JP4844252B2 - Thermal mass flow meter - Google Patents

Description

  The present invention relates to a thermal mass flowmeter that measures a mass flow rate of a fluid flowing in a pipe based on a temperature distribution in a fluid flow direction.

  A conventional thermal mass flow meter will be described with reference to FIG. FIG. 3 is a diagram showing an example of a conventional thermal mass flow meter, (A) is a cross-sectional view, and (B) is a graph showing the temperature distribution on the pipe surface. In (B), the vertical axis is the temperature, and the horizontal axis is the position in the flow direction of the pipe. In addition, the curve shown with the broken line has shown the temperature distribution in the state in which the fluid is not flowing in piping, and the curve shown by the continuous line has shown the temperature distribution in the state where the fluid is flowing in piping.

  As shown in FIG. 3A, the heating element 32 is brought into contact with the surface of the peripheral surface of the pipe 30, and the pipes are arranged at equidistant positions on the upstream side and the downstream side of the heating element 32 in the flow direction of the pipe 30. A pair of temperature sensors 34 (34a, 34b) for measuring the surface temperature of the are disposed. In this example, for example, a flow measurement chip 36 in which a heating element 32 and a temperature sensor pair 34 are formed on one substrate by MEMS (Micro Electro Mechanical System) technology is used, and the flow measurement chip 36 is attached to a pipe 30. The flow rate flowing through the pipe 30 is measured (for example, see Patent Document 1).

  The above-described thermal mass flowmeter heats the fluid in the pipe to a predetermined temperature by the heating element 32, and measures the surface temperature of the pipe 30 by the temperature sensor pair 34 separated from the heating element 32 by a certain distance. Assuming that the temperature distribution of the fluid heated by the heating element 30 follows a Gaussian distribution, when the fluid is stationary, as shown by the broken line in FIG. 3B, two temperature sensors 34a and 34b The detected temperatures are equal and the measured temperature difference between them is zero. As shown by the solid line in FIG. 3B, when a fluid flows in the pipe 30, the temperature distribution moves to the downstream side, causing a difference in temperature detected by the temperature sensors 34a and 34b. Since the temperature distribution on the surface of the pipe 30 moves downstream as the flow rate of the fluid flowing in the pipe 30 increases, when the apex of the temperature distribution on the surface of the pipe 30 is between the temperature sensors 34a and 34b, the temperature sensor The measured temperature difference between the pair 34 increases as the flow rate of the fluid flowing in the pipe 30 increases. Accordingly, there is a correlation between the flow rate of the fluid flowing in the pipe 30 and the measured temperature difference of the temperature sensor pair 34, and the flow of the fluid flows in the pipe 30 using the measured temperature difference of the temperature sensor pair 34 from this correlation. The flow rate of the fluid can be calculated.

In the thermal mass flowmeter using the flow rate measuring chip 36 in which the temperature sensors 34a and 34b paired with the heating element 32 are formed, the temperature sensor pair 34 paired by the MEMS technology is close to the heating element. Therefore, even when the amount of movement of the temperature distribution is small, the temperature sensors 34a and 34b adjust the temperature at a position where the curve indicating the temperature sensor temperature distribution (see FIG. 3B) has a steep slope. Even if the flow rate is very small, a large value can be obtained as the measurement temperature difference, and the flow rate measurement can be performed with high sensitivity.
US 6813944

However, using the MEMS technology to produce the heating element 32 and the temperature sensor pair 34 on a single substrate cannot be realized at low cost due to problems such as manufacturing equipment. Further, as shown in FIG. 3, the conventional thermal mass flow meter has a problem that a sufficient resolution cannot be obtained because the temperature detection area of the temperature sensor is small.
Therefore, an object of the present invention is to provide a thermal mass flow meter that can measure the flow rate of fluid flowing through a pipe with higher sensitivity than the conventional one.

The thermal mass flow meter according to the present invention is a chip type one surface side that is fixed so as to sandwich the pipe between the one surface side and the other surface side on the peripheral surface of the pipe through which the fluid flows, and heats the fluid in the pipe The heating element and the other surface side heating element are configured separately from the one surface side heating element and the other surface side heating element, and the upstream side and the downstream side of the heating element and the like along the fluid flow direction on one side. distance and the other surface side temperature sensor pair which is secured to a position corresponding to one side temperature sensor pairs one surface side temperature sensor pair and the other surface side of the anchored chip type on the position of, by one surface side temperature sensor pairs a calculation unit for determining the flow rate of the fluid from the detected temperature and the temperature detected by the other surface side temperature sensor pair flows through the pipe, but with a.

