WO2007113549A1

WO2007113549A1 - Cable installation

Info

Publication number: WO2007113549A1
Application number: PCT/GB2007/001222
Authority: WO
Inventors: Philip Alfred Barker; Graham Anthony Laidler
Original assignee: British Telecommunications Public Limited Company
Priority date: 2006-04-03
Filing date: 2007-04-02
Publication date: 2007-10-11

Abstract

A method for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, comprising the steps of: - introducing an air flow into the conduit, - introducing a signal into the conduit or into a bore communicating with the conduit, and - detecting a change in a phase shift of the signal caused by movement of the air flow.

Description

CABLE INSTALLATION

The present invention relates to the installation of cables, such as optical fibre units, wires, electrical cables or the like. More specifically, but not exclusively, the present invention relates to the blowing of fibre unit cables through pre-laid conduits.

Optical fibres are widely used within telecommunication systems for high-speed information transfer. A fibre unit, which could comprise a single optical fibre, or a bundle of optical fibres, is commonly installed into a protective optical conduit comprising optical fibre tubes, which have already been laid along the desired route, usually as a continuous span between convenient access points such as surface boxes or inspection chambers.

In this description, references to "cables" shall include where the context permits, individual optical fibres and fibre units as well as cables comprising such fibres and fibre units. "Conduits" shall include tubes and tube bores, but in the main refers to the route or path populated or to be populated by a fibre cable, and where the route comprises a number of tubes, the entire length of the route.

The conduits typically are made of plastic, each with a typical inner diameter of 3 to 6 mm or more, and are usually provided in a bundle comprising up to 24 or more tubes, which are held together within a protective outer sheath. Each fibre conduit tube can receive at least one fibre unit comprising one or more individual optical fibres. Large numbers of conduits - and bundles of conduits - are pre-installed across the access network and the distribution network between the local exchanges and the customer premises in a branching network system. With the advent of fibre to the premises (FTTP), the conduits will further extend to and into commercial and residential premises. Indeed it is a fundamental part of the push to FTTP in e.g. the UK that substantially all the network comprises optical fibre, extending from the core network to as many end customers as possible. To achieve this, optical fibre installation needs to be speedy, cost- and effort-efficient.

In the vast majority of cases, a dedicated path is described between two points with a single length of conduit tube. In an exceptional case, the conduit path may comprise a number of lengths of physically separate conduit tubes which are connecterised together in series with tube connectors. Choosing the correct conduit tube at the installation should in the normal case, result in the fibre unit emerging at the other end.

Problems however may arise which result in the fibre unit not reaching the correct destination. During installation, the operator is usually presented with a large number of conduit tubes, which could result in a mistake in identifying the correct conduit, especially if the operator is working in adverse conditions down a manhole or in poor lighting. This may be so even where conduits are coloured coded which helps to direct the operator to the correct conduit.

There is also the possibility that a conduit route is wrongly mapped in the records used by the operator so that one end of the conduit does not lead to the correct destination. Where the path comprises a number of tube lengths connectorised together in series, yet another problem may lie in broken connections between lengths of conduit tubes within the network, so that the fibre unit may get lost within the system during installation and never emerge at the destination. Yet another issue may be the possibility that the fibre unit, during installation, could be impeded by an imperfect connector or a tight bend or some other source of friction in the conduit, and again never emerge at the destination.

For any of these or other reasons, the fibre unit will emerge in the wrong place, or not at all. Add to that some uncertainty about the exact length of the conduit route down which the fibre unit is being installed, so that the operator cannot even accurately know in a timely manner when something has gone wrong.

One method of installing fibre units into the conduits is by pulling them through the conduits. However, the tension induced can cause damage to the fibre units and impair their operating performance. A known alternative method is the "blown fibre" technique whereby a compressed fluid such as compressed air is used to convey, or "blow", a fibre unit along a conduit from one end.

Currently, installing fibre units using the blown fibre method requires at least two operators: one situated at the head end of the conduit, where during installation air and the fibre unit is installed into the mouth of the conduit, and one at the remote end of the conduit, where air and the fibre unit emerges from the mouth of the conduit. The second remote end operator is required because the remote end is often some distance away - up to a kilometre or more - from the head end. The operator at the head end is therefore unable to know the status of the remote end during an installation without a second operator located there.

The head end operator monitors and operates a fibre installation mechanism - known in the art as a "blowing head" - that feeds the optical fibre into the conduit and controls the supply of compressed air. He starts the process by directing air into the mouth of the head end conduit. If the air is directed into the correct conduit, the remote end operator will sense the arrival of the air with an air flow meter temporarily connected to the end of the conduit, or more simply by feeling the air flow exiting the conduit against his hand if the air flow is sufficiently high. He then communicates this to the head end operator by radio or other means, to confirm to the head end operator that he is applying air to the correct conduit. The head end operator then introduces the fibre unit into the conduit and blows it through to the remote end of the conduit, whereupon the remote end operator advises his colleague on its arrival. The head end operator then turns off the air supply and the blowing head, and the process is complete.

