Radar tank gauge

• US 4,737,791 A
• Filed: 02/19/1986
• Issued: 04/12/1988
• Est. Priority Date: 02/19/1986
• Status: Expired due to Fees

• Current Assignee: IDEA, Inc.
• Original Assignee: IDEA, Inc.
• Inventors: Warren, Gary L., Jean, Buford R., Newton, Richard W., Clark, Billy V., Blanchard, Andrew J.
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): GREGORY, BERNARR E
• Application Number:
  US06/831,369
• Time in Patent Office: 783 Days
• Field of Search: 343/5 FT, 343/12 R, 343/14, 343/17.7, 73/290 R, 342/118, 342/120, 342/123, 342/124, 342/165, 342/172, 342/192, 342/193, 342/195-197
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal

Abstract

A sweep frequency, continuous wave (CW) radar tank gauge (3) providing measurement of the level of tank contents or ullage (19), having greatly improved accuracy through improved methods of processing calibrate and return signals directed toward the surface of tank contents (20). Use of sweep synchronous measurement (46) of time domain calibrate/return difference signals (42) and determination of a virtual "carrier" fundamental in the frequency domain, provide highly accurate measure of tank signal return times. The entire range of return signals is made available for processing and analysis (5), including distinguishable tank bottom reflections.

Claims

1. In a radar tank gauge having a directional antenna mounted in predetermined proximity to the surface of the tank contents, for transmitting a continuous wave swept frequency radio frequency signal to said surface, said gauge including simultaneous measurement and comparison of signals transmitted to and reflected from said surface, and generating a difference signal representive of the distance between the antenna and tank level, the improvement comprising;

means generating a periodic first measuring signal of predetermined frequency and duration;

means transmitting said first measuring signal to said surface;

means receiving the reflected first signal and generating a first return signal;

means generating a first difference signal representative of the frequency difference between said first signal and first return signal;

means measuring the frequency of said first difference signal in time phase synchronization with said transmitted measuring signal;

means storing groups of said measured first difference signals, said groups having a predetermined time period;

means transforming said first difference signal groups from time to frequency domain, thereby generating a power spectral density representation of said first difference signal;

means determining the frequency centroid of said transformed first difference signal, thereby generating a first carrier frequency value, said value closely representative of a true first difference frequency;

means simultaneously applying said first measuring signal to a delay line thereby generating a second reflected signal and second return signal, said second return signal representative of a known distance;

means deriving a second signal representative of the frequency difference between said first measuring signal and second return signal;

means measuring said second difference signal, said measurement having an interval in time phase synchronization with said first signal;

means storing said groups of said measured second difference signals, said groups having a predetermined time period;

means transforming said stored second difference signal groups from time to frequency domain, thereby generating a power spectral density representation of said second difference signal;

means determining the frequency centroid of said transformed second difference signal whereby a second carrier frequency closely representative of said known distance is determined;

means comparing said first and second carrier frequencies and generating a coefficient representative of the distance between said antenna and tank level;

means applying said coefficient to said known delay line length;

whereby said known distance is converted to said antenna/tank distance.

2. The improvement of claim 1 further comprising;

means storing a predetermined value of said coefficient, said coefficient representing a predetermined limit of said antenna/tank level distance;

means comparing said stored and antenna/surface distances;

whereby coefficients greater than said stored value are disregarded.