Flow Sensors

Abstract

The present disclosure provides a flow sensor, including a flow detection circuit, a switch control circuit and a control unit; the first end of the switch control circuit is electrically connected to the detection signal end and the calibration signal end respectively, and the second end of the switch control circuit is electrically connected to the flow detection circuit; the switch control circuit is used to disconnect the detection signal end from the flow detection circuit when receiving the calibration signal, and connect the calibration signal end to the flow detection circuit; the control unit is used to obtain the calibration electrical signal output by the flow detection circuit under the calibration signal to calibrate the flow sensor. Automatic calibration can be achieved, eliminating the pain of manual calibration, so the product does not need to be introduced into the fluid medium before leaving the factory, and it is also convenient for management, storage, packaging and transportation. In addition, self-calibration can be performed periodically, or it can be used on a per-time basis, and self-calibration is performed each time it is used to ensure the measurement accuracy of the flow rate measurement.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of sensors, and in particular relates to a flow sensor. Background Art

[0002] Thermal flow sensors use thermal principles to detect fluid flow, that is, they use the heat exchange relationship between the flowing fluid and the heat source (the object used for heating in the fluid or the heating body outside the measuring tube) to measure the flow. It is mainly composed of a bridge circuit and an output signal conditioning circuit. The flow sensitive element and the temperature compensation element are placed on the flow pipe, and form a bridge circuit with other resistance elements to convert the change of fluid flow into the change of the output voltage of the bridge arm to realize the detection of fluid flow.

[0003] The existing thermal flow sensor has a reduced accuracy due to the insufficient precision and poor consistency of the resistance value of the manufactured heating resistor.

[0004] In addition, the parameters of existing thermal flow sensors will drift during long-term use. In particular, the inner wall of the flow meter pipe will deposit impurities due to long-term immersion in liquid, causing a large change in the thermal conductivity of the flow meter and a large deviation in the measured flow rate.

[0005] In addition, when there is no liquid in the flow meter pipe of the existing thermal flow sensor, the bridge circuit is still powered on and heated, and the bridge circuit is "dry-burned" for a long time, resulting in a reduced life of the thermal flow sensor. Summary of the invention

[0006] The present disclosure aims to solve at least one of the technical problems existing in the prior art and provide a flow sensor.

[0007] In one aspect of the present disclosure, a flow sensor is provided, the flow sensor comprising a flow detection circuit, a switch control circuit and a control unit;

[0008] The first end of the switch control circuit is electrically connected to the detection signal end and the calibration signal end respectively, and the second end of the switch control circuit is electrically connected to the flow detection circuit; wherein,

[0009] The switch control circuit is used to disconnect the detection signal terminal from the flow detection circuit and connect the calibration signal terminal to the flow detection circuit when receiving the calibration signal;

[0010] The control unit is used to obtain the calibration electrical signal output by the flow detection circuit under the calibration signal to calibrate the flow sensor.

[0011] In some embodiments, the switch control circuit includes a first switch group and a second switch group; wherein,

[0012] The first switch group is electrically connected to the detection signal terminal and the flow detection circuit respectively;

[0013] The second switch group is electrically connected to the calibration signal terminal and the flow detection circuit respectively.

[0014] In some embodiments, the first switch group is disposed at an input end of the flow detection circuit or an output end of the flow detection circuit.

[0015] In some embodiments, the flow detection circuit includes a bridge circuit, and the bridge circuit includes a first bridge arm and a second bridge arm;

[0016] The second switch group includes a third switch and a fourth switch, two ends of the third switch are electrically connected to the calibration signal end and the second bridge arm respectively, and two ends of the fourth switch are electrically connected to the calibration signal end and the first bridge arm respectively;

[0017] When the first switch group is arranged at the input end of the flow detection circuit, the first switch group includes a first switch and a second switch, two ends of the first switch are electrically connected to the detection signal end and the first bridge arm respectively, and two ends of the second switch are electrically connected to the detection signal end and the second bridge arm respectively; and,

[0018] When the first switch group is arranged at the output end of the flow detection circuit, the first switch group includes a fifth switch, and two ends of the fifth switch are electrically connected to the output end of the bridge circuit and the detection signal end respectively.

