JP2019164045A - Thermal flowmeter - Google Patents

Abstract

An object of the present invention is to make it possible to measure a flow rate with higher accuracy by using a thermal flow meter provided in a measuring section which is thinner than the surroundings of a pipe. A temperature measuring section constituting a sensor section is formed on a main surface of a first substrate. The back surface 121b of the first substrate 121 is provided in contact with the outer wall of the measurement unit 101a in the pipe 101. The heater 112 constituting the sensor unit 102 is formed on the main surface 122 a of the second substrate 122. The back surface 122b of the second substrate 122 is provided in contact with the outer wall of the measurement unit 101a in the pipe 101. [Selection diagram] Fig. 1

Description

  The present invention relates to a thermal flow meter that measures a flow rate by utilizing an action of thermal diffusion in a fluid.

  Techniques for measuring the flow rate and flow velocity of a fluid flowing through a channel are widely used in the industrial and medical fields. There are various types of devices for measuring flow rate and flow velocity, such as electromagnetic flowmeters, vortex flowmeters, Coriolis flowmeters, and thermal flowmeters. Thermal flow meters can detect gases and liquids, have no pressure loss, and can measure mass flow. Such a thermal flow meter is suitable for measuring a minute liquid flow rate.

  Thermal flow meters include a method for measuring the flow rate based on the temperature difference between the upstream and downstream of the heater and a method for measuring the flow rate based on the power consumption of the heater. For example, when measuring the flow rate of the liquid, the heater temperature is operated by heating at a constant temperature such as plus 10 ° C. with respect to the liquid temperature, and the flow rate is calculated from the temperature difference between the upstream and downstream or the heater power.

  In such a thermal flow meter, in order to efficiently heat a fluid to be measured flowing through a pipe in a short time, a sensor unit is provided at a place formed thinner than other parts (see Patent Document 1). . With this configuration, it is possible to detect a temperature change due to the flow of the fluid with high sensitivity, and to measure the flow rate of the fluid to be measured with high accuracy.

Special table 2003-532099 gazette

  However, the portion where the pipe is thinned is in a state where gas generated from the liquid to be measured is easily transmitted. For this reason, permeation | transmission (outgas) of a gaseous component may generate | occur | produce from this location. In such a state, there is a case where outgas affects the sensor unit, and there is a problem that accurate flow rate measurement cannot be performed with high accuracy.

  The present invention has been made to solve the above-described problems, and enables more accurate flow measurement using a thermal flow meter provided in a measurement region that is thinner than the surroundings in a pipe. For the purpose.

  A thermal flow meter according to the present invention is configured to heat a fluid in a pipe that transports a fluid to be measured, a measurement area that is formed on the outer wall of the pipe and that is partially thinner than other parts, and the measurement area. And a temperature measuring unit configured to measure the temperature of the fluid in the measurement region, and the difference between the temperature of the heater and the temperature of the fluid at a position not affected by the heat of the heater is set. A sensor unit configured to output a sensor value corresponding to a state of thermal diffusion in the fluid heated by the heater when the heater is driven so as to have a set temperature difference; A flow rate calculation unit configured to calculate from a value; a first substrate with a temperature measurement unit formed on the main surface; and a second substrate with a heater formed on the main surface; Back side of the second substrate It is disposed in contact with the outer wall of the measurement area, the first substrate and the second substrate is composed of a material having a higher thermal conductivity than the material of the pipe.

  In the thermal flow meter, the first substrate and the second substrate may be made of silicon, ceramic, or metal.

  In the above thermal flow meter, the temperature measurement unit measures the temperature of the fluid upstream of the heater and is not affected by the heat of the heater, and the sensor unit measures the temperature of the heater and the temperature of the fluid measured by the temperature measurement unit. The heater power is output as a sensor value when the heater is driven so that the difference between the two becomes a set temperature difference.

