Ultrasonic liquid level monitor

• US 7,114,390 B2
• Filed: 02/17/2004
• Issued: 10/03/2006
• Est. Priority Date: 02/14/2003
• Status: Expired due to Fees

• Current Assignee: Adept Science & Technologies LLC
• Original Assignee: Adept Science & Technologies LLC
• Inventors: Lizon, David C., Kaduchak, Gregory, Sinha, Dipen N.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): FRANK, RODNEY T
• Application Number:
  US10/780,071
• Publication Number:
  US 20040173021A1
• Time in Patent Office: 959 Days
• Field of Search: 732/90.V, 732/90.R
• US Class Current: 73/290.00V
• CPC Class Codes: G01F 23/2961 for discrete levels G01F23/2962 - G01F23/2968 take precedence
• CPC Class Codes: G01F 23/2966 making use of acoustical resonance or standing waves
• CPC Class Codes: G01F 23/2967 for discrete levels

Abstract

The present invention includes an apparatus and method for continuous and point level liquid level detection in a closed container or pipe having an inaccessible interior volume such that it is difficult to retrofit these tanks with a level gauge that operates within the storage volume. The invention is based on a frequency domain analysis of the combined storage tank/fluid or pipe/fluid response to localized ultrasonic energy, and can be implemented using several excitation and signal analysis procedures, taking advantage of the transmission properties of the vessel wall in the vicinity of one of its longitudinal thickness resonances. Thus, significantly lower peak excitation voltages are required than with pulse-echo ultrasonic techniques.

Claims

1. An apparatus for measuring the level of a liquid having a surface in contact with a gas in a container, which comprises in combination:

(a) a transducer in physical contact with the outside of a wall of the container located below the surface of the liquid for generating at least two acoustic resonance responses in the liquid substantially perpendicular to the surface;

(b) a sweep generator for electrically exciting said transducer over a chosen range of acoustical frequencies and having a chosen waveform; and

(c) a receiver for measuring the acoustic frequencies for at least two resonant responses, whereby the level of the liquid is determined from the frequency difference between the frequencies of the resonant responses.

2. The apparatus for measuring liquid level in a container as described in claim 1, wherein the chosen waveform comprises a sine wave.

3. The apparatus for measuring liquid level in a container as described in claim 2, wherein the at least two resonant responses are analyzed by Fast Fourier Transform procedures.

4. The apparatus for measuring liquid level in a container as described in claim 1, wherein the chosen range of acoustical frequencies includes at least one acoustic wall resonance.

5. The apparatus for measuring liquid level in a container as described in claim 1, wherein the chosen waveform comprises a continuous frequency modulated waveform voltage excitation, V(t), having the form

$V$

( t ) = sin ⁡

( 2 ⁢

π

⁡

( f o + 1 2 ⁢

α

⁢

⁢

t ) ⁢

t ) ,

where t is the time, f_o is the initial frequency of the swept waveform, and α

is related to the rate of change of the instantaneous frequency, whereby a time-dependent response is produced in the liquid from which the liquid level is determined.

6. An apparatus for measuring the level of a liquid having a surface in contact with a gas in a container, which comprises in combination:

(a) means in physical contact with the outside of a wall of the container located below the surface of the liquid for generating at least two acoustic resonance responses in the liquid substantially perpendicular to the surface, and for determining the acoustic frequencies of at least two resonant responses; and

(b) means for electrically exciting said means for generating at least two acoustic resonance responses over a chosen range of acoustical frequencies and having a chosen waveform, whereby the level of the liquid is determined from the frequency difference between the frequencies of the resonant responses.

7. The apparatus for measuring liquid level in a container as described in claim 6, wherein said means for generating at least two acoustic resonance responses and for determining the acoustic frequencies of at least two resonant responses comprises an acoustic transducer and an acoustic receiver.

8. The apparatus for measuring liquid level in a container as describe in claim 6, wherein said means for electrically exciting said means for generating at least two acoustic resonance responses comprises a sweep generator.

