JP2005061995A - Method and device for flow measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly measure with accuracy the flow rate of fluid flowing inside, by utilizing the external tube as a fluid circulation passage without decoupling the external tube, wherein the fluid to be measured is circulated and thereby without pollution of the fluid to be measured. <P>SOLUTION: This device is equipped with a sensor unit 16, including a flow rate detection part having a heating element and a temperature-sensing element, a detection circuit 40 constituted by including the heating element and the temperature-sensing element of the flow rate detection part, for generating electrical output corresponding to the flow rate of the fluid in a flexible tube 14, a heat generation control means 50 for controlling heat generation from the heating element so that the output from the detection circuit is maintained at a prescribed value, an operation means 54 for acquiring a flow rate value, based on the control state of the heating element by the heat generation control means, and a pressing means for pressing the flow rate detection part onto the circumferential surface of the tube 14, to thereby deform the tube into a prescribed shape. The pressing means has a base part 20 and a movable part 24 which is detachable via a spacer 22. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for measuring the flow rate of a fluid flowing in a fluid flow passage without contacting the fluid.

  2. Description of the Related Art Conventionally, a thermal flow rate measuring device such as an indirectly heated type is used as a flow meter for measuring a flow rate of a fluid flowing in a fluid flow passage. As an indirectly heated flow measurement device, a sensor chip in which a thin film heating element and a thin film temperature sensing element are stacked on an insulating layer through a thin film technology between a fluid in a fluid flow path is used. The thing arranged so that heat transfer is possible is used. The sensor chip may be disposed in the fluid flow path so as to be in direct contact with the fluid, or may be disposed outside the fluid flow path so as to transfer heat between the sensor chip and the fluid without directly contacting the fluid. A heat transfer member may be protruded into the fluid flow path. By energizing the thin film heating element, the thin film temperature sensing element is heated, and the electrical characteristics based on the temperature rise of the thin film temperature sensing element, for example, the value of electric resistance is changed. The change in the electrical resistance value, that is, the temperature change in the thin film temperature sensing element changes according to the flow rate of the fluid flowing in the fluid flow path. The change in the electrical resistance value of the thin film temperature sensor varies depending on the temperature of the fluid. Therefore, a thin film temperature sensor for temperature compensation is installed in the electric circuit for measuring the change in the electrical resistance value of the thin film temperature sensor. Incorporating, the change of the flow rate measurement value due to the temperature of the fluid is minimized.

  An indirectly heated flow meter using such a thin film element is described in, for example, Japanese Patent Application Laid-Open No. 11-11866 (Patent Document 1). In this flow meter, an electric circuit including a bridge circuit is used to obtain an electric output corresponding to the flow rate of the fluid.

  There are a wide variety of fluids (fluids to be measured) that are subject to flow measurement, but in recent years flow measurement of fluids that require sophisticated hygiene management, such as medical chemicals injected into living bodies and biological fluids collected from living bodies. Alternatively, it is desired to determine the presence or absence of fluid circulation based on the flow rate measurement. In this case, if a flow meter having a heat transfer member protruding into the fluid flow path or a sensor chip disposed in the fluid flow path is used, the heat transfer member or sensor chip will come into contact with the fluid. In order to measure the flow rate of these fluids, heat transfer directly in contact with the fluid may cause contamination of the fluid, and further, the fluid may react with the heat transfer member or sensor chip to contaminate the fluid. It is preferable to use a non-contact type flow meter in which no member is used and a sensor chip is disposed outside the fluid flow path.

  On the other hand, as a flowmeter, conventionally, a flowmeter itself having a fluid flow passage in the housing and a sensor chip disposed in the housing adjacent to the fluid flow passage is used. A flow meter is interposed in the middle of the external conduit through which the fluid to be measured flows, and both ends of the fluid flow passage in the housing of the flow meter are connected to the divided portions of the external conduit.

