US3690147A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Torsional vibration densitometer
Assignee: Massachusetts Institute of Technology
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Filing: 1969-08-15
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Granted: 1972-09-12
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Expires: 1989-08-15
Abstract
Abstract A direct measurement of density of a fluid is made by coupling the fluid to a rod under torsional oscillation. The frequency of torsional oscillation is maintained at the resonant frequency by sensing the phase difference between the stress in the rod and the current in a driving coil which produces the force to sustain torsional oscillation in the rod. The stress is measured by strain gauges which provide the electrical signal for phase comparison with the driving coil current. The frequency of the current is controlled by a voltage controlled oscillator whose input is derived from the phase comparison to provide a frequency which is at the resonant frequency of the oscillatory rod as modified by the density of the fluid to which it is coupled. The precise relationship between fluid density and resonant frequency is established by calibration.
Inventors
- 👤 Howard W Kuenzler
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 23:44
CPC Classifications
G; G01; G01N; G01N9/00; G01N9/002; Y; Y10; Y10T; Y10T29/00; Y10T29/49; Y10T29/49826; Y10T29/49833
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
146 words
Apparatus for determining the density of a fluid comprising: a mechanically oscillatory member, means for coupling said fluid to said member, means for causing said member to oscillate at its resonant frequency comprising, a voltage controllable electrical oscillator, means for applying a sinusoidal torque to said mechanical member, means for providing a first alternating electrical signal which is in phase with the applied torque, means for sensing a second alternating electrical signal which is in phase with the strain of the mechanical member, means for comparing the phase of said first and second electrical signals to provide a control electrical signal responsive to the phase difference, and means for providing said control signal to said electrical oscillator to control its frequency to maintain the compared phase difference at 90*, means for measuring the frequency of said electrical oscillator whereby the density of the fluid is determined.
Claim 2
Dependent Claim
146 words
Apparatus for determining the density of a fluid comprising: a mechanically oscillatory member, means for coupling said fluid to said member, means for causing said member to oscillate at its resonant frequency comprising, a voltage controllable electrical oscillator, means for applying a sinusoidal torque to said mechanical member, means for providing a first alternating electrical signal which is in phase with the applied torque, means for sensing a second alternating electrical signal which is in phase with the strain of the mechanical member, means for comparing the phase of said first and second electrical signals to provide a control electrical signal responsive to the phase difference, and means for providing said control signal to said electrical oscillator to control its frequency to maintain the compared phase difference at 90*, means for measuring the frequency of said electrical oscillator whereby the density of the fluid is determined.
Claim 3
Dependent Claim
52 words
The apparatus of claim 1 wherein said mechanically oscillatory member comprises a rod rigidly attached to a frame at least at one end, said rod being free to undergo torsional oscillation, and said fluid coupling means comprises at least one radially projecting vane attached to said rod other than at said frame.
Claim 4
Dependent Claim
33 words
The apparatus of claim 2 wherein there are a plurality of said vanes attached to said rod at the same longitudinal position and spaced equally in angle around the circumference of said rod.
Claim 5
Dependent Claim
24 words
The apparatus of claim 3 wherein the plane of said vanes is axially and radially oriented with respect to the axis of said rod.
Claim 6
Dependent Claim
31 words
The apparatus of claim 4 comprising in addition said rod being rigidly attached at both ends to said frame, and said vanes are attached centrally along the length of said rod.
Claim 7
Dependent Claim
23 words
The apparatus of claim 3 wherein said pluraLity of vanes are of open configuration to allow free flow of fluid to said vanes.
Claim 8
Dependent Claim
12 words
The apparatus of claim 5 wherein said plurality of vanes numbers four.
Claim 9
Dependent Claim
69 words
The apparatus of claim 2 wherein said means for causing said rod to torsionally oscillate at the resonant frequency comprises a coil attached to said rod, a magnet providing a magnetic field for said coil, the plane of said coil being in the direction of said magnetic field and along the axis of said rod, means for providing an alternating current to said coil at the frequency of resonance.
Claim 10
Dependent Claim
112 words
The apparatus of claim 8 wherein said means for providing an alternating current in said coil at the frequency of resonance comprises a voltage-controlled oscillation means connected to said coil to provide said alternating current, a strain sensing means attached to said rod to provide an alternating current signal responsive to the strain of said rod, a phase comparison means connected to said coil and said sensing means for determining the phase difference between the alternating current of said coil and the voltage of said strain sensing means and for providing an electrical output to said voltage controlled oscillator to control its frequency to cause said measured phase difference to be 90*.
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) | 1975-09-12 | 1976-03-13 | 1976-09-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-09-12 | 1980-03-13 | 1980-09-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-09-12 | 1984-03-13 | 1984-09-12 | $7700.00 | Window Closed / Lapsed |