JP4936392B2 - Mass flow meter - Google Patents

Description

  The present invention relates to a mass flow meter capable of easily measuring a mass flow rate, for example, when measuring a blood flow rate in a cardiopulmonary assist circuit.

  Conventionally, various techniques have been developed and proposed for measuring the flow rates of various fluids. In this type of technology, as a method for measuring the flow rate with a relatively simple device, a method for measuring the flow rate by measuring various actions of the fluid flowing through the bent pipe has been proposed. For example, in Japanese Patent Laid-Open No. 9-79881, concentration measuring units are provided on the inside and outside of a bent pipe, respectively, and the concentration difference of the fluid on the inside and outside of the bent pipe is measured based on the concentrations measured by both concentration measuring units. A method for measuring the flow rate has been proposed.

Japanese Patent Laid-Open No. 4-276519 discloses a U-tube connected in a horizontal plane in a pipe, a strain gauge for measuring a bending moment and a strain gauge for measuring an axial force at a connection portion between the U-tube and the pipe. The mass flow rate of the fluid is measured by measuring the vertical downward fluid weight acting on the U-shaped pipe as the bending strain acting on the joint and the inertial force of the fluid acting in the horizontal plane as the axial strain. A method has been proposed. A technique for measuring a mass flow rate by detecting a Coriolis force acting on parallel pipes connected by a curved pipe is widely used as a Coriolis force flow meter.
Japanese Patent Laid-Open No. 9-79881 JP-A-4-276519 JP 2007-218775 A

  In the conventional technique for measuring the flow rate of fluid, the technique disclosed in Japanese Patent Application Laid-Open No. 9-79881 is difficult to measure with a fluid in which a change in concentration is difficult to occur. For example, it is not suitable for measuring the flow rate of blood flow. It is. Further, the technique disclosed in Japanese Patent Laid-Open No. 4-276519 has a drawback that it is difficult to measure the flow rate when the flow path resistance is changed because there is no static pressure compensation means. Further, the Coriolis flow meter requires a device that vibrates the U-shaped tube, and there is a problem that it becomes a large device.

  On the other hand, the inventors of the present application have proposed a mass flow meter disclosed in Japanese Patent Application Laid-Open No. 2007-218775 as shown in Patent Document 3. In this technique, a strain gauge is attached to a portion of the bent pipe where the centrifugal force or centripetal force of the fluid in the pipeline acts, and the mass flow rate is measured by guiding the signal to a bridge circuit. A strain gauge for temperature compensation is used, and the signal is also guided to a bridge circuit to easily perform static pressure compensation and temperature compensation, thereby enabling accurate flow rate measurement.

  In the mass flowmeter as previously proposed by the present inventors, it is possible to obtain an ultralight mass flowmeter that can be measured in the gram order by adopting the configuration as described above. In the mass flow meter using the bent pipe proposed earlier, when the bent pipe has elasticity, the force based on the fluid flow rate acting on the bent pipe should be accurately measured from the strain gauge attached to the pipe. In order to accurately detect the force due to the centrifugal force of the fluid acting on the pipe using this hard pipe, a thin-walled part is formed and a strain gauge is affixed. There was a need to do.

  In addition, for example, when measuring blood flow rate, it is necessary to connect a hard tube to a commonly used elastic tube, and a reliable connection structure of both tubes, and the hard tube is inadequate for blood due to contact with blood. It has been found that there is a problem that the tube made of a material that does not cause a reaction must be selected, and the entire tube must be expensive.

  Therefore, the present invention provides a mass flow meter that can measure the mass flow rate of various fluids flowing through an elastic tube by a simple method with a small, lightweight and inexpensive device. Main purpose.

