System for detecting and locating a temperature variation in a cable network by reflectometry

Abstract

The invention relates to a system (300) for detecting and locating a temperature increase in an environment consisting of several discrete zones (Z1-Z10), the system comprising a branched cable network comprising a plurality of branches (CS1-CS10) which are each intended to be deployed in one of the zones, and at least one reflectometry device (DR1) which is connected to one end of at least one branch of the network and configured to: - acquire an initial reflectometry measurement corresponding to an initial state of the branched cable network; - acquire a current reflectometry measurement corresponding to a current state of the branched cable network; - compare the current reflectometry measurement with the initial reflectometry measurement in order to deduce therefrom a temperature increase on one of the branches of the network; - when a temperature increase is detected, reconstruct the topology of the cable network from the initial reflectometry measurement and the current reflectometry measurement; and - identify the branch of the cable network for which a fault corresponding to a temperature increase has been detected, by evaluating a variation of at least one parameter of the reconstructed topology among the length of the branches of the network or the impedance of the loads at the end of the branches of the network.

Description

DESCRIPTION SYSTEM FOR DETECTING AND LOCATING TEMPERATURE VARIATIONS IN A CABLE NETWORK, BY REFLECTOMETRY

[0001] The invention relates to the detection and localization of temperature variations in a room to prevent the start of a fire. It also relates to methods and systems for analyzing the condition of a cable by reflectometry. The invention is particularly applicable to fire detection in environments such as buildings, means of transport (airplanes, trains), or nuclear power plants.

[0002] The invention aims to solve the general problem of detecting and locating a temperature increase in a room in order to prevent a potential fire and trigger an alarm. The invention also relates to monitoring the development and spread of a potential fire.

[0003] European patent EP3227651, concerning a method and device for detecting hot spots in an installation, particularly for detecting leaks in air ducts, describes a method based on a reflectometry test applied to a point-to-point cable of a given length. This solution is described in the context of its application to an aircraft for locating air duct leaks.

[0004] One drawback of this solution is its limited range, as it relies on the deployment of a single cable. It is well known that reflectometry methods are susceptible to signal attenuation over long cable runs. This problem is even more pronounced when the cable used is temperature-sensitive, as this type of cable is less suitable for transmitting reflectometry signals than some standard cables.

[0005] The publication "OMTDR-Based embedded cable diagnosis for multiple fire zones detection and location in aircraft engines," by Wafa Ben Hassen et al., 2017, IEEE Sensors, describes another solution based on an OMTDR (Orthogonal Multi-Tone Time Domain Reflectometry) multi-carrier signal for fire detection in aircraft engines. This solution also relies on a standard point-to-point cable, resulting in a lack of sensitivity and incompatibility for deployment in more complex infrastructures such as buildings. In particular, if the cable is cut, there is a loss of information about the evolving situation.

[0006] The invention aims to provide a fire detection and localization solution based on a reflectometry system that can be deployed in a complex environment composed of different independent zones, such as a building, a nuclear power plant, a train composed of several cars, or a tunnel. The invention also makes it possible to monitor the spread of fire.

[0007] The invention relates to a system for detecting a temperature increase in an environment consisting of several distinct zones, the system comprising a branched cable network including several branches, each intended to be deployed in one of the zones, and at least one reflectometry device connected to one end of at least one branch of the network and configured to: - Acquire an initial reflectometry measurement corresponding to an initial state of said branched cable network, - Acquire a current reflectometry measurement corresponding to a current state of said branched cable network, - Compare the current reflectometry measurement to the initial reflectometry measurement to deduce a temperature increase on one of the branches of said network, When a temperature increase is detected, reconstruct the cable network topology from the initial reflectometry measurement and the current reflectometry measurement. Identify the branch of the cable network for which a fault corresponding to a temperature increase has been detected by evaluating a variation in at least one parameter of the reconstructed topology among the length of the network branches or the impedance of the loads at the end of the network branches.

[0008] According to a particular aspect of the invention, at least one branch of the branched cable network is a heat-sensitive cable whose insulation melts when the temperature exceeds a given threshold so as to create a short circuit.

[0009] According to a particular aspect of the invention, at least one branch of the branched cable network is a temperature-sensitive cable in which at least one characteristic parameter, either permittivity or conductivity, varies with temperature.

[0010] According to a particular aspect of the invention, at least one reflectometry device is configured to detect an increase in temperature in the environment when the difference between the current reflectometry measurement and the initial reflectometry measurement is greater, in absolute value, than a predefined threshold.

