SIGNAL PROCESSING METHOD, SIGNAL PROCESSING APPARATUS, AND CORIOLIS FLOWMETER

• US 20110203388A1
• Filed: 12/01/2010
• Published: 08/25/2011
• Est. Priority Date: 02/19/2010
• Status: Active Grant

• Current Assignee: OVAL Limited (Arthur J Gallagher & Company)
• Original Assignee: OVAL Limited (Arthur J Gallagher & Company)
• Inventors: Shimada, Hideki, KITAMI, Hirokazu
• Granted Patent: US 8,725,432 B2
• Time in Patent Office: Days
• US Class Current: 73/861.356
• CPC Class Codes: G01F 1/8431 electronic circuits
• CPC Class Codes: G01F 1/8436 signal processing
• CPC Class Codes: G01F 1/8477 with multiple measuring conduits
• CPC Class Codes: G01N 2009/006 vibrating tube, tuning fork
• CPC Class Codes: G01N 9/002 using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis G01N9/34 takes precedence

Abstract

[Object] To provide a signal processing apparatus with which, even when a temperature of a fluid to be measured changes, even when air bubbles are mixed into the fluid, to be measured, or even when the fluid to be measured rapidly changes from gas to liquid, measurement may be always performed with constant precision and phase and density measurements may be performed with a small computing amount.

[Solving Means] A signal processing apparatus for a Coriolis flowmeter in which at least one flow tube or a pair of flow tubes which is included in a measurement flow tube is alternately driven by causing a vibrator to be actuated by a driving device to vibrate the at least one flow tube or the pair of flow tubes, and at least one of a phase difference and a vibration frequency proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes is detected by a velocity sensor or acceleration sensor which is a vibration detection sensor, to thereby obtain at least one of a mass flow rate and a density of a fluid to be measured, includes: a transmitter (90) for transmitting a frequency signal which is modulatable; and a frequency conversion section (85) for performing frequency conversion to add (or subtract) an output frequency F_X from the transmitter (90) to (or from) an input frequency detected by the velocity sensor or acceleration sensor and shifting a frequency value obtained by the frequency conversion to a constant value.

Claims

1. A signal processing method for a Coriolis flowmeter in which at least one flow tube or a pair of flow tubes which is included in a measurement flow tube is alternately driven by causing a vibrator to be actuated by a driving device to vibrate the at least one flow tube or the pair of flow tubes, and at least one of a phase difference and a vibration frequency proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes is detected by two velocity sensors or acceleration sensors which are vibration detection sensors, to thereby obtain at least one of a mass flow rate and a density of a fluid to be measured,

the signal processing method comprising:

performing frequency conversion to combine, based on an arbitrary oscillation frequency, each of two flow rate signals obtained by A/D conversion on input signals of the vibration frequency proportional to the Coriolis force acting on the at least one flow tube or the pair of flow tubes, which are detected by the two velocity sensors or acceleration sensors, to obtain a composite frequency signal;

measuring a frequency of the composite frequency signal associated with at least one of the two velocity sensors or acceleration sensors;

transmitting a control signal based on the measured frequency;

controlling a frequency of a sum or difference frequency component of the composite frequency signal to a constant value;

obtaining a resonance frequency of the at least one flow tube or the pair of flow tubes based on the control signal, calculating the density of the fluid to be measured based on the control signal; and

measuring a phase from the sum or difference frequency component of the composite frequency signal having the controlled frequency.

2. A signal processing method according to claim 1, wherein the frequency conversion for combining based on the arbitrary oscillation frequency includes:

multiplying an input signal SIN θ

₁ from the one of the two velocity sensors or acceleration sensors by the transmitted control signal cos θ

₂; and

filtering an output signal obtained by the multiplying by a frequency filter to extract only a low-frequency signal.

3. A signal processing method according to claim 1, wherein the frequency conversion for combining based on the arbitrary oscillation frequency includes:

multiplying an input signal SIN θ

₁ from the one of the two velocity sensors or acceleration sensors by the transmitted control signal cos θ

₂; and

filtering an output signal obtained by the multiplying by a frequency filter to extract only a high-frequency signal.

