JP6475080B2 - Thermal flow meter and method for improving tilt error - Google Patents

Description

  The present invention relates to a thermal flow meter for measuring a flow rate (flow velocity) of a fluid to be measured and a method for improving a tilt error thereof.

  Conventionally, as disclosed in Patent Document 1, as a flow meter, a heating element and two temperature measuring bodies sandwiching the heating element are provided on a substrate, and when the fluid to be measured passes, The heat on the heating element moves, and the mass flow rate is calculated based on the temperature difference generated between the two temperature measuring bodies by the moved heat.

JP 2004-117157 A Japanese Patent No. 4027470

  By the way, if the positional relationship between the heating element and the temperature measuring element is aligned in the level direction, that is, perpendicular to the vertical direction, there is no movement of heat when there is no fluid flow, so that a temperature difference occurs. There is no flow rate measured in this state.

  On the other hand, when the positional relationship between the heating element and the temperature measuring element is aligned in the vertical direction, the heat generated by the heating element is distributed in the opposite direction to the vertical direction (hereinafter referred to as “thermal convection effect”). ). For this reason, when there is no fluid flow, it must be output as zero. However, due to the thermal convection effect, a temperature difference occurs between the two temperature measuring elements, and the flow rate is output as if there is a flow. End up.

  For this reason, the mounting direction of the flow meter disclosed in Patent Document 1 cannot be measured accurately unless the substrate surface on which the heating element and the temperature measuring body are arranged is along the level direction. There was a problem of taking away the degree.

In view of the above problems, in Patent Document 2, the heat generated on the sensor element side is provided by providing a self-heating resistor (sensor element) on one side of the U-shaped tube and a heater element on the other side. A method is disclosed in which the flow due to convection is physically canceled out by the flow due to thermal convection that is forcibly generated on the heater element side.
However, as the flow meter, the flow meter disclosed in Patent Document 1 is simpler in structure and easier to manufacture than the U-tube type flow meter disclosed in Patent Document 2.

  The present invention was devised in view of the above circumstances, and it is possible to measure an accurate flow rate even when a plane including a heating element and a temperature measuring element is inclined from a level direction. An object of the present invention is to provide a thermal flow meter that can be used and a method for improving the tilt error.

  In order to achieve the above object, a thermal flow meter according to the present invention is a thermal flow meter installed in a pipe through which a fluid to be measured flows, and is provided with a heating element and the fluid to be measured from the heating element. When the heating element detects heat and the direction of the flow of the fluid to be measured includes a vertical component, the heating element detects when the heating element generates heat at two different temperatures. A storage device that stores information for correcting the measured flow rate of the fluid to be measured with respect to the temperature to be measured, and a correction unit that corrects the measured flow rate of the fluid to be measured based on the information. Features.

  A method for improving a tilt error of a thermal flow meter according to the present invention includes a procedure for measuring a first flow rate at a first temperature, a procedure for measuring a second flow rate at a second temperature, and the second temperature from the first temperature. In accordance with the procedure for identifying the direction of inclination of the substrate surface including the heating element and the temperature sensing element from the changes in the first flow rate and the second flow rate, and the information for correction And a procedure for performing a correction operation on the second flow rate and outputting a normal flow rate.

  According to the thermal type flow meter according to the present invention, an accurate flow rate can be measured even when a plane including a heating element and a temperature measuring element is inclined from the level direction.

It is a perspective view of the thermal type flow meter concerning a 1st embodiment of the present invention. It is sectional drawing seen from the II-II direction of FIG. 1 of the thermal type flow meter which concerns on 1st Embodiment. It is a circuit diagram of the thermal type flow meter concerning a 1st embodiment. It is a schematic diagram of the installation state of the thermal type flow meter which concerns on 1st Embodiment. It is a schematic diagram of the state which installed the thermal type flow meter which concerns on 1st Embodiment in the perpendicular direction. It is a figure which shows the relationship between the flow volume and deviation of 1st Embodiment. It is a figure where it uses for description of the procedure of the inclination error improvement method of the thermal type flow meter which concerns on 1st Embodiment. It is a figure which shows the relationship between the flow volume and deviation of 2nd Embodiment. It is a figure with which it uses for description of the flow volume correction value for every temperature with respect to each flow volume point in 2nd Embodiment.

Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.
[First Embodiment]

  First, a thermal flow meter according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of a thermal type flow meter according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view of the thermal flow meter according to the first embodiment viewed from the II-II direction in FIG. FIG. 3 is a circuit diagram of the thermal type flow meter according to the first embodiment. FIG. 4 is a schematic diagram of an installed state of the thermal type flow meter according to the first embodiment.

  The thermal flow meter 100 according to the first embodiment is realized by using the microchip having the element structure shown in FIGS. 1 and 2 and configured as shown in FIG. As shown in FIG. 2, the thermal flow meter 100 includes a substrate B provided with a cavity C, and an insulating film M disposed on the substrate B so as to cover the cavity C. The thickness of the substrate B is, for example, 0.5 mm, but is not limited to the illustrated thickness. The vertical and horizontal dimensions of the substrate B are, for example, about 1.5 mm, but are not limited to the illustrated dimensions. The portion of the insulating film M covering the cavity C forms a heat insulating diaphragm.

  Further, the thermal flow meter 100 includes a heating element (heater element) RH provided in the diaphragm part of the insulating film M and an upstream measurement provided in the diaphragm part of the insulating film M so as to sandwich the heating element RH. A temperature sensor (resistance element) R1, a downstream temperature measurement element (resistance element) R2, and a temperature sensor RR for measuring ambient temperature provided on the substrate B are provided. The temperature sensor RR is also composed of an electric resistance element or the like.

  The heating element RH is disposed at the center of the diaphragm portion of the insulating film M covering the cavity C. The heating element RH generates heat when electric power is applied, and heats a fluid to be measured such as an atmospheric gas in contact with the heating element RH. The upstream temperature measuring element R1 and the downstream temperature measuring element R2 provided adjacent to the heating element RH refer to the local temperature in the vicinity of the heating element RH when the heating element RH is not generating heat. Detect as temperature. The temperature sensor RR is disposed farther from the heating element RH than the upstream temperature measuring element R1 and the downstream temperature measuring element R2. The temperature sensor RR detects the gas temperature of the atmospheric gas that is in thermal equilibrium with the heating element RH as the equilibrium gas temperature. The temperature sensor RR is provided on the thermally conductive substrate B so as to be separated from the heating element RH via the insulating film M. For this reason, the temperature sensor RR is less affected by the heat generated by the heating element RH than the temperature measuring element R1 on the upstream side and the temperature measuring element R2 on the downstream side.

As a material of the substrate B, silicon (Si) or the like can be used, but is not limited to the exemplified material. As a material of the insulating film M, silicon oxide (SiO ₂ ) or the like can be used, but is not limited to the exemplified materials. The cavity C is formed by anisotropic etching or the like, but is not limited to the illustrated processing method. In addition, platinum (Pt) or the like can be used as a material for the heating element RH, the upstream temperature measuring element R1, the downstream temperature measuring element R2, and the temperature sensor RR, and can be formed by lithography or the like. Although not limited to the exemplified materials and manufacturing methods.

  As shown in FIG. 3, the thermal flow meter 100 includes a flow rate detection circuit 10 that detects a flow rate of a fluid to be measured using a bridge circuit of temperature measuring bodies R1 and R2, and a bridge of a heating element RH and a temperature sensor RR. And a heater control circuit 11 for controlling the heater using the circuit. The resistors R3 to R6 are external resistors, and their resistance values are determined from the balance of the heating element RH, the temperature sensor RR, and the temperature measuring elements R1 and R2, respectively.