[0011] According to a particular aspect of the invention, at least one reflectometry device is configured to acquire several successive current reflectometry measurements, identify, in the successive measurements, the same amplitude peak whose value exceeds a first predefined threshold, calculate the rate of change of the amplitude, the time position of said peak or the shape of said peak during the successive measurements and detect an increase in temperature in the environment when the rate of change exceeds a second predefined threshold.

[0012] According to a particular aspect of the invention, at least one reflectometry device is configured to acquire several successive current reflectometry measurements and determine a rate of change of temperature increase from the evolution of at least one parameter of the reconstructed topology.

[0013] According to a particular aspect of the invention, at least one reflectometry device is configured to detect a branch break due to temperature increase from the evaluation of at least one parameter of the reconstructed topology.

[0014] In one embodiment, the system according to the invention comprises several reflectometry devices respectively connected to different ends of the cable network and cooperating together to perform a distributed reflectometry test so as to detect and locate a fault corresponding to a temperature increase.

[0015] According to a particular aspect of the invention, the topologies respectively reconstructed from the reflectograms measured by each of the reflectometry devices are compared to resolve at least one ambiguity in the localization of the temperature increase in the cable network.

[0016] According to a particular aspect of the invention, the branched cable network comprises a main cable, one end of which is connected to the reflectometry device, and a plurality of secondary cables connected to the main cable.

[0017] According to one particular aspect of the invention, the deployment environment of the system is a building or a means of transport.

[0018] In one embodiment, the system according to the invention further comprises at least one database configured to record at least the current reflectometry measurement and the reconstructed cable network topology.

[0019] The invention also relates to a method for detecting a temperature increase in an environment consisting of several distinct zones, the method comprising the steps of: Deploy a branching cable network throughout the environment so that at least one network cable is present in each area. - Connect at least one reflectometry device to one end of the network, - Acquire an initial reference reflectometry measurement corresponding to an initial state of said branched cable network in a healthy state, - Acquire a current reflectometry measurement corresponding to a current state of said branched cable network, - Compare the current reflectometry measurement to the initial reflectometry measurement to deduce a temperature increase on one of the branches of said network, When a temperature increase is detected, reconstruct the cable network topology from the initial reflectometry measurement and the current reflectometry measurement. Identify the branch of the cable network for which a fault corresponding to a temperature increase has been detected by evaluating a variation in at least one parameter of the reconstructed topology among the length of the network branches or the impedance of the loads at the end of the network branches.

[0020] In one embodiment, the method according to the invention comprises: - several successive stages of acquiring a reflectometry measurement, the identification, in the successive measurements, of at least one identical amplitude peak whose value exceeds a first predefined threshold, - the calculation of the rate of change of the amplitude, the temporal position of said peak or the shape of said peak during successive measurements and - the detection of an increase in temperature in the environment when the rate of change exceeds a second predefined threshold.

[0021] In one embodiment, the method according to the invention comprises: - several successive stages of acquiring a reflectometry measurement, - the determination of a rate of change of the temperature increase from the evolution of at least one parameter of the reconstructed topology.

[0022] The invention also relates to the use of the system or method according to the invention to monitor the development of a fire spreading in the environment.

[0023] Other features and advantages of the present invention will become more apparent from the following description in relation to the following attached drawings.

[0024] [Fig. 1] represents a diagram illustrating the principle of reflectometry applied to fault detection on a cable according to the prior art,

[0025] [Fig. 2] represents a diagram illustrating the principle of reflectometry applied to the detection of a temperature rise in an area of ​​a cable,

[0026] [Fig. 3] represents a diagram illustrating a system for detecting an increase in temperature according to an embodiment of the invention,

[0027] [Fig. 4] represents a flowchart detailing the steps for implementing a method for detecting a temperature rise executed by the system in Figure 3,

[0028] [Fig. 5] represents an example of a heating detection system according to the invention comprising a network of three cables according to a first heating scenario,

[0029] [Fig. 6] represents a reflectogram measured for the network in Figure 5 in a healthy state and in a state corresponding to the first heating scenario illustrated in Figure 5,

[0030] [Fig. 7] represents the difference between the two reflectograms in Figure 6,

