CABLE INSTALLATION USING INDUCTION

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, particularly in the core or backbone network. 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, both commercial and residential, as possible. This involves the installation of millions of kilometres of optical fibre across the network, especially at the local access level which had previously been served by copper. To achieve widespread take-up, the optical fibre installation process needs to be speedy, cost- and effort-efficient.

An optical fibre unit, which could comprise a single optical fibre, or a bound bundle of typically 2 to 24 optical fibres, can be installed using what is known as the "blown fibre" method, described in EP108590. In this method, a fibre unit is propagated along a hollow tube pre-laid along the desired route, where compressed air is fed, or "blown" into the mouth of the tube. The viscosity of the flow of air travelling along inside the tube, together with the friction on the outer surface of the fibre unit, help to carry the fibre unit along the length of the tube.

The tubes or conduits typically are made of plastic, each with a typical inner diameter of 2.5 to 6 mm or more, and are usually provided in a bound bundle comprising up to 24 or more tubes, which are held together within a protective outer sheath. The tubes usually comprise a continuous span between convenient access points such as surface boxes, inspection chambers down man holes, or near telephone poles. Each fibre conduit tube can receive at least one fibre unit comprising one or more individual optical fibres. Large numbers of tube conduits - and bundles of conduits -

are pre-installed across the access network and the distribution network between the local exchanges and the customer premises, typically to locations which may require a future fibre connection.

When it is decided to populate these pre-installed tubes, the fibre cable or unit is installed in each tubular span by blowing it down the conduit from one end; alternatively the unit could be blown down a concatenation of spans in a single step if circumstances permit. This is repeated for each span, or concatenation of spans, until a continuous fibre path has been laid between the end points of the whole route.

A tubular path can be described between two access points, which may be hundreds of metres apart, by a single length of conduit tube. The conduit path may alternatively comprise a number of lengths of physically separate conduit tubes which are connected together e.g. in series. Either way, it is crucial to choose the correct conduit path during installation, so that the fibre unit emerges at the desired destination end. During installation however, the operator at one of the installation points would be presented with a large and potentially confusing number of conduit tube openings, each representing a path leading to a destination. The tube openings are usually mapped to their destinations e.g. by colour-coding. If however the tube openings are wrongly mapped, or the records otherwise inaccurate, mistakes can be in made in attempts to identifying the conduit path and the tube opening leading to the desired destination. This is especially so if the working conditions are poor e.g. in adverse weather up a telephone pole or down a manhole or in poor lighting.

Where the path comprises a number of tube lengths connectorised together, 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 connection 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 may, during installation, emerge in the wrong place, or in an extreme case, 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 may not even know in a timely manner when something has gone wrong.

The current response to this problem is to use two operators during installation, one at each end of the installation conduit path. The second operator at the destination end of the tubular path is required because the destination or 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 reporting the status back to the head end.

During a typical installation session, the first operator situated at the head end of the conduit fits a protective slug or bead on the tip of the fibre unit, then feeds this and compressed air into the mouth of the conduit with fibre installation apparatus - known in the art as a "blowing head" which is described in general in WO88/00713. Meanwhile the second operator locates himself at the desired end point of the fibre installation. The process commences by directing compressed air into the mouth of the head end conduit. If the air is directed into the correct conduit so that the tubular path leads to the desired destination, the remote end operator can eventually 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 the air is applied to the correct conduit. The head end operator upon receiving the news, then blows the fibre unit into the conduit through to the remote end, 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 installation process is complete.

This process is labour-intensive as two operators must work on a single installation.

This is in turn drives up the overall cost of optical fibre installation, a problem now especially significant in the FTTP context with the considerable installation volumes involved.

Various methods requiring only a single operator installation of blown fibre have been developed, to obtain a significant saving in manpower and cost requirements. 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 constructed of a porous material which allows air through but which will stop further progress of the fibre unit. The airstone is temporarily placed at the mouth of the destination remote end of the tube conduit. When the fibre ceases to travel down the tube, this is an indication that the far end of the fibre may have reached the destination end and has been retained by the airstone barrier. However, lack of further progress is ambiguous as to whether the fibre unit has indeed reached the porous airstone at the destination end, or if instead the fibre unit is caught on an obstruction at some intermediate point along the length of the conduit.

