US3795447A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Laser anemometer frequency to d.c. converter
Assignee: Individual
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Filing: 1971-06-23
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Granted: 1974-03-05
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Expires: 1991-06-23
Abstract
Abstract A method and apparatus for converting frequency information to a DC voltage for use particularly with a laser velocity measuring system whereby a laser beam is passed through a flowing media, and a portion of the Doppler shifted beam is optically combined with the non-shifted beam to produce a fixed homodyne signal which is then applied to a photodetector to produce a modulated electrical signal. This modulated electrical signal is then amplified and delayed by a fixed or variable time interval. Next, the delayed and undelayed signals are mixed together and the output integrated or applied to a low frequency filter to produce a DC signal having an amplitude proportional to the cosine of a constant times the velocity of the flowing media. The amplitude of the coefficient of the cosine function can be readily ascertained by adjusting the variable time delay line until the minimum or maximum value on the DC meter is observed, and then the velocity can be determined by adjusting the time delay until a DC meter has an average fluctuation of zero at which point the speed can be quickly determined from the value of the time delay. Alternatively, the delay line can be fixed and the signal from the flowing media can be mixed with a variable oscillator output signal to produce a signal at any given frequency which will give a zero reading on the DC meter. In a further embodiment a hold and track circuit is employed to cause the output to retain the previous tracked value whenever an interval occurs in which the signal is predominantly noise. In another embodiment a feed back loop is employed to vary the frequency of an oscillator, whose output is mixed with the velocity signal, in order to maintain a null at the output. In yet another embodiment, a digital system is employed to compare the frequency of the velocity signal with the frequency of the signal from a variable frequency oscillator.
Inventors
- 👤 N Welch
- 👤 R Ray
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 18:03
CPC Classifications
G; G01; G01P; G01P5/00; G01P5/26; G01S; G01S17/00; G01S17/02; G01S17/50
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
232 words
A velocity measuring system comprising: means for producing a beam of monochromatic light, means for directing at least a portion of said beam onto a flowing media so that at least a portion of the directed beam is shifted in frequency by an amount proportional to the velocity of said flowing media, means for combining at least a part of said shifted portion of said beam with an unshifted beam of monochromatic light to produce a combined beam, means for converting said combined beam into a first electrical signal, varying in amplitude in the same manner as said combined beam varied in intensity, means for delaying said first electrical signal for a given delay time so that a second electrical signal is produced, means for mixing said first and second signals to produce a third signal having a substantially time invariant component, means for removing time variant components from said third signal to produce a fourth signal having an ampliitude which is a function of said velocity, means for receiving said first electrical signal and for determining from said first signal when said fourth signal has a signal to noise ratio below a predetermined value, and means for tracking said fourth signal and holding the previously tracked value during intervals in which said receiving and determining means determines that said fourth signal has a signal to noise ratio below said predetermined value.
Claim 2
Dependent Claim
232 words
A velocity measuring system comprising: means for producing a beam of monochromatic light, means for directing at least a portion of said beam onto a flowing media so that at least a portion of the directed beam is shifted in frequency by an amount proportional to the velocity of said flowing media, means for combining at least a part of said shifted portion of said beam with an unshifted beam of monochromatic light to produce a combined beam, means for converting said combined beam into a first electrical signal, varying in amplitude in the same manner as said combined beam varied in intensity, means for delaying said first electrical signal for a given delay time so that a second electrical signal is produced, means for mixing said first and second signals to produce a third signal having a substantially time invariant component, means for removing time variant components from said third signal to produce a fourth signal having an ampliitude which is a function of said velocity, means for receiving said first electrical signal and for determining from said first signal when said fourth signal has a signal to noise ratio below a predetermined value, and means for tracking said fourth signal and holding the previously tracked value during intervals in which said receiving and determining means determines that said fourth signal has a signal to noise ratio below said predetermined value.
Claim 3
Dependent Claim
30 words
A system as in claim 1 further including an automatic gain amplifier for receiving said first signal and applying its output to said mixing means and to said delaying means.
Claim 4
Dependent Claim
85 words
A system as in claim 1 further including gate means connected to said receiving and determining means for passing said fourth signal to said tracking and holding means when said receiving and determining means determines that said fourth signal has a signal to noise ratio above said predetermined value and for preventing said fourth signal from being applied to said receiving and tracking means when said receiving and determining means determines that said fourth signal has a signal to noise ratio below said predetermined value.
Claim 5
Dependent Claim
113 words
A system as in claim 3 wherein said receiving and determining means includes an amplitude detector, an amplifier for receiving the output of said detector and a diode locking the output of said amplifier to ground, wherein said gate means is a field effect transistor having its gate connected to the output of said amplifier, one of its other terminals connected to the output of said removing means and its third terminal connected to said tracking and holding means and wherein said tracking and holding means includes a capacitor connected between said third terminal and ground for tracking said fourth signal and an emitter follower having its input connected to said third terminal.
Claim 6
Independent Claim
200 words
A method of measuring the velocity of a flowing media comprising the steps of: directing a beam of monochromatic light onto said media so that a portion of said beam is shifted in frequency an amount proportional to the velocity of said media, combining the shifted beam with an unShifted beam to produce a combined beam, converting said combined beam into a first electrical signal varying in amplitude in the same manner as said combined beam varied in intensity, mixing said first electrical signal with a sinusoidal signal from a variable frequency oscillator to produce a second electrical signal, delaying said second electrical signal in time to produce a third electrical signal, multiplying said third and second electrical signals together to produce a fourth signal having a substantially time invariant term which is proportional to said velocity, determining from said first signal when said fourth signal has a signal to noise ratio below a predetermined value, tracking said fourth signal during intervals in which said fourth signal has a signal to noise ratio above said predetermined value, and holding the previously tracked value during intervals in which said fourth signal has a signal to noise ratio above said predetermined value.
Claim 7
Independent Claim
200 words
A method of measuring the velocity of a flowing media comprising the steps of: directing a beam of monochromatic light onto said media so that a portion of said beam is shifted in frequency an amount proportional to the velocity of said media, combining the shifted beam with an unShifted beam to produce a combined beam, converting said combined beam into a first electrical signal varying in amplitude in the same manner as said combined beam varied in intensity, mixing said first electrical signal with a sinusoidal signal from a variable frequency oscillator to produce a second electrical signal, delaying said second electrical signal in time to produce a third electrical signal, multiplying said third and second electrical signals together to produce a fourth signal having a substantially time invariant term which is proportional to said velocity, determining from said first signal when said fourth signal has a signal to noise ratio below a predetermined value, tracking said fourth signal during intervals in which said fourth signal has a signal to noise ratio above said predetermined value, and holding the previously tracked value during intervals in which said fourth signal has a signal to noise ratio above said predetermined value.
References Cited (Backward Citations)
US2896162A
Cited
US3584956A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-03-04 | 1977-09-03 | 1978-03-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-03-04 | 1981-09-03 | 1982-03-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-03-04 | 1985-09-03 | 1986-03-05 | $7700.00 | Window Closed / Lapsed |