A method and apparatus for length calculation and integrity verification of duct

Abstract

An apparatus for testing and evaluating length and integrity of a duct includes a computer controlled pneumatic device, which runs through a predetermined test plan to conduct open and closed line tes

Description

Technical Field The present invention concerns a method and apparatus for testing underground ducting lines for the calculation of their length and the evaluation of their pneumatic integrity. Background Underground ducting lines and networks are in common use forthe distribution and protection of fragile infrastructure elements, such as fibre optical cables. Small diameter ducts, either buried individually or housed within other, larger buried ducts or tubes, are an efficient and unobtrusive method of routing the fibre optical network between network access points, such as above ground distribution cabinets or below ground manholes. Figure 1 gives a diagrammatic representation of a duct network, showing inground duct 1, an above ground network access point (commonly known as a ‘cabinet’) 2, and a below ground network access point (commonly known as a ‘manhole’) 3, containing a network node 4, used for arranging and splicing optical fibres. There is a requirement for these ducts to be airtight and watertight, to protect the potentially fragile fibre optical cable housed within from damage by items such as grit or small stones and to prevent the ingress of water into cablesand network access points. Additionally, an increasingly common method of cable installation within underground duct is the use of airblown fibre - supplying a flow of compressed air into the duct and pushing the fibre into the same duct, allowing the fibre to ‘float’ along the length of the duct. This method of installation allows for far greater lengths of fibre to be installed in one operation, minimizing the requirements to install shorter lengths of fibre and splice or joint them in multiple locations, and lessening the time and cost of installation. In order to facilitate air-blown fibre installation, an airtight void within the duct is required, as any splits, breaks ordisjoints will cause the installation to fail due to lost air, or in the case of large splits, potential fibre escape from the duct. Once a duct network has been installed underground, it becomes increasingly difficult and expensive to fault-find. Splits or disjoints in the duct network that prevents the installation of a fibre optical cable into said duct essentially render that particular duct line unusable, and while some redundancy may be built into the design of duct networks to account for this through the installation of extra ducts, these failure points may necessitate costly civil engineering works to dig up, identify and replace the offending sections of duct. In some instances, where ducts cross busy roads or other infrastructure, this cost could be vast, and unpalatable to network owners. Often, the duct network will be installed in the ground well in advance of potential fibre installation - months or years ahead is not uncommon. It is of vital importance that the duct network as installed remains in an air and watertight state in the intervening period. As such, proving and validating the integrity of underground duct networks is of great importance to network owners and their installation operatives, especially as installation contractors payment contracts may be tied to the handover of a correctly built duct system. Additionally, prior to performing an air-blown installation on an existing duct system, network owners and their operators are likely to want to re-prove the integrity of the system to guard against any potential damage that may have occurred, from, for example, other groundworks or rodent damage. As such, methodology for testing duct integrity has evolved, and a number of methods for proving duct integrity are known to exist and are in common use. One such known method is the capping of the distal end of the duct followed by the application of compressed air into the proximal end of the duct until a known pressure is achieved. By then switching off the inbound airflow and sealingthe duct at a known pressure, an overall sense of the integrity of the line can be observed by monitoring the pressure in the duct over a specified time period using an inline pressure gauge or similar monitoring method. Any leaks or disconnected elements causing pressure losses then being identified by a commensurate drop in pressure reading on the pressure gauge. Another such known method is to apply compressed air into the proximal end of an uncapped open duct and introduce a projectile of a known size (including but not limited to a ball bearing, a plastic calibration dart, or a sponge bullet) into the airflow. By providing a catching device at the distal end of the same duct, clear passage for a projectile of a known size can be proven, if the projectile arrives in the catching device after a reasonable period of time relative to the length of the duct. Often, this projectile will be chosen to be of a similar or larger cross-sectional profilethan the cable to be installed into the duct, essentially providing a ‘worst-case’ scenario, and ensuring that the cable to be installed will be able to negotiate corners, bends and connectors within the duct line. As a part of the prior art, known bistable catching devices are available which are open to atmosphere on installation, and have an internal aperture sized to accept a projectile of a known size and then seal on arrival of said projectile to allow pressurization of the duct without havingtofitan alternative end cap. In using these bistable catching devices, both tests described above can be completed sequentially-with