SYSTEM AND METHOD FOR OPTIMIZING SWEEP DELAY AND ALIASING FOR TIME DOMAIN REFLECTOMETRIC MEASUREMENT OF LIQUID HEIGHT WITHIN A TANK

• US 20100153029A1
• Filed: 12/03/2009
• Published: 06/17/2010
• Est. Priority Date: 01/08/2007
• Status: Active Grant

• Current Assignee: Meggitt Safety Systems, Inc. (Meggitt PLC)
• Original Assignee: Vibro-Meter, Inc.
• Inventors: Lavon, Ronie, Petriel, Kevin J., Tan, Zhenyu, Carvalho, Carlos E., Miskell, Thomas J.
• Granted Patent: US 8,794,063 B2
• Time in Patent Office: Days
• US Class Current: 702/55
• 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 device comprising:

a probe having a probe top and a probe bottom;

an electronics unit that cyclically transmits interrogation pulses to the probe and receives reflections therefrom for time domain reflectometric measurement of a layer in which the probe is immersed; and

a cable connecting the electronics unit and the probe;

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 from an initial delay value to a final delay value over a plurality of the interrogation pulse cycles; and

the initial delay value is set so as to substantially prevent collection of samples from reflections within a region of noninterest and so as to substantially allow collection of samples from reflections within a region of interest.

2. A layer height measuring device according to claim 1 wherein the region of noninterest is a region before the probe top, and the region of interest includes at least a portion of the probe.

3. A layer height measuring device according to claim 2 wherein the region of noninterest includes at least a portion of the cable.

4. A layer height measuring device according to claim 1 wherein the initial delay value is set so as to cause the aliased sample collection sweep to begin not more than 50% of the time domain length of the probe before the probe top.

5. A layer height measuring device according to claim 1 wherein the initial delay value is set so as to cause the aliased sample collection sweep to begin not more than 25% of the time domain length of the probe before the probe top.

6. A layer height measuring device according to claim 1 wherein the initial delay value is set so as to cause the aliased sample collection sweep to begin not more than 5% of the time domain length of the probe before the probe top.

7. A layer height measuring device according to claim 1 wherein the initial delay value is approximately the time domain length of the cable.

8. A layer height measuring device according to claim 1 wherein the initial delay value is set so as to cause the aliased sample collection sweep to start at or slightly prior to a time when a pulse reflected from the top of the probe would have just arrived at the receiver.

9. A layer height measuring device comprising:

a probe having a probe top and a probe bottom;

an electronics unit that cyclically transmits interrogation pulses to the probe and receives reflections therefrom for time domain reflectometric measurement of a layer in which the probe is immersed; and

a cable connecting the electronics unit and the probe;

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 from an initial delay value to a final delay value over a plurality of the interrogation pulse cycles; and

the final delay value is set so as to substantially allow collection of samples from reflections within a region of interest and so as to substantially prevent collection of samples from reflections within a region of noninterest.

10. A layer height measuring device according to claim 9 wherein the region of interest includes at least a portion of the probe, and the region of noninterest is a region after the probe bottom.

11. A layer height measuring device according to claim 9 wherein the final delay value is set so as to cause the aliased sample collection sweep to end not more than 50% of the time domain length of the probe after the probe bottom.

12. A layer height measuring device according to claim 9 wherein the final delay value is set so as to cause the aliased sample collection sweep to end not more than 25% of the time domain length of the probe after the probe bottom.

13. A layer height measuring device according to claim 9 wherein the final delay value is set so as to cause the aliased sample collection sweep to end not more than 5% of the time domain length of the probe after the probe bottom.

14. A layer height measuring device according to claim 9 wherein the final delay value less the initial delay value is approximately the time domain length of the probe.

15. A layer height measuring device according to claim 9 wherein the final delay value is set so as to cause the aliased sample collection sweep to end at or slightly after a time when a pulse reflected from the probe bottom would have just arrived at the receiver.

16. A layer height measuring device according to claim 9 wherein a size of an incremental increase in the delay as each successive sample is collected during the aliased sample collection sweep is of constant time domain length.

17. A layer height measuring device according to claim 9 wherein a size of an incremental increase in the delay as each successive sample is collected during the aliased sample collection sweep is of constant space domain length.

18. A layer height measuring device comprising:

a probe having a probe top and a probe bottom;

an electronics unit that cyclically transmits interrogation pulses to the probe and receives reflections therefrom for time domain reflectometric measurement of a layer in which the probe is immersed; and

a cable connecting the electronics unit and the probe;

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 from an initial delay value to a final delay value over a plurality of the interrogation pulse cycles;

the initial delay value is set so as to substantially prevent collection of samples from reflections within a first region of noninterest and so as to substantially allow collection of samples from reflections within a first region of interest; and

the final delay value is set so as to substantially allow collection of samples from reflections within a second region of interest and so as to substantially prevent collection of samples from reflections within a second region of noninterest.

