JP2012168045A - Coriolis flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coriolis flowmeter which can remove the influence of external noise components with a relatively simple configuration.SOLUTION: In a coriolis flowmeter for measuring mass flow rate using interaction by coriolis force between a measurement fluid and a vibrating measurement tube, there are provided: a vibration sensor for detecting external noise components applied to the measurement tube; and an operation unit for canceling external noise components applied to the measurement tube based on output signals of the vibration sensor.

Description

  The present invention relates to a Coriolis flow meter, and more particularly, to removal of the influence of external noise components such as external vibration and piping vibration on a measurement tube.

  The Coriolis flowmeter is a measuring device that measures mass flow rate by utilizing an interaction caused by Coriolis force between a measurement fluid and a vibrating measurement tube.

  FIG. 7 is a configuration explanatory view showing an example of a conventional Coriolis flow meter. Two U-shaped measurement tubes 2 and 3 are fixed to the pipe 1 through which the measurement fluid flows in a cantilever shape in parallel so as to communicate with the pipe 1.

  A pair of magnets and drive coils (not shown) are arranged at the apexes of the measurement tubes 2 and 3, and a pair of magnet sensor coils (not shown) are arranged on the upstream side and the downstream side. Then, the output of the sensor coil generated by electromagnetic induction is positively fed back to the drive coil, and the resonance frequency is in a direction substantially orthogonal to the parallel surface of the measurement tubes 2 and 3 with the fixed ends of the measurement tubes 2 and 3 as axes. Self-excited oscillation.

  When the measurement fluid flows through the measurement tubes 2 and 3, Coriolis force Fc is generated on the inflow side and the outflow side as the measurement tubes 2 and 3 are raised or lowered. Since this force is in the opposite direction on the inflow side and the outflow side, torque is generated and a twist angle is generated in the measurement tubes 2 and 3. Since the Coriolis force Fc is proportional to the mass flow rate of the fluid, the mass flow rate can be measured by detecting the twist angle of the measurement tubes 2 and 3. That is, the mass flow rate can be obtained from the phase difference between the two signals, and at the same time, the mass or density of the fluid can be obtained from the signal frequency.

  Incidentally, external noise components such as external vibrations and piping vibrations are added to the measurement tubes 2 and 3, and measurement errors due to these external noise components occur. These external noise components applied to the measurement tubes 2 and 3 can be grasped as in-phase components.

  Therefore, when the two measurement tubes 2 and 3 fixed in parallel in the form of a cantilever are self-excited at the resonance frequency, the phases of the drive signals are shifted by 180 degrees so that the external noise component is reduced. They try to counteract the effects of each other.

  Non-Patent Document 1 discloses the operating principle and structure of a Coriolis flow meter.

Shuji Urabe, Kiyoaki Koyama, “Coriolis flow meter ROTAMASS3 series”, Yokogawa Technical Report, Yokogawa Electric Corporation, 2010, Vol. 53 No. 2 (2010) p. 23-26

  However, according to the conventional double pipe configuration as shown in FIG. 7, the two U-shaped measurement tubes 2 and 3 must be formed in the same structure and fixed to the pipe 1 in the same state. As a result, the number of parts increases.

  In addition, if the state of the bubbles contained in the measurement fluid flowing through the measurement tubes 2 and 3 is different, a phase difference is generated and a measurement error occurs, which is not preferable, and measures for removing the bubbles are also necessary.

  The present invention solves such problems, and an object of the present invention is to provide a Coriolis flowmeter capable of removing the influence of an external noise component with a relatively simple configuration.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In the Coriolis flowmeter that measures the mass flow rate by utilizing the interaction caused by Coriolis force between the measurement fluid and the vibrating measurement tube,
A vibration sensor for detecting an external noise component applied to the measurement tube;
An arithmetic unit that cancels out an external noise component applied to the measurement tube based on an output signal of the vibration sensor,
It is characterized by providing.

The invention according to claim 2 is the Coriolis flow meter according to claim 1,
The vibration sensor is a directional microphone.

The invention according to claim 3 is the Coriolis flow meter according to claim 1 or 2,
The calculation unit is an analog calculation unit.

The invention according to claim 4 is the Coriolis flow meter according to claim 1 or 2,
The arithmetic unit is a digital arithmetic unit.

The invention according to claim 5 is the Coriolis flow meter according to claim 4,
An input selection unit that selectively selects an output signal of the measurement tube and an output signal of the vibration sensor is provided in the preceding stage of the digital calculation unit.

  As a result, it is possible to perform high-accuracy mass flow measurement with a single measurement tube without being affected by external noise components.

