JP3137211B2 - Coriolis mass flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis mass flowmeter and, more particularly, to a signal processing system for measuring the deformation of a vibrating pipe due to Coriolis force and converting the deformation into a mass flow rate.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of a conventional straight tube type Coriolis mass flow meter. In FIG. 3, reference numeral 1 denotes a pipe through which a measurement fluid can flow, and both ends of the pipe 1 are fixed by fixing portions 2 and 3. 4 is fixed parts 2 and 3
The excitation means is provided at the center of the pipe 1 between the two, and excites the pipe 1 in a direction perpendicular to the central axis of the pipe 1 and displaces the pipe 1 up and down. Reference numerals 5 and 6 denote vibration detecting means for detecting the vibration of the pipe 1.

In such a configuration, FIG.
3 shows a vibration pattern. In FIG. 4, a and b are vibration patterns that the pipe 1 represents at each moment when excited by the excitation means 4, and c and d are patterns of asymmetric flexural vibrations expressed by the Coriolis force acting on the fluid flowing through the pipe 1. It is. Actually, the pipe 1 vibrates in a form in which the two types of vibration patterns are superimposed. This vibration is detected by the vibration detecting means 5 and 6, and a vibration displacement signal is output. This vibration displacement signal is input to a signal processing circuit (not shown) and is converted into a mass flow rate.

Conventionally, as a signal processing method for the mass flow rate conversion, there have been a time difference measurement method and a synchronous rectification method. These methods are described below.

[0005] The vibration state of the pipe in a state where no fluid is flowing through the pipe 1 is shown by a solid line in FIG. At this time, only the excitation vibration occurs. On the other hand, when the fluid flows through the pipe 1, vibrations due to the Coriolis force due to the fluid appear as shown in FIG. This amplitude is proportional to the mass flow rate flowing through the pipe 1, and the phase is shifted from the excitation vibration by 90 °. Therefore, assuming that the amplitude of the excitation vibration is constant, the vibration of the pipe 1 is changed from the excitation vibration to the vibration having a phase difference proportional to the vibration displacement due to the Coriolis force, as shown by the dotted line in FIG. Become. That is, the vibration has a phase difference proportional to the mass flow rate. Therefore, the mass flow rate can be obtained by measuring the phase difference.

The time difference measuring method is a method of measuring the phase difference as a time difference. However, since this method is a time difference measurement circuit, the device becomes complicated, the measurement resolution depends on the time difference counting clock, and it is not suitable for detecting a minute flow rate, and directly measuring time is generally inaccurate.

On the other hand, in the synchronous rectification system, FIG.
In this method, only the vibration displacement due to the Coriolis force is detected. As described above, this vibration displacement is proportional to the mass flow rate. This method is a method of performing synchronous rectification as shown in FIG. 5 (c) and performing integration over one cycle, thereby canceling the amplitude of the excitation vibration and measuring only the amplitude of the vibration due to Coriolis force. can do. Here, the timing at which the synchronous integration is performed is performed by, for example, a signal from a vibration detecting unit attached to the center of the same pipe. However, in this method, the device becomes complicated because of the synchronous rectification timing signal generation circuit, and the vibration amplitude generated by the Coriolis force is very small with respect to the excitation vibration amplitude (for example, several hundreds in the case of a straight tube type). Therefore, the timing was greatly influenced by the timing of performing the synchronous rectification. In addition, since the timing signal is created from the average value of the upstream and downstream vibration displacement signals or the output of the vibration detection means located at the center, the other mode vibration and noise are mixed, and the shape function changes due to temperature change. Therefore, there is a high possibility that the timing is shifted, and the signal processing method is likely to cause an error.

That is, in the conventional signal processing method of mass flow rate conversion, the apparatus becomes complicated, and the measurement accuracy and the measurement resolution are not sufficient.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is based on a displacement signal of a vibrating pipe obtained from a vibration detecting means. Is to take out stably and accurately. In particular, it provides a Coriolis mass flow meter that can obtain a Coriolis component by calculating a Coriolis component by calculating two vibration displacement signals, upstream and downstream, without using a timing signal in which the phase difference between the excitation vibration component and the phase difference is combined. It is intended to do so.

