Radar level gauge system and method with transmission line probe and stepped frequency sweep

Patent metadata

Field	Value
Publication number	US-2023063153-A1
Application number	US-202217859108-A
Country	US
Kind code	A1
Filing date	Jul 7, 2022
Priority date	Aug 24, 2021
Publication date	Mar 2, 2023
Grant date	—

Abstract

A method of determining a filling level of a product in a tank, comprising the steps of: generating an electromagnetic transmit signal exhibiting a measurement sweep across a time series of piece-wise constant frequencies being within a measurement frequency range starting at a first frequency, and ending at a second frequency higher than the first frequency, a difference between frequencies in each pair of adjacent frequencies in the frequency range being equal to the first frequency; guiding the transmit signal towards and into the product in the tank; guiding an electromagnetic reflection signal back towards the transceiver; mixing the reflection signal with an electromagnetic reference signal, resulting in a mixer output indicative of a difference between the reflection signal and the reference signal; forming a measurement signal based on the mixer output; and determining the filling level based on the measurement signal.

First claim

What is claimed is:

1 . A method of determining a filling level of a product in a tank using a radar level gauge system comprising a transceiver, a transmission line probe, and processing circuitry, the method comprising the steps of:
generating an electromagnetic transmit signal exhibiting a measurement sweep across a time series of piece-wise constant frequencies being within a measurement frequency range starting at a first frequency, and ending at a second frequency higher than the first frequency, a difference between frequencies in each pair of adjacent frequencies in the frequency range being equal to the first frequency; guiding the transmit signal towards and into the product in the tank; guiding an electromagnetic reflection signal resulting from reflection of the transmit signal at impedance discontinuities encountered thereby, back towards the transceiver; mixing the reflection signal with an electromagnetic reference signal exhibiting a reference sweep across a time series of piece-wise constant reference frequencies, the reference signal being in phase with the transmit signal at a start of the measurement sweep and exhibiting a constant frequency difference in relation to the transmit signal across the measurement sweep, the mixing resulting in a mixer output indicative of a difference between the reflection signal and the reference signal; forming a measurement signal based on the mixer output; and determining the filling level based on the measurement signal.

2 . The method according to claim 1 , wherein the step of forming the measurement signal comprises the steps of:
measuring an amplitude and a phase of the mixer output for each frequency of the transmit signal; forming a frequency domain measurement signal indicative of the amplitude and the phase of the mixer output as a function of the frequency of the transmit signal; and transforming the frequency domain measurement signal to a time domain measurement signal.

3 . The method according to claim 2 , wherein the step of the forming the frequency domain measurement signal further comprises the step of:
adding mirrored data sets for negative frequencies, each mirrored data set for a negative frequency value being a complex conjugate of a data set of the measured amplitude and phase of the mixer output for the corresponding positive frequency value.

4 . The method according to claim 2 , wherein the step of transforming includes performing inverse digital fourier transformation on the frequency domain measurement signal.

5 . The method according to claim 1 , further comprising the step of:
filtering at least one of the mixer output and the measurement signal using a bandpass filter having a passband including a frequency being identical to the frequency difference between the reference signal and the transmit signal.

6 . The method according to claim 1 , wherein the frequency difference between the reference signal and the transmit signal is non-zero.

7 . The method according to claim 1 , wherein the first frequency of the measurement sweep is in the range0.5 MHz to 4 MHz.

8 . The method according to claim 1 , wherein the second frequency of the measurement sweep is in the range 500 MHz to 4 GHz.

9 . A radar level gauge system, for determining a filling level of a product in a tank, the radar level gauge system comprising:
a transceiver for generating, transmitting, and receiving electromagnetic signals; a transmission line probe coupled to the transceiver and configured to guide an electromagnetic transmit signal from the transceiver towards and into the product in the tank, and guide an electromagnetic reflection signal resulting from reflection of the transmit signal at impedance discontinuities encountered thereby, back towards the transceiver; and processing circuitry coupled to the transceiver for determining the filling level based on a timing relation between the reflection signal and the transmit signal, wherein the radar level gauge system is configured to:
generate the transmit signal to include a measurement sweep across a time series of piece-wise constant frequencies being within a measurement frequency range starting at a first frequency, and ending at a second frequency higher than the first frequency, a difference between frequencies in each pair of adjacent frequencies in the frequency range being equal to the first frequency;
mix the reflection signal with an electromagnetic reference signal exhibiting a reference sweep across a time series of piece-wise constant reference frequencies, the reference signal being in phase with the transmit signal at a start of the measurement sweep and exhibiting a constant frequency difference in relation to the transmit signal across the measurement sweep, the mixing resulting in a mixer output indicative of a difference between the reflection signal and the reference signal;
form a measurement signal based on the mixer output; and
determine the filling level based on the measurement signal.

10 . The radar level gauge system according to claim 9 , wherein the radar level gauge system is configured to:
form a frequency domain measurement signal indicative of an amplitude and a phase of the mixer output as a function of the frequency of the transmit signal; and transform the frequency domain measurement signal to a time domain measurement signal.

11 . The radar level gauge system according to claim 10 , wherein the radar level gauge system is configured to form the frequency domain measurement signal by determining data sets of the amplitude and phase of the mixer output for different frequencies of the transmit signal and adding mirrored data sets for negative frequencies, each mirrored data set for a negative frequency value being a complex conjugate of a data set of the measured amplitude and phase of the mixer output for the corresponding positive frequency value.

12 . The radar level gauge system according to claim 10 , wherein the radar level gauge system is configured to transform the frequency domain measurement signal to the time domain measurement signal by performing inverse digital fourier transformation on the frequency domain measurement signal.

13 . The radar level gauge system according claim 9 , wherein the transceiver further comprises a bandpass filter arranged and configured to filter one of the mixer output and the measurement signal.

14 . The radar level gauge system according to claim 9 , wherein the transmission line probe is a single conductor probe configured to guide the transmit signal and the reflection signal as surface waves.

15 . The radar level gauge system according to claim 9 , wherein the transmission line probe is one of a coaxial probe and a parallel wire transmission line probe.

Assignees

• Rosemount Tank Radar Ab

Inventors

• Eriksson Mikael

Classifications

• G01S13/88

  Radar or analogous systems specially adapted for specific applications (electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00) · CPC title

• G01S7/003

  Transmission of data between radar, sonar or lidar systems and remote stations · CPC title

• G01S7/41

  using analysis of echo signal for target characterisation; Target signature; Target cross-section · CPC title

• G01S13/347

  using more than one modulation frequency · CPC title

• G01S7/352

  Receivers · CPC title