CN113155218A - Variable-power thermal mass flowmeter and calibration method thereof - Google Patents
Variable-power thermal mass flowmeter and calibration method thereof Download PDFInfo
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- CN113155218A CN113155218A CN202110415048.9A CN202110415048A CN113155218A CN 113155218 A CN113155218 A CN 113155218A CN 202110415048 A CN202110415048 A CN 202110415048A CN 113155218 A CN113155218 A CN 113155218A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
- G01F1/86—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
Abstract
A variable power thermal mass flowmeter and a calibration method thereof utilize the variable power to compensate the error of flow and eliminate the influence of temperature on the flow indication. Including the watchcase, probe holder and microprocessor, four ADC converters, DAC converter and constant current source, set up heating and temperature probe and medium temperature probe concurrently on the probe holder, set up watchcase temperature probe on watchcase or probe holder, first ADC converter input is connected to the first line of temperature probe and fourth line concurrently in the heating, sampling resistance input is connected to the second line of temperature probe concurrently in the heating, DAC converter output is connected to the third line of temperature probe concurrently in the heating, the constant current source positive terminal is connected to the first line of medium temperature probe, second ADC converter input is connected to medium temperature probe second line and third line, the first line connection of medium temperature probe fourth line and watchcase temperature probe, third ADC converter input is connected to watchcase temperature probe second line and third line, the constant current source is connected to the watchcase temperature probe fourth line.
Description
Technical Field
The invention relates to a metering instrument and a metering method, in particular to a variable power thermal mass flowmeter and a calibration method thereof.
Background
Thermal mass flowmeters use the principle of thermal diffusion and have two temperature sensors, one of which is heated to a temperature above the fluid temperature and the other of which is used to sense the fluid temperature, when placed in a medium. The flow rate of the medium is increased, the heat quantity taken away by the medium is increased, the temperature difference of the two temperature sensors is reduced along with the increase of the flow rate of the medium, the flow is calculated by measuring the temperature difference between the heating probe and the fluid temperature by utilizing the fact that the speed of heat conduction and the flowing speed of the medium form a certain curve relation. However, the temperature difference has temperature drift at different fluid temperatures, and the difference between different environmental temperatures and the fluid temperatures affects the reading of the flowmeter, thereby affecting the accuracy of calculation. CN102519527 discloses a thermal type constant power gas flowmeter, in which 2 sensing elements are packaged: firstly, heating element, its second temperature sensing element, the preparation degree of difficulty is big, and the reliability is low, and is bulky, and zero temperature coefficient can not be accomplished to heating element, so the temperature drift is big. The zero calibration part and the leakage meter compensation part are adopted, the heating element is required to be reduced to the same temperature as the temperature sensing element under the zero standard, so that a long time is required, the calibration is required when the environment changes or the power is turned on and off, the measurement efficiency is influenced, the zero calibration is only carried out, the correction effect on the generated measurement error caused by the fact that the environment temperature is different from the fluid temperature is not achieved, the temperature indication drift is large, and the practicability is poor.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provide a variable power thermal mass flowmeter and a calibration method thereof, which are used for compensating flow errors by using variable power and eliminating the influence of temperature on flow readings.
The technical solution of the invention is as follows:
1. a variable power thermal mass flowmeter and its calibration method, including the watchcase with medium flow channel, probe seat and microprocessor, its characteristic is: the variable power thermal mass flowmeter is also provided with first to fourth ADC converters, a DAC converter and a constant current source, wherein a heating and temperature measuring probe and a medium temperature measuring probe are respectively arranged at the parts of a probe seat corresponding to a medium flow passage, and a shell temperature measuring probe is arranged on a shell or the probe seat; the heating and temperature measuring probe, the medium temperature measuring probe and the shell temperature measuring probe are all of four-wire system, and a first wire and a second wire and a third wire and a fourth wire in each probe are connected; the first line and the fourth line of the heating and temperature measuring probe are connected with the input end of a first ADC converter, the second line of the heating and temperature measuring probe is connected with the input end of a sampling resistor, the third line of the heating and temperature measuring probe is connected with the output end of a DAC converter, the first line of the medium temperature measuring probe is connected with the positive end of a constant current source, the second line and the third line of the medium temperature measuring probe are connected with the input end of a second ADC converter, the fourth line of the medium temperature measuring probe is connected with the first line of the watchcase temperature measuring probe, the second line and the third line of the watchcase temperature measuring probe are connected with the input end of a third ADC converter, the fourth line of the watchcase temperature measuring probe is connected with the negative end of the constant current source, the output end of the sampling resistor is grounded and is connected with the input end of the sampling resistor together to the input end of the fourth ADC converter, the output ends of the first ADC converter to the fourth ADC converter are connected with the corresponding input ends of the microprocessor, and the input end of the DAC converter is connected with the output end of the microprocessor.
