Thermal type flowmeter and method for correction

Abstract

To measure an accurate flow rate even if fluid to be measured is changed.SOLUTION: A saturation time before a temperature of fluid stops increasing in a temperature measurement position for a temperature measurement unit 103 to measure a temperature is measured, power consumption of a heater 102 from the beginning of driving of the heater 102 to the saturation time is measured, the time from the beginning of driving of the heater 102 to when the power consumption of the heater 102 becomes 63.2% in the saturation time is determined as a time constant, heat resistance of fluid is determined from the increasing temperature in the temperature measurement position for the temperature measurement unit 103 to measure the temperature and the saturation power consumption of the heater 102 in the saturation time, and a heat capacity of the fluid is determined by dividing the time constant by the heat resistance of the fluid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a thermal flow meter and a correction method. [Background technology]

[0002] Thermal flow meters include a method of measuring the flow rate by the temperature difference between the upstream and downstream of a heater, and a method of measuring the flow rate by the power consumption of the heater. For example, when measuring the flow rate of a liquid, the heater is operated by heating to a constant temperature, such as 10°C above the liquid temperature, and the flow rate is calculated from the temperature difference between the upstream and downstream or the power of the heater. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-010322 A Summary of the Invention [Problem to be solved by the invention]

[0004] In this way, thermal flow meters convert (convert) heater output, such as the heater temperature difference or heater power, into flow rate. This conversion (conversion formula) is specific to the fluid being measured. For this reason, if the type or physical properties of the fluid being measured are unknown, or if the measurement target is changed, an error may occur when converting the heater output into flow rate, and an accurate flow rate may not be output.

[0005] The present invention has been made to solve the above problems, and has an object to make it possible to measure an accurate flow rate even if the fluid to be measured is changed. [Means for solving the problem]

[0006] The thermal flow meter according to the present invention includes a pipe for transporting a fluid to be measured, a heater configured to heat the fluid in a measurement area of ​​the pipe, a temperature measurement unit configured to measure the temperature of the fluid in the measurement area, a sensor circuit configured to output a sensor value corresponding to a state of thermal diffusion in the fluid heated by the heater when the heater is driven so that a difference between the temperature of the heater and the temperature of the fluid at a temperature measurement position not affected by the heater becomes a set temperature difference that is set, a correction circuit configured to obtain a correction value obtained by correcting the sensor value with a correction coefficient, a flow rate calculation circuit configured to calculate a flow rate of the fluid from the correction value, a fluid stopping unit configured to stop the flow of the fluid, and a start-up circuit configured to start driving the heater after stopping the flow of the fluid in the fluid stopping unit, and a heater. the temperature measuring circuit is configured to measure the saturation time from when the heater starts to be driven until the temperature of the fluid at the temperature measurement position stops rising; a power measuring circuit configured to measure the power consumption of the heater from when the heater starts to be driven until the saturation time is reached; a time constant determining circuit configured to calculate the time from when the heater starts to be driven until the power consumption of the heater at the saturation time is 63.2% as a time constant; a resistance calculating circuit configured to calculate the thermal resistance of the fluid from the increased temperature at the temperature measurement position and the saturation power consumption of the heater at the saturation time; a heat capacity calculating circuit configured to calculate the heat capacity of the fluid by dividing the time constant by the thermal resistance of the fluid; and a correction coefficient determining circuit configured to calculate a correction coefficient from the relationship between the heat capacity calculated by the heat capacity calculating circuit and the reference heat capacity of a reference fluid.

[0007] In one configuration example of the above thermal flow meter, the temperature measurement unit measures the temperature of the fluid at the temperature measurement position, and the sensor circuit outputs the heater power as a sensor value when the heater is driven so that the difference between the heater temperature and the fluid temperature measured by the temperature measurement unit becomes the set temperature difference.

