JP3245144B2 - Method for measuring the mass flow of a gaseous or vaporous fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the mass flow rate of a gaseous or vaporous fluid according to the Coriolis principle.

[0002]

2. Description of the Related Art Coriolis mass flow rate /
The densitometer, as is known, has at least one measuring tube which is excited by mechanical vibration and is passed through by a fluid, which measuring tube can be bent or straight. The details will be described later with reference to FIG.

[0003] Usually, at least one exciter and at least two vibration sensors are arranged in the measuring tube, the vibration sensors being spaced from one another in the direction of flow. The measuring tube oscillates at a mechanical resonance frequency, which is often predetermined by its material and its dimensions, but varies with the density of the fluid. In other cases, the vibration frequency of the measuring tube is not exactly its mechanical resonance frequency, but a frequency near it.

[0004] Vibration sensors emit analog sensor signals, the frequency of these sensor signals being the same as the vibration frequency of the measuring tube, these sensor signals being out of phase with each other when a fluid flows through the measuring tube. ing. From this, a time difference signal, for example a time difference signal between the zero crossings of the sensor signal, can be derived, which is directly proportional to the mass flow, as described, for example, in US-A 41 87 721. I have.

[0005] However, an angle difference can also be formed from the phase shift, which is described in US-A 5648 616 or EP.
As described in -A 866 319, it is directly proportional to the mass flow rate divided by 2π times the resonance frequency f of the measuring tube.

[0006] These proportionalities can always be assumed accurately in the measurement of the mass flow of liquids, and thus guarantee a measurement accuracy of 0.1% in today's Coriolis mass flow / density meters. Can be.

[0007] It has been found by the present inventor that when measuring gaseous or vapor-like fluids, the above-mentioned exact proportionality can often not be assumed, which results in a small accuracy.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for measuring the mass flow of a gaseous or vaporous fluid according to the Coriolis principle which can give accurate results which are suitable for the measurement of liquids. Is to do so.

[0009]

According to the present invention, a gaseous or vaporous fluid flowing through at least one measuring tube of a mass flow case of a Coriolis mass flow / density meter is provided according to the present invention. A method for measuring mass flow, in which the measuring tube is predefined in operation by its material and its dimensions, but the vibration frequency which is varied by the density of the fluid, also the mechanical current of the measuring tube It vibrates at a vibration frequency equal to or close to the resonance frequency, and a first vibration sensor that emits a first sensor signal and a second vibration sensor that emits a second sensor signal flow in the measurement tube. Are arranged at a distance from each other, and an exciter is arranged on the measuring tube, and the measuring tube is surrounded by a support frame or a supporting tube, or Alternatively, in the case where the sensor is vibrated by a support plate, a signal related to a phase shift of the sensor signal is formed from the first sensor signal and the second sensor signal. Was multiplied by a function related to.

[0010]

In a first advantageous embodiment of the invention, the signal relating to the phase shift is a time difference signal between the zero crossings of the sensor signal.

In a second advantageous embodiment of the invention, the signal relating to the phase shift is an angular difference, which is divided by 2π times the oscillation frequency f.

In a third advantageous embodiment of the invention, which can also be applied in the first and second embodiments, the function f (c) is given by the formula: f (c) = ｛1 + bｂ (2π ・ f • d / c) ² ｝ ⁻¹ (where b is determined by calibration,
The same constant for all standard diameters of the measuring tube, d
Is the inner diameter of the measuring tube).

In another advantageous embodiment of the invention, the speed of sound c
Is approximately represented by a function f (T _m ) related to the current temperature T _m of the measuring tube. In particular, the function f (T _m ) is obtained by the following equation: c = c ₀ + c ₁ · T _m (where c: ₀ and c ₁ are constants peculiar to the fluid).

[0014]

An advantage of the present invention is that the speed of sound of the fluid and thus indirectly the compressibility of the fluid are also taken into account in the measurement, and thus the accuracy of the mass flow measurement of gaseous or vaporous fluids is virtually eliminated. The accuracy of the measurement can be the same.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS The invention and further advantages will be explained in more detail by means of the embodiments shown in the drawings.

FIG. 1 shows, in a vertical longitudinal side view, partially in section, a mass flow case 1 of a Coriolis mass flow / density meter suitable for the method according to the invention. The case is passed through by the gaseous or vaporous fluid to be measured--but not shown for the sake of clarity--in the course of a tube conduit of known diameter, for example via flanges 2,3. Can be inserted. Instead of a flange, the mass flow case 1 can also be connected to the aforementioned pipe conduit by other known means, for example by a tri-clamp connection or a screw connection.

