Device for determining the length of an inert electrical cable, and method for detecting the breaking of an inert electrical cable

Abstract

Device (1,100) for monitoring an inert cable for a certain monitoring period, in particular for detecting an event occurring during this monitoring period, such as its cutting, said device being configured to repeatedly determine the value of a parameter representative of the length of a selected strand pair within said cable, and to detect an event of a sudden decrease in this value, said device being characterized in that it comprises a main board (20) and a plurality of daughter boards (30), each daughter board being configured to determine on an inert strand pair a parameter representative of the length of said strand pair, and to transmit this parameter to the main board, and the main board being configured to compare, for each daughter board, the length-representative parameters to a threshold value,and to trigger an alert if this threshold value is exceeded. Figure for the abbreviation: [Fig.1].

Description

Title of the invention: Device for determining the length of an inert electrical cable, and method for detecting the breaking of an inert electrical cable. Technical field of the invention

[0001] The invention relates to the field of electrical engineering, and more particularly to the measurement of electrical parameters of a linear electrical conductor such as an electrical cable. More specifically, the invention relates to a device for determining the length of an inert electrical cable, that is to say, an electrical cable that is not part of a live electrical circuit. The invention is particularly applicable to cables composed of twisted copper pairs, such as ADSL (Asymmetric Digital Subscriber Line) cables.

[0002] The invention also relates to the use of such a device for determining the length of an inert electrical cable of a given type. The invention further relates to a method for monitoring the integrity of an inert electrical cable, and more particularly for detecting its severance, using the device according to the invention. Severing the cable leads to a reduction in its uninterrupted length. This detection or monitoring method can be implemented on an ad hoc basis, but also continuously to detect the theft of inert electrical cables in real time, in a variety of situations.

[0003] The invention also relates to a radioelectric system for monitoring inert cables which comprises a plurality of devices according to the invention. State of the art

[0004] Electricity network operators face the problem of electrical cable theft. This problem mainly concerns low-voltage cables or disconnected cables left in place, because in these cases the thief who cuts and slices the cable is not at risk of electrocution. Furthermore, cutting and stealing a cable that is not energized does not disrupt the operation of a technical system and is therefore difficult to detect in real time. These thefts can occur at installation sites or construction sites, and may involve disconnected cables that have been left in place awaiting removal, or new cables that are stored awaiting installation. They can also occur in equipment yards.These thefts can be committed by members of an organized criminal network that, through experience, often includes thieves operating in the field, dealers / financiers, and recyclers. These thefts can also be committed by employees of companies that collect cables on demand. from their owner to introduce them into the recycling stream; in this case it is most often a partial theft of a batch by cutting a longer length than planned or reported (knowing that the total length of an inert cable laid is not always well documented).

[0005] There is a clear need to be able to easily determine the length of an inert electrical cable, whether connected or disconnected, preferably without uncoiling it. There is also a need to be able to detect a break in an inert electrical cable, whether connected or disconnected, in order to be able to issue an alert.

[0006] The present invention provides a simple solution to these problems. Brief description of the figures

[0007] [Fig-1] schematically shows a device according to the invention and the main components of the motherboard.

[0008] [Fig.2] schematically shows a daughterboard of the device according to the invention, with its main components.

[0009] [Fig.3] schematically shows a typical embodiment of the process according to the invention.

[0010] [Fig.4] schematically shows part of the process according to the invention which concerns the selection of a pair of supervisable strands.

[0011] [Fig.5] schematically shows part of the process according to the invention which concerns the identification of an event.

[0012] [Fig.6] schematically shows part of the process according to the invention which concerns the activation of a relay following the detection of an event.

[0013] [Fig.7] schematically shows part of the process according to the invention which concerns sending an alert to a client server following the detection of an event.

[0014] [Fig.8] schematically shows a radioelectric network according to the invention.

[0015] [Fig.9] refers to Example 1 and shows the evolution of the length of eight cables monitored by the same device according to the invention. This is a test aimed at determining the stability of the signal under stationary conditions.

[0016] [Fig. 10] is an enlarged selection of [Fig. 9] and represents the signal for the cable presenting the least stable signal.

[0017] [Fig. 11] is an enlarged selection of [Fig. 9] and represents the signal for the cable presenting the most stable signal.

[0018] [Fig. 12] refers to Example 2 and shows the evolution of the length of eight cables monitored by the same device according to the invention. In this test, the cables were cut at certain points.

[0019] [Fig. 13] refers to [Fig. 12], of which it shows cable no. 4 in a vertical enlargement. Curve (a) shows the cable length as determined with the device according to the invention after calibration, and curve (b) shows the cable length determined by echometry.

