US 5,406,842 A · Method and apparatus for material level measurement using stepped frequency microwave signals

Abstract

A method and apparatus for measuring a level of a material in a tank includes providing a stepped frequency microwave signal to an antenna of a transmitter and receiving in the antenna a received signal from a surface of the material at the level to be measured. A measuring signal containing ranging and calibrating signals is processed in even and odd sample sets input to contiguous narrowband filters formed digitally in a processor using DFT and other algorithms to form true in-phase and quadrature outputs. These outputs are combined and further processed using an interpolation algorithm to isolate ranging and calibration frequency components and to accurately measure the distances represented by such components. The calibration distance associated with the calibration frequency component is compared to a known delay line length and any determined error is used to correct the ranging distance associated with the ranging frequency component.

Claims12

Dependent claims

A method for measuring a level of a material in a tank, the method comprising the steps of:

providing a stepped frequency microwave signal to an antenna of a transmitter;
directing a transmitted signal toward the material in the tank;
receiving in the antenna a received signal from a surface of the material at the level to be measured;
mixing the received signal and the stepped frequency signal to produce a measuring signal;
sampling the measuring signal to produce measured samples;
multiplying the measured samples by stored weights;
separating odd and even numbered sample sets comprising in-phase and quadrature sample input sets, respectively, from the measured samples;
processing the in-phase and quadrature sample input sets in a bank of contiguous narrow band filters using a Fourier transform algorithm to produce a plurality of output records;
processing the plurality of output records in a signal processor to produce a ranging frequency signal and a calibration frequency signal;
and
determining the level of the material from the ranging frequency signal and the calibration frequency signal.

8 more elements

An apparatus for measuring a level of a material in a tank comprising:

an antenna;
a stepped frequency transmitted receiver coupled to the antenna wherein the stepped frequency transmitter/receiver comprises:
a microwave frequency generator;
a frequency select control coupled to the microwave frequency generator, the frequency select control for controlling the microwave frequency generator;
a mixer coupled to the microwave frequency generator, the mixer for mixing the second stepped frequency microwave signal and the first stepped frequency microwave signal to produce a measuring signal;
and
a filter/amplifier coupled to the mixer, the filter/amplifier for receiving the measuring signal and for producing a filter/amplifier output;
a delay line of calibrated length;
and
a coupler coupled to the delay line and to the antenna, wherein the first stepped frequency microwave signal introduced into the delay line produces a calibration frequency signal, the stepped frequency transmitter/receiver for providing a first stepped frequency microwave signal to the antenna to be transmitted to the level of the material in the tank, and the stepped frequency transmitter/receiver for receiving a second stepped frequency microwave signal in response;
and
a signal processor for processing a measuring signal derived from the stepped frequency microwave signal and the received signal to determine the level of the material in the tank, wherein the signal processor comprises:
an analog to digital (A/D) converter coupled to the filter/amplifier of the transmitter/receiver, the A/D converter for receiving the filter/amplifier output and for producing digital samples;
a digital multiplier coupled to the AID converter, the digital multiplier for multiplying the digital samples by a plurality of weights;
a discrete Fourier transform (DFT) coupled to the digital multiplier, the DFT for filtering the digital samples to produce output sample pairs;
a sample quadrature corrector coupled to the DFT, the sample quadrature corrector for sorting, combining, and phase correcting the output sample pairs;
and
a filter output magnitude calculator coupled to the sample quadrature corrector, the filter output magnitude calculator for converting the output sample pairs to output records.

15 more elements

Dependencies are inferred from the claim text.

Method and apparatus for material level measurement using stepped frequency microwave signals

Life of this patent

Method and apparatus for material level measurement using stepped frequency microwave signals

Life of this patent

Abstract

Claims12