These, together with other methods like those described in WO91 /03756 or WO/9812588, also describe how fibre arrival can be detected by the single operator at the head end of the installation; the initial step of detecting that the compressed air fed into the head tube end is not addressed in the above techniques.

WO2007/113544, the applicant's co-pending application describes a method for detecting the emergence of the leading end of the fibre unit from the remote end of the conduit, by sensing the metallic property of the bead which marks the following of the rest of the fibre unit. However this does not include the sensing of airflow, only of ¹

the fibre unit. The operator would have to employ a different method (e.g. by stationing the second operator at the remote end) to confirm that air has been applied down the correct conduit, before the fibre unit is installed into the conduit.

A method developed by the applicant covered in WO2006/103419 does describe a device which permits the detection of the arrival of both air as well as the remote end of the fibre unit at the opening of the remote tube end. The device uses a low-mass wind vane which rotates in the presence of air flow, and which rotation is stopped when the fibre end arrives and gets "caught" in the blades of the wind vane. The change in status of the wind vane can be captured as indicia of air or fibre arrival.

In general, the present invention provides methods and devices for aspects relating to the installation of cables such as optical fibre units into conduit tubes using e.g. the blown fibre method, so that in particular, a single operator can operate substantially on his own at one end, to determine if compressed air and/or the fibre unit fed into a conduit has reached its intended destination. The invention can be used where the operator has to choose between 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/or the fibre unit will reach or reaches the intended destination. In view of the possible volumes that may be deployed in FTTP initiatives, the invention also addresses the need for cost-efficiency in being relatively cheap to manufacture and simple to operate.

A first aspect of the present invention provides a device for use with a conduit having a first conduit end and a conduit second end, into which conduit a cable can be installed using a flow of air into the first conduit end, the device being suitable for confirming that the air is flowing out from the second conduit end, the device comprising a housing, - means to enable connection of the device to the second conduit end, a detector arranged to detect an electrical property change, and an actuator for causing an electrical property change detectable by the

detector, wherein in use, the air flowing into the device causes the detector and the actuator to move relative to each other, causing an electrical property change detectable by the detector.

The actuator comprises a component having a metallic or other property which changes an electric property of the detector, such as its inductance. Other measurable electrical properties or characteristics can also be used, such as the detector's capacitance, its Q factor, resistance, or the like. Preferably however, the inductance change is used for being easily measured. If inductance change is the measured property, the detector may take the form of e.g. an induction coil being part of an oscillator circuit. The actuator which has a metallic property, is arranged to be able to move in and out of the immediate vicinity of the detector; in particular the actuator can take two specific positions relative to the detector which clearly change the frequency tone of the oscillator, which is conveyed to the operator at the head end that a change has taken place i.e. that the air has arrived at the far end.

In preferred embodiments, the device is configured also to detect arrival of the optical fibre which is sent down the conduit into which the compressed air is pumped, after confirmation of an air flow at the remote end is received by way of e.g. a radio frequency communication or other communication means. The detection of the arrival of, specifically the protective metallic bead which is crimped onto the end of the fibre unit, is also obtained by an inductance change resulting from the presence of the bead near the detector at the far end.

Embodiments of the invention further include means to keep or hold the actuator in one of either a "resting" or an "activated" position. The installation session starts with the device in the rest position, and it is activated by the flow of air into the device housing during the initial step of confirming that air is flowing out of the desired tube. The change of position to the second position causes an air vent to open within the device housing so that the air fed into the conduit at the head end can flow out, as is required for a blown fibre installation. While the actuator is in its second, activated

position, the fibre is fed into and through the tube.

In a second aspect of the invention, there is provided a system for use with a conduit having a first conduit end and a conduit second end, into which conduit a cable can be installed using a flow of air into the first conduit end, comprising a device of the invention.

In preferred implementations of the system, the equipment at the head end, comprising in the main the blowing head and the air compressor, is configured ^" to receive and to respond to the transmitted signal comprising the detected tones.

The operator can advantageously use the device at the remote end of the installation, and the head end apparatus together so that it can initially be determined that air is flowing to and from the correct remote end, and the fibre unit then installed into the conduit as the next step. By using this kit, the operator need not travel to the remote end, nor need there be a second operator located at the remote end for the purpose of detecting the arrival of the airflow.