  In order to solve the above problems, the mass flow meter according to the present invention has a bridge derived from a strain gauge for detecting centrifugal force and a strain gauge for static pressure / temperature compensation attached to an elastic tube mounted in a hard bent tube probe. The flow rate is measured by the output of the circuit. As a result, the elastic tube through which the fluid flows and the sensor probe are separated from each other, so that the manufacture becomes easy, and it is possible to attach to the existing elastic tube from the outside. Furthermore, by using an elastic tube, it becomes possible to measure the flow rate of a fluid that is difficult to flow through a metal tube, and it is possible to detect a greater amount of distortion due to centrifugal force than a hard tube. In addition, in order to increase the strain amount of the elastic tube in the rigid bent tube probe, a through hole is formed in the strain detection unit, and the elastic tube is pressed against the hole in order to catch local strain.

  More specifically, the present invention as described above is the following mass flow meter. That is, the room charge flow meter according to the present invention includes an elastic tube through which a fluid flows, a rigid bent tube probe that houses the elastic tube and can maintain a predetermined shape in the housed state of the elastic tube, A curved pipe outer strain gauge affixed to the outer peripheral surface of the elastic tube at a portion where the through hole formed in the outer peripheral portion of the bent portion of the hard bent tube probe opens, and a through hole formed in the straight tube portion of the hard bent tube probe And a straight pipe strain gauge affixed to the outer peripheral surface of the elastic pipe of the portion to be bent, and the mass flow rate is measured by guiding the signal of the curved pipe outer strain gauge and the signal of the straight pipe strain gauge to a bridge circuit. To do.

  In addition, another mass flow meter according to the present invention includes an elastic tube through which a fluid flows, a rigid bent tube probe that stores the elastic tube and can maintain a predetermined shape in the storage state of the elastic tube, A curved tube outer strain gauge affixed to the outer peripheral surface of the elastic tube in a portion where a through hole formed in the outer peripheral portion of the bent portion of the hard bent tube probe is formed, and an inner peripheral portion of the bent portion of the hard bent tube probe A curved pipe inner strain gauge affixed to the outer peripheral surface of the elastic pipe at the portion where the through hole is opened, and the signal of the bent pipe outer strain gauge and the signal of the bent pipe inner strain gauge are guided to a bridge circuit to reduce the mass flow rate. It is characterized by measuring.

  Further, according to another mass flow meter of the present invention, in the mass flow meter, the hard bent tube probe can be divided into two parts, and can be integrally attached to the elastic tube by covering from the outside of the elastic tube. It is characterized by.

  Another mass flow meter according to the present invention is characterized in that, in the mass flow meter, the elastic tube and the rigid bent tube probe are formed of a transparent material.

  Another mass flow meter according to the present invention is characterized in that, in the mass flow meter, the outer peripheral portion of the elastic tube to which the strain gauge is attached is formed by the opening of the through hole of the rigid bent tube probe. .

  Further, according to another mass flow meter of the present invention, in the mass flow meter, the elastic tube is constrained by both ends of the hard bent tube probe to maintain a predetermined bent shape of the elastic tube. Is characterized in that a gap is formed between the outer peripheral surface of the elastic tube and the inner peripheral surface of the hard bent tube.

  Another mass flow meter according to the present invention is characterized in that, in the mass flow meter, the rigid bent tube probe is made to be highly rigid and the influence of external force is reduced.

Since the present invention is configured as described above, the following various effects can be obtained.
1. By simply bending and fixing an elastic straight tube with a hard bent tube probe, it can be used as a mass flow meter using centrifugal force generated in the bent part, and it is small, lightweight and inexpensive by a simple method. The apparatus can reliably measure the mass flow rate.
2. It is possible to attach a rigid bent tube probe from the outside using an existing elastic tube flowing various fluids as it is, and it is possible to provide a mass flow meter that can be easily attached.
3. Since an elastic tube is used, the amount of change in the pipe line due to the mass flow rate can be increased and the mass flow rate can be measured more accurately than the mass flow meter proposed in Patent Document 3.
4). Since an elastic tube using a polymer material having chemical resistance can be used, it is possible to measure a mass flow rate of a fluid that cannot flow through a normal metal tube, such as blood or special chemicals.
5. By using a transparent elastic tube or a transparent rigid bent tube probe, the mass flow rate can be measured while observing the flow of the fluid inside.
6). Unlike the mass flow meter proposed in Patent Document 3, there is no need for metal bending or thin-wall processing, which facilitates processing.
7). Unlike the mass flow meter proposed in Patent Document 3, it is possible to reduce the influence of external force applied to the mass flow meter.

