Communications: directive radio wave systems and devices (e.g. – Determining distance – Material level within container
Reexamination Certificate
2002-08-01
2003-09-30
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
Material level within container
C342S175000, C073S29000R
Reexamination Certificate
active
06628229
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods and apparatus for measuring liquid or granular solids product levels in containers. In particular, the present invention relates to stabilization of oscillators in low power pulsed radar level transmitters.
BACKGROUND OF THE INVENTION
Low power pulsed radar level transmitters typically include transmit and receive oscillators that are offset from one another by a frequency offset. The stability of the radar level transmitter output depends on stabilizing the frequency offset. In one stabilization scheme, one of the two oscillators has been used to control the frequency of the other oscillator in an effort to stabilize the offset frequency. In another stabilization scheme, the frequency offset is sensed and used to control the frequency of one of the oscillators in an effort to stabilize the offset frequency. High power stabilization techniques with complex circuitry or crystal ovens cannot be used without exceeding the power supply limitations of an energy limited 4-20 mA loop that powers the level transmitter. The stabilization achieved within the power limitation has been inadequate, and a method and apparatus are needed that can stabilize a frequency offset without using power or energization in excess of that available from a two wire, 4-20 mA loop that provides all of the power or energization to the radar level transmitter.
SUMMARY OF THE INVENTION
Disclosed is a level transmitter that includes a first pullable oscillator circuit that provides a transmit frequency output, and a second pullable oscillator circuit that provides a receive frequency output. The receive frequency output is offset from the transmit frequency output by a frequency offset.
A first pulse generator receives the transmit frequency output and provides microwave transmit pulses couplable to the product level. A second pulse generator receives the receive frequency output and provides microwave gating pulses.
A gate receives the microwave gating pulses and is coupled to the product level for receiving microwave transmit pulses reflected back from the product level that are delayed by a reflection delay time. The gate provides a gated delayed pulse output. A controller receives the gated delayed pulse output and provides a level output representative of the product level.
A reference crystal oscillator circuit provides a reference frequency output that couples to the first and second pullable oscillators. The transmit and receive frequency outputs are pulled as functions of the reference frequency output.
REFERENCES:
patent: 5563605 (1996-10-01), McEwan
patent: 5589838 (1996-12-01), McEwan
patent: 5609059 (1997-03-01), McEwan
patent: 5610611 (1997-03-01), McEwan
patent: 5672975 (1997-09-01), Kielb et al.
patent: 5774091 (1998-06-01), McEwan
patent: 6055287 (2000-04-01), McEwan
patent: 6072427 (2000-06-01), McEwan
patent: 6107957 (2000-08-01), Cramer et al.
patent: 6137438 (2000-10-01), McEwan
patent: 6191724 (2001-02-01), McEwan
patent: 6281833 (2001-08-01), Pringle et al.
patent: 6300897 (2001-10-01), Kielb
patent: 6320532 (2001-11-01), Diede
patent: 6373261 (2002-04-01), Kielb et al.
patent: 298 15 069 (1999-02-01), None
“Phase-Locked Loop Design Fundamentals”, by G. Nash et al., Motorola Semiconductor Application Note, AN535, 1994, pp. 1-12.
“The MC145170 in Basic HF and VHF Oscillators”, by D. Babin et al., Motorola Semiconductor Technical Data, AN1207, 1998, pp. 1-6.
“Offset Reference PLLs for Fine Resolution or Fast Hopping”, by M. Smith, Motorola Semiconductor Technical Data, AN1277, 1996, pp. 1-8.
“MC145170 PSpice Modeling Kit”, by O. Cogburn, Motorola Semiconductor Application Note, AN1671, 1998, pp. 1-16.
“PLL Frequency Synthesizer with Serial Interface”, Motorola Intelligence Everywhere, MC145170-2, 1999, pp. 1-26.
Webpages entitled “MC145170-2: PLL Frequency Synthesizer with Serial Interface”, 2 pgs.
Electronic Designers' Handbook, First Edition by R. Landee et al., p. 25-10.
“Novel Methods of Measuring Impurity Levels in Liquid Tanks”, by M. Weiss et al.,IEEE MTT-S Digest, 1997, pp. 1651-1654.
Johnson James A.
Lovegren Eric R.
Rosemount Inc.
Sotomayor John B.
Westman Champlin & Kelly P.A.
LandOfFree
Stabilization of oscillators in a radar level transmitter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Stabilization of oscillators in a radar level transmitter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Stabilization of oscillators in a radar level transmitter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3079838