In the thermal mass flowmeter of the present invention, the one surface side temperature sensor constituting the one surface side temperature sensor pair and the other surface side temperature sensor constituting the other surface side temperature sensor pair are electrically connected to each other. They are connected in parallel manner.

In a thermal mass flow meter, heat is generated by a heating element to heat the pipe, and the flow rate of the fluid flowing inside the pipe is measured by moving the apex position of the temperature distribution. If it is affected by something other than the amount of heat generated, accurate flow measurement will not be possible. Therefore, it is preferable that the heating element, the temperature sensor, and the part to which the piping is attached are isolated from the external environment.
Therefore, an example of a preferred embodiment of the thermal mass flowmeter of the present invention is that the lead terminal of the other surface side heating element and the lead terminal of the other surface temperature sensor are supported from the other surface side of the pipe and the other surface side heat generation. The other surface side substrate covering the region including the element and the other surface side temperature sensor pair, and the one surface side heat insulating material covering the region including the one surface side heating element and the one surface side temperature sensor pair from the one surface side of the pipe. Furthermore, it is equipped.

In the above case, the heat insulation effect of the one surface side heat insulating material and the other surface side substrate is determined by their thermal conductivity and thickness. If the heat insulation effect of the one-surface-side heat insulating material or the other-surface-side substrate is low, the inner temperature is affected by the outer temperature change, and accurate flow rate measurement becomes difficult. Although the heat insulation effect can be enhanced by increasing the thickness of the one-surface-side heat insulating material or the other-surface-side substrate, it is disadvantageous in terms of cost because a large amount of materials such as heat-insulating adhesive and silicone are required. In addition, when a large amount of heat insulating adhesive is used, it takes time to dry the heat insulating adhesive, resulting in a problem that workability is lowered.
Therefore, between the other surface side substrate and the main body portion of the other surface side heating element and the main body portion of the other surface side temperature sensor, and the one surface side heat insulating material and the main body portion of the one surface side heating element and the one surface side temperature sensor. An air layer may exist between the main body portion. A substance used as a heat insulating material such as a viscous heat insulating adhesive or silicone has a temperature of 300 K and a pressure of 0.1 MPa. It has a thermal conductivity of several W / mK. On the other hand, the thermal conductivity of still air is 0.026 W / mK under the same conditions (from Mechanical Engineering Handbook “Thermal Engineering”), which is one order of magnitude smaller than that of the above heat insulating material, and the air layer is insulated. It has better heat insulation than wood.

The other side substrate is a wiring substrate on which a wiring pattern is formed, and the region including the other side heating element and the other side temperature sensor pair is a recess provided on the wiring substrate, and the lead terminal of the other side heating element. And the lead terminal of the temperature sensor on the other side is preferably fixed to a part of the wiring pattern and electrically connected.
Furthermore, the lead terminal of the one surface side temperature sensor may be fixed to and electrically connected to a part of the wiring pattern together with the corresponding lead terminal of the other surface side temperature sensor.

  The one side heating element and the other side heating element are preferably fixed to the pipe with a heat conductive adhesive.

  One of the preferable uses of the thermal mass flowmeter of the present invention is a pipe through which a mobile phase flows in a high-speed liquid chromatograph in which the thermal mass flowmeter is attached.

  The thermal mass flowmeter of the present invention does not use a flow rate measuring chip in which a heating element and a temperature sensor pair are integrally formed on one substrate, but a heating element and a temperature sensor pair manufactured independently. Because the pipe is placed between the one side and the other side of the pipe, the flow rate of the fluid flowing in the pipe is highly sensitive and inexpensive without using expensive MEMS technology. It can be measured.

  Furthermore, the one surface side temperature sensor constituting the one surface side temperature sensor pair and the other surface side temperature sensor constituting the other surface side temperature sensor pair are electrically connected in parallel to each other corresponding to both surfaces. As a result, the S / N ratio is improved, and the measurement sensitivity is further increased.

