Method and apparatus for continuously measuring volumetric flow

A method of directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising the steps of:

• applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• determining substantially noise-free and substantially noisy frequencies of said excitation signal;
• calculating from said cross-correlation data weighting values for each frequency of said excitation signal, whereby said weighting values have values approaching one for said substantially noise-free frequencies of said excitation signal and values approaching zero for said substantially noisy frequencies of said excitation signal;
• weighting said cross-correlation data with said weighting values so as to substantially eliminate the effect of received data at frequencies containing a predetermined amount of noise;
• and
• calculating a signal representative of volumetric flow of said fluid from said weighted cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

A method of directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising the steps of:

• obtaining a background noise spectra of the system;
• determining the frequencies of predominant noise amplitudes of the background noise spectra;
• selecting frequencies of an excitation signal so as to differ from said frequencies of said predominant noise amplitudes;
• applying to said fluid, at said system entry point, a quantity of indicator under control of said excitation signal having said selected frequencies;
• sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• calculating a signal representative of volumetric flow of said fluid from said cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

A method of directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising the steps of:

• applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• obtaining a background noise spectra of the system;
• determining the frequencies of predominant noise amplitudes of the background noise spectra;
• selecting said frequencies of said excitation signal so as to differ from said frequencies of said predominant noise amplitudes;
• and
• calculating a signal representative of volumetric flow of said fluid from said cross-correlation data and from said quantity of said indicator applied under control of said excitation signal at said selected frequencies.

A method of directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising the steps of:

• (a) applying to said fluid, at said system entry point, a quantity of indicator under control of excitation signals comprising three adjacent pseudorandom noise sequences;
• (b) sensing a time-dependent response of said fluid to said excitation signals at said system exit point to obtain response signals having a plurality of data points;
• (c) determining the average power of response signals resulting from the input of said three adjacent pseudorandom noise sequences;
• (d) fitting a quadratic curve to data points corresponding to the average power of said response signals resulting from the input of said three adjacent pseudorandom noise sequences;
• (e) subtracting a portion of the fitted quadratic curve associated with the response signal for an intermediate pseudorandom noise sequence of said three adjacent pseudorandom noise sequences, data point by data point, from the response signal for said intermediate pseudorandom noise sequence so as to obtain drift adjusted response data;
• (f) selecting three different adjacent pseudorandom noise sequences;
• (g) repeating steps (c)-(f) for each of said selected pseudorandom noise sequences so as to obtain a drift adjusted response signal;
• (h) cross-correlating said excitation signal with said drift adjusted response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• (i) calculating a signal representative of volumetric flow of said fluid from said cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

A method of directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising the steps of:

• applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• removing from said response signal data representing an aberrant noise event so as to obtain a noise event edited response signal, said aberrant noise event data including a spike in said response signal having an abnormally large amplitude over a short time interval with respect to the remainder of said response signal;
• cross-correlation said excitation signal with said noise event edited response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• calculating a signal representative of volumetric flow of said liquid from said cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

A method of directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising the steps of:

• applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• calculating a signal representative of volumetric flow of said fluid from said quantity of said indicator applied under control of said excitation signal and from a transfer function of said system, wherein said calculating step comprises the step of generating said volumetric flow signal according to the expression:
• ##EQU58## where:
• .omega. is each respective frequency of said excitation signal,
• k.sub.3 =2P/C, P being the rate of indicator infusion per unit time, and C being the specific density of indicator volume in said fluid, where C=4180.multidot.2.multidot.c.multidot..rho..multidot..gamma./60, and where c is the specific heat for said fluid, .rho. is the density of said fluid, and .gamma. is the specific gravity of said fluid,
• H(.omega.) is the transfer function of said system,
• S.sub.xx (.omega.) is the spectral density of said excitation signal, and
• S.sub.xy (.omega.) is the cross-spectral density of said excitation and response signals.

A method of directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising the steps of:

• (a) determining a distribution function model which mathematically model the distribution of an indicator in said system;
• (b) applying to said fluid, at said system entry point, a quantity of said indicator under control of an excitation signal having a plurality of frequencies;
• (c) sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• (d) cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• (e) comparing said cross-correlation data to said distribution function model;
• (f) adjusting said distribution function model to fit said cross-correlation data;
• (g) calculating a signal representative of volumetric flow of said fluid from said quantity of said indicator applied under control of said excitation signal and from said adjusted distribution model;
• (h) repeating said steps (b) through (g) to produce a plurality of said volumetric flow signals;
• and
• (i) averaging said plurality of volumetric flow signals to produce an average volumetric flow signal.

An apparatus for directly measuring volumetric flow of a fluid between a system entry point and a system exit pint, comprising:

• means for applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• means for sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• means for cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• means for comparing said cross-correlation data to a distribution function model which mathematically models the distribution of said indicator in said system;
• means for adjusting said distribution function model to fit said cross-correlation data;
• and
• means for calculating a signal representative of volumetric flow of said fluid from said quantity of said indicator applied under control of said excitation signal and from said adjusted distribution function model.

