阅读说明：本技术 热式流量计 (Thermal flowmeter ) 是由 山崎吉夫 松永晋辅 于 2019-06-12 设计创作，主要内容包括：本发明提供一种可靠地对配管内不存在液体的空状态进行检测的热式流量计。设置空状态检测部(8),将通过控制部(5)把温度差(TRh－TRr)控制为固定值时的、供给至加热器(3)的供给电力P与阈值Pth进行比较,在供给至加热器(3)的供给电力P比阈值Pth小的情况下,判断为配管(2)内中不存在液体的空状态。阈值Pth被确定为比下述的供给至加热器(3)的供给电力P低的值,即,以设想的作为测定对象的液体中热导率最低的液体为基准,并且该热导率最低的液体在配管(2)内的流动处于停止状态下的、通过控制部(5)把温度差(TRh－TRr)控制为固定值时的、供给至加热器(3)的供给电力P。(The invention provides a thermal flowmeter which can reliably detect the empty state without liquid in a pipe. An empty state detection unit (8) is provided, and when the supply power P supplied to the heater (3) is compared with a threshold value Pth when the temperature difference (TRh-TRr) is controlled to a fixed value by a control unit (5), and when the supply power P supplied to the heater (3) is smaller than the threshold value Pth, it is determined that there is no empty state of the liquid in the pipe (2). The threshold value Pth is determined as a value lower than the supply power P to be supplied to the heater (3) when the temperature difference (TRh-TRr) is controlled to a fixed value by the control unit (5) with reference to a liquid having the lowest thermal conductivity among the liquids to be measured assumed and in a state where the flow of the liquid having the lowest thermal conductivity in the pipe (2) is stopped.)

1. A thermal flowmeter is characterized by comprising:

a pipe configured to flow a liquid to be measured;

a heater provided in the pipe and configured to generate heat upon receiving supply of electric power;

a temperature sensor provided upstream of the heater and configured to detect a temperature of the liquid;

a control unit configured to obtain a temperature difference between a heat generation temperature of the heater detected from a change in resistance value of the heater and a temperature of the liquid detected by the temperature sensor, and to control power supplied to the heater so that the temperature difference becomes a fixed value;

a sensor output unit configured to output, as a sensor output, a value corresponding to a state of heat diffusion in the liquid when the temperature difference is controlled to a fixed value by the control unit;

a flow rate calculation unit configured to calculate a flow rate of the liquid flowing through the pipe based on a sensor output from the sensor output unit; and

and an empty state detection unit configured to compare the supply power supplied to the heater when the temperature difference is controlled to a fixed value by the control unit with a predetermined threshold value, and determine that an empty state in which the liquid is not present in the pipe is present when the supply power supplied to the heater is smaller than the threshold value.

2. Thermal flow meter according to claim 1,

the threshold value is determined as a value lower than the power to be supplied to the heater when the temperature difference is controlled to a fixed value by the control unit with reference to a liquid having the lowest thermal conductivity among the liquids to be measured, which are assumed to be the objects of measurement, and with the flow of the liquid having the lowest thermal conductivity in the pipe being stopped.

3. Thermal flow meter according to claim 2,

the liquid having the lowest thermal conductivity among the liquids to be measured is assumed to be a fluorinated liquid.

4. Thermal flow meter according to any of claims 1 to 3,

the sensor output unit outputs, as the sensor output, the power supplied to the heater when the temperature difference is controlled to a fixed value by the control unit.

5. Thermal flow meter according to any of claims 1 to 3,

the sensor output unit outputs, as the sensor output, a temperature difference of the liquid upstream and downstream of the heater when the temperature difference is controlled to a fixed value by the control unit.

Technical Field

The present invention relates to a thermal flowmeter for measuring a flow rate of a fluid flowing through a pipe by utilizing a heat diffusion effect in the fluid.

Background

Conventionally, a technique for measuring a flow rate or a flow velocity of a fluid flowing through a flow path has been widely used in the industrial and medical fields. As devices for measuring a flow rate or a flow velocity, there are various types such as an electromagnetic flowmeter, a vortex flowmeter, a coriolis flowmeter, and a thermal flowmeter, and they are used in different ways depending on the application.