In a third aspect of the invention, there is provided a method for use with a conduit having a first conduit end and a conduit second end, into which conduit a cable can be installed using a flow of air into the first conduit end, and to confirm that the air is flowing out of the from the second conduit end, the method comprising attaching a device of any one of claims 1 to 12 to the second conduit end, applying the flow of air into the first conduit end, - causing the actuator of the device to move relative to the detector of the device, and causing an electrical property change detected by the detector.

By using this method, the operator can determine if the correct conduit has been selected, where there are a number of conduits to choose from, or otherwise to determine that the conduit into which air is introduced will emerge, and does indeed emerge, at the remote end of the conduit.

In an implementation of the invention, this method further includes the detection of fibre arrival at the remote end of the installation.

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

Figures 1 A and 1 B depict a device of the invention in use during airflow detection;

Figures 2A and 2B depict a device of the invention in use during cable arrival detection;

Figures 3A and 3B depict an alternative embodiment of the invention;

Figures 4A and 4B depict another alternative embodiment of the invention;

Figure 5 depicts the main components of apparatus used in a blown fibre installation at the head end; Figure 6 depicts a device of the invention and its enclosure; and

Figure 7 depicts a device of the invention with an alternative enclosure.

Figures 1A and 1 B depict a first embodiment of the invention based on detection of an electrical property change, in this example being an inductance change. It consists of a substantially cylindrical or tubular housing (20) which has one open end and one closed end. The open end is configured to connect with the mouth of the optical fibre tube at the remote end of the installation e.g. in a friction fit. The housing is fabricated from a non-metallic material, such as an injection-moulded plastic, which is relatively simple and cheap to manufacture.

A piston (26) is also generally tubular with one open end and one closed end, and is disposed substantially co-axially within the housing, where the piston. The open end of the piston faces the same direction as the open end of the housing. The piston is configured to slide along its longitudinal axis within the housing. It is fabricated from metal, or else includes metal elements e.g. it can consist of an injection-moulded plastic containing metal filings. An induction coil (24) capable of sensing the presence of a metallic object, is mounted on the external surface so that is surrounds

the housing. The coil is part of a tunable oscillator circuit (22), which is connected to a signal processor (28) capable of detecting tones generated by the oscillator, which tones - and any tone changes - can be transmitted by a radio frequency (RF) transmitter (30). The induction coil (24) and the piston (26) are positioned relative to each other so that they may move in and out of proximity of each other, such that the presence of the metallic properties of the piston changes the electrical characteristics of the coil, primarily its induction, which in turn changes the properties of the oscillator, specifically the tuning, which changes the frequency of the tone it produces. In alternative embodiments the frequency of the tone produced by the oscillator may be unchanged by the proximity of the piston to the coil. In those embodiments the change in the electrical characteristics of the coil produced by the proximity of the piston to the coil are designed preferably to change the amplitude or the phase, or both, of the tone produced by the oscillator. In all of these embodiments the change in the frequency, amplitude or phase of the tone produced by the oscillator is the indicator that signifies the arrival of air and/or the fibre unit at the remote end of the conduit. This applies to all the descriptions below in which a change in frequency only of the oscillator tone is given as example.

The housing (20) and the piston (26) each include a set of air vents. The air vents of the piston (32) align with the air vents of the housing (34) when the piston is in a specific position within the housing.

In the space between the closed end of the piston and the closed end of the housing is an arrangement to hold the piston in one of two positions: the first "rest" position being that the metallic piston (26) is located proximate to the induction coil (24) as shown in Figure 1A, and the second "activated" position being where the two sets of air vents (32/34) are in alignment as shown in Figure 1 B. The piston is configured to slide between these two positions within the housing. The arrangement comprises a spring (40) extending from the closed end of the housing, which holds the piston in the first rest position. The second activated position is obtained by the cooperation of a metal disc (36) and a magnet (38).

In the embodiment shown, the metal disc is disposed on the closed end of the piston and the magnet on the closed end of the housing although of course the locations of these two components may be reversed. Although the piston is made partially or even fully of metal, the metal disc may be required in practice to ensure that the attraction of the piston assembly to the magnet is sufficiently strong. As the purpose of this assembly is to hold the piston in the second activated position, it would be possible to use any suitable alternative that would achieve this end, e.g. a spring- loaded latch actuated by the travel of the piston.