This process is labour-intensive as a minimum of two operators must work on a single installation. The head end operator needs to be skilled in the operation of the blowing head, while the remote end operator is required to alert his colleague to the status of the installation at the remote end.

Methods whereby a single operator at the head end of a conduit can detect the arrival of an optical fibre at the remote end of the conduit are known.

In the simplest method, the length of the conduit route is known, allowing the operator to know that the fibre has (probably) arrived at the remote end when the required length of fibre unit has been played out. This relies on the map record of conduit route being up to date and accurate, and presumes a completely smooth and obstruction-free conduit route. Neither of these can be guaranteed in practice.

Another known practice is to install at the remote end of the conduit a barrier of porous material such as an "airstone" which is placed at the remote end of the conduit, which will allow air through but which will stop further progress of the fibre unit. This cease in progress is detected by the blowing head which then stops further ingress. However even when the progress of the fibre has ceased, the operator at the head end cannot be certain that the fibre unit has reached the porous barrier at the end of the conduit, or if instead the fibre unit is caught on an obstruction at some point along the length of the conduit.

As described in WO9103756, a solution is to position a light source at the remote end of the conduit and a light detector is positioned at the head end. The arrival of the- optical fibre at the remote end is indicated by the detection of light by the detector at the head end. One problem with this method is that an early, or "false", indication of the arrival of the optical fibre may occur if stray light is inadvertently introduced into the conduit at a location between the head end and remote end, e.g. at an open ' inspection chamber. This method also relies on adequate light being coupled into the advancing end of the optical fibre to be detected by the detector, however the coupling process is inefficient and is further degraded in proportion to the length of the optical fibre due to normal attenuation properties, so this method may not be practicable on long lengths of optical fibre. A second method described in this document uses a previously installed optical fibre to create part of a light "circuit" with the blown optical fibre. This method is not as suitable for installing the first optical fibre in a conduit. Furthermore, any previously installed fibre units may be carrying live traffic and so would not be available to use for the installation of additional fibres.

Another known method is to use a blowing head such as that described in WO/9812588, which is configured to stop driving the fibre unit when it senses that fibre movement within the conduit is slowing down or stopping owing to an obstruction. When used in conjunction with a porous airstone at the remote end, the fibre unit would stop moving when it reaches the destination end. However, as the sealed-off end is just one type of obstruction the fibre unit may encounter on the conduit route, this method fails to positively identify when the fibre unit has reached and emerged from the conduit at the remote end without travelling to the remote end for a visual inspection.

Accordingly, in a general aspect, the present invention provides methods and devices for aspects relating to the installation of cables such as fibre units into conduit tubes, in particular, allowing a single operator to operate substantially on his own to determine if air fed into a conduit is reaching its intended destination, and/or if and when the fibre unit fed into the conduit has reached its destination. The invention can be used where the operator has to choose one of a number of conduits, or where there is a single conduit but where it is desirable to unambiguously confirm that the air and fibre unit reaches the intended destination.

A first aspect of the invention provides a method for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, comprising the steps of: introducing an air flow into the conduit, introducing a signal into the conduit or into a bore communicating with the conduit, and detecting a change in a phase shift of the signal caused by movement of the air flow.

By using this method, an operator may determine if the air being fed into the conduit at the head end is flowing from the correct remote end tube; if not then the air is either being fed down the wrong tube, or there is some other problem. In any event this may prevent an aborted installation session. This implementation of the invention can be performed at the remote end of the conduit, in which the operator can choose to use the bore communicating with the conduit; otherwise the steps can be performed directly using the conduit itself.

The person skilled in the art will recognise that any form of signal in the form of e.g. a mechanical wave which propagates through a medium such as air or other fluid in the conduit can be used to detect a change in the velocity of the medium. As such, it will be appreciated that the method according to the invention can be used to detect movement in applications other than a blown fibre installation, due to the possibility to detect movements and speeds of the medium within the conduit or other container or even outside of containment means. In the present application however the signal used will typically be an acoustic signal (e.g. a sonar signal) which is preferably well suited for travelling through the respective medium whose velocity is to be detected. An acoustic signal with a frequency above the human hearing range is often convenient.

In a preferred implementation of his aspect of the invention, a square wave in the form of an acoustic sound wave is fed into the conduit or the bore through which the air is to flow. The acoustic path of the sound wave can be one which is reflected within the conduit, and which phase shift is 180 degrees allowing for detection of air flow direction. In further preferred implementations, the signal is introduced at the angle acute to the conduit, which satisfies both the requirement for a signal path of sufficient length to detect air flows within the conduit, and for placement of the detection means relative thereto. One way of achieving this is to reflect the signal so that the reflection occurs within the conduit through which air is to travel. Preferably, the operator at the head end can be alerted when air flow through the conduit is detected by a confirmatory signal sent from the remote end.

