Fluid temperature adjusting method for flowmeter and constant temperature difference type thermal flowmeter thereof

Abstract

The fluid temperature adjusting method is based on the constant temperature difference type flowmeter, a heat exchange device is installed at the fluid inlet end of the constant temperature difference type flowmeter, and the heat exchange device forms a heat exchange area in the constant temperature difference type flowmeter; comprising the following steps that the temperature b before heat exchange before fluid enters a heat exchange area, the temperature c after heat exchange after the fluid leaves the heat exchange area, the approaching temperature d when the fluid approaches a temperature measuring element of the constant temperature difference type flowmeter and the flow value L of the constant temperature difference type flowmeter are obtained; and based on the obtained data parameters, the heat exchange power of the heat exchange device is output when the approaching temperature d is kept consistent with the preset temperature a in combination with a fuzzy control algorithm. The heat exchange power of the heat exchange device is output through the fuzzy control algorithm, so that even if the temperature of the fluid changes, effective adjustment can be conducted through the heat exchange device, the temperature of the fluid is kept unchanged as much as possible, and therefore the accuracy of the thermal flow meter is improved.

Description

Technical Field

[0001] This invention relates to the field of thermal flow meters, and more specifically, to a fluid temperature control method for flow meters and a constant temperature difference thermal flow meter thereof. Background Technology

[0002] The theoretical basis of thermal flow meters is Jeans's Law. This law states that the heat removed from a heat-exchange wire is proportional to the square root of the fluid velocity, the fluid's thermodynamic properties, and the temperature difference between the wire and the fluid. Existing isothermal flow meters operate on the principle of maintaining a constant temperature difference between the heat exchange element and the fluid, and then measuring the required heat exchange power to maintain this constant temperature difference. The specific calculation formula is P = (A + B * (Qm)^n) * ΔT, where A and B are constants, and n is an exponent between 0.5 and 0.75. The constants A and B in this formula actually include the fluid's thermal conductivity and specific heat capacity (Cp). However, in isothermal mode, if ΔT remains constant, the relationship between the heat exchange power P and the mass flow rate Qm mainly depends on the fluid's Cp, and is less affected by the thermal conductivity (especially at medium to high flow rates). This makes the only major interfering variable the fluid's specific heat capacity.

[0003] However, in some cases, due to heat exchange between the fluid and the external environment during the flow of the fluid in the pipeline, the temperature of the fluid itself changes, which in turn changes the constant temperature difference set by the flow meter. For example, if the temperature of the fluid decreases, the constant temperature difference ΔT will increase, resulting in a decrease in the accuracy of the flow rate output by the flow meter. Summary of the Invention

[0004] To overcome the problem that the measurement results of constant temperature difference thermal flow meters in the prior art are affected by changes in fluid temperature, this invention provides a fluid temperature adjustment method for flow meters and a constant temperature difference thermal flow meter thereof. After the fluid temperature changes, the fluid temperature can be adjusted to keep the fluid temperature at or close to the target temperature, so that the constant temperature difference ΔT between the thermal flow meter and the fluid is kept as constant as possible.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a fluid temperature control method for a flow meter, based on a constant temperature difference flow meter, wherein a heat exchange device is installed at the fluid inlet end of the constant temperature difference flow meter, and the heat exchange device forms a heat exchange area within the constant temperature difference flow meter. The method includes the following steps: Step 1: Obtain the pre-heat exchange temperature b of the fluid before entering the heat exchange zone, the post-heat exchange temperature c of the fluid after leaving the heat exchange zone, the approach temperature d of the fluid approaching the temperature sensing element of the constant temperature difference flow meter, and the flow rate L of the constant temperature difference flow meter. Step 2: Based on the data parameters obtained in Step 1, and combined with the fuzzy control algorithm, output the heat exchange power of the heat exchange device when the approximate temperature d is kept consistent with the preset temperature a.

[0006] In the above technical solution, different temperature sensors are used to obtain the temperature at different locations. The purpose of maintaining the proximity temperature d consistent with the preset temperature a is to ensure that the temperature of the fluid reaching the temperature sensing element remains stable at a constant value, thereby keeping the temperature difference between the temperature sensing element of the thermal flow meter and the fluid temperature constant, and reducing the large deviation in the measurement results of the thermal flow meter caused by changes in fluid temperature.