A plunger rod (44) connected to the closed end of the piston is pushed outwardly of the device when the piston is in the activated position, and a button (42) located at the end of the rod allows for the piston to be re-set to the rest position by the operator pressing the same to disengage the magnet and the metal disc sufficiently for the spring to urge the piston back in the first, resting position.

The use of the device to sense a flow of air from the mouth of the conduit at the remote or far end of a blown fibre installation will now be described. At the start of the installation operation, the operator travels to the remote or destination end of the installation, and connects the above device to the mouth of the conduit from which it is hoped that the compressed air fed from the head end, will emerge. The device is set (or reset using the button (42)) so that it is in the first rest position, where the piston (26) is in proximity with, and actuates, the induction coil (24), and the air vents (34 and 36) are out of alignment, as shown in Figure 1A. The oscillator circuit (22) thus outputs a tone of a specific frequency "A" indicative of the specific location, of the metallic piston in the rest position or state. This is transmitted by RF as a status signal indicate that the sensor is active and functioning, and that the piston is in the correct rest position, to the operator when he arrives at the head end of the installation, which may be a kilometre or more away. This provides assurance that the device of the invention is working before starting the installation operation.

The operator chooses a conduit opening to direct pressurised air from an air compressor into. At the start of the blown fibre installation, the air pressure in and

along the conduit is at a steady state level and air flow is zero. If the air is directed into the correct conduit opening, air eventually flows through to the remote end of the conduit, and into the housing (20) of the device. Because the two sets of air vents (32 and 34) are out of alignment, the housing is substantially air-tight. The increase in air pressure (e.g. up to 10 bar) within the housing caused by the air flow, gradually exceeds the pushing force of the spring (40) and causes the piston to slide towards the second, activated position. During this, the proximity of the metal disc (36) to the magnet (38) located opposite ends to each other increases. When the magnetic attraction between these two components eventually exceeds the force of air pressure within the main section of the housing and the opposing force of the spring, the piston snaps to take the second activated position shown in Figure 1B at which point the two components are magnetically coupled together.

In the activated position, the two sets of air vents (32 and 34) are in alignment so that the air flow into the housing exhausts to the atmosphere as depicted by the arrows in

Figure 1B, resulting in a reduction of the air pressure within the housing. The force opposing that of the spring is now removed and the force of the air flow through the housing is insufficient in itself to hold the piston in that location, but the magnet arrangement helps holds the piston in the activated position. At this stage, the steady air flow through the conduit essential to the blown fibre installation procedure, is attained.

In the travel in the metallic piston from the resting to the activated position, the piston moves out of the immediate range of the induction coil (24). This changes the frequency of the tone produced by the oscillator (22). Depending on design considerations, the tone will either increase or decrease to a new frequency "B" generated by the piston's location at the activated position. In practice the change in the frequency of the tone will be relatively rapid and abrupt because of the increasing magnetic pull causing the piston to eventually snap to the activated position. In any event, frequency "B" will be distinguishable from frequency "A". The new frequency is detected and a corresponding status signal is automatically transmitted to the operator at the head end via the radio channel or by other means. The operator can

at that point be assured that compressed air is being fed into the correct conduit mouth at the head end.

Of course, if the operator did not feed the air down the correct conduit, none of the above will occur. In such a case, the operator will realise, from not receiving any signal from the remote end after a suitable time period, that something is amiss. He can then take appropriate steps e.g. selecting another conduit end to connect to the air compressor. He will at least be aware that the fibre unit should not be installed into the first-chosen tube.

The use of the device to further sense the arrival of a fibre unit fed into the mouth of the conduit at the remote or far end of a blown fibre installation will now be described with reference to Figures 2A and 2B.

First, a supply of fibre unit is prepared by crimping or otherwise crimping a slug or a bead (6) to the tip of one end, which protects the fragile glass fibre from damage. The bead typically has a rounded end which eases the fibre unit's progress through the conduit path. It is often made from, or includes, metal; brass is a preferred material as it does not rust.

After the operator at the head end receives confirmation by RF or by e.g. a short message service text message that air is flowing from the desired destination conduit, a fibre unit (2) is fed into the same conduit (4) into which the compressed air is being fed.