[0008] In one configuration example of the above thermal flow meter, the temperature measurement unit is composed of a first temperature measurement unit, a second temperature measurement unit, and a third temperature measurement unit, the first temperature measurement unit measures the temperature of the fluid at the temperature measurement position, the second temperature measurement unit measures the temperature of the fluid at a position upstream of the heater and affected by the heat of the heater, and the third temperature measurement unit measures the temperature of the fluid at a position downstream of the heater and affected by the heat of the heater, and the sensor circuit outputs as a sensor value the temperature difference between the fluid temperature measured by the second temperature measurement unit and the fluid temperature measured by the third temperature measurement unit when the heater is driven so that the difference between the heater temperature and the fluid temperature measured by the first temperature measurement unit becomes a set temperature difference.

[0009] A correction method according to the present invention is a correction method for determining a correction value for a thermal flow meter comprising: a pipe for transporting a fluid to be measured; a heater configured to heat the fluid in a measurement area of ​​the pipe; and a temperature measurement unit configured to measure the temperature of the fluid in the measurement area, the method comprising: a sensor circuit configured to output a sensor value corresponding to a state of thermal diffusion in the fluid heated by the heater when the heater is driven so that a difference between the temperature of the heater and the temperature of the fluid at a temperature measurement position not affected by the heater becomes a set temperature difference; a correction circuit configured to determine a correction value obtained by correcting the sensor value with a correction coefficient; and a flow rate calculation circuit configured to calculate a flow rate of the fluid from the correction value, the correction method comprising: a first step of stopping the flow of the fluid; a second step of stopping the flow of the fluid and then starting to drive the heater; a third step of measuring the saturation time from when the heater starts to drive until the temperature of the fluid at the temperature measurement position stops rising; a fourth step of measuring the power consumption of the heater from when the heater starts to drive until the saturation time is reached; a fifth step of calculating the time from when the heater starts to drive until the power consumption of the heater at the saturation time is 63.2% as a time constant; a sixth step of calculating the thermal resistance of the fluid from the increased temperature at the temperature measurement position and the saturation power consumption of the heater at the saturation time; a seventh step of calculating the heat capacity of the fluid by dividing the time constant by the thermal resistance of the fluid; and an eighth step of calculating a correction coefficient from the relationship between the heat capacity calculated in the sixth step and the reference heat capacity of a reference fluid.

[0010] In one configuration example of the above correction method, the temperature measurement unit measures the temperature of the fluid at the temperature measurement position, and the sensor circuit outputs the heater power as a sensor value when the heater is driven so that the difference between the heater temperature and the fluid temperature measured by the temperature measurement unit becomes a set temperature difference.

[0011] In one configuration example of the above correction method, the temperature measurement unit is composed of a first temperature measurement unit, a second temperature measurement unit, and a third temperature measurement unit, the first temperature measurement unit measures the temperature of the fluid at the temperature measurement position, the second temperature measurement unit measures the temperature of the fluid at a position upstream of the heater and affected by the heat of the heater, and the third temperature measurement unit measures the temperature of the fluid at a position downstream of the heater and affected by the heat of the heater, and the sensor circuit outputs as a sensor value the temperature difference between the temperature of the fluid measured by the second temperature measurement unit and the temperature of the fluid measured by the third temperature measurement unit when the heater is driven so that the difference between the temperature of the heater and the temperature of the fluid measured by the first temperature measurement unit becomes a set temperature difference. Effect of the Invention

[0012] As described above, according to the present invention, the heat capacity of the fluid to be measured is determined by measuring the temperature of the fluid while the flow of the fluid to be measured is stopped, making it possible to correct the sensor value and to measure an accurate flow rate even if the fluid to be measured is changed. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a configuration diagram showing the configuration of a thermal flow meter according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a characteristic diagram showing the relationship between the flow rate and the sensor value for fluids having different heat capacities. [Diagram 3] FIG. 3 is a flowchart illustrating a correction method according to an embodiment of the present invention. [Figure 4] FIG. 4 is a configuration diagram showing a partial configuration of another thermal type flow meter according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A thermal flow meter according to an embodiment of the present invention will be described below with reference to Fig. 1. This thermal flow meter includes a pipe 101, a heater 102, a temperature measurement unit 103, a sensor circuit 104, a correction circuit 105, a flow rate calculation circuit 106, a fluid stopping unit 107, a start-up circuit 108, a time measurement circuit 109, a power measurement circuit 110, a time constant determination circuit 111, a resistance calculation circuit 112, a heat capacity calculation circuit 113, and a correction coefficient determination circuit 114.

