JPS62162921A - Mass flowmeter - Google Patents

Abstract

PURPOSE:To improve temp. characteristic and accuracy by selecting materials for prescribed constituting parts and compensating various changes by temp. CONSTITUTION:The karman vortex street acting as alternating force is generated by a fluid contact part 133 of a vortex generating body 13 according to the flow rate of the fluid flowing in a pipeline 11, by which lift is changed. This change is detected by stress detecting sensors 141, 142 which consist of the 1st and 2nd piezo-electric elements, etc. to form a sensor part 14 together with a push bar 147, etc. and are provided to a recess 134 of an upper outside cylindrical part 135 of the body 13. The materials for the cylindrical part 135 and the sensor part 14 are so selected that the thermal expansion of the pipeline 11 and the body 13, the change of the Young's modulus of the cylindrical part 135 and the sensor part 14, and the constant change of the detecting parts 141, 142 are subjected to temp. compensation. As a result, the temp. characteristic is improved and the accuracy of the mass flowmeter is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention (ii) [IR] relates to a mass flowmeter that measures the mass flow rate of a measurement fluid using Karman vortices.

(Prior Art) It has been known for a long time that when an object is placed in a fluid, vortices are generated alternately and regularly from the side surface of the object, and the fluid flows downstream in a line. This array is called a Karman vortex street, and the number of vortices generated per unit time (generation frequency) is proportional to the flow rate of the fluid.

Therefore, a vortex generator is placed in the pipe that guides the fluid to be measured, and the vortex generator generates a vortex proportional to the flow velocity.The change in lift caused by the vortex is measured using sensors such as piezoelectric elements, strain gauges, capacitance, and inductance. Vortex flowmeters have been put into practical use that measure the flow velocity and flow rate of fluid by detecting and extracting only the frequency of the detection signal. Incidentally, the flow rate that one generally wants to know is often the T1 flow rate not only in processes that involve chemical changes, but also in transactions. Furthermore, when the fluid to be measured is gas or steam, its density changes greatly depending on temperature and pressure, and even when it is a liquid, its density changes considerably depending on temperature. For this reason, the mass flow rate is measured either by installing it in parallel with a vortex flowmeter to measure temperature and pressure, or by measuring the density with a density meter. However, using a density meter and a vortex flowmeter is complicated and expensive, and using a combination of a temperature or pressure gauge and a vortex flowmeter is not only complicated and expensive, but also makes it difficult to measure the humidity of the fluid, resulting in poor viscosity and responsiveness. Too bad.

By the way, as shown in Figure 1+, when the vortex generator 2 is arranged in the pipe 1 and the measurement fluid is flowed into the pipe 1, the average drag force F, the fluctuating lift force F, and the pressure acting on the vortex generator 2 are Loss ΔP
generally has the relationship shown by the following equation.

However, C port: Drag coefficient CL r Fluctuation lift coefficient Cp: Pressure loss coefficient ρ: Density V: Flow velocity average drag F9. If the drag coefficient Cp, the variable lift coefficient CL, and the pressure loss coefficient Cp are constants, the fluctuating lift force F and pressure loss ΔP are proportional to ρ■2, so by dividing the vortex frequency f-, ρV can be obtained. .

As such, an example of detecting the fluctuating lift force and dividing it by the vortex frequency is disclosed in Japanese Patent Application Laid-Open No. 57-61916 "Measuring Apparatus Using Karman Vortex".

JP-A No. 57-61916 will be explained below.

FIG. 12 is an explanatory diagram of the structure of this Japanese Patent Application Laid-Open No. 57-61916. In the figure, Ia is a pipe through which the measurement fluid flows, 2
A is a columnar vortex generator inserted perpendicularly into the pipe line 1a, and its both ends are fixed to the pipe line 1a. The main body 21a of the vortex generator 2a is made of stainless steel or the like, and has a cross-sectional shape, such as a trapezoid, that does not produce a Karman vortex street in the measured fluid and stably enhances lift changes.

