JP2884796B2 - 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 for calculating a mass flow rate by using a displacement signal corresponding to a displacement generated when a single pipe is vibrated at a plurality of frequencies, and particularly to an external vibration noise. The present invention relates to a Coriolis mass flowmeter improved so as to operate stably with respect to pressure.

[0002]

2. Description of the Related Art FIG. 6 is a perspective view showing a configuration of a conventional Coriolis mass flow meter of a straight tube type which is an improvement base. 10
Is a pipe through which the measurement fluid F can flow,
Both ends of the pipe 10 are fixed by fixing parts 11 and 12.

A vibrator 14 is disposed at a central portion 13 of these fixed portions 11 and 12, and vibrates the pipe 10 in a direction perpendicular to the center axis of the pipe 10 to displace vertically. Let it. Displacement sensors 15, 16 for measuring the displacement of the pipe 10 are provided between the central portion 13 and the fixed portions 11, 12.
Is arranged.

Next, the operation of the Coriolis mass flowmeter configured as described above will be described with reference to a vibration explanatory diagram shown in FIG. When a small vibration is applied from a vibrator 14 arranged in the central portion 13 in a state where the measurement fluid F is flowing through the pipe 10, the primary portion 13 as shown in FIG. Pipe 10 at a resonance frequency with a large amplitude
Vibrates.

This vibration is applied to the central portion 13 by the pipe 10
It can be considered that the upstream portion and the downstream portion of the oscillating member are rotating and vibrating around the fixed portions 11 and 12, respectively. Therefore, if this angular velocity is ω and the distance between the fixed ends 11 and 12 is L, this angular velocity ω Coriolis force is generated in the pipe 10 in proportion to the product of the flow rate Q of the fluid F and the distance L.
A deformation occurs in which the bending vibration is reversed between the upstream portion and the downstream portion with respect to the central portion 13. The mass flow rate Q can be known by measuring this deformation with the displacement sensors 15 and 16.

[0006]

However, in the conventional Coriolis mass flowmeter described above, a small vibration is given to a pipe by a vibrator, the pipe is resonated to have a large amplitude, and this displacement is detected by a displacement sensor. Since external vibration noise equal to the resonance frequency is applied to this pipe, large vibrations are generated even with small noise, making it difficult to control the amplitude of the drive mode by the vibrator. There is a problem that an error occurs.

[0007]

According to the present invention, as a main structure for solving the above-mentioned problems, a pipe having both ends fixed and through which a measurement fluid is passed, and a pipe provided at a predetermined position on the pipe. One frequency and at least a second frequency different therefrom
And at least two vibrating means arranged to be able to detect displacement of the pipe at different positions .
And Displacement sensor, a first signal processing means for outputting a first flow rate signal by the flow rate calculated using the first frequency component of the out destination of the displacement signal detected by the displacement of the sensor of these displacement signal a second signal processing means for outputting a second flow rate signal by the flow rate calculation using the second frequency components of a low first frequency component
At least using the second frequency component to drive the vibrating means.
And a noise discriminating means for discriminating the presence or absence of noise based on at least the first flow signal and the second flow signal based on these flow fluctuations and estimating and outputting a normal flow signal. It is something to do.

[0008]

[For work] First, the pipe and the first frequency at a predetermined position on the pipe both ends is passed is measured fluid within a fixed
By vibrating means at least at a second frequency different from this
Excite. In addition, small pipes located at different locations on the pipe
At least two displacement sensors detect the displacement of the pipe .
Next, the first signal processing means calculates the flow rate using the first frequency component of the displacement signals detected by the displacement sensors and outputs a first flow rate signal. The second signal processing means calculates a flow rate using the second frequency component of the displacement signal and outputs a second flow rate signal. Further, the driving means uses the first frequency component and at least the second frequency component.
The vibration means is driven. Thereafter, the noise determining means determines the presence or absence of noise and outputs the estimated normal flow signal based on the flow rate variation of this, such as using the first flow signal and the second flow rate signal.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of one embodiment of the sensor side of the present invention. FIG. 2 is a block diagram showing a configuration of an embodiment mainly on the signal processing side of the present invention. Parts having the same functions as those of the conventional Coriolis mass flow meter shown in FIG. 6 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

The pipe 10 is fixed at both ends of a cylindrical case 17 which also functions as a vibration isolator.
It is 2. Flanges 18 and 19 to be connected to a mating pipe are fixed to outer ends of these fixing portions 11 and 12.