[0019] In some embodiments, the calibration signal includes a first calibration signal and a second calibration signal;

[0020] The control unit is used to respectively obtain a first calibration voltage output by the flow detection circuit under the first calibration signal and the current ambient temperature, and a second calibration voltage output under the second calibration signal;

[0021] The control unit is further used to calculate the resistance value of the detection resistor in the flow detection circuit according to the first calibration voltage and the second calibration voltage, so as to calibrate the detection resistor.

[0022] In some embodiments, the calibration signal is a periodic calibration signal;

[0023] The control unit is further used to periodically calibrate the flow sensor according to the periodic calibration signal.

[0024] In some implementations, the control unit is further configured to determine that the flow sensor has failed when the resistance of the detection resistor exceeds a preset threshold.

[0025] In some embodiments, the control unit is further configured to calculate a thermal conductivity of the fluid medium flowing through the flow sensor according to the first calibration voltage, the second calibration voltage, and the ambient temperature.

[0026] In some embodiments, the control unit is further configured to send a shutdown signal to the switch control circuit when the thermal conductivity exceeds a thermal conductivity safety threshold;

[0027] The switch control circuit is used to disconnect the detection signal end from the flow detection circuit when receiving the shutdown signal.

[0028] In some embodiments, the control unit is further configured to periodically test whether the thermal conductivity is lower than the thermal conductivity safety threshold after issuing the shutdown signal, and if so, issue a closing signal to the switch control circuit;

[0029] The switch control circuit is used to reconnect the detection signal end and the flow detection circuit when receiving the closing signal.

[0030] In some embodiments, the first calibration signal is a power-on signal, and the second calibration signal is a signal indicating that the fluid medium fills the flow sensor but is not flowing.

[0031] In some implementations, the calibration signal terminal uses a constant voltage source or a constant current source.

[0032] In another aspect of the present disclosure, a flow sensor is provided, the flow sensor comprising a flow detection circuit, a switch control circuit and a control unit;

[0033] The first end of the switch control circuit is electrically connected to the detection signal end and the calibration signal end respectively, the second end of the switch control circuit is electrically connected to the flow detection circuit, and the switch control circuit selectively conducts the flow detection circuit with one of the detection signal end and the calibration signal end; wherein,

[0034] The control unit is used to send a shutdown signal to the switch control circuit when the thermal conductivity of the flow sensor exceeds a thermal conductivity safety threshold;

[0035] The switch control circuit is used to disconnect the detection signal end from the flow detection circuit when receiving the shutdown signal.

[0036] In another aspect of the present disclosure, a flow sensor is provided, the flow sensor comprising a flow detection circuit, a switch control circuit and a control unit;

[0037] The first end of the switch control circuit is electrically connected to the detection signal end and the calibration signal end respectively, the second end of the switch control circuit is electrically connected to the flow detection circuit, and the switch control circuit selectively conducts the flow detection circuit with one of the detection signal end and the calibration signal end; wherein,

[0038] The control unit is used to determine that the flow sensor is failed and send a shutdown signal to the switch control circuit when the resistance value of the detection resistor of the flow sensor exceeds a preset threshold value;

[0039] The switch control circuit is used to disconnect the detection signal end from the flow detection circuit when receiving the shutdown signal.