  The flow rate detection circuit 10 includes a bridge circuit formed by temperature measuring elements R1 and R2, resistors R3 and R4, and an operational amplifier (hereinafter referred to as “op-amp”) U1. The positive input terminal of the operational amplifier U1 is electrically connected between the upstream temperature measuring element R1 and the downstream temperature measuring element R2 connected in series. Further, the positive input terminal of the operational amplifier U1 is grounded via the downstream temperature measuring element R2, and is electrically connected to the resistor R3 via the upstream temperature measuring element R1. The negative input terminal of the operational amplifier U1 is electrically connected between the resistors R3 and R4 connected in series. Furthermore, the negative input terminal of the operational amplifier U1 is grounded via a resistor R4 and electrically connected to the upstream temperature measuring element R1 via a resistor R3. The output terminal of the operational amplifier U1 is electrically connected to a flow rate calculation unit / correction unit 20 such as a central processing unit (CPU). A flow rate calculation unit / correction unit (hereinafter simply referred to as “correction unit”) 20 takes in the voltage amplified by the operational amplifier U1, and calculates or corrects the flow rate. The correction unit 20 is electrically connected to a storage device 30 that stores information for correcting the measurement flow rate of the fluid to be measured. The correction unit 20 corrects the measured flow rate of the fluid to be measured based on the information stored in the storage device 30.

  The heater control circuit 11 includes a heating element RH, a temperature sensor RR for measuring ambient temperature, a bridge circuit formed by resistors R5 and R6, and an operational amplifier U2. The + input terminal of the operational amplifier U2 is electrically connected between the heating element RH and the resistor 5 connected in series. Further, the + input terminal of the operational amplifier U2 is grounded via the heating element RH and electrically connected to the resistor R6 via the resistor R5. The negative input terminal of the operational amplifier U2 is electrically connected between the temperature sensor RR and the resistor R6 connected in series. Further, the negative input terminal of the operational amplifier U2 is grounded via the temperature sensor RR and electrically connected to the resistor R5 via the resistor R6. The output terminal of the operational amplifier U2 is electrically connected to the resistors R5 and R6. The heating element RH generates heat at about 60 ° C., for example.

  As shown in FIG. 4, the thermal flow meter 100 according to the first embodiment is installed in a pipe 40 through which a fluid to be measured such as an atmospheric gas flows. The thermal flow meter 100 according to the present embodiment includes a heating element RH as a fluid to be measured, an upstream temperature measuring element R1 that detects heat given from the heating element RH to the fluid under measurement, and a downstream side temperature. It is installed facing the body R2.

  The basic principle of the thermal flow meter 100 is that the temperature detected by the downstream temperature measuring element R2 is the temperature detected by the upstream temperature measuring element R1 when the fluid heated by the heating element RH flows. Therefore, the flow velocity is calculated from this temperature difference.

  FIG. 5 is a diagram when the thermal flow meter is installed so that the fluid to be measured flows vertically upward. At this time, the temperature detected by the downstream temperature measuring element (upper temperature measuring element in FIG. 5) R2 due to the heat moved upward in the vertical direction is reduced to the upstream temperature measuring element (in FIG. 5, lower). It becomes higher than the temperature detected by the side temperature sensor R1. Originally, when the fluid to be measured does not flow through the flow tube, the output of the thermal flow meter 100 must be zero. As described above, there is a difference in the detected temperatures of the temperature measuring elements R1 and R2. As a result, the output appears as if the fluid to be measured is flowing.

  Next, a method for correcting such deviation of the zero point (output when the flow rate is not flowing) will be described. FIG. 6 shows detection by the temperature measuring elements R1 and R2 when the temperature of the heating element is changed to two different temperatures when the substrate surface of the thermal flow meter is arranged in the vertical direction as shown in FIG. This is a relationship showing the difference between the measured temperatures T1 and T2 (equivalent to flow rate error Δt = T1−T2).