The top 22a of the vortex generator 2a is made of stainless steel or the like, has a recess 23a, and is integrally formed with the main body 21a by welding or the like. 231a is the vortex generator 2 due to the recess 23a.
This is the outer cylindrical portion formed in a. Reference numeral 41a denotes an element body made of a piezoelectric element, which is sealed in the recess 23a of the vortex generator 2a with an insulating material 3a such as glass, and is formed integrally with the generator m. The element main body 41a has a disk shape and is arranged so that its center coincides with the neutral axis of the vortex generator 2a. Furthermore, as shown in FIG. 13, the element main body 41a is divided into left and right parts on the front and back sides, respectively, symmetrically. The first piezoelectric sensor 4 is provided with l poles 42a, 43a, 44a, and 45a, and the portion sandwiched between the electrodes 42a and 43a
6a, and the portion sandwiched between electrodes 44a and 45a forms a second piezoelectric sensor 47a.

And the first. The electrodes 42a and 45a and 1! The poles 43a and 44a are connected, and the electrode 42
Lead wires 48a and 49a are taken out from a and 44a, respectively, through the insulating material 3a. 8a is a detection signal processing circuit that converts AC charge q detected by piezoelectric sensors 46a and 47a into AC voltage e. 9a is a comparator for converting the AC voltage e into a pulse signal P of a constant level. IOa is an F/V converter that converts the pulse signal P of the comparator output into a DC voltage E proportional to its frequency.
, convert to Ila is a rectifying and smoothing circuit that rectifies and smoothes the AC voltage e and converts it into a DC voltage E2 proportional to its amplitude. +2a is an arithmetic circuit that performs desired arithmetic operations on the outputs E, E, of the F/V converter IOa and the rectifier and smoothing circuit 11a, and extracts a signal related to the density of the fluid or the FIIi flow rate from the output. be.

In the present invention configured in this manner, when the measuring fluid flows into the pipe line 1a, the vortex generator 2a generates a Karman vortex and receives a lift change based on the generation of the vortex. When the vortex generating body 2a receives a change in lift, a stress change in the opposite direction is generated inside the vortex generating body 2a across the neutral axis as shown in the figure. This stress change occurring in the vortex generator 2a is transmitted to the element body 41a which is integrally attached to the vortex generator 2a through an insulating material 3a. Therefore, the first. In the second piezoelectric sensors 46a and 47a, changes in the amount of charge that are in opposite phases to each other occur in response to changes in lift force. The amount of electric charge generated in the piezoelectric sensors 46a and 47a is extracted differentially, and the lead wires 48a and 49a
An alternating charge q is generated between them. Exchange f? The charge q is converted into an alternating voltage e by the detection signal processing circuit 8a. If the frequency of the AC type rEe is taken out via the comparator 9a and the F/V converter loa, it becomes proportional to the vortex frequency f, that is, the flow velocity V, as in equation (4), as in a general vortex flowmeter. lt pressure E1 is obtained.

El -KIV "' (4) However, K1 is a proportional constant. On the other hand, if the amplitude of the AC voltage e is taken out through the rectifying and smoothing circuit 11a, the output E2 of the rectifying and smoothing circuit 11a is given by the following equation, where ρ is the density of the fluid. It will be done.

E, −K2 pv” ---(
5) However, K2 is a proportional constant and its output Eo is as follows. If the cross-sectional area of the pipe 1a is S, the quality Fj17M
mQm is Qm = ρVS ”' (7)
Since Eo is given by, Eo becomes as follows, and becomes a signal proportional to the mass flow rate.

If the arithmetic circuit 12a divides E by t'&E2, the output Eo will be as follows, and a signal proportional to the density of the fluid can be obtained.

(Problem to be solved by the invention) However, now, the variable lift force FL, drag force FD and vortex frequency output (volume flow rate) FV due to Karman vortices are as follows:
V...(2) However, FL; Fluctuation lift force Fb; Drag force Fv; Vortex frequency output (volume flow rate) CL; Fluctuation lift coefficient Cp: Drag coefficient ρ; Density ■: Flow velocity d; Diameter of the vortex generator facing the flow D: 1 for the inner diameter of the pipe; constant Therefore, in equation (6), becomes.

Here, the first step detects the fluctuating lift F. The second piezoelectric sensors 46a and 47a are made of an insulating material 3a and a vortex generator 2a.
is integrally attached to the Therefore, as the ambient temperature changes, (1) the thermal expansion of the pipe line 1a and the vortex generator 2a (-0.5%/100°C in the case of stainless steel material); (2) the piezoelectric element becomes inconsistent as shown in Figure 12; If the piezoelectric element is made of an insulating material such as glass, the change in Young's modulus of glass with temperature is significantly different from the change in Young's modulus of stainless steel with temperature, so the stress σ applied to the piezoelectric element changes significantly depending on the temperature.

