US4866260A
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US
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Method and means for measuring the frequency of a periodic signal
Assignee: C R O U Z E T (SOCIETE ANONYME FRANCAISE)
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Filing: 1988-09-20
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Granted: 1989-09-12
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Expires: 2008-09-20
Abstract
Abstract Frequency measurement involves anti-foldover filtering (1) of an analog signal whose frequency i.e. to be measured, followed by sampling of the filtered analog signal and analog-digital conversion of the samples, then digital band-pass filtering (3) on a slaved basis. Associated calculation (4-7) utilizes a linear regression having a single coefficient a for the linear relation between successive digitized samples (2) and to estimate the coefficient a for approximation of the frequency to be measured. The invention is particularly applicable to signals from a probe having nuclear magnetic resonance used in measuring intensity of the terrestrial magnetic field disturbed by metallic masses.
Inventors
- 👤 Jean-Louis Lescourret
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 13:50
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/32; G01R33/36; G01R33/3621; G01R23/00; G01R23/02
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
245 words
A method of measuring the frequency F x of a periodic signal S(t), where S(t)=A Sin 2πF x +B(T), comprising the steps of (i) filtering (1) the signal S(t) to limit foldover frequency distortion; (ii) sampling (2) the filtered signal at a sampling rate of Fe=1/Te, where T e is the period of the filtered signal, and generating a digital signal comprising a series of digitized values of the samples, (iii) filtering the digital signal using a narrow band-pass filter (3) having a predetermined central frequency, thereby increasing a signal-to-noise ratio of said digital signal, (iv) performing a linear regression on said digitized values of said signal to produce a series of smoothed digital values constituting a smoothed digital output signal comprising values consisting of, said linear regression using based on a single coefficient a, by means of a least square calculating method of a linear relation between successive ones of said digitized samples, wherein an intermediate digitized sample S n+1 is related to a previous digitized sample S n and a subsequent digitized sample S n+2 as: S.sub.n+2 +S.sub.n =a·S.sub.n+1 wherein a=2 cos 2πF x Te, (v) calculating, at a rate Fe/N, wherein N is a predetermined integer, an estimation a of the coefficient a to derive the frequency F x according to the relation F x =(Fe/2π) arc cos (a/2), and (vi) controlling the central frequency of the narrow band-pass filter to be equal to an estimated frequency of the sampled digitized signal.
Claim 2
Independent Claim
245 words
A method of measuring the frequency F x of a periodic signal S(t), where S(t)=A Sin 2πF x +B(T), comprising the steps of (i) filtering (1) the signal S(t) to limit foldover frequency distortion; (ii) sampling (2) the filtered signal at a sampling rate of Fe=1/Te, where T e is the period of the filtered signal, and generating a digital signal comprising a series of digitized values of the samples, (iii) filtering the digital signal using a narrow band-pass filter (3) having a predetermined central frequency, thereby increasing a signal-to-noise ratio of said digital signal, (iv) performing a linear regression on said digitized values of said signal to produce a series of smoothed digital values constituting a smoothed digital output signal comprising values consisting of, said linear regression using based on a single coefficient a, by means of a least square calculating method of a linear relation between successive ones of said digitized samples, wherein an intermediate digitized sample S n+1 is related to a previous digitized sample S n and a subsequent digitized sample S n+2 as: S.sub.n+2 +S.sub.n =a·S.sub.n+1 wherein a=2 cos 2πF x Te, (v) calculating, at a rate Fe/N, wherein N is a predetermined integer, an estimation a of the coefficient a to derive the frequency F x according to the relation F x =(Fe/2π) arc cos (a/2), and (vi) controlling the central frequency of the narrow band-pass filter to be equal to an estimated frequency of the sampled digitized signal.
Claim 3
Dependent Claim
51 words
A method according to claim 1, wherein the sampling step (2) is performed at a sampling rate Fe lower than the frequency F x to be measured and the filtering (1) prior to sampling is performed using a band-pass filter (8, 9) centered on the frequency F x to be measured.
Claim 4
Dependent Claim
45 words
A method according to claim 1, wherein filtering (1) of the signal S(t) prior to sampling is performed using a low-pass band and sampling (2) of the filtered signal is performed at a sampling rate Fe higher than the frequency F x to be measured.
Claim 5
Dependent Claim
25 words
A method according to claim 1, wherein said linear regression starts relative to the mean values of variables estimated at a time temporal horizon NTe.