  In the thermal flow meter, the temperature measurement unit includes a first temperature measurement unit, a second temperature measurement unit, and a third temperature measurement unit, and the first temperature measurement unit controls the thermal effect of the heater upstream of the heater. The second temperature measurement unit measures the temperature of the fluid at a position that is affected by the heat of the heater on the upstream side of the heater, and the third temperature measurement unit is on the downstream side of the heater. The temperature of the fluid at a position affected by the heat of the heater is measured, and the sensor unit drives the heater so that the difference between the temperature of the heater and the temperature of the fluid measured by the first temperature measurement unit becomes a set temperature difference. The temperature difference between the fluid temperature measured by the second temperature measurement unit and the fluid temperature measured by the third temperature measurement unit is output as a sensor value.

  As described above, according to the present invention, since the first substrate and the second substrate are used, the flow rate can be measured with higher accuracy by using the thermal flow meter provided in the measurement region thinner than the periphery in the pipe. An excellent effect is obtained.

FIG. 1 is a configuration diagram showing the configuration of the thermal flow meter in the embodiment of the present invention. FIG. 2 is a cross-sectional view showing a partial configuration of the thermal flow meter in the embodiment of the present invention. FIG. 3 is a configuration diagram showing the configuration of another thermal flow meter according to the embodiment of the present invention.

  Hereinafter, a thermal flow meter according to an embodiment of the present invention will be described with reference to FIGS. This thermal flow meter includes a pipe 101 that transports a fluid to be measured, a sensor unit 102, and a flow rate calculation unit 103. The pipe 101 is made of, for example, a synthetic resin such as a fluororesin. The pipe 101 has a measurement region 101a formed on the outer wall of the pipe 101 and partially formed thinner than other parts. The measurement region 101a has, for example, a partially recessed shape. The thickness of the thinnest portion in the measurement region 101a is, for example, about 100 μm.

  In the embodiment, the sensor unit 102 includes a temperature measurement unit 111, a heater 112, a control unit 113, and a power measurement unit 114.

  The temperature measuring unit 111 is formed (mounted) on the main surface 121 a of the first substrate 121. The temperature measurement unit 111 is, for example, a temperature sensor element such as a thermopile made up of wiring patterns that form a plurality of thermocouples. The back surface 121b of the first substrate 121 is provided in contact with the outer wall of the measurement region 101a in the pipe 101. The first substrate 121 is in thermal contact with both the temperature measurement unit 111 and the outer wall of the measurement region 101a.

  Similarly, the heater 112 is formed (mounted) on the main surface 122 a of the second substrate 122. The heater 112 includes, for example, a heater element serving as a heating resistor and a temperature sensor element for fluid temperature measurement. The back surface 122b of the second substrate 122 is provided in contact with the outer wall of the measurement region 101a in the pipe 101. The second substrate 122 is in thermal contact with both the heater 112 and the outer wall of the measurement region 101a. The temperature measuring unit 111 measures the temperature of the fluid.

  The first substrate 121 and the second substrate 122 are bonded and fixed to the outer wall of the measurement region 101a in the pipe 101 with, for example, a heat conductive adhesive. The first substrate 121 and the second substrate 122 are made of a material having higher thermal conductivity than the material forming the pipe 101. By configuring the first substrate 121 and the second substrate 122 from a material having good thermal conductivity, the temperature of the fluid flowing through the pipe 101 is easily transmitted to the temperature measuring unit 111, and the heat from the heater 112 is transferred to the fluid. It becomes easy to convey. The first substrate 121 and the second substrate 122 are made of, for example, silicon, ceramic, or metal. The first substrate 121 and the second substrate 122 may be made of single crystal silicon, for example. In addition, the plate thickness of the first substrate 121 and the second substrate 122 may be equal to or less than the thickness of the pipe wall of the pipe 101 other than the measurement region 101a.

  In the embodiment, the sensor unit 102 includes a temperature measurement unit 111, a heater 112, a control unit 113, and a power measurement unit 114. Since the second substrate 122 on which the heater 112 is mounted is provided downstream of the first substrate 121, the heater 112 is provided downstream of the temperature measuring unit 111 mounted on the first substrate 121.