However, by dividing the external pipe to interpose the flow meter, a connection means between the external pipe and the fluid flow path in the housing of the flow meter becomes necessary, and the device configuration becomes complicated. Since the fluid is easily contaminated, it is not preferable to use such a conventional method as it is, particularly when measuring the flow rate of the fluid that requires the above-mentioned high hygiene management.
JP-A-11-118566

  Therefore, the present invention does not divide the external piping through which the fluid to be measured flows, and therefore there is no risk of contamination of the fluid to be measured. The external piping is used as a fluid flow path, and the flow rate of the fluid flowing in the fluid is measured. The object is to provide a method for measuring with good accuracy.

  Furthermore, an object of the present invention is to provide a flow rate measuring apparatus that is used for carrying out the above method and has a simplified configuration.

According to the present invention, the object as described above is achieved.
A method for measuring the flow rate of a fluid flowing in a pipe,
A flexible tube is used as the piping, and a flow rate detection unit having a heating element and a temperature sensing body is pressed against the outer peripheral surface of the tube to deform the tube into a predetermined shape, and the tube and the flow rate detection unit A heat transfer path in a predetermined form with
After that, by the heat generation control means so as to maintain the output of the detection circuit configured to include the heating element and the temperature sensing element and generating an electrical output corresponding to the flow rate of the fluid in the tube at a predetermined value. A flow rate measuring method characterized by controlling heat generation of the heating element and obtaining a flow rate value based on a control state by the heat generation control means;
Is provided.

  In one aspect of the present invention, the tube is made of a material having a thermal conductivity of 0.05 W / (m · ° C.) to 1 W / (m · ° C.). In one aspect of the present invention, the tube is made of synthetic resin or synthetic rubber. In one aspect of the present invention, the flow rate detection unit is pressed against the outer peripheral surface of the tube through a thin thermal conductor thin plate connected thereto. In one aspect of the present invention, the thermal good conductor sheet is a metal sheet.

Furthermore, according to the present invention, the object as described above is achieved.
An apparatus for measuring the flow rate of a fluid flowing in a pipe made of a flexible tube,
A flow rate detector having a heating element and a temperature sensing element;
A detection circuit configured to include the heating element and the temperature sensing element and generate an electrical output corresponding to the flow rate of the fluid in the tube;
Heat generation control means for controlling the heat generation of the heating element so as to maintain the output of the detection circuit at a predetermined value;
Arithmetic means for obtaining a flow rate value based on the control state of the heating element by the heat generation control means;
A flow rate measuring device comprising: a pressing means for pressing the flow rate detection unit against the outer peripheral surface of the tube to deform the tube into a predetermined shape;
Is provided.

  In one aspect of the present invention, the tube is made of a material having a thermal conductivity of 0.05 W / (m · ° C.) to 1 W / (m · ° C.). In one aspect of the present invention, the tube is made of synthetic resin or synthetic rubber. In one aspect of the present invention, a heat good conductor thin plate connected to the flow rate detection unit is provided, and the pressing means presses the flow rate detection unit against the outer peripheral surface of the tube via the heat good conductor thin plate. In one aspect of the present invention, the thermal good conductor sheet is a metal sheet.

  In one aspect of the present invention, the pressing means includes a base part for supporting a sensor unit including the flow rate detection part, and a movable part movable with respect to the base part, and the movable part is the base part. On the other hand, a first state in which the tube is deformed into the predetermined shape by applying a pressing force to the tube by the flow rate detection unit, and a second state in which the application of the pressing force to the tube by the flow rate detection unit is released. Take. In one aspect of the present invention, the movable portion is attached to the base portion by a hinge.

  According to the present invention, since the flexible tube through which the non-measurement fluid flows is used as it is as the fluid flow path, there is no fear of contamination of the fluid to be measured, and the flow rate of the fluid can be measured with sufficient accuracy. In addition, according to the present invention, there is provided a flow rate measuring device that is used for carrying out the above method and has a simplified configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a flow rate measuring device according to the present invention in which a flow rate measuring method according to the present invention is implemented, FIGS. 2 and 3 are partially enlarged views thereof, and FIG. FIG. 5 is a circuit configuration diagram thereof.