A second aspect of the invention provides a method for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, comprising the steps of: introducing a cable into the conduit at the first conduit end, introducing a signal into the conduit or into a bore communicating with the conduit, and detecting a change in a property of the signal caused by movement of the cable.

Detection of the arrival of the fibre unit at the remote end of the conduit can be achieved by using essentially the same method as that employed to detect the air is flowing to and from the remote end of the conduit. The steps could include all the preferred ones described for the detection of air flow - e.g. using a reflected signal, etc. This advantageously saves on the need to have two sets of equipment and techniques. In a preferred implementation, the method includes detection of air flow, and then of the arrival of the fibre unit at the remote end.

A third aspect of the invention provides a device for use in connection with installing a cable using an air flow into a conduit having a first conduit end and a second conduit end, comprising a transmitter for transmitting a signal into the conduit, and a detector to detect a change in a property of the signal caused by movement of one or both of the air flow and the cable.

This device is adapted to be capable of sensing air and/or fibre unit arrival at the remote end. It can be coupled to the conduit at the remote end or at any other point, and is adapted to be capable of detecting the speed of air and/or fibre unit travel within the conduit as well. In one embodiment, the device could include a bore which communicates with the conduit, so that the air or fibre unit moving through the conduit can travel into the bore. The skilled person would understand that the device can be configured either to work specifically only using the conduit alone, or using a bore communicating with the conduit, or configured to be adaptable to both.

Preferably, the device causes the signal to be reflected for detection, and includes a vent allowing air travelling into the conduit or bore to escape to prevent pressure build up that would affect the continued air flow as well as the movement of the fibre into the device.

A fourth aspect of the invention provides an installation for installing a cable into a conduit having a first conduit end and a second conduit end, comprising an air source to introduce air into the conduit at the first conduit end, driving means to mechanically drive a cable through the conduit, and a device comprising a transmitter for transmitting a signal into the conduit, and a detector to detect a change in a property of the signal caused by movement of one or both of the air flow and the cable.

A blown fibre installation comprises means to advance the fibre unit through the conduit, which mechanical driving force is provided by the drive wheels of a blowing head, and viscous drag created by the flow of compressed air along the conduit. Use of the device will allow the operator to positively know that air is flowing to the correct remote end of the conduit, and if and when the fibre unit has arrived, so that he can know when to end the installation session.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 depicts an airstone of the prior art;

Figure 2 depicts a fibre bead of the prior art;

Figures 3A and 3B are respectively views of the head and remote ends of a blown fibre installation according to the invention; Figure 4 is a cross section view of an embodiment of a device for sensing air arrival;

Figure 5 is a graph illustrating how air flow arrival and speed is detected;

Figures 6A, 6B and 6C are alternative embodiments of the invention; and

Figure 7 depicts an embodiment of a device for sensing fibre unit arrival.

Figure 1 shows a prior art "airstone" (2), which is used in current blown fibre installations. As noted above, the airstone is connected to the remote end of the conduit. It comprises a housing (4) which is substantially cylindrical and which is rounded at one end. At the other end is a collar (6) which permits the airstone to be connected to an optical fibre tube (T) by friction fit. The housing comprises a compressed granular body which allows air to flow from the fibre tube (T) into, and then out of the airstone, via the housing. Figure 2 depicts a prior art fibre "bead" (10). It comprises a head portion (12), a neck (14), and includes a slot within it to accommodate the tip or leading end of the fibre unit (F). It is typically made of a metal such as brass, which is corrosion-resistant and sufficiently malleable to be crimped at the neck (14) onto the end of the fibre unit (1) by an operator using pliers. After use when the fibre has reached the remote end of the installation, the bead is cut off and discarded. Its main function is to protect the leading end of the fibre during installation, from bumping into the sides of the tube, and from damage when the leading end reaches the airstone (2), and to ensure a smooth path through fibre tube connectors.

The apparatus and set up for a typical blown fibre installation is shown in Figures 3A and 3B. The head end of the installation is depicted in Figure 3A, where the head end tube (T1) is fed with an air supply (22) and the fibre unit (F) in the direction of arrow "X". A blowing head (20) is attached to the tube, which provides a mechanical pushing force via drive wheels, to drive the fibre unit (F) through the tube (T1 ). The air compressor supplying the air (22) is connected to the blowing head so that the air is channelled into the tube via the blowing head. The fibre unit is driven along the conduit by a combination of the viscous drag generated by the air flowing along the conduit, and the drive wheels of the blowing head.

In Figure 3B, the remote end of the conduit (T2) can be the Other end of the same tube (T1) or a physically separate tube connectorised at an immediate point. In an embodiment of the invention, a sensing device (30) is connected to the remote end tube (T2). This comprises a housing (32) and includes a bore (34) to which the outlet end of tube (T2) can be fitted, the bore terminating in a bore end (35). Air and fibre fed into the conduit from the head end can enter the bore in the direction of arrow "X". The sensing device includes means for the air to escape from the device in the form of a disc of porous material (36) located at the bore end (35). The disc (36) can be made from the same, material as that for a conventional airstone (2) or other suitable materials, so that the fibre end retained within the device while the air may flow freely out of the bore. The means for air escape could also be located elsewhere within the device, and the means could alternatively comprise vents.

