Apparatus and method for measuring the level of a fluid

• US 20010035048A1
• Filed: 03/07/2001
• Published: 11/01/2001
• Est. Priority Date: 03/07/2000
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Gualtieri, Devlin M.
• Granted Patent: US 6,505,509 B2
• Time in Patent Office: Days
• US Class Current: 73/290V
• CPC Class Codes: G01F 23/284 Electromagnetic waves

Abstract

An apparatus for detecting a fluid level is disclosed, which includes a coaxial sensor having a pair of conducting tubes positioned with respect to each other in spaced coaxial arrangement, a coaxial transmission line connected to the sensor, a means for injecting a standing wave into the coaxial sensor, a summer for summing the injected wave and a reflected wave connected to the sensor, a means for adjusting the frequency of the injected wave in response to the voltage and phase of the summed signal, and a processor for processing and displaying the frequency as a representation of the level of the fluid. A method for detecting the fluid level is also disclosed.

Claims

1. An apparatus for detecting the level of a fluid, comprising:

a radio frequency transmission line;

a conductor proximate to the transmission line providing a return current path, wherein said conductor is spaced from the transmission line by insulating spacers to provide a characteristic impedance;

generating means for generating a standing wave, said generating means connected to the transmission line;

summing means for summing the standing wave and a reflected wave, said summing means connected between the generating means and the transmission line;

a detector for detecting the voltage and phase of the summed standing wave and reflected wave;

means for adjusting the frequency of the generating means in response to the voltage and phase of the summed signal; and

means for comparing the adjusted frequency with reference data for determining the level of the fluid.

2. The apparatus of

claim 1

, wherein the summing means is a “

T”

network, including;

a first resistor connected to the output of a voltage controlled oscillator;

a second resistor connected to a amplifier/detector; and

a third resistor connected to a system ground;

wherein each resistor is connected to the transmission line.

3. The apparatus of

claim 2

, wherein the impedance measured with respect to ground at any junction of the “

T”

network is between 50 and 300 ohms.

4. An apparatus for detecting the level of a fluid, comprising:

a radio frequency transmission line;

a conductor proximate to the transmission line providing a return current path, wherein said conductor is spaced from the transmission line by insulating spacers to provide a characteristic impedance;

generating means for generating a standing wave at a fixed frequency, said generating means connected to the transmission line;

summing means for summing the standing wave and a reflected wave, said summing means connected between the generating means and the transmission line;

a detector for detecting the voltage and phase of the summed standing wave and reflected wave; and

means for comparing the detected voltage and phase with reference data for determining the level of the fluid.

5. An apparatus for detecting a fluid level, comprising:

a coaxial sensor immersed in a fluid;

means for injecting a radio frequency wave into said coaxial sensor;

means for summing said injected wave and a reflected wave, said means electrically connected to said coaxial sensor;

means for adjusting the frequency of the injected wave in response to a voltage and phase of the summed signal; and

means for processing and displaying the frequency as a representation of fluid level.

6. The apparatus of

claim 5

, wherein the coaxial sensor comprises a first electrically conductive tube, and a second electrically conductive tube positioned within the first tube and secured by at least one insulator, wherein an inside diameter of the first tube is greater than an outside diameter of the second tube.

7. The coaxial sensor of

claim 6

, wherein the first tube is equal in length to the second tube.

8. An apparatus for detecting a fluid level, comprising:

a coaxial radio frequency transmission line sensor immersed in a fluid;

means for injecting a radio wave of a fixed frequency into said coaxial transmission line sensor;

means for summing said injected wave and a reflected wave, said means electrically connected to said coaxial radio frequency transmission line sensor;

means for detecting the voltage and phase of the result of the summing of the injected wave and reflected wave; and

means for comparing the detected voltage and phase with reference data for determining the level of the fluid.

9. The apparatus of

claim 8

, wherein the coaxial radio frequency transmission line sensor comprises a first electrically conductive tube, and a second electrically conductive tube positioned within the first tube and secured by at least one insulator, wherein an inside diameter of the first tube is greater than an outside diameter of the second tube.

10. An apparatus for detecting a fluid level, comprising:

a radio frequency transmission line;

a conductor proximate to the transmission line providing a return current path, wherein said conductor is spaced from the transmission line by insulating spacers to provide a characteristic impedance;

generating means for generating a standing wave, said generating means connected to the radio frequency transmission line;

summing means for summing the standing wave and a reflected wave, said summing means connected between the generating means and the transmission line;

an amplifier connected to the transmission line, for amplifying the sum of the standing wave and the reflected wave;

an A/D converter connected to an output of the amplifier; and

a computer connected to the A/D converter for processing digital data received from the A/D converter.

11. The apparatus of

claim 10

, wherein said standing wave source is a variable frequency oscillator.

12. The apparatus of

claim 10

, wherein said standing wave source is a constant frequency oscillator.

13. The apparatus of

claim 10

, wherein the summing means comprises a resistor network for measuring a voltage difference representing a relative change in the overall length of the apparatus created by a change in a level of the fluid to be measured.

14. A method for detecting a level of a fluid, comprising the steps of:

inserting a radio frequency transmission line into a fluid;

introducing a radio frequency voltage into the transmission line;

detecting a voltage that is the sum of the introduced radio frequency voltage and a standing wave voltage reflected by the end of the transmission line; and

determining the level of the fluid by comparing the summed voltage with stored fluid level reference data.

15. A method according to

claim 14

, wherein the introduced RF voltage has a constant frequency.

16. A method according to

claim 15

, further comprising the steps of adjusting the frequency of the standing wave voltage to determine at least one relative minimum or relative maximum voltage;

and

determining the level of the fluid by comparing the frequency of the detected relative minimum or relative maximum voltage with stored fluid level reference data.

17. An apparatus for detecting the level of a fluid, comprising:

a sensor having a first tube constructed of electrically conductive material having an inside diameter and a second tube constructed of electrically conductive material having an outside diameter, said outside diameter of the second tube being less than said inside diameter of the first tube, wherein said second tube is affixed inside of said first tube by insulating spacers;

a coaxial cable connected at a first end to said second tube;

generating means for generating a standing wave, said generating means connected to a second end of said coaxial cable for introducing the standing wave into the coaxial cable;

summing means for summing the standing wave and a reflected wave, said summing means connected to the second end of the coaxial cable;

a voltage detector for detecting a voltage of the summed standing wave and reflected wave; and

means for comparing the detected voltage level with reference data for determining the level of the fluid.

18. The apparatus of

claim 17

, wherein the summing means is a “

T”

network, including;

a first resistor connected to the output of a voltage controlled oscillator;

a second resistor connected to a amplifier/detector; and

a third resistor connected to a system ground;

wherein each resistor is connected to a second end of said coaxial cable.

19. The apparatus of

claim 17

, wherein an impedance of said coaxial cable is equal to an impedance of said sensor.

20. The apparatus of

claim 19

, wherein the impedance of the coaxial sensor is determined by the equation

Z=138 log₁₀ (b/a)

wherein “

b”

is the inner diameter of the first tube and “

a”

is the outer diameter of the second tube.