4. A signal processing method according to claim 1, wherein:

the input signals of the vibration frequency proportional to the Coriolis force acting on the at least one flow tube or the pair of flow tubes, which are detected by the two velocity sensors or acceleration sensors, are sampled by the A/D conversion to obtain digital signals; and

the composite frequency signal obtained by the frequency conversion based on the transmitted control signal is controlled so that the frequency of the sum or difference frequency component of the composite frequency signal is ¼

of a sampling frequency for the A/D conversion.

5. A signal processing apparatus for a Coriolis flowmeter in which at least one flow tube or a pair of flow tubes which is included in a measurement flow tube is alternately driven by causing a vibrator to be actuated by a driving device to vibrate the at least one flow tube or the pair of flow tubes, and at least one of a phase difference and a vibration frequency proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes is detected by a velocity sensor or acceleration sensor which is a vibration detection sensor, to thereby obtain at least one of a mass flow rate and a density of a fluid to be measured,

the signal processing apparatus comprising:

a transmitter for transmitting a frequency signal which is modulatable; and

a frequency conversion section for performing frequency conversion to add (or subtract) an output frequency F_X from the transmitter to (or from) an input frequency detected by the velocity sensor or acceleration sensor and shifting a frequency value obtained by the frequency conversion to a constant value.

8. A signal processing apparatus according to claim 5, wherein the frequency conversion section comprises:

a multiplier for multiplying a reference signal cos θ

₂ from the transmitter by an input signal SIN θ

₁ from the first A/D converter; and

a low-pass filter for filtering an output signal obtained by the multiplication by the multiplier through a frequency filter to extract only a low-frequency signal.

9. A signal processing apparatus according to claim 5, wherein the frequency conversion section comprises:

a multiplier for multiplying a reference signal cos θ

₂ from the transmitter by an input signal SIN θ

₁ from the first A/D converter; and

a high-pass filter for filtering an output signal obtained by the multiplication by the multiplier through a frequency filter to extract only a high-frequency signal.

6. A signal processing apparatus for a Coriolis flowmeter in which at least one flow tube or a pair of flow tubes which is included in a measurement flow tube is alternately driven by causing a vibrator to be actuated by a driving device to vibrate the at least one flow tube or the pair of flow tubes, and at least one of a phase difference and a vibration frequency proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes is detected by a pair of velocity sensors or acceleration sensors which are a pair of vibration detection sensors, to thereby obtain at least one of a mass flow rate and a density of a fluid to be measured,

the signal processing apparatus comprising:

a transmitter for transmitting a frequency signal which is modulatable;

a first frequency conversion section for performing frequency conversion to add (or subtract) an output frequency from the transmitter to (or from) an input signal frequency obtained by converting a signal of one of the pair of vibration detection sensors into a digital signal by a first A/D converter, to adjust a frequency value obtained by the frequency conversion to a constant value; and

a second frequency conversion section for performing frequency conversion to add (or subtract) the output frequency from the transmitter to (or from) an input signal frequency obtained by converting a signal of another one of the pair of vibration detection sensors into a digital signal by a second A/D converter, to adjust a frequency value obtained by the frequency conversion to a constant value.

14. A signal processing apparatus according to claim 6, wherein the frequency conversion section comprises:

a multiplier for multiplying a reference signal cos θ

₂ from the transmitter by an input signal SIN θ

₁ from the first A/D converter; and

a low-pass filter for filtering an output signal obtained by the multiplication by the multiplier through a frequency filter to extract only a low-frequency signal.

16. A signal processing apparatus according to claim 6, wherein the frequency conversion section comprises:

a multiplier for multiplying a reference signal cos θ

₂ from the transmitter by an input signal SIN θ

₁ from the first A/D converter; and

a high-pass filter for filtering an output signal obtained by the multiplication by the multiplier through a frequency filter to extract only a high-frequency signal.

7. A signal processing apparatus for a Coriolis flowmeter in which at least one flow tube or a pair of flow tubes which is included in a measurement flow tube is alternately driven by causing a vibrator to be actuated by a driving device to vibrate the at least one flow tube or the pair of flow tubes, and at least one of a phase difference and a vibration frequency proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes is detected by a pair of vibration detection sensors, to thereby obtain at least one of a mass flow rate and a density of a fluid to be measured,

the signal processing apparatus comprising:

a transmitter for transmitting a frequency signal which is modulatable;

a first frequency conversion section for shifting in frequency, to a constant frequency signal, an input signal frequency obtained by converting a signal of one velocity sensor of the pair of vibration detection sensors into a digital signal by a first A/D converter, based on an output frequency from the transmitter to move the input signal frequency to another frequency band;

