Patent Application
20080033698
The invention may best be understood by referring to the following detailed description and accompanying drawings which illustrate the invention. In the drawings:
Leakage measurements of signal from a CATV plant including, for example, CATV cables, taps, fittings, drops and other CATV plant facilities, may readily be made by, for example, CATV system employees during their conduct of their daily activities. Such leakage measurements, stored in leakage measurement equipment of the type described in, for example, Trilithic Seeker GPS leakage management system available from Trilithic, Inc., 9710 Park Davis Drive, Indianapolis, Ind. 46235, the disclosure of which is hereby incorporated herein by reference, are uploaded from such CATV system employee equipment into a server at a CATV headend, for example, at the ends of the employees' shifts. Such CATV system employees' daily activities may include, for example, visiting subscriber sites to conduct maintenance and repairs, driving the CATV system to log leakage levels, and so on.
This activity can provide a database of cable system leakage strengths measured at multiple locations, which can be determined with considerable accuracy by associating with each such measurement a location, such as a latitude and longitude provided by a Global Positioning System (GPS) device. Such data sets might look like the following table when sorted in order of descending detected leakage level and eliminating leakage levels below a certain threshold (10 μV in this example):
Using this data, which, again, is typically extracted from a larger data set accumulated over days, weeks, months, etc., of data collection and then sorted and limited by differences of latitude and longitude from the largest system leak in the list, the location and magnitude of a leakage source giving rise to this data may be isolated. The method employs leakage signal strength versus distance considerations.
Leakage detectors and their associated antenna systems are calibrated to be accurate at a fixed distance from a radiation source, such as the source of a leak. It is not uncommon in the CATV industry to use three meters as a measurement standard. So, in the case of a 10 μV/m leak, for example, which is calibrated to be accurate at a distance of three meters from the leakage source, a leak indicated as having a strength of 10 μV/m could reside anywhere on a radius three meters from the leakage antenna. If the leakage strength were doubled to 20 μV/m and the antenna were six meters from the source, the leakage detecting instrument would still indicate a leakage signal strength of 10 μV/m. So, for a given measured 10 μV/m leak, one can envision an inverted cone of potential leakage sources and leakage signal strengths which would all give rise to the same 10 μV/m reading at the location of the leakage detecting antenna, with the x and y dimensions of the cone being the longitude and latitude of the cone's surface at various points and z being the indicated strength of the leakage signal. In this example, there is a three meter circle of potential 10 μV/m leaks around the leakage antenna, a six meter circle of 20 μV/m leaks, a nine meter circle of 30 μV/m leaks, and so on in circles of increasing radius at increasing heights (z values) corresponding to increasing leakage signal strength. If one imagines the location for this 10 μV/m reading on the leakage detector to be defined by latitude and longitude coordinates with x mapping to longitude, y mapping to latitude and z mapping to leakage level, then the increasing circles around the current location of the leakage detector can be visualized as a cone standing on its apex. Every leak stored in the database can be represented in this way with its apex at the GPS-determined position of the antenna at the time the particular leakage signal strength is measured. The equation for each leakage cone may then be written as:
z=L
1sqrt((x−x1)2+(y−y1)2)
where sqrt is the square root operator;
x1=the longitude of the measured leak; and,
y1=the latitude of the measured leak.
For purposes of this discussion, zn will indicate the nth detected leak. Using (arbitrarily) the first four rows of the above data set, the following four equations are obtained:
z
1
=L
1sqrt((x−x1)2+(y−y1)2);
z
2
=L
2sqrt((x−x2)2+(y−y2)2);
z
3
=L
3sqrt((x−x3)2+(y−y3)2); and,
z
4
=L
4sqrt((x−x4)2+(y−y4)2),
where xn, yn and zn are the longitude, latitude and leakage signal strength displayed in the nth row of the above table, and
L
1=26/3 μV/m;
L
2=23/3 μV/m;
L
3=21/3 μV/m; and
L
4=20/3 μV/m,
using the above convention, leakage signal strength detected at three meters from the leakage antenna. From the above table:
x1=−85.594748°;
x2=−85.594720°;
x3=−85.594722°;
x4=−85.594746°;
y1=39.502145°;
y2=39.502003°;
y3=39.502089°; and,
y4=39.502066°.
If the intersection of two adjacent inverted cones, for example, z1 and z2, is plotted, the intersection is an arc 20, as illustrated in
Again, looking into any of these cones z1, z2, z3, z4 from above, at any given leakage signal strength (that is, any vertical elevation), it may be visualized as a circle. In
Now that a specific x and y, that is, longitude and latitude, of interest have been identified, those values can be substituted back into any one of the equations above for z1, z2, z3 or z4 to calculate the strength of the leak at that x and y. For purposes of illustration, the equation for z1 will be used to demonstrate this. First, the differences (y−y1) and (x−x1) in latitude and longitude need to be converted into meters. Tables stored in instruments such as the above-mentioned server at a CATV headend, a separate computer associated therewith, or calculators provided in such instruments, or some combination of these, are used for these conversions, since such conversions depend upon the latitudes and longitudes which are the subjects of the calculations, that is, upon the curvature of the earth's surface at the latitudes and longitudes of interest. See, for example, http://www.csgnetwork.com/degreelenllavcalc.html, for such a calculator.
z
1=(26/3)sqrt((x+85.594748°)2+(y−39.502145°)2);
z
2=(23/3)sqrt((x+85.594720°)2+(y−39.502003°)2);
z
3=(21/3)sqrt((x+85.594722°)2+(y−39.502089°)2); and,
z
4=(20/3)sqrt((x+85.594746°)2+(y−39.502066°)2).
The longitudes and latitudes are normalized to coordinates which lie fairly centrally among them, in this case, −85.594735°, 39.502070°. See
z
1=(26/3)sqrt((0.000013°)2+(−0.000075°)2);
z
2=(23/3)sqrt((−0.000015°)2+(0.000067°)2);
z
3=(21/3)sqrt((−0.000013°)2+(0.000019°)2); and,
z
4=(20/3)sqrt((0.000011°)2+(0.000004°)2),
where, at this latitude and longitude, 14×10−6°˜1.55435 m and 67×10−6°≈5.76273 m at x=−85.594735° and y≈39.502070°. Picking z1 and converting the latitude and longitude differences to meters as discussed above yields a leakage strength of about 51.7285 μV/m at the location of the leak.
This application claims the benefit under 35 U.S.C. § 119(e) of the Aug. 7, 2006 filing date of U.S. S. N. 60/836,036, titled “Leakage Location Method,” the complete disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60836036 | Aug 2006 | US |