Furthermore, the watchcase temperature probe is arranged at a position, far away from the medium channel, of the watchcase or the probe seat.
Furthermore, the heating and temperature measuring probe, the medium temperature measuring probe and the meter shell temperature measuring probe adopt platinum resistors.
The calibration method of the variable power thermal mass flowmeter comprises the following steps:
firstly, connecting a flowmeter to be calibrated and a standard meter in series and introducing constant airflow, wherein the constant airflow is more than or equal to 50% of the maximum measuring range of the flowmeter to be calibrated;
step two, measuring a target power P0 of a heating and temperature measuring probe 1 of the flowmeter to be calibrated when the same temperature difference of T1 and T2 is kept and T2 is different, obtaining a polynomial coefficient by functionally mapping the corresponding target power P0 and T2, eliminating the power of temperature drift, establishing a P0-T2 comparison table, and storing the P0-T2 comparison table into a memory connected with the MCU; the T1 is the surface temperature of the heating and temperature measuring probe, the T2 is the fluid temperature measured by the medium temperature measuring probe and the value range is TB-TA, TB is less than the minimum Tmin of the environmental temperature in one year, and TA is greater than the maximum Tmax of the environmental temperature in the same year;
step three, calibrating a corresponding relation curve F3 of the temperature difference T1-T2 between the heating and temperature measuring probe and the medium temperature measuring probe and different flow rates of the fluid by standard calibration equipment, and storing the curve in the memory;
fourthly, acquiring the voltage of the heating and temperature measuring probe 1 in real time by using the first ADC (analog to digital converter) 5, acquiring the current of the heating and temperature measuring probe 1 in real time by using the sampling resistor 8 and the fourth ADC 13, obtaining the resistance value and the real-time power value P1 by using the MCU7, and converting the temperature value T1 by using the MCU7 according to the temperature-resistance value comparison relation of the heating and temperature measuring probe 1;
the constant current source 4 is used for driving the medium temperature measuring probe 2, a certain voltage is generated by the medium temperature measuring probe 2, the voltage is input to the MCU7 through the second ADC converter 11, the resistance value of the medium temperature measuring probe is obtained by the MCU7 according to the voltage value and the current value of the constant current source, and the temperature value T2 is converted according to the temperature-resistance comparison relation of the heating and temperature measuring probe 2;
fifthly, the converted T2 value is compared with the P0-T2 table in the second step, the power of the heating and temperature measuring probe 1 is controlled through a DAC converter, and the real-time power value P1 is made to be consistent with the target power value P0;
calculating the current flow velocity V of the flowmeter to be calibrated:
V＝F3*(T1-T2)
wherein T1-T2 is the temperature difference between the heating and temperature measuring probe and the medium temperature measuring probe;
and step seven, calculating the corrected flow rate V2 of the flowmeter to be calibrated by using a fluid temperature and external temperature unequal correction formula:
V2＝V-(Vu-Vd)/(T2u-T2d)*(T3-T2)*V/Vm；
in the formula: v is the current flow rate of the flowmeter to be calibrated, T2 is the fluid temperature, T3 is the watchcase temperature measured by the watchcase temperature probe, and Vm is the upper limit of the measuring range of the flowmeter;
the standard table test flow rate is Vu when T3 ═ Tu, where Tu ═ room temperature + T0, fluid temperature is T2 u; the standard table test flow rate is Vd when T3 equals Td, room temperature-T0, fluid temperature T2 d; the value of T0 is 10-20 ℃.
Further, the difference value of Tmin and TB and the difference value of TA and Tmax in the second step are respectively 10-20 ℃.
