Measuring and testing – With fluid pressure – Dimension – shape – or size
Patent
1989-03-03
1992-03-03
Williams, Hezron E.
Measuring and testing
With fluid pressure
Dimension, shape, or size
73 495, 73 405R, G01M 300
Patent
active
050921614
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to detection of blockages, holes, discontinuities and surface qualities in ducts or tubes.
BACKGROUND OF THE INVENTION
Lightweight transmission line packages can be installed
in a duct by a procedure known as `fibre blowing`. The technique involves blowing compressed gas along the duct into which the transmission line is to be installed and feeding the transmission line package into the duct at the same time so that the package is urged along the duct by viscous drag of the gas flow. The technique is of particular importance to optical fibre transmission lines which can be damaged by the tension that is produced in pulled installation techniques. In new installations ducts for transmission lines are usually underground or incorporated into the structure of a building and it is difficult and/or costly to install new ducting at a subsequent date to cope with increased demand for lines or for replacement lines. Therefore when ducts are first installed additional ducts for future use will be laid, and it may be several years after the duct installation that fibre packages are actually blown through some of these ducts. A degree of over capacity may also mean that there is a choice of which duct to use. A problem that arises with this system is that, during the time between duct laying and installation of fibre, damage may occur to one or more of the ducts which renders them temporarily or permanently unsuitable for use. For example, a complete blockage caused by the duct being crushed would make it impossible for the fibre to be installed, a partial blockage may make installation very difficult and puncture may cause such a loss of the blowing gas that installation is slow or impossible and also exposes any installed fibre to potential damage from water flooding into the duct. Thus it is desirable to be able to ascertain the state of a duct prior to installation, and in the event of a fault to know its type and location. There are also occasions when the continuity or state of a duct containing an installed transmission line may require monitoring.
BRIEF SUMMARY OF THE INVENTION
Accordingly the invention provides a method of testing a duct, the method comprising introducing a pulse of compressed gas into the duct to establish a pressure wavefront advancing through the duct, determining after at least one interval during travel of the wavefront along the duct a value indicative of pressure at a particular location to give an indication of a characteristic of the duct that influences the rate of pressure change at a given location of the duct as the wavefront advances therethrough.
The invention also provides apparatus for testing a duct, the apparatus comprising means for introducing a pulse of compressed gas into the duct to establish a pressure wavefront advancing through the duct, a sensor for establishing a set of values indicative of pressure variation at a particular location as the wavefront travels along the duct, means for comparing said pressure variation with a set of values indicative of a reference pressure variation and determining whether there is a significant difference between the monitored and reference variations and means for establishing the interval between the introduction of the pulse and the onset of any significant difference between the monitored and reference pressure variations.
Another aspect of the invention provides apparatus for testing a duct, the apparatus comprising means for introducing a pulse of compressed gas into the duct to establish a pressure wavefront advancing through the duct, a sensor for monitoring pressure at a predetermined location a predetermined interval after introduction of the pulse into the duct to establish a value for the relative speed of travel of the wavefront along the duct.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is now described by way of example with reference to the accompanying drawings in which:
FIG. 1 illustrates a prototype embodiment of the invention;
FIG. 2 shows a pressure
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Jenkins Peter D.
Wiltshire Bruce
British Telecommunications public limited company
Miller Craig
Williams Hezron E.
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