[0010]

According to the first aspect of the present invention,
When the fluid to be measured passes through the vibrating pipe,
Coriolis that measure the mass flow rate by detecting the generated Coriolis force
In the orifice mass flow meter, the upstream side of the vibrating pipe and
Output from a pair of vibration detection means
Signal processing means for converting the displacement signal
And two of the two vibration detection means output from the pair of vibration detection means.
The product of one of the displacement signals squared and one of the two displacement signals
Integrate each product of one and the other for one cycle of vibration
After calculating the sum and difference of the two integral values, respectively,
To calculate the square root of the quotient divided by
Characterized in that the mass flow rate is determined more.
It is a Coriolis mass flow meter. Further, in claim 2 of the present invention,
When the fluid to be measured passes through the vibrating pipe,
The mass flow rate by detecting the Coriolis force generated
In the Coriolis mass flow meter, the upstream side of the vibrating pipe
And output from a pair of vibration detection means installed on the downstream side
That converts the displacement signal (A ₀ , B ₀ ) to mass flow rate
Processing means, at the center of said pair of vibration detecting means
A third vibration detecting means, wherein the pair of vibration detecting means
The two displacement signals (A ₀ , B ₀ ) output from the third
The displacement signal (R ₁ ) output from the vibration detecting means and
Of the displacement signal (R ₂ ) of the displacement signal of
The integral product (E ₁ , F ₁ , G ₁ , H ₁ ) is integrated for one cycle of vibration.
And the addition and subtraction of these four integral values (E ₂ , F ₂ , G ₂ , H ₂ )
(E ₂ + G ₂ , F ₂ −H ₂ , E ₂ −G ₂ , −F ₂ −H ₂ )
After each, the difference (F ₂ −H ₂ ) is divided by the sum (E ₂ + G ₂ )
The quotient (K / J), the difference of (E ₂ -G ₂₎ sum (-F ₂ -H ₂₎
The quotient (L / M) divided by is obtained, and this quotient (K / J) and
Calculating the mass flow rate based on a quotient (L / M)
And a Coriolis mass flowmeter.

[0011]

According to the present invention, an upstream / downstream vibration displacement signal obtained by the vibration detecting means, or a vibration displacement signal obtained by the upstream / downstream vibration detecting means and the vibration detecting means provided at the center of the pipe. By performing the above-mentioned arithmetic processing on the base signal obtained in the above by the signal processing means, the Coriolis vibration can be relatively easily performed without performing the synchronous rectification with the timing signal strictly synchronized with the excitation vibration component. Only components can be separated.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Figure
1 is a signal processing means used in the Coriolis mass flow meter of the present invention.
FIG. 2 is a configuration diagram showing a first embodiment of the present invention. In FIG.
5 and 6 are a pair of vibrators installed on the upstream and downstream sides of the pipe.
The motion detecting means 7 is provided with a vibration output from the vibration detecting means 5 and 6.
This is a signal processing unit to which a dynamic displacement signal is input. This signal
In the processing means 7, reference numeral 71 designates the amplitudes of the upstream and downstream vibrations.
An automatic gain controller 72 for controlling the vibration;
Output (A₀) Multiplied by each other (A₁= A₀×
A₀) And 73 are the outputs of the automatic gain controller 71 (B₁) And vibration
The output (A₀) Multiplier (B)_Two= B₁
× A₀), 74 and 75 are the outputs (A₁,
B_Two) Are integrated, and the integration interval is
One cycle of movement. 76 is the output of the integrators 74 and 75
(A _Two, B_Three) (C)₁= A_Two+ B_Three), 7
7 is the output of the integrator 74 (A_Two) To the output of integrator 75
(B_Three) Is subtracted (C)_Two= A_Two-B_Three), 78 decreased
The output of the arithmetic unit 77 (C_Two) To the output of adder 76 (C₁)
Divider (C_Three= C_Two/ C₁) And 79 are of the divider 78
Output (C_Three) To find the square root of (C)_Four= √C_Three)so
is there.

In such a configuration, the vibrations of the pipe are detected by the vibration detecting means 5 and 6, and the electric signals A ₀ and B ₀ representing the displacement.
Is converted to A ₀ = a ₀ sinωt + ca ₀ cosωt B ₀ = b ₀ sinωt−cb ₀ cosωt where A ₀ is the vibration amplitude at the upstream, B ₀ is the vibration amplitude at the downstream, the sin component is the excitation vibration, and the cos component is the Coriolis force. Vibration is represented respectively.

Here, an automatic gain controller 71 adjusts the amplitudes of the upstream and downstream vibrations so as to be equal. The multiplication factor at this time is a ₀ / b ₀ . As a result, the two signals are A ₀ = a ₀ sin ωt + ca ₀ cos ωt B ₁ = a ₀ sin ωt−ca ₀ cos ωt, and are input to the multipliers 72 and 73, respectively.

