RADAR LIQUID LEVEL DETECTION USING STEPPED FREQUENCY PULSES

• US 20110163910A1
• Filed: 02/19/2007
• Published: 07/07/2011
• Est. Priority Date: 02/22/2006
• Status: Active Grant

• Current Assignee: Enraf B. V.
• Original Assignee: Enraf B. V.
• Inventors: Sai, Bin
• Granted Patent: US 8,319,680 B2
• Time in Patent Office: Days
• 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
• CPC Class Codes: G01S 13/36 with phase comparison between the received signal and the contemporaneously transmitted signal

Abstract

The invention relates to a method for accurately determining the level L of a liquid by means of radar signals emitted to the liquid surface and radar signals reflected from the liquid surface. The invention further relates to a device for accurately determining the level of a liquid by means of the method according to the invention, which device comprises at least a radar antenna disposed above the liquid for emitting radar signals to the liquid and receiving radar signals reflected from the liquid surface, as well as means for determining the liquid level on the basis of the emitted radar signals and the reflected radar signals.

Claims

1. A method for accurately determining a level of a liquid comprising:

emitting radar signals towards the liquid, the emitted radar signals having multiple frequencies and multiple first phases;

receiving radar signals reflected from the liquid, the reflected radar signals having the multiple frequencies and multiple second phases;

determining multiple phase differences between the emitted radar signals and the reflected radar signals; and

deriving the level of the liquid based on the phase differences.

2. The method according to claim 1, wherein deriving the level of the liquid comprises:

determining a frequency difference between successively emitted and received radar signals having different frequencies; and

determining a phase shift between the phase differences associated with the successively emitted and received radar signals.

3. The method according to claim 2, wherein deriving the level of the liquid further comprises:

deriving a less accurate level value based on the frequency difference and the phase shift.

4. The method according to claim 3, wherein deriving the level of the liquid further comprises:

deriving a value of a wrapping factor between the emitted radar signals and the reflected radar signals based on the less accurate level value.

5. The method according to claim 4, wherein the value of the wrapping factor is rounded to a nearest integer.

6. The method according to claim 4, wherein the level of the liquid is determined based on the value of the wrapping factor and at least one of the phase differences.

7. The method according to claim 4, wherein the level of the liquid is determined by:

L=Δ

φ

_1tv/(4π

f₁)

wherein L represents the level of the liquid;

wherein v represents a velocity of the radar signals through a medium;

wherein f₁ represents a first frequency of the radar signals; and

wherein Δ

φ

_1t represents an actual phase difference between the emitted radar signal having the first frequency and the reflected radar signal having the first frequency.

8. The method according to claim 7, wherein the less accurate level value is determined by:

L′

=Δ

ψ

_1-2v/(4π

Δ

f₁₂)

wherein L′

represents the less accurate level value;

wherein Δ

f₁₂ represents the frequency difference between the first frequency of the radar signals and a second frequency of the radar signals; and

wherein Δ

ψ

_1-2 represents the phase shift between the phase difference associated with the first frequency of the radar signals and the phase difference associated with the second frequency of the radar signals.

9. The method according to claim 8, wherein the actual phase difference is determined by:

Δ

φ

_1t=Δ

φ

₁+2kπ

wherein Δ

φ

₁ represents a measured phase difference between the emitted radar signal having the first frequency and the reflected radar signal having the first frequency; and

wherein k represents the value of the wrapping factor.

10. The method according to claim 9, wherein the value of the wrapping factor is determined by

k=|2fL′

/v|

wherein f represents one of the frequencies of the radar signals.

11. A system for accurately determining a level of a liquid comprising:

a radar antenna configured to emit radar signals to the liquid and to receive radar signals reflected from the liquid, the emitted radar signals having multiple frequencies and multiple first phases, the reflected radar signals having the multiple frequencies and multiple second phases; and

a processing unit configured to determine the level of the liquid based on the emitted radar signals and the reflected radar signals, wherein the processing unit is configured to determine the level of the liquid by determining multiple phase differences between the emitted radar signals and the reflected radar signals and deriving the level of the liquid based on the phase differences.

12. The system according to claim 11, wherein the processing unit is configured to derive the level of the liquid by:

determining a frequency difference between successively emitted and received radar signals having different frequencies; and

determining a phase shift between the phase differences associated with the successively emitted and received radar signals.

13. The system according to claim 12, wherein the processing unit is configured to derive the level of the liquid further by:

deriving a less accurate level value based on the frequency difference and the phase shift; and

deriving a value of a wrapping factor between the emitted radar signals and the reflected radar signals based on the less accurate level value.

14. The system according to claim 13, wherein the processing unit is configured to determine the level of the liquid based on the value of the wrapping factor and at least one of the phase differences.

15. The system according to claim 14, wherein the processing unit is configured to determine the level of the liquid using an equation:

L=Δ

φ

_1tv/(4π

f₁)

wherein L represents the level of the liquid;

wherein v represents a velocity of the radar signals through a medium;

wherein f₁ represents a first frequency of the radar signals; and

wherein Δ

φ

_1t represents an actual phase difference between the emitted radar signal having the first frequency and the reflected radar signal having the first frequency.

16. The system according to claim 15, wherein the processing unit is configured to determine the less accurate level value using an equation:

L′

=Δ

ψ

_1-2v/(4π

Δ

f₁₂)

wherein L′

represents the less accurate level value;

wherein Δ

f₁₂ represents the frequency difference between the first frequency of the radar signals and a second frequency of the radar signals; and

wherein Δ

ψ

_1-2 represents the phase shift between the phase difference associated with the first frequency of the radar signals and the phase difference associated with the second frequency of the radar signals.

17. The system according to claim 16, wherein the processing unit is configured to determine the actual phase difference using an equation:

Δ

φ

_1t=Δ

φ

₁+2kπ

wherein Δ

φ

₁ represents a measured phase difference between the emitted radar signal having the first frequency and the reflected radar signal having the first frequency; and

wherein k represents the value of the wrapping factor.

18. The system according to claim 17, wherein the processing unit is configured to determine the value of the wrapping factor using an equation

k=|2fL′

/v|

wherein f represents one of the frequencies of the radar signals.

19. A device comprising a processing unit, the processing unit configured to determine a level of a liquid based on emitted radar signals and reflected radar signals, the emitted radar signals having multiple frequencies and multiple first phases, the received radar signals having the multiple frequencies and multiple second phases;

wherein the processing unit is configured to determine the level of the liquid by determining multiple phase differences between the emitted radar signals and the reflected radar signals and deriving the level of the liquid based on the phase differences.

20. The device of claim 19, wherein the processing unit is configured to derive the level of the liquid by:

determining a frequency difference between successively emitted and received radar signals having different frequencies;

determining a phase shift between the phase differences associated with the successively emitted and received radar signals;

deriving a less accurate level value based on the frequency difference and the phase shift;

deriving a value of a wrapping factor between the emitted radar signals and the reflected radar signals based on the less accurate level value; and

determining the level of the liquid based on the value of the wrapping factor and at least one of the phase differences.