That is, the eddy signal stress σ detected in the element main body 41a is approximately expressed as follows. However, here, El3; Young's modulus hs of the outer cylinder portion 23a;
;Lift force■ Errors occur due to changes in the d constant depending on the quality of the piezoelectric element. In a vortex flowmeter, the output frequency is the target, so changes in the sensitivity of the piezoelectric sensors 46a and 47a with respect to temperature are not a problem, but in the case of a mass flowmeter, the absolute value of lift is required, so the piezoelectric sensor 46a , 47a
Sensitivity changes due to temperature changes have a large effect on measured values, resulting in large measurement errors.

The present invention solves this problem.

An object of the present invention is to provide a highly accurate mass flowmeter with good temperature characteristics by performing temperature compensation.

(Means for Solving the Problems) In order to achieve this object, the present invention provides a mass flowmeter that measures the mass flow rate of a measured fluid using a Karman vortex signal that acts as an alternating force. A stress-receiving force composed of a columnar force-receiving body inserted perpendicularly into a conduit, a recess provided in the axial direction of the force-receiving body and forming an outer cylindrical portion of the force-receiving body, and a piezoelectric element disposed in the recess. A columnar fixing rod inserted into the detection part and the recess with a gap that prevents side surfaces from coming into contact with each other, one end of which presses and fixes the stress detection sensor in the recess, and the other end of which is fixed at the opening of the recess; and the stress detection member. and an insulator that insulates the sensor part, thermal expansion of the pipe and vortex generator due to temperature changes, changes in Young's modulus of the outer cylindrical part and the sensor part, and a piezoelectric element. The materials of the outer cylinder part and the sensor part are selected and configured so that the fixed surface pressure of the piezoelectric element increases as the temperature rises so as to compensate for humidity changes in the d constant due to temperature changes of the stress detection part. This is a mass flowmeter that is characterized by:

(Function) In the above configuration, when the measurement fluid flows into the pipe, the vortex generator generates a vortex proportional to the flow velocity of the measurement fluid. This vortex causes an alternating force to act on the force receiving body. This alternating force is detected as stress by a stress detecting section provided in the force receiving body, and the vortex frequency and the absolute value of the fluctuating lift signal are detected, and the mass flow rate is detected.

In this case, a temperature change occurs in the force receiving body due to the high temperature measurement fluid or the like.

Examples will be described below.

(Example) Figures 1 (A) and (B) are explanatory diagrams of the configuration of one embodiment of this manual. (A) is a front view, (B) is a side view, and Figure 2 is the detection of Figure 1. FIG. 2 is a configuration explanatory diagram showing a vessel part in cross section.

In the figure, 10 is a vortex flowmeter detector, and 20 is a vortex flowmeter converter.

In the vortex flow meter detector 10, 11 is a pipe through which the fluid to be measured flows, 12 is a cylindrical nozzle provided perpendicularly to the pipe 11, and 13 is a columnar vortex inserted perpendicularly into the pipe 11 through the nozzle 12. The generator is made of stainless steel or the like, and its upper end 131 is fixed to the nozzle 12 by screws or welding.
The lower end 132 is supported in the conduit 11 by a plug.

The fluid-contacting portion 133 of the vortex generator 13 that comes into contact with the fluid to be measured has a cross-sectional shape such as a trapezoid so as not to generate a Karman vortex street in the fluid to be measured and to stably enhance lift changes, and has a cross-sectional shape such as a trapezoid on the upper end 131 side. It has a recess 134. 135 is an outer cylindrical portion formed in the vortex generator 13 by the recess 134. 14 is a sensor section, in which a first stress detection sensor 142 and a second stress detection sensor 14 are installed in the recess 134 of the vortex generator 13.
1 are pressed and fixed at regular intervals. Then,
As shown in FIG. 3, the first and second stress detection sensors 142 and 141 are arranged on the same side or both sides of ff1A so that the stress generated in the vortex generator 13 by the disturbance force N becomes zero. In the following, a case where they are arranged on the same side will be explained. In the sensor part 14, the underlay of stainless steel, etc. +4
3 serves as a buffer between the first stress detection sensor 142 and the bottom surface of the recess 134, and compensates for the difficulty in controlling the roughness of the bottom surface of the recess 134 during processing. A first spacer 144 made of stainless steel, an insulating plate 145 made of ceramic, and a second spacer 146 made of stainless steel determine the distance between the first stress detection sensor 142 and the second stress detection sensor 141, and provide insulation between them. It is for carrying out. The push rod 147 made of stainless steel etc. is the sensor 141.14.
2 is welded to the upper end 131 of the vortex generator 13 in a pressed state, and the sensors 141 and 142 are pressed and fixed.

