pressure sensor core, respectively. The output terminal of the instrumentation amplifier is connected to the analog-to-digital converter input pin of the microcontroller. The LCD screen is connected to the display interface of the microcontroller. The output terminal of the constant current source is connected to the excitation terminal of the differential pressure sensor core. The input terminal of the voltage regulator is connected to an external power supply, and the output terminal of the voltage regulator provides a reference operating voltage for the differential pressure sensor core and the instrumentation amplifier. The power input terminal is connected to an external two-wire power supply circuit. The alarm circuit is connected in parallel between the power input terminal and ground. The alarm circuit includes an electronic switch and a current limiting adjustment network. The control terminal of the electronic switch is connected to the digital output pin of the microcontroller, and the output terminal of the electronic switch is grounded through the current limiting adjustment network. When the microcontroller detects an abnormal state, it controls the electronic switch to conduct, causing the flow meter to draw additional current from the external power supply circuit to generate a current jump signal.

[0005] As a preferred embodiment of the present invention, the differential pressure sensor core adopts a piezoresistive sensor and the sensor housing is made of stainless steel, thereby possessing the ability to withstand long-term stable operation in a highly corrosive fluid environment.

[0006] As a preferred embodiment of the present invention, the gain of the instrumentation amplifier is set by a precision resistor connected between the gain setting pins of the instrumentation amplifier. The gain setting value is determined based on the full-scale output voltage of the differential pressure sensor core and the input range of the microcontroller analog-to-digital converter, so that the instrumentation amplifier can effectively amplify weak differential signals while maintaining ultra-low operating current.

[0007] As a preferred technical solution of the present invention, the microcontroller is configured to periodically wake up and collect data from the analog-to-digital converter, and enter a low-power sleep mode during the collection interval. The microcontroller performs linearization and temperature compensation processing on the collected data according to the pre-stored calibration coefficients and then outputs a linear voltage signal, so that the normal operating current of the whole machine does not exceed 100 microamps.

[0008] As a preferred technical solution of the present invention, the microcontroller stores a dynamic margin calibration algorithm. During calibration, the target output voltage corresponding to the full scale is set to a preset value that is lower than the upper limit of the output capability of the instrumentation amplifier and the microcontroller, so that the signal processing link maintains a linear operating range near the full scale.

[0009] As a preferred technical solution of the present invention, the current limiting adjustment network includes a fixed resistor and an adjustable resistor connected in series. By adjusting the resistance value of the adjustable resistor, the current flowing through the current limiting adjustment network when the electronic switch is turned on is changed, so that the current jump amplitude when the alarm is triggered can be adapted to the trigger threshold of different external monitoring systems.

[0010] As a preferred embodiment of the present invention, the control terminal of the electronic switch is connected to the digital output pin of the microcontroller through a voltage divider drive network. The voltage divider drive network is used to convert the output level of the microcontroller into a gate voltage suitable for driving the electronic switch to turn on.

[0011] As a preferred embodiment of the present invention, an alarm indicator light is also included. The alarm indicator light is connected to another digital output pin of the microcontroller. The alarm indicator light uses a low-dropout light-emitting diode with a forward voltage drop of no more than 1.8 volts and an operating current of no more than 2 mA, so that the system power supply bus voltage will not drop significantly when the alarm indicator light is lit.

[0012] As a preferred technical solution of the present invention, the voltage regulator adopts a low-dropout linear voltage regulator, and its output terminal is connected to the power supply terminal of the differential pressure sensor core and the power supply terminal of the instrumentation amplifier through a filter capacitor, so as to provide a stable reference voltage for the signal acquisition link and suppress the transmission of external power supply voltage fluctuations to the sensor and the instrumentation amplifier.