the projectile being launched at the proximal end and subsequently caught by the device at the distal end thus sealing the duct and allowing the pressurization of said duct. An example of a testing methodology containing both the above testing processes can be found in Figure 2. This methodology of testing, while ensuring a nominally clear and airtight duct, does not allow for any validation of the test being completed, or any traceability of said test. As such, it is impossible for operators and installers to have full confidence in the state of the network. Furthermore, as the fibre optic industry develops, many network operators are purchasing existing duct networks, and require a means of ensuring the integrity of the network either to determine an acceptable cost of purchase, orto do the due diligence required on the state of the network asset before attempting to install costly fibre optic cable. Additionally, there is no known method of calculating the length of an inground duct network. While network owners should have detailed maps and plans of their installed assets, it is entirely possible that these have been lost, misplaced or destroyed over time-especially as networks change hands from company to company. Additionally, the real-world state of the installed network may necessarily differ from the planned network installation due to unanticipated conditions discovered during installation of the duct. The importance to the network owner of having a knowledge of the exact condition and length of their inground network cannot be overstated. Prices for installation contracts, purchasing of lengths of cable, and potentially the architecture of the fibre optic network itself all rely on the knowledge of the length of duct linking accessible assets such as street cabinets or below ground closures. Summary It is a purpose of the present invention to provide a method and apparatus for an improved means of testing and validating the integrity and length of an inground duct network, which overcomes at least some of the shortcomings mentioned in the above. According to a first aspect of the invention, there is provided an apparatus for testing and evaluating lengths of duct, comprising a computer controlled pneumatic device which, when connected to a compressed air supply, runs through a predetermined test plan to conduct open and closed line testing on a duct using calculations based on the flow rate and pressure of the compressed air being supplied to the duct under test, and a memory system, which when receiving data from the controller, provides feedback on the length and integrity of the duct under test. The testing apparatus cycles through a number of steps to initiate the test; Firstly, ensuring the supplied flow of air meets the requirements for performing the test, namely air flow and air pressure using internal flow and pressure sensors. The upper and lower limits for acceptable flow and pressure being defined by the user. Secondly, conducting an open line duct test, using flow and pressure sensors within the apparatus to monitor the combination of flow and pressure being delivered to the duct, and thereby comparing the observed values with an empirically gathered dataset, and predicting the length of the duct under test based on said dataset. Thirdly, firing a projectile along the length of the duct from the proximal to the distal end where it seals a bistable sealing device located on the distal end of the duct and recording the projectile transit time via monitoring of the change in air pressure and flow rate Fourthly, pressurizing the now sealed duetto a predetermined pressure value before sealing the duct and monitoring pressure change for a predetermined time period, the values for both the pressure and time being defined by the user. At all stages, monitoring and logging all input and output variables to an inbuilt device memory, with the ability to output results in a digital or physical format. In some implementations, the apparatus is controlled by a human machine interface. The human machine interface (HMI), facilitating communication with the microcontroller comprises a means for the user to input instructions to the testing apparatus, for example push buttons, alphanumeric keyboard, or touchscreen. The HMI also comprises a method of graphically displaying live and / or post-test results and feedback to the user. This may take the form of, for example, a 7 segment LED display, an LCD screen, a graphical user interface accessible via a wireless network or any other similar method allowing communication of the test results to the user. In some implementations, the apparatus comprises an array of duct connections to facilitate consecutive testing of a plurality of ducts. The outbound connections between the apparatus and the ducts to be tested comprise a plurality of connections, and may number one, two or more. When multiple duct connections are included within the apparatus, the HMI allows the selection of active ducts under test through an input selection method, dependent on the HMI type. In some implementations, the apparatus comprises a GPS location verification facility. The GPS location verification records the GPS co-ordinates of the test location, along with the time and date of the test, and writes these to the device memory. This information can also be communicated to the user via the HMI, and printed to any report generated. According to a first aspect of the invention, there is provided a method for testing and evaluating duct length and integrity, comprising an open-line duct test to measure flow and pressure on the open duct, and the firing of a projectile A along the duct, to seal a bistable sealing device B at the distal end of the duct, and a pressure test on the