JP2934136B2 - Coriolis flow meter - 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 flowmeter, and more particularly, to a Coriolis flowmeter for determining a Coriolis force acting on a measuring tube as a time difference signal of a detection signal at a vibration detection position of the measuring tube.

[0002]

2. Description of the Related Art When a measuring tube is supported at both ends and a central portion of the supported measuring tube is driven alternately in a direction perpendicular to an axis,
When the fluid moves, a phase difference occurs between the inflow side and the outflow side of the measurement tube around the center of the measurement tube. This phase difference is
Coriolis flowmeters that are based on Coriolis force and are proportional to the mass flow rate and that measure the mass flow rate by detecting the phase difference are well known. Thus, the detection of the phase difference
The measurement is performed by measuring a time difference when the measurement tube at the detection position passes through the reference plane with a plane passing through the pipe axis of the measurement pipe in a stationary state of the measurement pipe as a reference plane. Specifically, the time difference is obtained by shaping the waveforms of the signals of the displacement detectors of the measurement tubes attached to the symmetrical positions on the inflow side and the outflow side of the measurement tubes into square waves, respectively. It is determined from the number of clocks of a constant frequency counted between time differences.

[0003]

As described above, the Coriolis flowmeter supports the measuring tube at two points, and applies vibration around the supporting point to the supported measuring tube with the supporting point as a node. It is a mass flow meter for detecting Coriolis force acting on a fluid flowing through a measurement tube. However, the phase difference signal of the measurement tube generated at a predetermined symmetrical position between the inflow side and the outflow side of the measurement tube due to the Coriolis force is an extremely small amount compared with the drive amplitude of the measurement tube. Therefore, the time difference detected in proportion to the phase difference signal is also very small. In order to measure this time difference with high resolution, it is necessary to increase the clock frequency. However, since the Coriolis flowmeter is mounted between the upstream and downstream pipes, it is easily affected by external vibration and noise caused by the pipes, and stable time difference measurement cannot be performed by simply using a clock having a high resolution.

SUMMARY OF THE INVENTION An object of the present invention is to provide a Coriolis flowmeter having a time difference detecting means capable of obtaining an averaged and stable time difference with little noise effect without using a clock for time difference measurement. It is assumed that.

[0005]

In order to solve the above-mentioned problems, the present invention provides (1) a measuring pipe through which a fluid flows, and a supporting member for supporting the measuring pipe at two points in a flow direction at an interval. ,
Driving means for driving the measurement tube around the support member, at a symmetric position between the support members of the measurement tube,
A first detector and a second detector for detecting the vibration of the measuring tube, and detecting a time on a reference time axis from a vibration signal detected by the first detector and the second detector; In a Coriolis flowmeter having time difference detecting means for determining a mass flow rate, the time difference detecting means shapes the vibration signal detected by the first detector into a sine wave signal, and converts the shaped sine wave signal into an inverse sine wave. A first conversion circuit that converts the vibration signal detected by the second detector into a sine wave signal, and converts the shaped sine wave signal into an inverse sine wave signal; A first amplitude control circuit for controlling the amplitude of the inverse sine wave signal output from the first conversion circuit to be constant, and a first amplitude control circuit for controlling the amplitude of the inverse sine wave signal output from the second conversion circuit The inverse sine wave signal controlled by Second controlling the equal amplitude amplitude
An amplitude control circuit, a subtraction circuit for subtracting the output of each of the first amplitude control circuit and the second amplitude control circuit, a cycle measurement circuit for measuring a cycle of the vibration signal, and a cycle of the measured vibration signal And a multiplication circuit for multiplying the output of the subtraction circuit, and obtaining the time difference from the output of the multiplication circuit. (2) In the above (1), the time difference detection means includes a first conversion circuit. (3) The (1) or (3), wherein the second conversion circuit is a waveform conversion circuit that outputs a triangular wave signal having the same phase as the first vibration signal, and outputs the second conversion circuit as a triangular wave signal having the same phase as the second vibration signal. In 2), the time difference detecting means clips the triangular wave signal controlled to a constant amplitude by the first amplitude control circuit and the second vibration control circuit with a voltage smaller than the triangular wave signal peak voltage, Is characterized in that the output as square wave signal.