[0040] The flow sensor disclosed in the present invention, when the flow sensor needs to be calibrated, connects the flow detection circuit with the calibration signal end through the switch control circuit provided, so that the flow sensor can be calibrated according to the calibration electrical signal output by the flow detection circuit under the calibration signal. Conversely, when calibration is not required, the flow detection circuit is connected with the detection signal end through the switch control circuit provided to achieve real-time measurement of parameters such as the flow velocity and flow rate of the fluid medium. Therefore, the flow sensor disclosed in the present invention can achieve automatic calibration, eliminating the pain of manual calibration, so that the product does not need to be introduced into the fluid medium before leaving the factory, and is also convenient for management, storage, packaging and transportation. In addition, the flow sensor disclosed in the present invention can be self-calibrated periodically (such as every day), or used on a per-time basis, and self-calibrated each time it is used to ensure the measurement accuracy of the flow rate measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a structural schematic diagram of a flow sensor according to an embodiment of the present disclosure;

[0042] Figure 2 It is a structural schematic diagram of a flow sensor according to another embodiment of the present disclosure;

[0043] Figure 3 It is a structural schematic diagram of a flow sensor according to another embodiment of the present disclosure;

[0044] Figure 4 It is a schematic structural diagram of a flow sensor according to another embodiment of the present disclosure. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0046] like Figure 1 As shown, this embodiment relates to a flow sensor 100, which includes a flow detection circuit 110, a switch control circuit 120 and a control unit 130. The first end of the switch control circuit 120 is electrically connected to the detection signal terminal Udc and the calibration signal terminal Udc1 respectively, and the second end of the switch control circuit 120 is electrically connected to the flow detection circuit 110.

[0047] Specifically, Figure 1 As shown, when receiving the calibration signal, the switch control circuit 120 disconnects the detection signal terminal Udc from the flow detection circuit 110, and connects the calibration signal terminal Udc1 to the flow detection circuit 110. The control unit 130 is used to obtain the calibration electrical signal output by the flow detection circuit 110 under the calibration signal to calibrate the flow sensor 100.

[0048] The flow sensor of this embodiment, when it is necessary to calibrate the flow sensor, the flow detection circuit is connected to the calibration signal end through the switch control circuit provided, so that the flow sensor can be calibrated according to the calibration electrical signal output by the flow detection circuit under the calibration signal. On the contrary, when calibration is not required, the flow detection circuit is connected to the detection signal end through the switch control circuit provided to achieve real-time measurement of parameters such as the flow velocity and flow rate of the fluid medium. Therefore, the flow sensor of this embodiment can achieve automatic calibration, eliminating the pain of manual calibration, so that the product does not need to be introduced into the fluid medium before leaving the factory, and is also convenient for management, storage, packaging and transportation. In addition, the flow sensor of this embodiment can be self-calibrated periodically (such as every day), or it can be used by the times, and self-calibrated each time it is used to ensure the measurement accuracy of the flow rate measurement.

[0049] For example, Figure 2 As shown, the switch control circuit 120 includes a first switch group 121 and a second switch group 122. The first switch group 121 is electrically connected to the detection signal terminal Udc and the flow detection circuit 110 respectively. The second switch group 122 is electrically connected to the calibration signal terminal Udc1 and the flow detection circuit 110 respectively.

[0050] Specifically, Figure 3 As shown, the first switch group 121 can be arranged at the input end of the flow detection circuit 110. Figure 4 As shown, the first switch group 121 can also be arranged at the output end of the flow detection circuit 110. Of course, in addition to this, those skilled in the art can also design the arrangement position of the first switch group 121 according to actual needs, and this embodiment does not limit this.

[0051] The following description is made by assuming that the first switch group is respectively arranged at the input end and the output end of the flow detection circuit.

[0052] like Figure 3 As shown, the first switch group 121 is arranged at the input end of the flow detection circuit 110. The flow detection circuit 110 includes a bridge circuit REC, and the bridge circuit REC includes a first bridge arm and a second bridge arm, the first bridge arm is connected in series with a temperature measuring resistor Rt and a first fixed resistor R1, the second bridge arm is connected in series with a heating resistor Rh and a second fixed resistor R2, the first switch group 121 includes a first switch S1 and a second switch S2, and the second switch group 122 includes a third switch S3 and a fourth switch S4.