Another alternative, but less preferred way, would be to connect a conventional airstone (2) to the bore end (35) so that it projects from the device (30).

In a typical blown fibre installation according to the invention, the operator connects a sensing device (30) to the remote end of the conduit tube through which the fibre unit is to emerge. He then returns to the head end to start the blown fibre installation process. The operator first determines that air introduced into the head end of the conduit does flow to the desired remote end, before introducing the optical fibre into the conduit (T1). He turns on the compressor located at the head end to generate the air flow (22 in Figure 3A) into the conduit, and if all is well (i.e. the operator has chosen the correct conduit, the conduit route is correctly mapped, etc.), the air flows in the direction of arrow "X" through the conduit to the remote end of the conduit as shown in Figure 3B.

The air flows to and out of the mouth of the conduit (T2) and into the sensing device (30) connected to the conduit. At this stage, the fact of air arrival could be alerted to the operator at the head end by e.g. a radio signal sent from the remote end.

After the operator has determined that air is indeed flowing to the correct remote end, the optical fibre unit (F) is fitted with a fibre bead (B in Figure 2) and then introduced into the head end of the conduit. The fibre unit is driven along the conduit by a combination of the viscous drag generated by the air flowing along the conduit, and the drive wheels of the blowing head (20).

In Figure 3B, the device 30 is shown as being positioned at the mouth of the remote end of the conduit, in place of the conventional airstone (2 in Figure 1). Although this is a preferred position, the device can be positioned in other places to realise the advantages of the invention, as will be described below.

Two problems in particular are addressed by the device according to the invention: first, the determination that air fed into the head end of the conduit using the compressor has arrived at the remote end, and second, that the fibre unit fed into the head end has arrived at the remote end. By using the device and methods described herein, a single operator located at the head end of the conduit may positively know whether air has been fed into the correct tube, and when the fibre unit has reached the remote end.

Figure 4 is a cross sectional view of one embodiment of a sensing device (50) according to the invention. This device can take the size and proportions of a matchbox, and be made of a cost-efficient material such as a plastic. It will be installed on the remote end of the conduit on tube (T2 in Figure 3B) prior the start of the blown fibre installation session, by a simple push-fit or the like.

As described earlier against Figure 3A, the housing (32) includes a bore (34) though which air and the fibre can enter. The device further includes acoustic channel entrance and exit sections (40a, 40b). The acoustic entrance and exit channels are in this embodiment set at about 30 degrees to the longitudinal axis of the device bore

(34), and intersect and interface with the device bore as shown to form an acoustic channel comprising an entrance, bore and exit section; the total physical length of the acoustic channel is approximately 250mm.

During use of the sensing device, a mechanical wave signal such as an acoustic or sound signal (42) is transmitted as a transmitted signal (42a) along the first, transmission acoustic channel (40a) in the direction of arrow "Y". The transmitted signal (42a) is reflected at the floor of the device bore (34) and transmitted at an angle of about 30 degrees along the second, reception acoustic channel (40b) in the direction of arrow "Z" as a reflected received signal (42b).

The acoustic signal (42) is generated using a suitable signal generator and transmitted with a miniature loudspeaker - these functions can be performed with a single device (44). The received signal (42b) is received within the reception channel (40b) by a receiver (46) - this could be a miniature microphone. The transducers (the acoustic signal generator/transmitter and receiver) are small units which can be located within the acoustic channels so that the entrances to the channels are sealed off from the bore as shown. The signals are measured and compared by e.g. a processor. In the present embodiment, the processor drives the transmitter with a square wave at 4OkHz and detects the received signal, after amplification, as another square wave of differing phase; the actual phase shift is determined by measuring the time between the leading edge of each driving pulse and the next occurring leading edge of the received amplified signal.

As the signals within the acoustic channels comprise sound waves travelling through air, disturbance of the air medium through which the sound waves are travelling will cause a phase shift. Where the air flow is travelling in the direction of arrow "X", the sound path is reduced, and the phase angle of the acoustic wave shifted. The phase angle reduces approximately proportionally with the speed of the air flow.

In an example where the acoustic path length of the acoustic signal is about 25cm from transmitter (44) to receiver (46), and where the portion of the acoustic path within the bore (34) is about 10cm, it will take about 0.00075 seconds for a 40kHz wave travelling at a rate of about 330m/s, to travel from the transmitter to the receiver though unmoving air within the bore. When air arrives at and starts flowing through the bore, the transmitted signal (42a) is carried by the air moving within the bore. The frequency of the received signal (42b) detected by the receiver is the same, but is shifted in time.

Figure 5 is a graph illustrating the shift in phase caused by the movement of the air medium when the acoustic signal is travelling through the bore. Thus detection of a phase shift is an indication that air is flowing within the device bore. By measuring the phase shift or angle change, it is further possible to measure the speed at which the air is travelling within the bore.