19. A layer height measuring device according to claim 18 wherein

the first region of noninterest includes at least a portion of the cable, the initial delay value being not substantially more than the time domain length of the cable;

the first region of interest and the second region of interest respectively include at least a portion of the probe, the final delay value less the initial delay value being not substantially more the time domain length of the probe; and

the second region of noninterest is a region after the probe bottom, the final delay value being set so as to cause the aliased sample collection sweep to not extend substantially beyond the probe bottom.

20. A layer height measuring device according to claim 18 wherein substantially all of the aliased sample collection is carried out between a time when an interrogation pulse edge reflected from the probe top would have just arrived at the electronics unit and a time when the interrogation pulse edge reflected from the probe bottom would have just arrived at the electronics unit.

21. 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.

22. A layer height measuring system according to claim 21 wherein the height of at least one of the layers is determined by converting a time domain height to a space domain height.

23. A layer height measuring system according to claim 22 wherein the conversion is carried out by an impedance-based compensation for dielectric constant.

24. A layer height measuring system according to claim 22 wherein the conversion is carried out by a time-based compensation for dielectric constant.

25. A layer height measuring system according to claim 21 wherein the height of the first layer is measured directly.

26. A layer height measuring system according to claim 25 wherein the direct measurement of the first layer is carried out using a spatial profile thereof.

27. A layer height measuring system according to claim 25 wherein the direct measurement of the first layer is carried out using a time of flight therethrough.

28. A layer height measuring system according to claim 21 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.

29. A layer height measuring system according to claim 28 wherein the height of the second layer is measured directly using a spatial profile thereof.

30. A layer height measuring system according to claim 28 wherein the height of the second layer is measured directly using a time of flight therethrough.

31. A layer height measuring system according to claim 21 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.

32. A layer height measuring system according to claim 21 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.

33. A layer height measuring system according to claim 32 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.

34. A layer height measuring system according to claim 32 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.

35. A layer height measuring system according to claim 21 wherein

the bounded region of known length is the probe;

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

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

36. A layer height measuring system according to claim 21 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.

37. A layer height measuring system according to claim 21 wherein the first and second boundaries of the bounded region are respectively locked onto and tracked in closed-loop fashion.

38. A layer height measuring system according to claim 21 wherein the processor is further configured by the memory to perform the step of determining the dielectric constant of at least one of the layers.

39. A layer height measuring system according to claim 21 wherein the processor is further configured by the memory to perform the step of determining the temperature of at least one of the layers.

40. A layer height measuring system according to claim 21 wherein the processor is further configured by the memory to perform the step of determining the mass of at least one of the layers.

41. 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 electronics unit being configured so as to be capable of;

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

carrying out aliased sample collection within the bounded region;

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

obtaining a dielectric constant for the second layer;

using the obtained dielectric constant of the second layer to convert a measured time domain height of the second layer to a space domain height of the second layer; and

determining a height of the first layer in a manner that is insensitive to the dielectric constant of the first layer by process of elimination from the known length of the bounded region and the space domain height of the second layer.

42. 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 electronics unit being configured so as to be capable 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.

43. 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.

44. A layer height measuring system comprising:

a plurality of transmission lines respectively including a plurality of probes and a plurality of cables respectively connecting the probes to a common electronics unit;

the electronics unit cyclically transmitting interrogation pulses to the probes and receiving reflections therefrom for time domain reflectometric measurement in time-shared fashion;

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 different bounded region for each of the transmission lines;

optimizing a sweep offset and a sweep gain independently for each of the transmission lines so as to cause swept sample collection to occur substantially only within the bounded region of that transmission line; and

detecting a third impedance transition within the bounded region independently for each of the transmission lines, 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.

45. A 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.

46. A layer height measuring system comprising:

probe means for outputting a signal in correspondence to a dielectric constant of a layer in which the probe means is immersed;

electronics means for cyclically transmitting interrogation pulses to the probe means and for receiving reflections therefrom for time domain reflectometric measurement; and

cable means for connecting the electronics means and the probe means;

aliased sample collection means for 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 from an initial delay value to a final delay value over a plurality of the interrogation pulse cycles;

sweep offset optimizing means for optimizing a sweep offset of the aliased sample collection means in correspondence to a time domain length of at least a portion of the cable means;

sweep gain optimizing means for optimizing a sweep gain of the aliased sample collection means in correspondence to a time domain length of at least a portion of the probe means; and

processing means for carrying out processing to determine the height of the layer in correspondence to the signal output from the probe means.