The multiplier 72 multiplies the signal by itself, and A ₁ = A ₀ ² = (a ₀ sinωt + ca ₀ cosωt) ² = a ₀ ² ((1−cos 2ωt) / 2} + 2ca ₀ ² sinωt · cosωt + (Ca ₀ ) ² {(1 + cos2ωt) / 2}. Also, the multiplier 73 is multiplied by the other displacement _{signal, B 2 = B 1 × A} 0 = (a 0 sinωt-ca 0 cosωt) (a 0 sinωt + ca 0 cosωt) = a 0 2 sin 2 ωt-c 2 a ₀ ² cos ² ωt = a ₀ ² {(1−cos 2ωt) / 2} −ca ₀ ² {(1 + cos 2ωt) / 2}, which are input to the integrators 74 and 75, respectively.

In the integrators 74 and 75, integration is performed in one cycle from an arbitrary timing.

[0017]

(Equation 1)

[0018]

(Equation 2) However, T ₀ is arbitrary.

The outputs of the integrators 74 and 75 are supplied to an adder 7
6 and a subtractor 77 to perform an operation.
The output is C ₁ = A ₂ + B ₃ = 2 (2π / ω) a ₀ ² C ₂ = A ₂ −B ₃ = 2 (2π / ω) c ² a ₀ ² , which is input to the divider 78. .

In the divider 78, C ₂ / C ₁ is calculated. C ₃ = C ₂ / C ₁ = {2 (2π / ω) c ² a ₀ ² } / {2 (2π / ω) a ₀ ² } = c ² This quotient C ₃ is input to the arithmetic unit 79, A square root is required. C ₄ = √C ₃ = c

By such an operation, "c", that is,
The vibration amplitude ratio generated by the Coriolis force is determined.
The vibration amplitude ratio c is a parameter proportional to the mass flow rate, as is known as the principle of the Coriolis mass flow meter, and is expressed as the mass flow rate Q after conversion.

As described above, according to the first embodiment,
By subjecting the upstream and downstream vibration displacement signals obtained by the vibration detection means to the above-described arithmetic processing by the signal processing means,
Even without performing synchronous rectification with a timing signal strictly synchronized with the excitation vibration component, the mass flow rate can be obtained relatively easily by separating only the Coriolis vibration component.

In the above embodiment, the signal processing is
An analog circuit may be used. After A / D conversion,
Digital processing may be performed. Further, the configuration may be such that the automatic gain controller 71 is not provided. In this case, the positions of the vibration detection means 5 and 6 may be appropriately set so that the vibration amplitudes of the upstream and downstream are equalized structurally. If the integration time is sufficiently long for one cycle of the vibration, there is no need to stick to the time of one cycle, and the integrator may be a simple first-order delay circuit. Therefore, the integrator becomes simpler and does not depend on the integration time, so that an improvement in accuracy can be expected. Further, the vibration detecting means may be any type such as a displacement sensor, a speed sensor, and an acceleration sensor, and is finally converted into a displacement signal and output. Further, the shape and structure of the pipe may be any shape such as a U-shaped pipe, a straight pipe, a multiple pipe such as a loop pipe or a parallel pipe.

FIG. 2 is a block diagram showing a second embodiment of the Coriolis mass flow meter according to the present invention. In FIG. 2, the same elements as those in FIG. 1 or FIG. 3 are denoted by the same reference numerals, and redundant description will be omitted. 2, 8 is a vibration detecting means provided in the central portion of the pipe 1, to its output based signal R _1. Reference numeral 9 denotes a signal processing unit to which the vibration displacement signals A ₀ , B ₀ and the base signal R ₁ output from the vibration detection units 5, 6, 8 are input. In this signal processing unit 9, 91 is a phase shifter, a base signal R ₁ obtained by the 90 ° phase-based signal R ₂ by the phase shifter 91. 90
° The transfer method may be a simple configuration such as an integrator. 9
Reference numerals 2a to 92d denote multipliers for multiplying the outputs A ₀ and B ₀ of the vibration detecting means 5 and 6 by the base signals R ₁ and R ₂ , respectively. The outputs (products) are E ₁ , F ₁ , G ₁ and H. _Set to ₁ . 93a-9
3d is a integrator integrating over the multiplier the product of 92a-92d E _1, F _1, G _1, H ₁ to each one cycle, the integration start time is arbitrary (integral value E _2, F ₂ , G ₂ , H ₂ ). 94a~94d are subtractor for subtracting the output of the integrator _{93a~93d (E 2, F 2,} G 2, H 2).
Incidentally, the combination of addition and subtraction, the adder-subtracter 94a is (E ₂
+ G ₂ ), the adder / subtractor 94b is (F ₂ −H ₂ ),
4c is (E ₂ -G _2), adder-subtracter 94d is (-F ₂ -H ₂₎
And the outputs are J, K, L, and M. 95a, 9
5b is the upstream and downstream adders / subtractors (94a and 94b).
b, a divider for dividing the outputs (J and K, L and M) of 94c and 94d), and 96 is a subtractor.