  In these drawings, reference numeral 14 denotes an external pipe constituting a fluid flow path, and the pipe 14 is, for example, a flexible tube made of synthetic resin or synthetic rubber through which a medical drug solution as a fluid to be measured flows. Examples of the tube 14 include polyethylene having a thermal conductivity of 0.33 W / (m · ° C.) and an inner diameter of 2.0 mm and a thickness of 0.2 mm, or a thermal conductivity of 0.15 to 0.21 W. An inner diameter of 1.0 mm and a wall thickness of 0.8 mm made of polyvinyl chloride / (m · ° C.), or an inner diameter of polyvinyl chloride having a thermal conductivity of 0.15 to 0.21 W / (m · ° C.). An example having a thickness of 0.7 mm and a thickness of 0.3 mm is exemplified. The tube 14 is preferably made of a material having a thermal conductivity of 0.05 W / (m · ° C.) to 1 W / (m · ° C.). If the thermal conductivity of the tube 14 is too small, heat transfer between the flow rate detection unit and the fluid to be measured tends to be insufficient, and if the thermal conductivity of the tube 14 is too large, the measurement is performed via the tube. There is a tendency that the ratio of heat exchange with the outside other than the fluid becomes large and the detection circuit output corresponding to the required flow rate of the fluid to be measured cannot be obtained.

  Reference numeral 16 denotes a sensor unit, in which a flow rate detection unit and a fluid temperature detection unit are arranged. That is, as shown in FIG. 4, in the sensor unit 16, the flow rate detection unit 4 is fixed to one surface (the lower surface in the drawing) of the metal thin plate 2 as a heat good conductor thin plate. As described above, a thin film heating element and a thin film temperature sensor are laminated via an insulating layer, and a sensor chip is further provided with a protective film. The terminals of the thin film heating element and the thin film temperature sensing element of the flow rate detection unit 4 are connected to the external leads 8 by bonding wires 6, respectively. As shown in FIG. 2, the fluid temperature detection unit 4 ′ has substantially the same configuration as the flow rate detection unit 4 except that it does not have a thin film heating element, and the metal thin plate 2 ′. It is fixed to the lower surface of the. The terminal of the thin film temperature sensing element is connected to the external lead 8 'by a bonding wire. A part of the external leads 8, 8 ′, the metal thin plates 2, 2 ′, the flow rate detection unit 4, the fluid temperature detection unit 4 ′, and the bonding wire 6 are sealed with a resin mold 10. The upper surface portions corresponding to the flow rate detection unit 4 and the fluid temperature detection unit 4 ′ of the metal thin plates 2 and 2 ′ are exposed portions exposed to the outside, and the tube 14 is pressed thereon (that is, the flow rate detection unit 4 and The fluid temperature detector 4 'is pressed against the tube 14 through the thin metal plates 2 and 2'). Note that the flow rate detection unit 4 and the fluid temperature detection unit 4 'may be disposed on the upper surface portion of the thin metal plate 2 or 2'. In this case, the tube 14 is pressed directly against the flow rate detection unit 4 and the fluid temperature detection unit 4 ′ (that is, the flow rate detection unit 4 and the fluid temperature detection unit 4 ′ are pressed directly against the tube 14).