[0053] like Figure 3 As shown, the two ends of the first switch S1 are electrically connected to the detection signal terminal Udc and the first bridge arm respectively. The two ends of the second switch S2 are electrically connected to the detection signal terminal Udc and the second bridge arm respectively. The two ends of the third switch S3 are electrically connected to the calibration signal terminal Udc1 and the second bridge arm respectively. The two ends of the fourth switch S4 are electrically connected to the voltage signal terminal Udc1 and the first bridge arm respectively.

[0054] For example, Figure 3 As shown, the flow detection circuit 110 also includes an operational amplifier circuit A and a transistor Q. The first input end of the operational amplifier circuit A is electrically connected to the output end of the first bridge arm, and the second input end of the operational amplifier circuit A is electrically connected to the output end of the second bridge arm. The control electrode of the transistor Q is electrically connected to the output end of the operational amplifier circuit A, the first electrode of the transistor Q is electrically connected to the detection signal end Udc, and the second electrode of the transistor Q is electrically connected to the first switch S1 and the second switch S2 respectively.

[0055] For example, Figure 4 As shown, the first switch group 121 is arranged at the output end of the flow detection circuit 110. The first switch group 121 includes a fifth switch S5, and two ends of the fifth switch S5 are electrically connected to the output end of the bridge circuit REC and the detection signal end Udc respectively. Figure 4As shown, the first input end of the operational amplifier circuit A is electrically connected to the output end of the first bridge arm, and the second input end of the operational amplifier circuit A is electrically connected to the output end of the second bridge arm. The first end of the fifth switch is electrically connected to the output end of the operational amplifier circuit A, and the second end of the fifth switch is electrically connected to the control electrode of the transistor. The first electrode of the transistor Q is electrically connected to the detection signal terminal Udc, and the second electrode of the transistor Q is electrically connected to the input end of the first bridge arm. The first end of the third resistor R3 is electrically connected to the detection signal terminal Udc, and the second end of the third resistor R3 is electrically connected to the second bridge arm.

[0056] For example, Figures 1 to 3 As shown, the calibration signal includes a first calibration signal and a second calibration signal. The control unit 130 is used to respectively obtain the first calibration voltage output by the flow detection circuit 110 under the first calibration signal and the current ambient temperature, and the second calibration voltage output under the second calibration signal. The control unit 130 is also used to calculate the resistance values ​​of the heating resistor Rh and the temperature measuring resistor Rt in the flow detection circuit 110 according to the first calibration voltage and the second calibration voltage, so as to calibrate the heating resistor Rh and the temperature measuring resistor Rt.

[0057] It should be noted that there is no specific limitation on the first calibration signal and the second calibration signal. For example, the first calibration signal may be a power-on signal, and the second calibration signal may be a signal indicating that the fluid medium fills the flow sensor but does not flow. Of course, those skilled in the art may also select other two or more stages of calibration signals according to actual needs, and this embodiment does not limit this.

[0058] Specifically, Figure 3 As shown, when the device is powered on, the first switch S1 and the second switch S2 are opened, and the third switch S3 and the fourth switch S4 are closed. The output voltages Vout1 and Vout2 of the flow detection circuit 110 are respectively recorded as Voutk1 and Voutk1, and the ambient temperature value is recorded as Tk. At this time, the resistance value of the heating resistor Rh is calculated as: Rhk = (Udc1-Voutk2)*R2 / Voutk2. The resistance value of the temperature measuring resistor Rt is recorded as: Rtk = (Udc1-Voutk1)*R1 / Voutk1. When the flow meter is full of fluid but the fluid is not flowing, the resistance value of the heating resistor Rh is obtained by the same method and is recorded as Rhy = (Udc1-Vouty2)*R2 / Vouty2, and the resistance value of the temperature measuring resistor Rt is recorded as: Rty = (Udc1-Vouty1)*R1 / Vouty1. Therefore, the heating resistor Rh and the temperature measuring resistor Rh can be calibrated according to the resistance values ​​of the heating resistor Rh and the temperature measuring resistor Rt calculated twice.