[0006]

The respective sine wave signals detected at the symmetrical positions from the support positions on the inflow side and the outflow side of the measuring tube are converted into inverse sine wave signals, and have a phase difference of ± (π / 2 ) Is a triangular wave signal having a peak value, input to a subtraction circuit, calculate a phase difference from the subtraction value, and multiply this by a period of a sine wave of the detected vibration signal to obtain a time difference proportional to the Coriolis force. Ask.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing a Coriolis flow meter according to the present invention, a basic structure of a Coriolis flow meter will be described first. FIG. 4 is a basic structural view for explaining a Coriolis flowmeter according to the present invention, in which reference numeral 20 denotes a Coriolis flowmeter main body,
1 is a base, 22 is a measuring tube, 23 and 24 are support members, 25
Is a driving means, 26 is a first detector, and 27 is a second detector.

The Coriolis flowmeter main body 20 includes a measurement tube 22 through which a fluid flows, and a first support member 23 fixed to a base 21 supporting the measurement tube 22 at two points separated by a distance L in the flow direction.
, A second support member 24, a driving means 25 for driving the measuring pipe 22 at a central portion of the supported measuring pipe 22 in a direction perpendicular to the axis OO, and the measuring pipe 22 by Coriolis force by the driving of the driving means 25. Detectors 26 and 2 for detecting the phase displacement occurring in
It consists of seven.

The driving means 25 comprises, for example, a magnetic body 25a fixed to the measuring tube 22 and a coil 25b fixed to the base 21 in opposition to the magnetic body 25a.
b, a sine-wave driving current is applied to
Are driven in the directions of the arrows ± ω ₁ and ω ₂ around the support members 23 and 24.

The detectors 26 and 27 are composed of magnets 26a and 27a of the same standard having the same principle structure and detection coils 26 and 27, respectively.
b, 27b, and the magnets 26a, 27a
The detection coils 26b and 27b are fixed to the base 21 at symmetrical positions from the inlet and the outlet.

The Coriolis flowmeter main body 2 having the above configuration
0 is sine-wave driven by the driving means 25, the detector 2
Sine wave signals having a small phase difference due to the Coriolis force acting on the measuring tube 22 are detected at 6, 27. When the fluid is flowing in the direction of arrow Q, the measuring tube 22 has + ω ₁ ,
When driven - [omega] ₂ direction, sine-wave signals of the first detector 26, to the sinusoidal signal of the second detector 27, a phase delay that is proportional to Coriolis forces generated. Conversely, −ω ₁ , −
the opposite of the phase lag when driven omega ₂ directions.

The present invention detects a phase delay, that is, a phase difference φ as a time difference ΔT, and its principle will be described. The sine wave signal output from the first detector 26 is y ₁ , and the sine wave signal output from the second detector 27 is y ₂
Y ₁ = A ₁ sin ωt (1) y ₂ = A ₁ sin (ωt + φ) (2) where A ₁ and A ₂ are amplitude, ω is drive angular velocity, and t is time.

When the equations (1) and (2) are each divided by the amplitude, sin ωt = y ₁ / A ₁ (3) sin (ωt + φ) = y ₂ / A ₂ (4) Equations (3) and (4) Sine ^-1 (sin ωt) = sin ^-1 (y ₁ / A ₁ ) = ωt (5) sin [sin (ω + φ)] = sin ^-1 (y ₂ / A ₂ ) = ωt + φ (6)

From equations (5) and (6), φ = sin ⁻¹ (y ₂ / A ₂ ) −sin ⁻¹ (y ₁ / A ₁ ) (7) where f is the frequency of the output signal. Since the time difference ΔT is ΔT = (φ / 2π) × (1 / f) (8), from (7) and (8), if the period is 1 / f = t _f , then ΔT = (1 / 2π) × {Sin ⁻¹ (y ₂ / A ₂ ) −sin ⁻¹ (y ₁ / A ₁ )} × t _f (9), and the time difference ΔT can be calculated.