  The horizontal axis indicates the flow rate (L / min) of the fluid to be measured flowing through the flow tube. It can be seen that the larger the flow rate, the smaller the influence of thermal convection (the vertical axis deviation).

  The thermal flow meter used in the first embodiment has a flow rate correction table for the temperatures α and β of the heating element RH on the substrate B under a certain pressure, fluid, and product installation direction conditions ( Where α> β). This flow rate correction table is a flow rate correction value at a certain flow point as shown in FIG.

  FIG. 6 shows differences measured in four types of situations. More specifically, the relationship when the fluid to be measured flows vertically upward with the temperature of the heating element as α ° C. (Relation 1), the temperature of the heating element as β ° C. (where α> β) The relationship when flowing vertically upward (Relation 2), the temperature of the heating element as β ° C (where α> β), the relationship when flowing the fluid to be measured vertically downward (Relation 3), and the temperature of the heating element There are four types of relationships (Relationship 4) when the fluid to be measured is flowed vertically downward at α ° C. (where α> β).

  In the present invention, it is noted that if the temperature of the heating element is changed, the influence (deviation) of the thermal convection changes accordingly, and this relationship is held in the storage device 30 of the thermal flow meter 100 in advance by a table or the like. If this is done (see FIGS. 3 to 5), it is possible to read the correction value from the temperature and flow rate of the heating element at the time of measurement, and to correct the output of the thermal flow meter 100. Since the temperature difference tends to decrease as the flow rate increases, the lower the flow rate, the higher the accuracy. However, it is not something that cannot be used at higher flow rates.

  Next, with reference to FIG. 7, a procedure example of the method for improving the tilt error of the thermal flow meter according to the first embodiment will be described. FIG. 7 is a diagram for explaining the procedure of the method for improving the tilt error of the thermal type flow meter according to the first embodiment.

  When the flow direction of the fluid to be measured includes a vertical component (see FIG. 5), the method for improving the tilt error of the thermal flow meter according to the first embodiment is performed. First, as shown in FIG. 7, the temperature Td11 detected by the upstream temperature measuring element R1 and the temperature Td12 detected by the downstream temperature measuring element R2 at the first temperature T1 are measured, and the flow rate L1 is determined. Measure (ST1). The flow rate L1 at the first temperature T1 is stored in the storage device 30 (see FIGS. 3 and 5). Further, the temperature Td21 detected by the upstream temperature measuring element R1 and the temperature Td22 detected by the downstream temperature measuring element R2 are measured at the second temperature T2, and the flow rate L2 is measured (ST2). The flow rate L2 at the second temperature T2 is stored in the storage device 30 (see FIGS. 3 and 5).

  Next, the correction unit 20 determines whether the heating element RH and the temperature measuring elements R1 and R2 have increased or decreased from the flow rate L1 to the flow rate L2 with respect to the change from the first temperature T1 to the second temperature T2. The direction of the inclination of the substrate surface including (whether forward or backward in the flow) is specified (ST3). Then, the correction unit 20 reads the correction value (deviation ΔL) from the flow rate and deviation relationship table shown in FIG. 6 stored in the storage device 30 and performs a correction operation for adding or subtracting the flow rate L1 or L2 to perform a normal operation. The flow rate L is output (ST4).

  As described above, the thermal flow meter 100 according to the first embodiment causes the heating element RH to generate heat at two different temperatures when the flow direction of the fluid to be measured includes a vertical component. Information for correcting the measured flow rate of the fluid to be measured with respect to the temperatures detected by the temperature measuring bodies R1 and R2, respectively, is stored in the storage device 30, and the correcting unit 20 is based on the stored information. Correct the measured flow rate. Therefore, according to the thermal flow meter 100 according to the present embodiment, even when the plane of the substrate B including the heating element RH and the temperature measuring elements R1 and R2 is inclined from the level direction, it is accurate. The excellent effect of being able to measure the correct flow rate is exhibited.

