Communications: directive radio wave systems and devices (e.g. – Determining distance – Material level within container
Reexamination Certificate
1999-07-02
2001-10-09
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
Material level within container
C342S082000, C342S085000
Reexamination Certificate
active
06300897
ABSTRACT:
BACKGROUND OF THE INVENTION
Pulsed time-of-flight radar gauges are utilized for the measurement of level in process storage tanks. These gauges are mounted on the top of storage tanks, and transmit a pulse of microwave energy toward the surface of the product being stored in the tank. The gauge then receives energy which is reflected from the surface of the product, and calculates the level of the product based upon the time of flight of the pulse.
A PRIOR ART circuit
110
for creating the transmit and sample clocks is shown in FIG.
2
. Circuits of this type are described in U.S. Pat. No. 5,563,605 McEwan. This circuit has the advantage that only one oscillator
112
is required, as the sample clock
114
is generated by continuously increasing phase delay in a variable delay generator
116
controlled by a delay control ramp
118
. The phase delay circuit can be designed to be repeatable, therefore, errors due to changes in the difference frequency are reduced using this circuit design. However, this circuit has the disadvantage of having significant phase jitter or instability in the sample clock. This is a result of performance limitations of the high speed comparator required as part of the phase delay generator.
There is a need for a radar gauge circuit that is stabilized without the use of expensive, complex circuitry.
SUMMARY OF THE INVENTION
In the present invention, a controller feeds back a control output to a clock source. The feedback stabilizes a first frequency separation between first and second clock frequencies generated by the clock source. A separation sensing circuit is coupled to the clock source and generates an evaluation output as a function of the first frequency separation. The evaluation output is coupled to the controller for controlling the control output. A radar gauge circuit receives the first or transmit frequency and the second or sample frequency and controls radar transmission and level sampling as a function of the transmit and sampling frequencies. The radar gauge circuit generates a level output that is stabilized and corrected as a function of the frequency separation.
REFERENCES:
patent: 4044353 (1977-08-01), Levy
patent: 4737791 (1988-04-01), Jean et al.
patent: 4847623 (1989-07-01), Jean et al.
patent: 5563605 (1996-10-01), McEwan
patent: 5651286 (1997-07-01), Champion et al.
patent: 5659321 (1997-08-01), Burger et al.
patent: 5672975 (1997-09-01), Kielb et al.
patent: 5701006 (1997-12-01), Schaefer
patent: 5851083 (1998-12-01), Palan
patent: 6072427 (2000-06-01), McEwan
patent: 6087978 (2000-07-01), Lalla et al.
patent: 6107957 (2000-08-01), Cramer et al.
patent: 6130637 (2000-10-01), Meszaros et al.
patent: 6137438 (2000-10-01), McEwan
patent: 298 15 069 U (1998-12-01), None
patent: 98 14763 (1998-04-01), None
“Smart Transmitter Using Microwave Pulses to Measure the Level of Liquids and Solids in Process Applications,” H. Lang et al., OISA, pp. 731-742 (1993).
Electronics Designer's Handbook, 2nd Edition, Giacoletto, p. 25-10 (1977).
Rosemount Inc.
Sotomayor John B.
Westman Champlin & Kelly P.A.
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