In such a configuration, the pipe 1
Output A of the attached vibration detecting means 5 and 6 ₀, B₀Is A₀(T) = Asinωt + BcosωtB₀(T) = Asinωt−Bcosωt.

Here, the mass flow rate Q to be obtained is expressed as follows: Q = kB / A (k: an arbitrary constant). Conventionally, using A ₀ and B ₀ , transfer as A ₀ (t) = {(A ² + B ² ) sin (ωt + Φ) Φ = tan ⁻¹ (B / A) ≒ (B / A) ∝Q The mass flow rate was determined by measuring the difference Φ as a time difference.

It is assumed that the two base signals R ₁ and R ₂ are represented by the following equations. R ₁ (t) = C sin ωt R ₂ (t) = C cos ωt Basically,

[0028]

(Equation 3)

Thus, since X = (AC / 2) · 2π / ω Y = (BC / 2) · 2π / ω, the mass flow rate Q is as follows: Q = k · Y / X = k · B / A Can calculate. However, it is more realistic to consider a case where an unknown phase shift θ is present in the base signals R ₁ and R ₂ , and even in this case, the mass flow rate can be obtained.
Therefore, the outputs A ₀ and B ₀ of the vibration detecting means 5 and 6 and the base signals R ₁ and R ₂ are multiplied by the multipliers 92a to 92d, respectively. The outputs E ₁ , F ₁ , G ₁ , and H ₁ are respectively represented by the following equations. _{E 1 (t) = (Asinωt} + Bcosωt) sin (ωt + θ) F 1 (t) = (Asinωt + Bcosωt) cos (ωt + θ) G 1 (t) = (Asinωt-Bcosωt) sin (ωt + θ) H 1 (t) = (Asinωt- Bcosωt) cos (ωt + θ)

The product E of the multipliers 92a to 92d is₁, F₁,
G₁, H₁Into one cycle in each of the integrators 93a to 93d.
Integrate across. Output E of integrators 93a-93d₁,
F₁, G ₁, H₁Are represented by the following equations. E_Two(T) = (2π / ω) ｛(A / 2) cos θ + (B / 2) sin θ｝ F_Two(T) = (2π / ω) {(B / 2) cos θ− (A / 2) sin θ} G_Two(T) = (2π / ω) ｛(A / 2) cos θ− (B / 2) sin θ｝ H_Two(T) = (2π / ω) {− (B / 2) cos θ− (A / 2) sin θ}

The outputs E _{2 of} the integrators 93a to 93d,
The above-described addition and subtraction of F ₂ , G ₂ , and H ₂ are performed by the adders / subtractors 94a to 94d, respectively. The outputs J, K, L, and M are represented by the following equations. J = E ₂ + G ₂ = A · (2π / ω) cos θ K = F ₂ −H ₂ = B · (2π / ω) cos θ L = E ₂ −G ₂ = B · (2π / ω) sin θ M = − F ₂ −H ₂ = A · (2π / ω) sin θ

The outputs J of the adders / subtractors 94a to 94d are J,
K, L and M are divided by the upstream and downstream sides, respectively.
By dividing by a and 95b, _two outputs Q ₁ and Q ₂ corresponding to the mass flow rate Q can be obtained on the upstream side and the downstream side. Q ₁ = k · K / J = k · B / A Q ₂ = k · L / M = k · B / A

The two mass flow rates Q ₁ and Q ₂ ideally show equal values. However, two vibration detecting means 5,
6 do not always show the same value due to the difference in the sensitivity and the like. Therefore, a difference between the two mass flow values is obtained by using a mechanism for adjusting the sensitivity of the vibration detection means so that the two mass flow values become equal, that is, a subtractor 96 shown in the figure, and the vibration detection means 6 You just have to return.