9. The apparatus for measuring liquid level in a container as described in claim 6, wherein the chosen waveform comprises a sine wave.

10. The apparatus for measuring liquid level in a container as described in claim 9, wherein the at least two resonant responses are analyzed by Fast Fourier Transform procedures.

11. The apparatus for measuring liquid level in a container as described in claim 6, wherein the chosen range of acoustical frequencies includes at least one acoustic wall resonance.

12. The apparatus for measuring liquid level in a container as described in claim 6, wherein the chosen waveform comprises a continuous frequency modulated waveform voltage excitation, V(t), having the form

$V$

( t ) = sin ⁡

( 2 ⁢

π

⁡

( f o + 1 2 ⁢

α

⁢

⁢

t ) ⁢

t ) ,

where t is the time, f_o is the initial frequency of the swept waveform, and α

is related to the rate of change of the instantaneous frequency, whereby a time-dependent response is produced in the liquid from which the level is determined.

13. A method for measuring the level of a liquid having a surface in contact with a gas in a container, which comprises the steps of:

a. generating at least two acoustic resonances in the liquid substantially perpendicular to the surface of the liquid; and

b. determining the frequency of at least two acoustic resonances, whereby the level of the liquid is determined from the frequency difference between the frequencies of the acoustic resonances.

14. The method for measuring liquid level in a container as described in claim 13, wherein the acoustic resonances are generated using a waveform comprising a sine wave.

15. The method for measuring liquid level in a container as described in claim 14, wherein the sine wave is swept over frequencies comprising at least one acoustic wall resonance of a wall of the container perpendicular to the surface of the liquid.

16. The method for measuring liquid level in a container as described in claim 13, wherein the acoustic resonances are generated using a waveform comprising a continuous frequency modulated waveform voltage excitation, V(t), having the form:

$V<br><br>\left(t\right)=\sin <br><br>\left(2<br><br>\mathrm{\pi <br><br>}<br><br>\left(f_o+\frac{1}{2}<br><br>\mathrm{\alpha <br><br>}<br><br><br><br>t\right)<br><br>t\right),$

where t is the time, f_o is the initial frequency of the swept waveform, and α

is related to the rate of change of the instantaneous frequency, whereby a time-dependent response is produced in the liquid from which the liquid level is determined.

17. An apparatus for measuring the level of a liquid having a surface in contact with a gas in a container, which comprises in combination:

(a) a transducer in physical contact with the outside of a wall of the container located below the surface of the liquid for generating acoustic resonance responses in the liquid substantially parallel to the surface;

(b) a generator for electrically exciting said transducer; and

(c) a receiver for detecting the presence of resonant responses from the liquid, whereby if no resonant responses are detected, the level of the liquid is below said transducer.

18. An apparatus for measuring the level of a liquid having a surface in contact with a gas in a container, which comprises in combination:

(a) means in physical contact with the outside of a wall of the container located below the surface of the liquid for generating acoustic resonance responses in the liquid substantially parallel to the surface, and for detecting resonant responses; and

(b) means for electrically exciting said means for generating acoustic resonance responses, whereby if no resonance responses are detected, the level of the liquid is below said means for detecting resonant responses.

19. An apparatus for measuring the level of a liquid having a surface in contact with a gas in a container, which comprises in combination:

(a) means in physical contact with the outside of a wall of the container located below the surface of the liquid for generating acoustic resonance responses in the liquid substantially parallel to the surface;

(b) means for electrically exciting said means for generating acoustic resonance responses; and

(c) means for detecting the presence of resonant responses from the liquid, whereby if no resonant responses are present, the level of the liquid is below said means for detecting the presence of resonant responses.

20. A method for measuring the level of a liquid having a surface in contact with a gas in a container, which comprises the steps of:

(a) generating at least two acoustic resonances in the liquid substantially parallel to the surface of the liquid; and

(b) detecting the presence of acoustic resonances from the liquid whereby if no acoustic resonances are detected, the level of the liquid is below a location where said step of generating at least two acoustic resonances in the liquid can be performed.