[0031] [Fig. 8] represents the system of figure 5 in a second warm-up scenario,

[0032] [Fig. 9] represents a differential measurement between the reflectogram measured for the network in Figure 5 in a healthy state and in a state corresponding to the second heating scenario illustrated in Figure 8,

[0033] [Fig. 10] represents the system of figure 5 in a third warm-up scenario,

[0034] [Fig. 11] represents a differential measurement between the reflectogram measured for the network in Figure 5 in a healthy state and in a state corresponding to the second heating scenario illustrated in Figure 10,

[0035] [Fig. 12] represents a comparative example of a prior art heating detection system in the same environment as the system shown in Figure 5,

[0036] [Fig. 13] represents several examples of reflectograms corresponding to the second heating scenario for different heating intensities,

[0037] [Fig. 14] represents an enlarged portion of the reflectogram in Figure 13 corresponding to the end of the second zone,

[0038] [Fig. 15] represents three examples of topology reconstructed from the reflectograms in Figure 13,

[0039] [Fig. 16] represents the system of figure 5 in another heating configuration leading to cable rupture,

[0040] [Fig. 17] represents an example of a measured reflectogram and a reconstructed reflectogram for the example described in Figure 16,

[0041] [Fig. 18] represents the network topology of Figure 16 reconstructed from the reflectogram of Figure 17.

[0042] Figure 1 illustrates the principle of reflectometry applied to cable condition analysis, according to the prior art. The principle consists of injecting a signal with a controlled waveform at an injection point INJ in the cable. The incident wave Ol propagates along the cable until it encounters an impedance discontinuity AZ caused by an electrical fault. Part of the wave is transmitted OT to the cable end FC, and part of the wave is reflected back to the injection point INJ. Using measuring equipment, the reflected signal is measured. Analysis of the measured signal allows the fault to be detected and located.

[0043] A correlator performs the cross-correlation between the generated signal and the received signal in order to produce a time-domain reflectogram R(t). If the reflectometry signal used is a simple time pulse, the COR can be made optional.

[0044] The time reflectogram R(t) has a characteristic amplitude peak of the DF fault at a time abscissa which is related to the distance between the signal measurement point and the DF fault and to the signal propagation speed in the cable.

[0045] As is known in the field of reflectometric diagnostic methods, the position of D The NF of the non-obvious fault on the cable, in other words its distance from the signal injection point, can be directly obtained from the measurement, on the time-domain reflectogram, of the duration t D NF between the first amplitude peak recorded on the reflectogram and the amplitude peak corresponding to the signature of the defect.

[0046] Several known methods are possible for determining the position of D NF- A first method consists of applying the relationship linking distance and time: d DNF = V.IDNF / 2 WHERE V is the signal propagation speed in the cable. Another possible method is to apply a proportionality relationship of the type of D NF / t D NF = L / t0 where L is the length of the cable and t0 is the time, measured on the reflectogram, between the amplitude peak corresponding to the impedance discontinuity at the injection point and the amplitude peak corresponding to the reflection of the signal on the end of the cable.

[0047] Figure 2 illustrates the principle of applying a reflectometry diagnostic to detect and locate a temperature variation on a cable.

[0048] The heated zone CH has an input interface and an output interface l2, both corresponding to impedance discontinuities at which the incident wave 01 can be reflected. The heated zone CH of the cable has a length Ld. The cable, with characteristic impedance Zc1, is thus divided into three zones as illustrated in Figure 2. The two unheated zones have a characteristic impedance Zc1 equal to that of the unheated cable. The heated zone has a characteristic impedance Zc2.

[0049] The temperature increase in the heated zone CH will therefore modify certain physical parameters of the cable, such as relative permittivity or conductivity, and will vary the characteristic impedance in this zone. Each interface of the heated zone CH introduces two reflection coefficients in opposite phase = ■ ■ ' ' Z Z C c 2 ~ 2 + Z Z C c 1^ and r2= . Zc1+Zc2

[0050] The detection capability and localization accuracy of the heated area CH depends on the time width or bandwidth of the signal injected into the cable as well as the electrical characteristics of the cable such as resistance and temperature rise.

[0051] Figure 3 represents a diagram of a 300 temperature increase detection device according to one embodiment of the invention.

[0052] The 300 device consists of at least one DFL reflectometry device comprising at least one signal generator, one digital-to-analog converter, one coupler for injecting the analog signal into a cable network, and one A measurement device for measuring a reflected signal and digitizing it via an analog-to-digital converter. The DRi reflectometry device also includes a processing unit for calculating and analyzing a reflectogram obtained from a measurement of the reflected signal. Calculating the reflectogram may involve a correlation calculation between the measured signal and the signal injected into the cable, particularly when the signal differs by more than a simple time pulse.