  A second-side substrate that supports the lead terminal of the second-side heating element and the second-side temperature sensor from the second-side surface of the pipe and covers a region including the second-side heating element and the second-side temperature sensor pair; The one side heat generating element, the one side heat generating element, and the one side heat insulating material that covers the region including the one side heat generating element and the one side temperature sensor pair from the one side of the pipe. The measurement part including the temperature sensor pair on the other side and the temperature sensor pair on the other side can be isolated from the outside, so that the temperature of the measurement part is less susceptible to disturbances such as changes in the temperature of the outside air, and the accuracy of flow measurement is improved. improves.

  Between the other surface side substrate and the main body portion of the other surface side heating element and the main body portion of the other surface side temperature sensor, and the one surface side heat insulating material, the main body portion of the one surface side heating element and the main body portion of the one surface side temperature sensor. If an air layer exists between the two, the heat insulating effect of the measurement portion can be further enhanced by utilizing the high heat insulating property of the air layer.

The other side substrate is a wiring substrate on which a wiring pattern is formed, and the region including the other side heating element and the other side temperature sensor pair is a recess provided on the wiring substrate, and the lead terminal of the other side heating element. If the lead terminal of the temperature sensor on the other side is fixed to a part of the wiring pattern and electrically connected, the circuit configuration of the thermal mass flow meter can be simplified.
Furthermore, if the lead terminal of the one side temperature sensor is fixed to a part of the wiring pattern together with the corresponding lead terminal of the other side temperature sensor, it corresponds to the one side temperature sensor and its one side temperature sensor. The other side temperature sensor can be connected in parallel without complicating the circuit configuration.

FIG. 1 is a diagram showing an embodiment of a thermal mass flow meter for measuring the flow rate of a mobile phase flowing in a high-performance liquid chromatograph pipe, where (A) is a sectional view and (B) is a temperature distribution of the pipe. It is a graph to show. In (B), the vertical axis indicates the temperature, and the horizontal axis indicates the position of the pipe 2 in the flow direction. The curve shown by the broken line shows the temperature distribution on the pipe surface caused by the heater when no mobile phase is flowing in the pipe, and the curve shown by the solid line is when the mobile phase is flowing in the pipe. 2 shows the temperature distribution on the pipe surface caused by the heater.
In the following embodiments, the pipe 2 is arranged in a horizontal plane, and one side of the pipe 2 is an upper side and the other side is a lower side. Further, in this embodiment, the pipe 2 is arranged in the horizontal plane, but even when the pipe 2 is arranged in the vertical direction or with an inclination, the one surface side is the upper side and the other surface side is the lower side.

  In FIG. 1 (A), 2 is a piping of a high performance liquid chromatograph. The mobile phase flows from the left side to the right side in the pipe 2 as indicated by arrows in the figure. On the peripheral surface of the pipe 2, a heater chip 4a, which is a heating element, is arranged on the upper side of the pipe 2 so as to sandwich the pipe 2, and the heater chip 4b is located on the lower side of the pipe 2 on the opposite side of the heater chip 4a. Has been placed.

A temperature sensor chip 6a is disposed on the upstream side of the heater chip 4a on the upper side of the pipe 2, and a temperature sensor chip 8a is disposed on the downstream side of the heater chip 4a on the upper side of the pipe 2. The temperature sensor chips 6a and 8a are arranged at an equal distance from the heater chip 4a, and constitute an upper temperature sensor chip pair.
The temperature sensor chip 6b is arranged at a position corresponding to the opposite side of the temperature sensor chip 6a below the pipe 2, and the temperature sensor chip 8b is arranged at a position corresponding to the opposite side of the temperature sensor chip 8a below the pipe 2. Yes. The temperature sensor chips 6b and 8b constitute a lower temperature sensor chip pair.

The heater chips 4a and 4b and the temperature sensor chips 6a, 6b, 8a and 8b are fixed to the pipe 2 with a heat conductive adhesive 10 such as a heat conductive silicone sealant KE3467 (a product of Shin-Etsu Chemical Co., Ltd.). .
As the heater chips 4a and 4b, for example, a chip diode ISS387 (product of Toshiba Corporation) or a chip resistor RK73H1JT (product of Koa Corporation) can be used. The temperature sensor chips 6a, 6b, 8a, and 8b are chips in which thermocouples and diodes are formed.

