JP6475081B2 - 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.

  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 includes at least a first part and a second part that are pipes through which a fluid to be measured flows, and in which the flow directions of the fluid to be measured are opposite to each other. A pipe, a first flow meter provided in the first portion, and a second flow meter provided in the second portion and having the same characteristics as the first flow meter, the first flow meter and the first flow meter Each of the two flow meters has a heating element and a temperature measuring element for detecting heat given from the heating element to the fluid to be measured, and the output of the first flow meter and the second flow meter The direction of the flow of the fluid to be measured in the pipe is specified from the output of the first flow meter and the second flow meter, and the temperature difference of the temperature measuring body with respect to the direction of the flow of the fluid to be measured is determined. To correct the output of the flow meter that is determined to be installed in the opposite direction And correcting on the basis of the distribution.

  In addition, the method for improving the tilt error of the thermal flow meter according to the present invention includes a procedure for specifying the flow direction of the fluid under measurement of each flow meter in the piping from the output of the first flow meter and the output of the second flow meter. Based on the information for correcting the output of the flow meter in which the temperature difference of the temperature measuring element is attached in the opposite direction with respect to the flow direction of the fluid to be measured, of the first flow meter and the second flow meter And a correction procedure.

  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 one 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 this Embodiment. It is a circuit diagram of the thermal type flow meter concerning this embodiment. It is a schematic diagram of the state which installed the thermal type flow meter which concerns on this Embodiment in the perpendicular direction. It is a figure which shows the relationship between a flow volume and a deviation. 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 this 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, a thermal flow meter according to an 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 an embodiment of the present invention. FIG. 2 is a cross-sectional view of the thermal type flow meter according to the first embodiment of the present invention as seen from the II-II direction in FIG. FIG. 3 is a circuit diagram of the thermal type flow meter according to the present embodiment. FIG. 4 is a schematic diagram of an installed state of the thermal flow meter according to the present embodiment.

  The thermal flow meter 100 according to the present embodiment is realized by using the microchip having the element structure shown in FIGS. 1 and 2 and configuring the detection circuit 1 as shown in FIG. 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 present embodiment is a pipe through which a fluid to be measured such as an atmospheric gas flows, and a first portion 31 in which the flow directions of the fluid to be measured are opposite to each other. It is installed in a U-shaped pipe 30 having at least a second portion 32. A first flow meter 101 is installed in the first portion 31, and a second flow meter 102 is installed in the second portion 32. The first flow meter 101 and the second flow meter 102 include a heating element RH that applies heat to the fluid to be measured, an upstream temperature measuring body R1 that detects heat applied to the fluid to be measured from the heating element RH, and The downstream temperature measuring element R2 is arranged in the same configuration as shown in FIGS.

  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.

  As shown in FIG. 4, when the thermal flow meter 100 is installed in the vertical direction, the heat generated by the heating element RH moves upward due to thermal convection. At this time, in the first flow meter 101, the temperature detected by the upstream temperature sensor (upper temperature sensor in FIG. 4) R1 is the downstream temperature sensor due to the heat that has moved upward in the vertical direction. It becomes higher than the temperature detected by the body (lower temperature measuring body in FIG. 4) R2. Originally, when the fluid to be measured does not flow through the flow tube, the output of the first flow meter 101 must be zero. As described above, there is a difference between 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. In FIG. 4, F indicates the flow direction of the fluid to be measured, and H indicates the influence direction of the thermal convection.

  Next, a method for correcting such an error of the zero point (output when the flow rate is not flowing) will be described. FIG. 5 shows a flow rate error caused by the installation (tilt) direction 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. It is the relationship which showed.

  In FIG. 5, the horizontal axis indicates the flow rate (L / min) of the fluid to be measured flowing in the flow tube, and the vertical axis indicates the deviation (L / min) from the flow rate output when the substrate surface is arranged in the horizontal direction. ). As FIG. 5 shows, it turns out that the influence (deviation of a vertical axis | shaft) of thermal convection becomes small, so that flow volume becomes large.

  FIG. 5 also shows differences measured in four 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).

  Note that 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, the relationship between the flow rate and the deviation is located between relationship 1 and relationship 2. Experiments have also shown that this is the relationship. However, in relation 1 and relation 2 in FIG. 5, as the flow region becomes a high flow rate, there is almost no difference in the deviation, and it is difficult to perform accurate correction. On the other hand, in relation 3 and relation 4 in FIG. 5, even when the flow region becomes a high flow rate, a clear difference is observed in the deviation.