This embodiment of the device of Figure 4 is designed so that the maximum expected change in phase shift (i.e. between the phase shift when air is stationary within the acoustic channel and when air is flowing at its maximum expected speed in the forward direction - i.e. towards the receiver) is definitely less than one wavelength (otherwise there could be two different possible air speeds corresponding to the same phase shift) and preferably less than half of a wavelength (so that "negative" air speeds - i.e. where the air is travelling in the direction from the receiver to the transmitter). In the present embodiment the maximum expected air speed is about 10 m/s (an expected maximum throughput of air is 20 litres per minute for an 8mm internal diameter conduit, which corresponds to about a speed of 7 m/s). In the present embodiment a sonar signal of frequency 4OkHz is used which gives rise to a wavelength of approximately (330m/s)/(40kHz) (λ = v/f) » 8.25mm and thus a half wavelength of about 4mm. The acoustic path length, l_a, within the bore is given approximately by:

Ia = Ib ■ Vs / (V₈ + V_m)

where I_b is the physical length of the acoustic channel within the bore, v_s is the speed of sound through the medium and v_m is the speed of the medium. Thus for an anticipated maximum speed of the medium of 10m/s, the maximum anticipated change in the acoustic path length is approximately l_b .(1 - 330/340) or about 0.03 l_b. Thus l_b should be less than 4mm/0.03 = 130mm, so a path length of about 10cm has been chosen in the present case.

Once the phase shift is detected, this fact can be transmitted in the form of e.g. a radio signal back to the single operator at the head end of the conduit.

It is preferable to use as the acoustic signal an ultrasonic signal of about 4OkHz because this type of signal is inaudible to the human ear, and because small, inexpensive components for its transmission and reception are known and readily available, e.g. those manufactured by Farnell under parts number 213-214 (transmitter) and 213-226 (receiver). Thus it is within the scope of the invention to use any signal comprising a mechanical wave travelling through air as a medium, although of course practical considerations could intervene, e.g. the generation of an extremely low frequency wave may require a loudspeaker which is disproportionately large to the device itself.

The transducers could also be located within the device otherwise than described above within the housing, or be physically separate device(s) connected to the sensing device.

In one arrangement, the transducers could be sited at further within the acoustic channels as shown in Figure 6A. Alternatively, they could be sited at or very near to the interfacing section at which the device bore (34) and acoustic channels (42) intersect, and positioned thereat to direct the transmitted and received signals directly into the device bore. Thus, the acoustic channels are reduced in length or else rendered unnecessary: this would have the advantage of reducing the likelihood of air and/or the fibre unit from migrating into the acoustic channels, as well as obviating the need for acoustically-transparent barriers at the interface.

The frequency of 4OkHz for the acoustic signal is preferred because it has a wavelength of 7.5mm which is ideal for the application and the anticipated air velocities in the bore. Furthermore, inexpensive off-the-shelf components for transmission and reception of such frequencies are known and readily available (e.g. those manufactured by Farnell mentioned above). This frequency is also inaudible to the human ear. However any signal comprising a mechanical wave of any frequency requiring air as a medium is within the scope of the invention. For example, if a wide range of air velocities was expected in the bore, a use of an acoustic signal with a lower frequency (and hence a larger wavelength) or of a shorter bore section of the acoustic channel, would be preferred (alternatively, the device could have a larger bore, thus causing a reduction in the speed of the air for a given total volume of air flowing through the bore per unit of time, etc.).

The barrier against which the reference sound wave signal is reflected also need not be located within the device bore, as long as the received signal is receivable by the receiver.

Yet other variations would also be clearly possible - the acoustic channel angles do not need to be set at 30 degrees to the axis of the device bore. This is a suitable angle permitting use of commonly-available and cheap transducers. It is also a sufficiently acute angle relative to the device bore (34) to permit the acoustic signal to travel along a sufficient distance along the bore to permit sensing of any air flow movement. Detection of air flow is still possible at less acute angles, but will tend to decrease as the angle between the axis of the bore and the channel(s) tend towards 90 degrees. To improve the sensitivity of the detection method, the bore could be made larger in diameter, or the acoustic signal used could be of a higher frequency. This will permit the acoustic signal a longer period within the bore for the purpose of sensing air flow. Maximum sensitivity is at 0 degrees along the tube, although transducer placement within the tube may be a problem.

The skilled person would also recognise that the step of reflecting the acoustic signal (42) for measurement and comparison is not essential to detect any phase shifts indicating the presence of air flow in the device bore. For example, the acoustic channels could be arranged so that the transmitter is located in the transmission acoustic channel on one side of the bore, and the receiver in the reception channel on the other side of the bore as depicted in Figure 6B. In this embodiment, the signal (42a) transmitted by the transmitter (44) travels in the direction of arrow "Y" into the bore. Any air flow along the bore in the direction of arrow "X" will cause a phase shift in the acoustic signal received by the receiver (46) in the reception channel (40b). Various variations in the configuration of the acoustic channel are available: some are depicted in Figure 6C. Acute angles and right-angled acoustic paths can be offset or not, and can also be arranged so that the acoustic signal is introduced into the bore against air flow direction, so that the signal is compressed instead. These may however increase the size of the housing required as compared to an embodiment of the invention using a reflected received signal.