  Here, the gap between the heater chips 4a and 4b, the gap between the temperature sensor chips 6a and 8a, and the gap between the temperature sensor chips 6b and 8b are, for example, heat from a thermally conductive silicone sealant KE3467 (a product of Shin-Etsu Chemical Co., Ltd.). It may be filled with the conductive adhesive 10. Then, the heat transfer between the heater chips 4a and 4b and the pipe and the heat transfer between the temperature sensor chips 6a, 6b, 8a and 8b and the pipe are improved.

In FIG. 1 (B), in the state where the mobile phase is not flowing in the pipe 2, the positions of the heater chips 4a and 4b are set as the apexes of the temperature distribution so that the curve indicating the temperature distribution is indicated by the broken line. The temperature is distributed symmetrically about the position. Therefore, in this state, the temperature at the position of the temperature sensor chips 6a and 6b and the temperature at the position of the temperature sensor chips 8a and 8b are equal, and the difference between them is zero.
On the other hand, when the mobile phase flows in the pipe 2, the curve indicating the temperature distribution moves to the downstream side (right side in the figure) as indicated by the solid line, and the temperature and temperature at the position of the temperature sensor chips 6a and 6b. A difference occurs in the temperature of the positions of the sensor chips 8a and 8b.

  Assuming that there is an apex of the temperature distribution between the position of the temperature sensor chip 6a, 6b and the position of the temperature sensor chip 8a, 8b, the apex of the temperature distribution is due to an increase in the flow rate of the mobile phase flowing in the pipe 2. Since it moves downstream, the difference between the temperature detected by the temperature sensor chips 6a and 6b and the temperature detected by the temperature sensor chips 8a and 8b increases with an increase in the flow rate of the mobile phase, and a correlation is established between them. By measuring this correlation in advance and preparing it as calibration curve data, if the difference between the temperature detected by the temperature sensor chips 6a and 6b and the temperature detected by the temperature sensor chips 8a and 8b is detected, Based on the calibration curve data, the flow rate of the mobile phase flowing in the pipe 2 can be calculated.

上記式（１）において、ｋはボルツマン定数、Ｔは絶対温度（Ｋ）、Ｒは抵抗値（Ω）、Δｆは雑音の周波数帯域（Ｈｚ）である。 Here, it is preferable that the temperature sensor chips 6a and 6b and the temperature sensor chips 8a and 8b are electrically connected in parallel. This is based on the following reason.
An SN ratio (SNR) obtained by taking a ratio between the signal voltage and the noise voltage E (V) is used as an index representing the temperature detection resolution in the temperature sensor chips 6a, 6b, 8a, and 8b. The noise voltage E (V) can be expressed by the following equation (1).

In the above formula (1), k is a Boltzmann constant, T is an absolute temperature (K), R is a resistance value (Ω), and Δf is a noise frequency band (Hz).

When temperature detection is performed with one temperature sensor chip, if the voltage for driving the temperature sensor chip is a constant voltage V ₀ , the resistance value R is represented by R = V ₀ / I, and the current I flowing from the temperature sensor chip is It is determined. At this time, if the fixed resistance for converting the current flowing from the temperature sensor chip into a voltage is r (Ω) and the noise voltage of the fixed resistance r is Er (V), the two different types of noise voltages are the mean square. Since it is calculated | required, SNR can be represented by following Formula (2).

となる。 On the other hand, when two temperature sensor chips driven at a constant voltage are connected in parallel to detect temperature, the total current flowing from these temperature sensor chips is 2I. Therefore, the total resistance value R ′ of these two temperature sensor chips is

It becomes.

となる。 Therefore, the noise voltage E ′ when the temperature sensor chips are connected in parallel is obtained from the equation (1):

It becomes.

式（２）と式（３）によりＳＮＲ／ＳＮＲ’は次式（４）で表わされる。

If the SN ratio in this case is SNR ′, SNR ′ can be expressed by the following equation (3).

SNR / SNR ′ is expressed by the following equation (4) from the equations (2) and (3).