[0007] When the heat exchanger is a heating device, if the near temperature d is lower than the preset temperature a, the power of the heat exchanger is adjusted, taking into account the pre-exchange temperature b, the post-exchange temperature c, and the flow rate L, to increase the heat exchange power and raise the fluid temperature. The heat exchange power adjustment is based on a fuzzy control algorithm. Considering the pre-exchange temperature b, the post-exchange temperature c, and the flow rate L, it integrates the heating efficiency of the heat exchanger at a given flow rate. It also takes into account potential heat loss and temperature changes after the fluid travels a distance, and considers the temperature difference between the post-exchange temperature c and the near temperature d. Therefore, by combining the multiple data obtained in this scheme, the heat exchange efficiency of the heat exchanger is calculated and output through the fuzzy control algorithm, ensuring that the temperature of the fluid after heat exchange is as close as possible to and consistent with the preset temperature a. Although this scheme is based on the adjustment after the fluid temperature changes, the fuzzy control algorithm can quickly readjust the fluid temperature to be close to or consistent with the preset temperature a. In other words, only the instantaneous flow rate at certain times will be accurate. However, in the long run, the flow rate value detected by the thermal flow meter will be more accurate.

[0008] This method can also be used when the fluid temperature is lower than the temperature range of the thermal flow meter. The fluid is heated to a temperature within the thermal flow meter's temperature range, which can also be the target temperature. This further expands the applicable temperature range of the thermal flow meter. When the approach temperature d is greater than the preset temperature a, the heat exchange device stops operating.

[0009] When the heat exchanger is used as a refrigeration device, it is suitable for pipelines transporting cooling water. The preset temperature 'a' can be set lower than the original temperature of the cooling water. When the approach temperature 'd' is higher than the preset temperature 'a', the power of the heat exchanger is adjusted, taking into account the pre-exchange temperature 'b', the post-exchange temperature 'c', and the flow rate 'L', to increase the heat exchange power and lower the fluid temperature. When the approach temperature 'd' is lower than the preset temperature 'a', the heat exchanger stops operating.

[0010] Preferably, in step two, the specific process is as follows: S2.1: Convert the data parameters obtained in step one into the input of the fuzzy control algorithm, and convert the heat exchange power into the output of the fuzzy control algorithm; S2.2: Based on the input quantity and the output quantity, set the corresponding range of possible values ​​and fuzzy subsets, and establish a general formula for the membership degree of any input quantity belonging to a certain fuzzy subset; S2.3: Establish a rule base that covers all combinations of the aforementioned fuzzy subsets; S2.4: Calculate the trigger strength of each rule in the rule base and generate a fuzzy output set; S2.5: Convert the "fuzzy output set" into an accurate output quantity.

[0011] Preferably, in step S2.1, the inputs of the fuzzy control algorithm are the main deviation E, the flow rate influence factor F, and the comprehensive change rate EC; the outputs of the fuzzy control algorithm are the power adjustment amount ΔP and the final output heat exchange power P.

[0012]

[0013]

[0014]

[0015]

[0016] in, The system's rated flow rate; Let d be the current time. d is the period before period T; T = control period; , and These are all weighting coefficients; Rated flow rate Under these conditions, the basic power required to maintain d=a; Specific heat capacity of the fluid; For fluid density; The temperature before heat exchange at the rated flow rate; This refers to the fixed losses of the system.

[0017] Preferably, in step S2.2, for any input quantity, the general formula for membership degree is specifically as follows:

[0018] in, For input quantity is In the case of , the membership degree of the corresponding fuzzy subset to which it belongs; The left boundary of the fuzzy subset (the left point where membership degree = 0); The right boundary of the fuzzy subset (the right point where membership degree = 0); The core point (the point with a membership degree of 1).

[0019] Preferably, in step 2.3, the core of establishing the rule base is that the larger the flow influence factor F, the higher the power adjustment ΔP is required under the same main deviation E.

[0020] Preferably, in step S2.4, the fuzzy output set is formed by superimposing the fuzzy outputs corresponding to each rule; the fuzzy output is the membership function of the trigger strength with respect to the output subset, specifically as follows:

[0021]

[0022]

[0023] In the formula, Trigger strength; The membership degree of the principal deviation E to the fuzzy subset A; Let F be the membership degree of the flow influence factor F to the fuzzy subset B; Let EC be the membership degree of the comprehensive rate of change EC to the fuzzy subset C; This is the fuzzy output corresponding to the i-th rule; Let ΔP be the membership degree of the power regulation amount to the output subset D; This is a fuzzy output set.

