System and method for optimizing sweep delay and aliasing for time domain reflectometric measurement of liquid height within a tank

• US 8,794,063 B2
• Filed: 12/03/2009
• Issued: 08/05/2014
• Est. Priority Date: 01/08/2007
• Status: Active Grant

• Current Assignee: Meggitt Safety Systems, Inc. (Meggitt PLC)
• Original Assignee: Meggitt Incorporated (Amphenol Corporation)
• Inventors: Miskell, Thomas J., Tan, Zhenyu, Petriel, Kevin J., Carvalho, Carlos E., Lavon, Ronie
• Primary Examiner(s): Williams, Hezron E
• Assistant Examiner(s): KOLB, NATHANIEL J
• Application Number:
  US12/630,305
• Publication Number:
  US 20100153029A1
• Time in Patent Office: 1,706 Days
• Field of Search: 732/90.V
• US Class Current: 73/290.V
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/18 wherein range gates are used

Abstract

A layer height measuring system in one embodiment has a transmission line including a probe for measuring a height of a first layer within a tank and a cable that connects the probe to an electronics unit. The electronics unit cyclically transmits interrogation pulses to the probe and receives reflections therefrom for time domain reflectometric measurement of the height of the first layer. The layer height measuring system may also have a memory and a processor configured by the memory to perform the steps of detecting first and second impedance transitions corresponding to first and second boundaries of a bounded region of known length; optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only within the bounded region; and detecting a third impedance transition within the bounded region, the third impedance transition corresponding to an interface between the first layer and a second layer, the first and second layers having respectively different dielectric constants.

Claims

1. A layer height measuring system comprising:

a transmission line including

a probe for measuring a height of a first layer within a tank and

a cable that connects the probe to an electronics unit;

the electronics unit cyclically transmitting interrogation pulses to the probe and receiving reflections therefrom for time domain reflectometric measurement of the height of the first layer;

a memory; and

a processor configured by the memory to perform the steps of;

detecting first and second impedance transitions corresponding to first and second boundaries of a bounded region of known length;

optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only within the bounded region; and

detecting a third impedance transition within the bounded region, the third impedance transition corresponding to an interface between the first layer and a second layer, the first and second layers having respectively different dielectric constants,

wherein at least one of said first and second impedance transitions comprises a fluid-fluid interface.

2. A layer height measuring system according to claim 1, wherein the height of at least one of the layers is determined by converting a time domain height to a space domain height carried out by an impedance-based compensation for dielectric constant.

3. A layer height measuring system according to claim 1, wherein the height of the first layer is measured directly using a spatial profile thereof.

4. A layer height measuring system according to claim 1, wherein the height of the first layer is measured directly using a time of flight therethrough.

5. A layer height measuring system according to claim 1 wherein the height of the first layer is measured indirectly by process of elimination from the known length of the bounded region less the measured height of the second layer.

6. A layer height measuring system according to claim 5 wherein the height of the second layer is measured directly using a spatial profile thereof.

7. A layer height measuring system according to claim 5 wherein the height of the second layer is measured directly using a time of flight therethrough.

8. A layer height measuring system according to claim 1 wherein the height of the first layer is measured indirectly by process of elimination so that the measurement of the height of the first layer is insensitive to the dielectric constant of the first layer.

9. A layer height measuring system according to claim 1 wherein

the bounded region of known length is a liquid layer;

the first and second boundaries of the bounded region are respectively the top and the bottom of the liquid layer;

and the interface between layers having respectively different dielectric constants is a liquid-liquid interface.

10. A layer height measuring system according to claim 1 wherein the first and second boundaries of the bounded region are respectively locked onto and tracked in closed-loop fashion.

11. A method for measuring the height of a layer with a layer height measuring system comprising a transmission line including a probe for measuring a height of a first layer within a tank, comprising the steps of:

detecting first and second impedance transitions corresponding to first and second boundaries of a bounded region of known length;

optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only within the bounded region; and

detecting a third impedance transition within the bounded region, the third impedance transition corresponding to an interface between the first layer and a second layer, the first and second layers having respectively different dielectric constants,

wherein the detection of the third impedance transition is carried out using a spatial profile method when a signal-to-noise ratio thereof is good, but is carried out using a time-of-flight method when the signal-to-noise ratio of the spatial profile method would be poor.