A vibrator 20 is provided at the center (L / 2) of the pipe 10, and a vibrator 2 is provided at a position L / 4 from the fixed portion 11.
1 and a vibration exciter 2 at a position 3 L / 4 from the fixed portion 11.
2 are arranged, and a displacement sensor 23 is provided at a position facing the vibrator 21 with respect to the pipe 10.
Displacement sensors 24 are respectively arranged at positions facing the second sensor 2. Although not shown, the temperature sensor 25 is also arranged inside the case 17.

The displacement sensors 23 and 24 are configured as sensors using optical fibers, for example, and detect the amount of light using an LED and an optical diode to detect vertical displacement. The vibrators 20, 21, and 22 use a coil and an iron core to generate vibration in the vertical direction with a vibration current flowing through the coil. The vibrator 20 generates primary mode resonance with respect to the pipe 10, and the vibrators 21 and 22 generate secondary mode resonance.

The displacement signals output from the displacement sensors 23 and 24 are respectively provided by displacement / voltage converters (D / V) 26 and 2.
7, where it is converted into voltage signals V1, V2. The voltage signal V1 is output to a high-pass filter 28 selected to pass the secondary mode component and a low-pass filter 29 selected to pass the primary mode component. _Are output as output voltages V _H1 and V _L1 . Moreover, also the voltage signal V2, the high pass filter 30 and B - are outputted in Pasufuiruta 31, is output to the output terminal of which such as the output voltage V _H2 and V _L2.

The output voltages V _L1 and V _L2 correspond to the primary mode component (low frequency component) of the pipe vibration, and the output voltages V _H1 and V _H2 correspond to the secondary mode component (high frequency component) of the pipe vibration. I do. Of these, the primary mode components V _L1 and V _L2 are
The vibrator 20 arranged at the center of the pipe 10 is vibrated through the second mode 2, and the secondary mode components V _H1 and V _H2 are
The vibrators 21 and 22 arranged at L / 4 and 3L / 4 of the pipe 10 are vibrated via 34. As a result, resonance of the primary mode and the secondary mode occurs simultaneously in the pipe 10,
These resonances are maintained.

Furthermore, 1 Tsugimo - The de component V _L1 and V _L2 adder-subtracter 35, 2 Tsugimo - de component V _H1 and V _H2 adder-subtractor 36
, And these mode components are added and subtracted for each mode component, and the flow rate calculation circuit 3
7 and 38, respectively. Flow rate calculation circuit 37, 3
A temperature signal is input to the temperature sensor 8 from the temperature sensor 25.

The flow rate calculation circuits 37 and 38 execute a flow rate calculation for each mode using the addition signal and the subtraction signal, and use the temperature signal output from the temperature sensor 25 for each of the modes. After performing the correction, the flow rate signals Q2, Q1
Output as The flow signals Q2 and Q1 are output to the noise discriminating circuit 39, respectively, and a predetermined noise discrimination operation described later is executed to finally obtain a flow signal Q3 estimated as a correct flow signal.

Next, the operation of the embodiment constructed as described above will be described with reference to FIG.
This will be described with reference to FIG. 5 which is an explanatory diagram of the vibration in the secondary mode and FIG. 5 is a flowchart.

When the pipe 10 is vibrated by the vibrator 20 as shown by the dotted line in FIG. 3 while the measurement fluid F is flowing through the pipe 10, the Coriolis as shown by the solid line in FIG. A displacement based on the force occurs. This displacement is detected by the displacement sensors 23 and 24 and the displacement / voltage converters 26 and 2
The voltage is converted into a voltage at 7 and fed back to the drive circuit 32 via the low-pass filters 29 and 31. The drive output of the drive circuit 32 further vibrates the vibrator 20. Due to these positive feedback effects, the amplitude of the pipe 10 increases and oscillates in a form that matches the resonance frequency of the primary mode.