[0053] The DFL reflectometry device is connected to a branching cable network comprising a main CP cable and several secondary CSi-CS cables, each connected to the main CP cable. Each secondary cable is deployed in a respective ZZ zone. 10 of a building or a means of transport. Each secondary cable can be a standard cable or a heat-sensitive cable.

[0054] In a first embodiment, a temperature-sensitive cable consists of an insulator whose material melts when the temperature exceeds a given threshold, thereby creating a short circuit. In a second embodiment, a temperature-sensitive cable has at least one characteristic parameter, such as permittivity or conductivity, that varies with temperature.

[0055] The cable network topology is not limited to that described in Figure 3 and is more generally chosen according to the building to be instrumented. In particular, the number of secondary cables is equal to the number of zones in the building to be instrumented.

[0056] In one embodiment, several DRi, DR2, DR3 reflectometry devices are connected to different ends of the cable network and cooperate together to implement a distributed reflectometry test as described in Applicant's patent applications FR3012616 or FR3012617.

[0057] As an illustration, Figure 3 shows a point-to-point line L connected to the reflectometry device DR1 and deployed in the environment to be covered so as to traverse all areas of the environment. The line L necessarily has a much greater length than each secondary cable.

[0058] However, as explained in the preamble, reflectometry devices have lower sensitivity for long cables due to signal attenuation during their propagation along the cable.

[0059] The invention therefore offers the advantage of improved detection sensitivity by using a network of branched cables.

[0060] In general, the structure of the cable network can be more complex than that described in Figure 3, and is related to the complexity of the building's architecture in which network is deployed. For example, each branch of the network can have several sub-branches. Generally, the network can include any number of junctions, each junction connecting any number of cable branches together.

[0061] Figure 4 details the steps performed by the 300 system to detect and locate a temperature increase in one of the Zi-Z zones in which the cable network is deployed.

[0062] In step 401, an initial reflectometry measurement is performed on the cable network in a healthy state.

[0063] In step 402, a reflectometry measurement is then performed at a later time.

[0064] In step 403, a comparison is made between the two measurements to detect a change characteristic of an increase in heat in one of the Z^-Z zones w .

[0065] If a temperature increase is detected in step 404, a reconstruction of the cable network topology is determined in step 405 and then in step 406, the area impacted by the heat increase is located using the reconstructed topology and more precisely by evaluating at least one parameter of the reconstructed topology among the impedance of the loads at the ends of the network branches and the length of the network branches.

[0066] Step 405 can be performed using a topology reconstruction algorithm that takes as input the initial reflectometry measurement and / or the current reflectometry measurement. The algorithm used is, for example, the one described in one of the patent applications FR3070075, FR3070211, FR3082947.

[0067] Figures 5 to 12 illustrate an implementation of the invention for a simple example of a cable network composed of three branches L1, L2, L3 arranged in three zones Z1, Z2, Z3 of a given environment. In this example, the two cables L2, L3 are terminated by an open circuit, but the load at the end of the cable can be of any value.

[0068] A TDR reflectometry device is connected to one end of the first cable L1. The signal injected into the cable network is, for example, a Gaussian time-domain pulse, but other more complex signals can be considered.

[0069] In the example in Figure 5, an increase in heat (start of fire) occurs in zone Z1.

[0070] Figure 6 shows a first reflectogram 601 measured for the cable network of Figure 5 in a healthy state. This reflectogram corresponds to the reference measured in step 401 of the method. The reflectogram 601 has a first peak corresponding to the injection signal, a second negative peak corresponding to the reflection of the signal on the junction of the network between the three branches and which is located at a time of flight corresponding to the length L1 of the first cable, a third positive peak corresponding to the reflection of the signal on the end of the cable L3 and a fourth positive peak corresponding to the reflection of the signal on the end of the cable L2.

[0071] The second reflectogram 602 is the one measured at stage 402 after the start of the fire in zone Z1.

[0072] On this second reflectogram, we observe a negative peak followed by a positive peak in zone 603 of the reflectogram, corresponding to the part of the cable L1 that undergoes the temperature increase in zone Z1. The spacing between the two peaks in zone 603 depends on the width of the heated area of ​​the cable.