[0059] For example, Figures 1 to 3 As shown, the calibration signal can also be a periodic calibration signal. The control unit 130 is also used to periodically calibrate the flow sensor 100 according to the periodic calibration signal. For example, self-calibration is performed every day, or self-calibration is performed every time it is used to ensure the measurement accuracy of the flow rate measurement, etc. This embodiment does not specifically limit this.

[0060] For example, Figures 1 to 3 As shown, the control unit 130 is also used to determine that the flow sensor 100 is failed when the resistance of the heating resistor Rh exceeds a preset threshold. The calculation method of the heating resistor Rh is as described above. After respectively calculating the resistance values ​​Rhk and Rhy of the heating resistor Rh, if the resistance value is significantly greater than the preset threshold, it can be determined that the flow sensor is failed.

[0061] For example, Figures 1 to 3 As shown, the control unit 130 is further used to calculate the thermal conductivity of the fluid medium flowing through the flow sensor 100 according to the first calibration voltage, the second calibration voltage and the ambient temperature.

[0062] Specifically, Figure 3 As shown, after calculating the output voltages Voutk1, Voutk2 and Vouty1, Vouty2 of the flow detection circuit 110 and the ambient temperature value Tk, the control unit 130 automatically calculates the thermal conductivity of the fluid medium according to the output voltages Voutk1, Voutk2 and Vouty1, Vouty2 and the ambient temperature value Tk, and the fitting curve of the flow rate and the output voltage Vout can be queried using the thermal conductivity and the temperature value; different flow rates carry away different amounts of heat, causing corresponding changes in the resistance of the heating resistor Rh, and different resistance values ​​of the heating resistor Rh cause real-time changes in the output voltage Vout value, and ultimately the real-time flow rate is obtained by looking up a table.

[0063] For example, Figures 1 to 3 As shown, the control unit 130 is further used to send a shutdown signal to the switch control circuit 120 when the thermal conductivity exceeds the thermal conductivity safety threshold. The switch control circuit 120 is used to disconnect the detection signal terminal Udc from the flow detection circuit 110 when receiving the shutdown signal.

[0064] Specifically, Figure 3As shown, the control unit 130 automatically calculates the thermal conductivity of the fluid medium according to the output voltages Voutk1, Voutk2 and Vouty1, Vouty2 and the ambient temperature value Tk, and then compares the thermal conductivity with a preset thermal conductivity safety threshold. If the thermal conductivity exceeds the thermal conductivity safety threshold, it indicates that there is no fluid medium in the flow sensor 100. At this time, the control unit 130 sends a shutdown signal. When the switch control circuit 120 receives the shutdown signal, the first switch S1 and the second switch S2 are opened, thereby disconnecting the detection signal terminal Udc from the bridge circuit REC, thereby avoiding the long-term dry burning of the bridge circuit REC in the flow detection circuit 110 and improving the service life of the flow sensor 100.

[0065] In addition, after the bridge circuit REC is disconnected from the detection signal terminal Udc, the control unit 130 is also used to periodically test whether the thermal conductivity is lower than the thermal conductivity safety threshold. The specific calculation method of the thermal conductivity is as described above and will not be repeated here. If the thermal conductivity is lower than the thermal conductivity safety threshold, it indicates that the flow sensor 100 is full of fluid medium, and the control unit 130 sends a closing signal to the switch control circuit 120. When the switch control circuit 120 receives the closing signal, the first switch S1 and the second switch S2 are closed again, thereby connecting the detection signal terminal Udc to the bridge circuit REC, and then the bridge circuit REC can be immediately restored to work when the flow sensor 100 is full of fluid medium.

