JP2021092452A - Thermal flowmeter and flow rate measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize accurate flow rate measurement in a very small flow rate range. SOLUTION: A thermal flow meter includes a pipe 1 for flowing a fluid to be measured, a temperature measuring element 2a for detecting a first temperature of the fluid, and a temperature measuring element 2b for detecting a second temperature of the fluid. A heat generation / temperature measuring element 2c that detects the heat generation temperature at the same time as heat generation, and a control unit that heats the heat generation / temperature measuring element 2c so that the heat generation temperature is higher than the first temperature or the second temperature by a certain value. 10 and the power measuring unit 6 for measuring the power consumption of the heat generation / temperature measuring element 2c, and when the temperature difference between the second temperature and the first temperature is equal to or less than a predetermined threshold value, the first flow measurement mode is set. In the case of the switching unit 7 that sets the second flow rate measurement mode when the temperature difference is larger than the threshold, and in the case of the first flow rate measurement mode, the power consumption is converted into the value of the fluid flow rate, and in the case of the second flow rate measurement mode. Is provided with a flow rate deriving unit 8 that converts the temperature difference (TRr2-TRr1) into the value of the flow rate of the fluid. [Selection diagram] Fig. 1

Description

The present invention relates to a thermal flow meter and a flow rate measuring method capable of measuring the flow rate of an extremely minute fluid.

Conventionally, a thermal flow meter having a structure in which a sensor chip is attached to a pipe through which a fluid flows has been known (see Patent Document 1 and Patent Document 2).
FIG. 7 is a diagram illustrating the principle of the thermal flowmeter. In the thermal flow meter shown in FIG. 7, the temperature sensor 101 and the heater 102 are arranged in the pipe 100 through which the fluid to be measured is circulated, and the difference between the temperature TRh of the heater 102 and the temperature TRr of the temperature sensor 101 (TRh-). The heater 102 is heated so that TRr) becomes constant. At this time, since the flow rate of the fluid has a reproducible correlation with the power consumption of the heater 102, the flow rate can be calculated from the power consumption.

When the heater 102 is driven so that the temperature TRh of the heater 102 is higher than the fluid temperature TRr by a constant temperature and the flow rate is calculated based on the power consumption of the heater 102, the power consumption of the heater 102 is high in a very small flow rate range. There was a problem that the power consumption was lower than that when the flow rate was zero, and accurate flow rate measurement could not be performed. The cause of this problem is that the heat of the heater 102 is transferred to the temperature sensor 101 via the pipe 100. The flow rate range in which the power consumption of the heater 102 is reduced depends on the amount of heat transferred to the temperature sensor 101 on the upstream side. Therefore, for example, in the case of the quartz pipe 100, a phenomenon that the heater power consumption decreases in the flow rate range of less than 0.01 mL / min occurs as shown in FIG.

In the extremely small flow rate range, the temperature sensor 101 shows a temperature higher than the actual liquid temperature due to the influence of heat transfer from the heater 102 to the temperature sensor 101, and as a result, the temperature of the heater 102 becomes higher than the temperature that should be controlled originally. Therefore, the power consumption of the heater 102 increases. The effect of heat transfer is greatest when the flow rate is zero, and the effect of heat transfer disappears as the flow velocity increases. As a result, the power consumption of the heater 102 decreases because the region exceeds the increase in power consumption. On the other hand, in a flow rate region larger than the extremely small flow rate region, the increase in power consumption due to the increase in flow velocity exceeds the decrease in power consumption due to the influence of heat transfer, and as a result, the power consumption of the heater 102 is increased according to the increase in flow velocity. Will increase.

As described above, since it is not possible to accurately measure the flow rate in the extremely small flow rate range, the conventional thermal flow meter has dealt with this by setting the extremely small flow rate range as a dead zone.

Japanese Unexamined Patent Publication No. 2011-209038 Jikkenhei 02-057027

The present invention has been made to solve the above problems, and an object of the present invention is to provide a thermal flow meter and a flow rate measuring method capable of realizing accurate flow rate measurement in a very small flow rate range.