[0073] Figure 7 shows the difference between the two reflectograms 601 and 602 as calculated in step 403 of the method. This difference clearly identifies the double peak 700 corresponding to the heated area of ​​cable L1.

[0074] Thus, a first possible test to carry out step 404 of detecting an increase in temperature consists of looking for the presence of a double peak composed of two peaks of opposite signs in the difference 700 calculated in step 403. If the amplitude of one or both of the peaks exceeds a predefined threshold, we can conclude that there is heating of the cable.

[0075] In one embodiment, a more sophisticated detection test involves performing several successive reflectometry measurements over time and evaluating the rate of change of the amplitude of the characteristic peak in the heated area. Indeed, a temperature increase leads to a change in the characteristics related to the impedance discontinuity caused by heating, and therefore a change over time in one of the characteristics of the peaks (at the input and output of the defect), such as the amplitude, waveform, and time position corresponding to this discontinuity. One possible test consists of measuring the rate of change of the peak amplitude, equal to the peak amplitude divided by the measurement time, comparing this rate to a predefined threshold, and concluding that heating has occurred if the rate exceeds the threshold.

[0076] A similar line of reasoning can be applied to the evolution over time of the peak waveform and the peak's temporal position. In particular, the peak characteristic of a temperature increase may exhibit a double-peak shape. It can also be distorted and generally evolves according to the cable's thermal characteristics in response to thermal stress.

[0077] In other words, another possible test is to measure the rate of change of the peak position equal to the time abscissa of the peak in the reflectogram divided by the time of measurement and to compare this rate to the predefined threshold.

[0078] More generally, the shape of the signal can be compared between several successive measurements. For example, the signal is taken within a time window around the peak value, and the evolution of the signal shape within this time window can be evaluated over time. For example, the root mean square error is calculated between two signals corresponding to two successive measurements, and the rate of change of this error is calculated by dividing this error by the time difference between the two measurements.

[0079] Step 405 allows the network topology to be reconstructed from the initial reflectogram 601 and thus a correspondence is made between each portion of the reflectogram and the associated cable of the cable network.

[0080] Once this correspondence is established, it is possible to conclude that the double peak 603 characteristic of a temperature increase is located on the L1 cable in the Z1 zone.

[0081] More generally, the search for a double peak in the reflectogram is replaced by the search for a signature characteristic of a heating zone, this signature being dependent on the waveform of the signal injected into the cable, in particular the width of the pulse (when the signal is impulsive) but also the size of the heating zone and its intensity.

[0082] Figure 8 illustrates another scenario in which heating is located in zone Z2.

[0083] Figure 9 shows the differential measurement obtained by calculating the difference between a reflectogram measured for the state of the network shown in Figure 8 and the initial reflectogram 601.

[0084] On this differential measurement, we observe a double peak 900 located in the area of ​​the reflectogram corresponding to cable L2 and therefore to a heating located in the Z2 area.

[0085] Figure 10 illustrates yet another scenario in which heating is located in the Z3 zone.

[0086] Figure 11 shows the differential measurement obtained by calculating the difference between a reflectogram measured for the state of the network shown in Figure 10 and the initial reflectogram 601.

[0087] On this differential measurement, we observe a double peak 1000 located in the area of ​​the reflectogram corresponding to cable L3 and therefore to a heating located in the Z3 area.

[0088] The invention has the advantage of better detection sensitivity because the path traveled by the reflectometry signal from the injection point to the different inspection areas is minimized due to the branched network topology.

[0089] For comparison, Figure 12 illustrates an example of a heating detection system based on a simple 1200 point-to-point cable. To cover the three zones Z1, Z2, Z3 to be monitored, the total cable length required in this example is 48 m, which results in significant signal attenuation during its journey from the TDR injection equipment to the end of the cable E.

[0090] Conversely, by using a branched cable network according to the invention as shown in Figure 5, the total distance traveled by the signal to the ends of the network is equal to the maximum between L1+L2 and L1+L3, which allows for better sensitivity in detecting the characteristic signature of a heating zone in the reflectogram.

[0091] Steps 405 and 406 of the method according to the invention, which aim to locate heating from the measured reflectogram and the reconstructed topology, are now described in more detail.

[0092] At step 405 the topology reconstruction algorithm provides the network topology from the reflectogram, i.e. the respective lengths of each branch of the network, the junctions and the impedance values ​​at the end of each branch.

