JP2009103589A - Thermal flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a thermal flowmeter for measuring a flow rate over a wide range of measurements. <P>SOLUTION: The thermal flowmeter for controlling the temperature of a liquid flowing in a flow path and measuring a flow rate, based on the temperature difference of a fluid between the upstream side and the downstream side in a temperature control section, includes: the flow path, formed with a wetted section entirely made of glass; a heat transfer means provided on the flow path; a first temperature difference detecting means provided on the flow path and spaced equidistant from the heat transfer means; a second temperature difference detecting means provided on the flow path and spaced equidistant from the heat transfer means, outside the first temperature difference detecting means; and a calculation control means for controlling the temperature of the liquid flowing in the flow path by use of the heat transfer means, selecting the first or second temperature difference detecting means, in response to the measured flow rate, and obtaining the flow rate, based on the detected temperature difference. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermal type flow meter that controls the temperature of a liquid flowing in a flow path and measures a flow rate based on a temperature difference between upstream and downstream fluids of a temperature control portion, and in particular, the flow rate can be measured in a wider measurement range. It relates to a possible thermal flow meter.

  Prior art documents related to a thermal flow meter that controls the temperature of the liquid flowing through the conventional flow path and measures the flow rate based on the temperature difference between the upstream and downstream fluids of the temperature control portion include the following. is there.

Japanese Patent Laid-Open No. 05-077975 Japanese Patent Laid-Open No. 07-159215 JP-A-10-082678 JP 2002-168668 A JP 2006-010322 A JP 2006-226996 A

  FIG. 5 is a structural block diagram showing an example of such a conventional thermal flow meter. In FIG. 5, 1 is a flow path composed of a thin metal tube, 2 is a heat transfer means such as a heater that heats the temperature of the fluid flowing through the flow path 1 to a constant temperature, and 3 and 4 are thermistors and platinum measuring devices. Temperature detection means 5 such as a temperature resistor is an arithmetic control means such as a CPU (Central Processing Unit) for obtaining a flow rate based on the temperature difference between the upstream and downstream fluids.

  As shown by “FL01” in FIG. 5, a heat transfer means 2 is provided in the central portion of the flow path 1 through which the liquid to be measured flows, and is located on the flow path 1 at equal intervals from the heat transfer means 2. Temperature detection means 3 and 4 are provided.

  The outputs of the temperature detection means 3 and 4 are connected to the calculation control means 5, respectively, and a control signal for temperature control from the calculation control means 5 is connected to the heat transfer means 2.

  Here, the operation of the conventional example shown in FIG. 5 will be described with reference to FIG. FIG. 6 is a characteristic curve diagram showing an example of the temperature distribution of the liquid to be measured in the flow path with respect to the position of the flow path. The arithmetic control unit 5 controls the heat transfer unit 2 so that the liquid to be measured has a constant temperature that is about several degrees higher than the temperature of the liquid to be measured that has been measured in advance.

  In such a state, when the flow rate is zero, as indicated by “CH11” in FIG. 6, the temperature distribution has a symmetric temperature distribution centered on the installation position of the heat transfer means 2 indicated by “HT11” in FIG. For this reason, the temperature in the installation position of the temperature detection means 3 and 4 shown by "TS11" and "TS12" in FIG. 6 becomes equal. In other words, the temperature difference is zero.

  On the other hand, when the fluid in the flow path 1 flows, the peak of the temperature distribution shifts to the downstream side as indicated by “CH12” in FIG. Therefore, the temperatures at the installation positions of the temperature detecting means 3 and 4 indicated by “TS11” and “TS12” in FIG. 6 are different from each other, and a temperature difference as indicated by “DT11” in FIG. 6 is generated. .

  Since such a temperature difference becomes a signal depending on the flow rate of the liquid to be measured, the flow rate of the liquid to be measured flowing through the flow path 1 can be obtained by the arithmetic control unit 5 based on such a temperature difference.