FIG. 1 is a block diagram for explaining an example of the time difference detecting means according to the present invention.
A vibration signal input terminal, 2 a second vibration signal input terminal, 3 a first integration circuit, 4 a second integration circuit, 5 a first conversion circuit, 6
Is a second conversion circuit, 7 is a first amplitude control (AGC) circuit, 8
Is a second amplitude control (AGC) circuit, 9 is a subtraction circuit, 10 is a period measurement circuit, and 12 is an output terminal, which is a block circuit for implementing the above equation (9).

The first integration circuit 3 and the second integration circuit 4 are the same circuit, and both remove noise and harmonic components contained in the vibration signal of the detector and shape the waveform into a sine wave. The first conversion circuit 5 and the second conversion circuit 6 are the same circuits, and both are circuits that convert a sine wave vibration signal whose waveform is shaped into an inverse sine wave signal. The first AGC circuit 7 and the second AGC circuit 8 have the same circuit configuration, and both control the amplitude values of the first and second inverse sine wave signals to be equal.

The first vibration signal input terminal 1, the first integration circuit 3, the first conversion circuit 5, and the first AGC circuit 7 are connected in series, and the second vibration signal input terminal 2 is similarly connected to the second integration circuit 4, The second conversion circuit 6 and the second AGC circuit 8 are connected in series, the first AGC circuit 7 and the second AGC circuit 8 are connected to a subtraction circuit 9, and the subtraction circuit 9 is connected to one input terminal of a multiplication circuit 11. . On the other hand, the second inverse sine wave signal of the second conversion circuit 6 is connected to the cycle measuring circuit 10 and connected to the other input terminal of the multiplying circuit 11 for a cycle having a cycle equal to the measured vibration signal. The signal is multiplied by the period t _f and output from the output terminal 12.

The time difference measuring means of FIG. 1 having the above configuration will be described with reference to Table 1 and FIG. Table 1 shows the relationship between the sine wave and the inverse sine wave with respect to the phase of the vibration signal, and FIG.
FIG. 4 is a waveform diagram illustrating the principle of phase difference detection. The vibration signal input from the first vibration signal input terminal 1 is shaped by the first integration circuit 3 to become a sinx periodic signal shown in FIG. The sine wave sinx is a periodic function having peak values at 2 / 4π and 6 / 4π and zero-crossing at an integral multiple of π. In addition, sin ^-1 (sin
x) has peak values ± π / 2 at 2π / 4 and 6 / 4π,
It becomes a triangular wave signal that crosses zero at the position of an integral multiple of π.

[0019]

[Table 1]

On the other hand, the vibration signal input from the second vibration signal input terminal 2 has a phase difference φ with the vibration signal of the first detector 1, and the phase difference φ is as shown in FIG. On the vertical axis. Therefore, the inverse sine wave sin ^-1 (sinx + φ) has a phase difference φ and becomes the same triangular wave signal as sin ^-1 (sinx).

FIG. 2 (4) shows sin ^-1 (sinx) of FIG. 2 (2).
2 (3) is a trapezoidal periodic function that zero-crosses at a phase of an integral multiple of substantially π / 2 obtained by subtracting sin ^-1 {sin (x + φ)} by a subtraction circuit 9, and the height of the trapezoid Is 2φ, the time delay of falling is Δt, and the height of the trapezoid changes in proportion to the phase difference φ. Thus, in the phase difference signal phi, the phase is a phase difference, averaged for height is detected as a constant phase difference signal phi at a time of approximately [pi phi is detected, therefore, by multiplying the period t _f The time difference signal ΔT proportional to the obtained Coriolis force is also averaged, and a time difference signal free from noise is detected.

As is clear from the above description, the sine wave si
nx and the inverse sine wave sin ^-1 (sinx) are periodic functions having the same period, and since the inverse sine wave sin ^-1 (sinx) is a triangular wave,
Even if sinx is directly converted into a triangular wave, a similar trapezoidal phase difference signal can be detected. That is, the first and second conversion circuits 5 and 6 are used as waveform conversion circuits for converting a sine wave into a triangular wave having the same period, and the other circuits are configured in exactly the same way as the circuit shown in FIG. ΔT is obtained. Further, as shown in FIG. 3, the phase difference φ can be similarly detected by a trapezoidal wave obtained by clipping the top of the triangular wave with a constant voltage.