[0015] The pipe 101 transports a fluid to be measured. The heater 102 heats the fluid in a measurement region of the pipe 101. The heater 102 can be composed of, for example, a heater element that serves as a heating resistor, and a temperature sensor element for measuring the temperature of the fluid. The temperature measurement unit 103 measures the temperature of the fluid in the measurement region. The temperature measurement unit 103 can be, for example, a temperature sensor element such as a thermopile composed of a wiring pattern constituting a plurality of thermocouples. The heater 102 is provided downstream of the temperature measurement unit 103.

[0016] The sensor circuit 104 outputs a sensor value corresponding to the state of thermal diffusion in the fluid heated by the heater 102 when the heater 102 is driven so that the difference between the temperature of the heater 102 and the temperature of the fluid at a temperature measurement position not affected by the heat of the heater 102 becomes the set temperature difference. The sensor circuit 104 controls and drives the heater 102 so that the difference between the temperature of the heater 102 and the temperature of the fluid at the above-mentioned temperature measurement position measured by a temperature measurement unit 103 upstream of the heater 102 becomes the preset temperature difference. The sensor circuit 104 supplies power to the heater 102 and controls the supplied power. The sensor circuit 104 adjusts the supplied drive voltage by feedback-controlling the voltage supplied to the bridge circuit constituting the heater 102 so that the output voltage of the bridge circuit becomes zero.

[0017] The correction circuit 105 obtains a correction value by correcting the sensor value output by the sensor circuit 104 with a correction coefficient. The flow rate calculation circuit 106 calculates the flow rate of the fluid from the correction value. The flow rate calculation circuit 106 calculates the flow rate from the correction value using a coefficient as physical property data that is set in advance.

[0018] Fluid stopping unit 107 stops the flow of the fluid flowing through pipe 101. Fluid stopping unit 107 can be composed of a valve provided on the upstream side of pipe 101, and can stop the flow of the fluid flowing through pipe 101 by fully closing the valve.

[0019] The start-up circuit 108 starts driving the heater 102 after causing the fluid stop unit 107 to stop the flow of the fluid. The time measurement circuit 109 measures the saturation time from when the heater 102 starts driving until the temperature rise of the fluid at the temperature measurement position stops (until the temperature rise saturates).

[0020] The power measurement circuit 110 measures the power consumption of the heater 102 from when the heater 102 starts to be driven until the saturation time is reached. For example, the drive power of the heater element (heater 102) can be calculated from the voltage applied to the heater element constituting the heater 102 and the voltage applied to a bridge circuit including this heater element.

[0021] The time constant determination circuit 111 determines, as a time constant, the time from the start of driving the heater 102 until the power consumption of the heater 102 during the saturation time measured by the time measurement circuit 109 reaches 63.2%. The resistance calculation circuit 112 determines the thermal resistance of the fluid from the temperature rise at the temperature measurement position (the temperature at which the temperature rise saturates: saturation temperature) and the saturation power consumption of the heater 102 during the saturation time. The thermal resistance can be determined by "thermal resistance = temperature rise ÷ saturation power consumption."

[0022] The heat capacity calculation circuit 113 obtains the heat capacity of the fluid by dividing the time constant by the thermal resistance of the fluid. As is well known, since there is a relationship of "time constant = thermal resistance x heat capacity", the heat capacity of the fluid can be obtained by dividing the time constant by the thermal resistance of the fluid.

[0023] The correction coefficient determination circuit 114 determines a correction coefficient from the relationship between the heat capacity determined by the heat capacity calculation circuit 113 and the reference heat capacity of the reference fluid serving as a reference. The correction coefficient determination circuit 114 sets the determined correction coefficient in the correction circuit 105. The reference heat capacity of the reference fluid is determined in advance and set in the correction coefficient determination circuit 114.