Note that the sensor section 14 is configured to come into contact with the vortex generator 13 only through the underlay 143 and the upper part of the push rod 147. Thus, the stress detection sensors 141, 142 and the underlay 143. Spacer 144°146, insulating plate 145 and push rod 147
A sensor portion I4 is formed by the above. Stress detection sensor 141
．． Reference numeral 142 is a disk-shaped piezoelectric element 140, which is arranged so that its center coincides with the neutral axis of the vortex generator 13. Furthermore, as shown in the perspective view of FIG. 4(A), the piezoelectric element +40 is divided into left and right electrodes on the front and back sides of the piezoelectric element +40, respectively, with respect to the flow direction of the measuring fluid (direction of the arrow in the figure).
01.1402.1403.1404 are provided, and as shown in Fig. 4(B), stress (compressive stress) is generated in opposite directions across the neutral axis due to bending moment due to force in the direction of the arrow (direction of lift of the vortex). and tensile stress), the electric charge generated between the electrodes 1401 and 1402, and the electric charge generated between the electrodes 140
The polarization is reversed so that the charges generated between 3 and 1404 have the same polarity. Therefore, as shown in FIG. 4(C), charges of opposite polarity are generated between the two electrodes in response to stresses occurring in the same direction. In addition, the amount of electric charge generated by the stress in the flow direction of the measured fluid is canceled between the electrodes, and the amount of electric charge generated by pipe vibration in the flow direction is
The amount of charge also cancels out between the electrodes and does not appear. The second stress detection sensor 141 uses the sum of charges of the same polarity generated between electrodes 1401 and 1402 and electrodes 1403 and 1404 as an output charge q1, and in order to cancel charges of opposite polarity, electrodes +401 and 1403 are pushed together. Bar +
The electrodes 1402 and 1404 are commonly connected to a lead wire 1481 via a spacer 146 . The first stress detection sensor 142 uses the sum of the charges of the same polarity generated between the electrodes 1401, 1402 and 1403, 1404 as the output charge 92, cancels the charges of the opposite polarity, and reverses the polarity with ql. , electrode +401
．． and 1403 are commonly connected to a lead wire 1482 via a spacer 144, and electrodes 1402 and 1404 are commonly connected via an underlay 143 to the vortex generator 13, that is, a reference point. The lead wires 1481 and 1482 are taken out to the outside through the through holes provided in each part of the sensor section 14 and the hermetic seal 148, and connected to the vortex flow meter converter 20. In order to prevent condensation, a gas with a low dew point is filled in a portion of the vortex generator 13 surrounded by the recess 134 and the sensor portion 14, and the push rod 147 is provided with a communication hole 149 for the filled gas. ing. Reference numeral 15 denotes a labyrinth flow path provided at the intersection of the vortex generator 13 and the pipe line 11. Labyrinth channel! 5, as shown in FIG.
A fin +51 attached to the vortex generating body 13 and forming a slight gap with the conduit 11, and an enlarged chamber 152 following the fin +51 form a pair, and are composed of at least one pair or more.

Therefore, thermal expansion of the conduit 11 and the vortex generator 13 due to temperature changes, changes in the Young's modulus of the outer cylinder portion 135 and the sensor portion I4, and changes in the d constant due to temperature changes in the stress detection portion made of a piezoelectric element. The materials of the outer cylinder part and the sensor part are selected and configured so that the fixed surface pressure of the piezoelectric element increases as the temperature rises so as to compensate for the temperature.

FIG. 6 is a block diagram of the electrical circuit 30 (not shown in second rgJ) of FIG.