[0066] For example, Figure 3 and Figure 4 As shown, the calibration signal terminal Udc1 may adopt a pulse power supply, a high voltage power supply, etc. Alternatively, the calibration signal terminal Udc1 may also adopt a constant voltage source or a constant current source, etc., which is not specifically limited in this embodiment.

[0067] like Figure 1 As shown, this embodiment also relates to another structure of a flow sensor 100, the flow sensor 100 includes a flow detection circuit 110, a switch control circuit 120 and a control unit 130. The first end of the switch control circuit 120 is electrically connected to the detection signal terminal Udc and the calibration signal terminal Udc1 respectively, and the second end of the switch control circuit 120 is electrically connected to the flow detection circuit 110, and the switch control circuit 120 selectively connects the flow detection circuit 110 to one of the detection signal terminal Udc and the calibration signal terminal Udc1. The control unit 130 is used to send a shutdown signal to the switch control circuit 120 when the thermal conductivity of the flow sensor 100 exceeds the thermal conductivity safety threshold. The switch control circuit 120 is used to disconnect the detection signal terminal Udc from the flow detection circuit 110 when receiving the shutdown signal.

[0068] For the flow sensor of this embodiment, when the thermal conductivity exceeds the thermal conductivity safety threshold, it indicates that there is no fluid medium in the flow sensor, and the control unit sends a shutdown signal to the switch control unit, so that when the switch control unit receives the shutdown signal, it shuts down the flow detection circuit and the detection signal end, thereby avoiding long-term dry burning of the flow detection circuit and increasing the service life of the flow sensor.

[0069] It should be noted that, for the specific structure of the switch control circuit, reference may be made to the relevant records in the previous text, which will not be elaborated here.

[0070] like Figures 1 to 4 As shown, the present disclosure also relates to another structure of a flow sensor 100, the flow sensor 100 includes a flow detection circuit 110, a switch control circuit 120 and a control unit 130. The first end of the switch control circuit 120 is electrically connected to the detection signal terminal Udc and the calibration signal terminal Udc1 respectively, the second end of the switch control circuit 120 is electrically connected to the flow detection circuit 110, and the switch control circuit 120 selectively conducts the flow detection circuit 110 with one of the detection signal terminal Udc and the calibration signal terminal Udc1.

[0071] Specifically, the control unit 130 is used to determine that the flow sensor 100 is invalid when the resistance of the detection resistor of the flow sensor 100 exceeds a preset threshold value, and send a shutdown signal to the switch control circuit 130. The switch control circuit 120 is used to disconnect the detection signal terminal Udc from the flow detection circuit 110 when receiving the shutdown signal.

[0072] The flow sensor of this embodiment can determine that the flow sensor has failed when it detects that the resistance of the detection resistor in the flow sensor exceeds a preset threshold value. At this time, it is necessary to disconnect the flow detection circuit from the detection signal end. On the one hand, it can prevent the flow sensor from outputting an erroneous flow detection signal. On the other hand, it can also promptly remind the user to replace or repair the flow sensor.

[0073] It should be noted that, for the specific structure of the switch control circuit, reference may be made to the relevant records in the previous text, which will not be elaborated here.