[0024] As shown in Figure 2, if the heat capacity of the fluid is different, the sensor value will be different. The heat capacity has the relationship (a)<(b)<(c)<(d). Therefore, it is important to correct the sensor value according to the heat capacity of the fluid to be measured. For this reason, if the fluid to be measured is unknown, it is necessary to calculate the heat capacity and correct the sensor value according to the calculated heat capacity.

[0025] According to the embodiment, since the heat capacity of the fluid to be measured is obtained as described above, it becomes possible to correct the sensor value, and an accurate flow rate can be measured even if the fluid to be measured is changed.

[0026] Next, a correction method according to an embodiment of the present invention will be described with reference to Fig. 3. This correction method is a method for determining a correction value for the thermal type flow meter described above.

[0027] First, in a first step S101, the fluid stopping unit 107 stops the flow of the fluid flowing through the pipe 101. After the flow of the fluid is stopped, in a second step S102, the start-up circuit 108 starts driving the heater 102. After driving the heater 102 starts, in a third step S103, the time measurement circuit 109 measures the saturation time until the temperature of the fluid at the temperature measurement position where the temperature measurement unit 103 measures the temperature stops increasing.

[0028] Next, in a fourth step S104, the power measuring circuit 110 measures the power consumption of the heater 102 from the start of driving the heater 102 until the saturation time is reached. Next, in a fifth step S105, the time constant determining circuit 111 determines, as a time constant, the time from the start of driving the heater 102 until the power consumption of the heater 102 at the saturation time becomes 63.2%.

[0029] Next, in a sixth step S106, the resistance calculation circuit 112 calculates the thermal resistance of the fluid from the temperature rise at the temperature measurement position where the temperature measurement unit 103 measures the temperature and the saturation power consumption of the heater 102 during the saturation time. Next, in step S107, the heat capacity calculation circuit 113 calculates the heat capacity of the fluid by dividing the time constant by the thermal resistance of the fluid. After this, in an eighth step S108, the correction coefficient determination circuit 114 calculates a correction coefficient from the relationship between the calculated heat capacity and the reference heat capacity of the reference fluid that serves as a reference. The calculated correction coefficient is set in the correction circuit 105. The reference heat capacity of the reference fluid is calculated in advance.

[0030] As described above, since the heat capacity of the fluid to be measured is obtained, it is possible to correct the sensor value, and an accurate flow rate can be measured even if the fluid to be measured is changed.

[0031] As shown in Fig. 4, the sensor values ​​can be obtained using a first temperature measurement unit 103a, a second temperature measurement unit 103b, and a third temperature measurement unit 103c. The first temperature measurement unit 103a measures the temperature of the fluid at a temperature measurement position upstream of the heater 102 and not affected by the heat of the heater 102. The second temperature measurement unit 103b measures the temperature of the fluid at a position upstream of the heater 102 and affected by the heat of the heater 102. The third temperature measurement unit 103c measures the temperature of the fluid at a position downstream of the heater 102 and affected by the heat of the heater 102.

[0032] The sensor circuit 104a outputs, as a sensor value, the temperature difference between the fluid temperature measured by the second temperature measuring unit 103b and the fluid temperature measured by the third temperature measuring unit 103c when the heater 102 is driven so that the difference between the temperature of the heater 102 and the fluid temperature measured by the first temperature measuring unit 103a becomes the set temperature difference. The other configurations are the same as those of the thermal flowmeter described using FIG. 1, and therefore description thereof will be omitted here.

[0033] As is well known, when the heater 102 is driven so that the difference between the temperature of the fluid at a temperature measurement position (the position of the first temperature measurement unit 103a) that is not thermally affected by the heater 102 is a preset temperature difference, there is a correlation between the temperature difference between the fluid temperature upstream of the heater 102 (the value measured by the second temperature measurement unit 103b) and the fluid temperature downstream of the heater 102 (the value measured by the third temperature measurement unit 103c) and the flow rate of the fluid. In addition, this correlation is reproducible for the same fluid / flow rate / temperature. Therefore, as described above, the flow rate can be calculated by using a predetermined correlation coefficient (constant) from the difference (temperature difference) between the temperature measured by the second temperature measurement unit 103b and the temperature measured by the third temperature measurement unit 103c while the heater 102 is being controlled.