a second frequency conversion section for shifting in frequency, to a constant frequency signal, an input signal frequency obtained by converting a signal of another velocity sensor of the pair of vibration detection sensors into a digital signal by a second A/D converter, based on the output frequency from the transmitter to move the input signal frequency to another frequency band; and

a frequency measurement section for measuring a frequency of a first frequency signal, which is obtained as the constant frequency signal through the shifting by and output from the first frequency conversion section, and outputting the measured frequency of the first frequency signal to the transmitter to control, based on the frequency after the shifting by the first frequency conversion section, output frequencies from the first frequency conversion section and the second frequency conversion section so that the input signal frequency obtained by converting the signal of the one velocity sensor of the pair of vibration detection sensors into the digital signal by the first A/D converter is a desired frequency.

10. A signal processing apparatus according to claim 7, wherein:

the frequency measurement section comprises a multiplier connected to the first frequency conversion section, a low-pass filter connected to the multiplier, and a transmitter for frequency measurement which is connected to the low-pass filter and receives an output signal from the low-pass filter;

the multiplier compares an output signal sin(θ

+θ

_Xn) from the first frequency conversion section with a phase of an output signal cos δ

from the transmitter for frequency measurement and outputs a difference signal and a sum signal to the low-pass filter;

the low-pass filter filters an output signal from the multiplier through a frequency filter to extract only a low-frequency signal; and

a phase amount V of a fundamental output waveform is generated based on the low-frequency signal output from the low-pass filter and satisfies a condition of V=0 by the transmitter for frequency measurement.

11. A signal processing apparatus according to claim 7, further comprising a clock for synchronizing an output of the first A/D converter and an output of the second A/D converter to synchronize a digital signal of one of the pair of vibration detection sensors which is output from the first A/D converter and a digital signal of another one of the pair of vibration detection sensors which is output from the second A/D converter.

12. A signal processing apparatus according to claim 7, wherein the phase measurement section performs processing of a discrete Fourier transform (DFT) or a fast Fourier transform (FFT).

15. A signal processing apparatus according to claim 7, wherein the frequency conversion section comprises:

a multiplier for multiplying a reference signal cos θ

₂ from the transmitter by an input signal SIN θ

₁ from the first A/D converter; and

a low-pass filter for filtering an output signal obtained by the multiplication by the multiplier through a frequency filter to extract only a low-frequency signal.

17. A signal processing apparatus according to claim 7, wherein the frequency conversion section comprises:

a multiplier for multiplying a reference signal cos θ

₂ from the transmitter by an input signal SIN θ

₁ from the first A/D converter; and

a high-pass filter for filtering an output signal obtained by the multiplication by the multiplier through a frequency filter to extract only a high-frequency signal.

13. A Coriolis flowmeter in which at least one flow tube or a pair of flow tubes which is included in a measurement flow tube is alternately driven by causing a vibrator to be actuated by a driving device to vibrate the at least one flow tube or the pair of flow tubes, and at least one of a phase difference and a vibration frequency proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes is detected by a pair of velocity sensors or acceleration sensors which are a pair of vibration detection sensors, to thereby obtain at least one of a mass flow rate and a density of a fluid to be measured,

the Coriolis flowmeter comprising:

a transmitter for transmitting a frequency signal which is modulatable;

a first frequency conversion section for shifting in frequency, to a constant frequency signal, an input signal frequency θ

obtained by converting a signal of one velocity sensor of the pair of vibration detection sensors into a digital signal by a first A/D converter, based on an output frequency θ

_Xn from the transmitter to move the input signal frequency to a desired frequency band;

a second frequency conversion section for shifting in frequency, to a constant frequency signal, an input signal frequency θ

obtained by converting a signal of another velocity sensor of the pair of vibration detection sensors into a digital signal by a second A/D converter, based on the output frequency θ

_Xn from the transmitter to move the input signal frequency to a desired frequency band; and

a frequency measurement section for measuring a frequency of a first frequency signal, which is obtained as the constant frequency signal through the shifting by and output from the first frequency conversion section, and outputting the measured frequency of the first frequency signal to the transmitter to control the output frequency so that the frequency after shifting by each of the first frequency conversion section and the second frequency conversion section is a desired frequency.