[0020] The following reference numerals are used in the figures and in the description: 1,100 Device according to the invention 2 Connection cables (straps) 10 Box 20 Motherboard 21 Power Supply Unit 22 Processor (typically a single-board computer) 23 Input terminal block for 2 24 Daughter card terminal block 25 Communication Unit 26 Relay unit with one relay (26-1 to 26-8) for each daughter card 30-1 to 30-8 Daughter cards 31 Connection module, designed to cooperate with 24 32 Lightning protection device 33 Power Supply Unit 34 Capacitive measurement unit 341 Microcontroller with clock for 34 35 Microcontroller 36 Interface Unit 200 Central Computer Machine 300 User computer machine The four-digit numerical markers denote process steps. Objects of the invention

[0021] According to the invention, the problem is solved by a device for monitoring an inert cable for a certain monitoring period, in particular for detecting an event occurring during this monitoring period, such as its cutting, said device being configured to repeatedly determine the value of a parameter representative of the length of a selected pair of strands within said cable, and to detect an event of a sudden decrease in this value, said device being characterized in that it comprises a main board and a plurality of daughter boards, each daughter board being configured to determine on an inert pair of strands a parameter representative of the length of said pair of strands, and to transmit this parameter to the main board, and the motherboard being configured to compare, for each daughterboard, the parameters representing the length to a threshold value, and to trigger an alert if this threshold value is crossed.

[0022] This device represents the first object of the present invention.

[0023] According to other advantageous features of this device: - Said parameter representing the length of a pair of strands is determined from a capacitive measurement, said capacitive measurement circuit preferably being located on each daughterboard. - The motherboard includes a relay unit, enabling the activation of a relay for each daughterboard when a threshold is exceeded. The daughterboard includes a microcontroller configured to acquire charge-discharge cycle time measurements of the capacitance represented by the cable strand pair, to store this data, optionally to perform digital filtering of this data, and to transmit it to the motherboard. - The motherboard is configured to communicate with a remote computer, in particular to transmit the measurements acquired by all the daughterboards.

[0024] The device according to the invention can be implemented in the form of a housing comprising a motherboard and a plurality of daughterboards (for example, eight), each of which determines the length of a strand pair. The measurements performed by each daughterboard are collected, digitally filtered, and managed by the motherboard, which also manages the relays and alarms. The data is transmitted to a data collection server.

[0025] The device according to the invention allows the monitoring of an inert cable over a significant period of time. Indeed, a very high degree of stability is observed in these measurements over time if the length of the cable or its capacitive environment does not change.

[0026] A second object of the present invention is a method for monitoring an inert cable for a certain monitoring period, in particular for detecting an event occurring during this monitoring period, such as its being cut, said method comprising:

[0027] - the selection of a pair of superimposable strands, - the connection of said pair of strands to a device capable of determining the capacitance of said pair of strands, - the repeated measurement during said monitoring period of a parameter representative of the length of said strand pair resulting from the determination of the capacity of said strand pair, - the monitoring of said parameter representing length by said device.

[0028] A calibration of said representative length parameter can be performed to express a unit of length, said calibration preferably being established using using an echometer. This is done during the commissioning of the device on a given worksite, allowing for precise adjustment of the measurements taken by the daughterboards. This calibration process guarantees the reliability of the cable length measurements.

[0029] In the method according to the invention, an alert can be triggered when said parameter representing the length crosses a certain threshold indicating a break in said cable.

[0030] Said pair of strands may be part of a data transmission cable installed on a switch, the connection between said strands and said device being made via a patch cord, one end of which is connected to said device, either directly or via a splitter head.

[0031] Yet another object of the present invention is the use of a device according to the invention for monitoring inert cables, said cables being cables having twisted strand pairs, and in particular data transmission cables, said inert cables being in particular installed cables left in place awaiting dismantling, or cables waiting at a storage site, in particular awaiting installation or recycling.

[0032] Yet another object of the present invention is a radio network for monitoring the length of a plurality of inert cables, comprising:

[0033] - a plurality of devices according to the invention,

[0034] - a central computer machine configured to communicate in a bidirectional communication with said devices, preferably via their motherboard, to centralize measurements received by said plurality of devices, to transmit data to a user computer, to reroute alerts generated by a device to a user computer and / or a user monitoring installation, and to calibrate and maintain the devices,

[0035] - and at least one user computer configured to communicate bidirectionally with said central computing machine, in particular to perform consistency checks of capacity measurement when selecting the strand pair, to input the cable length determined by calibration, to input the threshold value, and to export data generated by said device and / or said central computing machine.

[0036] Description of the invention a. Terminology and general information

[0037] An "inert" cable is defined here as an electrical cable in which at least one pair of strands is not energized. This electrical cable may be a cable intended for the transmission of electrical energy or a cable intended for data transmission. It comprises a plurality of copper strands covered with insulation.

[0038] The term "twisted pair" (or simply "twisted pair") refers to a pair of copper strands covered with insulation and twisted together. These strands usually have a diameter between 0.3 mm and 1.0 mm, with 0.4 mm and 0.5 mm being the most common diameters, although strands with diameters of 0.6 mm and 0.8 mm are also known. Twisting the strands makes them more resistant to electromagnetic coupling with external interference and reduces outward electromagnetic radiation that could interfere with nearby pairs. Invented by Graham Bell in 1881 for telephony, the twisted pair is used today in cables for data transmission.