  Here, the sensor unit 102 drives the heater 112 so that the difference between the temperature of the heater 112 and the temperature of the fluid at a position not affected by the heat of the heater 112 becomes a set temperature difference. The sensor value corresponding to the state of thermal diffusion in the fluid heated by the heater 112 is output. In the embodiment, the difference between the temperature of the heater 112 and the temperature of the heater 112 measured by the temperature measuring unit 111, for example, the temperature of the fluid upstream of the heater 112, is set in advance by the control unit 113. The heater 112 is controlled and driven so as to achieve the set temperature difference.

  For example, the control unit 113 includes a power supply circuit that supplies power to the heater 112, a temperature difference detection circuit, and a control circuit that controls the power supplied by the power supply circuit. For example, the control circuit feedback controls the voltage supplied to the bridge circuit so that the output voltage of the bridge circuit constituting the heater 112 becomes 0, and adjusts the drive voltage supplied by the power supply circuit.

  The power measuring unit 114 measures and outputs the power of the heater 112 controlled by the control unit 113. The power measuring unit 114 is constituted by, for example, a heater power detection circuit. The heater power detection circuit obtains drive power in the heater element from, for example, the voltage applied to the above-described heater element constituting the heater 112 and the voltage applied to the bridge circuit including the heater element.

  The electric power output from the electric power measurement part 114 which comprises the sensor part 102 mentioned above becomes a sensor value. The flow rate calculation unit 103 calculates the flow rate of the fluid from the power (sensor value) of the heater 112 measured and output by the power measurement unit 114. The flow rate calculation unit 103 includes, for example, a flow rate calculation circuit that calculates a flow rate from a sensor value using a coefficient as physical property data set in advance.

  According to the embodiment, the temperature measurement unit 111 and the heater 112 are in a state of being spaced apart from the measurement region 101a, which is thinner than the periphery of the pipe 101, with the first substrate 121 and the second substrate 122 interposed therebetween. As a result, according to the embodiment, the temperature measurement unit 111 and the heater 112 can prevent the influence of the outgas in the measurement region 101a, and can measure the flow rate with higher accuracy.

  Here, operation | movement of the thermal type flow meter in embodiment is demonstrated in detail. As is well known, when the heater 112 is driven so that the difference between the temperature of the heater 112 and the temperature of the fluid at a position not affected by the heat of the heater 112 becomes the set temperature difference, There is a correlation between the power consumed and the fluid flow rate. This correlation is also reproducible at the same fluid / flow rate / temperature. Therefore, as described above, the flow rate calculation unit 103 uses a predetermined correlation coefficient (constant) based on the power measured by the power measurement unit 114 while the heater 112 is controlled by the control unit 113. Can be calculated.

  As shown in FIG. 3, the temperature measuring unit (first temperature measuring unit) 111, the heater 112, the control unit 113, the temperature measuring unit (second temperature measuring unit) 116, and the temperature measuring unit (third temperature measuring unit). The sensor unit 102 ′ may be configured from 117. The temperature measurement unit 111 is provided in the measurement region 101 a via the first substrate 123. The temperature measurement unit 116 is provided in the measurement region 101 c via the first substrate 124. The temperature measurement unit 117 is provided in the measurement region 101 d through the first substrate 125. The heater 112 is provided in the measurement region 101 b through the second substrate 122. The first substrates 123, 124, and 125 and the second substrate 122 are made of, for example, silicon, ceramic, or metal having good thermal conductivity. The first substrate 123, 124, 125 and the second substrate 122 may be made of, for example, single crystal silicon.

  In this configuration, the control unit 113 sets in advance a difference between the temperature of the heater 112 and the temperature of the fluid that is measured by the temperature measurement unit 111 and that is not affected by the heat of the heater 112, for example, upstream of the heater 112. The heater 112 is controlled and driven so that the set temperature difference is the same.

  The temperature measurement unit 116 is provided on the downstream side of the temperature measurement unit 111 and on the upstream side of the heater 112. The temperature measuring unit 117 is provided on the downstream side of the heater 112. The temperature measuring unit 116 and the temperature measuring unit 117 measure the temperature of the fluid.