It has been earlier noted that when air has been confirmed to be flowing to and from the remote end of the conduit by the device, a preferably radio signal is sent to the operator at the head end. Upon receipt of this signal, the fibre unit can be fed into the tube confirmed to have been correctly identified at the head end. The device of Figure 4 and the methods used can also be used to detect the arrival of the fibre unit at the remote end.

It is expected that when air flow reaches the device bore (34), the acoustic signal will change a first time to mark this. The signal should remain relatively steady in its phase shifted state for as long as the air continues to flow within the bore at a relatively steady velocity. When the fibre unit arrives in the bore of the device, the acoustic signal is changed a second time. For example, the fibre, or the bead (e.g. B in Figure 2) attached to fibre end, may restrict or block the air flow within the bore. The receiver can detect this further phase shift, which may be interpreted as an indication that the fibre unit has arrived within the sensing device at the remote end of the conduit.

Cost-savings can be realised by using the same sensing device and the method to detect the arrival of air, and subsequently the arrival of the fibre unit.

Although the device and method are described to be deployed at the remote end as shown in Figure 3B, to enable determination that air and fibre reaches the remote end, they can be also used for other purposes. For example, the device could be fashioned as a sleeve to be used as a connector at intermediate points along the conduit route, for detection of the path taken by the air flow. This allows the operator to track the progress and movement of the air and the fibre unit for purposes in addition to, or other than for, installing blown fibre - such as in the detection of gaps leading to air leaks in the conduit tube network.

By providing some mechanism for enabling an acoustic signal to enter and exit a conduit, a device could be created which can be placed at any point along a conduit to determine if air is flowing through it, without having to pierce the conduit. For example, it could be possible to simply use a quite strongly amplified transmitter and a dampening mechanism for preventing the acoustic signal passing through the conduit wall or the exterior of the conduit, alternatively some sort of gel or other material could be used to form acoustic windows into the conduit.

The device could also be used to measure the velocity of air travelling within tubes and conduits if suitably calibrated. The phase shift of the acoustic varies with speed, so that as speed increases so does the phase shift because the acoustic path gets stretched with increasing speed or compressed with decreasing speed.

Although developed specifically for detection of air flow arrival and speeds in the particular context of the installation of blown fibre, the skilled person would realise the applicability of the apparatus and methods in other contexts and industries concerned with the detection of fluid flow and speed, such as within conduits and pipes for gas, water or oil.

Turning back to the context of a blown fibre installation, the above device and method can advantageously be used with components and methods that will positively indicate arrival of the fibre unit at the device. Figure 7 shows an embodiment of the device of Figure 4, further including the components for the aspect of the device which allow detection of arrival of the fibre unit within the device, which is based on detection of the presence of the bead (e.g. B in Figure 2) coupled to the end of the fibre unit.

In Figure 7, the device bore (34) as described previously, terminates in an air-porous barrier (36). An induction loop (60) is positioned at or near the air-porous barrier.

Here, the magnetic sensor takes the form of a coil of copper which is wrapped around the bore. Preferably the wall of the bore should be as thin as possible (e.g. about 1 mm thick) and/or the coil wrapped as closely to the bore as possible, to attain the greatest sensitivity of the coil. The loop forms part of an LC oscillator (64), which resonates at a constant frequency ω₀ =1/(LC)^1/2. In the present embodiment, a

Hartley oscillator is used in which both the frequency and amplitude of oscillation are affected if there is a change in the inductance and quality (Q value) of the oscillator.

The induction loop is made of a coil of very fine copper wire having a diameter of about 0.2mm, and the coil will be in the order of 15 turns. However the exact number of turns is not critical to invention, nor is the size of the wire, although the number of turns used is related to the coil diameter.

Prior to installation, a bead (B) is attached to the fibre unit (F). In this aspect of the invention, the bead must include some metal or some other material with a relatively high permeability. When the fibre unit arrives at the remote end of the conduit, it travels out of the tube (T2 in Figure 3B) and into the sensing device (50) along the bore (34). Its progress is finally halted when the beaded end of the fibre unit reaches the porous barrier (36) which permits air to escape, but retains the fibre unit within the bore. At this point, the bead (B) is lodged within close proximity of the induction coil (60) and serves as an electromagnetic actuator to the sensing device, by acting as a metallic core which changes the inductance of the coil and the Q-value of the oscillator. The changes in inductance and Q-value cause both frequency and amplitude to vary, so either or both of which can therefore be monitored and measured. As the change in amplitude is greater with the preferred type of bead used in the present embodiment, however, it is easier and preferable to monitor this. The change is detected by a comparator and is a clear indication of the arrival of the beaded fibre unit. An alert can then be signalled back to the single operator at the head end of the conduit, allowing him to terminate the installation session.