すなわち、

符号＊は掛け算の×を表わす。
また、

すなわち、

From the above equation (4),

That is,

The sign * represents multiplication x.
Also,

That is,

Therefore, the SN ratio (SNR ′) when temperature detection is performed by connecting temperature sensor chips in parallel is always performed by one temperature sensor chip regardless of the resistance values R and r and the temperature T. It can be seen that the signal-to-noise ratio (SNR) is two times or more when performing. In other words, by placing two temperature sensor chips at the same measurement position and connecting the temperature sensor chips in parallel to detect the temperature, the S / N ratio can be improved more than twice, and highly sensitive measurement is possible. Can be done.
Therefore, by using the temperature sensor chips 6a and 6b and 8a and 8b connected in parallel electrically, the resolution can be improved as compared to using each temperature sensor chip 6a, 6b, 8a, and 8b alone. .

  In this embodiment, the temperature sensor chips 6a and 6b and 8a and 8b are connected to a calculation unit (not shown). The calculation unit reads the detected temperatures of the temperature sensor chips 6a, 6b, 8a, and 8b, and based on a calibration curve that is obtained and stored in advance from the temperature difference between the upstream side and the downstream side of the heater chips 4a and 4b. The flow rate of the mobile phase flowing inside is calculated. The arithmetic unit here can be realized by a CPU or a personal computer.

When the temperature sensor chips 6a and 6b and 8a and 8b are connected in parallel, one temperature information is obtained from each of the temperature sensor chips 6a and 6b and 8a and 8b, and these four temperature sensor chips 6a. 6b, 8a, 8b are regarded as a pair of temperature sensor chips, and the temperature difference between the upstream side and the downstream side of the heater chips 4a, 4b is obtained.
In that case, the difference between the temperature detected by the set of temperature sensor chips 6a and 6b connected in parallel and the temperature detected by the set of temperature sensor chips 8a and 8b (hereinafter referred to as the detected temperature) is measured in advance in the calculation unit. The correlation between the difference) and the flow rate of the fluid flowing in the pipe 2 is stored as a calibration curve. Then, the flow rate of the fluid flowing in the pipe 2 is automatically calculated based on the detected temperature difference and the calibration curve.

  The correlation between the detected temperature difference and the fluid flow rate is established only when the apex of the temperature distribution exists between the position of the temperature sensor chips 6a and 6b and the position of the temperature sensor chips 8a and 8b. If the apex of the temperature distribution does not exist between the position of the temperature sensor chips 6a and 6b and the position of the temperature sensor chips 8a and 8b, the flow rate of the mobile phase is calculated based on the calibration curve based on this correlation. I can't do it. This is because when the peak of the temperature distribution is on the downstream side of the position where the temperature sensor chips 8a and 8b are arranged, the flow rate of the fluid flowing in the pipe 2 is further increased and the peak of the temperature distribution is further on the downstream side. Even if it moves, the phenomenon that the temperature difference between the temperature sensor chips 6a and 6b and the temperature sensor chips 8a and 8b decreases, and the detected temperature of the temperature sensor chips 6a and 6b and the temperature detected by the temperature sensor chips 8a and 8b are reduced. This is because the relationship that the difference increases as the flow rate of the mobile phase increases does not hold.

  FIG. 2 is a view showing another embodiment of the thermal mass flow meter, (A) is a plan view, (B) is a sectional view at the XX position of (A), and (C) is a view of (A). It is sectional drawing in a YY position. In this embodiment, a cover 18 is provided to cover the measurement portion from above the thermal mass flow meter, but is not shown in FIG.

  Also in the thermal mass flowmeter of this embodiment, the temperature sensor chip 6a is disposed on the upstream side of the heater chip 4a on the upper side of the pipe 2 as in the embodiment of FIG. A temperature sensor chip 8a is disposed on the downstream side of 4a. The temperature sensor chips 6a and 8a are arranged at an equal distance from the heater chip 4a, and constitute an upper temperature sensor chip pair. Further, the temperature sensor chip 6b is arranged at a position below the pipe 2 on the opposite side of the temperature sensor chip 6a, and the temperature sensor chip 8b is arranged at a position below the pipe 2 on the opposite side of the temperature sensor chip 8a. Has been. The temperature sensor chips 6b and 8b constitute a lower temperature sensor chip pair.

The heater chips 4a and 4b and the temperature sensor chips 6a, 6b, 8a and 8b are fixed to the pipe 2 with a heat conductive adhesive 10 such as a heat conductive silicone sealant KE3467 (a product of Shin-Etsu Chemical Co., Ltd.). .
As the heater chips 4a and 4b, for example, a chip diode ISS387 (product of Toshiba Corporation) or a chip resistor RK73H1JT (product of Koa Corporation) can be used. The temperature sensor chips 6a, 6b, 8a, and 8b are chips in which thermocouples and diodes are formed.
Each of the heater chips 4a, 4b and the temperature sensor chips 6a, 6b, 8a, 8b includes two lead terminals extending laterally from the lower surface of the main body portion.