[0013] As a preferred embodiment of the present invention, a switching buck converter is further provided between the power input terminal and the voltage regulator, which converts the external power supply voltage into the input voltage required by the voltage regulator.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention selects low-power devices in the differential pressure sensor core, instrumentation amplifier, and microcontroller, and adopts a periodic wake-up working mode to control the normal operating current of the entire device to within 100 microamps. This ensures that the electrical energy of the circuit meets the limitations of intrinsically safe explosion-proof equipment under normal operation and foreseeable fault conditions, reducing maintenance frequency and operational risks in high-risk environments. The invention employs an active load-type current switching mechanism composed of electronic switches and a current-limiting regulation network in the alarm circuit. This mechanism only activates the additional current branch during abnormal triggering, consuming no additional power under normal conditions. Simultaneously, the adjustable resistor in the current-limiting regulation network allows the alarm current amplitude to flexibly adapt to different external monitoring systems. Finally, this invention uses a dynamic margin algorithm in the calibration program to set the full-scale target output voltage below the upper limit of the amplifier and microcontroller output capabilities, avoiding calibration errors and measurement nonlinearities caused by signal link output saturation near the full scale. Attached Figure Description

[0015] Figure 1This is a system block diagram of an ultra-low power flow meter according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the microcontroller and peripheral circuits according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the power supply, sensor, and alarm circuit according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the three-dimensional structure of a printed circuit board according to an embodiment of the present invention.

[0016] 1. Differential pressure sensor core; 2. Instrumentation amplifier; 3. Microcontroller; 4. LCD display; 5. Voltage regulator; 6. Constant current source; 7. Electronic switch; 8. Current limiting regulation network; 9. Alarm indicator light; 10. Power input terminal. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides an ultra-low power flow meter suitable for fluid differential pressure measurement and flow calculation in high-risk environments such as underground coal mine gas, petrochemicals, and explosive dust. This flow meter constructs a full-link ultra-low power signal acquisition and processing channel, and integrates an active load-type current jump alarm mechanism and anti-breakdown visual alarm indication, keeping the normal operating current of the entire unit at around 100 microamps, thus meeting the stringent energy limits for intrinsically safe explosion-proof equipment.

[0019] Reference Figure 1As shown, the ultra-low power flow meter of the present invention includes a differential pressure sensor core 1, an instrumentation amplifier 2, a microcontroller 3, an LCD display 4, a voltage regulator 5, a constant current source 6, an electronic switch 7, a current limiting adjustment network 8, an alarm indicator 9, and a power input terminal 10. The power input terminal 10 is connected to an external two-wire power supply circuit. The external power supply voltage is stepped down by a switching buck converter and then fed into the voltage regulator 5. The output of the voltage regulator 5 provides a precise reference operating voltage for the differential pressure sensor core 1 and the instrumentation amplifier 2. The output of the constant current source 6 is connected to the excitation terminal of the differential pressure sensor core 1, providing a highly stable constant excitation current for the sensor bridge. Under the action of fluid differential pressure, the differential pressure sensor core 1 outputs a weak differential voltage signal. This signal is amplified by the instrumentation amplifier 2 and then sent to the analog-to-digital converter of the microcontroller 3 for digital acquisition. The microcontroller 3 performs linearization, temperature compensation, and calibration processing on the acquired digital signal, and displays the calculated flow rate value in real time on the LCD display 4. Electronic switch 7 and current limiting network 8 are connected in series and then in parallel between power input terminal 10 and ground to form an alarm circuit. The control terminal of electronic switch 7 is connected to the digital output pin of microcontroller 3. Alarm indicator light 9 is connected to another digital output pin of microcontroller 3.