Variations within the scope of the invention are possible. For example, the coil is located at or near the end of the bore so as to realise the advantage of a continuous reading of the bead's presence as the metal core within the coil. This allows for an unambiguous indication of the bead's arrival within the bore. However, location of the coil elsewhere in the device - indeed, location anywhere else within the conduit - would allow for the detection of the momentary change in the inductance in the coil indicating that the bead has passed through it. As with the ultrasonic phase shift detection method described above, this could allow an operator to track the progress and movement of the beaded fibre unit along the conduit and/or.conduit network. For example, the bore of the device may be configured to extend and taper beyond the housing (32) so that upon arrival, the beaded fibre unit comes to a rest within a narrower section of the bore so that the coil (60) can be actuated by the presence of the bead acting as a metallic core.

Different materials will cause the oscillator to resonate at different frequencies. In the present embodirηent, the coil responds to the arrival of beads made from various metals such as aluminium, brass, steel or copper. The applicants currently use a bead made of brass or aluminium as they do not rust. If this is less of an issue, alternative fibre unit arrival detection methods within the scope of the invention can be realised. For example, by substituting the induction coil with a magnetic sensor, the arrival of a bead made of a magnetic material (which need not include metal) or otherwise a ferrous material (any material exhibiting quite strong ferro- or para- magnetism should be suitable) could be detected as a Hall probe causing a change in the magnetic flux of the magnetic sensor. This change can again be sent to the operator using e.g. a radio link. The skilled person may realise yet other implementations of the detection method, such as using electromagnetic proximity sensing methods, for example by sensing the change in the capacitance of a capacitor formed so as permit the bead to pass between the plates of the capacitor, in which case the bead should be made of a material having a relatively high dielectric constant.

In the current application in the context of blown fibre installations, use of a sensing method with no moving parts is particularly advantageous. This is because air flows and movements within the tube could be disturbed by a moving sensor device. The sensor itself could be affected by the air, as well as by debris and particularly the microspheres which coat the fibre units (which enhance the effect of viscous drag during installation, and which could fall off and blown along the conduit by the pressurised air). In an even more preferred embodiment the sensor is contactless as so that it can be placed outside the conduit tube (where the device is to be placed at the intermediate section of the conduit without need to pierce the tube) or the bore of the device, as shown in Figure 7. However in other applications it would certainly be possible to place the sensing device within the conduit or bore, or other containment device or otherwise, to realise the purpose of the invention. By doing so, it is also possible in some embodiments of the invention to track the speed at which the actuator bead is travelling within the conduit.

Yet other variations would be apparent to the skilled person: for example, the sensing device need not be located right next to the conduit or bore; it could be located some distance away if it is sufficiently sensitive to the movement of the actuating bead. Also, the locations of the sensing device and the actuator could be reversed, so that the sensor is placed on the fibre unit at its tip or elsewhere along its length, and the actuator placed within, around or proximate to the conduit or tube through which the fibre unit will travel. The principle of the invention requires only that the sensor detects the actuator and registers the change in the electromagnetic property.

The invention does not require that the actuator be coupled to a fibre unit or indeed any object at all. A system can be set up so that the proximity of the electromagnetic actuator to the sensor can have the significance of indicate presence or movement. Accordingly, it is possible to use this aspect of the invention to detect e.g. movement and/or presence of air or such other medium carrying the actuator, which could be made very lightweight and/or mobile by the provision of e.g. wheels of skids.

As noted above, alerts are sent from the remote end to the operator at the head end to alert or inform him about the arrival of air or of the fibre unit at the sensing device. This is conveniently implemented using radio signals, which can be transmitted to e.g. a hand held device. Alternatively the receiving device could be integral to a piece of equipment used at the head end, e.g. the blowing head and/or the compressor. It is possible also to automate this part of the process, so that upon receipt of a signal that air has arrived at the remote end, the blowing head could start plying fibre into the conduit; or the apparatus shutting themselves off upon receipt of a signal that the fibre unit has arrived,

As noted above, the size of the housing of the device is about the size of a matchbox (dimensions very approximately 55mm x 35mm x 15mm), within which is fitted the transmitter and receiver, and the induction coil. A power source (e.g. a battery) is also included, as is a radio unit and antenna for sending confirmatory signals to the head end of the conduit. A printed circuit board is installed along a wall of the housing, which may include a processor, for detecting, comparing etc. the acoustic signals for a phase shift, and for determining any inductance change in the coil. The skilled person would appreciate that some or all of these components could comprise separate apparatus or devices sited outside the housing but connected thereto. The embodiment of the invention as shown in Figure 7 is designed for use at the remote end of the conduit to detect fibre arrival. However, as discussed in connection with the phase shift detection aspect of the device, this proximity sensor - preferably a contactless version - could also be placed non-invasively at any point around a conduit to detect the passing of a suitable bead through the conduit at that point.