The thermal flowmeter can detect gas, and has the advantages of almost no pressure loss, capability of measuring mass flow rate, and the like. In addition, a thermal flowmeter capable of measuring the flow rate of a corrosive liquid by forming a flow path with a glass tube is also used (see patent documents 1 and 2). The thermal flowmeter for measuring the flow rate of the liquid as described above is suitable for measuring a minute flow rate.

The thermal flowmeter includes a system (system 1) in which the power supplied to the heater is used as the sensor output, and a system (system 2) in which the temperature difference between the upstream and downstream sides of the heater is used as the sensor output. For example, when the fluid is water and the flow rate of the water is measured, the power supplied to the heater is controlled so that the heater temperature becomes a fixed temperature such as positive 10 ℃ with respect to the water temperature, the power supplied to the heater at this time or the temperature difference between the upstream and downstream sides of the heater is set as a sensor output (a value corresponding to the state of heat diffusion in the fluid), and the flow rate of the water is determined from the sensor output.

[ mode 1 ]

Fig. 5 is a diagram illustrating the principle (mode 1) of a thermal flowmeter for measuring the flow rate of fluid based on the electric power supplied to the heater. In embodiment 1, a water temperature sensor (temperature measuring element) 101 and a heater (heat generation-temperature measuring element) 102 are provided in a pipe 100 through which a fluid to be measured flows, and electric power P supplied to the heater 102 is controlled so that a temperature difference between a temperature (heat generation temperature) TRh detected from a change in resistance value of the heater 102 and a temperature (water temperature) TRr detected by the water temperature sensor 101 becomes a fixed value (TRh-TRr ═ Const). At this time, the flow rate Q of the fluid and the supply power P supplied to the heater 102 are in a relationship of Q ∞ P, and therefore the flow rate Q can be calculated from the supply power P supplied to the heater 102.

[ mode 2 ]

Fig. 6 is a diagram illustrating the principle (mode 2) of a thermal flowmeter for measuring the flow rate of fluid based on the temperature difference between the upstream and downstream sides of the heater. In embodiment 2, a water temperature sensor (temperature measuring element) 101, a heater (heat generation-temperature measuring element) 102, an upstream temperature sensor (temperature measuring element) 103, and a downstream temperature sensor (temperature measuring element) 104 are provided in a pipe 100 through which a fluid to be measured flows, and electric power P supplied to the heater 102 is controlled so that a temperature difference between a temperature (heat generation temperature) TRh detected from a change in the resistance value of the heater 102 and a temperature (water temperature) TRr detected by the water temperature sensor 101 becomes a fixed value (TRh-TRr ═ Const). At this time, since the temperature difference (TRu-TRd) between the temperature TRu of the fluid detected by the upstream temperature sensor 103 and the temperature TRd of the fluid detected by the downstream temperature sensor 104 is in the relationship of Q ∈ (TRu-TRd), the flow rate Q can be calculated from the temperature difference (TRu-TRd) between the upstream and downstream sides of the heater 102.

In addition, in the above-described mode 1, the supply power P supplied to the heater 102 is output as a sensor, and in the above-described mode 2, the temperature difference (TRu-TRd) upstream and downstream of the heater 102 is output as a sensor. Here, when the sensor output is S, it is known that the sensor output S is simply expressed by the following expression (1).

S＝(A+B·μ^1/2)·ΔT····(1)

In the equation (1), A, B is a constant determined by the area of the water temperature sensor 101, the heater 102, and the like, the thermal conductivity of the fluid, the density of the fluid, the viscosity of the fluid, the specific heat capacity, and the like, μ is the flow rate, and Δ T is the heating temperature of the heater 102 (the heating temperature from the water temperature).