The measurement part on which the heater chips 4a and 4b and the temperature sensor chips 6a, 6b, 8a and 8b are arranged is covered with a substrate 12 as a lower heat insulating material and a cover 18 as an upper heat insulating material and is isolated from the outside. Yes. The substrate 12 in this embodiment is a printed circuit board on which a wiring pattern 16 made of, for example, a metal film is formed. The printed board 12 is, for example, a glass epoxy board or a polyimide board. A rectangular groove 14 is formed in the printed circuit board 12, and the wiring pattern 16 is drawn out from the groove 14 toward the outside. The lead terminals of the heater chips 4a and 4b and the temperature sensor chips 6a, 6b, 8a and 8b are electrically connected to the wiring pattern 16 and drawn out to the outside.
The cover 18 is disposed so as to cover the measurement portion from above the printed circuit board 12. A gap is provided between the cover 18, the heater chip 4a, and the temperature sensor chips 6a and 8a, and an air layer 20 is interposed. The cover 18 is made of a heat insulating material, or is coated with a heat insulating adhesive such as TORAYPEF (registered trademark, a product of Toray Industries, Inc.) or silicone on the outside. As a result, the air in the measurement part is isolated from the outside air.

The positional relationship between the measurement portion including the pipe 2, the printed circuit board 12, and the cover 18 will be described with reference to FIG. Here, the part where the temperature sensor chips 6a and 6b are arranged will be described, but the part where the heater chips 4a and 4b and the temperature sensor chips 8a and 8b are arranged also has the same structure.
The temperature sensor chip 6b is fitted in the groove 14 of the printed circuit board 12 with the upper surface of the main body portion facing downward. The size of the groove 14 is such that there is a gap between the body portion of the temperature sensor chip 6b and the wall surface inside the groove 14, and the temperature sensor chip 6b is supported by the printed circuit board 12 only at the lead terminals 6a-1 and 6a-2. Is set to The temperature sensor chip 6b is supported by the wiring pattern 16 through lead terminals 6b-1 and 6b-2, and the lead terminals 6b-1 and 6b-2 are fixed to the wiring pattern 16 by solder 22 and are electrically connected. .

  The pipe 2 and the temperature sensor chip 6a are fixed to the lower surface of the main body portion of the temperature sensor chip 6b by the heat conductive adhesive 10, but the lead terminals 6a-1 and 6a-2 of the temperature sensor chip 6a are also used. The temperature sensor chip 6b is electrically connected and fixed to the wiring pattern 16 by the same solder 22 as the lead terminals 6b-1 and 6b-2. Therefore, since the lead terminal 6a-1 and the lead terminal 6b-1, and the lead terminal 6a-2 and the lead terminal 6b-2 are electrically connected, the temperature sensor chips 6a and 6b are electrically connected in parallel. It is connected. Here, the lead terminals 6a-1 and 6b-1 are positive electrodes or negative electrodes, and the lead terminals 6a-2 and 6b-2 are negative electrodes or positive electrodes.

  In the thermal mass flow meter of this embodiment, since the temperature sensor chips 6a and 6b and 8a and 8b for measuring the temperature at the same position are electrically connected in parallel, the SN ratio of the electric signal from the temperature sensor chip As a result, the temperature can be detected with high sensitivity. Thereby, the resolution of the flow rate measurement of the mobile phase flowing in the pipe 2 is increased, and the performance as a thermal mass flow meter is improved.

Since the measurement part including the part where the heater chips 4a and 4b and the temperature sensor chips 6a, 6b, 8a and 8b are arranged is isolated from the outside by the printed circuit board 12 and the cover 18, it is affected by the temperature change of the outside air. It is difficult to measure the flow rate with high accuracy.
Further, the heater chip 4b and the temperature sensor chips 6b and 8b are supported by the printed circuit board 12 only at the respective lead terminals, and a gap is provided between the inner wall surface of the groove 14 and an air layer is interposed therebetween. The heat insulating effect can be further enhanced by utilizing the high heat insulating property of the layer. Thereby, the thickness under the groove | channel 14 can be made thin and cost reduction can be aimed at. Similarly, since a space is provided between the heater chip 4a, the temperature sensor chips 6a and 8a and the cover 18 and an air layer is interposed, the heat insulating effect can be enhanced by utilizing the high heat insulating property of the air layer. .