[0034] The sensor circuit 104, the correction circuit 105, the flow rate calculation circuit 106, the start circuit 108, the time measurement circuit 109, the power measurement circuit 110, the time constant determination circuit 111, the resistance calculation circuit 112, the heat capacity calculation circuit 113, and the correction coefficient determination circuit 114 according to the above-mentioned embodiment may be a computer device equipped with a CPU (Central Processing Unit), a main storage device, an external storage device, a network connection device, etc., and the functions (correction methods) of the above-mentioned circuits may be realized by the CPU operating (executing the program) according to a program deployed in the main storage device. The above-mentioned program is a program for a computer to execute the correction method shown in the above-mentioned embodiment. The network connection device connects to a network. Also, each function may be distributed to multiple computer devices.

[0035] In addition, the sensor circuit 104, the correction circuit 105, the flow rate calculation circuit 106, the start-up circuit 108, the time measurement circuit 109, the power measurement circuit 110, the time constant determination circuit 111, the resistance calculation circuit 112, the heat capacity calculation circuit 113, and the correction coefficient determination circuit 114 according to the above-mentioned embodiment can be configured by a programmable logic device (PLD: Programmable Logic Device) such as an FPGA (field-programmable gate array). For example, the above-mentioned circuits can be provided in the logic element of the FPGA. Each circuit can be written into the FPGA by connecting a predetermined writing device. Furthermore, each of the above-mentioned circuits written into the FPGA can be confirmed by a writing device connected to the FPGA.

[0036] As described above, according to the present invention, the heat capacity of the fluid to be measured is determined by measuring the temperature of the fluid while the flow of the fluid to be measured is stopped, making it possible to correct the sensor value and to measure an accurate flow rate even if the fluid to be measured is changed.

[0037] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0038] 101...piping, 102...heater, 103...temperature measurement section, 104...sensor circuit, 105...compensation circuit, 106...flow rate calculation circuit, 107...fluid stopping section, 108...start-up circuit, 109...time measurement circuit, 110...power measurement circuit, 111...time constant determination circuit, 112...resistance calculation circuit, 113...heat capacity calculation circuit, 114...correction coefficient determination circuit.

Claims

1. A pipe for transporting a fluid to be measured; a heater configured to heat the fluid in a measurement region of the pipe; a temperature measurement unit configured to measure a temperature of the fluid in the measurement region; a sensor circuit configured to output a sensor value corresponding to a state of thermal diffusion in the fluid heated by the heater when the heater is driven so that a difference between a temperature of the heater and a temperature of the fluid at a temperature measurement position not affected by the heater becomes a set temperature difference; a correction circuit configured to obtain a correction value by correcting the sensor value by a correction coefficient; a flow rate calculation circuit configured to calculate a flow rate of the fluid from the correction value; a fluid stop configured to stop the flow of the fluid; a start circuit configured to stop the flow of the fluid through the fluid stopping portion and then start driving the heater; a time measurement circuit configured to measure a saturation time from when the heater starts to be driven until when the temperature of the fluid at the temperature measurement position stops increasing; a power measurement circuit configured to measure the power consumption of the heater from the start of driving the heater until the saturation time is reached; a time constant determination circuit configured to determine, as a time constant, a time from the start of driving the heater until the power consumption of the heater during the saturation time reaches 63.2%; a resistance calculation circuit configured to calculate a thermal resistance of the fluid from a temperature rise at the temperature measurement position and a saturation power consumption of the heater during the saturation time; a heat capacity calculation circuit configured to calculate a heat capacity of the fluid by dividing the time constant by a thermal resistance of the fluid; a correction coefficient determination circuit configured to determine the correction coefficient from the relationship between the heat capacity determined by the heat capacity calculation circuit and a reference heat capacity of a reference fluid serving as a reference; A thermal flow meter comprising:

2. 2. The thermal flow meter according to claim 1, The temperature measurement unit measures the temperature of the fluid at the temperature measurement position, The sensor circuit outputs, as the sensor value, the electric power of the heater when the heater is driven so that a difference between a temperature of the heater and a temperature of the fluid measured by the temperature measuring unit becomes the set temperature difference. Thermal flow meter.