FIG. 3 shows a time difference measuring means according to the present invention.
FIG. 3 is a waveform diagram for explaining another embodiment, and FIG.
First, the top of the inverse sine wave sin ^-1 (sinx) whose peak value is controlled to be constant by the first and second AGC circuits 7 and 8 is clipped at a constant voltage, for example, ± V at a constant voltage to form a trapezoidal wave. FIG. 3 (2) similarly shows the inverse sine wave sin ^-1 {sin (x + φ)}
Is clipped at a constant voltage ± V, and the phase difference φ
Is a trapezoidal signal having a height ± φ which becomes 0 near the clipped time as shown in FIG. 3C, and the same effect as the circuit of FIG. 1 can be obtained. In the above description, the straight measuring tube shown in FIG. 4 is described. However, the measuring tube does not need to be a straight tube, and the same time difference detection can be applied to a curved tube.

[0024]

As is apparent from the above description, the present invention has the following effects. (1) There is no need to use a clock to detect a time difference proportional to the Coriolis force. (2) Since the phase difference signal is represented by the height of a trapezoidal wave, a constant height is obtained for each half cycle of the vibration, and a value obtained by averaging the time difference signal obtained by multiplying the phase difference and the cycle is obtained. Can be (3) In addition, since the height of the trapezoidal wave is constant, it is hardly affected by noise.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a time difference detection unit according to the present invention.

FIG. 2 is a waveform diagram illustrating the principle of phase difference detection.

FIG. 3 is a waveform diagram for explaining another embodiment of the time difference measuring means according to the present invention.

FIG. 4 is a basic structural diagram for explaining a Coriolis flowmeter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st vibration signal input terminal, 2 ... 2nd vibration signal input terminal, 3 ... 1st integration circuit, 4 ... 2nd integration circuit, 5 ... 1st conversion circuit, 6 ... 2nd conversion circuit, 7 ... 1st Amplitude control (AG
C) circuit, 8 second amplitude control (AGC) circuit, 9 subtraction circuit, 10 cycle measurement circuit, 12 output terminal, 20 body of Coriolis flow meter, 21 base, 22 measurement tube, 23,
24 support member, 25 driving means, 26 first detector,
27 ... second detector.

Claims (3)

(57) [Claims] 1. A measuring tube through which a fluid flows, a supporting member for supporting the measuring tube at two points in a flow direction at a distance, a driving means for driving the measuring tube around the supporting member, and the measuring tube A first detector and a second detector for detecting the vibration of the measuring tube at a symmetric position between the support members, and a reference time axis based on the vibration signals detected by the first detector and the second detector. In the Coriolis flowmeter having a time difference detecting means for calculating a mass flow rate in proportion to the time difference, the time difference detecting means shapes the vibration signal detected by the first detector into a sine wave signal, A first conversion circuit for converting the shaped sine wave signal into an inverse sine wave signal, and shaping the vibration signal detected by the second detector into a sine wave signal, and converting the shaped sine wave signal into an inverse sine wave signal A second conversion circuit for converting the A first amplitude control circuit for controlling the amplitude of the inverse sine wave signal output from the first conversion circuit to be constant, and a first amplitude control for controlling the amplitude of the inverse sine wave signal output from the second conversion circuit. A second amplitude control circuit for controlling the amplitude to be equal to the amplitude of the inverse sine wave signal controlled by the circuit, a first amplitude control circuit, and a subtraction circuit for subtracting the output of each of the second amplitude control circuits; A period measuring circuit that measures the period of the vibration signal, and a multiplication circuit that multiplies the measured period of the vibration signal by the output of the subtraction circuit, and obtains a time difference based on the output of the multiplication circuit. Coriolis flowmeter. 2. A waveform converter, wherein the time difference detecting means outputs a first conversion circuit as a triangular wave signal having the same phase as the first vibration signal, and outputs a second conversion circuit as a triangular wave signal having the same phase as the second vibration signal. The Coriolis flowmeter according to claim 1, wherein the Coriolis flowmeter is a circuit. 3. The triangular wave signal controlled to a constant amplitude by the first amplitude control circuit and the second vibration control circuit is clipped by the time difference detecting means with a voltage smaller than the triangular wave signal peak voltage to generate a trapezoidal wave signal. The Coriolis flowmeter according to claim 1, wherein the Coriolis flowmeter outputs the output.