[Second Embodiment]
Next, a thermal type flow meter according to the second embodiment of the present invention will be described with reference to FIGS. 3, 5 and 8. FIG. 8 is a diagram showing the relationship between the flow rate and the deviation in the second embodiment.

  The thermal flow meter according to the second embodiment is different from the first embodiment in the flow rate-deviation relationship table stored in the storage device 30. That is, as shown in FIG. 8, when the temperature of the heating element is γ ° C. (where α> γ> β) and the fluid to be measured is flowed vertically upward, the relationship between the flow rate and the deviation is the relationship 1 described above. It has been experimentally found that the relationship is located between and.

The thermal flow meter used in the second embodiment is the same as that of the thermal flow meter 100 of the first embodiment, and the heating element RH of the substrate B mounted on the thermal flow meter used is the same. The flow rate correction value at the temperature γ ° C. when the temperature is γ ° C. (where α>γ> β) and the flow rate is zero can be obtained from the measured value at that time as in the following equation.
If the measured value is Qr0, dr0 = Qr0-0

  If the temperature relationship of the heating element is α> γ> β, dγ0 exists between dα0 and dβ0, and similarly, flow rate correction values dγn at other flow points also exist between dαn and dβn. As a result, as shown in FIG. 9 (b), the flow rate correction value dγn at other flow rate hopoints can be obtained from dαn and dβn by calculation from the relationship between dγ0 and dα0, dβ0. In this way, the tilt error can be improved by correcting the measured value using the corrected flow rate value dγn obtained.

  The thermal type flow meter according to the second embodiment basically has the same effects as those of the first embodiment. In particular, according to the thermal type flow meter according to the second embodiment, even when the temperature of the heating element is γ ° C. (where α> γ> β) and the fluid to be measured is caused to flow vertically upward, There is an advantageous effect that the output of the meter can be corrected.

[Other Embodiments]
Although the present invention has been described by the embodiments as described above, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques should be apparent to those skilled in the art.

  In the first and second embodiments, the relationship table between the flow rate and the deviation is stored in the storage device 30, but the storage device 30 may have the flow rate correction value as a function expression. For example, a flow rate correction value at a flow rate x [L / min] at a temperature α can be expressed by a flow rate functional expression dα (x), and a flow rate correction value at a flow rate x [L / min] at a temperature β can be expressed by a flow rate functional equation dβ (x). When the flow rate correction value of zero flow rate at temperature γ is known, the flow rate correction value at flow rate x [L / min] is the relationship between the correction value at zero flow rate at temperatures α, β, and γ and the temperature α. , Β can be obtained from the function expression of the temperature correction value. Thus, it should be understood that the present invention includes various embodiments and the like not described herein.

20 Flow rate calculation unit / correction unit 30 Storage device 40 Piping 100 Thermal flow meter RH Heating element (heater element)
R1, R2 Temperature sensor (resistance element)

Claims (2)

A thermal flow meter installed in a pipe through which the fluid to be measured flows,
A heating element;
A temperature sensing element for detecting heat applied to the fluid to be measured from the heating element;
When the flow direction of the fluid to be measured includes a vertical component, the fluid to be measured with respect to the temperatures detected by the temperature measuring body when the heat generating body is heated at two different temperatures. A storage device for storing information for correcting the measured flow rate of
A correction unit that corrects the measured flow rate of the fluid to be measured based on the information;
A thermal flow meter comprising: A procedure for measuring a first flow rate at a first temperature;
A procedure for measuring a second flow rate at a second temperature;
A procedure for identifying the direction of inclination of the substrate surface including the heating element and the temperature sensing element from the change in the first flow rate and the second flow rate with respect to the change from the first temperature to the second temperature
A procedure for performing a correction operation on the first flow rate or the second flow rate based on the information for correction and outputting a normal flow rate;
A method for improving a tilt error of a thermal type flow meter, comprising:

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