[0039] For data transmission, a distinction is made between drop cables, which connect user workstations to a concentration point (CP) and typically comprise one or more dozen identical pairs; distribution cables, which connect concentration points to sub-distributors (SDs) and typically comprise one or a few hundred identical pairs; and transport cables, which connect sub-distributors to distributors and can comprise several hundred, or even several thousand, identical twisted copper pairs. These cables are low-voltage cables, their operating voltage being, for example, 42 V.

[0040] As used herein, the term "twisted copper pair" or "twisted pair" applies to conductive strands of all types, and includes in particular any strand made of a metal other than copper (for example, silver or aluminum). We generically use the term "pair of strands" to encompass all cases of conductors and cables.

[0041] The term "local loop" refers to the terminal part of the network for which there is metallic continuity between the user's installation and the nearest switch. This switch is typically a local switch (CL), but can also be a self-routing switch (CAA).

[0042] Data distribution or transmission cables can have a considerable linear mass. For example, a transmission cable comprising 2,700 twisted copper pairs with a strand diameter of 0.4 mm represents a mass of approximately 7.3 kg per linear meter. a. Detailed description of the invention

[0043] The invention applies to electrical cables comprising at least two insulated strands, preferably of identical diameter. To implement the method according to the invention, the cable must be inert.

[0044] According to the invention, the capacitance of a pair of strands contained in the cable is determined. The pair of strands on which the capacitance is determined must be inert, i.e., it must not be connected to a voltage source. This determination is made at at regular intervals. The capacitance is determined on one or more pairs of inert strands that form a cable. The determined capacitance expresses the length of the strand pair. Typically, only one strand pair is monitored per cable. If the device according to the invention is configured to monitor a plurality of strand pairs, it is preferable to allocate this ability to monitor multiple strand pairs to the monitoring of multiple cables rather than to the monitoring of multiple strand pairs within the same cable.

[0045] Preferably, two inert strands are selected, forming a strand pair. The other strands of the cable do not need to be inert; this allows monitoring of a cable that is in service (except for the strand pair that has been disconnected and is used for the process according to the invention).

[0046] According to a preferred embodiment of the invention, said two strands of the pair of strands form a twisted pair of strands. Such twisted strands are used in particular in telephone cables or data cables (of the DSL or ADSL type, for example), as patch cables, distribution cables or transmission cables.

[0047] The invention can also be used for inert electric current transport cables, using two strands forming a pair.

[0048] The invention can be used for shielded or unshielded cables. More specifically, a pair of strands forming part of a shielded cable can be used, or the capacitance between a strand and the shield can be measured.

[0049] The invention can be used for cables that remain in place where they were originally installed, for example underground and / or in a building; to carry out the method according to the invention, it is not necessary to remove them from their sheaths. The invention can also be used for cables that have been removed from their sheaths.

[0050] The invention makes it possible to monitor the capacitance of a pair of strands. Any sudden change in this capacitance that is detected is likely to indicate that the cable has been cut. Detecting such an event can be useful, but it is often insufficient because the challenge lies in precisely determining the cut length, particularly for locating the point of the cut in the field. The measured capacitance can be converted into units of length by applying a conversion constant. This conversion constant can be an approximate value, reflecting the experience that the capacitance of a pair of insulated copper strands is on the order of 50 nF / km. The precise value depends on the type of cable, its condition, the capacitive environment (particularly humidity), and other factors.

[0051] If it is desired to document the cable length in units of length with greater precision, a calibration must be carried out beforehand for each pair The conversion constant for a given strand pair is monitored. This allows the conversion constant to be experimentally determined and subsequently applied to that pair. This calibration transforms the capacitance measured by the device according to the invention into a unit of length. This calibration is performed using methods known to those skilled in the art, preferably with the aid of an echometer.

[0052] The initial length of the cable is entered. This entry can be made on a human-machine interface provided in the device according to the invention, or preferably on a computer machine that is part of the same radio network as the device according to the invention; in this case, it is said computer machine that sends the calibration value to the device for each measurement channel (i.e., for each daughter card).

[0053] As mentioned above, this calibration is not necessary if the device according to the invention is intended to be used simply to detect variations in cable length, without the possibility of accurately determining the length of cable that has been cut. This method of using the device according to the invention is probably not suitable for most users' needs, but it can be considered without departing from the scope of the present invention.

[0054] The device then periodically measures a parameter representative of the electrical capacitance of a pair of the cable. Any significant change in the value of this capacitance parameter indicates a change in the cable length. The device according to the invention thus makes it possible to detect the severing of a cable; such an event may indicate that a cable theft by cutting is in progress.

[0055] The device can be configured to transmit periodic measurements of Cable length to a monitoring server via IP; this transmission can be via GSM or any other wireless method. Such a wireless connection, particularly IP / GSM, allows for deployment over a large area (national, for example) and centralized monitoring.