It is a configuration explanatory view showing an embodiment of the present invention. It is operation | movement explanatory drawing of FIG. It is a block diagram which shows the specific example of the analog calculating part used by this invention. It is a block diagram which shows the specific example of the phase measurement part 20 in FIG. It is a block diagram which shows the specific example of the digital calculating part used by this invention. It is a block diagram which shows the specific example of DSP27 in FIG. It is composition explanatory drawing which shows an example of the conventional Coriolis flowmeter.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of an embodiment of the present invention, and the same reference numerals are given to portions common to FIG. The difference between FIG. 1 and FIG. 7 is that there is only one measuring tube 2 and a vibration sensor 4 that detects an external noise component applied to the measuring tube 2 is provided.

  In FIG. 1, a piping 1 is provided with a vibration sensor 4 that detects an external noise component applied to a measurement tube 2. A driving unit 5 including a pair of magnets and a driving coil is provided at the apex of the measuring tube 2, and Coriolis sensors 6 and 7 each including a magnet sensor coil are provided on the upstream side and the downstream side, respectively.

  FIG. 2 is an explanatory diagram of the operation of FIG. When vibration of a specific frequency is applied to the measurement tube 2 through which the measurement fluid flows through the driving unit 5, the output signals of the Coriolis sensors 6 and 7 are based on the interaction caused by the Coriolis force between the measurement fluid and the measurement tube 2 that vibrates. The phase changes in proportion to the flow rate of the measurement fluid. In this phase measurement, as described above, external noise gives an error to the phase measurement result.

  Therefore, in the present invention, the external noise transmitted to the measurement tube 2 is detected by the vibration sensor 4 using the fact that the phase of the external noise does not match the vibration phase of the measurement tube 2 at a specific frequency, and the measurement tube 2 The external noise transmitted and the external noise detected by the vibration sensor 4 are combined by phase inversion to cancel the external noise.

  Although external noise in all directions is applied to the pipe 1 and the measurement tube 2, the vibration sensor 4 needs to detect only the component in the direction in which the measurement tube 2 shakes based on the Coriolis force. For this reason, for example, in a ribbon type dynamic microphone in which a permanent magnet and a movable metal ribbon are combined, a speed type microphone having a directivity of a type in which both sides of the ribbon are open to space is used.

  This speed microphone exhibits high sensitivity to sound from both directions perpendicular to the ribbon surface, and extremely low sensitivity to sound from a direction parallel to the surface. Using this directivity, a speed type microphone is fixed to the pipe 1 as the vibration sensor 4 so that only external noise that shakes in the same direction as the direction in which the Coriolis sensors 6 and 7 are captured can be captured.

  The Coriolis flowmeter is designed with a heavy weight so that the Coriolis force is not easily transmitted to the pipe 1. Here, the external noise is transmitted to the measurement tube 2 to which Coriolis force is applied even if there is some attenuation. Therefore, the vibration of the external noise detected by the vibration sensor 4 from the pipe 1 is phase-inverted and adjusted so as to have the same level as the external noise applied to the Coriolis sensors 6 and 7, and synthesized with the output signals of the Coriolis sensors 6 and 7. To cancel the external noise.

FIG. 3 is a block diagram showing a specific example of the analog calculation unit used in the present invention.
The output signal of the vibration sensor 4 is input to the amplifier 8, and variable resistors 9 and 10 are connected in parallel between the output terminal of the amplifier 8 and the common potential point. The variable terminal of the variable resistor 9 is input to the inverting input terminal of the operational amplifier OP1 via the resistor 11, and the variable terminal of the variable resistor 10 is input to the inverting input terminal of the operational amplifier OP2 via the resistor 12.

  The output signal of the Coriolis sensor 6 is input to the non-inverting input terminal of the first operational amplifier OP1 through the amplifier 13 and the resistor 14, and the output signal of the Coriolis sensor 7 is input to the second operational amplifier through the amplifier 15 and the resistor 16. It is input to the non-inverting input terminal of OP2.

  The inverting input terminal of the first operational amplifier OP1 is connected to the output terminal via the resistor 17, and the non-inverting input terminal is connected to the common potential point via the resistor 18. The output signal of the first operational amplifier OP1 is input to the drive coil constituting the drive unit 5 through the amplifier 19 and also to the phase measurement unit 20.

  The inverting input terminal of the second operational amplifier OP2 is connected to the output terminal via the resistor 21, and the non-inverting input terminal is connected to the common potential point via the resistor 22. The output signal of the second operational amplifier OP2 is input to the phase measuring unit 20.

  The phase measuring unit 20 performs arithmetic processing for measuring the phase using the output signal of the first operational amplifier OP1 and the output signal of the second operational amplifier OP2.