[0074] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A flow sensor, characterized in that: The flow sensor includes a flow detection circuit, a switch control circuit and a control unit; The first end of the switch control circuit is electrically connected to the detection signal end and the calibration signal end respectively, and the second end of the switch control circuit is electrically connected to the flow detection circuit; wherein, The switch control circuit is used to disconnect the detection signal terminal from the flow detection circuit and connect the calibration signal terminal to the flow detection circuit when receiving the calibration signal; The control unit is used to obtain the calibration electrical signal output by the flow detection circuit under the calibration signal to calibrate the flow sensor; The switch control circuit comprises a first switch group and a second switch group; wherein the first switch group is electrically connected to the detection signal end and the flow detection circuit respectively; the second switch group is electrically connected to the calibration signal end and the flow detection circuit respectively; the first switch group is arranged at the input end of the flow detection circuit or the output end of the flow detection circuit; The flow detection circuit comprises a bridge circuit, the bridge circuit comprises a first bridge arm and a second bridge arm, the first bridge arm is connected in series with a temperature measuring resistor and a first fixed resistor, and the second bridge arm is connected in series with a heating resistor and a second fixed resistor; The second switch group includes a third switch and a fourth switch, two ends of the third switch are electrically connected to the calibration signal end and the second bridge arm respectively, and two ends of the fourth switch are electrically connected to the calibration signal end and the first bridge arm respectively; When the first switch group is arranged at the input end of the flow detection circuit, the first switch group includes a first switch and a second switch, two ends of the first switch are electrically connected to the detection signal end and the first bridge arm respectively, and two ends of the second switch are electrically connected to the detection signal end and the second bridge arm respectively; and, When the first switch group is arranged at the output end of the flow detection circuit, the first switch group comprises a fifth switch, and two ends of the fifth switch are electrically connected to the output end of the bridge circuit and the detection signal end respectively; The calibration signal includes a first calibration signal and a second calibration signal; The control unit is used to respectively obtain a first calibration voltage output by the flow detection circuit under the first calibration signal and the current ambient temperature, and a second calibration voltage output under the second calibration signal; The control unit is further used to calculate the resistance value of the detection resistor in the flow detection circuit according to the first calibration voltage and the second calibration voltage, so as to calibrate the detection resistor.

2. The flow sensor according to claim 1, characterized in that: The calibration signal is a periodic calibration signal; The control unit is further used to periodically calibrate the flow sensor according to the periodic calibration signal.

3. The flow sensor according to claim 1, characterized in that: The control unit is further configured to determine that the flow sensor has failed when the resistance of the detection resistor exceeds a preset threshold.

4. The flow sensor according to claim 1, characterized in that: The control unit is further used to calculate the thermal conductivity of the fluid medium flowing through the flow sensor according to the first calibration voltage, the second calibration voltage and the ambient temperature.

5. The flow sensor according to claim 4, characterized in that: The control unit is further configured to send a shutdown signal to the switch control circuit when the thermal conductivity exceeds a thermal conductivity safety threshold; The switch control circuit is used to disconnect the detection signal end from the flow detection circuit when receiving the shutdown signal.

6. The flow sensor according to claim 5, characterized in that: The control unit is further used to periodically test whether the thermal conductivity is lower than the thermal conductivity safety threshold after sending the shutdown signal, and if so, send a closing signal to the switch control circuit; The switch control circuit is used to reconnect the detection signal end and the flow detection circuit when receiving the closing signal.

7. The flow sensor according to claim 1, characterized in that: The first calibration signal is a power-on signal, and the second calibration signal is a signal indicating that the fluid medium fills the flow sensor but is not flowing.

8. The flow sensor according to any one of claims 1 to 7, characterized in that: The calibration signal terminal adopts a constant voltage source or a constant current source.