[0056] The transmission can be encrypted to ensure adequate cybersecurity. The measurements taken by the device can be time-stamped; this can be done by the device itself or by the server. They can be logged. They can be retransmitted to a supervisor. They can be displayed by the server, and / or formatted and / or processed in tables.

[0057] We now describe the device 1 according to the invention, first in relation to [Fig. 1]. It typically takes the form of a housing 10 closed by a lid, and having a first terminal block 23, called the input terminal block, with at least one pair of terminals 23-1 intended to be connected to the pair of strands of the cable to be monitored. Typically (and as shown in [Fig. 1]), the device is configured to allow the simultaneous connection and monitoring of a plurality of pairs of strands, for example eight pairs. The pairs of strands forming this plurality of strand pairs may belong to the same cable or to different cables.

[0058] The device 1 comprises a motherboard 20 and at least one daughterboard 30, each daughterboard being configured to be connected to a pair of strands to be monitored. This connection is made via the input terminal block located on the motherboard 20. Typically, the daughterboards 30 are inserted vertically into a second terminal block 24, referred to as the daughterboard terminal block. Typically, this daughterboard terminal block 24 is located on the motherboard 20, as this ensures a more robust attachment of this terminal block to the motherboard.

[0059] The connection of the strand pair to the input terminal block 23 can be a direct connection or an indirect connection. In the case of an indirect connection, the strands forming the strand pair are typically connected to the input terminal block by means of patch cords 2 (sometimes called a "jab," but those skilled in the art more commonly use the term "strap"). Typically, one end of each patch cord 2 is connected to a patch panel where the strands of the cable to be monitored arrive; this may be a distribution panel, which may be located, for example, in a telephone exchange, or a sub-distribution panel.

[0060] A daughterboard 30 is schematically represented in [Fig.2]. The daughterboard includes at least one power supply unit 33 capable of powering the various components, the lightning protection unit 32, a capacitive measuring unit 34, a microcontroller 35, and at least one interface unit 36. It also has a connection module 31 enabling its physical and functional connection to the so-called "daughterboard terminal block" located on the motherboard.

[0061] The power supply unit 33 is isolated. The advantage of providing a power supply unit 33 on each of the daughterboards is that it provides galvanic and electrical isolation of each of the measurement circuits on the different daughterboards. Isolating each measurement circuit reduces potential interference and therefore increases the accuracy of the metrology.

[0062] From the input terminal block 23 located on the motherboard, the circuit enters the daughterboard 30 via the connection module 31. On the daughterboard, the circuit first passes through a lightning protection device 32 which is mounted on the daughterboard 30. In the event that this lightning protection device proves to be insufficiently protective, it is preferable that the daughterboard be damaged and not the motherboard, the daughterboard being less expensive and easier to replace.

[0063] The daughterboard has a microcontroller 35. This microcontroller performs four functions: acquiring measurements of the duration of the charge-discharge cycles of the The capacity represented by the pair of cable strands, the storage of this data, the filtering of this data, and the communication with the motherboard. This microcontroller can, for example, be of the STM32® type.

[0064] The capacitive measuring unit 34 is located at the output of the lightning protection device. It includes a capacitive measuring circuit configured to charge a resistor and discharge it through the strand. The larger the capacitance, the longer the charge-discharge cycle time. The capacitive measuring circuit includes a microcontroller 341. This microcontroller includes a clock; the number of clock cycles required to complete a charge-discharge cycle in the strand pair is recorded.

[0065] By way of example, the clock may have a frequency of 16 MHz. For a data transmission cable with a length of 2000 m, a capacitance of approximately 100 nF is measured. The acquisition time is on the order of 40 milliseconds (abbreviated "ms"), which allows approximately 25 measurements per second to be acquired on the same pair of strands.

[0066] The acquisition of duration data is periodic, with this period typically ranging from 1 ms to 100 ms. A number of these successive data points are dynamically stored in the microcontroller of the daughterboard 35, each new incoming data point erasing the oldest data point still in memory. More precisely, the number N of successive data points stored can be, for example, between approximately 100 and approximately 800, preferably between approximately 250 and approximately 650. This data is digitally filtered, and the median value is retained. It is this median duration value (or another characteristic parameter of the cable length, such as capacitance or length determined taking calibration into account) that is sent back from the daughterboard to the mainboard when the latter sends the request to the former.During a sudden change in cable capacitance (for example, in the event of a break), it is necessary to wait until at least half of the N data points have been acquired before returning the current cable length value. As a first example, with N = 400, if for a cable 2000 m long with a capacitance of approximately 100 nF (acquisition time 40 ms), the capacitance suddenly drops to 50 nF, the measurement time after the break increases to approximately 20 ms, or 50 measurements per second. The daughterboard can then send new data to the mainboard after four seconds. As a second example, also with N = 400, for a cable 10 km long with a capacitance of approximately 500 nF (corresponding to 5 measurements per second), the new data corresponding to the length after the break is sent back to the mainboard after 40 seconds.

[0067] The method according to the invention does not require very fine granularity because it compares a first steady state characterized by a first capacitance value (representing a length that is stable) to a second stationary state characterized by a second value; knowing that in the absence of a change in the length of the cable, these first and second capacitance values ​​are identical.