  Therefore, in the present invention, the output of the flowmeter that is flowing vertically downward is always used, and the correction value is corrected more accurately by using the vertically downward correction value in the correction table as shown in part A of FIG. The flow rate value can be calculated. By examining the detected temperature difference, it is possible to determine in which direction it is installed. The temperature difference is detected from the first flow meter 101 and the second flow meter 102 to determine which is attached in the opposite direction with respect to the flow direction, and the flow rate is calculated using only the temperature difference from the reversely attached flow meter. To do.

  Next, referring to FIG. 6, a procedure example of the method for improving the tilt error of the thermal flow meter according to the present embodiment will be described. FIG. 6 is a diagram for explaining the procedure of the method for improving the tilt error of the thermal flow meter according to the present embodiment.

  When the first flow meter 101 and the second flow meter 102 include a vertical component as shown in FIG. 4, the method for improving the tilt error of the thermal flow meter according to the present embodiment is performed.

  As shown in FIG. 6, first, the temperature detected by the temperature sensing element R1 on the upstream side of the first flow meter 101 and the temperature detected by the temperature measuring element R2 on the downstream side are measured, and the first flow meter 101 is measured. Is obtained (ST1). Further, the temperature detected by the temperature measuring element R1 upstream of the second flow meter 102 and the temperature detected by the temperature measuring element R2 downstream are measured, and the output of the second flow meter 102 is obtained (ST2). . Next, the correction unit 10 specifies the flow direction of the fluid to be measured of each of the flow meters 101 and 102 in the U-shaped pipe 30 from the output of the first flow meter 101 and the output of the second flow meter 102 ( ST3). Further, the correction unit 10 detects a temperature difference from the first flow meter 101 and the second flow meter 102, and the temperature measuring bodies R1 and R2 are reversed with respect to the flow direction of which flow meter 101 (or 102). It is determined whether the orientation is attached (ST4).

  If it is determined that the direction of the flow of the fluid to be measured and the attachment of the temperature measuring elements R1 and R2 are reversed in the first flow meter 101 and the second flow meter 102 (ST4 / YES), Based on the vertically downward information in the relationship table between the flow rate and the deviation stored in the storage device 20, the output of the flow meter 101 (or 102) in which the temperature measuring elements R1 and R2 are mounted in the opposite direction with respect to the direction of fluid flow. (ST5). On the other hand, when any of the first flow meter 101 and the second flow meter 102 is not mounted with the temperature measuring bodies R1 and R2 in the reverse direction with respect to the flow direction of the fluid to be measured (ST4). / NO), the correction unit 10 does not perform correction control.

  As described above, the thermal flow meter 100 according to the present embodiment is based on the flow direction of the fluid to be measured in the U-shaped pipe 30 from the output of the first flow meter 101 and the output of the second flow meter 102. Of the first flow meter 101 and the second flow meter 102, the output of the flow meter 101 or 102, which is determined to include the first direction component, is corrected. Is corrected based on the information for this (the relationship table between the flow rate and the deviation shown in FIG. 5). 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.

[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. It should be understood that the present invention includes various embodiments and the like not described herein.

10 Correction unit 20 Storage device 100 Thermal flow meter 101 First flow meter 102 Second flow meter RH Heating element (heater element)
R1, R2 Temperature sensor (resistance element)

Claims (2)

A pipe through which the fluid to be measured flows, and a pipe having at least a first portion and a second portion in which the flow directions of the fluid to be measured are opposite to each other;
A first flow meter provided in the first portion;
A second flow meter provided in the second part and having the same characteristics as the first flow meter,
The first flow meter and the second flow meter are respectively
A heating element, and a temperature measuring element for detecting heat applied to the fluid to be measured from the heating element,
From the output of the first flow meter and the output of the second flow meter, specify the direction of the flow of the fluid to be measured in the pipe,
Of the first flow meter and the second flow meter, the output of the flow meter that has been determined that the temperature difference of the temperature measuring body is attached in the opposite direction with respect to the flow direction of the fluid to be measured. A thermal flow meter that corrects based on information for correction. From the output of the first flow meter and the output of the second flow meter, a procedure for specifying the direction of the flow of the fluid under measurement of each flow meter in the piping,
Based on the information for correcting the output of the flow meter in which the temperature difference of the temperature measuring body is attached in the opposite direction to the direction of the flow of the fluid to be measured, of the first flow meter and the second flow meter. The procedure to correct,
A method for improving a tilt error of a thermal type flow meter, comprising:

Images