[0020] Reference Figure 3 The circuit connections of the sensor signal acquisition section are further explained as shown. In this embodiment, the differential pressure sensor core 1 is a piezoresistive differential pressure sensor. The sensor housing is made of 316L stainless steel, possessing excellent corrosion resistance and high-pressure resistance, enabling long-term stable operation in highly corrosive fluids and harsh working environments. In this embodiment, the constant current source 6 is a programmable constant current source chip U4. The positive input terminal of this chip is connected to the system power supply, and its output terminal is connected to the excitation terminal of the differential pressure sensor core 1 through a setting resistor R16. Adjusting resistor R17 sets the excitation current value provided by the constant current source 6 to the sensor bridge. The positive and negative output terminals of the differential pressure sensor core 1 are connected to the non-inverting input terminal (pin 3) and the inverting input terminal (pin 2) of the instrumentation amplifier 2 through the sensor interface P6, respectively. A boost resistor R18 is connected between the negative output terminal of the differential pressure sensor core 1 and ground. This resistor is used to boost the common-mode voltage of the sensor output signal to within the common-mode input range of the instrumentation amplifier 2, ensuring that the instrumentation amplifier 2 can still operate normally under low-voltage power supply conditions. In this embodiment, instrumentation amplifier 2 is a low-power precision instrumentation amplifier with a self-operating current of only 50 microamps. The gain of instrumentation amplifier 2 is set by the precision resistor R15 connected between its pin 1 and pin 8, and the gain calculation formula is as follows: Based on the output voltage amplitude of the differential pressure sensor core 1 at full-scale pressure and the input range of the built-in analog-to-digital converter of the microcontroller 3, the required signal amplification factor can be obtained by selecting an appropriate resistance value for R15. Pin 5 of the instrumentation amplifier 2 is the reference voltage input terminal, connected to the precise reference voltage provided by the voltage regulator 5. The output terminal (pin 7) of the instrumentation amplifier 2 is connected to the analog-to-digital converter input pin PA3 of the microcontroller 3 via the DC blocking capacitor C18.

[0021] In this embodiment, voltage regulator 5 employs a high-precision, low-dropout linear regulator U1. Its input is connected to the intermediate voltage output of a switching buck converter, and its output provides a stable 2.5V reference voltage. This reference voltage serves simultaneously as the bridge power supply reference for the differential pressure sensor core 1 and the reference voltage source for the instrumentation amplifier 2. Filter capacitors C1 and C2 are connected in parallel at the output of voltage regulator 5 to suppress high-frequency ripple and transient interference, ensuring the purity of the reference voltage. Since the bridge output voltage of the differential pressure sensor core 1 and the amplification reference of the instrumentation amplifier 2 both directly depend on the stability of this reference voltage, using a low-dropout linear regulator effectively isolates external power supply voltage fluctuations from being transmitted to the signal acquisition link, fundamentally eliminating initial measurement drift caused by slight changes in the power supply voltage.

[0022] Reference Figure 3 The power input terminal 10 shown corresponds to interface P5 in the circuit, through which the external two-wire power supply circuit is connected. A switching buck converter U3 and its peripheral circuitry are located between P5 and the voltage regulator 5. The input terminal of the switching buck converter U3 is connected to the positive terminal of P5. Its enable terminal uses capacitors C14 and C15 for soft-start control, and the feedback terminal uses a voltage divider network composed of resistors R8 and R11 to set the output voltage value. The switching pin provides a stable 3.3V DC voltage to the subsequent circuitry through inductor L1 and the output filter capacitor bank. This 3.3V voltage serves as the main power rail of the system, powering the input terminals of the microcontroller 3, the LCD screen 4, and the voltage regulator 5.

[0023] Reference Figure 2The diagram further illustrates the connection relationship between the microcontroller 3 and its peripheral circuits. In this embodiment, the microcontroller 3 uses an ultra-low power microcontroller chip U2, which integrates a 12-bit analog-to-digital converter (ADC) and a digital-to-analog converter (DAC). The ADC input pin PA3 of the microcontroller 3 receives the analog voltage signal output from the instrumentation amplifier 2. The microcontroller 3, controlled by its internal program, periodically wakes up from a low-power sleep mode, activates the ADC to acquire the voltage value on the PA3 pin, and performs linearization and temperature compensation calculations on the acquired data based on the five-point calibration coefficients pre-stored in its internal flash memory. This converts the nonlinear raw signal output by the sensor into a digital quantity that linearly corresponds to the actual fluid differential pressure. The microcontroller 3 then outputs a linear voltage signal from a designated pin of 0.7V to 2.5V via its internal DAC or a pulse-width modulated output through a resistor divider, where 0.7V corresponds to zero pressure and 2.5V corresponds to full-scale pressure. The microcontroller 3 further calculates the corresponding flow rate value based on the differential pressure value and pipeline parameters, and drives the LCD screen 4 to display the current measurement value in real time via the display interface. Under normal measurement conditions, microcontroller 3 returns to low-power sleep mode after completing one data acquisition and processing cycle, and wakes up again when the next sampling cycle arrives. In this way, the average power consumption of microcontroller 3 is reduced to an extremely low level. Combined with the microamplitude operating current of differential pressure sensor core 1, the quiescent current of instrumentation amplifier 2 of only 50 microamps, and the low power consumption of LCD display 4, the normal operating current of the whole machine is strictly controlled at around 100 microamps.

