Apparatus and method for measuring the level of a fluid

• US 6,505,509 B2
• Filed: 03/07/2001
• Issued: 01/14/2003
• Est. Priority Date: 03/07/2000
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Gualtieri, Devlin M.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): WILSON, KATINA M
• Application Number:
  US09/800,548
• Publication Number:
  US 20010035048A1
• Time in Patent Office: 678 Days
• Field of Search: 732/90.R, 732/90.V, 73/17.3, 73/18.3, 735/49, 340/621, 367/87, 367/95, 367/189, 324/323, 324/601, 324/76.11, 324/92, 181/124
• US Class Current: 73/290.00V
• 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 and comprising:

a radio frequency transmission line comprising an inner conductor and an outer conductor proximate to said inner conductor and providing a return current path, wherein the outer conductor is spaced from the inner conductor by insulating spacers to provide a characteristic impedance;

generating means connected to the inner conductor for injecting an injected wave into the transmission line;

summing means for creating a standing wave which is the sum of the injected wave and a reflected wave reflected by the end of the transmission line, said summing means being connected between the generating means and the transmission line;

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

means for adjusting the frequency of the generating means in response to the voltage and phase of the standing wave; and

means for comparing the adjusted frequency with reference data for determining the level of the fluid between the inner and outer conductors.

2. The apparatus of claim 1 wherein the transmission line is a coaxial sensor and the inner conductor is a first cylinder and the outer conductor is a second cylinder encompassing the first cylinder.

3. The apparatus of claim 2 wherein at least the outer surface of the first cylinder and the inner surface of the second cylinder are Teflon coated.

4. The apparatus of claim 2 further including an end plug having small entry holes therein positioned between the first and second cylinders.

5. The apparatus of claim 2 further comprising a glass tube between the first and second cylinders.

6. The apparatus of claim 1, wherein the summing means is a “

T”

network including;

a first resistor connected to the output of a variable frequency oscillator;

a second resistor connected to an amplifier/detector; and

a third resistor connected to a system ground, and wherein each resistor is connected to the transmission line.

7. The apparatus of claim 6 wherein each resistor is connected to the transmission line through an intermediate coaxial cable.

8. The apparatus of claim 6, wherein the impedance measured with respect to ground at any junction of the “

T”

network is between 50 and 300 ohms.

9. An apparatus for detecting the level of a fluid and comprising:

a coaxial sensor defining a radio frequency transmission line and including an inner conductor and an outer conductor encompassing the inner conductor and providing a return current path, said outer conductor being spaced from said inner conductor by insulating spacers to provide a characteristic impedance and the fluid whose level is to be measured being placed between said inner and said outer conductors;

generating means connected to the inner conductor for injecting an injected wave into the transmission line;

summing means for creating a standing wave which is the sum of the injected wave and a reflected wave reflected from the end of the transmission line, said summing means being connected between the generating means and the transmission line;

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

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

10. An apparatus for detecting a fluid level and comprising

a coaxial sensor comprising an inner conductor and an outer conductor encompassing said inner conductor, the fluid whose level is to be detected being between said inner and said outer conductors;

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

means for summing said injected wave and a reflected wave reflected from the end of the coaxial sensor, said summing means being 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 injected and reflected waves; and

mean for processing the frequency and based thereon displaying a representation of the fluid level.

11. The apparatus of claim 10 wherein said injecting means and said summing means are connected to said coaxial sensor through an intermediate coaxial cable.

12. The apparatus of claim 10 wherein said inner and outer conductors comprise a first and a second electrically conductive tube respectively, the first tube being positioned within the second tube and secured by at least one insulator, wherein an inside diameter of the second tube is greater than an outside diameter of the first tube.

13. The apparatus of claim 12 wherein the first tube is equal in length to the second tube.

14. An apparatus for detecting a fluid level and comprising:

a coaxial radio frequency transmission line sensor in which is the fluid whose level is to be detected;

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 reflected from the end of said of said coaxial radio frequency transmission line sensor, said summing means being 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 the reflected wave; and

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

15. The apparatus of claim 14, 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 and the fluid whose level is to be detected is between said first and second tubes.

16. An apparatus for detecting a fluid level and comprising:

a radio frequency transmission line comprising an inner conductor and an outer conductor providing a return path and spaced from the inner conductor by insulating spacers to provide a characteristic impedance, the fluid whose level is to be detected being between the inner and outer conductors;

a source for generating and injecting an injected wave into the radio frequency transmission line;

summing means for summing the injected wave and a reflected wave, said summing means being connected between the source and the transmission line;

an amplifier connected to the transmission line for amplifying the sum of the injected weave and the reflected wave;

an analog-to-digital converter connected to the output of the amplifier; and

a computer connected to the analog-to-digital converter for processing the digital data received from the analog-to-digital converter.

17. The apparatus of claim 16, wherein said source is a variable frequency oscillator.

18. The apparatus of claim 16, wherein said source is a constant frequency oscillator.

19. The apparatus of claim 16, wherein the summing means comprises a resistor network for measuring a voltage difference representing a relative change in the position of the fluid level between the inner and outer conductors.

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

locating the fluid between the inner and outer conductors of a radio frequency transmission line;

introducing a radio frequency voltage into the transmission line;

detecting a voltage that is a sum of the introduced radio frequency voltage and a reflected 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.

21. The method according to claim 20, wherein introduced radio frequency voltage has a constant frequency.

22. The method according to claim 20, further comprising the steps of

adjusting the frequency of the injected wave voltage to determine at least one relative minimum or 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.

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

a coaxial 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 to said first tube by insulating spacers;

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

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

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

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

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

24. The apparatus of claim 23 wherein said reflected wave is reflected from the end of said coaxial sensor and the fluid whose level is to be detected is between said first and said second tubes of said coaxial sensor.

25. The apparatus of claim 23, wherein the summing means is a “

T”

network including;

a first resistor connected to the output of a variable frequency oscillator;

a second resistor connected to an amplifier/detector; and

a third resistor connected to a system ground, and wherein each resistor is connected to the second end of said coaxial cable.

26. The apparatus of claim 23, wherein an impedance of said coaxial cable is equal to an impedance of said coaxial sensor.

27. The apparatus of claim 26, 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.