An apparatus for directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising:

• means for applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• means for sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• means for cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• means for determining substantially noise-free and substantially noisy frequencies of said excitation signal;
• means for calculating from said cross-correlation data weighting values for each frequency of said excitation signal, whereby said weighting values have values approaching one for said substantially noise-free frequencies of said excitation signal and values approaching zero for said substantially noisy frequencies of said excitation signal;
• means for weighting said cross-correlation data with said weighting values so as to substantially eliminate the effect of received data at frequencies containing a predetermined amount of noise;
• and
• means for calculating a signal representative of volumetric flow of said fluid from said weighted cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

An apparatus for directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising:

• setup means for obtaining a background noise spectra of the system, determining the frequencies of predominant noise amplitudes of the background noise spectra, and selecting frequencies of an excitation signal so as to differ from said frequencies of said predominant noise amplitudes;
• means for applying to said fluid, at said system entry point, a quantity of indicator under control of said excitation signal having said selected frequencies;
• means for sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• means for cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• means for calculating a signal representative of volumetric flow of said fluid from said cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

An apparatus for directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising:

• means for applying to said fluid, at said system entry point, a quantity of indicator under control of excitation signals comprising three adjacent pseudorandom noise sequences;
• means for sensing a time-dependent response of said fluid to said excitation signals at said system exit point to obtain response signals having a plurality of data points;
• drift removal means including processing means for removing low frequency drift of said response signal by performing the steps of:
• (a) determining the average power of response signals resulting from the input of said three adjacent pseudorandom noise sequences;
• (b) fitting a quadratic curve to points corresponding to the average power of said response signals resulting from the input of said three adjacent pseudorandom noise sequences;
• (c) subtracting a portion of the fitted quadratic curve associated with the response signal for an intermediate pseudorandom noise sequence of said three adjacent pseudorandom noise sequences, data point by data point, from the response signal for said intermediate pseudorandom noise sequence so as to obtain drift adjusted response data;
• (d) selecting three different adjacent pseudorandom noise sequences;
• and
• (e) repeating steps (a)-(d) for each of said selected pseudorandom noise sequences so as to obtain a drift adjusted response signal;
• means for cross-correlating said excitation signal with said drift adjusted response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• means for calculating a signal representative of volumetric flow of said fluid from said cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

An apparatus for directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising:

• means for applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• means for sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• means for removing from said response signal data representing an aberrant noise event so as to obtain a noise event edited response signal, said aberrant noise event data including a spike in said response signal having an abnormally large amplitude over a short time interval with respect to the remainder of said response signal;
• means for cross-correlating said excitation signal with said noise event edited response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• means for calculating a signal representative of volumetric flow of said fluid from said cross-correlation data and from said quantity of said indicator applied under control of said excitation signal.

An apparatus for directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising:

• means for applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• means for sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• means for cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• and
• means for calculating a signal representative of volumetric flow of said fluid from said quantity of said indicator applied under control of said excitation signal and from a transfer function of said system, said calculating means comprising processing means for generating said volumetric flow signal according to the expression:
• ##EQU68## where:
• .omega. is each respective frequency of said excitation signal,
• k.sub.3 =2P/C, P being the rate of indicator infusion per unit time, and C being the specific density of indicator volume in said fluid, where C=4180.multidot.2.multidot.c.multidot..rho..multidot..gamma./60, and where c is the specific heat for said fluid, .rho. is the density of said fluid, and .gamma. is the specific gravity of said fluid,
• H(.omega.) is the transfer function of said system,
• S.sub.xx (.omega.) is the spectral density of said excitation signal, and
• S.sub.xy (.omega.) is the cross-spectral density of said excitation and response signals.

An apparatus for directly measuring volumetric flow of a fluid between a system entry point and a system exit point, comprising:

• means for repeatedly applying to said fluid, at said system entry point, a quantity of indicator under control of an excitation signal having a plurality of frequencies;
• means for sensing a time-dependent response of said fluid to said excitation signal at said system exit point to obtain a response signal having a plurality of data points;
• means for cross-correlating said excitation signal with said response signal to obtain a cross-correlation function signal representing cross-correlation data;
• means for determining a distribution function model which mathematically models the distribution of an indicator in said system and for comparing said cross-correlation data to said distribution function model;
• means for adjusting said distribution function model to fit said cross-correlation data;
• means for calculating a signal representative of volumetric flow of said fluid from said quantity of said indicator applied under control of said excitation signal and from said adjusted distribution function model for each application of said quantity of said indicator;
• and
• means for averaging said volumetric flow signals for each application of said quantity of said indicator to produce an average volumetric flow signal.