  The mass flow meter according to the present invention enables the mass flow rate of various fluids flowing through the elastic tube to be reliably measured by a small, light and inexpensive device by a simple method. A problem is that an elastic tube in which a fluid flows, a rigid bent tube probe that accommodates the elastic tube and can maintain a predetermined shape in the accommodated state of the elastic tube, and an outer periphery of a bent portion of the rigid bent tube probe A curved tube outer strain gauge affixed to the outer peripheral surface of the elastic tube at the portion where the through hole formed in the portion opens, and an elastic tube outer surface at the portion where the through hole formed in the straight tube portion of the rigid bent tube probe opens Straight pipe strain gauge or curved pipe affixed to the outer peripheral surface of the elastic pipe at the part where the through hole formed in the inner peripheral part of the bent part of the hard bent pipe probe opens And a train gauge guides the signals of the strain gages to the bridge circuit was solved by measuring the mass flow rate.

  Embodiments of the present invention will be described with reference to the drawings. 1 and 2 show a first embodiment of the present invention, and shows an example in which an elastic tube 3 through which a fluid flows, for example, from an inlet 1 to an outlet 2 is bent at a bent portion 4. Yes. As the elastic tube 3, when this mass flow meter is used for detecting the amount of blood circulated, it is guaranteed that there is no blood coagulation, for example, a polymer material such as a silicon tube or a Tygon tube. In addition, a tube made of any elastic material can be used according to various uses such as a chemical resistant resin.

  In particular, in the present invention, the tube is easily deformed by the pressure of the fluid flowing in the tube and the bent shape is changed, so that the centrifugal force flowing accurately through the curved tube portion with a strain gauge attached to the tube wall as will be described later. Since it is a technology that takes into account that changes cannot be detected, the degree of elasticity of whether or not a predetermined bending state can be maintained depends on the fluid pressure in the tube, the material of the tube, the thickness, etc. It depends on each application and environment.

  In the illustrated embodiment, a hard bent tube probe 5 as shown is used to cover the outside of the elastic tube 3 so that the elastic tube 3 maintains a predetermined bent shape at the bent portion 4. The rigid bent tube probe 5 has such a rigidity that the deformation of the elastic tube 3 can be surely prevented. Similar to the elastic tube, in addition to the relationship between the fluid pressure in the tube and the elasticity of the tube, the elastic tube probe 5 Depending on the ease of bending, etc., it can be manufactured in any thickness, bending degree, and outer peripheral shape with metal or hard resin. In that case, if the bent shape of the elastic tube can be maintained in a predetermined shape, a support structure for the elastic tube can be arbitrarily designed.

  In the illustrated embodiment, the rigid bent tube probe 5 is halved in the vertical direction so that both can be brought into close contact with each other at the joint 6. Thereby, for example, a part of the elastic tube 3 through which blood flows is bent and inserted into a semicircular groove opened on the upper side of the lower bent tube probe 7, and the lower side of the upper bent tube probe 8. The hard bent tube probe 5 can be easily attached by covering the upper side of the elastic tube 3 with a semicircular groove that is open at the top. At this time, in particular, the elastic tube 3 may be strongly pressed at both ends of the hard bent tube probe 5 to prevent the entire elastic tube from being dragged into the hard bent tube probe by the fluid flowing in the elastic tube.

  In the illustrated embodiment, an example is shown in which the rigid bent tube probe 5 is halved and detachable. However, without being separable, a through hole having an inner diameter somewhat larger than the elastic tube is formed, and the elastic tube is preliminarily formed. It may be in a state of passing through the through hole. However, in order to affix a strain gauge as will be described later to the elastic tube, it is preferable to affix the strain gauge to the elastic tube in advance. For this purpose, it is preferable to halve the rigid bent tube probe 5 as described above. In addition, by forming the rigid bent tube probe 5 from a transparent material and further using the elastic tube 3 as a transparent material, the flow rate can be measured while observing the state of the fluid flowing through the mass flow meter portion. .