Claim 6
Dependent Claim
47 words
A method according to claim 1, wherein the sampling frequency Fe is less than the frequency to be measured, and the frequency to be measured is determined by adding to a calculated frequency Fa the product of the sampling rate Fe and a predetermined integer entity K.
Claim 7
Dependent Claim
96 words
A method according to claim 1, wherein step of filtering the digital signal is performed according to a band-pass function such that: S.sub.n +2=(λa*)S.sub.n+1 -λ.sup.2 S.sub.n +γS.sub.n+2 where: λ is a constant representing damping and width of the filter at -3dB, a* is an estimate of a filtered on a low-pass basis in order to smooth the value of a parameter determining centering of the band-pass γ is a framing constant fixing static gain for the band-pass S n+2 is an unfiltered sample at instant (n+2)Te, and s n is a filtered sample at instant nTe.
Claim 8
Dependent Claim
32 words
A method according to claim 1, further comprising a step of subsampling (6) at a rate L times lower than for the coefficient a in determining (7) the frequency to be measured.
Claim 9
Dependent Claim
27 words
A method according to claim 1, wherein the value of the coefficient a is determined using a predetermined frequency desynchronization performed in an interpolator or extrapolator filter.
Claim 10
Dependent Claim
40 words
A method according to claim 1, wherein further comprising an initialization step for (16) calculating estimates of a and of F x over several seconds and calculating a mean value using estimates as an initial value of F x .
Claim 11
Dependent Claim
144 words
A frequency meter for measuring the frequency F x of a periodic signal S(t), where S(t)=A Sin 2πF x +B(T), comprising: a series connection of an anti-foldover analog filter (1), and means (2) for sampling and performing analog-to-digital conversion of said periodic signal for generating a digital signal comprising a series of digital values representing said periodic signal, a slaved digital band-pass filter (3) having an input receiving said digital signal and an output for supplying a filtered digital signal, and calculating means (4-7) for performing a linear regression calculation on said filtered digital signal, said linear regression calculation using a single coefficient a for determining a linear relationship between successive digitized samples of said filtered digital signal from the slaved digital band-pass filter, said calculating means further generating an estimation of the coefficient a from which the frequency to be measured is approximated.
Claim 12
Dependent Claim
144 words
A frequency meter for measuring the frequency F x of a periodic signal S(t), where S(t)=A Sin 2πF x +B(T), comprising: a series connection of an anti-foldover analog filter (1), and means (2) for sampling and performing analog-to-digital conversion of said periodic signal for generating a digital signal comprising a series of digital values representing said periodic signal, a slaved digital band-pass filter (3) having an input receiving said digital signal and an output for supplying a filtered digital signal, and calculating means (4-7) for performing a linear regression calculation on said filtered digital signal, said linear regression calculation using a single coefficient a for determining a linear relationship between successive digitized samples of said filtered digital signal from the slaved digital band-pass filter, said calculating means further generating an estimation of the coefficient a from which the frequency to be measured is approximated.
Claim 13
Dependent Claim
62 words
A frequency meter according to claim 10, further comprising an input stage for receiving said periodic signal including an anti-foldover analog filter having a band-pass filter (102, 104) using switching of capacitances according to a switching signal, and a first programmable divider (15) responsive to a reference clock signal (13) and controlled by the calculating means (4-7) to produce the switching signal.
Claim 14
Dependent Claim
22 words
A frequency meter according to claim 11, wherein the anti-folder analog filter (1) comprises at least one low-pass smoothing filter (103, 105).
Claim 15
Dependent Claim
41 words
A frequency meter according to claim 11, further comprising a second programmable divider (14) responsive to the reference clock signal (13) and controlled by the calculating means (4-7) to provide a coupling signal for the sampling and analog-digital conversion means (2).
Claim 16
Dependent Claim
48 words
A frequency meter according to claim 13, in which the calculating means (4-7) controls the first and second programmable dividers (15, 14), said calculating means further including a switching unit (10) for calculating switching and sampling rates, and monitoring means (11) for monitoring said switching and sampling rates.
Claim 17
Dependent Claim
27 words
A frequency meter according to claim 11, further comprising an initialization unit (16) connected to the input of the unit (10) for calculating switching and sampling rates.
Claim 18
Dependent Claim
28 words
A frequency meter according to claim 10, further comprising a digital low-pass filter by which the slaved digital filter (3) is controlled by the calculating means (4, 5).
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-09-11 | 1993-03-13 | 1993-09-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-09-11 | 1997-03-13 | 1997-09-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-09-11 | 2001-03-13 | 2001-09-12 | $7700.00 | Window Closed / Lapsed |