  The fluid flow rate can be calculated from the temperature difference between the temperature of the fluid measured by the temperature measuring unit 116 and the temperature of the fluid measured by the temperature measuring unit 117. In this example, the temperature difference between the temperature of the fluid measured by the temperature measuring unit 116 and the temperature of the fluid measured by the temperature measuring unit 117 is the sensor value.

  As is well known, the heater 112 is driven so that the difference between the temperature of the heater 112 and the temperature of the fluid at a position not affected by the heat of the heater 112 becomes a preset temperature difference. There is a correlation between the temperature difference between the temperature of the fluid upstream of the heater 112 and the temperature of the fluid downstream of the heater 112 and the flow rate of the fluid. This correlation is also reproducible at the same fluid / flow rate / temperature. Therefore, as described above, in a state where the heater 112 is controlled by the control unit 113, a predetermined phase is determined based on the difference (temperature difference) between the temperature measured by the temperature measurement unit 116 and the temperature measured by the temperature measurement unit 117. The flow rate can be calculated by using the relation number (constant).

  As described above, according to the present invention, since the first substrate and the second substrate are used, a more accurate flow rate can be obtained by using a thermal flow meter provided in a measurement region that is thinner than the surroundings in the pipe. It becomes possible to measure.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  DESCRIPTION OF SYMBOLS 101 ... Pipe, 101a ... Measurement area, 102 ... Sensor part, 103 ... Flow rate calculation part, 111 ... Temperature measurement part, 112 ... Heater, 113 ... Control part, 114 ... Electric power measurement part, 121 ... 1st board | substrate, 121a ... Main Front surface, 121b ... back surface, 122 ... second substrate, 122a ... main surface, 122b ... back surface.

Claims (4)

Piping for transporting the fluid to be measured;
A measurement region formed on the outer wall of the pipe and partially formed thinner than the other parts;
A heater configured to heat the fluid in the measurement region; and a temperature measurement unit configured to measure the temperature of the fluid in the measurement region. A sensor corresponding to the state of thermal diffusion in the fluid heated by the heater when the heater is driven so that the difference between the temperature of the fluid at a position where it is not received and the temperature of the fluid is set. A sensor unit configured to output a value;
A flow rate calculation unit configured to calculate the flow rate of the fluid from the sensor value;
A first substrate having the temperature measuring portion formed on the main surface;
The heater includes a second substrate formed on a main surface;
The back surface of the first substrate and the back surface of the second substrate are disposed in contact with the outer wall of the measurement region;
The first substrate and the second substrate are made of a material having higher thermal conductivity than the material of the piping. The thermal flow meter according to claim 1, wherein
The thermal flowmeter, wherein the first substrate and the second substrate are made of silicon, ceramic, or metal. The thermal flow meter according to claim 1 or 2,
The temperature measuring unit measures the temperature of the fluid at a position upstream of the heater and not affected by the heat of the heater;
The sensor unit is configured to measure the electric power of the heater when the heater is driven so that a difference between the temperature of the heater and the temperature of the fluid measured by the temperature measurement unit becomes the set temperature difference. A thermal flowmeter that outputs as a value. The thermal flow meter according to claim 1 or 2,
The temperature measuring unit includes a first temperature measuring unit, a second temperature measuring unit, and a third temperature measuring unit,
The first temperature measurement unit measures the temperature of the fluid at a position upstream of the heater and not affected by the heat of the heater,
The second temperature measurement unit measures the temperature of the fluid at a position that is affected by the heat of the heater upstream of the heater,
The third temperature measurement unit measures the temperature of the fluid at a position that is affected by the heat of the heater downstream from the heater,
The sensor unit drives the heater so that a difference between a temperature of the heater and a temperature of the fluid measured by the first temperature measurement unit becomes the set temperature difference. A thermal flow meter characterized in that a temperature difference between the temperature of the fluid measured by the measurement unit and the temperature of the fluid measured by the third temperature measurement unit is output as the sensor value.

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