[0068] The motherboard includes, among other things, the daughterboard terminal block which has already been described, a processor 22 which will be described below, a relay unit 26 and a power supply unit 21 capable of supplying the various components.

[0069] Communication between a daughterboard and its motherboard can be achieved using a communication unit 25 (bus) controlled by a processor 22 such as a single-board computer (SBC). For example, a Raspberry Pi® or equivalent SBC can be used. This processor 22, located on the motherboard 20, periodically sends a request to each daughterboard 30 to obtain the filtered median value of the characteristic parameter of the cable length. This characteristic parameter of the cable length can be the length itself. This assumes that the conversion of the duration value into a length value has been performed by the microprocessor of the daughterboard, using calibration; this conversion of the duration value into a length value may involve a conversion of the duration value into a capacity value.The query frequency can be, for example, between approximately 1 second and approximately 10 seconds, preferably between approximately 2 seconds and approximately 6 seconds. A value of 3 seconds is suitable.

[0070] The motherboard stores (typically in the processor 22 described above) the values ​​transmitted by the daughterboards, so that they can be sent back to them in the event of a power outage. The motherboard compares each value received from a daughterboard with a threshold value that has been communicated to the motherboard by the remote computer on the radio network according to the invention. If a difference is deemed significant, an alarm is triggered.

[0071] The single-card computer 22 performs several functions.

[0072] It manages the daughter cards 30, and in particular the communication between the motherboard and the daughter cards, it manages the calibration of the device, it checks the thresholds, and it manages the start-up of the device.

[0073] It can also be configured to check if the device cover has remained open.

[0074] It communicates with the remote computer machine. This communication is bidirectional.

[0075] Regarding communication between the motherboard and the remote computer, the motherboard collects measurements from all daughterboards and transmits them periodically (for example, every 30 seconds) to the remote computer. This transmission can be carried out, for example, via a 4G connection from the communication unit 25. An MQTT protocol can be used. SSL / TLS encryption can be used.

[0076] Typically, for each monitored cable the following information is communicated periodically (for example every 30 seconds): the cable identification, the current cable length as determined by capacitive measurement (typically expressed in meters), the conversion constant from unit of capacitance to unit of length (which may be a calibration constant), the capacitance (typically expressed in nano-Farad or pico-Farad), the length before the last cut determined by echometry, the threshold value, and the timestamp.

[0077] The motherboard can be configured to generate an alert if a daughterboard's threshold value is exceeded. This exceeding can, for example, activate a relay. The relay unit 26 located on the motherboard includes a relay 26-1, 26-2, 26-3, 26-4, 26-5, 26-6, 26-7, 26-8 dedicated to each daughterboard 30-1, 30-2, 30-3, 30-4, 30-5, 30-6, 30-7, 30-8. Each relay is configured to transmit an alert to the motherboard, which in turn transmits it (typically via an MQTT (Message Queuing Telemetry Transport) message) to a remote computer, to generate an alert intended, for example, for a response team.

[0078] Each relay can be connected to third-party equipment, for example to an alarm control panel or a programmable logic controller (PLC), to report the alarm status of each cable monitored by a daughterboard. In parallel, these alarm statuses are transmitted wirelessly to a remote computer, which can forward them to another centralized monitoring system (such as supervisory / hypervision software), display them on a web interface, or send them via SMS to the various response teams.

[0079] Thus, not only is each device according to the invention totally autonomous with respect to the others forming part of the same radio network according to the invention, but also the information resulting from the monitoring of each cable can be processed in a totally independent manner from each other.

[0080] The method according to the invention is now described. A method for using the device according to the invention to monitor an inert cable is schematically represented in [Fig.3].

[0081] In a first step 1100, which is detailed in [Fig.4], a pair of supervisable strands is selected.

[0082] In a second step 1200 the pair of supervisable strands is connected to the device according to the invention.

[0083] In a third step 1300, which is detailed below, the device is calibrated to allow the parameter representing the cable length to be expressed in units of length. This step is optional, since the device and method according to the invention can be used to monitor an inert cable without knowing its precise length.

[0084] In a fourth step 1400, the cable capacitance is monitored. As described above in relation to the capacitive measurement unit of the daughterboard, the capacitance of the strand pair to be monitored is measured periodically.

[0085] In a fifth step 1500, which is detailed in [Fig. 5], a significant change in cable capacitance is detected, and an alert issued by the device is managed. The measurements taken by each daughterboard are collected, digitally filtered, and managed by the main board, which also manages the relays and alarms. When an event is detected, a relay is activated on the main board, and simultaneously, an alert is transmitted to the client server.

[0086] An embodiment of the first step 1100, in relation to [Fig. 4], is described in greater detail here. In this step, at least one pair of inert strands is selected. This selection advantageously includes a specific test to ensure that this pair is inert and supervised.

