Adaptive echo threshold

Patent metadata

Field	Value
Publication number	US-10775221-B2
Application number	US-201715720054-A
Country	US
Kind code	B2
Filing date	Sep 29, 2017
Priority date	Sep 29, 2017
Publication date	Sep 15, 2020
Grant date	Sep 15, 2020

Abstract

A radar level gauge comprising transceiver circuitry configured to obtain a tank signal including a peak representing a surface echo, and at least one peak caused by a ghost echo in a neighborhood of the surface echo. The gauge further includes a tank signal filter receiving the tank signal as input and providing an echo threshold profile, the threshold profile having at least one local maximum substantially coinciding with one of the peaks in the tank signal, and processing circuitry configured to use the echo threshold profile to disregard peaks in the tank signal which are associated with ghost reflections.
The filtering of the tank signal thus provides an adaptive threshold, which is aligned with the peak(s) in the tank signal. By using this threshold in the surface echo identification, at least some ghost echoes occurring in the tank signal may be disregarded.

First claim

What is claimed is:

1. A radar level gauge for determining a distance to a surface of a product in a tank, said gauge comprising:
transceiver circuitry configured to:
generate and transmit an electromagnetic transmit signal S T ,
receive an electromagnetic return signal reflected from the tank, and
combine the return signal with the transmit signal to form a tank signal, said tank signal including a plurality of peaks representing echoes from the interior of said tank, one of said peaks representing a surface echo, and at least one peak caused by a ghost echo in a neighborhood of said surface echo;

a tank signal filter receiving said tank signal as input and providing an echo threshold profile, said echo threshold profile representing a threshold as a function of distance to the surface and having at least one local maximum substantially coinciding with one of said peaks in said tank signal;
an echo tracking module configured to receive said tank signal and said echo threshold profile, and to identify a surface echo in the tank signal by comparison with said echo threshold profile, thereby disregarding peaks in said tank signal which are associated with ghost reflections; and
processing circuitry configured to:
determine said distance based on said surface echo.

2. The radar level gauge according to claim 1 , wherein said processing circuitry is configured to distinguish a surface echo from other echoes in the tank signal by:
identifying a set of echoes in the tank signal, and
selecting said surface echo as one of the echoes in said set,
wherein said threshold profile serves to reduce a number of echoes in said set.

3. The radar level gauge according to claim 1 , wherein said echo threshold profile has a continuous derivative.

4. The radar level gauge according to claim 1 , wherein the filter is parametrized, and includes parameters representing at least width above peak and width below peak, said parameters being selected to ensure that the resulting threshold profile exceeds ghost echoes surrounding a strong peak.

5. The radar level gauge according to claim 1 , further including a directional antenna connected to the transceiver circuitry, said directional antenna intended to be mounted in a top of said tank to emit the transmit signal towards said surface.

6. The radar level gauge according to claim 1 , further including a transmission line probe connected to the transceiver circuitry, said transmission line probe intended to be suspended in the tank and extend beyond said surface.

7. The radar level gauge according to claim 1 , wherein said tank signal is a frequency domain signal.

8. The radar level gauge according to claim 7 , wherein said transmit signal is a frequency modulated continuous wave (FMCW).

9. The radar level gauge according to claim 1 , wherein said transmit signal is a train of distinct pulses, and said tank signal is a time domain signal.

10. A method implemented in a radar level gauge, for determining a process variable of product in a tank, comprising the steps of:
generating an electromagnetic transmit signal and allowing it to propagate into the tank,
receiving an electromagnetic return signal caused by a reflection of said transmit signal in the tank,
combining the return signal with the transmit signal to form a tank signal, said tank signal including a plurality of peaks representing echoes from the interior of said tank, one of said peaks representing a surface echo, and at least one peak caused by a ghost echo in a neighborhood of said surface echo,
filtering the tank signal to provide an echo threshold profile, said threshold profile representing a threshold as a function of distance to the surface and having at least one local maximum substantially coinciding with one of said peak in said tank signal, and
processing said tank signal to distinguish said surface echo from other echoes, and determine said process variable based on said surface echo,
wherein said echo threshold profile is used in said processing to disregard peaks in said tank signal which are associated with ghost echoes.

11. The method according to claim 10 , wherein the step of processing the tank signal includes:
identifying a set of echoes, and
selecting said surface echo as one of the echoes in said set,
wherein said echo threshold profile serves to reduce a number of echoes in said set.

12. The method according to claim 10 , wherein said echo threshold profile has a continuous derivative.

13. The method according to claim 10 , wherein the step of filtering the tank signal includes applying a filter having a set of adjustable parameters, and wherein said adjustable parameters are set based on characteristics of ghost echoes occurring in a particular radar level gauge.

14. The method according to claim 10 , wherein said tank signal is a frequency domain signal.

15. The method according to claim 14 , wherein said transmit signal is a frequency modulated continuous wave (FMCW).

16. The method according to claim 10 , wherein said transmit signal is a train of distinct pulses, and said tank signal is a time domain signal.

Assignees

• Rosemount Tank Radar Ab

Inventors

• Blomberg Urban
• Larsson Lars Ove
• Delin Håkan

Classifications

• G01S7/2922

  by using a controlled threshold · CPC title

• 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

• G01S13/18

  wherein range gates are used · CPC title

• G01F23/284 Primary

  Electromagnetic waves · CPC title

• G01S7/354

  Extracting wanted echo-signals (Doppler systems G01S13/50) · CPC title