  As a result, the temperature of the liquid to be measured flowing through the flow path 1 is controlled by the heat transfer means 2, the temperature of the fluid upstream and downstream of the heat transfer means 2 is measured by the two temperature detection means 3 and 4, and the arithmetic control is performed. By obtaining the flow rate based on the temperature difference of the temperature by means 5, it becomes possible to measure the flow rate of the liquid to be measured.

  However, the conventional example shown in FIG. 5 has a problem that the flow rate of the liquid corroding the metal cannot be measured because a metal thin tube or the like is used as the flow path 1.

  For this reason, the above-mentioned “Patent Document 2” describes a thermal flow meter (mass flow sensor) in which a flow path is formed on a glass substrate having excellent corrosion resistance.

  7 and 8 are a perspective view and a cross-sectional view showing another example of the conventional thermal flow meter described in "Patent Document 2". 7 and 8, 6 is a glass substrate, 7 and 9 are silicon substrates, 8 is a heat transfer means, and 10 is a flow path formed in the glass substrate 6.

  A flow path 10 having a long hole is formed in the central portion of the glass substrate 6 by ultrasonic processing, laser processing, sand blast processing, wet etching, or the like. A silicon substrate 7 is bonded to the upper surface of the glass substrate 6 by anodic bonding.

  Further, a silicon substrate 9 is bonded to the lower surface of the glass substrate 6 by anodic bonding, and “HL21” and “HL22” in FIG. 7 are attached to the silicon substrate 9 adjacent to both end portions of the flow path 10 formed in the glass substrate 6. Are formed, which function as inflow holes or discharge holes for the liquid to be measured, respectively.

  Further, a heat transfer means 8 (also serving as a temperature detection means) such as a heater made of a metal having a large resistance temperature coefficient such as platinum or nickel is formed on the silicon substrate 7, and is formed on the silicon substrate 7 and the glass substrate 6. The wiring is appropriately formed.

  Here, in the conventional example shown in FIGS. 7 and 8, although the flow path 10 is formed on the glass substrate 6, the silicon substrates 7 and 9 are used on the upper and lower surfaces of the flow path 10. Again, there is a problem with corrosion resistance.

  On the other hand, by replacing the silicon substrates 7 and 9 with a glass substrate in the conventional example shown in FIGS. 7 and 8, all the wetted parts become glass and the corrosion resistance is improved, but the glass has a low thermal conductivity. When the flow rate of the liquid flowing through the flow path is large, the liquid immediately below the heat transfer means 8 is not sufficiently warmed.

  For this reason, when the temperature immediately below the heat transfer means 8 is not sufficiently warmed, the temperature difference between the upstream side and the downstream side changes as the flow rate increases.

  On the other hand, when the flow rate is small and the temperature just below the heat transfer means 8 is sufficiently warm, the temperature difference between the upstream side and the downstream side increases as the flow rate increases.

  That is, FIG. 9 is a characteristic curve diagram showing the relationship between the temperature difference between the upstream side and the downstream side and the flow rate. As shown in “TD31” in FIG. 9, the temperature difference between the upstream side and the downstream side is a peak. There was a problem that the measurable flow rate range becomes extremely narrow.

  For example, although the corrosion resistance is improved by replacing the silicon substrates 7 and 9 with glass substrates in the conventional example shown in FIGS. 7 and 8, the flow rate as shown by “AR31” in FIG. There is a problem that the flow rate can be measured only under the condition that the temperature immediately below the means 8 is sufficiently warm.

  In order to solve such problems, “Patent Document 5” related to the application of the present applicant has been devised. 10 is a configuration block diagram showing another example of the thermal flow meter described in “Patent Document 5”, and FIG. 11 is a plan view and a cross-sectional view showing a specific example of the sensor portion of another example of the thermal flow meter. It is.

  10 and 11, 11 and 12 are glass substrates, 13 is a heat transfer means such as a heater, 14 and 15 are temperature detection means such as a thermistor and a platinum resistance temperature detector, 16 is a flow path through which the liquid to be measured flows, Reference numeral 17 denotes arithmetic control means such as a CPU for obtaining a flow rate based on the temperature difference between the upstream and downstream fluids.