now closed duct. In some implementations, the test methodology is undertaken by use of the aforementioned apparatus, as a means of automating the testing protocol. In some implementations, the test methodology is repeatable for the purposes of testing a plurality of ducts consecutively. Where the capacity of the supplied compressed air is high enough, testing can be undertaken simultaneously, otherwise testing is undertaken sequentially, with each individual duct being tested and vented in sequence. In some implementations, projectile A is a calibration dart, and bistable sealing device B is shaped to receive the same dart and seal to pressure. Brief Description of the Drawings Figure 1 shows a diagrammatic representation of a prior art underground fibre optic network. Figure 2 shows a process flowchart giving instruction for a known prior art integrity testing protocol. Figure 3 shows a process flow chart giving instruction for one embodiment of the current invention allowing the determination of the integrity and length of the duct under test. Figure 4 shows a diagrammatic representation of one embodiment of the current invention, giving instruction for a pneumatic system layout for a testing apparatus Figure 5a shows a cross-sectional cutaway view of an in situ prior art bistable duct end sealing device in its open state, airflow indicated by dashed arrow Figure 5b shows a cross-sectional cutaway view of an in situ prior art bistable duct end sealing device in its open state, with a calibration dart en route, airflow indicated by dashed arrow Figure 5c shows a cross-sectional cutaway view of an in situ prior art bistable duct end sealing device having received the calibration dart, airflow indicated by dashed arrow Figure 5d shows a cross-sectional cutaway view of an in situ prior art bistable duct end sealing device having received the calibration dart and pressurised to its closed state, airflow indicated by dashed arrow Figure 6 shows a diagrammatic representation of one embodiment of the current invention, in use in an underground duct network Detailed Description Figure 3 describes an example process flow for an embodiment of the invention, giving instruction for a method of carrying out duct integrity and length testing using a specialised testing apparatus. This given embodiment of the testing method describes a sequence of steps to be undertaken. Firstly, operator input is provided via an HMI. In a preferred embodiment of the invention, various parameters are set by the operator within the HMI, including but not limited to: duct diameter and number of ducts under test. Secondly, the apparatus runs through a series of internal tests to calibrate itself against the inbound air supply, and ensure a consistent air supply of high enough flow and pressure. The apparatus also records various atmospheric conditions - including but not limited to, air temperature and atmospheric air pressure. Thirdly, the apparatus uses the data gathered in the second step and compares it against baseline parameters to make a go / no-go decision based on there being sufficient air supply, as previously measured. A no-go decision is communicated back to the operator via the HMI, allowing the operator to rectify the air supply and reattempt. A go decision allows the apparatus to progress to the next step. Fourthly, provided the go decision is reached by the controller, the apparatus performs an open line test of the unsealed duct, and monitors both the pressure and flow to calculate the length of the duct under test by using said pressure and flow values in comparison with an empirically gathered data set. Fifthly, a calibration dart is introduced into the duct under test by means of, for instance, disconnecting and reconnecting the duct, or by a specialised dart loading apparatus connected to said duct. With the dart loaded into the test duct, the operator triggers a launch signal via the HMI to conduct an integrity test. Compressed air is directed into the duct under test, propelling the calibration dart from the proximal to the distal end of the duct, where it is collected by and subsequently seals, a bistable device, allowing pressure to build up within the duct, and causing flow rate to decrease as a consequence. The transit time of the dart from launch to the time at which this pressure build-up occurs is registered, and used to further predict the length of the duct using air velocity calculations, and comparison with said empirically gathered dataset and the calibrated length generated by the preceding open line duct test. With the duct pressurised to a pre-determined value, the duct is sealed at the proximal end by the apparatus, and at the distal end by the sealing of the dart within the bistable sealing device. With both ends of the duct sealed, the duct pressure is monitored over a user-determined period of time, and based on the pressure loss over the time period a conclusion is reached on the integrity of the duct. Finally, the apparatus feeds back all the gathered information to the operator via the HMI, and / or generates a report containing all the gathered information. In some embodiments of the invention, the apparatus can be programmed to finalise the measurement of one duct, before automatically progressing onto the next ducts in sequence, with a plurality of duct connections built into the apparatus, and the number of ducts under test selectable via the HMI as described above. The method of testing described involves the use of pneumatic and electronic components to create a circuit capable of performing the testing methodology described in Figure 3. Figure 4 describes an example of one such circuit layout giving detail of various components that can make up the system. In an example embodiment of the