Disclosure of Invention

[ problems to be solved by the invention ]

In such a thermal flowmeter, when the fluid is a liquid, it is necessary to determine whether or not the pipe is in a state where no liquid is present (empty state). However, the conventional thermal flowmeter has no means for determining whether or not the flowmeter is in an empty state, and cannot distinguish between an empty state and a state in which the flow rate is zero (the pipe contains a liquid but the flow of the liquid is stopped).

The present invention has been made to solve the above-described problems, and an object thereof is to provide a thermal flowmeter capable of reliably detecting an empty state in which no liquid is present in a pipe.

[ means for solving the problems ]

To achieve the above object, the present invention is characterized by comprising: a pipe (2) through which a liquid to be measured flows; a heater (3) which is provided in the pipe and configured to generate heat upon receiving a supply of electric power; a temperature sensor (4) which is provided upstream of the heater and is configured to detect the temperature of the liquid; a control unit (5) configured to obtain a temperature difference between the heat generation temperature of the heater detected from the change in the resistance value of the heater and the temperature of the liquid detected by the temperature sensor, and to control the power supplied to the heater so that the temperature difference becomes a fixed value; sensor output units (6, 11) configured to output, as a sensor output (S), a value corresponding to a state of heat diffusion in the liquid when the temperature difference is controlled to a fixed value by the control unit; a flow rate calculation unit (7) configured to calculate the flow rate of the liquid flowing through the pipe based on the sensor output from the sensor output unit; and an empty state detection unit (8) configured to compare the supply power supplied to the heater when the temperature difference is controlled to a fixed value by the control unit with a predetermined threshold value (Pth), and determine that an empty state in which no liquid is present in the pipe exists when the supply power supplied to the heater is smaller than the threshold value.

In the present invention, the supply power supplied to the heater when the temperature difference is controlled to a fixed value is compared with a predetermined threshold value, and when the supply power supplied to the heater is smaller than the threshold value, it is determined that there is no empty state of the liquid in the pipe. For example, the threshold value is determined to be a value lower than the supply power to the heater when the temperature difference is controlled to a fixed value by the control unit with the liquid having the lowest thermal conductivity among the assumed liquids to be measured as a reference and the flow of the liquid having the lowest thermal conductivity in the pipe being in a stopped state, and when the supply power to the heater is smaller than the threshold value, it is determined that there is no empty state of the liquid in the pipe.

In the above description, the components on the drawings corresponding to the components of the invention are shown by reference numerals with parentheses, as an example.

[ Effect of the invention ]

As described above, according to the present invention, since the supply power supplied to the heater when the temperature difference is controlled to a fixed value by the control unit is compared with the predetermined threshold value, and it is determined that there is no empty state of the liquid in the pipe when the supply power supplied to the heater is smaller than the threshold value, it is possible to reliably detect an empty state in which no liquid is present in the pipe by distinguishing the empty state from a state in which the flow rate is zero.

Drawings

Fig. 1 is a block diagram showing a configuration of a main part of a thermal type flow meter according to an embodiment of the present invention.

Fig. 2 is a graph showing a relationship between the flow rate Q of the liquid flowing through the pipe and the supply power P to the heater when the temperature difference (TRh-TRr) is controlled to a fixed value.

Fig. 3 is an enlarged view of the vicinity of the flow zero point in fig. 2.

Fig. 4 is a diagram showing an application example of the present invention to a system (system 2) in which a temperature difference between the liquid upstream and downstream of the heater is used as a sensor output.

Fig. 5 is a diagram illustrating the principle (mode 1) of a thermal flowmeter for measuring the flow rate of fluid based on the electric power supplied to the heater.

Fig. 6 is a diagram illustrating the principle (mode 2) of a thermal flowmeter for measuring the flow rate of fluid based on the temperature difference between the upstream and downstream sides of the heater.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Fig. 1 is a block diagram showing a configuration of a main part of a thermal type flowmeter 1(1A) according to an embodiment of the present invention. The thermal flow meter 1A is realized by hardware including a processor and a storage device, and a program for realizing various functions in cooperation with the hardware, and the thermal flow meter 1A includes a pipe 2, a heater (heating/temperature measuring element) 3, a water temperature sensor (temperature measuring element) 4, a control unit 5, an electric power measuring unit (sensor output unit) 6, a flow rate calculating unit 7, and an empty state detecting unit 8.