[0024] The peripheral circuitry of microcontroller 3 also includes a crystal oscillator circuit for generating a precise clock reference. A 32.768 kHz crystal oscillator X1 is connected between the low-speed clock input pins PC14 and PC15 of microcontroller 3, with its two ends grounded through load capacitors C3 and C4 respectively, providing a time base for the real-time clock and low-power wake-up function of microcontroller 3. An 8 MHz crystal oscillator X2 is connected between the high-speed clock input pins of microcontroller 3, with its two ends grounded through load capacitors C5 and C7 respectively, providing the main clock source when microcontroller 3 performs data acquisition and calculation tasks. The reset pin NRST of microcontroller 3 is connected to the power supply through a pull-up resistor R4, and a reset button SW1 is also connected for manual reset. Multiple power supply pins VDD and analog power supply pins VDDA of microcontroller 3 are bypassed to ground via decoupling capacitors C8 to C12 to suppress high-frequency interference. The LCD display 4 is connected to microcontroller 3 through interface P2, which includes data lines, write enable lines, segment code screen drive signals, and key input lines. The microcontroller 3 also has a reserved serial debugging interface P3 and a serial communication interface P4, which are used for program burning and debugging and communication with the host computer, respectively.

[0025] Regarding the implementation of full-scale anti-saturation calibration, the microcontroller 3 has a dynamically reserved margin calibration algorithm pre-stored in its internal flash memory. During production calibration, a five-point method is used to calibrate the flow meter, applying standard pressure at zero, 25%, 50%, 75%, and 100% of the range and recording the corresponding sensor outputs. The calibration program sets the target output voltage corresponding to the full scale to a preset value slightly lower than the upper limit of the output capabilities of the instrumentation amplifier 2 and the microcontroller 3. In this embodiment, this preset value is 2.45 volts, not the theoretical full-scale bias voltage of 2.5 volts. When full-scale pressure is applied to the differential pressure sensor core 1, the microcontroller 3 adjusts its internal calibration coefficient to precisely position the output at 2.45 volts, thus reserving a 50 millivolt margin for the signal processing link. This method fundamentally avoids output nonlinearity and calibration errors caused by individual device deviations or temperature drift leading to the amplifier circuit and microcontroller output approaching the saturation limit near the full scale, ensuring the linearity and accuracy of measurement data across the entire range.