[0093] When incipient heating occurs on a branch of the network, it causes a non-obvious fault on that branch, which can be detected on the reflectogram measured using step 404 described previously. However, when the cable network is complex, the precise location of the fault can be ambiguous and difficult to determine using the reflectogram alone.

[0094] For this reason, in step 405, the topology reconstruction algorithm is applied again to the reflectogram measured in step 402. At the beginning of the warm-up, when the fault on the cable is a non-obvious fault, the topology reconstruction algorithm will not consider this fault as a significant element of the topology. However, the impedance and the position of the mismatch at the end of this branch are affected because some of the energy of the reflectometry signal is reflected back onto the non-obvious fault.

[0095] Figure 13 shows three measured reflectograms corresponding to the scenario in Figure 8, i.e., heating in the Z2 zone.

[0096] The labeled reflectogram Z d / Z c =1 corresponds to a healthy network, that is, one without defects. The labeled reflectogram Z d / Z c =2 corresponds to an impedance defect Z d =2Z c present in zone 2. The labeled reflectogram Z d / Z c =3 corresponds to an impedance defect Z d =3Z c present in zone 2.

[0097] The double peak 1300 on the reflectogram corresponds to the defect in zone 2. It is located between peak 1301 of the end of line L3 and peak 1302 of the end of line L2.

[0098] Figure 14 shows a magnified version of the reflectogram area around peak 1302 at the end of line L2. It can be seen that the amplitude of this peak changes (in this example, it decreases) as a function of the evolution of the non-obvious defect. It can also be seen that the position of this peak also changes as a function of the evolution of the non-obvious defect.

[0099] Figure 15 shows the three reconstructed topologies as a function of the fault impedance.

[0100] For the initial healthy network (Zd / Zc=1), the branch length L2 is 65.3 m and the impedance at the end of this branch is Z2=397 Ω. When the incomplete fault due to heating appears (Zd / Zc=2), the topology reconstruction algorithm indicates a branch length L2=65.5 m and an impedance at the end of the branch equal to Z2=387 Ω. When the incomplete fault amplifies (Zd / Zc=3), the topology reconstruction algorithm indicates a branch length L2=65.9 m and an impedance at the end of the branch equal to Z2=370 Ω.

[0101] In all three scenarios, the length of the L3 branch and the impedance at the end of the L3 branch do not change.

[0102] Therefore, from the reconstructed topology and its comparison with the initial topology, we can deduce which branch the fault is located on. In this example, since the length and impedance of branch L2 have changed compared to the initial topology while the parameters of branch L3 remain stable, the fault is likely located on branch L2.

[0103] Furthermore, by performing regular reflectogram measurements and reconstructing the network topology from these measurements each time, one can identify an evolution in the severity of the fault by monitoring the evolution of the branch lengths and the impedances at the branch ends.

[0104] When heating continues until the cable breaks completely, the reconstructed network topology will be significantly modified, with a new branch length (shortened at the break point) and a new impedance at the end of the branch (high impedance if it is an open circuit).

[0105] Furthermore, as previously stated, the use of several reflectometry devices connected to different ends of the network allows the method according to the invention to be applied several times in different locations and thus resolves any ambiguities in heating localization.

[0106] Figure 16 illustrates this operation by revisiting the example from Figure 5 and considering this time that branch L2 of the cable network has overheated to such an extent that the cable has broken. In this situation, two new, separate cable networks, RS1 and RS2, are obtained.

[0107] Figure 17 shows, on the same diagram, the reflectogram measured 1701 from the reflectometry device TDR1 and the reflectogram reconstructed 1702 from this measurement. We see the peak 1301 corresponding to the reflection of the signal at the junction between the branches of the network, followed by a high-amplitude peak 1700 which corresponds to the direct fault (here an open circuit) that occurred following the break in the cable of length L2.

[0108] Figure 18 shows the topology of the RS1 network reconstructed from the reflectogram in Figure 17. In this new topology, branch L2 has been shortened from 65.5 m to 40 m, with a branch impedance Z2 = 3900 Ohms, corresponding to an open circuit. The branch break can therefore be clearly identified thanks to this reconstruction.

[0109] In such a situation, the use of a second reflectometry device TDR2 connected to the end of the branch of length L2 makes it possible, in the event of a cable break, to continue monitoring each of the two new cable networks thus formed.

[0110] This allows for redundancy in measurements taken and continuous monitoring of the evolution of a fire in a building instrumented by the cable network, regardless of which branches of the network are impacted.