  Means for applying a pressing force to the tube will be described. The sensor unit 16 is fixed on the base 20, and a movable part 24 is attached on the base via a spacer 22. This attachment can be performed by screwing the male screw 26 into the female screw hole formed in the base portion 20 through the movable portion 24 and the through hole formed in the spacer 22. The height of the spacer 22 is such that when the movable portion 24 is attached to the base portion 20 as described above, the tube 14 is sandwiched between the lower surface of the movable portion 24 and the metal thin film exposed portion of the sensor unit 16. The flow rate detection unit 4 and the fluid temperature detection unit 4 ′ are pressed against the tube via the thin metal plates 2 and 2 ′, so that the tube 14 is deformed into a predetermined shape and contacts the thin metal plate with a predetermined contact area. (That is, a heat transfer path having a predetermined form is formed between the tube 14 and the flow rate detection unit 4 and the fluid temperature detection unit 4 ′). When the movable portion 24 is removed from the base portion 20, the pressing force applied to the tube 14 is released, and the tube has a free shape with an original circular cross section as shown in the figure. That is, the state where the movable part 24 is attached to the base 20 is the first state of the movable part, and the state where the movable part 24 is detached from the base 20 is the second state of the movable part. In the first state, in a predetermined form between the flow rate detection unit 4 and the fluid temperature detection unit 4 ′ and the fluid in the tube via the tube and the metal thin plate with a contact area increased by deformation due to pressing. Heat exchange is possible. Since the tube is not a good heat conductor such as metal but has a relatively low thermal conductivity, there is substantially no heat exchange with the outside of the measurement portion (ie, a deformed portion of the tube) through the tube, For this reason, the flow rate can be measured with good measurement accuracy.

  FIG. 5 shows a specific circuit configuration for the flow rate measurement using the flow rate detection unit 4 and the fluid temperature detection unit 4 ′. The circuit for measuring the flow rate is the same as the circuit of the indirectly heated flow meter as described in, for example, JP-A-11-118566, and an electric signal corresponding to the instantaneous flow rate of the liquid flowing in the tube 14. Is output. Moreover, it is also possible to output an electric signal corresponding to the integrated flow rate by appropriately integrating. This will be further described below.

  A DC voltage V <b> 1 is supplied to the bridge circuit (detection circuit) 40. The bridge circuit 40 includes a thin film temperature sensitive resistor 4b of the flow rate detector 4, a thin film temperature sensitive resistor 4a 'of the fluid temperature detector 4', and resistors 43 and 44. Potentials Va and Vb at points a and b of the bridge circuit 40 are input to the differential amplification / integration circuit 46.

  On the other hand, the DC voltage V2 is supplied to the thin film heating resistor 4a via the transistor 50 as a heat generation control means for controlling the current supplied to the thin film heating resistor 4a of the flow rate detecting unit 4. That is, in the flow rate detection unit 4, based on the heat generated by the thin film heating resistor 4a, the temperature sensing by the thin film temperature sensing resistor 4b is performed under the influence of heat absorption by the fluid in the tube 14. As a result of the temperature sensing, the difference between the potentials Va and Vb at the points a and b of the bridge circuit 40 is obtained.

  The value of (Va−Vb) changes as the temperature of the temperature sensitive resistor 4b changes according to the flow rate of the fluid. By appropriately setting the resistance values of the resistors 43 and 44 of the bridge circuit 40 in advance, the value of (Va−Vb) can be made zero in the case of a desired desired fluid flow rate. At this reference flow rate, the output of the differential amplification / integration circuit 46 is constant (a value corresponding to the reference flow rate), and the resistance value of the transistor 50 is also constant. In that case, the voltage applied to the thin film heating resistor 4a is also constant, and the voltage at point P at this time indicates the reference flow rate.

  When the fluid flow rate increases or decreases, the output of the differential amplification / integration circuit 46 changes in polarity (depending on whether the resistance-temperature characteristic of the temperature-sensitive resistor 4b is positive or negative) and magnitude according to the value of (Va−Vb), In response to this, the output of the differential amplifier / integrator circuit 46 changes.

  When the liquid flow rate increases, the temperature of the temperature sensitive resistor 4b decreases, so that the differential amplifying / integrating circuit 46 increases the amount of heat generated by the thin film heating resistor 4a (that is, increases the power). A control input for decreasing the resistance value of the transistor 50 is made with respect to the base of the transistor 50.