  The thermal mass flowmeter of the embodiment described with reference to FIG. 1 and FIG. 2 has a total of four temperature sensor chips 6a, one at an equidistant position on the upstream side and downstream side of the heater chips 4a, 4b. 6b, 8a, 8b are arranged, but the present invention is not limited to this, and two or more at the same distance positions on the upstream side and the downstream side of the heater chips 4a, 4b, respectively, a total of 8 or more. The temperature sensor chip may be arranged.

It is a figure which shows one Example of a thermal mass flowmeter, (A) is sectional drawing, (B) is a graph which shows the temperature distribution on the piping surface. It is a figure which shows the other Example of a thermal mass flowmeter, (A) is a top view, (B) is sectional drawing in the XX position of (A), (C) is YY of (A). It is sectional drawing in a position. It is a figure which shows an example of the conventional thermal mass flowmeter, (A) is sectional drawing, (B) is a graph which shows the temperature distribution of piping surface.

Explanation of symbols

2 Piping 4a, 4b Heater chip 6a, 6b, 8a, 8b Temperature sensor chip 10 Thermally conductive adhesive 12 Printed circuit board 14 Groove 16 Wiring pattern 18 Cover 20 Air layer

Claims (5)

A chip-type one side heating element and the other side heating element that are fixed so as to sandwich the pipe between the one side and the other side of the peripheral surface of the pipe through which the fluid flows, and heat the fluid in the pipe,
The one surface side heating element and the other surface side heating element are configured as separate bodies, and are fixed to the upstream side and the downstream side of the heating element at equidistant positions along the fluid flow direction on the one surface side. A chip-type one-side temperature sensor pair and the other-side temperature sensor pair fixed at a position corresponding to the one-side temperature sensor pair on the other-side side,
A calculation unit for obtaining a flow rate of the fluid flowing in the pipe from the detection temperature by the one-side temperature sensor pair and the detection temperature by the other-side temperature sensor pair;
The lead terminal of the other surface side heating element and the lead terminal of the other surface side temperature sensor are supported from the other surface side of the pipe, and the region including the other surface side heating element and the other surface side temperature sensor pair is covered. The other side substrate,
One surface side heat insulating material that covers the region including the one surface side heating element and the one surface side temperature sensor pair from the one surface side of the pipe;
Equipped with a,
The one surface side temperature sensor constituting the one surface side temperature sensor pair and the other surface side temperature sensor constituting the other surface side temperature sensor pair are electrically connected in parallel to each other on the both surfaces side, and are upstream. It constitutes a temperature sensor pair and a downstream temperature sensor pair,
The calculation unit is configured to obtain a flow rate of the fluid flowing in the pipe from a temperature difference between a temperature detected by the upstream temperature sensor pair and a temperature detected by the downstream temperature sensor pair,
The other surface side substrate is a wiring substrate on which a wiring pattern is formed, and the region including the other surface side heating element and the other surface side temperature sensor pair is a recess provided in the wiring substrate,
The thermal mass flowmeter in which the lead terminal of the other surface side heating element and the lead terminal of the other surface side temperature sensor are fixed to a part of the wiring pattern and are also electrically connected . Between the other surface side substrate and the main body portion of the other surface side heating element and the main body portion of the other surface side temperature sensor, and the one surface side heat insulating material and the main body portion of the one surface side heating element and the one surface. The thermal mass flowmeter according to claim 1 , wherein an air layer exists between the main body portion of the side temperature sensor. The heat terminal according to claim 1 or 2 , wherein a lead terminal of the one surface side temperature sensor is fixed to a part of the wiring pattern together with a corresponding lead terminal of the other surface side temperature sensor, and is also electrically connected. Type mass flow meter. The thermal mass flowmeter according to any one of claims 1 to 3 , wherein the one-side heating element and the other-side heating element are fixed to the pipe with a heat conductive adhesive. The thermal mass flowmeter according to any one of claims 1 to 4 , wherein the pipe is a pipe through which a mobile phase flows in a high performance liquid chromatograph.

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