AC charge Q1 detected at 141 and 142. Q2 is an AC voltage E31. Convert to E32. 33 is an addition/subtraction circuit,
The outputs from the charge converters 31 and 32 are added to form an AC voltage E33. 34 is a second amplifier circuit, which receives AC voltage E.
3m is amplified and made into AC voltage ES4. 35 is a detection circuit that detects the AC voltage E34 and sets it as ES5. 36 is a rectifier circuit that removes ripples from the AC voltage E311. 37
is a filter circuit that removes low-frequency or high-frequency noise contained in the AC voltage E33 to obtain an AC voltage E)7. 38 is a first amplifier circuit that amplifies the AC voltage E37 and converts the AC voltage [:3. shall be. 39 is a Schmitt trigger circuit that converts the AC voltage E28 into a constant level pulse signal 1'ss.
Convert to 41 is an F/V converter, which receives a pulse signal P.
31 into a DC voltage E41 proportional to its frequency. , 42 is a divider circuit, which includes an F/V converter 41 and a rectifier circuit v! Perform desired calculations on the outputs En+ and E3a of I36,
Its output is a signal E related to the density or mass flow rate of the fluid.
Take out 42. 43 is a gate circuit in which the AC voltage E from the fIIJ1 amplifier circuit 38 is Schmitt 1? Tl butterfly 1
Me! αUto II 1 Noveno 17t9 key; Shin 2. In this case, the output of the divider circuit 42 is set to 0. Thus, the time constant of the rectifier circuit 36 and the time constant of the F/V converter 41 are made substantially the same and are configured to be greater than the beat frequency of the vortex signal.

In the above configuration, in order to accurately detect the absolute value of the fluctuating lift signal, a signal conversion circuit (charge converter 31° 32 and addition/subtraction circuit 33) with a flat f characteristic within the vortex frequency band converts the physical quantity into an electrical quantity. After that, a second amplifier circuit 34 which similarly has a flat f characteristic within the vortex frequency band
The signal was amplified and inputted directly to the detection circuit 35.

On the other hand, in the vortex frequency detection, after passing through the signal conversion circuit (charge converter 31, 32 and addition/subtraction circuit 33), a filter circuit 37 and a first amplifier circuit are used to reduce high frequency and low frequency noise contained in the vortex signal. After passing through 38, it was input to a Schmitt circuit (comparator) 39.

As a result of the above, by separating the variable lift signal detection circuit and the vortex frequency detection circuit immediately after the signal conversion circuit,
It was possible to both accurately measure the absolute value of the fluctuating lift signal and reliably detect the vortex frequency.

Therefore, the errors caused by the temperature of the mass flowmeter are: (1) thermal expansion of the pipe line 11 and the vortex generator 13, (2) temperature change in the Young's modulus of the material, (2) change in the d constant due to the degree of rotation of the piezoelectric element, There are some reasons.

Among these, ■ The coefficient of thermal expansion of the pipe I+ and the vortex generator 13 is as follows: When the fluid temperature of the device is t, the factor Kt is KL
= Ko(1-3ac t -to)) Here, Ko: At room temperature, factor a: is the linear expansion coefficient of the pipe I+ and the vortex generator 13, and as the temperature rises, the factor K( becomes smaller (minus (There will be a direction error.)

(2) As for the Young's modulus of the material due to the temperature change β, as shown in FIG. 7, the Young's modulus of the metal material decreases as the temperature rises, so the error appears in the negative direction.

(2) Change in the d constant due to the temperature of the piezoelectric element As shown in FIG. 8, the d constant of the piezoelectric element (for example, in the X-cut direction of the crystal) decreases as the temperature rises, and the error appears in the negative direction.

On the other hand, when the fluid temperature of the measurement fluid is t, the surface pressure P acting on the piezoelectric element is as follows. However, here, α0; coefficient of linear expansion αl of the outer cylinder portion 135; coefficient of linear expansion Lo of the sensor portion 14; length Ll of the outer cylinder portion 135; length Eo of the sensor portion 14: Young’s modulus of the outer cylinder portion 135 El: Young's modulus of the sensor section 14^0; Cross-sectional area of the outer cylinder section 13 A+ r Cross-sectional area of the sensor section 14 On the other hand, the LE electron output sensitivity Q is as shown in FIG.
If the surface pressure is within Po, it is proportional to the surface pressure P.

Therefore, by appropriately selecting the value of k in equation (2), the surface pressure can be set within the proportional region within the working fluid temperature.

Now, as shown in Fig. 9, if the usage range is P, < P < P2, then ΔQ day Q2 - Q.

Here, Q2 is Qa by appropriately selecting the value of k.
= Q+(I + C3a +
Let β + γ )t)・−0[D.

As described above, the error caused by the temperature of the mass flowmeter becomes negative as the temperature rises. Therefore, the surface pressure P of the piezoelectric element and the θth equation, O<P<P.

The sensor part 14 and the outer cylindrical part 1 are arranged so that the surface pressure P increases as the temperature rises by setting an appropriate value mk within the sensor part 14 and the outer cylinder part 1.
If the material is set to 35, the temperature error can be reduced to zero.