[0024] Preferably, in step S2.5, specifically: Will The possible value range is discrete into N points; power regulation amount Precise for discrete points and its membership degree Weighted average:

[0025] In the formula, if the denominator If it is zero (extreme case, triggered without rules), then It is zero.

[0026] A constant temperature difference thermal flow meter is used to implement the fluid temperature control method for the flow meter as described in claims 1-7. It includes a pipe body, a temperature sensing element installed in the pipe body, a heat exchange device installed at the fluid inlet end of the pipe body, a first temperature sensor, a second temperature sensor, and a third temperature sensor. The heat exchange device forms a heat exchange area within the constant temperature difference flow meter. The first temperature sensor is installed within the pipe body and located at the fluid inlet end of the heat exchange area. The second temperature sensor is installed within the pipe body and located at the fluid outlet end of the heat exchange area. The third temperature sensor is installed within the pipe body and close to the temperature sensing element.

[0027] Furthermore, the third temperature sensor and the temperature measuring element are arranged side by side in the radial direction of the tube body.

[0028] Furthermore, the heat exchange device includes a spiral heat exchange tube, and the probes of the first temperature sensor, the second temperature sensor, the third temperature sensor, and the temperature measuring element used to measure the temperature are all located in the area projected along the axial direction of the spiral heat exchange tube.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. Using the pre-heat exchange temperature b, post-heat exchange temperature c, near temperature d, and flow rate L as parameters of the fuzzy control algorithm, the fuzzy control algorithm outputs the heat exchange power that the heat exchange device can use to heat the fluid to a near temperature d that is close to or consistent with the preset temperature a. This allows the heat exchange device to effectively regulate the fluid temperature even if the fluid temperature changes, keeping the fluid temperature as constant as possible, thereby improving the accuracy of the thermal flow meter.

[0030] 2. The addition of a heat exchange device can also be used to heat the fluid to within the temperature range of the thermal flow meter when the fluid temperature is lower than the temperature range of the thermal flow meter, thereby expanding the usable temperature range of the thermal flow meter. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of a constant temperature difference thermal flow meter according to the present invention; Figure 2 This is a schematic diagram of the layout of the temperature measuring element and the third temperature sensor of the present invention; Figure 3 This is a flowchart of a fluid temperature control method for a flow meter according to the present invention.

[0032] In the diagram, 1-pipe body; 2-temperature sensing element; 3-heat exchange device; 4-first temperature sensor; 5-second temperature sensor; 6-third temperature sensor. The arrows indicate the direction of fluid flow. Detailed Implementation

[0033] The accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0034] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "long," and "short" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0035] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings: Example 1 like Figure 1 The image shows an embodiment 1 of a constant temperature difference type thermal flow meter, as follows: Figure 1 The illustration shows an embodiment 1 of a constant temperature difference type thermal flow meter, including a pipe body 1, a temperature sensing element 2 installed in the pipe body 1, a heat exchange device 3 installed at the fluid inlet end of the pipe body 1, a first temperature sensor 4, a second temperature sensor 5, and a third temperature sensor 6; the heat exchange device 3 forms a heat exchange area within the constant temperature difference type flow meter, the first temperature sensor 4 is installed inside the pipe body 1 and located at the fluid inlet end of the heat exchange area, the second temperature sensor 5 is installed inside the pipe body 1 and located at the fluid outlet end of the heat exchange area, and the third temperature sensor 6 is installed inside the pipe body 1 and close to the temperature sensing element 2.

[0036] The working principle or workflow of this embodiment is as follows: Based on the measurement principle of the constant temperature difference thermal flow meter, the temperature sensing element 2 is also a heating element. It is heated by electricity to make its temperature higher than the fluid temperature, maintaining a constant temperature difference between the heating element and the fluid. Then, it measures how much heating power is needed to maintain this constant temperature difference. Process: Fluid flow rate increases → attempts to remove more heat, causing the temperature difference to tend to decrease → feedback circuit immediately increases heating power to maintain the original temperature difference. The first temperature sensor 4 detects the temperature of the fluid before heat exchange by the heat exchange device 3, and the second temperature sensor 5 detects the temperature of the fluid after heat exchange by the heat exchange device 3. The third temperature sensor 6 detects the fluid temperature near the temperature sensing element 2.