The mass flow case 1 of FIG. 1 has only one straight measuring tube 4 whose end on the fluid inlet side is connected to the flange 2 by, for example, an end plate 13 on the fluid inlet side. The end on the fluid outlet side is fixed to the flange 3 via, for example, an end plate 14 on the fluid outlet side. The measuring tube 4 is pressed tightly, in particular vacuum tight, into the end plates 13, 14, for example by welding, brazing or rolling (in this respect US-A 56 1).
0 342).

[0018] The method of the present invention is based on Japanese Patent Application No. Hei.
It can be used either in the clamp-on type Coriolis mass flow case according to 550003 or in the mass flow case with only one measuring tube according to EP-A 849 568. Instead of just one straight measuring tube, the mass flow case of the Coriolis mass flow / density meter consists of only one measuring tube bent in one plane,
It can have a measuring tube, for example in the form of an arc, as described, for example, in US-A 57 05 754.

However, a plurality of, in particular two, straight measuring tubes as described in US-A 47 93 191 or a plurality of such as described in US-A 41 27 028,
In particular, two bent measuring tubes are also possible.

The method according to the invention can also be used in a mass flow case with one measuring tube and one dummy tube, as described in US Pat. No. 5,311,126. Finally, the method of the present invention provides that the mass flow case is U
It is also applicable to Coriolis mass flow / density meters having at least one threaded measuring tube corresponding to SA 55 57 973 or UA-A 56 75 093.

In FIG. 1, flanges 2 and 3 and end plate 1
3, 14 are fixed to a support tube 15, which is also fixed by screws, one of these screws 5 being completely visible in cross section in the upper right. End plates 13, 14
Can be welded or brazed tightly, in particular vacuum tight, to the inner wall of the support tube 15. However, the support tube 1
5 and the end plates 13 and 14 can be integrally formed. Instead of the support tube 15, a support frame or a support plate can be used.

As a means for causing the measuring tube 4 to vibrate, in particular resonantly vibrate, preferably resonant bending, at the center between the flanges 2 and 3 and the end plates 13 and 14 and between the support tube 15 and the measuring tube 4 For example, an electromagnetic exciter 16 arranged in the intermediate space of this type, which has a permanent magnet 161 fixed to the measuring tube 4 and a coil 162 fixed to the support tube 15, Permanent magnets 161 protrude into these coils, and the permanent magnets can reciprocate in these coils.

In FIG. 1, the exciter 16 causes the measuring tube 4 to bend and vibrate in the plane of the drawing, so that a Coriolis force is generated even in this plane even when a fluid is flowing. Causes a phase shift between the section on the exit side and the section on the exit side.

Further, a first vibration sensor 17 and a second vibration sensor 18 for vibrating the measurement tube 4 are arranged in an intermediate space between the measurement tube 4 and the support tube 15.
The vibration sensor 17 or 18 is connected to the end plate 13 or 14
And preferably at the same distance from the exciter 16, preferably from the exciter, that is to say from the center of the measuring tube 4.

The vibration sensors 17 and 18 are electromagnetic vibration sensors in FIG.
71 or 181 and a coil 172 or 182 fixed to the support tube 15, into which a permanent magnet 171 or 181 protrudes, and is movable reciprocally in these coils. The first sensor signal x ₁₇ or the second sensor signal x ₁₈ occurs in the vibration sensor 17 or 18.

[0026] The end plate 13 has a temperature feeler 19 is fixed, the temperature feeler issues a temperature signal x ₁₉ representing the current temperature of the measuring tube 4. A platinum resistor is preferably used as the temperature feeler, which is fixed to the end plate 13 by, for example, gluing.

Finally, FIG. 1 shows a casing 21 which is still fixed to the support tube 15, this casing being, inter alia, an exciter 16 and vibration sensors 17, 18.
, But serves for protection of conductors not shown for clarity of the drawing.

The casing 21 has a neck-shaped transition piece 22 to which an electronic device casing 23 is fixed for receiving the measuring and operating circuits of the mass flow / density meter. Transition piece 22 and electronic device casing 2
In the event that 3 adversely affects the vibration characteristics of the support tube 15, these transition pieces and the electronics casing can be arranged separately from the mass flow case 1. In that case, there is only a cable connection between the electronic device and the mass flow case 1.

FIG. 2 shows, in the form of a block diagram, a measuring circuit for implementing the method according to the invention for a mass flow / density meter having measuring tubes of the various constructions described above. This measuring circuit includes a sub-circuit 3 for generating a mass flow signal “q _f ” and a density signal “σ” from the aforementioned sensor signals x ₁₈ and x _19.
Contains one. As the partial circuit 31, any suitable defined circuit can be used, in particular the circuit described in US Pat. No. 5,648,616, which has already been mentioned above.