[0111] In general, periodic monitoring of measured reflectograms and topologies reconstructed from these reflectograms makes it possible to monitor the appearance of heating and its evolution until the rupture of a cable, but also the evolution of a fire in different rooms of a building when several cables are broken during the fire.

[0112] When a cable break is detected, as in the example in Figure 17, the direct fault generates a significant amplitude peak in the reflectogram, which is taken into account by the topology reconstruction algorithm to generate the new topology of the modified network. In the example in Figure 16, the new lengths L2 and L'2 can be determined by applying a topology reconstruction algorithm to the reflectograms measured by the TDR1 and TDR2 devices, respectively.

[0113] In this situation, the reference reflectometry measurement is updated for each of the new networks obtained with the new measurements taken after the detection of a cable break.

[0114] One advantage of using multiple reflectometry devices distributed throughout the cable network is that it allows monitoring of the evolution of a fire even in the event of a cable break.

[0115] The device according to the invention offers the advantage of flexibility with respect to the environment and the areas to be monitored, particularly their criticality. Specifically, the cable network can be heterogeneous and include standard, coaxial, twisted-pair, multi-conductor, or even heat-sensitive cables. The cables exhibiting the highest sensitivity—that is, those for which the amplitude of the impedance mismatch signature on the reflectogram associated with the heating zone is most pronounced—are positioned in the most critical areas. A critical area is defined, for example, as an area of ​​a sensitive building where the start of a fire must be detected with greater reliability than in other areas.

[0116] In particular, heat-sensitive cables exhibit greater sensitivity, especially cables whose insulation melts to create a short circuit that will be detected more reliably than a low-intensity temperature increase for a standard cable.

[0117] The DRT reflectometry device can be a simple vector network analyzer or an electronic board or more generally any device implemented by means of software and / or hardware elements.

[0118] The invention also has the advantage of allowing the use of existing cable infrastructure in the environment to be monitored. For example, in some buildings, temperature-sensitive cables or communication or power cables are already deployed on site and can be used alone or in conjunction with other cables to instrument the entire building using the device according to the invention.

[0119] When a temperature increase is detected in an area, the DRi reflectometry device may include a visual and / or audible alert system. It may also include a display interface to indicate the area where the temperature increase was detected.

[0120] Knowledge of a building's plan and matching this plan with reconstructed topologies also makes it possible to predict the spread of a fire and to determine which rooms are likely to be impacted by the fire by locating and monitoring the evolution of heating.

[0121] The invention makes it possible in particular to detect the appearance of heating at very early stages and to monitor its evolution up to very advanced stages leading to the rupture of a cable.

[0122] According to another embodiment of the invention, reflectometry measurements and associated topology reconstructions are performed periodically to ensure continuous monitoring of fire progression. The measurements and reconstructed topologies are advantageously stored in one or more databases to allow for retrospective replay of the cable network's degradation, thus enabling users to implement measures to enhance building safety. The databases can be integrated into the reflectometry devices and communicate with each other via wireless communication devices, or they can be located in a remote network with which the reflectometry devices communicate via radio communication.

[0123] Indeed, knowledge of the kinetics of fire spread, particularly its speed of evolution, makes it possible to improve the safety of the building or to provide information to firefighters to guide the intervention forces.

[0124] Thus, the traceability of the fire's evolution is improved, allowing for a better understanding of the phenomena that cause the overheating.

Claims

DEMANDS 1. A system for detecting and locating (300) a temperature increase in an environment consisting of several distinct zones (Z1-Z10), the system comprising a branched cable network comprising several branches (CSi-CS), each intended to be deployed in one of the zones, and at least one reflectometry device (DFL) connected to one end of at least one branch of the network and configured to: - Acquire (401) an initial reflectometry measurement corresponding to an initial state of said branched cable network, - Acquire (402) a current reflectometry measurement corresponding to a current state of said branched cable network, - Compare (403) the current reflectometry measurement to the initial reflectometry measurement to deduce (404) a temperature increase on one of the branches of said network, - When a temperature increase is detected, reconstruct (405) the cable network topology from the initial reflectometry measurement and the current reflectometry measurement, Identify (406) the branch of the cable network for which a fault corresponding to a temperature rise has been detected by evaluating a change in at least one parameter of the reconstructed topology among the length of the network branches or the impedance of the loads at the end of the network branches.