Further, in the second step, the fluid temperature T2 is set to be a temperature value corresponding to 5-10 equi-divisions in the TB-TA range.
Further, the different flow rates of the fluid in the third step are flow rate values corresponding to 20-50 equal division points according to the maximum measuring range of the flowmeter to be calibrated.
Further, the standard calibration device in the third step is a venturi sonic nozzle calibration device.
Further, the temperature-resistance value corresponding relation of the heating and temperature measuring probe and the temperature-resistance value relation of the medium temperature measuring probe in the fourth step are that the heating and temperature measuring probe and the heating and temperature measuring probe are respectively put into an oil tank, and resistance value connecting lines measured by the maximum value, the middle value and the minimum value are selected according to the temperature measuring range of the probe.
The invention has the beneficial effects that: the flowmeter has the advantages of low manufacturing cost and high reliability, adopts variable power, improves the precision of the flowmeter through temperature-power correction and correction of the difference value between the temperature of the meter shell (the ambient temperature) and the temperature of the fluid, improves the accuracy of repeated measurement, and eliminates the influence of the ambient temperature and the temperature of the fluid on the measurement precision of the flowmeter.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a control schematic of the present invention;
fig. 3 is a control flow diagram of the present invention.
In the figure: 1. the device comprises a heating and temperature measuring probe, 2 a medium temperature measuring probe, 3 a meter shell temperature measuring probe, 4 a constant current source, 5 a first ADC (analog to digital converter), 6 a DAC (digital to analog converter), 7 a microprocessor, 8 a sampling resistor, 9 a probe seat, 10 a meter shell, 1001 a medium flow channel, 1002 a blind hole, 11 a second ADC, 12 a third ADC and 13 a fourth ADC.
Detailed Description
Example 1
As shown in fig. 1, the variable power thermal mass flowmeter according to the present invention includes a case 10 having a medium flow channel 1001 therein, a probe holder 9, and a microprocessor 7, the microprocessor 7 is of a model MSP430F169, the variable power thermal mass flowmeter further includes first to fourth ADC converters 5 to 13, a DAC converter 6, and a constant current source 4, the heating and temperature measuring probe 1 and the medium temperature measuring probe 2 are respectively disposed at a position of the probe holder 9 corresponding to the medium flow channel 1001, the ADC converter is of a model AD7799, the DAC converter is of a model DAC8531, a blind hole 1002 is disposed on the case 10, and the case temperature measuring probe 3 is disposed in the blind hole 1002. The heating and temperature measuring probe 1, the medium temperature measuring probe 2 and the shell temperature measuring probe 3 are respectively made of platinum resistors PT100 and are all made of four wires, and a first wire and a second wire and a third wire and a fourth wire in each probe are connected; the first line and the fourth line of the heating and temperature measuring probe 1 are connected with the input end of a first ADC converter 5, the second line of the heating and temperature measuring probe 1 is connected with the input end of a sampling resistor 8, the third line of the heating and temperature measuring probe 1 is connected with the output end of a DAC (digital-to-analog converter) 6, the first line of the medium temperature measuring probe 2 is connected with the positive end of a 0.5mA constant current source 4, the second line and the third line of the medium temperature measuring probe 2 are connected with the input end of a second ADC converter 11, the fourth line of the medium temperature measuring probe 2 is connected with the first line of the watchcase temperature measuring probe 3, the second line and the third line of the watchcase temperature measuring probe 3 are connected with the input end of a third ADC converter 12, the fourth line of the watchcase temperature measuring probe 3 is connected with the negative end of the constant current source 4, the output end of the sampling resistor 8 is grounded and is connected with the input end of a fourth ADC converter 13 together, the output ends of the first ADC converter 5 to the fourth ADC converter 13 are connected with the corresponding input end of a microprocessor 7, the input end of the DAC converter 6 is connected with the output end of the microprocessor 7.
The watchcase temperature probe 3 can also be arranged on the probe seat and is far away from the medium channel.
As shown in fig. 2 and 3, the calibration method of the variable power thermal mass flowmeter includes the steps of:
before leaving a factory, connecting a flowmeter to be calibrated with a standard meter (a flowmeter matched with the flowmeter to be calibrated) in series and then introducing a constant airflow, wherein the constant airflow is 60% of the maximum measuring range of the flowmeter to be calibrated.