[0037] The beneficial effects of this embodiment are as follows: The constant temperature difference thermal flow meter of this embodiment can additionally acquire fluid temperature values ​​from multiple different locations. After calculating these values, the heating power of the heat exchange device 3 is controlled, ensuring that the fluid temperature remains essentially constant, thereby improving the accuracy of the constant temperature difference thermal flow meter. Furthermore, for fluid temperatures outside the measurement range of the constant temperature difference thermal flow meter, the heat exchange device 3 can also heat the fluid to within the measurement range, thus widening the temperature range of the constant temperature difference thermal flow meter.

[0038] Example 2 Example 2 of a constant temperature difference type thermal flow meter differs from Example 1 in that: The third temperature sensor 6 and the temperature measuring element 2 are arranged side by side in the radial direction of the pipe body 1. After the third temperature sensor 6 and the temperature measuring element 2 are arranged side by side, the temperatures of different laminar flows at the same radial cross section of the pipe body can be detected, and the temperatures of the two can be closer.

[0039] The heat exchange device 3 includes a spiral heat exchange tube. The first temperature sensor 4, the second temperature sensor 5, the third temperature sensor 6, and the temperature sensing element 2, along with their probes for measuring temperature, are all located within the area projected along the axial direction of the spiral heat exchange tube. The portion of the fluid flowing through the spiral heat exchange tube is the heat exchange section. Measuring the temperature and flow rate of this section ensures that the spiral heat exchange tube can rapidly exchange heat with the fluid, and that changes in the power of the heat exchange device 3 are promptly and quickly reflected in the fluid. If the heat exchange device 3 is a heating device, the spiral heat exchange tube can be a spiral electric heating tube. If the heat exchange device 3 is a cooling device, the spiral heat exchange tube can be filled with coolant, and the heat exchange efficiency can correspond to the flow rate of the coolant.

[0040] The remaining features and working principles of this embodiment are the same as those of Embodiment 1.

[0041] Example 3 An embodiment of a fluid temperature control method for a flow meter, based on the isothermal differential thermal flow meter of embodiment 1 or embodiment 2, includes the following steps: Step 1: Obtain the pre-heat exchange temperature b of the fluid before entering the heat exchange zone, the post-heat exchange temperature c of the fluid after leaving the heat exchange zone, the approach temperature d of the fluid approaching the temperature sensing element of the constant temperature difference flow meter, and the flow rate L of the constant temperature difference flow meter. Step Two: Based on the data parameters obtained in Step One, and combined with a fuzzy control algorithm, output the heat exchange power of the heat exchange device when maintaining the approximate temperature d and the preset temperature a. The specific process is as follows: S2.1: Convert the data parameters obtained in step one into the input of the fuzzy control algorithm, and convert the heat exchange power into the output of the fuzzy control algorithm; Specifically, the inputs of the fuzzy control algorithm are the main deviation E, the flow rate influence factor F, and the comprehensive change rate EC; the outputs of the fuzzy control algorithm are the power adjustment ΔP and the final output heat exchange power P; the main deviation E reflects the static difference between the near temperature d and the preset temperature a (the core adjustment basis); the flow rate influence factor F can quantify the deviation of the flow rate value L from the heat demand (the larger L is, the more heat is required); the comprehensive change rate EC integrates "the dynamic trend of d, heating efficiency (cb), and flow rate influence (F)" to avoid over-adjustment.

[0042]

[0043]

[0044]

[0045]

[0046]

[0047] in, The rated flow rate of the system can be manually set according to the pipeline design; Let d be the current time. d is the period before period T; T = control period; , and These are all weighting coefficients; Rated flow rate Under these conditions, the basic power required to maintain d=a; Specific heat capacity of the fluid; For fluid density; The temperature before heat exchange at the rated flow rate; This refers to the fixed losses of the system.

[0048] S2.2: Based on the input quantity and the output quantity, set the corresponding possible value range and fuzzy subset, and establish a general formula for the membership degree of any input quantity belonging to a certain fuzzy subset; the possible value range of the input quantity and the output quantity can be set and adjusted according to the system situation. For example, if the temperature change range of the fluid in the pipeline is detected through use or experiment, then the temperature change range can be set as the possible value range of the main deviation E.

[0049] In this embodiment, the fuzzy subsets of the input and output quantities can be referred to Table 1 below.

[0050] Table 1. Range of possible values ​​and fuzzy subsets for input and output quantities.

[0051] The physical meaning of the fuzzy subset corresponding to each input or output quantity can be seen in Table 2 below.