The thermal flow meter of the present invention has a pipe configured to circulate the fluid to be measured and a first measurement arranged in the pipe and configured to detect a first temperature of the fluid. A temperature element, a second temperature measuring element arranged at a position of the pipe on the downstream side of the first temperature measuring element, and configured to detect a second temperature of the fluid, and the first temperature measuring element. A heat generation / temperature measuring element arranged at a location of the pipe downstream of the temperature measuring element 2 and configured to detect the heat generation temperature at the same time as heat generation, and the heat generation temperature is the first temperature or A control unit configured to generate heat by supplying power so as to be higher than the second temperature by a certain value, and measuring the power consumption of the heat generation / temperature measuring element. When the difference between the second temperature and the first temperature is equal to or less than a predetermined threshold value, the first flow rate measurement mode is set, and the second temperature and the first temperature are set. A switching unit configured to set the second flow rate measurement mode when the difference between the temperature and the temperature is larger than the threshold value, and the power consumption is converted into the flow rate value of the fluid in the case of the first flow rate measurement mode. It is characterized by including a flow rate deriving unit configured to convert the difference between the second temperature and the first temperature into the value of the flow rate of the fluid in the case of the second flow rate measurement mode. To do.
Further, in one configuration example of the thermal flow meter of the present invention, the flow rate deriving unit sets the difference between the power consumption or the second temperature and the first temperature as a preset flow rate conversion type or flow rate. It is characterized in that it is converted into a value of the flow rate of the fluid using a conversion table.

Further, the present invention is more than a pipe for circulating the fluid to be measured, a first temperature measuring element arranged in the pipe and detecting the first temperature of the fluid, and the first temperature measuring element. It is arranged at the location of the pipe on the downstream side, a second temperature measuring element for detecting the second temperature of the fluid, and a location of the pipe on the downstream side of the second temperature measuring element. This is a flow rate measurement method using a thermal flow meter equipped with a heat generation / temperature measuring element that detects the heat generation temperature at the same time as heat generation, and the heat generation temperature is constant than the first temperature or the second temperature. The first step of supplying power so as to increase the value and causing the heat generation / temperature measuring element to generate heat, the second step of measuring the power consumption of the heat generation / temperature measuring element, and the second temperature. When the difference from the first temperature is equal to or less than a predetermined threshold value, the first flow rate measurement mode is set, and when the difference between the second temperature and the first temperature is larger than the threshold value, the second flow rate measurement mode is set. A third step as a mode, a fourth step of converting the power consumption into a value of the flow rate of the fluid in the case of the first flow rate measurement mode, and the first step in the case of the second flow rate measurement mode. It is characterized by including a fifth step of converting the difference between the temperature of 2 and the first temperature into the value of the flow rate of the fluid.

According to the present invention, two temperature measuring elements are provided on the upstream side of the heat generating / temperature measuring element, and the heat generating temperature of the heat generating / temperature measuring element is higher than the first temperature or the second temperature of the fluid by a certain value. When the difference between the second temperature and the first temperature is equal to or less than a predetermined threshold value, the power consumption is converted into a flow rate value in the first flow rate measurement mode. When the difference between the second temperature and the first temperature is larger than the threshold value, the difference between the second temperature and the first temperature is converted into the value of the flow rate. Accurate flow rate measurement in a small flow rate range can be realized.

FIG. 1 is a block diagram showing a configuration of a thermal flowmeter according to an embodiment of the present invention. FIG. 2 is a flowchart illustrating the operation of the temperature acquisition unit, the control calculation unit, and the power regulator of the thermal flow meter according to the embodiment of the present invention. FIG. 3 is a flowchart illustrating the operation of the power measuring unit, the switching unit, and the flow rate derivation unit of the thermal flow meter according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of the relationship between the temperature difference between the temperature measuring elements and the flow rate of the fluid in the extremely minute flow rate region. FIG. 5 is a diagram showing an example of the relationship between the temperature difference between the temperature measuring elements and the flow rate of the fluid in the extremely minute flow rate region when the position of the temperature measuring element is changed. FIG. 6 is a block diagram showing a configuration example of a computer that realizes the thermal flowmeter according to the embodiment of the present invention. FIG. 7 is a diagram illustrating the principle of the conventional thermal flowmeter. FIG. 8 is a diagram showing an example of the relationship between the heater power consumption and the flow rate of the fluid.

Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a thermal flowmeter according to an embodiment of the present invention. The thermal flow meter includes a pipe 1 made of, for example, quartz that allows the fluid to be measured to flow, a temperature measuring element 2a (temperature sensor) such as platinum arranged in the pipe 1, and a temperature measuring element 2a downstream of the temperature measuring element 2a. A temperature measuring element 2b (temperature sensor) such as platinum arranged at the location of the pipe 1 and a heat generation / temperature measuring element such as platinum arranged at the location of the pipe 1 downstream of the temperature measuring element 2b. The element 2c (heater), the temperature acquisition unit 3a for acquiring the temperature TRr1 (first temperature) of the fluid detected by the temperature measuring element 2a, and the temperature TRr2 (second temperature) of the fluid detected by the temperature measuring element 2b. The temperature acquisition unit 3b for acquiring the temperature), the temperature acquisition unit 3c for acquiring the temperature TRh (heat generation temperature) detected by the heat generation / temperature measuring element 2c, and the temperature difference (TRh-TRr1) are set to a constant value. A control calculation unit 4 that calculates the operation amount, a power regulator 5 that supplies power according to the operation amount to the heat generation / temperature measuring element 2c to generate heat, and a power measurement that measures the power consumption of the heat generation / temperature measurement element 2c. A switching unit that sets the first flow rate measurement mode when the temperature difference (TRr2-TRr1) is equal to or less than a predetermined threshold value, and sets the second flow rate measurement mode when the temperature difference (TRr2-TRr1) is larger than the threshold value. 7 and, in the case of the first flow rate measurement mode, the power consumption is converted into the value of the flow rate of the fluid, and in the case of the second flow rate measurement mode, the temperature difference (TRr2-TRr1) is converted into the value of the flow rate of the fluid. It includes a lead-out unit 8. The control calculation unit 4 and the power regulator 5 constitute a control unit 10.

The temperature measuring elements 2a and 2b and the heat generating / temperature measuring elements 2c are each formed on a silicon chip. The surface of the silicon chip on which the temperature measuring elements 2a and 2b are formed is adhered to the pipe 1 so as to face the outer wall of the pipe 1, so that the temperature measuring elements 2a and 2b are fixed to the pipe 1. .. The method of fixing the heat generation / temperature measuring element 2c is the same as the method of fixing the temperature measuring elements 2a and 2b.
The heat generation / temperature measuring element 2c is not limited to platinum, and can be replaced with a general metal material. Further, the temperature measuring elements 2a and 2b are not limited to platinum resistors, and for example, a thermopile made of aluminum and polysilicon may be used.

Next, the operation of the thermal flowmeter of this embodiment will be described. FIG. 2 is a flowchart illustrating the operations of the temperature acquisition units 3a, 3b, 3c, the control calculation unit 4, and the power regulator 5.
The temperature acquisition units 3a and 3b acquire the temperatures TRr1 and TRr2 of the fluid flowing through the pipe 1, respectively (step S100 in FIG. 2). Specifically, the temperature acquisition units 3a and 3b detect the resistance values of the temperature measuring elements 2a and 2b, respectively, and acquire the fluid temperatures TRr1 and TRr2 from the relationship between the resistance values and the temperature. Similarly, the temperature acquisition unit 3c acquires the temperature TRh of the heat generation / temperature measuring element 2c (step S100).

In the control calculation unit 4, the temperature difference (TRh-TRr1) obtained by subtracting the temperature TRr1 of the fluid on the upstream side from the temperature TRh of the heat generation / temperature measuring element 2c becomes a constant value (a control target value, for example, 10 ° C.). The operation amount is calculated as follows (FIG. 2, step S101). As a control calculation algorithm for calculating the manipulated variable, for example, there is a PID.
The power regulator 5 supplies power according to the amount of operation calculated by the control calculation unit 4 to the heat generation / temperature measuring element 2c to generate heat (step S102 in FIG. 2).

In this way, until the operation of the thermal flow meter is completed (YES in step S103 of FIG. 2), the processes of steps S100 to S102 are executed for each control cycle, and the temperature TRh of the heat generation / temperature measuring element 2c is the fluid on the upstream side. The temperature is controlled to be higher than the temperature TRr1 by a certain value.
In this embodiment, the operation amount is calculated so that the temperature difference (TRh-TRr1) becomes a constant value, but the operation amount is calculated so that the temperature difference (TRh-TRr2) becomes a constant value. May be good. However, since the flow rate range in which output inversion occurs is wider when the temperature TRr2 is used than when the temperature TRr1 is used, the heat generation / temperature measuring element and the temperature measuring element are constant in the practical thermal flowmeter. It is far away. That is, it is originally preferable to use the temperature difference (TRh-TRr1).