Similarly, the measurement fluid F is supplied to the pipe 1
When the pipe 10 is vibrated by the vibrators 21 and 22 as shown by a dotted line in FIG.
At 0, a displacement is generated based on the Coriolis force as shown by the solid line in FIG. This displacement is detected by displacement sensors 23 and 24, converted into a voltage by displacement / voltage converters 26 and 27, and fed back to driving circuits 33 and 34 via high-pass filters 28 and 30 to drive the driving circuits 33 and 34. The vibrators 21 and 22 are further vibrated by the output. Due to these positive feedback effects, the amplitude of the pipe 10 increases and oscillates in a form that matches the resonance frequency of the secondary mode.

In this case, these primary and secondary modes are used.
When the vibrations of each mode are operating in the linear region, they vibrate independently without interfering with each other and do not affect other modes. This vibration is caused by the pipe 1
Since the upstream portion and the downstream portion of 0 can be considered to be rotating and vibrating around the fixed portions 11 and 12, respectively, Coriolis force proportional to the product of this angular velocity ω and the flow rate Q of the measurement fluid F is applied to the pipe 10. Occurs, thereby causing the 1 as shown in FIG.
In the next mode, a deformation occurs in which the bending vibration is reversed in the upstream portion and the downstream portion with respect to the central portion 13 of the pipe 10. The mass flow rate Q can be known by measuring this deformation with the displacement sensors 15 and 16.

In the secondary mode, as shown in FIG. 4, since the central portion 13 of the pipe 10 is bent in the same direction, this is detected by the displacement sensors 15 and 16, and the mass flow rate Q is determined. You can know. As can be seen from FIGS. 3 and 4, the vibration of the pipe 10 and the vibration caused by the Coriolis force have the same frequency but a phase difference of 90 °. Note that FIG.
In FIG. 4, for the sake of explanation, the amplitude of the vibration of the pipe 10 and the amplitude of the vibration due to the Coriolis force are described as being at the same level, but in reality the latter is on the order of 1/100 of the former.

[0022] Thus, 1 Tsugimo is detected by the displacement sensor 23 - De components primary detected with reference to FIG. _{3 A 1 sinω 1 t + A} 1 k 1 cosω 1 t (1) , and the displacement sensor 24 mode - de component becomes _{a 1 sinω 1 t-a 1} k 1 cosω 1 t (2).

Next, 2 Tsugimo is detected by the displacement sensor 23 - De components _{A 2 sinω 2 t-A 2} k 2 cosω 2 t (3) with reference to FIG. 4, and the detected displacement sensor 24 2 Tsugimo that - de component becomes _{-A 2 sinω 2 t-a 2} k 2 cosω 2 t (4). Here, A ₁ and A ₂ are conversion constants at the displacement sensors 23 and 24, and k ₁ and k ₂ are coefficients indicating the influence of Coriolis force.

To calculate the Coriolis component of the primary mode using the equations (1) to (4), the calculation of (1)-(2) is performed as follows.
To calculate the vibration amplitude of the primary mode, the calculation of (1) + (2) is performed. To calculate the Coriolis component of the secondary mode, the calculation of (3) + (4) is performed. To calculate the vibration amplitude of the mode, the operations of (3)-(4) are performed by adding
Execute at 5, 36.

The results of these calculations by the adders / subtractors 35 and 36 are output to flow rate calculation circuits 37 and 38, where the temperature is corrected using the temperature signal from the temperature sensor 25, and the range is adjusted and the like. Range flow signal Q2,
It is output as Q1.

These flow rate signals Q2 and Q1 are input to the noise discriminating circuit 39, and the calculation as shown in the flowchart of FIG. 5 is executed. First, the flow rate signals Q2 and Q1 from the flow rate calculation circuits 37 and 38 are determined in step 1 to determine whether or not these flow rate signals Q2 and Q1 fall within a predetermined range. If there is, go to step 2.

Here, when these flow signals Q2 and Q1 are equal or within a small error range,
In step 3, the average of the two is calculated, and this average is output as the final flow signal. Flow signal Q2, Q1
If the value exceeds the range of the error, the process proceeds to step 4, where the flow signal having the smaller time change rate among the flow signals Q2 and Q1 is output as a normal flow signal.