The pipe 2 is made of, for example, glass, and a liquid (water in this example) to be measured flows therethrough. The heater 3 is provided on the outer wall of the pipe 2, and generates heat upon receiving power supply from the control unit 5.

The water temperature sensor 4 is provided on the outer wall of the pipe 2 on the upstream side of the heater 3, and detects the temperature of the liquid flowing through the pipe 2 as TRr. The water temperature sensor 4 is provided at a position not affected by the heat of the heater 3 by separating the water temperature sensor 4 from the heater 3 to some extent. The temperature TRr of the liquid detected by the water temperature sensor 4 is sent to the control unit 5.

The control unit 5 receives the heat generation temperature TRh of the heater 3 detected from the change in the resistance value of the heater 3 and the temperature TRr of the liquid from the water temperature sensor 4, obtains a temperature difference (TRh-TRr) between the heat generation temperature TRh and the temperature TRr of the liquid, and controls the electric power supplied to the heater 3 so that the temperature difference becomes a fixed value (for example, 10 ℃).

The electric power measuring unit 6 measures the supply electric power P supplied to the heater 3 when the temperature difference (TRh-TRr) is controlled to a fixed value by the control unit 5, and transmits the measured supply electric power P to the flow rate calculating unit 7 as a sensor output (a value corresponding to the state of heat diffusion in the liquid) S.

The flow rate calculating unit 7 converts the sensor output S (the supply power P) from the power measuring unit 6 into a value of a flow rate by using a preset flow rate conversion formula, thereby obtaining the flow rate Q of the liquid flowing through the pipe 2.

The empty state detection unit 8 receives as a branch input the sensor output S (supply power P) from the power measurement unit 6 to be sent to the flow rate calculation unit 7, that is, the supply power P to be supplied to the heater 3 when the temperature difference (TRh-TRr) is controlled to a fixed value by the control unit 5, compares the received supply power P to be supplied to the heater 3 with a predetermined threshold Pth, and determines that there is an empty state in which no liquid is present in the pipe 2 when the supply power P to be supplied to the heater 3 is smaller than the threshold Pth.

In the present embodiment, the threshold Pth is set to a value lower than the supply power P supplied to the heater 3, and the supply power P supplied to the heater 3 is set to a value as follows: the value of the supply power P to be supplied to the heater 3 is set when the temperature difference (TRh-TRr) is controlled to a fixed value by the control unit 5 with reference to the liquid having the lowest thermal conductivity among the liquids to be measured assumed and the flow of the liquid having the lowest thermal conductivity in the pipe 2 being stopped.

Fig. 2 shows a relationship between the flow rate Q of the liquid flowing through the pipe 2 and the supply power P to the heater 3 when the temperature difference (TRh-TRr) is controlled to a fixed value. Fig. 2 shows, as an example, the relationship between the flow rate Q of the liquid to be measured, i.e., "water", "30% sulfuric acid", "50% hydrogen peroxide", "isopropyl alcohol" and "fluorinated liquid", and the supplied power P. Fig. 3 is an enlarged view of the vicinity of the flow zero point in fig. 2. In the figure, P0 represents electric power (empty electric power) in an empty state in which no liquid is present in the pipe 2.

As can be seen from fig. 3, the electric power P0 in the null state is a value smaller than that when the flow rate is zero. When the pipe 2 is empty, the pipe is filled with gas (air), and the thermal conductivity of the gas is lower than that of the liquid, so that the heat of the heater 3 is not easily transmitted. As a result, the power consumption of the heater 3 decreases, and the power supply P to the heater 3 decreases.

In the present embodiment, the liquid having the lowest thermal conductivity among the liquids to be measured is assumed to be the fluorinated liquid, and the threshold Pth is determined to be a value lower than the supply power P to be supplied to the heater 3 when the temperature difference (TRh-TRr) is controlled to a fixed value by the control unit 5 in a state where the flow of the fluorinated liquid in the pipe 2 is stopped.

