Blown installation of optical fibres and method and apparatus for determining the length of a passage along which an optical fibre is to be blown

• US 20040231401A1
• Filed: 05/20/2004
• Published: 11/25/2004
• Est. Priority Date: 05/21/2003
• Status: Active Grant

• Current Assignee: Prysmian Cables & Systems Limited (Prysmian SPA)
• Original Assignee: Pirelli General, PLC
• Inventors: Sutehall, Ralph
• Granted Patent: US 7,207,208 B2
• Time in Patent Office: Days
• US Class Current: 73/37.9
• CPC Class Codes: G01B 13/02 for measuring length, width or thickness G01B13/08 takes precedence
• CPC Class Codes: G02B 6/4485 Installing in protective tubing by fluid drag during manufacturing
• CPC Class Codes: G02B 6/52 using fluid, e.g. air

Abstract

An apparatus (12) is provided for use in determining a length at least representative of the length of a tube that defines a passage in an optical fibre cable (10) along which an optical fibre unit can be installed by blowing. The apparatus (12) comprises a pressure reservoir (32) in which a gas at a known pressure can be stored, outlet piping (34) connected with the pressure reservoir (32) and having an outlet end spaced from the reservoir for connection to a tube of the optical fibre cable (10). The apparatus has a pressure detecting arrangement (42) for detecting gas pressure in a tube connected with the outlet end of the outlet piping (34). In use, the gas stored in the pressure reservoir (32) is released into the tube and knowing the pressure of the gas when stored in the pressure reservoir, the volume of the reservoir and the pressure of gas in the tube after release of the gas from the pressure reservoir, it is possible to determine the volume of the passage defined by the tube and knowing that volume, it is possible to determine the length of the tube.

Claims

1. A method of determining a length L_t at least representative of the length of a tube that defines a passage in an optical fibre cable along which an optical fibre unit can be installed by blowing, said method comprising the steps of providing a first volume V₁ containing a gas at a first pressure P₁, releasing said gas into a second volume V₂ that comprises said passage, determining a second gas pressure P₂ in said second volume V₂ after release of said gas from said first volume, determining said second volume V₂ by reference to said first pressure P₁, second pressure P₂ and said first volume V₁ and determining said length L_t by reference to said second volume V₂.

2. A method as claimed in claim 1, wherein said second volume comprises said passage and said first volume V₁.

3. A method as claimed in claim 2, wherein said second volume is determined from the relationship

4. A method as claimed in claim 1, wherein said length L_t is determined from the relationship

5. A method as claimed in claim 1, wherein said first volume V₁ comprises a volume V_p defined by a pressure reservoir.

6. A method as claimed in claim 5, wherein said first volume V₁ is equal to said volume V_p of said pressure reservoir.

7. A method as claimed in claim 1, wherein said second volume V₂ and/or said length L_t is/are determined by a computing module.

8. A method as claimed in claim 1, further comprising monitoring said pressure P₂ to determine the presence of gas leakage.

9. A method as claimed in claim 1, further comprising providing a plurality of discrete volumes for containing gas at said first pressure P₁, selecting said first volume V₁ based on an assumed said length L_t and arranging a connection between said discrete volumes to provide said selected first volume V₁.

15. A method as claimed in claim 1 or claim 10, wherein said gas is compressed air.

10. A method of determining a length at least representative of the length of a tube in an optical fibre cable along which an optical fibre unit can be installed by blowing, the optical fibre cable having a first end and a second end and comprising sheathing housing at least one said tube and the method comprising:

connecting a pressure reservoir having a known volume with the or one said tube at said first end of the optical fibre cable;

providing sealing at said second end of the optical fibre cable such that an end of said tube connected to the pressure reservoir is sealed at said second end of the optical fibre cable;

releasing a gas at a known pressure from said pressure reservoir into said tube connected with said pressure reservoir;

determining a pressure of the gas that is in said tube connected with said pressure reservoir after said release of gas;

determining the volume of said tube connected with said pressure reservoir by reference to said known volume, known pressure and determined pressure; and

determining a length at least representative of the length of said tube connected with said pressure reservoir by reference to said volume thereof and an inside diameter thereof.

11. A method as claimed in claim 10, further comprising filling said pressure reservoir with said gas to said known pressure.

12. A method as claimed in claim 10, further comprising monitoring said pressure in said tube connected with said pressure reservoir after said release of gas to determine the presence of gas leakage.

13. A method as claimed in claim 10, comprising the step of determining said volume of said tube connected with said pressure reservoir by means of the relationship

14. A method as claimed in claim 13, comprising the step of determining said length at least representative of said length of the tube connected to said pressure reservoir by means of the relationship

16. Optical fibre cable length determining apparatus for use in determining a length at least representative of the length of a tube that defines a passage in an optical fibre cable along which an optical fibre unit can be installed by blowing, said apparatus comprising a pressure reservoir in which a gas at a known pressure can be stored, outlet piping connected with said pressure reservoir and having an outlet end spaced from said reservoir for connection to said tube and a pressure detecting arrangement for detecting gas pressure in said tube connected with said outlet end.

17. Apparatus as claimed in claim 16, wherein said pressure detecting arrangement comprises a transducer that provides an electrical signal indicative of said pressure.

18. Apparatus as claimed in claim 16, wherein said pressure indicating arrangement comprises a display that provides a visual indication of said pressure.

19. Apparatus as claimed in claim 16, further comprising valving provided in said outlet piping between said pressure reservoir and said outlet end, said pressure detecting arrangement being arranged to detect said gas pressure between said pressure reservoir and said valving.

20. Apparatus as claimed in claim 16, further comprising inlet piping connected with said pressure reservoir, said inlet piping having an inlet end spaced from said pressure reservoir for connection with means for filling said pressure reservoir with gas.

21. Apparatus as claimed in claim 20, further comprising valving provided in said inlet piping between said pressure reservoir and said inlet end.

22. Apparatus as claimed in claim 16, wherein said pressure reservoir comprises a prefilled cartridge releasably connectable to said outlet piping.

23. Apparatus as claimed in claim 16, wherein said pressure detecting arrangement is arranged to detect gas pressure in said pressure reservoir for detecting pressure of a gas stored in said reservoir.

24. Apparatus as claimed in claim 16, further comprising a computing unit connected or connectable with said pressure detecting arrangement, said computing unit being arranged for use in determining said length of said tube on the basis of pressure detected by said pressure detecting means and an input measurement of the diameter of a said passage.

25. Apparatus as claimed in claim 16, wherein said pressure reservoir comprises a plurality of units each defining a volume for storing gas, said units being selectively connectable such that, in use, a user can select a volume for said pressure reservoir by varying the number of said units that are connected.

26. An installation comprising an optical fibre cable comprising at least one tube defining a passage along which an optical fibre can be installed by blowing and apparatus as claimed in claim 16 having said outlet end connected with a first end of the or one said tube of said cable.

27. A method of determining a length L_t at least representative of the length of a passage along which an optical fibre unit can be installed by blowing, said method comprising the steps of providing a first volume V₁ containing a gas at a first pressure P₁, releasing said gas into a second volume V₂ that comprises said passage, determining a second gas pressure P₂ in said second volume V₂ after release of said gas from said first volume, determining said second volume V₂ by reference to said first pressure P₁, second pressure P₂ and said first volume V₁ and determining said length L_t by reference to said second volume V₂.

28. A method as claimed in claim 27, wherein said length L_t is determined from the relationship