  As shown by “FL41” in FIG. 10, a heat transfer means 13 is provided in the central portion of the flow path 16 through which the liquid to be measured flows, and is located on the flow path 16 at equal intervals from the heat transfer means 13. Temperature detection means 14 and 15 are provided.

  Further, as indicated by “TU41” and “TD41” in FIG. 10, the outputs of the temperature detecting means 14 and 15 are respectively connected to the arithmetic control means 17 and from the arithmetic control means 17 as indicated by “CT41” in FIG. A control signal for temperature control is connected to the heat transfer means 13.

  Furthermore, the specific example of the sensor part of another example of a thermal type flow meter is demonstrated in detail using FIG.

  A rectangular groove is formed along the longitudinal direction of the glass substrate 12 at the central portion in the short direction of the glass substrate 12 by ultrasonic processing, laser processing, sandblasting, wet etching, or the like. In addition, the glass substrate 11 is bonded to the glass substrate 12 on the side where the rectangular groove is formed by bonding, thermocompression bonding, or the like, and a flow path 16 is formed in which the liquid contact portion is entirely made of glass.

  Further, a heat transfer means 13 such as a heater is formed on the glass substrate 11 on the side not in contact with the flow path 16 and on the central portion of the flow path 16 by vapor deposition, sputtering, or the like. Temperature detecting means 14 and 15 are formed by vapor deposition, sputtering or the like on the glass substrate 11 on the upper side and not in contact with the flow path 16 and at equal intervals from the heat transfer means 13.

  That is, since the heat transfer means 13 and the temperature detection means 14 and 15 are formed on the glass substrate 11 on the side not in contact with the flow path 16, they are in a non-wetted state.

  Here, the operation of another example of the thermal flow meter shown in FIGS. 10 and 11 will be described with reference to FIG. FIG. 12 is a characteristic curve diagram showing the relationship between the temperature difference between the upstream side and the downstream side with respect to the flow rate, the temperature sum, and the value obtained by dividing the temperature difference by the temperature sum. However, description of operations similar to those of the conventional example shown in FIG.

  The arithmetic control means 17 controls the heat transfer means 13 so that the liquid under measurement has a constant temperature that is several degrees higher than the temperature of the liquid under measurement measured in advance.

  In such a state, the temperature difference between the temperatures detected by the upstream temperature detection means 14 and the downstream temperature detection means 15 becomes a signal that depends on the flow rate of the liquid to be measured. The flow rate of the liquid to be measured flowing through the flow path 16 can be obtained by the arithmetic control means 17.

  However, as described in the above-described conventional example, when the liquid contact portion of the flow path is all made of glass, for example, the temperature difference is indicated by “TD51” in FIG. 12 because of the small thermal conductivity of the glass. Thus, there is a problem that the characteristic has a peak and the measurable flow rate range becomes extremely narrow.

  For this reason, the arithmetic control means 17 obtains the temperature difference between the temperatures detected by the upstream temperature detection means 14 and the downstream temperature detection means 15 and at the upstream temperature detection means 14 and the downstream temperature detection means 15. The temperature difference is normalized by finding the temperature sum of the detected temperatures and dividing the temperature difference by the temperature sum.

  For example, the temperature sum of the temperatures detected by the upstream temperature detecting means 14 and the downstream temperature detecting means 15 is a characteristic curve as shown by “TA51” in FIG. By dividing the temperature difference indicated by “TD51” in FIG. 12, a normalized temperature difference characteristic curve indicated by “NT51” in FIG. 12 is obtained.

  Since the normalized temperature difference as indicated by “NT51” in FIG. 12 shows a monotonic increase in a wide flow range, it can be seen that a wide flow range can be measured.