  On the other hand, when the fluid flow rate decreases, the temperature of the temperature sensitive resistor 4b rises, so that the differential amplification / integration circuit 46 reduces the amount of heat generated by the thin film heating resistor 4a (that is, reduces power). The control input for increasing the resistance value of the transistor 50 is made from the base of the transistor 50.

  As described above, the heat generation of the thin film heating resistor 4a is fed back so that the output corresponding to the fluid flow rate from the detection circuit 40 including the temperature sensitive resistor 4b always becomes the target value regardless of the change in the fluid flow rate. Be controlled. At that time, the voltage (voltage at point P) applied to the thin film heating resistor 4a corresponds to the fluid flow rate, and is taken out as a flow rate output. This flow rate output is A / D converted by the A / D converter 52 and converted into a digital signal. A digital signal corresponding to the flow rate value is input to the CPU 54 as a calculation means, and the CPU 54 calculates a flow rate value based on a pre-stored calibration curve and outputs the signal.

  The fluid temperature detector 4 'is used to obtain a flow rate value that has been compensated for the temperature of the fluid.

  6 and 7 are schematic partial configuration diagrams showing still another embodiment of the flow rate measuring device according to the present invention in which the flow rate measuring method according to the present invention is implemented. FIG. 6 shows the movable portion of the pressing means in the first state. FIG. 7 shows a time when the movable part of the pressing means is in the second state. In these drawings, members having the same functions as those in FIGS. 1 to 5 are given the same reference numerals.

  This embodiment is different from the embodiment described above with reference to FIGS. 1 to 5 in that the movable portion 24 is attached to the base portion 20 with a hinge 23. When the movable portion 24 of the pressing means is in the first state, as shown in FIG. 6, the rotating tip portion of the movable portion 24 and the portion of the base portion 20 corresponding thereto are at a required distance by the connecting member 28. Maintained.

  The apparatus of the embodiment described with reference to FIGS. 1 to 5 was manufactured, and the change in the voltage (sensor output) at point P with respect to the change in the flow rate of water flowing in the synthetic resin tube (polyethylene tube) was measured. The result of repeating this measurement five times with the same apparatus is shown in FIG. There was little variation in five implementations, and sufficient measurement accuracy was obtained.

  In FIG. 9, the device of the embodiment described with reference to FIGS. 1 to 5 is manufactured, and the voltage at the point P (sensor output) with respect to the flow rate change in the minute flow rate region of the water flowing in the synthetic resin tube (polyethylene tube). ) Shows the result of measuring the change. It was found that measurement in a minute flow rate range of about 2 mL (milliliter) / h is possible. FIG. 10 shows the measurement results of the rising response of the sensor output when the fluid flow state is suddenly about 0 to 10 mL / h. The response was found to be good.

  In FIG. 11, the apparatus of the embodiment described with reference to FIGS. 1 to 5 is manufactured, and each of a synthetic resin tube (polyethylene tube) [invention example] and a metal pipe (stainless steel pipe) [comparative example] Shows the results of measuring the voltage change at point P over time when water was circulated at two constant flow rates (0.2 L / h, 2 L / h). In the case of metal piping, the change in voltage output with time was large, but in the case of a synthetic resin tube, the change in voltage output with time was small, and sufficient measurement accuracy was obtained.

It is a schematic block diagram which shows one Embodiment of the flow measuring device by this invention. It is the elements on larger scale of the apparatus of FIG. It is the elements on larger scale of the apparatus of FIG. FIG. 2 is a partial cross-sectional view of the apparatus of FIG. It is a circuit block diagram of the apparatus of FIG. It is a general | schematic fragmentary block diagram which shows another embodiment of the flow volume measuring apparatus by this invention. It is a schematic partial block diagram of the apparatus of FIG. It is a figure which shows the example of the change of the sensor output with respect to the flow volume in the flow measuring device by this invention. It is a figure which shows the example of the change of the sensor output with respect to the micro flow rate in the flow measuring device by this invention. It is a figure which shows the example of the rising response of the sensor output in the flow measuring device by this invention. It is a figure which shows the example of the time fluctuation of the sensor output in the flow measuring device by this invention with a comparative example.