The temperature correction mechanism is shown in FIG.

It goes without saying that the configuration of the electric circuit portion that processes the vortex signal is not limited to the above-described embodiment.

(Effects of the Invention) As explained above, the present application provides a mass flow meter that measures the mass flow rate of a fluid to be measured using a Karman vortex signal that acts as an alternating force. A columnar force-receiving body, a recess provided in the axial direction of the force-receiving body and forming an outer cylindrical portion of the force-receiving body, a stress detecting portion made of a piezoelectric element disposed in the recess, and a side surface of the recess. A columnar fixing rod inserted with a gap between them so that they do not come into contact, one end of which presses and fixes the stress detection sensor ff1l into the recess, and the other end of which is fixed at the opening of the recess, and an insulator that insulates the stress detection part. d due to thermal expansion of the conduit and the vortex generator due to temperature changes, changes in the Young's modulus of the outer cylinder portion and the sensor portion, and temperature changes of the stress detection portion made of a piezoelectric element. The mass flowmeter is characterized in that the materials of the outer cylinder part and the sensor part are selected and configured so that the fixed surface pressure of the piezoelectric element increases as the fixed surface pressure of the piezoelectric element rises by 1 m degree so as to compensate for the change in constant with temperature. With this structure, it is possible to prevent temperature errors from occurring.

Therefore, according to the present invention, a highly accurate mass flowmeter with good temperature characteristics can be realized.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram of an embodiment of the present invention, (A) is a front view, (B) is a side view, FIG. 2 is a configuration explanatory diagram showing a cross section of the detector section of FIG. The figure is an operation explanatory diagram of Figure 2, Figures 4 and 5 are explanatory diagrams of the main parts of Figure 2, Figure 6 is an electric circuit diagram of wIJ1 diagram, and Figures 7 to 10 are diagrams of Figure 2. FIG. 11 is an explanatory diagram of the lift force etc. when a vortex generator is arranged in a pipe, and FIG. 12 is a diagram of a conventional structure commonly used in the past. Vortex generator, 131 ...Top end, +32...Bottom end, 133...Tangential body part, +34
... Recessed part, 135 ... Outer cylinder part, 14 ... Sensor part, +40 ... Piezoelectric element, 141 ... Second stress detection sensor, 142 ... First stress detection sensor, +43・
...Underlayment, 144...First spacer, 145...
Insulating plate, +46... Second spacer, 147... Push rod, 148... Hermetic seal, 1481.1
482...Lead wire, 149...Communication hole, +401
．． 1402.1403.1404... Electrode, 15...
・Laborability channel, 151...Fin, 152...
- Expansion chamber, 20... Vortex flowmeter converter, 30... Electric circuit, 31.32... Charge converter, 33...
- Addition/subtraction circuit, 34... Second amplifier circuit, 35... Detection circuit, 36... Rectifier circuit, 37... Filter circuit, 38... First amplifier circuit, 39... Schmitt trigger circuit , 41... F/V converter, 42... division circuit, 43... gate circuit. Figure 1 (A) Figure 2 1481 Lead Ibarama Figure 4 (A) Brother' n Surprise Figure 7 Figure 9 Figure 10 Figure 11 Figure 13 (A) Figure 13 (B) Figure 13 (C )

Claims (1)

[Claims] In a mass flow meter that measures the mass flow rate of a fluid to be measured using a Karman vortex signal that acts as an alternating force, there is a columnar force-receiving body inserted perpendicularly into the pipeline of the fluid to be measured, and an axial direction of the force-receiving body. a recess provided in the force-receiving body and forming an outer cylindrical portion;
A stress detection unit made of a piezoelectric element disposed in the recess is inserted into the recess with a gap such that the side surfaces do not contact each other, one end presses and fixes the stress detection sensor to the recess, and the other end is fixed at the opening of the recess. a sensor section including a columnar fixing rod and an insulator that insulates the stress detection section;
Temperature compensation is provided for thermal expansion of the conduit and the vortex generator due to temperature changes, changes in Young's modulus of the outer cylinder portion and the sensor portion, and changes in the d constant due to temperature changes of the stress detection portion made of a piezoelectric element. A mass flowmeter characterized in that materials of the outer cylinder part and the sensor part are selected so that the fixed surface pressure of the piezoelectric element increases as the temperature rises.