  As a result, the temperature of the liquid to be measured flowing through the channel 16 whose liquid contact part is entirely made of glass is controlled by the heat transfer means 13, and the upstream side and the downstream side of the heat transfer means 13 by the two temperature detection means 14 and 15. The temperature of the fluid is measured, the temperature difference of the temperature is calculated by the arithmetic control means 17 to obtain a normalized temperature difference, and the flow rate is obtained on the basis of the normalized temperature difference. This makes it possible to measure a wide flow rate range of the liquid to be measured.

However, in another example of the thermal flow meter shown in FIG. 10 and FIG. 11, as the flow rate of the fluid to be measured flowing through the flow path (thin tube) increases, the temperature distribution change amount with respect to the flow rate change decreases, and the temperature difference ( Flow rate signal) is saturated. For this reason, even when the flow rate is obtained based on the standardized temperature difference, there is a problem that the measurement range becomes narrow.
Therefore, the problem to be solved by the present invention is to realize a thermal flow meter capable of measuring a flow rate in a wider measurement range.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the temperature difference between the upstream and downstream fluids of the temperature control part,
A flow path in which all the liquid contact parts are made of glass, heat transfer means provided in the flow path, and a first temperature difference provided on the flow path at equal intervals from the heat transfer means Detection means; second temperature difference detection means provided on the flow path and outside the first temperature difference detection means and at equal intervals from the heat transfer means; and the flow path Calculation control means for controlling the temperature of the liquid flowing through the heat transfer means and calculating the flow rate based on the detected temperature difference by selecting the first or second temperature difference detection means according to the flow rate to be measured. By providing, it becomes possible to measure the flow rate in a wider measurement range.

The invention according to claim 2
In the thermal type flow meter which is the invention according to claim 1,
The arithmetic control means is
When it is determined that the flow rate to be measured is in the low flow rate region, the flow rate is obtained based on the temperature difference detected by the first temperature difference detection unit closest to the heat transfer unit, and the flow rate to be measured is in the high flow rate region. When it is determined that there is, the flow rate can be measured in a wider measurement range by obtaining the flow rate based on the temperature difference detected by the second temperature difference detection unit farthest from the heat transfer unit.

The invention described in claim 3
In the thermal type flow meter which is the invention according to claim 1,
The temperature difference characteristic curve with respect to the flow rate of the first temperature difference detection means and the temperature difference characteristic curve with respect to the flow rate of the second temperature difference detection means overlap with each other. By adjusting the interval between the two temperature difference detection means, the flow rate can be measured in a wider measurement range.

The present invention has the following effects.
According to the first, second, and third aspects of the invention, the first temperature difference detecting means is provided on the flow path at equal intervals from the heat transfer means, and the first temperature difference detection is provided on the flow path. The second temperature difference detection means is provided outside the means and at equal intervals from the heat transfer means, and the temperature difference detection means (combination of temperature detection means) is appropriately selected according to the flow rate to be measured. This makes it possible to measure the flow rate in a wider measurement range.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration block diagram showing an embodiment of a thermal flow meter according to the present invention, and FIG. 2 is a plan view and a cross-sectional view showing a specific example of a sensor portion of an embodiment of the thermal flow meter according to the present invention. is there.

  In FIG. 1, 18 is a glass substrate, 19 is a flow path formed in the glass substrate 18, 20 is a heat transfer means such as a heater that heats the temperature of the fluid flowing through the flow path 19 to a constant temperature, 21, 22, Reference numerals 23, 24, 25 and 26 denote temperature detection means such as a thermistor and a platinum resistance temperature detector, and 27 denotes arithmetic control means such as a CPU for obtaining a flow rate based on the temperature difference between the upstream and downstream fluids. In addition, 18, 19, 20, 21, 22, 23, 24, 25 and 26 constitute a flow meter chip 50.

  The temperature detection means 23 and the temperature detection means 24 are the first temperature difference detection means, the temperature detection means 22 and the temperature detection means 25 are the second temperature difference detection means, and the temperature detection means 21 and the temperature detection means 26 are the third. These temperature difference detecting means are respectively configured.

  The fluid to be measured is injected from the inflow hole indicated by “IN61” in FIG. 1, and the fluid to be measured is discharged from the outflow hole indicated by “OT61” in FIG. Therefore, the fluid to be measured flows in the flow path 19 in the direction indicated by “FL61” in FIG.