When the fibre unit (2) led by the metallic bead (6) advances out of the conduit opening at the remote end into the housing of the device as shown in Figures 2A and 2B, the electrical properties of the induction coil (24) change which causes the oscillator's tone to shift from frequency "B" to a new frequency "C". It is possible for the value of frequency "C" to be substantially the same as that for frequency "A" without affecting the operation of the sensor, as long as the oscillator tone (22) clearly and distinguishably changes when the bead signifying the fibre unit arrives

within proximity of the induction coil.

Unlike the relatively abrupt frequency change pattern in the air-detection step described above against Figure 1 , the change from frequency "B" to frequency "C" in Figure 2 is more gradual, and the frequency change peaks quickly and momentarily as the bead advances past the induction coil and embeds in the piston beyond the immediate vicinity of the coil. The frequency thus changes momentarily from frequency "B" to frequency "C" and then back to substantially "B" again. The signal processor (28) accommodates these different characteristics and delivers (30) an unambiguous status signal to the operator at the head end, who then knows that the fibre cable has arrived and that the installation is complete.

The blowing head can then be tuned off, either manually by the operator, or in a further embodiment the receipt of the status signal could be linked to the blowing head so that the blowing head can be automatically switched off on receipt of the signal as further discussed below against Figure 5. At this point, the operator travels back to the remote site to remove the device from the conduit ending, and to reset it by pushing the button (42) so that the piston within the housing returns to its rest position for the device's next use.

As the skilled person would be aware, the components of the device can be used in various combinations and can be substituted by various other components. Some exemplary embodiments will now be discussed.

Figures 3 and 4 show embodiments of the invention in which only a portion of the piston comprises metal, as compared with the embodiment discussed against Figures 1 and 2 where the whole piston consisted of, or included, metal. Specifically, the piston includes a band of metal, or metal constituents (50). The embodiments shown in Figure 3 ad 4 are equally effective to cause a frequency change when the piston in each case is caused to slide to the activated position upon an increase in air pressure within the housing chamber: the metal band moves out of the immediate detection zone of the induction coil in the case of the device of e.g. Figure 3A, while

the metal band moves into the immediate vicinity of the coil in the case of the device of Figure 4. In the case of the device of Figure 4 however, it should be noted that the persistent presence of the metal band in the immediate vicinity of the coil in the activated state may result in a smaller and less easily-detected frequency change upon arrival of the fibre unit, caused by the metal bead at the leading end of the fibre unit.

The skilled person would also realise that the band (50) and the induction coil (24) can be placed at various locations along the length of the housing, so as to obtain different results and effects. For example, an induction coil can be placed near the end of the device in the immediate proximity of the terminal location within the housing where the bead will rest, to provide a clear continuous signal to the operator that the fibre bead has arrived at the remote end of the installation. This could be a second or further coil in addition to a first which is located at the position shown in e.g. Figure 1. The plunger rod (44) arrangement and reset button (42) are optional to the operation of the device, and may not be needed in a disposable version of the device. The spring (40) can be replaced by any resilient/biasing component which urges the piston to the first resting position.

In a preferred embodiment of the invention, the pushing force of the spring against the piston can be pre-selected so that the piston is caused to travel only when air pressure within the housing reaches a pre-determined level. Preferably, this air pressure level should approximate that of the air applied at the head end: by way of example, the applicants feed air compressed to 10 bar into the tube. This allows the operator to start the fibre installation process only when the desired air pressure level is attained within the conduit, as blown fibre may not propagate successfully through the tube if there is insufficient air flow therein. In further embodiments, the resilience level of the spring may be adjustable or selected, and can be used to measure air pressure levels within the housing during an installation.

As noted above, the detection of the presence or absence of the metallic piston and/or bead within the housing can be achieved by sensing or measuring changes in

other electrical properties or characteristics of the detector, such as its capacitance, its Q factor, resistance, or the like.

As a further design consideration, the force of the spring in the activated position should be less than the magnetic force holding the piston in place. Furthermore, the coupling strength of the magnetic arrangement should be sufficiently robust to avoid the piston accidentally springing back to the resting position, yet allow for the device to be reset by an operator without too much difficulty after an installation.