[0030] When the liquid flows through the measurement tube 4, the mass flow rate signal "q _f" is usually already represents the mass flow rate q ', that is the measurement result of the liquid. This can be physically attributed to the following. That is, in the case of liquid measurement, the following condition is practically always satisfied: (2π · f · d) / c≪1 (1) (where c is a fluid, in this case the sound velocity of the liquid) And d is the wall thickness of the measuring tube 4 and f is the current vibration frequency of the measuring tube). Thus, for liquids: q _f = C · δγ = (C · δφ) / (2πf) ( 2) (where C is a constant determined by calibration, a so-called calibration constant, and δγ is the first-mentioned time difference, for example, the time difference between the zero crossing points of the sensor signals x ₁₇ and x ₁₈ , δφ is the angle difference described first).

On the other hand, FIG. 2 corresponding to the method of the present invention
In the circuit arrangement, before the gaseous or final mass flow rate signal representative of the mass flow rate signal q of vaporous fluid "q" is caused, the mass flow rate signal "q _f" is as it were additionally modified You.

The signal q _f is a function f related to the sound velocity c of the fluid.
Multiplied by (c). This function is, for example, the formula: f (c) = {1 + b · (2π · f · d / c) 2} −1 (3) (where b is checked by calibration,
The same constant for all standard diameters of the measuring tube, d
Is the inner diameter of the measuring tube).

In the embodiment of FIG. 2, the mass flow q is:

[0034]

(Equation 1)

[0035]

In equation (4), c₀, C₁Is specific to gas
Constants or constants specific to steam.
Have the values entered for the In this case, the temperature signal
No. x ₁₉Is proportional to the temperature measured in Celsius
Is assumed.

[0037]

[Table 1]

The mass flow signal “q _f ” from the partial circuit 31
Is supplied to the dividend input point of the first division circuit 32. At the output of the first division circuit a mass flow signal "q" is generated. The output of the first adder circuit 33 is supplied to the divisor input point of the divider circuit. The first input point of this adder circuit is
Is supplied.

The output of the first multiplying circuit 34 is supplied to a second input point of the adding circuit. A signal "b" representing the aforementioned constant b is supplied to a first input point of the multiplication circuit. Since this constant is checked during calibration, this signal "b" is stored in an electronic memory, such as an EEP, as is usual for calibration values.
It is stored in the ROM. From this memory, the signal "b" is supplied to the aforementioned input point of the multiplication circuit 34.

The output of the second multiplier 35 is supplied to a second input point of the multiplier 34, and the same signal is supplied to the first and second input points of the second multiplier. In other words, these signals are supplied from one output point of the second division circuit 36. The multiplication circuit 35 is therefore a division circuit 3
6 acts as a squaring circuit for the output signal. This division circuit has a first dividend input point, to which a signal “f” representing the current vibration frequency f of the measuring tube 4 is supplied. This signal is a sensor signal x ₁₇ , x ₁₈
Can be formed in an ordinary format from (for example,
See US-A 56 48 616).

The dividing circuit 36 further has a second input point, to which a signal "d" representing the wall thickness d of the measuring tube 4 is supplied. This signal is from a first electronic memory 37, for example an EEPROM, in which all values of the wall thickness d occurring in the field are stored. That is, the wall thickness d changes variously according to the diameter of the measuring pipe 4, and the diameter of the measuring pipe changes variously according to the standard value of the above-mentioned pipe conduit in which the mass flow rate case is inserted. A first select signal s ₁ is continuously supplied to a select input point of the memory 37, and the select signal causes the Coriolis mass flow rate /
The densitometer manufacturer inputs the value of the wall thickness d for each type.

The division circuit 36 has a divisor input point at the end.
The output of the second adder circuit 38 is supplied to the divisor input point.
Be paid. The first input point of this adder circuit is a third multiplication circuit.
Connected to the output point of the path 39.
Is the temperature signal x ₁₉And its second
The input point is connected to the first output point of the second electronic memory 40
Have been. This memory is, for example, an EEPROM
There can be.

The signals "c ₀ " and "c ₁ " are stored in the memory 40, and these signals represent the values of the constants c ₀ and c ₁ entered in the above-mentioned table. The first output point of the memory 40 has a signal "c ₁ " and the second output point has a signal "c ₀ ". This second output point is connected to a second input point of the adder circuit 38. Further, the memory 40 has a second
It has a select input points that are supplied with the select signal s _2, the second select signal the user of the Coriolis mass flow / density meter by a signal belonging to a fluid to be just measured "c _0" , “C ₁ ” is adjusted.