  As shown by “FL61” in FIG. 1, a heat transfer means 20 is provided in the central portion of the flow path 19 through which the liquid to be measured flows, and is located on the flow path 19 at equal intervals from the heat transfer means 20. Temperature detection means 23 and 24 (first temperature difference detection means) are provided.

  Similarly, on the flow path 19, outside the temperature detection means 23 and 24 (the side where the heat transfer means 20 is not provided), and at a position equidistant from the heat transfer means 20, the temperature detection means 22. And 25 (second temperature difference detecting means) are provided.

  Further, on the flow path 19, outside the temperature detection means 22 and 25 (the side where the heat transfer means 20 is not provided), and at a position equidistant from the heat transfer means 20, the temperature detection means 21 and 26 (third temperature difference detecting means) is provided.

  The outputs of the temperature detection means 21, 22, 23, 24, 25 and 26 are connected to the calculation control means 27, respectively, and the drive signal for temperature control from the calculation control means 27 is connected to the heat transfer means 20. .

  Furthermore, the specific example of the flowmeter chip | tip 50 of one Example of the thermal type flow meter which concerns on this invention is demonstrated in detail using FIG. In FIG. 2, 28 is a glass substrate, and 18, 19, 20, 21, 22, 23, 24, 25 and 26 are assigned the same reference numerals as in FIG.

  A rectangular groove is formed along the longitudinal direction of the glass substrate 18 at the central portion in the short direction of the glass substrate 18 by ultrasonic processing, laser processing, sandblasting, wet etching, or the like. In addition, a glass substrate 28 is bonded to the glass substrate 18 on the side where the rectangular groove is formed by adhesion, thermocompression bonding, or the like, and a flow path 19 in which the liquid contact portion is entirely made of glass is formed.

  Further, a heat transfer means 20 such as a heater is formed on the glass substrate 28 on the side not in contact with the flow path 19 and on the central portion of the flow path 19 by vapor deposition, sputtering, etc. Temperature detecting means 23 and 24 are formed on the glass substrate 28 located on the upper side and not in contact with the flow path 19 at equal intervals from the heat transfer means 20 by vapor deposition or sputtering.

  Similarly, on the glass substrate 28 located on the side of the flow path 19 that is not in contact with the flow path 19 and outside the temperature detection means 23 and 24 (the side where the heat transfer means 20 is not provided), and The temperature detecting means 22 and 25 are formed at equal intervals from the heat transfer means 20 by vapor deposition or sputtering.

  Further, on the glass substrate 28 located on the side of the flow path 19 that does not contact the flow path 19 and outside the temperature detection means 22 and 25 (the side where the heat transfer means 20 is not provided), and Temperature detection means 21 and 26 are formed at positions equidistant from the heat transfer means 20 by vapor deposition or sputtering.

  That is, the heat transfer means 20 and the temperature detection means 21, 22, 23, 24, 25 and 26 are formed on the glass substrate 28 on the side not in contact with the flow path 19, so that they are in a non-contact state.

  The operation of the embodiment shown in FIG. 1 will be described with reference to FIGS. FIG. 3 is a flowchart for explaining the operation of the arithmetic control means 27, and FIG. 4 is a characteristic curve diagram showing the relationship between the temperature difference between the upstream side and the downstream side and the flow rate.

  The flow measurement range of the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the temperature difference between the upstream and downstream fluids of the temperature control part is the heat transfer means and the upstream and downstream sides. It depends on the distance relationship with the temperature detection means (temperature difference detection means).

  For example, the longer the distance between the heat transfer means 20 and the temperature difference detection means, the higher the flow rate region is and the sensitivity is not saturated, but the sensitivity is insufficient in the low flow rate region. On the other hand, when the distance between the heat transfer means 20 and the temperature difference detection means is short, sensitivity is obtained in the low flow rate region, but when the flow rate increases, the temperature difference (flow rate signal) is saturated.

