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 20050265687A1
• Filed: 05/18/2005
• Published: 12/01/2005
• 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
• Granted Patent: US 7,204,126 B2
• Time in Patent Office: Days
• US Class Current: 385/147
• CPC Class Codes: G01B 13/02 for measuring length, width or thickness G01B13/08 takes precedence

Abstract

A method of determining a length L_d at least representative of the length of a passage along which an optical unit or cable is to be installed by blowing, comprises the steps of flowing a pressurised gas into the passage at a substantially constant pressure P₁ and substantially constant flow rate V_f until gas pressure within the passage reaches a predetermined level P₂. The time period t_f during which the pressurised gas was flowed into the passage is determined and then the length L_d is determined by reference to the time period t_f.

Claims

1. A method of determining a length L_d at least representative of the length of a passage along which an optical fibre cable or unit is to be installed by blowing, said method comprising the steps of flowing a pressurised gas into said passage at a substantially constant pressure P₁ and substantially constant flowrate V_f, determining the time t_f taken to provide a predetermined gas pressure P₂ within said passage and determining said length L_d by reference to said time t_f.

2. A method as claimed in claim 1, further comprising determining a volume V_d at least approximating to a volume defined by said passage by reference to said flowrate V_f and said time t_f.

3. A method as claimed in claim 2, further comprising determining a volume V₁ of gas flowed into said passage by multiplying said flow rate V_f by said time period t_f and determining said volume V_d from the relationship

4. A method as claimed in claim 3, wherein said length L_d is determined from the relationship

5. A method as claimed in claim 2, wherein said volume V_d is determined by a computing module.

6. A method as claimed in claim 1, comprising determining said length L_d by reference to said time period t_f by reference to a plot of length against time for a specified passage diameter and said predetermined pressure P_2.

7. A method as claimed in claim 1, wherein said length L_d is determined by a computing module.

8. A method as claimed in claim 1, wherein said passage is defined by ducting (10).

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

11. A method as claimed in claim 9, further comprising monitoring said pressure P₂ in said ducting after said step of supplying said gas to determine the presence of gas leakage.

12. A method as claimed in claim 9, further comprising the step of determining said length L_d at least representative of said length of the ducting by means of the relationship

13. A method as claimed in claim 1, wherein said gas is compressed air.

14. A method as claimed in claim 9, wherein said gas is compressed air.

10. A method of determining a length at least representative of a length of ducting in which an optical fibre unit or cable is to be installed by blowing, the ducting having a first end and a second end and the method comprising:

connecting a compressor with said first end of the ducting;

providing sealing at said second end of the ducting;

supplying a gas at a substantially constant pressure P₁ and substantially constant flowrate V_f from said compressor into said ducting until a predetermined pressure P₂ exists in said ducting;

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

determining a volume V_d indicative of a volume defined by said ducting by determining a pumped gas volume VI by multiplying said flowrate V_f by said time period t_f and the relationship

$\frac{P_1<br><br>V_1}{P_2}=V_d;<br><br>\mathrm{and}$

determining a length L_d at least representative of the length L_d of said ducting by reference to said volume V_d and an inside diameter of said ducting.

15. Apparatus for determining a length (L_d) at least representative of a length of a passage along which an optical fibre unit or cable is to be installed by blowing, said apparatus comprising a flow control device (16;

116) for receiving a supply of compressed gas and outputting said compressed gas at a substantially constant pressure (P₁) and flow rate (V_f) for supply to a said passage and a computing system that determines said length (L_d) of a said passage to which said gas is output based on signals indicative of a time period (t_f) in which gas output by said flow control device is supplied to said passage to raise the pressure in said passage to a predetermined pressure (P₂).

16. Apparatus as claimed in claim 15, further comprising a compressor, said flow control device being integral with said compressor.