3. 2. The thermal flow meter according to claim 1, The temperature measurement unit includes a first temperature measurement unit, a second temperature measurement unit, and a third temperature measurement unit, The first temperature measurement unit measures a temperature of the fluid at the temperature measurement position, the second temperature measurement unit measures a temperature of the fluid at a position upstream of the heater and affected by the heat of the heater; the third temperature measurement unit measures a temperature of the fluid at a position downstream of the heater and affected by the heat of the heater; The sensor circuit outputs, as the sensor value, a temperature difference between the temperature of the fluid measured by the second temperature measurement unit and the temperature of the fluid measured by the third temperature measurement unit when the heater is driven so that the difference between the temperature of the heater and the temperature of the fluid measured by the first temperature measurement unit becomes the set temperature difference. Thermal flow meter.

4. A pipe for transporting a fluid to be measured; a sensor circuit including a heater configured to heat the fluid in a measurement area of ​​the piping, and a temperature measurement unit configured to measure a temperature of the fluid in the measurement area, and configured to output a sensor value corresponding to a state of thermal diffusion in the fluid heated by the heater when the heater is driven so that a difference between a temperature of the heater and a temperature of the fluid at a temperature measurement position not affected by the heater becomes a set temperature difference; a correction circuit configured to obtain a correction value by correcting the sensor value by a correction coefficient; a flow rate calculation circuit configured to calculate a flow rate of the fluid from the correction value; A correction method for determining the correction value of a thermal flow meter comprising: a first step of stopping the flow of the fluid; a second step of starting to drive the heater after stopping the flow of the fluid in the first step; a third step of measuring a saturation time from when the heater starts to be driven until when the temperature of the fluid at the temperature measurement position stops increasing; a fourth step of measuring the power consumption of the heater from the start of driving the heater until the saturation time is reached; a fifth step of determining, as a time constant, a time from the start of driving the heater until the power consumption of the heater reaches 63.2% of the power consumption of the heater during the saturation time; a sixth step of determining a thermal resistance of the fluid from a temperature rise at the temperature measurement position and a saturated power consumption of the heater during the saturation time; a seventh step of determining a heat capacity of the fluid by dividing the time constant by a thermal resistance of the fluid; an eighth step of determining the correction coefficient from the relationship between the heat capacity determined in the sixth step and the reference heat capacity of a reference fluid; A correction method comprising:

5. 5. The correction method according to claim 4, The temperature measurement unit measures the temperature of the fluid at the temperature measurement position, The sensor circuit outputs, as the sensor value, the electric power of the heater when the heater is driven so that a difference between a temperature of the heater and a temperature of the fluid measured by the temperature measuring unit becomes the set temperature difference. Correction method.

6. 5. The correction method according to claim 4, The temperature measurement unit includes a first temperature measurement unit, a second temperature measurement unit, and a third temperature measurement unit, The first temperature measurement unit measures a temperature of the fluid at the temperature measurement position, the second temperature measurement unit measures a temperature of the fluid at a position upstream of the heater and affected by the heat of the heater; the third temperature measurement unit measures a temperature of the fluid at a position downstream of the heater and affected by the heat of the heater; The sensor circuit outputs, as the sensor value, a temperature difference between the temperature of the fluid measured by the second temperature measurement unit and the temperature of the fluid measured by the third temperature measurement unit when the heater is driven so that the difference between the temperature of the heater and the temperature of the fluid measured by the first temperature measurement unit becomes the set temperature difference. Correction method.

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