  For this reason, it is possible to measure the flow rate in a wider measurement range by appropriately selecting a combination of temperature detection units (temperature difference detection unit) according to the flow rate measured by the arithmetic control unit 27.

  That is, firstly, the calculation control means 27 controls the heat transfer means 20 so that the liquid to be measured has a constant temperature that is several degrees higher than the previously measured temperature of the liquid to be measured.

  In this state, in “S001” in FIG. 3, the arithmetic control means 27 determines whether or not the flow rate to be measured is a low flow rate region as indicated by “RG71” in FIG.

  If it is determined in “S001” in FIG. 3 that the region is a low flow rate region, the calculation control means 27 is the temperature detection means that is the closest to the heat transfer means 20 in “S002” in FIG. The temperature difference between the temperature detection means 24 and the temperature detection means 24 is obtained, and the flow rate of the liquid to be measured flowing through the flow path 19 is obtained based on the temperature difference.

  For example, when the flow rate to be measured is in the low flow rate region indicated by “RG71” in FIG. 4, the temperature detection unit 23 and the temperature difference detection unit closest to the heat transfer unit 20 as indicated by “CH71” in FIG. The flow rate of the liquid to be measured flowing through the flow path 19 is obtained using the characteristic of the temperature difference with the detection means 24.

  If it is determined in “S001” in FIG. 3 that it is not in the low flow rate region, the calculation control means 27 in “S003” in FIG. 3 determines the medium flow rate as indicated by “RG72” in FIG. It is determined whether it is an area.

  If “S003” in FIG. 3 determines that the flow rate is in the middle flow rate range, the calculation control means 27 determines the temperature difference from the heat transfer means 20 to the intermediate position (closest to the second) in “S004” in FIG. A temperature difference between the temperature detection means 22 and the temperature detection means 25 as detection means is obtained, and the flow rate of the liquid to be measured flowing through the flow path 19 is obtained based on the temperature difference.

  For example, when the flow rate to be measured is in the middle flow rate region indicated by “RG72” in FIG. 4, the temperature difference detection means at the intermediate position (closest to the second) from the heat transfer means 20 as indicated by “CH72” in FIG. The flow rate of the liquid to be measured flowing through the flow path 19 is obtained using the characteristic of the temperature difference between a certain temperature detection means 22 and the temperature detection means 25.

  If it is determined in “S003” in FIG. 3 that it is not in the middle flow rate region, the arithmetic control means 27 determines that the flow rate to be measured is in a high flow rate region as indicated by “RG73” in FIG. 3, in “S005”, the calculation control means 27 obtains a temperature difference between the temperature detection means 21 and the temperature detection means 26 which is the temperature difference detection means farthest from the heat transfer means 20 (closest to the third). Based on the temperature difference, the flow rate of the liquid to be measured flowing through the flow path 19 is obtained.

  For example, when the flow rate to be measured is in the high flow rate region indicated by “RG73” in FIG. 4, it is the temperature difference detecting means farthest (closest to the third) from the heat transfer means 20 as indicated by “CH73” in FIG. The flow rate of the liquid to be measured flowing through the flow path 19 is obtained using the characteristic of the temperature difference between the temperature detection means 21 and the temperature detection means 26.

  As a result, the first temperature difference detection means is provided on the flow path at equal intervals from the heat transfer means, on the flow path and outside the first temperature difference detection means, and from the heat transfer means. The second and third temperature difference detection means are sequentially provided at equally spaced positions, and the temperature difference detection means (combination of temperature detection means) is appropriately selected according to the flow rate to be measured, thereby providing a wider measurement range. It is possible to measure the flow rate.

  In the embodiment shown in FIG. 1, a thermal flow meter having three temperature difference detection means (combination of temperature detection means) is illustrated for simplicity of explanation, but of course, the number of temperature difference detection means May be plural (two or more).