In certain embodiments, the movement of the piston itself can be detected as signifying the presence of air and/or the fibre unit in the device. In such examples, the movement away from the first resting position can itself be sensed to indicate e.g. an airflow within the housing. A subsequent movement (which could be in the same direction as the first movement away from the first position, or in the reverse or other direction) could be sensed as a further indication of e.g. fibre unit arrival within the housing. For example, the piston could be urged away from the first rest position upon air arrival, and the bead of the fibre unit could push it to the second, further position indicating its presence in the housing.

Figure 5 depicts the main apparatus components located at the head end of the optical fibre conduit or tube, where the operator is located. There, he operates a blowing head which controls the forces propelling an optical fibre unit (2) into the conduit or tube (4), which forces comprise a pair of drive wheels (6) and a supply of pressurised air (8) typically from a compressor. The drive wheels mechanically drive the fibre unit into the tube, while the compressed air is fed into the conduit to create within it the laminar air flow which will bear the fibre unit along and through the tube.

The blowing head may be capable of detecting that the fibre unit is no longer progressing through the tube - which could be a result of the fibre arriving at the remote end, or else it is otherwise caught or stuck within the tube. In response, the blowing head stops the drive wheels from further pushing the fibre unit into the tube. The receipt (or non-receipt) of confirmation that the fibre bead has arrived at the

remote end via the radio receiver (5) allows the operator to decide what to do next: to end the successful installation, or else to take remedial action.

In a preferred embodiment, the head end apparatus (in the main, the blowing head and the air compressor) is configured to respond (7) to the receipt of a signal indicative of fibre arrival at the remote end, by terminating the installation session e.g. by turning themselves off, or going into a standby mode. There is a particular synergy in doing so in the case of the blowing head, due to this component's already- existing capability to sense lack of further progress of the fibre within the tube: receipt of the fibre arrival signal confirms the cause of the lack of fibre progress. Similarly, the apparatus at the head end could be configured to respond to the initial signal that air is flowing from the remote end conduit, by automatically starting the fibre installation process.

Figures 6 and 7 depict two embodiments of the full enclosure surrounding the device, which may be about 8cm long for use with a conduit having an external diameter of typically 3mm in the case of small-bore conduits, up to 15mm and more for large bore conduits. In a preferred embodiment the coupling flange fixed to the device housing may be adjustable to tightly fit the conduit in use, or the coupling flange may be removable from the housing whereupon the another flange size suitable for the conduit in use is selected for attachment to the housing. In either case the flange ensures mechanically robust and substantially airtight coupling between the housing (20) and the conduit (4).

In Figure 6, the device comprises two injection moulded plastic sections: the inner tubular housing (20), and the outer enclosure (52). Fine gauze dust shields (60) are provided on the air vent openings (32 and 34) to prevent or discourage contamination of the interior of the device. The outer enclosure is configured to avoid the air vents so that the arriving air vents to atmosphere and allows essential air flow along the conduit. The reset button (42) is also located outside the outer enclosure. Once assembled, the only service-removable part is the battery cover protecting the dry cell battery (56) on the outer enclosure surface. Should it be found desirable to

replace the dust shields, then they too could be made to be service-removable. A minimal number of service-removable parts is however advantageous for easy maintenance.

An internal antenna (54) used for transmitting signals about air and fibre arrival to the head end, may be incorporated within the enclosure, or alternatively an external antenna (55) could be used for greater range/gain in operational situations where radio reception may be impaired (e.g. down a manhole). Ideally, the fibre conduit at the remote end is long enough to extend the fibre conduit route to ground/surface level for the purposes of the installation process, in which case radio reception is improved and a reliable channel may be established with the head end operator. Should there be insufficient length of conduit, a bridging length of conduit can be temporarily attached for purposes of the installation.

Figure 7 shows an alternative outer enclosure (62) consisting a simple injection- moulded box. In this implementation, only the reset button (42) stands proud of the outer enclosure. All the other elements of the device can be enclosed, even the air vent openings (32 and 34), although the gauze dust shields (60) must be configured to allow for sufficient air flow through the conduit and out of the device for purposes of the blown fibre installation session.

The methods, devices, components 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 and conduit types and sizes. In particular, the apparatus and methods relating to air flow detection and the methods and apparatus relating to fibre arrival detection are depicted in this description to be used together in a preferred embodiment. However they will work independently of each other on their own, to realise the advantages of the respective inventions.