As described above, according to the second embodiment,
By subjecting the vibration displacement signal obtained by the two upstream and downstream vibration detecting means and the base signal obtained by the vibration detecting means provided at the center of the pipe to the above-described arithmetic processing by the signal processing means, Even without performing synchronous rectification with a timing signal strictly synchronized with the excitation vibration component, the mass flow rate can be obtained relatively easily by separating only the Coriolis vibration component. Also, in this case, there is no need to perform an operation to find the square root after integration, as compared with the first embodiment, and the mass flow rate can be obtained only by simple four arithmetic calculations. Further, since two mass flow values are obtained, automatic gain control and the like can be performed using the two mass flow values.

Since the mass flow rate can be obtained even if an unknown phase difference θ is present in the base signal, an apparatus for generating the base signal (the vibration detecting means 8 in the apparatus shown in FIG. 2) is not always necessary. Absent. That is, the output of the vibration detecting means 5 or 6 may be used as the base signal.

Further, in the above embodiment, the vibration detecting means may be any type such as a displacement sensor, a speed sensor, and an acceleration sensor, and is finally converted into a displacement signal and outputted. Furthermore, the shape and structure of the pipe are U-shaped, straight,
Any shape such as a multiple tube such as a loop tube or a parallel tube may be used.

[0037]

As described above, according to the present invention, according to the present invention, the calculation of the two vibration displacement signals, upstream and downstream, can be performed without using a timing signal in which the phase difference is combined with the excitation vibration component. It is possible to realize a Coriolis mass flowmeter that is stable, requires high accuracy and requires a Coriolis component, and can simplify the apparatus.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of signal processing means used for a Coriolis mass flow meter according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the signal processing means used in the Coriolis mass flow meter of the present invention.

FIG. 3 is a configuration diagram showing an example of a conventional Coriolis mass flow meter.

FIG. 4 is a diagram for explaining the operation of the device in FIG. 3;

FIG. 5 is a diagram illustrating a method for measuring the deformation of a pipe due to Coriolis force.

[Explanation of symbols]

 5, 6, 8 Vibration detecting means 7, 9 Signal processing means 71 Automatic gain controller 72, 73, 92a to 92d Multiplier 74, 75, 93a to 93d Integrator 76 Adder 77, 96 Subtractor 78, 95a, 95b Divider 79 Arithmetic unit (square root) 91 Phase shifter 94a-94d Adder / subtractor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/84

Claims (2)

(57) [Claims] 1. A Coriolis mass flowmeter for measuring a mass flow rate by detecting a Coriolis force generated when a fluid to be measured passes through a vibrating pipe, wherein the Coriolis mass flowmeter is installed on an upstream side and a downstream side of the vibrating pipe. A signal processing unit for converting a displacement signal output from a pair of vibration detection units into a mass flow rate, wherein the two displacements output from the pair of vibration detection units are provided.
Product of one of the signals squared and one of the two displacement signals
Each of the products multiplied by the other is integrated for one cycle of vibration,
A Coriolis mass flowmeter, wherein the mass flow rate is obtained by calculating a sum and a difference of two integral values, and then calculating a square root of a quotient obtained by dividing the difference by the sum. 2. A Coriolis mass flowmeter for measuring a mass flow rate by detecting a Coriolis force generated when a fluid to be measured passes through an oscillating pipe, wherein the Coriolis mass flowmeter is installed upstream and downstream of the oscillating pipe. A signal processing means for converting displacement signals (A ₀ , B ₀ ) output from the pair of vibration detecting means into a mass flow rate, comprising a third vibration detecting means at a central portion of the pair of vibration detecting means, Two displacement signals output from the pair of vibration detecting means
Products (E ₁ , F 0 ) obtained by multiplying (A ₀ , B ₀ ) by a displacement signal (R ₁ ) output from the third vibration detecting means and a signal obtained by shifting the displacement signal by 90 ° (R ₂ ) , respectively. _1, G _1,
H ₁ ) is integrated for one cycle of vibration, and these four integrated values are obtained.
(E ₂ , F ₂ , G ₂ , H ₂ ) addition and subtraction (E ₂ + G ₂ , F ₂ −
H ₂ , E ₂ -G ₂ , -F ₂ -H ₂ ), and then the difference
(F ₂ -H ₂₎ divided by the sum (E ₂ + G ₂₎ the quotient (K /
J), the quotient obtained by dividing the difference (E ₂ −G ₂ ) by the sum (−F ₂ −H ₂ )
(L / M), the quotient (K / J) and the quotient (L / M)
A Coriolis mass flowmeter characterized in that the mass flow rate is obtained based on the following .