Step two, maintaining the temperature difference of 30 ℃ between T1 and T2, measuring the current and voltage of the heating and temperature measuring probe 1 of the flowmeter to be calibrated when the temperature difference is different from T2, obtaining the target power P0 of the probe, obtaining a polynomial coefficient through function mapping of the corresponding P0 and T2, eliminating the power of temperature drift, then obtaining a P0-T2 comparison table, and storing the P0-T2 comparison table into a memory connected with the MCU; the T1 is the surface temperature of the heating and temperature measuring probe, the T2 is the temperature of the fluid (air) measured by the medium temperature measuring probe, the value range of the temperature of the fluid (air) is from TB to TA, 8 test points are averagely selected, TB is less than the minimum value (-20 ℃) of the environmental temperature in one year, TB is-37 ℃, TA is greater than the maximum value (45 ℃) of the environmental temperature in the same year, and TA is 61 ℃.
And step three, calibrating a corresponding relation curve F3 of the temperature difference T1-T2 between the heating and temperature measuring probe 1 and the medium temperature measuring probe 2 and 40 different flow rates by standard calibration equipment, and storing the corresponding relation curve in the memory, wherein the 40 different flow rates correspond to the flow rate values of 40 equally divided points of the maximum measuring range of the flowmeter to be calibrated, and the standard calibration equipment is Venturi sonic nozzle calibration equipment.
Fourthly, acquiring the voltage of the heating and temperature measuring probe 1 in real time by using the first ADC (analog to digital converter) 5, acquiring the current of the heating and temperature measuring probe 1 in real time by using the sampling resistor 8 and the fourth ADC 13, obtaining the resistance value and the real-time power P1 by using the MCU7, and converting the temperature value T1 of the heating and temperature measuring probe 1 by using the microprocessor according to the comparison relation of the probe temperature and the resistance value; the constant current source 4 is used for driving the medium temperature measuring probe 2, a certain voltage is generated by the medium temperature measuring probe 2, the voltage is input to the MCU7 through the second ADC converter 11, the resistance value of the medium temperature measuring probe 2 is obtained by the MCU according to the voltage value and the current value of the constant current source, and the temperature value T2 of the medium temperature measuring probe is converted according to the temperature-resistance value comparison relation of the medium temperature measuring probe 2;
the temperature-resistance curve of the heating and temperature measuring probe 1 and the temperature-resistance curve of the medium temperature measuring probe 2 are resistance connecting lines measured by placing the corresponding probes into an oil tank and selecting the maximum value, the middle value and the minimum value according to the temperature measuring range of the probes.
And step five, controlling the power of the heating and temperature measuring probe 1 through a DAC (digital-to-analog converter) by utilizing a stored P0-T2 comparison table according to the temperature value T2 of the medium temperature measuring probe calculated in the step four, so that the real-time power value P1 of the heating and temperature measuring probe 1 is consistent with the target power value P0.
And step six, calculating the current flow rate of the flowmeter to be calibrated by using the V-F3 (T1-T2), wherein T1-T2 is the temperature difference between the heating and temperature measuring probe 1 and the medium temperature measuring probe 2.
And step seven, calculating the corrected flow rate V2 of the flowmeter to be calibrated by using a fluid temperature and external temperature unequal correction formula:
V2＝V-(Vu-Vd)/(T2u-T2d)*(T3-T2)*V/Vm；
in the formula: v is the current flow rate of the flowmeter to be calibrated, T2 is the fluid temperature, T3 is the shell temperature detected by the shell temperature probe 3, and Vm is the upper limit of the measuring range;
the calibration table tests a flow rate of Vu when T3 ═ Tu, where Tu is room temperature + T0 and the fluid temperature is T2 u; the calibration table test flow rate is Vd when T3 equals Td, room temperature-T0, and fluid temperature is T2 d; the room temperature is 20 ℃, T0 ═ 15 ℃, Tu ═ room temperature + T0 ═ 35 ℃, Td ═ room temperature-T0 ═ 5 ℃.
After leaving the factory, a user obtains a flow rate value by using 485 communication, or the flow rate value is displayed on a liquid crystal screen or a 4-20ma current signal is directly output; and accumulating the flow rate by adopting a timer to obtain the flow Q, and storing the Q value into a nonvolatile memory for a client to read or display on a display screen.