  A circular through hole 9 is provided outside the bent portion 4 at a substantially bent central portion of the hard bent tube probe 5, whereby a circular open surface 10 is formed in the elastic tube 3 inside the through hole 9. Further, a through hole 13 similar to the through hole 9 is provided outside the straight pipe portion 12, whereby a circular open surface 14 is formed in the elastic tube 3 inside the through hole 13.

  A curved tube outer strain gauge 15 is attached to the open surface 10 of the elastic tube 3 by the through hole 9 with an adhesive or the like, and similarly, a straight tube strain gauge 16 is attached to the open surface 14 of the through hole 13. The signal of each strain gauge is guided to the bridge circuit 17, the output is amplified by the amplifier circuit 18, and is output to the outside from the flow rate output device 19 as a mass flow rate.

  Among these strain gauges, the bent tube outer strain gauge 15 is attached to the outside of the bent tube portion 11, so that a centrifugal force corresponding to the flow rate of the fluid flowing in the elastic tube 3 acts on this portion, and the centrifugal force is reduced. The mass flow rate is measured by detecting the force. In addition, although the centripetal force is generated simultaneously with the centrifugal force as described above, only the action of the centrifugal force will be described here. On the other hand, since the straight pipe strain gauge 16 is provided in the straight pipe portion of the elastic pipe, it performs static pressure compensation and temperature compensation by measuring the static pressure of the fluid, in which the centrifugal force of the fluid does not act. The size of the open surfaces 10 and 14 of the elastic tube 3 to which the strain gauges 15 and 16 are attached is large enough to allow the strain gauge to be attached, and the elastic tube 3 is locally localized by the pressure of the internal fluid at the open surface portion. It is set to such an extent that a large distortion can be detected.

  The circuit configuration for processing the signal of each strain gauge is described in detail in the Patent Document 3 previously proposed by the inventors of the present invention. In the present invention, for example, a circuit as shown in FIG. It can be implemented depending on the configuration. That is, in the example shown in FIG. 3, the resistance value as the detection signal of the curved pipe outer strain gauge 15 is input to the portion A of the bridge circuit 17, and the resistance value as the detection signal of the straight pipe strain gauge 16 is input to the bridge circuit 17. Are input to the C portion adjacent to the A portion, and the others are fixed resistors.

  Accordingly, a centrifugal force signal corresponding to the flow rate of the fluid by the curved pipe outer strain gauge 15 in the bent pipe portion is input to the A portion of the bridge circuit 17, and the straight pipe strain gauge 16 in the straight pipe portion where the centrifugal force does not act. Is input to the portion B so that the static pressure and temperature values detected by the curved strain gauge 15 can be compensated. In this bridge circuit, it is also possible to employ a technique in which a total of four strain gauges as described in Patent Document 3 previously proposed are used and the signals are input to the bridge circuit.

  The signal of the bridge circuit 17 is amplified by the preamplifier 18 as in the conventional bridge circuit, and the flow rate output device 19 processes the voltage balance signal of the bridge circuit to calculate the flow rate. Through these processes, the strain gauge A signal that detects the total pressure of the centrifugal force and the static pressure of the fluid is compared with the signal of the strain gauge C that detects the pressure related to the static pressure and temperature of the fluid. Further, it is possible to perform processing for compensating the detected value of the strain gauge A. In this measuring device, in particular, a flow rate signal can be obtained by the power supply 20 for the bridge circuit, and accurate measurement can be performed with a small amount of current.

  The above is a mass flow meter that uses a single bridge circuit, but if it is lightweight, the detection signals of the centrifugal force detection strain gauge and the compensation strain gauge are guided to separate bridge circuits to detect the centrifugal force. It is also possible to add a comparison operation circuit for comparing and calculating the output of the strain gauge for output and the output of the compensation strain gauge.