[0026] Reference Figure 3The implementation of the alarm circuit is further explained below. The alarm circuit is connected in parallel between the power input terminal 10 and ground, and is composed of an electronic switch 7 and a current limiting adjustment network 8 connected in series. In this embodiment, the electronic switch 7 is a metal-oxide-semiconductor field-effect transistor Q1. The current limiting adjustment network 8 is composed of a fixed resistor R6 and an adjustable resistor R10 connected in series. The positive terminal of the power input terminal 10 is connected to one end of the adjustable resistor R10 through the fixed resistor R6, and the other end of the adjustable resistor R10 is connected to the drain of the electronic switch 7. The source of the electronic switch 7 is grounded. The gate of the electronic switch 7 is connected to the digital output pin PB8 of the microcontroller 3 through a voltage divider drive network. This voltage divider drive network is composed of resistors R12 and R13. One end of R12 is connected to the PB8 pin of the microcontroller 3, and the other end is connected to the gate of the electronic switch 7. R13 is connected between the gate of the electronic switch 7 and ground. Under normal measurement conditions, the PB8 pin of the microcontroller 3 remains at a low level, the electronic switch 7 is in the off state, the alarm circuit does not consume any additional current, and does not affect the normal ultra-low power consumption of about 100 microamps of the whole machine. When the microcontroller 3 detects excessive fluid pressure or equipment malfunction through sensor data or built-in algorithms, the PB8 pin is pulled high to output a high level. After voltage division by R12 and R13, a sufficient driving voltage is established on the gate of the electronic switch 7, causing the electronic switch 7 to turn on instantaneously. After turning on, the external power supply forms a current path through the current-limiting branch composed of R6 and R10, causing the flow meter to actively draw additional current from the external two-wire power supply circuit, and the current consumption of the whole machine surges instantaneously to more than 1.95 mA. After the external monitoring system detects this characteristic current jump of more than 1.95 mA, it determines that the switching condition has been met and triggers an alarm. The tester can precisely set the amplitude of this surge current by adjusting the resistance value of the adjustable resistor R10. In this embodiment, R6 is 10 kΩ, and the value of R10 ranges from 0 to 20 kΩ. By changing the resistance value of R10, the alarm trigger current can be adjusted to different levels to adapt to various industrial monitoring systems with different trigger thresholds. Meanwhile, due to the presence of the fixed resistor R6, even if the adjustable resistor R10 is adjusted to zero resistance, the peak current flowing through the current-limiting branch is still limited to a safe range by R6 and will not exceed the limit of the maximum current of the intrinsically safe explosion-proof equipment.

[0027] In this embodiment, the alarm indicator light 9 uses a special LED with extremely low forward voltage drop and extremely low operating current. Its forward voltage drop is 1.8 volts and its operating current is 2 mA. The alarm indicator light 9 is connected to the digital output pin PA15 of the microcontroller 3 through a current-limiting resistor R5. When an alarm is triggered, the microcontroller 3 simultaneously controls the PA15 pin to output a high level, driving the alarm indicator light 9 to light up or flash, providing a visual alarm indication on site. Because the forward voltage drop and operating current of this special LED are much lower than those of conventional LEDs, when the system suddenly drives the alarm indicator light 9 to light up under normal operating conditions that consume only about 100 microamps, the instantaneous pull-down effect on the system power supply bus voltage is minimal, and it will not cause the LCD screen 4 to flicker or the microcontroller 3 to reset and restart due to voltage drop. This design fundamentally solves the industry problem of system crashes caused by a sudden increase in current when the alarm light is lit in ultra-low power instruments, ensuring the reliability of the instrument in long-term high-risk maintenance-free environments.

[0028] Through the above embodiments, those skilled in the art can realize an ultra-low power flow meter with a normal operating current of around 100 microamps. This flow meter combines high-precision measurement, active jump alarm, and anti-collapse visual indication functions, and is suitable for high-risk application scenarios requiring intrinsically safe explosion-proof protection, such as underground coal mine gas, petrochemical, and explosive dust applications. (Refer to...) Figure 4 As shown, all the circuit components and functional modules mentioned above are integrated on a circular printed circuit board. The components are arranged compactly. The power input terminal 10, sensor interface P6, LCD display interface P2, serial debugging interface P3 and serial communication interface P4 are distributed on the edge of the circuit board for easy external connection. The microcontroller 3 is located in the center of the circuit board. The switching buck converter U3 and its inductor L1 and output filter capacitor group are arranged on one side of the circuit board near the power input terminal 10. The electronic switch 7 and voltage divider drive network R12, R13 and R14 in the alarm circuit are arranged on the other side of the circuit board. The adjustable resistor R10 is set on the surface of the circuit board for easy adjustment during calibration. The overall structure is compact and suitable for installation inside the flow meter housing.

[0029] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and all such modifications and variations fall within the scope of protection of the appended claims.

