Methods and apparatus for determining the position of an obstruction in a passage

• US 7,469,573 B2
• Filed: 10/12/2004
• Issued: 12/30/2008
• Est. Priority Date: 05/21/2004
• Status: Active Grant

• Current Assignee: Prysmian Cables & Systems Limited (Prysmian SPA)
• Original Assignee: Prysmian Cables & Systems Limited (Prysmian SPA)
• Inventors: Sutehall, Ralph
• Primary Examiner(s): Williams; Hezron
• Assistant Examiner(s): Gissel; Gunnar J
• Application Number:
  US11/569,216
• Publication Number:
  US 20070245807A1
• Time in Patent Office: 1,540 Days
• Field of Search: 73/37, 73/376, 73/495
• US Class Current: 73/37
• CPC Class Codes: G01B 13/02 for measuring length, width or thickness G01B13/08 takes precedence

Abstract

A method of determining the position of a blockage (192, 392) in a passage (15, 313) having a first end and a second end. The method comprises blowing a sealing device (200) into the passage to form a seal adjacent the blockage (192, 392), then blowing a gas into the passage from the first end, making at least one measurement concerning the gas blown into the passage from the first end and determining a distance D between the first end and the sealing device using the at least one measurement.

Claims

1. A method of determining the position of a blockage (192,392) in a passage (15,313) having a first end and a second end, said method comprising blowing a sealing device (200) into said passage to form a seal adjacent said blockage (192,392), then blowing a gas into said passage from said first end, making at least one measurement concerning said gas blown into said passage from said first end and determining a distance D between said first end and said sealing device using said at least one measurement.

2. A method as claimed in claim 1, wherein said sealing device (200) comprises a plastics sealing element.

3. A method as claimed in claim 1 or 2, further comprising venting said passage to atmosphere at said first end subsequent to blowing said sealing device into said passage such that between said first end and said sealing device, the pressure in said passage is atmospheric pressure.

4. A method as claimed in claim 1, 2 or 3, wherein said ducting is for installation of an optical fibre cable or optical fibre unit and further comprising blowing a test piece of said optical fibre cable or optical fibre unit into said passage to determine the presence of a blockage, prior to said step of blowing a sealing device into said passage.

5. A method as claimed in claim 4, wherein said test piece has a radiussed nosepiece fitted to a leading end thereof.

6. A method as claimed in claim 4 or 5, further comprising fitting a gas permeable end stop to the one of said first and second ends of the passage opposite to the one of said first and second ends at which said test piece is to be blown into the duct.

7. A method as claimed in any one of the preceding claims, further comprising providing a first volume V₁ containing a gas at a first pressure P₁, wherein said step of blowing a gas into said passage from said first end comprises releasing said gas into a second volume V₂ that comprises said passage between said first end and said sealing device, said step of making at least one measurement comprises measuring a second gas pressure P₂ which is the pressure in said second volume V₂ after release of said gas from said first volume V₁, said second volume V₂ is determined by reference to said first pressure P₁, second pressure P₂ and said first volume V₁ and said distance D is determined by reference to said second volume V₂.

8. A method as claimed in claim 7, wherein said second volume comprises said passage between said first end and said sealing device and said first volume V₁.

9. A method as claimed in claim 8, wherein said second volume is determined from the relationship

10. A method as claimed in claim 7, 8 or 9, wherein said distance D is determined from the relationship

11. A method as claimed in claim 7 to 10, wherein said first volume V₁ comprises a volume V_p defined by a pressure reservoir.

12. A method as claimed in claim 11, wherein said first volume V₁ is equal to said volume V_p of said pressure reservoir.

13. A method as claimed in any one of claims 7 to 12, wherein said second volume V₂ and/or said distance D is/are determined by a computing module.

14. A method as claimed in any one of claims 1 to 6, wherein said step of blowing a gas into said passage from said first end comprises flowing a pressurised gas into said passage at a substantially constant pressure P₁ and substantially constant flowrate V_f,, said step of making at least one measurement comprises determining the time t_f taken to provide a predetermined gas pressure P₂ within said passage and said distance D is determined by reference to said time t_f.

15. A method as claimed in claim 14, further comprising determining a volume V_d at least approximating to a volume defined by said passage between said first end and said sealing device by reference to said flowrate V_f and said time t_f.

16. A method as claimed in claim 15, further comprising determining a volume V₁ of said gas flowed into said passage from said first end by multiplying said flow rate V_f by said time period t_f and determining said volume V_d from the relationship

17. A method as claimed in claim 16, wherein said distance (D) is determined from the relationship

18. A method as claimed in claim 15, 16 or 17, wherein said volume V_d is determined by a computing module.

19. A method as claimed in claim 14, comprising determining said distance D by reference to said time period t_f by referring to a plot of length against time for a specified passage diameter and said predetermined pressure P₂.

20. A method as claimed in any one of claims 14 to 19, wherein said distance D is determined by a computing module.

21. A method of determining the position of a blockage (192) in a passage (15) having a first end and a second end, the method comprising:

providing sealing adjacent said blockage by blowing a sealing device (200) along said passage;

connecting a pressure reservoir (32, 132) having a known volume V₁ with the first end (38) of the passage;

releasing a gas at a known pressure Pi from said pressure reservoir (32, 132) into said passage;

determining a pressure P₂ of the gas that is in a portion of said passage (15) between said first end and said sealing after said release of gas;

determining the volume V₂ of said portion of said passage by reference to said known volume V₁, known pressure P₁ and determined pressure P₂; and

determining a length at least representative of a distance D between said first end and said sealing by reference to said determined volume V₂ and a diameter of said passage.

22. A method of determining the position of a blockage (392) in a passage (313) having a first end and a second end, the method comprising:

providing sealing (200) adjacent said blockage by blowing a sealing device (200) along the passage;

connecting a compressor with said first end of the passage;

supplying a gas at a substantially constant pressure P₁ and substantially constant flowrate V_f from said compressor into said passage until a predetermined pressure P₂ exists in said passage between said first end and said sealing;

determining the time period t_f during which said gas was supplied into said passage;

determining a volume V_d indicative of a volume defined by said passage between said first end and said sealing by determining a pumped gas volume V₁ by multiplying said flowrate V_f by said time period t_f and the relationship