2. A system for detecting and locating a temperature increase according to claim 1, wherein at least one branch of the branched cable network is a heat-sensitive cable whose insulation melts when the temperature exceeds a given threshold so as to create a short circuit.

3. A system for detecting and locating a temperature increase according to any one of the preceding claims, wherein at least one branch of the branched cable network is a temperature-sensitive cable in which at least one characteristic parameter among permittivity or conductivity varies with temperature.

4. A system for detecting and locating a temperature increase according to any one of the preceding claims, wherein at least one device for reflectometry (DRi) is configured to detect (404) an increase in temperature in the environment when the difference between the current reflectometry measurement and the initial reflectometry measurement is greater, in absolute value, than a predefined threshold.

5. A temperature rise detection and localization system according to any one of the preceding claims, wherein at least one reflectometry device (DR^) is configured to acquire (402) several successive current reflectometry measurements, identify, in the successive measurements, the same amplitude peak whose value exceeds a first predefined threshold, calculate the rate of change of the amplitude, the time position of said peak or the shape of said peak during the successive measurements and detect (404) a temperature rise in the environment when the rate of change exceeds a second predefined threshold.

6. A temperature rise detection and localization system according to any one of claims 1 to 4, wherein at least one reflectometry device (DRi) is configured to acquire (402) several successive current reflectometry measurements and determine a rate of change of the temperature rise from the change of at least one parameter of the reconstructed topology.

7. A temperature rise detection and localization system according to any one of the preceding claims, wherein at least one reflectometry device (DR^) is configured to detect a branch break due to temperature rise from the evaluation of at least one parameter of the reconstructed topology.

8. A system for detecting and locating a temperature increase according to any one of the preceding claims, comprising several reflectometry devices (DR 1 ; DR2, DR3) respectively connected to different ends of the cable network and cooperating together to perform a distributed reflectometry test in order to detect and locate a fault corresponding to a temperature increase.

9. A system for detecting and locating a temperature increase according to claim 8, wherein the topologies respectively reconstructed from the reflectograms measured by each of the reflectometry devices are compared to resolve at least one ambiguity in locating the temperature increase in the cable network.

10. A system for detecting and locating a temperature increase according to any one of the preceding claims, wherein the branched cable network comprises a main cable (CP) one end of which is connected to the reflectometry device and a plurality of secondary cables (CS1-CS10) connected to the main cable.

11. System for detecting and locating an increase in temperature according to any one of the preceding claims wherein the deployment environment of the system is a building or a means of transport.

12. A system for detecting and locating a temperature increase according to any one of the preceding claims, further comprising at least one database configured to record at least the current reflectometry measurement and the reconstructed cable network topology.

13. A method for detecting and locating a temperature increase in an environment consisting of several distinct zones, the method comprising the steps of: Deploy a branching cable network throughout the environment so that at least one network cable is present in each area. - Connect at least one reflectometry device to one end of the network, Acquire (401) an initial reference reflectometry measurement corresponding to an initial state of said branched cable network in a healthy state, - Acquire (402) a current reflectometry measurement corresponding to a current state of said branched cable network, - Compare (403) the current reflectometry measurement to the initial reflectometry measurement to deduce (404) a temperature increase on one of the branches of said network, - When a temperature increase is detected, reconstruct (405) the cable network topology from the initial reflectometry measurement and the current reflectometry measurement, Identify (406) the branch of the cable network for which a fault corresponding to a temperature rise has been detected by evaluating a change in at least one parameter of the reconstructed topology among the length of the network branches or the impedance of the loads at the end of the network branches.

14. A method for detecting and locating a temperature increase in an environment according to claim 13, comprising: - several successive acquisition steps (402) of a reflectometry measurement, the identification, in the successive measurements, of at least one same amplitude peak whose value exceeds a first predefined threshold, - the calculation of the rate of change of the amplitude, the temporal position of said peak or the shape of said peak during successive measurements and - the detection (404) of an increase in temperature in the environment when the rate of change exceeds a second predefined threshold.

15. A method for detecting and locating a temperature increase in an environment according to claim 13, comprising: - several successive acquisition steps (402) of a reflectometry measurement, - the determination of a rate of change of the temperature increase from the evolution of at least one parameter of the reconstructed topology.

16. Use of the system according to any one of claims 1 to 12 or of the method according to any one of claims 13 to 15 to monitor the development of a fire spreading in the environment.

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