[0087] In an advantageous embodiment, this specific test comprises two substeps. A pair of strands is selected 1110. In a first substep 1120, a voltage is checked across the terminals using a voltmeter. If a voltage is detected, this pair is not inert, and another pair of strands is selected 1125 and subjected to the same test 1120. If no voltage is detected, the capacitance value of the pair of strands is checked in a second substep 1130 to determine whether it is consistent. A measurement inconsistency may occur, for example, if the pair of strands is damaged or if the cable is immersed in water. Typically, the device is configured to accept a capacitance value between approximately 30 nF / km and approximately 70 nF / km as "consistent."This consistency check of the capacitance measurement assumes that the cable length is known approximately (which is normally the case), and that this value has been entered and is available to the software that manages step 1130; this data input is not shown in the diagram in [Fig. 4]. If 1140 this value is found to be consistent, 1150 this pair is considered supervised. Otherwise, 1025 another pair of strands is selected.

[0088] A more detailed embodiment of the second step 1200 is described here. In this step, the inert strand pair deemed supervised is connected, directly or indirectly, to the terminal block of the device. Direct connection does not require a specific description; here we describe the case of indirect connection from a patch panel. For this, a connection is established in a first substep between the terminal block of the device and the head of the splitter, typically using a jumper. In a second substep, a connection is established between the strands of the strand pair to be monitored, or, if this has already been done, it is checked whether any filters and / or Surge arresters located between the strands to be monitored and the head of the distribution block have been removed, bypassed, or otherwise neutralized so as not to distort the capacity measurement. The order of execution of these two substeps of the second step may be reversed.

[0089] A more detailed embodiment of the third step 1300 is described here. In this third step, the length of each strand of the inert pair to be monitored is determined using an echo meter. To do this, the pair of strands to be monitored is connected to the two terminals of an echo meter (normally using a patch cord), and the cable length is determined, which is directly deduced from the shape of the echo curve displayed on the screen. This length value is entered by a user on the web interface of the central server (which they access via their user computer), which transmits the information via the radio network to the device in question. The device in question is configured to use this length value to determine a calibration constant that allows the capacitance measurement to be converted into units of length.This calibration constant will remain stored in the device until it is replaced by a new calibration constant. The device communicates this calibration constant to the central computer for verification and archiving.

[0090] If the user does not wish to perform calibration, they can enter an approximate length value, or even an arbitrary value; this does not prevent the device from monitoring the inert cable and detecting an event. It is the localization of this event along the cable length that will be inaccurate or even impossible if the length is not properly calibrated initially.

[0091] A more detailed embodiment of the fifth step 1500 is described here, in relation to [Fig. 5], [Fig. 6], and [Fig. 7], which illustrate processes that take place in the motherboard processor. [Fig. 5] illustrates measurement management, [Fig. 6] illustrates relay management, and [Fig. 7] illustrates communication management with the server.

[0092] In this fifth step, an event is identified and the alert is handled. Periodically, measurements are sent from each daughterboard to the mainboard (step 1510). In step 1515, each value is compared to a user-predetermined threshold value; a default value may be defined initially. This step 1515 may be preceded by one or more data filtering steps. In particular, it may be stipulated that an average value from two or more successive measurements is calculated and entered into step 1515. It may also be stipulated that step 1515 is executed a predetermined number of times (for example, two or three times), and that an event (i.e., a comparison leading to the response "Yes") is retained in step 1515 only if each of the comparisons of these values ​​is a predetermined number. would lead to an event. In the absence of an event, the process returns to step 1526 towards the initial step 1510.

[0093] In the event of an occurrence, advantageously the alert is generated in two independent ways, namely: by sending a wired alarm to a relay 26 (step 1522) and by sending an alarm wirelessly to the communication management function with the server (step 1524). Steps 1522 and 1524 can be reversed, but this is not preferred. This communication redundancy ensures that the failure of one of the two systems does not affect the operation of the other. The process then returns to step 1526 and the initial configuration 1510, enabling it to receive data again from the daughterboard corresponding to the next measurement cycle.

[0094] [Fig. 6] illustrates the process that takes place in parallel following step 1522. In step 1530, the relay management interface is initialized. In step 1535, a request is sent to inquire about the reception of a new state. If a new state is received, it is compared to the previous state in step 1540. If it is different, in step 1545, this new state is translated into the hardware configuration at the level of the relay assigned to the daughterboard from which the alert signal originates. If no new state has been received (step 1537), or if the new state is identical to the previous state (step 1542), the process returns to state 1550, specifically to request 1535.

[0095] [Fig.7] illustrates the process which takes place at the end of step 1524, in a way In parallel, at step 1580 the server connection management interface is initialized. At step 1585 a request is sent to inquire about the receipt of an alarm. If an alarm is received, it is published to the server at step 1590. "Publishing" here means making the alarm available to a user by any appropriate means. If no alarm was received at step 1587, the process returns to step 1595 and the reset procedure of step 1580.