[0030] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An ultra-low power flow meter, characterized in that, The system includes a differential pressure sensor core (1), an instrumentation amplifier (2), a microcontroller (3), an LCD screen (4), a constant current source (6), a voltage regulator (5), a power input terminal (10), and an alarm circuit. The differential pressure sensor core (1) is used to convert the fluid differential pressure into a differential voltage signal. The non-inverting input terminal and the inverting input terminal of the instrumentation amplifier (2) are respectively connected to the positive output terminal and the negative output terminal of the differential pressure sensor core (1). The output terminal of the instrumentation amplifier (2) is connected to the analog-to-digital conversion input pin of the microcontroller (3). The LCD screen (4) is connected to the display interface of the microcontroller (3). The output terminal of the constant current source (6) is connected to the excitation terminal of the differential pressure sensor core (1). The output terminal of the voltage regulator (5) is connected to the excitation terminal of the differential pressure sensor core (1). The input terminal is connected to an external power supply. The output terminal of the voltage regulator (5) provides a reference working voltage for the differential pressure sensor core (1) and the instrumentation amplifier (2). The power input terminal (10) is connected to an external two-wire power supply circuit. The alarm circuit is connected in parallel between the power input terminal (10) and ground. The alarm circuit includes an electronic switch (7) and a current limiting adjustment network (8). The control terminal of the electronic switch (7) is connected to the digital output pin of the microcontroller (3). The output terminal of the electronic switch (7) is grounded through the current limiting adjustment network (8). When the microcontroller (3) detects an abnormal state, it controls the electronic switch (7) to turn on, so that the flow meter draws additional current from the external power supply circuit to generate a current jump signal.

2. The ultra-low power flow meter according to claim 1, characterized in that, The differential pressure sensor core (1) is a piezoresistive sensor, and the sensor housing is made of stainless steel.

3. The ultra-low power flow meter according to claim 1, characterized in that, The gain of the instrumentation amplifier (2) is set by a precision resistor connected between the gain setting pins of the instrumentation amplifier (2), and the gain setting value is determined based on the full-scale output voltage of the differential pressure sensor core (1) and the input range of the analog-to-digital converter of the microcontroller (3).

4. The ultra-low power flow meter according to claim 1, characterized in that, The microcontroller (3) is configured to periodically wake up and collect analog-to-digital converter data, and enter a low-power sleep mode during the collection interval. The microcontroller (3) performs linearization and temperature compensation processing on the collected data according to the pre-stored calibration coefficients and outputs a linear voltage signal so that the normal operating current of the whole machine does not exceed 100 microamps.

5. The ultra-low power flow meter according to claim 4, characterized in that, The microcontroller (3) stores a dynamic margin calibration algorithm. During calibration, the target output voltage corresponding to the full scale is set to a preset value that is lower than the upper limit of the output capability of the instrumentation amplifier (2) and the microcontroller (3).

6. The ultra-low power flow meter according to claim 1, characterized in that, The current limiting adjustment network (8) includes a fixed resistor and an adjustable resistor connected in series. The current flowing through the current limiting adjustment network (8) when the electronic switch (7) is turned on is changed by adjusting the resistance value of the adjustable resistor.

7. The ultra-low power flow meter according to claim 1, characterized in that, The control terminal of the electronic switch (7) is connected to the digital output pin of the microcontroller (3) through a voltage divider drive network. The voltage divider drive network is used to convert the output level of the microcontroller (3) into a gate voltage suitable for driving the electronic switch (7) to turn on.

8. The ultra-low power flow meter according to claim 1, characterized in that, It also includes an alarm indicator (9), which is connected to another digital output pin of the microcontroller (3). The alarm indicator (9) is a low-dropout light-emitting diode with a forward voltage drop of no more than 1.8 volts and an operating current of no more than 2 mA.

9. The ultra-low power flow meter according to claim 1, characterized in that, The voltage regulator (5) is a low differential pressure linear regulator, and its output terminal is connected to the power supply terminal of the differential pressure sensor core (1) and the power supply terminal of the instrumentation amplifier (2) through a filter capacitor.

10. The ultra-low power flow meter according to claim 1, characterized in that, A switching buck converter is also provided between the power input terminal (10) and the voltage regulator (5), which converts the external power supply voltage into the input voltage required by the voltage regulator (5).

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