9. A flow sensor, characterized in that: The flow sensor includes a flow detection circuit, a switch control circuit and a control unit; The first end of the switch control circuit is electrically connected to the detection signal end and the calibration signal end respectively, the second end of the switch control circuit is electrically connected to the flow detection circuit, and the switch control circuit selectively conducts the flow detection circuit with one of the detection signal end and the calibration signal end; The switch control circuit comprises a first switch group and a second switch group; wherein the first switch group is electrically connected to the detection signal end and the flow detection circuit respectively; the second switch group is electrically connected to the calibration signal end and the flow detection circuit respectively; the first switch group is arranged at the input end of the flow detection circuit or the output end of the flow detection circuit; The flow detection circuit comprises a bridge circuit, the bridge circuit comprises a first bridge arm and a second bridge arm, the first bridge arm is connected in series with a temperature measuring resistor and a first fixed resistor, and the second bridge arm is connected in series with a heating resistor and a second fixed resistor; The second switch group includes a third switch and a fourth switch, two ends of the third switch are electrically connected to the calibration signal end and the second bridge arm respectively, and two ends of the fourth switch are electrically connected to the calibration signal end and the first bridge arm respectively; When the first switch group is arranged at the input end of the flow detection circuit, the first switch group includes a first switch and a second switch, two ends of the first switch are electrically connected to the detection signal end and the first bridge arm respectively, and two ends of the second switch are electrically connected to the detection signal end and the second bridge arm respectively; and, When the first switch group is arranged at the output end of the flow detection circuit, the first switch group includes a fifth switch, and two ends of the fifth switch are electrically connected to the output end of the bridge circuit and the detection signal end respectively; wherein, The control unit is used to send a shutdown signal to the switch control circuit when the thermal conductivity of the flow sensor exceeds a thermal conductivity safety threshold; The switch control circuit is used to disconnect the detection signal terminal from the flow detection circuit when receiving the shutdown signal; The calibration signal includes a first calibration signal and a second calibration signal; The control unit is further used to respectively obtain a first calibration voltage output by the flow detection circuit under the first calibration signal and the current ambient temperature, and a second calibration voltage output under the second calibration signal; The control unit is further used to calculate the resistance value of the detection resistor in the flow detection circuit according to the first calibration voltage and the second calibration voltage, so as to calibrate the detection resistor.

10. A flow sensor, characterized in that: The flow sensor includes a flow detection circuit, a switch control circuit and a control unit; The first end of the switch control circuit is electrically connected to the detection signal end and the calibration signal end respectively, the second end of the switch control circuit is electrically connected to the flow detection circuit, and the switch control circuit selectively conducts the flow detection circuit with one of the detection signal end and the calibration signal end; The switch control circuit comprises a first switch group and a second switch group; wherein the first switch group is electrically connected to the detection signal end and the flow detection circuit respectively; the second switch group is electrically connected to the calibration signal end and the flow detection circuit respectively; the first switch group is arranged at the input end of the flow detection circuit or the output end of the flow detection circuit; The flow detection circuit comprises a bridge circuit, the bridge circuit comprises a first bridge arm and a second bridge arm, the first bridge arm is connected in series with a temperature measuring resistor and a first fixed resistor, and the second bridge arm is connected in series with a heating resistor and a second fixed resistor; The second switch group includes a third switch and a fourth switch, two ends of the third switch are electrically connected to the calibration signal end and the second bridge arm respectively, and two ends of the fourth switch are electrically connected to the calibration signal end and the first bridge arm respectively; When the first switch group is arranged at the input end of the flow detection circuit, the first switch group includes a first switch and a second switch, two ends of the first switch are electrically connected to the detection signal end and the first bridge arm respectively, and two ends of the second switch are electrically connected to the detection signal end and the second bridge arm respectively; and, When the first switch group is arranged at the output end of the flow detection circuit, the first switch group includes a fifth switch, and two ends of the fifth switch are electrically connected to the output end of the bridge circuit and the detection signal end respectively; wherein, The calibration signal includes a first calibration signal and a second calibration signal; The control unit is used to respectively obtain a first calibration voltage output by the flow detection circuit under the first calibration signal and the current ambient temperature, and a second calibration voltage output under the second calibration signal; The control unit is further used to calculate the resistance value of the detection resistor in the flow detection circuit according to the first calibration voltage and the second calibration voltage, so as to calibrate the detection resistor; The control unit is further configured to determine that the flow sensor is failed and send a shutdown signal to the switch control circuit when the resistance value of the detection resistor of the flow sensor exceeds a preset threshold value; The switch control circuit is used to disconnect the detection signal end from the flow detection circuit when receiving the shutdown signal.

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