invention, compressed air is first supplied to an input 21 of the apparatus using a suitable pneumatic connection. This compressed air can be supplied from a number of methods, but due to the location of testing environments is likely to be via a petrol or battery driven compressor to allow off-grid power supply. Air flowing into the system from the compressor then is directed through a flowmeter 22 and pressure sensor 23, both of which are powered by, and communicate data back to the controller 29. The controller 29 instantaneously broadcasts this information to the human machine interface 30 (HMI) via a suitable communication connection, and, providing inbound air flow and pressure fall within allowable limits set by the user a test is initiated using the HMI 30. On initiating the test, the controller 29 will: Firstly, perform an open-line duct test. Fora period of time set by the user in the system, the controller 29 will open the normally closed solenoid valve 24 to direct the compressed air into the duct connection 26, via the second pressure sensor 25. The second pressure sensor 25, along with the system flow rate measured at flowmeter 22 are then monitored by the controller 29 which takes comparative measurements of the flow and pressure in the duct 1. These measurements are then compared to a database of empirically gathered data held in memory within the controller 29 and a calibrated duct length value is generated and communicated back to the HMI 30. Following this first test completion, normally closed solenoid 27 is opened, and air is allowed to vent to atmosphere through vent 28. Secondly, a dart 12 is introduced into the proximal end of the duct 1, and a second test is launched via the HMI 30. Ina similar manner to the first test, air is directed into the duct 1, and a first timer is started by the controller 29. Flow a nd pressure are monitored throughout via the flow and pressure sensors 22 and 25 communicating back with the controller 29. As shown in figures 5a-d, the calibration dart 12 travels the length of the duct before engaging with the bistable catching device 11 at the distal end of the duct 1 and seals the catching device, stopping the flow of air and allowing pressure to build within the duct under test. The dropping of flow rate, measured by flowmeter 22, and corresponding rise in pressure, measured by pressure sensor 25, indicates that the distal end of the duct has been sealed, and air is no longer escaping. Thirdly, once the distal end of the duct is sealed, controller 29 reverts solenoid valve 24 to a closed state, and the first timer stops, while a second timer begins. Pressure within the duct under test is monitored by the controller 29 via pressure sensor 25 throughout. The time measured by the first timer can then be used with the measured flow rate of the air in a velocity-time equation to predict the distance the dart has travelled. This information is communicated backtothe HMI 30. The time measured by the second timer is setto a user-specified time period, and the pressure sensor 25 is monitored by the controller 29, which monitors the pressure loss over the time period, and communicates the results back to the HMI 30. Fourthly, the controller 29 delivers a full set of data to the HMI 30, which is then communicated to the user and converted to a full report. This data varies due to user preference and requirements, in the preferred embodiment of the invention this report contains some or all of the following: Date / time of test Inbound air pressure Inbound airflow Open-line duct test result, predicting the length of the duct Dart launch test, comprising: o Dart transit time o Calculated length of the duct o Dart velocity Pressure test result, comprising o Time under test o Pressure loss during test o Pass / fail result The above description describes an embodiment of the invention, and states its core features. Further, additional features can be combined with the essential features listed, including but not limited to in-built GPS verification and atmospheric monitoring, to ensure a validated test location and test conditions which are then written to the report created by the HMI 30.

Claims

1 An apparatus for testing and evaluating length and integrity of duct, comprising:• A computer controlled pneumatic device, which runs through a predetermined test plan to conduct open and closed line testing on a duct using calculations based on the flow rate and pressure of the compressed air being supplied to the duct under test.• A computer memory system, which when receiving data from the pneumatic device, provides feedback on the length and integrity of the duct under test.2 An apparatus according to claim 1, where the controller receives inputs from, and feeds data back to, a human-machine interface.3 An apparatus according to claim 1, comprising an array of pneumatic connections to facilitate consecutive testing of a plurality of ducts.4 An apparatus according to claim 1, wherein the controller includes a GPS location verification facility.5 A method for testing and evaluating length and integrity of duct, comprising:• An open-line duct test,• The firing of a projectile A through the duct,• The arrival of the projectile A, sealing a bistable device B affixed on the distal end of the duct,• A pressure test on the now closed duct.6 A method, according to claim 5, where the testing methodology is conducted by a specialized testing apparatus.7 A method, according to claim 5, comprising a multitude of consecutive test procedures to facilitate testing of a plurality of ducts.8 A method, according to claim 5, wherein the projectile A is a calibration dart, and thebistable sealing device B is shaped to receive the same dart.

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