Coriolis mass flow rate meter having a substantially increased noise immunity

Apparatus for a Coriolis mass flow rate meter comprising:

• a Coriolis metering assembly for measuring the mass flow rate of a fluid flowing therethrough, said assembly comprising:
• first and second flow tubes;
• inlet and outlet manifolds for respectively conducting said fluid into and out of both of said flow tubes, wherein said inlet manifold divides the fluid between both of said tubes and said outlet manifold combines the fluid exiting from both of said tubes;
• first and second mounting blocks, which receive corresponding ends of both of said flow tubes and are fixedly secured to said inlet and outlet manifolds, for respectively dividing the fluid emanating from said inlet manifold and routing said divided fluid into both of said flow tubes or combining the fluid emanating from both of said flow tubes and routing the combined fluid into said outlet manifold,
• means, responsive to a drive signal, for vibrating both of said flow tubes in an opposing sinusoidal pattern and at a resonant frequency thereof while said fluid flows therethrough;
• and
• first and second sensors for sensing movement of both of said flow tubes caused by opposing Coriolis forces induced by passage of the fluid through said flow tubes and for producing first and second sensor signals responsive to sensed movement;
• and
• circuit means, responsive to said sensor signals, for providing a measured value of the mass flow rate of the fluid that is passing through said metering assembly, said circuit means comprising:
• means, responsive to at least one of said sensor signals, for producing said drive signal;
• means for sampling said first and second sensor signals at a sampling frequency to yield first and second sampled sensor signals;
• means, responsive to one of the sampled sensor signals, for producing a power spectrum for a pre-selected sequence of frequencies contained within said one sampled sensor signal and for 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, responsive to said selecting means and connected to said sampling means, for setting the sampling frequency equal to a pre-defined multiple of said one frequency;
• means, responsive to said first and second sampled sensor signals, for transforming said first and second sensor signals using a pre-defined transformation from a time domain to a frequency domain so as to yield corresponding first and second frequency values, wherein said first and second frequency values are produced by separately evaluating said transformation for said first and second sensor sampled signals at the fundamental frequency;
• means responsive to said first and second frequency values for determining a phase difference occurring therebetween;
• and
• means, responsive to said phase difference, for providing a value of the mass flow rate of said fluid.

A method for measuring mass flow rate of a fluid using a Coriolis meter having a flow conduit with first and second sensors associated therewith for providing first and second sensor signals indicative of movement of the flow tube, said apparatus comprising the steps of:

• driving said flow conduit in a sinusoidal vibratory pattern and at a resonant frequency thereof while said fluid flows therethrough;
• sampling said first and second sensor signals at a sampling frequency to yield first and second sampled sensor signals;
• producing, in response to one of the sampled sensor signals, a power spectrum for a pre-selected sequence of frequencies contained within said one 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;
• setting the sampling frequency equal to a pre-defined multiple of said one frequency;
• transforming said first and second sensor signals using a pre-defined transformation from a time domain to a frequency domain so as to yield corresponding first and second frequency values, wherein said first and second frequency values are produced by separately evaluating said transformation for said first and second sensor sampled signals at the fundamental frequency;
• determining, in response to said first and second frequency values, a phase difference occurring therebetween;
• and
• providing, in response to said phase difference, a value of the mass flow rate of said fluid.

A method for use in a mass flow rate metering system for determining mass flow rate of a fluid passing therethrough, wherein said system utilize a Coriolis meter having a flow conduit with first and second sensors associated therewith for providing first and second sensor signals indicative of movement of said flow conduit induced by Coriolis forces caused by movement of the fluid through the 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 first and second sensor signals at a sampling frequency to yield first and second sampled sensor signals;
• during initialization:
• setting the sampling frequency to an initial pre-defined value;
• producing, in response to one of the sensor signals sampled at said initial value, a power spectrum for a pre-selected sequence of frequencies contained within said one 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;
• and
• 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 mass flow rate measurement;
• during mass flow rate measurement:
• transforming said first and second sensor signals using a pre-defined transformation from a time domain to a frequency domain so as to yield corresponding first and second frequency values, wherein said first and second frequency values are produced by separately evaluating said transformation at the fundamental frequency for said first and second sampled sensor signals;
• determining in response to said first and second frequency values a phase difference occurring therebetween;
• providing a value of the mass flow rate of the fluid in response to said phase difference;
• ascertaining, in response to either said first or second frequency value, a phase value of the corresponding first or second frequency value;
• and
• 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 signals transforming, phase difference determining, mass flow rate value providing, phase value ascertaining and sampling frequency varying steps so as to provide a succession of mass flow rate measurement values, whereby the sampling frequency that is used to produce substantially all of these mass flow rate measurement values substantially remains at the pre-defined integer multiple of the fundamental frequency.