[0052] Table 2 Physical meaning of fuzzy subsets

[0053] For any input quantity, the general formula for membership degree is as follows:

[0054] in, For input quantity is In the case of , the membership degree of the corresponding fuzzy subset to which it belongs; The left boundary of the fuzzy subset (the left point where membership degree = 0); The right boundary of the fuzzy subset (the right point where membership degree = 0); The core point (the point with a membership degree of 1).

[0055] S2.3: Establish a rule base that covers all combinations of the fuzzy subsets; the core of establishing the rule base is that the larger the flow influence factor F, the higher the power adjustment ΔP is required under the same main deviation E.

[0056] Some of the core rules in the rule base of this embodiment can be found in Table 3 below. Table 3 Some Rules

[0057] S2.4: Calculate the trigger strength of each rule in the rule base and generate a fuzzy output set; The fuzzy output set is formed by superimposing the fuzzy outputs corresponding to each rule; the fuzzy output is the membership function of the trigger strength for the output subset, specifically as follows:

[0058]

[0059]

[0060] In the formula, Trigger strength; The membership degree of the principal deviation E to the fuzzy subset A; Let F be the membership degree of the flow influence factor F to the fuzzy subset B; Let EC be the membership degree of the comprehensive rate of change EC to the fuzzy subset C; This is the fuzzy output corresponding to the i-th rule; Let ΔP be the membership degree of the power regulation amount to the output subset D; This is the set of fuzzy outputs. Fuzzy subset A, fuzzy subset B, and fuzzy subset C are references to the different fuzzy subsets mentioned above.

[0061] S2.5: Convert the "fuzzy output set" into an accurate output quantity.

[0062] Will The possible value range is discrete into N points; power regulation amount Precise for discrete points and its membership degree Weighted average:

[0063] In the formula, if the denominator If it is zero (extreme case, triggered without rules), then It is zero.

[0064] The principle of this embodiment: Heat exchange power adjustment is based on fuzzy control algorithm calculation. Considering the pre-exchange temperature b, post-exchange temperature c, and flow rate L, it integrates the heating efficiency of the heat exchange device for the fluid under a certain flow rate. Taking into account the potential heat loss and temperature change of the fluid after heat exchange over a distance, it also considers the temperature difference between post-exchange temperature c and the near-temperature d. Therefore, combining the multiple data obtained in this scheme, the heat exchange efficiency of the heat exchange device is calculated and output through the fuzzy control algorithm, allowing the temperature of the fluid after heat exchange to be as close as possible to and consistent with the preset temperature a. Although this scheme adjusts based on changes in fluid temperature, the fuzzy control algorithm can quickly readjust the fluid temperature to be close to or consistent with the preset temperature a. This means that only the instantaneous flow rate at certain times will be accurate, but in the long run, the flow rate value detected by the thermal flow meter will be more accurate.

[0065] This method can also be used when the fluid temperature is lower than the temperature range of the thermal flow meter. The fluid is heated to a temperature within the thermal flow meter's temperature range, which can also be the target temperature. This also broadens the applicable temperature range of the thermal flow meter. When the approach temperature d is greater than the preset temperature a, the heat exchange device stops operating.

[0066] The beneficial effects of this embodiment are as follows: 1. Using the temperature before heat exchange b, the temperature after heat exchange c, the near temperature d, and the flow rate L as parameters of the fuzzy control algorithm, the fuzzy control algorithm outputs the heat exchange power that the heat exchange device can heat the fluid to a near temperature d that is close to or consistent with the preset temperature a. This allows the heat exchange device to effectively adjust the fluid temperature even if the fluid temperature changes, keeping the fluid temperature as constant as possible, thereby improving the accuracy of the thermal flow meter.

[0067] 2. The addition of a heat exchange device can also be used to heat the fluid to within the temperature range of the thermal flow meter when the fluid temperature is lower than the temperature range of the thermal flow meter, thereby expanding the usable temperature range of the thermal flow meter.

[0068] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for regulating fluid temperature in a flow meter, characterized in that, Based on a constant temperature difference flow meter, a heat exchange device is installed at the fluid inlet end of the constant temperature difference flow meter, and the heat exchange device forms a heat exchange area inside the constant temperature difference flow meter. The method includes the following steps: Step 1: Obtain the pre-heat exchange temperature b of the fluid before entering the heat exchange zone, the post-heat exchange temperature c of the fluid after leaving the heat exchange zone, the approach temperature d of the fluid approaching the temperature sensing element of the constant temperature difference flow meter, and the flow rate L of the constant temperature difference flow meter. Step 2: Based on the data parameters obtained in Step 1, and combined with the fuzzy control algorithm, output the heat exchange power of the heat exchange device when the approximate temperature d is kept consistent with the preset temperature a.