12. The method of claim 11 wherein the detection of the third impedance transition is carried out using the spatial profile method when the third impedance transition is more than approximately 0.6 inch from the probe bottom, but is carried out using the time of flight method when the third impedance transition is within approximately 0.6 inch of the probe bottom.

13. The method of claim 11 wherein the detection of the third impedance transition is carried out using the spatial profile method when the third impedance transition is more than approximately 0.3 inch from the probe bottom, but is carried out using the time of flight method when the third impedance transition is within approximately 0.3 inch of the probe bottom.

14. A layer height measuring system comprising:

a transmission line including

a probe for measuring a height of a first layer within a tank and

a cable that connects the probe to an electronics unit;

the electronics unit cyclically transmitting interrogation pulses to the probe and receiving reflections therefrom for time domain reflectometric measurement of the height of the first layer;

a memory; and

a processor configured by the memory to perform the steps of;

detecting first and second impedance transitions corresponding to first and second boundaries of a bounded region of known length;

optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only within the bounded region;

detecting a third impedance transition within the bounded region, the third impedance transition corresponding to an interface between the first layer and a second layer, the first and second layers having respectively different dielectric constants,

determining the dielectric constant of at least one of the layers;

determining the temperature of at least one of the layers; and

determining the mass of at least one of the layers, wherein a volume of the tank is known.

15. A method for measuring a layer with a layer height measuring electronics unit comprising a transmitter capable of cyclically transmitting interrogation pulses for propagation along a transmission line, and an aliasing sampling receiver for receiving reflections from the transmission line, wherein aliased sample collection is carried out by causing a synchronized delay between times that the interrogation pulses are transmitted and times that the received reflections are sampled to be swept through a series of values over a plurality of the interrogation pulse cycles, the method comprising the steps of:

detecting first and second impedance transitions corresponding to first and second boundaries of a bounded region of known length;

optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only within the bounded region; and

detecting a third impedance transition within the bounded region, the third impedance transition corresponding to an interface between the first layer and a second layer,

wherein at least one of said first and second impedance transitions comprises a fluid-fluid interface.

16. A method of accurately measuring fluid level in a tank through use of an apparatus including a transmission line and an electronics unit, wherein

the transmission line includes a probe, and

the electronics unit includes

a transmitter capable of cyclically transmitting an interrogation pulse for propagation along the transmission line, and

an aliasing sampling receiver for receiving reflections from the transmission line,

wherein aliased sample collection is carried out by causing a synchronized delay between times that the interrogation pulses are transmitted and times that the received reflections are sampled to be swept through a series of values over a plurality of the interrogation pulse cycles;

the method comprising;

scanning the transmission line to detect first and second impedance transitions;

locking onto and tracking the first and second impedance transitions;

optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only between the first and second impedance transitions; and

detecting a third impedance transition between the first and second impedance transitions,

wherein at least one of said first and second impedance transitions comprises a fluid-fluid interface.

17. A non-transitory computer-readable medium having stored thereon computer-executable instructions for configuring a processor to perform the steps of:

cyclically transmitting an interrogation pulse and receiving reflections therefrom for time domain reflectometric measurement of a height of a first layer;

detecting first and second impedance transitions corresponding to first and second boundaries of a bounded region of known length;

optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only within the bounded region; and

detecting a third impedance transition within the bounded region, the third impedance transition corresponding to an interface between the first layer and a second layer,

wherein at least one of said first and second impedance transitions comprises a fluid-fluid interface.

18. A method for measuring layer height in a tank with a transmission line including a probe for measuring a height of a first layer within a tank and a cable that connects the probe to an electronics unit, the electronics unit cyclically transmitting interrogation pulses to the probe and receiving reflections therefrom for time domain reflectometric measurement of the height of the first layer, a memory, and a processor configured by the memory to perform the steps of:

detecting first and second impedance transitions corresponding to first and second boundaries of a bounded region of known length;

optimizing a sweep offset and a sweep gain so as to cause swept sample collection to occur substantially only within the bounded region;

detecting a third impedance transition within the bounded region, the third impedance transition corresponding to an interface between the first layer and a second layer, the first and second layers having respectively different dielectric constants,

determining the dielectric constant of at least one of the layers;

determining the temperature of at least one of the layers; and

determining the mass of at least one of the layers, wherein a volume of the tank is known.