Example 2
The calibration method of the variable power thermal mass flowmeter comprises the following steps:
as shown in fig. 2 and 3, the calibration method of the variable power thermal mass flowmeter includes the steps of:
before leaving a factory, connecting a flowmeter to be calibrated with a standard meter (a flowmeter matched with the flowmeter to be calibrated) in series and then introducing a constant airflow, wherein the constant airflow is 50% of the maximum measuring range of the flowmeter to be calibrated.
Step two, maintaining the temperature difference of 20 ℃ between T1 and T2, measuring the current and voltage of the heating and temperature measuring probe 1 of the flowmeter to be calibrated when the temperature difference is different from T2, obtaining the target power P0 of the probe, obtaining a polynomial coefficient through function mapping of the corresponding P0 and T2, eliminating the power of temperature drift, then obtaining a P0-T2 comparison table, and storing the P0-T2 comparison table into a memory connected with the MCU; the T1 is the surface temperature of the heating and temperature measuring probe, the T2 is the temperature of the fluid (air) measured by the medium temperature measuring probe, the value range of the temperature is that 9 test points are averagely selected in the range of TB-TA, TB is less than the minimum value (-20 ℃) of the environmental temperature in one year, TB is-35 ℃, TA is greater than the maximum value (45 ℃) of the environmental temperature in the same year, and TA is 60 ℃.
And step three, calibrating a corresponding relation curve F3 of the temperature difference T1-T2 between the heating and temperature measuring probe 1 and the medium temperature measuring probe 2 and 30 different flow rates by standard calibration equipment, and storing the corresponding relation curve in the memory, wherein the 30 different flow rates correspond to 30 equally divided points of the maximum measuring range of the flowmeter to be calibrated, and the standard calibration equipment is Venturi sonic nozzle calibration equipment.
Fourthly, acquiring the voltage of the heating and temperature measuring probe 1 in real time by using the first ADC (analog to digital converter) 5, acquiring the current of the heating and temperature measuring probe 1 in real time by using the sampling resistor 8 and the fourth ADC 13, obtaining the resistance value and the real-time power P1 by using the MCU7, and converting the temperature value T1 of the heating and temperature measuring probe 1 by using the microprocessor according to the comparison relation of the probe temperature and the resistance value; the constant current source 4 is used for driving the medium temperature measuring probe 2, a certain voltage is generated by the medium temperature measuring probe 2, the voltage is input to the MCU7 through the second ADC converter 11, the resistance value of the medium temperature measuring probe 2 is obtained by the MCU according to the voltage value and the current value of the constant current source, and the temperature value T2 of the medium temperature measuring probe is converted according to the temperature-resistance value comparison relation of the medium temperature measuring probe 2;
the temperature-resistance curve of the heating and temperature measuring probe 1 and the temperature-resistance curve of the medium temperature measuring probe 2 are resistance connecting lines measured by placing the corresponding probes into an oil tank and selecting the maximum value, the middle value and the minimum value according to the temperature measuring range of the probes.
And step five, controlling the power of the heating and temperature measuring probe 1 through a DAC (digital-to-analog converter) by utilizing a stored P0-T2 comparison table according to the temperature value T2 of the medium temperature measuring probe calculated in the step four, so that the real-time power value P1 of the heating and temperature measuring probe 1 is consistent with the target power value P0.
And step six, calculating the current flow rate of the flowmeter to be calibrated by using the V-F3 (T1-T2), wherein T1-T2 is the temperature difference between the heating and temperature measuring probe 1 and the medium temperature measuring probe 2.
And seventhly, obtaining the corrected flow velocity V2 of the flowmeter to be calibrated by using a fluid temperature and external temperature unequal correction formula:
V2＝V-(Vu-Vd)/(T2u-T2d)*(T3-T2)*V/Vm；
in the formula: v is the current flow rate of the flowmeter to be calibrated, T2 is the fluid temperature, T3 is the shell temperature detected by the probe 3, and Vm is the upper limit of the measuring range;
the calibration table tests a flow rate of Vu when T3 ═ Tu, where Tu is room temperature + T0 and the fluid temperature is T2 u; the calibration table test flow rate is Vd when T3 equals Td, room temperature-T0, and fluid temperature is T2 d; the room temperature is 20 ℃, T0 ═ 20 ℃, Tu ═ room temperature + T0 ═ 40 ℃, Td ═ room temperature-T0 ═ 0 ℃.