As described above, according to the present embodiment, since the supply power P supplied to the heater 3 when the temperature difference (TRh-TRr) is controlled to a fixed value by the control unit 5 is compared with the threshold Pth, and when the supply power P supplied to the heater 3 is smaller than the threshold Pth, it is determined that there is no empty state of the liquid in the pipe 2, it is possible to reliably detect an empty state in which no liquid is present in the pipe 2 by distinguishing the empty state from a state in which the flow rate is zero.

In the above-described embodiment, the case where the present invention is applied to the mode (mode 1) in which the supply power to the heater 3 is used as the sensor output S has been described, but the present invention may be applied to the mode (mode 2) in which the temperature difference (TRu-TRd) of the liquid upstream and downstream of the heater 3 is used as the sensor output S. Fig. 4 shows an example in which the present invention is applied to the mode 2.

In the thermal flow meter 1(1B) shown in fig. 4, an upstream temperature sensor (temperature measuring element) 9 for detecting the temperature TRu of the liquid on the upstream side of the heater 3 and a downstream temperature sensor (temperature measuring element) 10 for detecting the temperature TRd of the liquid on the downstream side of the heater 3 are provided on the outer wall of the pipe 2 with the heater 3 interposed therebetween. Further, a temperature difference calculation unit (sensor output unit) 11 is provided for the upstream temperature sensor 9 and the downstream temperature sensor 10.

The temperature difference calculation unit 11 calculates a temperature difference (TRu-TRd) between the temperature TRu of the liquid on the upstream side and the temperature TRd of the liquid on the downstream side of the heater 3) when the control unit 5 controls the supply power to the heater 3 so that the temperature difference (TRh-TRr) between the heat generation temperature TRh and the temperature TRr of the liquid is a fixed value, and transmits the calculated temperature difference (TRu-TRd) on the upstream side and the downstream side of the heater 3 to the flow rate calculation unit 7 as a sensor output (value corresponding to the state of heat diffusion in the liquid) S.

The flow rate calculating unit 7 converts the sensor output S (temperature difference (TRu-TRd) between the upstream and downstream sides of the heater 3) from the temperature difference calculating unit 11 into a value of a flow rate by using a preset flow rate conversion formula, thereby obtaining the flow rate Q of the liquid flowing through the pipe 2.

The power measuring unit 6 measures the supply power P supplied to the heater 3 when the temperature difference (TRh-TRr) is controlled to a fixed value by the control unit 5, and transmits the measured supply power P supplied to the heater 3 to the empty state detecting unit 8.

The empty state detection unit 8 receives the supply power P supplied to the heater 3 from the power measurement unit 6 as an input, compares the input supply power P supplied to the heater 3 with a predetermined threshold Pth, and determines that there is no empty state of the liquid in the pipe 2 when the supply power P supplied to the heater 3 is smaller than the threshold Pth.

In the above embodiment, the flow rate calculating unit 7 converts the sensor output S into a value of the flow rate using a flow rate conversion formula, but a flow rate conversion table in which a value of the flow rate Q corresponding to the sensor output S is registered may be used, and the value of the flow rate Q corresponding to the sensor output S may be obtained from the flow rate conversion table. In the above embodiment, the water temperature sensor 4 is provided on the outer wall of the pipe 2, but may be provided on the inner wall of the pipe 2.

[ extension of embodiment ]

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made in the configuration and detail of the present invention within the scope of the technical idea of the present invention. For example, in the description of the present invention, the empty state is defined as a state in which no liquid is present in the pipe 2 for convenience, but this does not strictly mean that no liquid is present in the pipe 2, and for example, a state in which a small amount of liquid in a droplet shape is present is obviously included.

Description of the symbols

1(1A, 1B) … thermal flowmeter, 2 … piping, 3 … heater, 4 … water temperature sensor, 5 … controller, 6 … power measuring unit, 7 … flow rate calculator, 8 … empty state detector, 9 … upstream temperature sensor, 10 … downstream temperature sensor, and 11 … temperature difference calculator.