  A second embodiment of the present invention is shown in FIG. In FIG. 4, the same parts as those in FIG. 2 of the first embodiment are denoted by the same reference numerals. In the example shown in FIG. 4, the elastic tube 3 is housed in a hard bent tube probe 5 having a predetermined bent shape, and a through hole 9 is formed in the outer peripheral portion of the bent portion 4, as in the above example. The curved pipe outer strain gauge 15 is affixed to the open surface 10 of the circumferential surface of the elastic pipe 3 generated by the above.

  In particular, in the embodiment shown in FIG. 4, a through hole 21 is formed in an inner portion of the bent portion 4 in the rigid bent tube probe 5, which faces the through hole 9 to which the bent tube outer strain gauge 15 is attached, A curved pipe inner strain gauge 23 is attached to the open surface 22 of the peripheral surface of the elastic pipe 3 generated by the through hole 21.

  Similar to the first embodiment, the bent tube outer strain gauge 15 detects the centrifugal force generated in the bent tube portion by the fluid flowing in the elastic tube 3 as the distortion of the elastic tube generated in the open surface 10 portion, and relates to the flow rate. Get a signal. On the other hand, the curved pipe inner strain gauge 23 generates a pressure drop corresponding to the centrifugal force of the bent pipe portion. By detecting this with the curved pipe inner strain gauge 23, the centrifugal force signal of the bent pipe outer strain gauge 15 is detected. Can be detected, whereby the action of centrifugal force can be detected more clearly.

  The signals of the curved pipe outer strain gauge 15 and the curved pipe inner strain gauge 23 are led to the bridge circuit 17 as in the first embodiment, and the output signal is amplified by the amplifier circuit 18 and output from the flow rate output device 19 to the outside. The bridge circuit 17 can be input in the same manner as in the above embodiment to detect the differential pressure of both signals and to compensate for temperature.

  In the above-described embodiment, the strain gauge is a hard bend tube probe that keeps the elastic tube in a predetermined shape, in close contact with the outer peripheral surface including the bent portion of the elastic tube and the straight pipe portion in the vicinity thereof, and the inner peripheral surface of the hard bent tube. The open surface of the outer periphery of the elastic tube to which the adhesive is attached is shown as an example formed by the through hole of the hard bent tube probe. However, for example, the present invention is carried out using a hard bent tube 5 as shown in FIG. be able to. In the figure, the same reference numerals are given to the same parts as those in the above embodiment, and the description thereof is omitted.

  In the rigid bent tube probe 5 shown in FIG. 5, the elastic tube 3 is constrained at the first end portion 25, and similarly, the elastic tube 3 is constrained at the second end portion 26 which is the other end portion. As in the above embodiment, the elastic tube 3 is maintained in a predetermined bent shape, and the portion other than the both ends of the hard bent tube is between the outer peripheral surface of the elastic tube 3 and the inner peripheral surface of the hard bent tube 5. A gap 27 is formed. In the rigid bent tube 5 as well, the through hole 9 is provided in the bent tube portion 11 and the strain gauge 9 is attached to the outer peripheral surface of the elastic tube from this portion. Moreover, the through-hole 13 is provided also in the straight pipe part 12, and the strain gauge 16 is affixed on the outer peripheral surface of an elastic pipe from this part.

  In the illustrated embodiment, an example in which a strain gauge is affixed to the straight pipe portion as in the example of FIG. 1 is shown, but in addition to that, a strain gauge is provided inside the bent pipe portion as in the example of FIG. Even if affixed, it can be carried out in the same manner.

  Even if such a hard bent tube is used, it is not necessary to use a hard bent tube as in the mass flow meter disclosed in Patent Document 3 previously proposed by the present inventors. When an elastic tube made of a material having a predetermined property is used as in measuring the blood discharge flow rate, the mass flow rate can be measured using the elastic tube as it is, as in the above embodiment. It is the same.