After leaving the factory, a user obtains a flow rate value by using 485 communication, or the flow rate value is displayed on a liquid crystal screen or a 4-20ma current signal is directly output; and accumulating the flow rate by adopting a timer to obtain the flow Q, and storing the Q value into a nonvolatile memory for a client to read or display on a display screen.
The above description is only exemplary of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. The utility model provides a variable power hot type mass flowmeter, includes watchcase (10), probe seat (9) and microprocessor (7) of establishing medium runner (1001) in, characterized by: the variable power thermal mass flowmeter is also provided with a first ADC converter (5) to a fourth ADC converter (13), a DAC converter (6) and a constant current source (4), wherein a heating and temperature measuring probe (1) and a medium temperature measuring probe (2) are respectively arranged at the parts, corresponding to a medium flow channel (1001), of a probe seat (9), and a watchcase temperature measuring probe (3) is arranged on a watchcase or the probe seat; the heating and temperature measuring probe (1), the medium temperature measuring probe (2) and the shell temperature measuring probe (3) are all made of four wires, and a first wire and a second wire and a third wire and a fourth wire are connected in each probe; the first line and the fourth line of the heating and temperature measuring probe (1) are connected with the input end of a first ADC (5), the second line of the heating and temperature measuring probe (1) is connected with the input end of a sampling resistor (8), the third line of the heating and temperature measuring probe (1) is connected with the output end of a DAC (6), the first line of the medium temperature measuring probe (2) is connected with the positive end of a constant current source (4), the second line and the third line of the medium temperature measuring probe (2) are connected with the input end of a second ADC (11), the fourth line of the medium temperature measuring probe (2) is connected with the first line of the watchcase temperature measuring probe (3), the second line and the third line of the watchcase temperature measuring probe (3) are connected with the input end of a third ADC (12), the fourth line of the watchcase temperature measuring probe (3) is connected with the negative end of the constant current source (4), the outlet end of the sampling resistor (8) is grounded and is connected with the input end of a fourth ADC (13), the output ends of the first ADC converter (5) to the fourth ADC converter (13) are connected with the corresponding input end of the microprocessor (7), and the input end of the DAC converter (6) is connected with the output end of the microprocessor (7).
2. The variable power thermal mass flow meter of claim 1, wherein: the watchcase temperature probe (3) is arranged at the position of the watchcase (10) or the probe seat (9) far away from the medium channel (1001).
3. The variable power thermal mass flow meter of claim 1, wherein: the heating and temperature measuring probe (1), the medium temperature measuring probe (2) and the meter shell temperature measuring probe (3) adopt platinum resistors.
4. The method for calibrating a variable power thermal mass flowmeter of claim 1, wherein:
firstly, connecting a flowmeter to be calibrated and a standard meter in series and introducing constant airflow, wherein the constant airflow is more than or equal to 50% of the maximum measuring range of the flowmeter to be calibrated;
step two, measuring a target power P0 of a heating and temperature measuring probe 1 of the flowmeter to be calibrated when the same temperature difference of T1 and T2 is kept and T2 is different, obtaining a polynomial coefficient by functionally mapping the corresponding target power P0 and T2, eliminating the power of temperature drift, establishing a P0-T2 comparison table, and storing the P0-T2 comparison table into a memory connected with the MCU; the T1 is the surface temperature of the heating and temperature measuring probe, the T2 is the temperature of fluid (air) measured by the medium temperature measuring probe and the value range is TB-TA, TB is less than the minimum Tmin of the environmental temperature in one year, and TA is greater than the maximum Tmax of the environmental temperature in the same year;
step three, calibrating a corresponding relation curve F3 of the temperature difference T1-T2 between the heating and temperature measuring probe and the medium temperature measuring probe and different flow rates of the fluid by standard calibration equipment, and storing the curve in the memory;