If the signals supplied to the sub-circuits 32 to 40 in FIG. 2 are digital signals, the function can be realized by a correspondingly programmed microprocessor. The partial circuit 31 is, for example, the aforementioned US-A
In the case where an analog signal is generated as in one of the circuits described in U.S. Pat. No. 5,648,616, an analog / digital converter can be provided between the output point of the partial circuit 31 and the input point of the division circuit 32. .

On the other hand, the partial circuit 31 is, for example, a US-A 5
An analog-to-digital converter is not required if a digital signal is to be generated, as in the other circuits described in 6 48 616 or in the circuit of EP-A 866 319 mentioned above.

The speed of sound c in FIG. 2, by a term c0 + c ₁ · x ₁₉ is utilized for temperature related speed of sound, is considered. However, other terms are also possible due to temperature relevance, for example: (5) and (6): c = z ₀ + z ₁ · T _m + z ₂ · p + z ₃ · T _{m ′} (5) ( Where z ₀ , z ₁ , z ₂ , z ₃ are constants specific to the fluid to be measured and p is the fluid pressure measured by the pressure sensor) or c = k ₀ · (T _m ) ^{1 / 2} (6) (where k ₀ is also a constant specific to the fluid to be measured) If equations (5) and (6) are used for consideration of sound velocity c, equation (5) ) And (6) can be used in place of the denominator term c ₀ + c ₁ · x ₁₉ in equation (4),
It can be selected also temperature signal x ₁₉ for that time T _m.

[Brief description of the drawings]

FIG. 1 is a partially sectional longitudinal side view of a mass flow case of a mass flow meter having a measuring tube.

2 shows, in the form of a block diagram, a measuring circuit for implementing the method according to the invention, for example for the mass flow meter of FIG. 1;

[Explanation of symbols]

Reference Signs List 1 mass flow case, 2 flange, 3 flange, 4 measuring tube, 5 screw, 13 end plate on fluid inlet side, 14 end plate on fluid outlet side, 15 support tube, 1
6 Exciter, 17 Vibration sensor, 18 Vibration sensor, 19 Temperature feeler, 21 Casing, 2
2 transition piece, 23 electronic device casing, 31 partial circuit, 32 first division circuit, 33 first addition circuit, 34 first multiplication circuit, 35 second multiplication circuit, 36 second division circuit, 37th division circuit 1 electronic memory, 38 second adding circuit, 39 third multiplying circuit, 40 second electronic memory, 161 permanent magnet,
162 coil, 171 permanent magnet, 172 coil, 181 permanent magnet, 182 coil, b constant signal, c ₀ constant signal, c ₁ constant signal, d wall thickness signal, f current vibration frequency signal, q mass flow signal, q _f mass flow signal, s ₁ first select signal, s ₂ second select signal, x ₁₇ sensor signal, x ₁₈ sensor signal, x ₁₉ temperature signal, sigma density signal

Continuation of the front page (56) References JP-A-11-6754 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1/84

Claims (6)

(57) [Claims] 1. A method for measuring the mass flow rate of a gaseous or vaporous fluid flowing in at least one measuring tube (4) of a Coriolis mass flow / density meter mass flow case (1). The tube is pre-determined during operation by its material and its dimensions and has a vibration frequency f which is varied depending on the density of the fluid, also at a vibration frequency equal to or close to the current mechanical resonance frequency of the measuring tube. Oscillates and a first sensor signal (x
₁₇₎ a first vibration sensor which emits (17) a second sensor signal (second vibration sensor which emits x ₁₈₎ (18) are spaced from one another in the flow direction, and the measurement An exciter (16) is arranged in the tube, and the measuring tube is of the type surrounded by a support frame or a support tube (15) or held oscillatingly on a support plate. 1 sensor signal (x ₁₇ )
And from the second sensor signal (x ₁₈ ), form a signal q _f related to the phase shift of the sensor signal and multiply this signal by a function f (c) related to the sound velocity c of the fluid,
A method for measuring the mass flow of a gaseous or vaporous fluid. 2. The method according to claim 1, wherein the signal related to the phase shift is a time difference signal δγ between zero crossings of the sensor signal.
The method of claim 1. 3. The method according to claim 1, wherein the signal related to the phase shift is an angle difference δφ, and the angle difference is divided by 2π times the vibration frequency f. 4. The function f (c) is calculated by the formula: f (c) = {1 + b · (2π · f · d / c) ² } ⁻¹ (where b is checked by calibration,
The same constant for all standard diameters of the measuring tube, d
Is the inner diameter of the measuring tube). 5. The sound velocity c is determined by measuring the current temperature T _m of the measuring tube (4).
4. The method according to claim 3, wherein the function is approximately represented by a function f (T _m ) related to. 6. The function f (T _m ) having the formula: c = c ₀ + c ₁ · T _m (where c ₀ and c ₁ are fluid-specific constants). Item 6. The method according to Item 5.