[0096] The radio network according to the invention, which makes it possible to advantageously use the device according to the invention and to implement the method according to the invention, is now described. [Fig. 8] shows an embodiment of a radio network according to the invention. It comprises at least one central computing machine 200, a plurality of devices according to the invention 100, and a plurality of user computing machines 300.

[0097] The central computing machine 200 is in bidirectional communication with a plurality of devices according to the invention 100-1a, 100-2a, 100-2b, 100-2c, 100-2d. This communication is typically an internet connection. Each of these devices is configured to monitor at least one strand pair, and preferably a plurality of strand pairs. Furthermore, the central computing machine 200 is in bidirectional communication with a plurality of user computer machines 300-1, 300-2. This connection is typically an internet connection.

[0098] In the example of [Fig.8], device 100-la belongs to the computer machine user user 300-1, and devices 100-2a, 100-2b, 100-2c and 100-2d belong to the computer machine user user 300-2.

[0099] The central computer 200 manages a plurality of devices 100; it acts as a server. This server collects data from the various devices according to the invention. It hosts a client interface for configuring, maintaining, and operating the devices.

[0100] Each new device 100 must be registered on this server. To do this, you connect to a specific interface on the server, open a specific page that allows you to register a new device, and upload a file containing the device's identification parameters and its public key. The server is configured to create the object for the new device as well as the objects for the cables associated (i.e., monitored) by this device.

[0101] The central computer machine 200 can be configured to act as a centralized interface for parameter setting, maintenance, site monitoring, and alert visualization. It can also act as a single intermediary to other computer monitoring systems, such as a user remote monitoring system, a supervisor, or a hypervisor.

[0102] The user computer 300 typically operates a web interface linked to the central computer 200. The user computer allows the user to configure the devices associated with that user. In particular, it allows the user to perform a consistency check of the capacitance 1140 when selecting a pair of supervised strands 1100. It also allows the user to enter the cable length, which has been determined by the user (typically by echometry) or is an estimated or approximate value, in cases where high accuracy of the cable length value is not required. The user computer also allows the user to define the alert threshold for each relay.It also allows the user to view data and alerts, create device subgroups for specific internal users, and export this data in an appropriate format.

[0103] In a variant (not shown in the figures) of this radio network according to the invention, said network further comprises, in place of one or more of the user computer machines 300, other servers such as a hypervisor.

[0104] The invention can have several different uses. It can be used to monitor cable laying sites. In this situation, it makes it possible to detect cable theft. More precisely, it makes it possible to detect, in real time (i.e., with a Response time (a few seconds or tens of seconds) is due to the decrease in cable capacitance, this capacitance representing the cable length. As mentioned above, to accurately determine the length of the cut cable, prior calibration is required, typically using an echometer.

[0105] According to the invention, the device or the radio network in which it is integrated is configured to generate an alert in the event of a sudden drop in cable capacity. Thus, a supervisor who knows the location of the device according to the invention, which measures the parameter representing the capacity, and who has a cable routing plan, can indicate to the interception teams where the event (which is likely to correspond to a cable-cutting theft) is taking place.

[0106] The invention also makes it possible to verify whether the length of cable cut by an authorized person corresponds to the length of cable for which he was authorized to cut, and / or corresponds to the length of cable that he declares to have taken (for example when depositing it at the recycling center).

[0107] The device and method according to the invention offer numerous advantages over measurement using an echo sounder. The device according to the invention is simpler than an echo sounder. It is significantly less expensive than an echo sounder, even taking into account the need for an echo sounder to perform the initial calibration of the device according to the invention. This significantly lower cost makes it possible to consider the widespread deployment of devices according to the invention, for example, in a storage area for new cables or cables destined for recycling.

[0108] The device and method according to the invention provide a function that was not previously available, namely the continuous monitoring of the length of an inactive cable. It allows for the monitoring of inactive cables and, more specifically, the detection of events related to cable cutting. In particular, it allows for the detection of cable cutting and the localization of the cut point on the cable. A timestamping function for the event can be added.

[0109] This monitoring function is performed discreetly: generally speaking, within the scope of the present invention, it is impossible to detect from the outside that an inert cable is under surveillance. The device takes the form of a small box that can be installed discreetly, typically in a secure location, such as a telephone exchange. If the device is installed in a storage area, it is often possible to place it in an existing cabinet or terminal. Since no operations need to be performed at the end of the cable, the subcontractor installing the cable or the thief is unaware that the cable is under surveillance and can be caught in the act.

[0110] The method according to the invention, based on a capacitance measurement, avoids having to intervene on both ends of the cable at the same time, unlike a resistive measurement which requires a short circuit or the connection of a loop resistor. [YES] Examples

[0112] Example 1: Device stability

[0113] A device according to the invention, comprising a motherboard and eight daughterboards, was used, capable of independently monitoring eight cables (labeled A to H). Each daughterboard was connected to a pair of strands of a different cable. These were inert data transmission or distribution cables, still in the conduits in which they had been installed while in service, connecting from the patch panel of a distribution frame located in a building to sub-distribution frames located in boxes by the roadside. Their lengths varied. Each daughterboard was calibrated by inputting the cable length value determined using an echometer. The capacitance was then recorded over several days. The result is shown in [Fig. 9], [Fig. 10], and [Fig. 11].In these figures, the horizontal axis represents time and the vertical axis the cable length, as determined from the capacitance measurement and calibration performed with the echometer.