The methods, devices and configurations described above and in the drawings are for ease of description only and not meant to restrict the invention to any particular embodiments. It will be apparent to the skilled person that various sequences and permutations on the methods and devices described are possible within the scope of this invention as disclosed; similarly the invention could be used in various similar scenarios and for various cable types. In particular, the apparatus and methods relating to air flow detection by ultrasound phase shift detection and the methods and apparatus relating to fibre unit arrival detection by detection of phase shift and/or a electromagnetic property in e.g. a coil, are depicted in this description to be used together advantageously in a preferred embodiment. However they will work independently of each other on their own, to realise the advantages of the respective inventions.

Claims

Claims:

1. A method for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, comprising the steps of: - introducing an air flow into the conduit, introducing a signal into the conduit or into a bore communicating with the conduit, and detecting a change in a phase shift of the signal caused by movement of the air flow.

2. A method according to claim 1 wherein the step of detecting a phase shift comprises detecting a phase shift of substantially 180 degrees.

3. A method according to any preceding claim wherein the step of introducing a signal comprise introducing a square wave.

4. A method according to any preceding claim wherein the step of introducing a signal comprises introducing a sound wave.

5. A method according to claim 4 wherein the step of introducing a sound wave comprises introducing a sound wave of substantially 4OkHz.

6. A method according to any preceding claim wherein the step of introducing the signal comprises introducing the signal at an acute angle to a longitudinal axis of the conduit or the bore.

7. A method according to claim 6 wherein the step of introducing the signal at an acute angle to a longitudinal axis of the conduit or the bore comprises introducing the wave at substantially 30 degrees to the longitudinal axis of the conduit or the bore.

8. A method according to claim 6 wherein the step of introducing a signal into the conduit or the bore comprises introducing a signal comprising a first wave section and a second wave section, the method further including the step of making a comparison between the first wave section with the second wave section and using results from the comparison for the step of detecting a phase shift in the signal.

9. A method according to claim 8 wherein the step of introducing a signal into the conduit or the bore comprises reflecting the first wave section to form the second wave section.

10. A method according to any preceding claim wherein the step of introducing the signal into the bore comprises introducing the signal into the bore communicating with the conduit at the second conduit end.

11. A method according to any preceding claim wherein the step of detecting a change in a property of the signal includes detection of a speed of movement of the air flow within the conduit or the bore.

12. A method according to any preceding claim further including the step of transmitting a confirmatory signal upon detection of a change in the property of the signal.

13. A method for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, comprising the steps of: introducing a cable into the conduit at the first conduit end, - introducing a signal into the conduit or into a bore communicating with the conduit, and detecting a change in a property of the signal caused by movement of the cable.

14. A method according to any one of claims 1 to 12 further including the steps of a method according to claim 13.

15. A device for use in connection with installing a cable using an air flow into a conduit having a first conduit end and a second conduit end, comprising a transmitter for transmitting a signal into the conduit, and a detector to detect a change in a property of the signal caused by movement of one or both of the air flow and the cable.

16. A device according to claim 15 further including a bore communicating with the conduit, wherein in use the transmitter is adapted to transmit the signal into the conduit or the bore.

17. A device according to claim 15 or claim 16 wherein the detector is adapted to detect a phase shift of the signal.

18. A device according to any one of claims 15 to 17 wherein the transmitter is adapted to transmit a sound wave through the conduit.

19. A device according to any one of claims 16 to 18 further including a channel adapted to communicate with the conduit such that in use the signal is transmitted through the channel into the conduit or the bore.

20. A device according to claim 19 wherein the channel communicates with the conduit or the bore at an acute angle to a longitudinal axis of the conduit or the bore.

21. A device according to any one of claims 15 to 20 wherein the mechanical comprises a first wave section and a second wave section.

22. A device according to any one of claims 19 to 21 , wherein the channel comprises a first channel section and a section channel section, the transmitter is positioned within the first channel section, the detector is positioned within the second channel section, and wherein in use the first wave section travels through the first channel section, and the second wave section travels through the second channel section.

23. A device according to claim 21 or 22 wherein the second wave section is a reflection of the first wave section.

24. A device according to claim 23 wherein the reflection is caused within the conduit or the bore.

25. A device according to any one of claims 15 to 24 wherein the device includes a vent to vent air flowing in the conduit or the bore.

26. A device according to any one of claims 15 to 25 adapted to be coupled to the conduit at or proximate to the second conduit end.

27. A device according to any one of claims 15 to 26 further including means to measure a speed of the air flow.

28. A device according to any one of claims 15 to 27 further means to transmitting a signal to the first end upon detection of a change in the property of the signal.

29. An installation for installing a cable into a conduit having a first conduit end and a second conduit end, comprising an air source to introduce air into the conduit at the first conduit end, driving means to mechanically drive a cable through the conduit, and a device according to any one of claims 15 to 28.