FIG. 3 is a flowchart illustrating the operations of the power measuring unit 6, the switching unit 7, and the flow rate derivation unit 8. When the temperature difference (TRr2-TRr1) between the temperature measuring elements 2b and 2a (TRr2-TRr1) is equal to or less than a predetermined threshold value Tref (YES in step S200 of FIG. 3), that is, when the flow rate range is larger than the minute flow rate range, the switching unit 7 is used. The first flow rate measurement mode for measuring the flow rate based on the power consumption P of the heat generation / temperature measuring element 2c is set as in the conventional case (step S201 in FIG. 3). Further, the switching unit 7 measures the flow rate based on the temperature difference (TRr2-TRr1) when the temperature difference (TRr2-TRr1) is larger than the threshold value Tref (NO in step S200), that is, in the case of a very small flow rate region. The flow rate measurement mode of No. 2 is set (step S202 in FIG. 3).

The power measuring unit 6 measures the power consumption P of the heat generation / temperature measuring element 2c (step S203 in FIG. 3). The power measuring unit 6 consumes the heat generating / temperature measuring element 2c according to the following equation based on, for example, the voltage V applied to the heat generating / temperature measuring element 2c from the power regulator 5 and the resistance value Rh of the heat generating / temperature measuring element 2c. Calculate the power P.
Q = V ² / Rh ・ ・ ・ (1)

In this way, the power consumption P required to raise the temperature TRh of the heat generation / temperature measuring element 2c by a certain value higher than the temperature TRr1 or TRr2 on the upstream side can be obtained.

In the case of the first flow rate measurement mode, the flow rate derivation unit 8 converts the power consumption P measured by the power measurement unit 6 into a flow rate value using a preset flow rate conversion formula, thereby converting the measurement target. The flow rate Q of the fluid is derived (step S204 in FIG. 3). When a flow rate conversion table in which the value of the flow rate Q corresponding to the power consumption P is registered is set instead of the flow rate conversion formula for converting the power consumption P into the flow rate Q, the flow rate derivation unit 8 sets the flow rate derivation unit 8. The value of the flow rate Q corresponding to the power consumption P may be obtained from the flow rate conversion table.

Further, in the case of the second flow rate measurement mode, the flow rate deriving unit 8 converts the temperature difference (TRr2-TRr1) between the temperature measuring elements 2b and 2a into a flow rate value using a preset flow rate conversion formula. As a result, the flow rate Q of the fluid to be measured is derived (step S205 in FIG. 3).
As shown in FIG. 4, since the linearity of the relationship between the temperature difference (TRr2-TRr1) and the flow rate Q is high in the extremely minute flow rate region, the flow rate Q can be obtained from the temperature difference (TRr2-TRr1).

When a flow rate conversion table in which the value of the flow rate Q corresponding to the temperature difference (TRr2-TRr1) is registered is set instead of the flow rate conversion formula for converting the temperature difference (TRr2-TRr1) into the flow rate Q. The flow rate deriving unit 8 may acquire the value of the flow rate Q corresponding to the temperature difference (TRr2-TRr1) from the flow rate conversion table.

The power measuring unit 6, the switching unit 7, and the flow rate deriving unit 8 execute the processes of steps S200 to S205 at regular time intervals until the operation of the thermal flowmeter is completed (YES in step S206 of FIG. 3).
In this way, in this embodiment, accurate flow rate measurement in a very small flow rate range can be realized.

The threshold Tref for determining whether the flow rate range is a micro flow range or a flow range larger than the micro flow range is the position of the temperature measuring elements 2a and 2b and the rising temperature of the heat generation / temperature measuring element 2c (control target value). (TRh-TRr1) or (TRh-TRr2)), it depends on the thickness of the adhesive that adheres the temperature measuring elements 2a and 2b and the heat generating / temperature measuring element 2c to the pipe 1, and the material and shape of the pipe 1. For example, since the temperature difference (TRr2-TRr1) between the temperature measuring elements 2b and 2a differs depending on the distance between the temperature measuring elements 2b and 2a, the appropriate threshold Tref also differs depending on the positions of the temperature measuring elements 2a and 2b.

50 in FIG. 5 shows the relationship between the temperature difference (TRr2-TRr1) and the flow rate Q when the distance D between the center point of the temperature measuring element 2a and the center point of the temperature measuring element 2b is 8.2 mm, and 51 is the distance. The relationship between the temperature difference (TRr2-TRr1) when D is 7.1 mm and the flow rate Q is shown, and 52 shows the relationship between the temperature difference (TRr2-TRr1) when the distance D is 5.8 mm and the flow rate Q. , 53 show the relationship between the temperature difference (TRr2-TRr1) and the flow rate Q when the distance D is 3.9 mm.