2. The fluid temperature control method for a flow meter according to claim 1, characterized in that, In step two, the specific process is as follows: S2.1: Convert the data parameters obtained in step one into the input of the fuzzy control algorithm, and convert the heat exchange power into the output of the fuzzy control algorithm; S2.2: Based on the input quantity and the output quantity, set the corresponding range of possible values ​​and fuzzy subsets, and establish a general formula for the membership degree of any input quantity belonging to a certain fuzzy subset; S2.3: Establish a rule base that covers all combinations of the aforementioned fuzzy subsets; S2.4: Calculate the trigger strength of each rule in the rule base and generate a fuzzy output set; S2.5: Convert the "fuzzy output set" into an accurate output quantity.

3. The fluid temperature control method for a flow meter according to claim 2, characterized in that, In step S2.1, the inputs of the fuzzy control algorithm are the main deviation E, the flow rate influence factor F, and the comprehensive change rate EC; the outputs of the fuzzy control algorithm are the power adjustment amount ΔP and the final output heat exchange power P. in, The system's rated flow rate; Let d be the current time. d is the period before period T; T = control period; , and These are all weighting coefficients; Rated flow rate Under these conditions, the basic power required to maintain d=a; Specific heat capacity of the fluid; For fluid density; The temperature before heat exchange at the rated flow rate; This refers to the fixed losses of the system.

4. The fluid temperature control method for a flow meter according to claim 3, characterized in that, In step S2.2, for any input quantity, the general formula for membership degree is specifically as follows: in, For input quantity is In the case of , the membership degree of the corresponding fuzzy subset to which it belongs; The left boundary of the fuzzy subset (the left point where membership degree = 0); The right boundary of the fuzzy subset (the right point where membership degree = 0); The core point (the point with a membership degree of 1).

5. The fluid temperature control method for a flow meter according to claim 4, characterized in that, In step 2.3, the core of establishing the rule base is that the larger the flow influence factor F, the higher the power adjustment ΔP is required under the same main deviation E.

6. The fluid temperature control method for a flow meter according to claim 5, characterized in that, In step S2.4, the fuzzy output set is formed by superimposing the fuzzy outputs corresponding to each rule; the fuzzy output is the membership function of the trigger strength for the output subset, specifically as follows: In the formula, Trigger strength; The membership degree of the principal deviation E to the fuzzy subset A; Let F be the membership degree of the flow influence factor F to the fuzzy subset B; Let EC be the membership degree of the comprehensive rate of change EC to the fuzzy subset C; This is the fuzzy output corresponding to the i-th rule; Let ΔP be the membership degree of the power regulation amount to the output subset D; This is a fuzzy output set.

7. The fluid temperature control method for a flow meter according to claim 6, characterized in that, In step S2.5, specifically: Will The possible value range is discrete into N points; power regulation amount Precise for discrete points and its membership degree Weighted average: In the formula, if the denominator If it is zero (extreme case, triggered without rules), then It is zero.

8. A constant temperature difference type thermal flow meter, comprising a tube body (1) and a temperature measuring element (2) installed on the tube body (1), characterized in that, The method for fluid temperature control for a flow meter according to claims 1-7 is further comprising a heat exchange device (3), a first temperature sensor (4), a second temperature sensor (5), and a third temperature sensor (6) installed at the fluid inlet end of the pipe body (1); the heat exchange device (3) forms a heat exchange area within the constant temperature difference flow meter; the first temperature sensor (4) is installed within the pipe body (1) and located at the fluid inlet end of the heat exchange area; the second temperature sensor (5) is installed within the pipe body (1) and located at the fluid outlet end of the heat exchange area; and the third temperature sensor (6) is installed within the pipe body (1) and close to the temperature sensing element (2).

9. The constant temperature difference type thermal flow meter according to claim 8, characterized in that, The third temperature sensor (6) and the temperature measuring element (2) are arranged side by side in the radial direction of the tube body (1).

10. The constant temperature difference thermal flow meter according to claim 8, characterized in that, The heat exchange device (3) includes a spiral heat exchange tube. The probes of the first temperature sensor (4), the second temperature sensor (5), the third temperature sensor (6), and the temperature measuring element (2) for measuring the temperature are all located in the area projected along the axial direction of the spiral heat exchange tube.

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