  FIG. 4 is a block diagram showing a specific example of the phase measurement unit 20, (A) shows an example using a Hilbert transform unit, and (B) shows an example using an FFT operation unit.

  In FIG. 4A, the output signal of the first operational amplifier OP1 includes a sin θ component, is converted into a digital signal by the A / D converter 20a, is input to the bandpass filter 20b, and is also converted into a Hilbert transform. Is input to the unit 20c. The band pass filter 20b outputs the sin θ component to the tan Δφ calculating unit 20d, and the Hilbert transform unit 20c outputs the cos θ component to the tan Δφ calculating unit 20d.

  On the other hand, the output signal of the second operational amplifier OP2 includes a sin θ + Δ component, which is converted into a digital signal by the A / D converter 20e, input to the bandpass filter 20f, and input to the Hilbert conversion unit 20g. The The band pass filter 20f outputs the sin θ + Δ component to the tan Δφ calculating unit 20d, and the Hilbert transform unit 20g outputs the cos θ + Δ component to the tan Δφ calculating unit 20d.

  The tan Δφ computing unit 20d receives a sin θ component input from the band pass filter 20b, a cos θ component input from the Hilbert transform unit 20c, a sin θ + Δ component input from the band pass filter 20f, and a cos θ + Δ component input from the Hilbert transform unit 20g. Based on the above, the phase difference tan Δφ is calculated.

  The bandpass filter 20b, the Hilbert transform unit 20c, the bandpass filter 20f, the Hilbert transform unit 20g, and the tan Δφ computing unit 20d are configured by, for example, a DSP, as shown by being surrounded by a one-dot chain line.

  In FIG. 4B, the output signal of the first operational amplifier OP1 including the sin θ component is converted to a digital signal by the A / D converter 20a and input to the FFT operation unit 20h, and the second operation including the sin θ + Δ component is performed. The output signal of the amplifier OP2 is converted into a digital signal by the A / D converter 20e and input to the FFT operation unit 20h.

  The FFT computation unit 20h performs all the computations of the phase difference Δφ by the bandpass filter 20b, the Hilbert transform unit 20c, the bandpass filter 20f, the Hilbert transform unit 20g, and the tan Δφ computation unit 20d of FIG.

  In general, the calculation amount in the configuration including the Hilbert transform unit in FIG. 4A is about 1/4 of the FFT calculation amount in FIG. 4B, and the calculation load can be reduced. With the progress, the calculation speed of the FFT calculation unit 20h is also increased, and the calculation load hardly becomes a problem. Note that the FFT operation unit 20h is also configured by, for example, a DSP as shown by being surrounded by a one-dot chain line.

  3 again, the variable resistor 9 adjusts the external noise component included in the output signal of the vibration sensor 4 to be equal to the external noise component included in the output signal of the Coriolis sensor 6, and the variable resistor 10 controls the vibration sensor. The external noise component included in the output signal 4 is adjusted to be equal to the external noise component included in the output signal of the Coriolis sensor 7.

  As a result, the phase measurement unit 20 receives the output signal of the Coriolis sensor 6 and the output signal of the Coriolis sensor 7 in which the external noise components included in each phase are canceled out. The calculation process is not affected by external noise components and can perform mass flow measurement with high accuracy.

  According to such a configuration, the U-shaped measurement tube does not have to be a double tube configuration as in the prior art and only one U-shaped measurement tube is required, and the external structure of the Coriolis flow meter can be simplified in a small size.

  Further, the shape of the measurement tube is not limited to the U-shape, and a single measurement tube such as a straight shape, an S-shape, or a V-shape may be used, and man-hours required for processing and assembly adjustment can be reduced.

  FIG. 5 is a block diagram showing a specific example of the digital arithmetic unit used in the present invention, and the same reference numerals are given to portions common to FIG. In FIG. 5, the output signal of the vibration sensor 4 is input to the switch SW1 of the input selection unit 23 via the amplifier 8, and the output signal of the Coriolis sensor 6 is input to the switch SW2 of the input selection unit 23 via the amplifier 13. The output signal of the Coriolis sensor 7 is input to the switch SW3 of the input selection unit 23 via the amplifier 15 through the amplifier 19 to the drive coil constituting the drive unit 5. The switches SW <b> 1 to SW <b> 3 constituting the input selection unit 23 are selectively on / off controlled by the switching control unit 24.

  The output signals of the vibration sensor 4 and the Coriolis sensors 6 and 7 selected by the input selection unit 23 are input to the A / D converter 26 via the anti-aliasing filter 25, converted into digital signals, and input to the DSP 27. .