fourthly, acquiring the voltage of the heating and temperature measuring probe 1 in real time by using the first ADC (analog to digital converter) 5, acquiring the current of the heating and temperature measuring probe 1 in real time by using the sampling resistor 8 and the fourth ADC 13, obtaining the resistance value and the real-time power value P1 by using the MCU7, and converting the temperature value T1 by using the MCU7 according to the temperature-resistance value comparison relation of the heating and temperature measuring probe 1;
the constant current source 4 is used for driving the medium temperature measuring probe 2, a certain voltage is generated by the medium temperature measuring probe 2, the voltage is input to the MCU7 through the second ADC converter 11, the resistance value of the medium temperature measuring probe is obtained by the MCU7 according to the voltage value and the current value of the constant current source, and the temperature value T2 is converted according to the temperature-resistance comparison relation of the heating and temperature measuring probe 2;
fifthly, the converted T2 value is compared with the P0-T2 table in the second step, the power of the heating and temperature measuring probe 1 is controlled through a DAC converter, and the real-time power value P1 is made to be consistent with the target power value P0;
calculating the current flow velocity V of the flowmeter to be calibrated:
V＝F3*(T1-T2)
wherein T1-T2 is the temperature difference between the heating and temperature measuring probe and the medium temperature measuring probe;
and step seven, calculating the corrected flow rate V2 of the flowmeter to be calibrated by using a fluid temperature and external temperature unequal correction formula:
V2＝V-(Vu-Vd)/(T2u-T2d)*(T3-T2)*V/Vm；
in the formula: v is the current flow rate of the flowmeter to be calibrated, T2 is the fluid temperature, T3 is the watchcase temperature measured by the watchcase temperature probe, and Vm is the upper limit of the measuring range of the flowmeter;
the standard table test flow rate is Vu when T3 ═ Tu, where Tu ═ room temperature + T0, fluid temperature is T2 u; the standard table test flow rate is Vd when T3 equals Td, room temperature-T0, fluid temperature T2 d; the value of T0 is 10-20 ℃.
5. The method for calibrating a variable power thermal mass flow meter according to claim 4, wherein: and in the second step, the difference value of Tmin and TB and the difference value of TA and Tmax are respectively 10-20 ℃.
6. The method for calibrating a variable power thermal mass flow meter according to claim 4, wherein: and in the second step, the value of the fluid temperature T2 is a temperature value corresponding to 5-10 equi-divisions in the TB-TA range.
7. The method for calibrating a variable power thermal mass flow meter according to claim 4, wherein: and in the third step, the different flow rates of the fluid are flow rate values corresponding to 20-50 equally divided points according to the maximum measuring range of the flowmeter to be calibrated.
8. The method for calibrating a variable power thermal mass flow meter according to claim 4, wherein: and in the third step, the standard calibration equipment is Venturi sonic nozzle calibration equipment.
9. The method for calibrating a variable power thermal mass flow meter according to claim 4, wherein: and in the fourth step, the temperature-resistance value corresponding relation of the heating and temperature measuring probe and the temperature-resistance value relation of the medium temperature measuring probe are that the heating and temperature measuring probe and the heating and temperature measuring probe are respectively put into an oil tank, and resistance connecting lines measured by the maximum value, the middle value and the minimum value are selected according to the temperature measuring range of the probes.
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| CN110520699A (en) * | 2017-04-18 | 2019-11-29 | 法国国家科学研究中心 | For measuring the device of gas velocity or flow |
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2021
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| JPH05157758A (en) * | 1991-12-04 | 1993-06-25 | Yamatake Honeywell Co Ltd | Compensating method for temperature characteristic of current speed sensor |
| CN101165462A (en) * | 2006-10-18 | 2008-04-23 | 株式会社岛津制作所 | Thermal mass flow meter |
| CN102519527A (en) * | 2011-12-16 | 2012-06-27 | 哈尔滨四远测控技术有限责任公司 | Thermal constant-power gas flow meter |
| CN106441472A (en) * | 2016-09-28 | 2017-02-22 | 合肥科迈捷智能传感技术有限公司 | Method for temperature drift inhibition of constant power type thermal type gas flowmeter |
| CN110520699A (en) * | 2017-04-18 | 2019-11-29 | 法国国家科学研究中心 | For measuring the device of gas velocity or flow |
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