As described above, the threshold value Tref has different appropriate values depending on the positions of the temperature measuring elements 2a and 2b, the temperature rise of the heat generating / temperature measuring elements 2c, the thickness of the adhesive, and the material and shape of the pipe 1. It is necessary to set it in consideration. For example, the distance D between the center point of the temperature measuring element 2a and the center point of the temperature measuring element 2b is 7.1 mm, the temperature rise of the heat generating / temperature measuring element 2c is 10 ° C., the thickness of the adhesive is 30 μm or less, and the pipe 1 is installed. When it is made of quartz glass and the inner wall is 100 μm or less, the threshold Tref is set to, for example, 0.9 ° C.

Of the thermal flowmeters of this embodiment, at least the control calculation unit 4, the switching unit 7, and the flow rate derivation unit 8 are a computer having a CPU (Central Processing Unit), a storage device, and an interface, and their hardware resources. It can be realized by a program that controls. A configuration example of this computer is shown in FIG. The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. The temperature acquisition units 3a, 3b, 3c and the power regulator 5 are connected to the I / F 202. In such a computer, a program for realizing the flow rate measuring method of the present invention is stored in the storage device 201. The CPU 200 executes the process described in this embodiment according to the program stored in the storage device 201.

The present invention can be applied to a thermal flow meter.

1 ... Piping, 2a, 2b ... Temperature measuring element, 2c ... Heat generation / temperature measuring element, 3a, 3b, 3c ... Temperature acquisition unit, 4 ... Control calculation unit, 5 ... Power regulator, 6 ... Power measuring unit, 7 ... Switching unit, 8 ... Flow rate derivation unit, 10 ... Control unit.

Claims (4)

Piping configured to circulate the fluid to be measured and
A first temperature measuring element arranged in the pipe and configured to detect a first temperature of the fluid, and a first temperature measuring element.
A second temperature measuring element arranged at a position of the pipe on the downstream side of the first temperature measuring element and configured to detect the second temperature of the fluid, and a second temperature measuring element.
A heat-generating / temperature-measuring element arranged at a location of the pipe on the downstream side of the second temperature-measuring element and configured to detect the heat-generating temperature at the same time as heat generation.
A control unit configured to generate heat by supplying electric power so that the heat generation temperature is higher than the first temperature or the second temperature by a certain value to generate heat of the heat generation / temperature measuring element.
A power measuring unit configured to measure the power consumption of the heat generation / temperature measuring element, and
When the difference between the second temperature and the first temperature is equal to or less than a predetermined threshold value, the first flow rate measurement mode is set, and when the difference between the second temperature and the first temperature is larger than the threshold value. A switching unit configured to be in the second flow rate measurement mode,
In the case of the first flow rate measurement mode, the power consumption is converted into the value of the flow rate of the fluid, and in the case of the second flow rate measurement mode, the difference between the second temperature and the first temperature is described. A thermal flow meter comprising a flow rate deriving unit configured to convert to a fluid flow rate value. In the thermal flow meter according to claim 1,
The flow rate deriving unit converts the power consumption or the difference between the second temperature and the first temperature into a flow rate value of the fluid using a preset flow rate conversion formula or flow rate conversion table. A thermal flowmeter featuring. A pipe that circulates the fluid to be measured, a first temperature measuring element that is arranged in the pipe and detects the first temperature of the fluid, and the pipe that is downstream of the first temperature measuring element. A second temperature measuring element that is disposed at a location and detects the second temperature of the fluid, and a second temperature measuring element that is disposed at a location of the pipe that is downstream of the second temperature measuring element, and generates heat at the same time as heat generation. It is a flow measurement method using a thermal flow meter equipped with a heat generation / temperature measuring element that detects temperature.
The first step of supplying electric power so that the heat generation temperature becomes higher than the first temperature or the second temperature by a certain value to generate heat of the heat generation / temperature measuring element.
The second step of measuring the power consumption of the heat generation / temperature measuring element and
When the difference between the second temperature and the first temperature is equal to or less than a predetermined threshold value, the first flow rate measurement mode is set, and when the difference between the second temperature and the first temperature is larger than the threshold value. In addition to the third step of setting the second flow rate measurement mode,
In the case of the first flow rate measurement mode, the fourth step of converting the power consumption into the flow rate value of the fluid, and
A flow rate measuring method comprising a fifth step of converting a difference between the second temperature and the first temperature into a value of the flow rate of the fluid in the case of the second flow rate measuring mode. In the flow rate measuring method according to claim 3,
In the fourth and fifth steps, the power consumption or the difference between the second temperature and the first temperature is set to the value of the flow rate of the fluid using a preset flow rate conversion formula or flow rate conversion table. A flow rate measuring method comprising a step of converting to.

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