  Further, in the characteristic curve diagram showing the relationship between the temperature difference between the upstream side and the downstream side shown in FIG. 4 and the flow rate, the characteristic curve of the temperature difference with respect to the flow rate of the adjacent temperature difference detection means (combination of temperature detection means) is shown. Although it is preferable that this overlaps (overlapping), the characteristic curve of the temperature difference with respect to the flow rate may of course not overlap.

  In order to overlap the temperature difference characteristic curves of adjacent temperature difference detection means (combination of temperature detection means), the interval between adjacent temperature difference detection means (combination of temperature detection means) is different. Can be realized by appropriately adjusting.

  In addition, since one thermal flow meter can cover a wide measurement range, there is no need to prepare a plurality of thermal flow meters in an application with a large flow rate change, and the cost and installation space can be reduced.

  In addition, there is no need for the manufacturer to line up a thermal flow meter corresponding to a plurality of measurement ranges, and by manufacturing one type of thermal flow meter and rewriting the program of the calculation control means, a plurality of thermal flow meters can be rewritten. Since the measurement range can be accommodated, the manufacturing cost can be reduced.

  Further, since the selection of the temperature difference detection means (combination of temperature detection means) is not performed by hardware but by software, there is no movable part and durability is increased.

  Further, in the embodiment shown in FIG. 1, the same measurement is possible even if the direction of the fluid to be measured flows in the opposite direction.

It is a block diagram showing the configuration of an embodiment of a thermal flow meter according to the present invention. It is the top view and sectional drawing which show the specific example of the sensor part of one Example of the thermal type flow meter which concerns on this invention. It is a flowchart explaining operation | movement of a calculation control means. It is a characteristic curve figure which shows the relationship between the temperature difference of an upstream and a downstream, and flow volume. It is a block diagram showing an example of a conventional thermal flow meter. It is a characteristic curve figure which shows an example of the temperature distribution of the to-be-measured liquid in a flow path with respect to the position of a flow path. It is a perspective view which shows another example of the conventional thermal type flow meter. It is sectional drawing which shows another example of the conventional thermal type flow meter. It is a characteristic curve figure which shows the relationship between the temperature difference of an upstream and a downstream, and flow volume. It is a block diagram which shows another example of a thermal type flow meter. It is the top view and sectional drawing which show the specific example of the sensor part of another example of a thermal type flow meter. It is a characteristic curve figure which shows the relationship of the value which divided the temperature difference of the upstream and downstream with respect to flow volume, a temperature sum, and the temperature difference divided by the temperature sum.

Explanation of symbols

1, 10, 16, 19 Flow path 2, 8, 13, 20 Heat transfer means 3, 4, 14, 15, 21, 22, 23, 24, 25, 26 Temperature detection means 5, 17, 27 Operation control means 6 11, 12, 18, 28 Glass substrate 7, 9 Silicon substrate 50 Flow meter chip

Claims (3)

In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the temperature difference between the upstream and downstream fluids of the temperature control part,
A channel in which the wetted parts are all made of glass,
A heat transfer means provided in the flow path;
First temperature difference detection means provided on the flow path and at equal intervals from the heat transfer means;
Second temperature difference detection means provided on the flow path and outside the first temperature difference detection means and at equal intervals from the heat transfer means;
Calculation for obtaining the flow rate based on the detected temperature difference by controlling the temperature of the liquid flowing through the flow path by the heat transfer means and selecting the first or second temperature difference detection means according to the flow rate to be measured. A thermal flow meter comprising a control means. The arithmetic control means is
When it is determined that the flow rate to be measured is a low flow rate region, the flow rate is obtained based on the temperature difference detected by the first temperature difference detection means closest to the heat transfer means,
The flow rate is obtained based on a temperature difference detected by the second temperature difference detection means farthest from the heat transfer means when it is determined that the flow rate to be measured is a high flow rate region. Thermal flow meter. The temperature difference characteristic curve with respect to the flow rate of the first temperature difference detection means and the temperature difference characteristic curve with respect to the flow rate of the second temperature difference detection means overlap with each other. 2. The thermal flow meter according to claim 1, wherein an interval between the two temperature difference detecting means is adjusted.

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