[0114] [Fig.9] shows the evolution of the length over time, for four hours. We can see that this length does not change, which is normal, since the cable was not cut during the monitoring period. We also see that the signal fluctuations are very small. [Fig. 10] shows a magnification of the vertical axis for cable B, which exhibited the most fluctuation (monitored for five days), and [Fig. 11] shows a magnification of the vertical axis for the cable that exhibited the least fluctuation. It is worth noting that the cable shown in [Fig. 10] is an atypical case among the eight cables monitored.

[0115] Generally speaking, the fluctuation is less than 3%, and for the most stable cables (such as that of [Fig. 11]) less than 0.25%. This remarkable stability makes it possible to set an alert threshold such that the cutting of about thirty meters of cable per kilometer can be detected, without risk of false positives.

[0116] The absolute value of the measured capacitance is on the order of 0.047 nF per meter of 4 gauge cable.

[0117] Example 2: Cable break detection

[0118] The device of Example 1, connected to the same cables, was subsequently used to detect cable cutting. The results are shown in [Fig. 12] and [Fig. 13], which are of the same type as [Fig. 9] to [Fig. 11]. [Fig. 12] shows the monitoring of the eight cables, with cuts of different lengths made at at different times. The measurements are time-stamped. [Fig. 13] shows the detail of the tracking of cable E from [Fig. 12]. The upper curve corresponds to the cable length determined by the device according to the invention, the lower curve (dotted line) corresponds to the cable length determined by echometry. The average relative error does not exceed 3.5%.

Claims

Demands

1. A device (1,100) for monitoring an inert cable for a certain monitoring period, in particular for detecting an event occurring during this monitoring period, such as its cutting, said device being configured to repeatedly determine the value of a parameter representative of the length of a selected strand pair within said cable, and to detect an event of a sudden decrease in this value, said device being characterized in that it comprises a main board (20) and a plurality of daughter boards (30), each daughter board being configured to determine on an inert strand pair a parameter representative of the length of said strand pair, and to transmit this parameter to the main board, and the main board being configured to compare, for each daughter board, the length-representative parameters to a threshold value,and to trigger an alert if this threshold value is exceeded.

2. Device according to claim 1, characterized in that said parameter representing the length of a pair of strands is determined from a capacitive measurement, a capacitive measurement circuit preferably being located on each daughterboard (30).

3. Device according to any one of claims 1 or 2, characterized in that said motherboard (20) includes a relay unit (26), enabling the activation of a relay for each daughterboard (30) in the event of crossing the threshold.

4. Device according to any one of claims 2 to 3, characterized in that the daughterboard (30) includes a microcontroller (341) configured to acquire charge-discharge cycle time measurements of the capacitance represented by the pair of cable strands, to store this data, optionally to perform digital filtering of this data, and to communicate it to the motherboard.

5. A method for monitoring an inert cable for a certain monitoring period, in particular for detecting an event occurring during this monitoring period, such as its cutting, said method comprising: - the selection of a pair of supervised strands, - the connection of said pair of strands to a device capable of determining the capacitance of said pair of strands, - the repeated measurement during said monitoring period of a parameter representative of the length of said pair of strands resulting from the determination of the capacitance of said pair of strands, - the monitoring of said parameter representative of the length by said device.

6. A method according to claim 5, wherein a calibration is performed of said parameter representing length to express a unit of length, said calibration preferably being established using an echometer.

7. A method according to any one of claims 5 to 6, wherein an alert is triggered when said length-representative parameter crosses a certain threshold indicating a break in said cable.

8. A method according to any one of claims 5 to 7, wherein said pair of strands is part of a data transmission cable installed on a switch, the connection between said strands and said device being made via a patch cord, one end of which is connected to said device, either directly or via a splitter head.

9. Use of a device according to any one of claims 1 to 4 for monitoring inert cables, said cables being cables having twisted strand pairs, and in particular data transmission cables, said inert cables being in particular installed cables left in place pending their dismantling, or cables waiting at a storage site, in particular awaiting their installation or recycling.

10. A radio network for monitoring the length of a plurality of inert cables, comprising: - a plurality of devices (100) according to any one of claims 1 to 4, - a central computer (200) configured to communicate bidirectionally with said devices (100), preferably via their motherboard (20), to centralize the measurements received by said plurality of devices, to transmit data to a user computer, to reroute alerts generated by a device to a user computer and / or a monitoring system user monitoring, and to be able to calibrate and maintain the devices, - and at least one user computer machine (300) configured to communicate bidirectionally with said central computer machine (200), in particular to perform the consistency check of the capacity measurement when selecting the strand pair, to enter the cable length determined by calibration, to enter the threshold value, and to export data generated by said device and / or said central computer machine.

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