  The DSP 27 is included in the Coriolis sensors 6 and 7 in advance by obtaining signal transmission coefficients in consideration of the way in which the external noise signal is transmitted to the positions of the vibration sensor 4 and the Coriolis sensors 6 and 7 in consideration of the signal transmission coefficients. Performs computation to cancel the external noise signal. Thereafter, the phase calculation between the Coriolis sensors 6 and 7 is performed in a state where the external noise signal is deleted.

  In addition, when the digital signal converted and output from the A / D converter 26 is subjected to Hilbert transform and the phase calculation between the Coriolis sensors 6 and 7 is performed, the signal transfer coefficient of each output signal described above is added before the Hilbert transform. Then, an operation for canceling the external noise signal included in the Coriolis sensors 6 and 7 may be performed.

  FIG. 6 is a block diagram showing a specific example of the DSP 27, (A) shows an example using a Hilbert transform unit, and (B) shows an example using an FFT operation unit.

  In FIG. 6A, the output data of the vibration sensor 4 converted into a digital signal by the A / D converter 26 is stored in the noise storage unit 27a, and the output data of the Coriolis sensor 6 is stored in the noise + sin θ storage unit 27b. The output data of the Coriolis sensor 7 is stored in the noise + sin θ + Δ storage unit 27c.

  The output data of the vibration sensor 4 stored in the noise storage unit 27a and the output data of the Coriolis sensor 6 stored in the noise + sin θ storage unit 27b are input to the sin θ calculation unit 27d. Then, the output data of the vibration sensor 4 is subtracted from the output data of the Coriolis sensor 6, and an operation for outputting only the sin θ component is performed. The sin θ component is input to the bandpass filter 27f and the Hilbert transform unit 27g.

  The output data of the vibration sensor 4 stored in the noise storage unit 27a and the output data of the Coriolis sensor 7 stored in the noise + sin θ + Δ storage unit 27c are input to the sin θ + Δ calculation unit 27e. Then, the output data of the vibration sensor 4 is subtracted from the output data of the Coriolis sensor 7, and an operation for outputting only the sin θ + Δ component is performed. The sin θ + Δ component is input to the bandpass filter 27h and the Hilbert transform unit 27i.

  The band pass filter 27f outputs the sin θ component to the tan Δφ calculating unit 27j, the Hilbert transform unit 27g outputs the cos θ component to the tan Δφ calculating unit 27j, and the band pass filter 27h outputs the sin θ + Δ component to the tan Δφ calculating unit 27j, and the Hilbert transform. The unit 27i outputs the cos θ + Δ component to the tan Δφ calculating unit 27j.

  The tan Δφ computing unit 27j receives a sin θ component input from the band pass filter 27f, a cos θ component input from the Hilbert transform unit 27g, a sin θ + Δ component input from the band pass filter 27h, and a cos θ + Δ component input from the Hilbert transform unit 27i. Based on the above, the phase difference tan Δφ is calculated.

  In FIG. 6B, the sin θ component output from the sin θ calculator 27d and the sin θ + Δ component output from the sin θ + Δ calculator 27e are input to the FFT calculator 27k.

  The FFT computation unit 27k performs all the computations of the phase difference Δφ by the bandpass filter 27f, the Hilbert transform unit 27g, the bandpass filter 27h, the Hilbert transform unit 27i, and the tan Δφ computation unit 27j of FIG.

  As described above, according to the present invention, a Coriolis flow meter capable of removing the influence of an external noise component can be realized with a relatively simple configuration, which is suitable for mass flow measurement of various measurement fluids.

DESCRIPTION OF SYMBOLS 1 Piping 2 Measurement tube 4 Vibration sensor 5 Drive part 6, 7 Coriolis sensor 8, 13, 15, 19 Amplifier 9, 10 Resistance (variable)
12, 16, 17, 21, 22 Resistance (fixed)
20 phase measurement unit 23 input selection unit 24 switching control unit 25 anti-aliasing filter 26 A / D converter 27 DSP

Claims (5)

In the Coriolis flowmeter that measures the mass flow rate by utilizing the interaction caused by Coriolis force between the measurement fluid and the vibrating measurement tube,
A vibration sensor for detecting an external noise component applied to the measurement tube;
An arithmetic unit that cancels out an external noise component applied to the measurement tube based on an output signal of the vibration sensor,
Coriolis flowmeter characterized by providing   The Coriolis flowmeter according to claim 1, wherein the vibration sensor is a microphone having directivity.   The Coriolis flowmeter according to claim 1, wherein the calculation unit is an analog calculation unit.   The Coriolis flowmeter according to claim 1 or 2, wherein the calculation unit is a digital calculation unit.   5. The Coriolis flow meter according to claim 4, wherein an input selection unit that selectively selects an output signal of the measurement tube and an output signal of the vibration sensor is provided in a preceding stage of the digital calculation unit.

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