  Based on the principle of the mass flowmeter according to the present invention as described above, the result of experimenting by creating a simple device is shown in FIG. In the figure, the triangle mark indicates the actual measurement result of the mass flow meter according to the present invention, and the square mark indicates the result measured with a commercially available precision mass flow meter provided in series in the experimental flow channel. As shown in the figure, although there are some variations, for example, in the field of flow measurement of an artificial heart pump, a mass flow meter that can be fully used is obtained by taking advantage of the features of the present invention as described above. In addition, further research and development of measuring instruments, signal processing software, etc. have found the possibility of more accurate mass flow measurement.

  The present invention as described above can be used as a mass flow meter in various fields. In particular, the flow measurement in a short-term cardiopulmonary circulatory circuit (PCPS or ECMO), and further, elasticity with chemical resistance. It can be effectively used for flow measurement in drug development that requires a tube.

It is a perspective view of 1st Example of this invention, and a figure which shows a signal processing functional block. It is sectional drawing of the same Example, and a figure which shows a signal processing functional block. It is explanatory drawing of the signal processing part of the Example. It is sectional drawing of 2nd Example of this invention, and a figure which shows a signal processing functional block. It is sectional drawing of the 3rd Example of this invention, and a figure which shows a signal processing functional block. It is a graph which compares and shows the result measured with the mass flowmeter of this invention, and the result measured with the commercially available precision mass flowmeter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inflow port 2 Outflow port 3 Elastic pipe 4 Bending part 5 Hard bending pipe probe 6 Joint part 7 Lower side bending pipe probe 8 Upper side bending pipe probe 9 Through-hole 10 Opening surface 11 Bending pipe part 12 Straight pipe part 13 Through-hole 14 Opening Surface 15 Curved pipe outer strain gauge 16 Straight pipe strain gauge 17 Bridge circuit 18 Amplifier circuit 19 Flow rate output device 20 Power supply 21 Through hole 22 Open surface 23 Curved pipe inner strain gauge

Claims (6)

An elastic tube through which fluid flows;
A rigid bent tube probe that houses the elastic tube and is capable of maintaining a predetermined shape in the housed state of the elastic tube;
A curved tube outer strain gauge affixed to the outer peripheral surface of the elastic tube in a portion where a through hole formed in the outer peripheral portion of the bent portion of the rigid bent tube probe is opened;
A straight tube strain gauge affixed to the outer peripheral surface of the elastic tube in a portion where a through hole formed in the straight tube portion of the rigid bent tube probe is opened;
A mass flow meter for measuring a mass flow rate by guiding a signal of the curved pipe outer strain gauge and a signal of the straight pipe strain gauge to a bridge circuit. An elastic tube through which fluid flows;
A rigid bent tube probe that houses the elastic tube and is capable of maintaining a predetermined shape in the housed state of the elastic tube;
A curved tube outer strain gauge affixed to the outer peripheral surface of the elastic tube in a portion where a through hole formed in the outer peripheral portion of the bent portion of the rigid bent tube probe is opened;
A curved tube inner strain gauge affixed to the outer peripheral surface of the elastic tube in a portion where a through hole formed in the inner peripheral portion of the bent portion of the hard bent tube probe is opened;
A mass flow meter for measuring a mass flow rate by guiding a signal of the bent tube outer strain gauge and a signal of the bent tube inner strain gauge to a bridge circuit.   The mass flowmeter according to claim 1 or 2, wherein the hard bent tube probe can be divided into two parts, and can be attached to the elastic tube by being integrated from the outside of the elastic tube.   The mass flowmeter according to claim 1 or 2, wherein the elastic tube and the hard bent tube probe are made of a transparent material.   The elastic tube is restrained by both ends of the hard bent tube probe to maintain a predetermined bent shape of the elastic tube, and a gap is formed between the outer peripheral surface of the elastic tube and the inner peripheral surface of the hard bent tube at portions other than the both ends. The mass flowmeter according to claim 1 or 2, wherein   The mass flowmeter according to claim 1, wherein the rigid bent tube probe has high rigidity to reduce the influence of external force.

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