Explanation of symbols

2, 2 'Metal thin plate 4 Flow rate detection unit 4a Thin film heating resistor 4b Thin film temperature sensing resistor 4' Fluid temperature sensing unit 4a 'Thin film temperature sensing resistor 6 Bonding wire 8, 8' External lead 10 Resin mold 14 Tube 16 Sensor Unit 20 Base 22 Spacer 23 Hinge 24 Movable part 26 Male screw 28 Connecting member 40 Bridge circuit (detection circuit)
43, 44 Resistor 46 Differential amplification / integration circuit 50 Heat generation control means (transistor)
52 A / D converter 54 Calculation means (CPU)

Claims (12)

A method for measuring the flow rate of a fluid flowing in a pipe,
A flexible tube is used as the piping, and a flow rate detection unit having a heating element and a temperature sensing body is pressed against the outer peripheral surface of the tube to deform the tube into a predetermined shape, and the tube and the flow rate detection unit A heat transfer path in a predetermined form with
After that, by the heat generation control means so as to maintain the output of the detection circuit configured to include the heating element and the temperature sensing element and generating an electrical output corresponding to the flow rate of the fluid in the tube at a predetermined value. A flow rate measuring method characterized by controlling heat generation of the heating element and obtaining a flow rate value based on a control state by the heat generation control means. The flow rate measuring method according to claim 1, wherein the tube is made of a material having a thermal conductivity of 0.05 W / (m · ° C.) to 1 W / (m · ° C.). The flow rate measuring method according to claim 1, wherein the tube is made of synthetic resin or synthetic rubber. The flow rate measuring method according to any one of claims 1 to 3, wherein the flow rate detection unit is pressed against the outer peripheral surface of the tube via a thin thermal conductor plate connected thereto. The flow rate measuring method according to claim 4, wherein the heat good conductor thin plate is a metal thin plate. An apparatus for measuring the flow rate of a fluid flowing in a pipe made of a flexible tube,
A flow rate detector having a heating element and a temperature sensing element;
A detection circuit configured to include the heating element and the temperature sensing element and generate an electrical output corresponding to the flow rate of the fluid in the tube;
Heat generation control means for controlling the heat generation of the heating element so as to maintain the output of the detection circuit at a predetermined value;
Arithmetic means for obtaining a flow rate value based on the control state of the heating element by the heat generation control means;
A flow rate measuring device comprising: pressing means for pressing the flow rate detection unit against the outer peripheral surface of the tube to deform the tube into a predetermined shape. The flow rate measuring device according to claim 6, wherein the tube is made of a material having a thermal conductivity of 0.05 W / (m · ° C.) to 1 W / (m · ° C.). The flow rate measuring device according to claim 6, wherein the tube is made of synthetic resin or synthetic rubber. The heat good conductor thin plate connected to the flow rate detection unit is provided, and the pressing means presses the flow rate detection unit against the outer peripheral surface of the tube through the heat good conductor thin plate. The flow measuring device according to any one of 8. The flow rate measuring device according to claim 9, wherein the thermal good conductor thin plate is a metal thin plate. The pressing means includes a base for supporting a sensor unit including the flow rate detection unit, and a movable unit movable with respect to the base, and the movable unit is configured to move the flow rate detection unit with respect to the base. The first state in which the tube is deformed into the predetermined shape by applying the pressing force to the tube by the second state and the second state in which the pressing force is not applied to the tube by the flow rate detection unit are characterized. The flow measuring device according to claim 6. The flow rate measuring device according to claim 11, wherein the movable part is attached to the base by a hinge.

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