If the flow signals Q2 and Q1 are not within the predetermined range in step 1,
Proceed to step 5 where the flow signals Q2, Q
It is determined whether at least one of the flow signals is normal. If this requirement is met, the process proceeds to step 6 and the normal flow rate signal is adopted as the final output. If it is determined in step 5 that none of the flow signals is normal, an error is displayed as an error. These operations are
It can be realized by using a discrete circuit or by performing a software operation using a microcomputer.

In the above embodiment, the primary mode and the secondary mode are used.
Although the description has been given as a combination of vibrations in the mode, other modes such as simultaneous vibration in the primary mode, the secondary mode, and the tertiary mode may be used. Alternatively, the vibrations may be simultaneously performed at different frequencies but in the same vibration mode. Further, when the values of the flow rate signals Q1 and Q2 are different as abnormality determination means, the values before these values are different may be continuously output as the final output value.

The shape of the pipe 10 is not limited to a single straight pipe, but may be a double pipe, a U-shaped pipe, a spiral pipe, or the like. The displacement sensor is a reflection type using an optical fiber, a slit type, a type using a coil and a magnet,
Various types such as those using a change in the capacity of a capacitor can be applied.

[0031]

As described above, according to the present invention, a normal flow signal is estimated and output by comparing the two flow signals with each other. Therefore, even when vibration noise from the outside mixes into the signal and the flow signal of one system becomes unstable, a normal flow signal can be output, and the influence of the vibration noise can be greatly reduced. it can.

In particular, in general, when a vibrating structure has a complicated shape or structure, the natural frequency increases and the frequency band in which vibration noise received from the outside increases, as shown in this embodiment. In a mass flow meter having a simple structure, the reliability of the configuration of the present embodiment can be improved without increasing the frequency band which is a weak point.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of one embodiment of a sensor side of the present invention.

FIG. 2 is a block diagram showing a configuration of an embodiment mainly on a signal processing side of the present invention.

FIG. 3 is an explanatory diagram of vibration in a primary mode for explaining the operation of the embodiment shown in FIG. 1;

FIG. 4 is an explanatory diagram of vibration in a secondary mode for explaining the operation of the embodiment shown in FIG. 1;

FIG. 5 is a flowchart showing a signal processing procedure of the embodiment shown in FIG. 2;

FIG. 6 is a perspective view showing a configuration of a conventional straight tube type Coriolis mass flow meter.

FIG. 7 is a vibration explanatory diagram illustrating an operation of the Coriolis mass flow meter shown in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Pipe 11,12 Fixed part 14,20,21,22 Vibrator 15,16,23,24 Displacement sensor 25 Temperature sensor 28,30 High pass filter 29,31 Low pass filter 35,36 Adder / subtracter 37,38 Flow rate calculation Circuit 39 Noise discrimination circuit

Claims (2)

(57) [Claims] 1. A and pipe ends measurement fluid therein is fixed is passed, the first frequency Toko at a predetermined position on the pipe
Vibrating means for vibrating at at least a second frequency different from this
When at least two variable-position sensor arranged so as to be able to detect a displacement of the pipe in different positions,
A first signal processing means for outputting a first flow rate signal by the flow rate computation using the first frequency component of the detected displacement signal displacement of the sensor of this, the second frequency component of the displacement signal A second signal processing means for calculating a flow rate using the first frequency component and outputting a second flow rate signal ;
Also drives the vibration means using the second frequency component
A driving unit, and a noise determining unit that determines presence or absence of noise based on at least the first flow signal and the second flow signal based on these flow fluctuations, and estimates and outputs a normal flow signal. Coriolis mass flowmeter. 2. The vibrating means vibrates at the first frequency.
A first vibrator, the first vibrator being vibrated at the second frequency;
Pair of second shakers arranged at a position different from the position of the machine
Wherein the driving means uses the first frequency component.
First driving means for driving the first vibrator by means of
A second drive for driving the second shaker using a frequency component
2. The chorio according to claim 1, wherein the chorio comprises means.
Re mass flow meter.