Coriolis densimeter having substantially increased noise immunity
First Claim
1. Apparatus for measuring density of a fluid passing through a Coriolis meter, wherein said meter utilizes a flow conduit having a sensor associated therewith for providing a sensor signal indicative of movement of said flow conduit, said apparatus comprising:
- means for driving the flow conduit in a sinusoidal vibratory pattern and at a resonant frequency thereof while said fluid flows therethrough;
means for sampling said sensor signal at a sampling frequency to yield a sampled sensor signal;
means for undertaking initialization comprising;
means for setting the sampling frequency to an initial pre-defined value;
means for producing, in response the sensor signal sampled at said initial value, a power spectrum for a pre-selected sequence of frequencies contained within said sampled sensor signal and selecting a particular one of said frequencies in said sequence at which said power spectrum reaches a maximum value as being a fundamental frequency at which said conduit is resonantly vibrating;
means for setting the sampling frequency to a second sampling frequency value, equal to a pre-defined integer multiple of said one frequency, for initial use during density measurement; and
means for obtaining a base-line density value for said fluid;
means for undertaking a density measurement comprising;
means for transforming said sensor signal using a pre-defined transformation from a time domain to a frequency domain so as to yield a frequency value, wherein said frequency value is produced by evaluating said transformation at the fundamental frequency for said sampled sensor signal;
means for ascertaining in response to said frequency value a phase value associated therewith;
means for providing a density value in response to the base-line density value and the ascertained phase value; and
means for varying the sampling frequency, in response to the ascertained phase value, in order to compensate for a change in the fundamental frequency caused by a substantially simultaneously occurring variation in density of the fluid flowing through the meter, whereby the sampling frequency substantially remains at the pre-defined integer multiple of the fundamental frequency.
0 Assignments
0 Petitions
Accused Products
Abstract
Apparatus and accompanying methods for use therein for a Coriolis mass flow rate meter which is substantially immune to noise, and more particularly, to such a meter that is substantially unaffected by noise that occurs at substantially any frequency different from a fundamental frequency at which the flow tube(s) in the meter vibrate. Specifically, the meter relies on measuring mass flow rate by determining the phase difference that occurs between real and imaginary components of the discrete fourier transform (DFT) of both the left and right velocity sensor waveforms evaluated at the fundamental frequency at which the flow tubes vibrate. The fundamental frequency is located, during an initialization operation, by providing a power spectrum, determined through use of the DFT of one of the sensor signals and then selecting that frequency at which the magnitude of the power spectrum reaches a maximum value. In addition, the frequency at which both velocity sensor signals is sampled is readjusted in response to any change in the phase of one of the velocity sensor signals, as transformed using the DFT, in order to assure that the sampling frequency always remains substantially equal to a pre-defined integer multiple of the fundamental frequency. Furthermore, the meter, through use of the numerical value of any such phase change, also provides a density indication which is also substantially immune to such noise.
134 Citations
12 Claims
-
1. Apparatus for measuring density of a fluid passing through a Coriolis meter, wherein said meter utilizes a flow conduit having a sensor associated therewith for providing a sensor signal indicative of movement of said flow conduit, said apparatus comprising:
-
means for driving the flow conduit in a sinusoidal vibratory pattern and at a resonant frequency thereof while said fluid flows therethrough; means for sampling said sensor signal at a sampling frequency to yield a sampled sensor signal; means for undertaking initialization comprising; means for setting the sampling frequency to an initial pre-defined value; means for producing, in response the sensor signal sampled at said initial value, a power spectrum for a pre-selected sequence of frequencies contained within said sampled sensor signal and selecting a particular one of said frequencies in said sequence at which said power spectrum reaches a maximum value as being a fundamental frequency at which said conduit is resonantly vibrating; means for setting the sampling frequency to a second sampling frequency value, equal to a pre-defined integer multiple of said one frequency, for initial use during density measurement; and means for obtaining a base-line density value for said fluid; means for undertaking a density measurement comprising; means for transforming said sensor signal using a pre-defined transformation from a time domain to a frequency domain so as to yield a frequency value, wherein said frequency value is produced by evaluating said transformation at the fundamental frequency for said sampled sensor signal; means for ascertaining in response to said frequency value a phase value associated therewith; means for providing a density value in response to the base-line density value and the ascertained phase value; and means for varying the sampling frequency, in response to the ascertained phase value, in order to compensate for a change in the fundamental frequency caused by a substantially simultaneously occurring variation in density of the fluid flowing through the meter, whereby the sampling frequency substantially remains at the pre-defined integer multiple of the fundamental frequency. - View Dependent Claims (2, 3, 4, 5, 6)
-
-
7. A method for measuring density of a fluid passing through a Coriolis meter, wherein said meter utilizes a flow conduit having a sensor associated therewith for providing a sensor signal indicative of movement of said flow conduit, said method comprising the steps of:
-
driving the flow conduit in a sinusoidal vibratory pattern and at a resonant frequency thereof while said fluid flows therethrough; sampling said sensor signal at a sampling frequency to yield a sampled sensor signal; during initialization; setting the sampling frequency to an initial pre-defined value; producing, in response the sensor signal sampled at said initial value, a power spectrum for a pre-selected sequence of frequencies contained within said sampled sensor signal and selecting a particular one of said frequencies in said sequence at which said power spectrum reaches a maximum value as being a fundamental frequency at which said conduit is resonantly vibrating;
multiple of said one frequency, for initial use during density measurement; andobtaining a base-line density value for said fluid; during density measurement; transforming said sensor signal using a pre-defined transformation from a time domain to a frequency domain so as to yield a frequency value, wherein said frequency value is produced by evaluating said transformation at the fundamental frequency for said sampled sensor signal; ascertaining in response to said frequency value a phase value associated therewith; providing a density value in response to the base-line density value and the ascertained phase value; varying the sampling frequency, in response to the ascertained phase value, in order to compensate for a change in the fundamental frequency caused by a substantially simultaneously occurring variation in density of the fluid flowing through the meter, and iteratively repeating the sensor signal transforming, phase value ascertaining, density value providing, and sampling frequency varying steps so as to provide a succession of density measurement values, whereby the sampling frequency that is used to produce substantially all of these density measurement values substantially remains at the pre-defined integer multiple of the fundamental frequency. - View Dependent Claims (8, 9, 10, 11, 12)
-
Specification