System for detecting heat generation in connectors between electrical cables

Abstract

A method for detecting hot spots in a connector (2) disposed on an electric wire, wherein a thermal impedance module (4, 4a, 4b, 4c) is disposed in the connector (2), the electric wire and the thermal impedance module have an overall thermal impedance, the method comprising the steps of determining a physical characteristic that is a function of the overall thermal impedance, and issuing an alarm for detecting and locating hot spots in the connector when the physical characteristic deviates from a predetermined reference value.

Description

[Technical Field]

[0001] The present invention relates to a method for detecting and locating heat generation in connectors forming joints between current-carrying cables, and further to a system for carrying out such a method, as well as a connector suitable for such a method. [Background technology]

[0002] The present invention relates to a device for protecting an electric network, which applies to the protection of any type of electric network, regardless of its nature, whether intended for power or data transmission.

[0003] The protection of electrical installations, whatever their nature, is fundamental for the safety of people and property. Indeed, electrical faults often lead to fires with tragic consequences. Electrical faults can also lead to electric shocks in sensitive areas or, more dramatically, to electrocution of people.

[0004] Some installations may involve very long bundles of cables (also called harnesses) used for supplying them. This is the case, for example, in the aviation sector, particularly for the Airbus A380, where the harness length may reach 500 km.

[0005] These harnesses can form complex topologies through joints, whether connectors or splices. Statistically, joints are known to constitute the weak links of wired networks, since they account for the majority of failures that occur. When large amounts of power flow, defective joints become sites of localized heating due to heat losses dissipated by the Joule effect or sparks from electric arcs.

[0006] Connectors can fail for several reasons, including imperfect pin engagement, twisted pins, broken pins, oxidation or deterioration of materials, poor surface condition, improper tightening, the presence of foreign matter, and moisture.

[0007] These anomalies can lead to three categories of failures: Obvious faults such as open or short circuits Soft failures (e.g., due to increased contact resistance, such as impedance failure) · Intermittent faults (e.g., poor connections and / or electrical arcs).

[0008] An open circuit obviously causes a fault, but is unlikely to cause an accident unless it also causes a series fault arc.

[0009] On the other hand, short circuits and impedance failures are problematic because they can cause an abnormal rise in temperature, which can lead to changes in the sheath due to melting of the plastic. According to Joule's law, the energy released is proportional to the contact resistance and to the square of the current circulating in the connector.

[0010] Electrical arcs are even more serious because the sparks they produce can be enough to start a fire on board, as has happened in the past. Electrical arcs can be either parallel arcs (the initiation of a short circuit) or series arcs (the initiation of an open circuit).

[0011] To ensure the quality of the contacts at the time of delivery of the system, they can be verified visually if there is visual access, or by continuity testing if there is mechanical access at both ends.During the life of the system, periodic inspections may be carried out during maintenance phases, which can be carried out by visual inspection or continuity testing if possible.

[0012] The present invention aims to detect and locate soft faults and intermittent electrical arc faults.

[0013] There are several techniques for checking the temperature of a connection: Optical infrared technology has the disadvantage of being bulky and requires one sensor per connection. Fiber optic technology has the drawback of requiring optical fiber to be threaded through each link and integrating the measurement system. Optical probe / thermocouple techniques have the disadvantage of being bulky and require one sensor per connection. · Acoustic technology has the disadvantage that it only applies to arcs. · Radio technology has the disadvantage that it only applies to arcs.

[0014] The object of the present invention is to overcome these drawbacks by proposing a method and a device for detecting and even locating hotspots in connectors that is small in volume and lighter in weight compared to the prior art, without the additional power supplies and communication buses required for additional sensors. Summary of the Invention

[0015] One object of the present invention is, inter alia, to remedy all or some of the above-mentioned drawbacks.

[0016] According to a first aspect of the present invention, a method for detecting hot spots in a connector capable of forming a joint between a current conducting cable of a first electric wire and a current conducting cable of a second electric wire is proposed, wherein the connector is disposed on the first electric wire, and a thermal sensitive impedance module is integrally disposed in the connector, and the electric wire and the thermal sensitive impedance module have an overall thermal sensitive impedance, and the method comprises: a. determining a physical property that is a function of said overall thermal impedance by measuring a physical quantity; b. issuing an alarm to detect and locate hot spots in the connector if the determined characteristic deviates from a predetermined reference value.

[0017] Therefore, a method is proposed for detecting hot spots in conductors that is small in volume and light in weight compared to the prior art, without the additional power supplies and communication buses required for additional sensors.

[0018] Preferably, the method further comprises the step of estimating a temperature at the thermal impedance module determined from said determined characteristic.

[0019] The determined characteristics can be obtained, for example, by means of reflectometry. Reflectometry can use, for example, signals whose autocorrelation function is a Dirac pulse. Reflectometry can be, for example, of the multicarrier type in the time domain (MCTDR, Multi-Carrier Time Domain Reflectometry) or the multitone orthogonal type in the time domain (OMTDR, Orthogonal Multi-tone Time Domain Reflectometry). Reflectometry of the SSTDR type (Spread Spectrum Time Domain Reflectometry) can also be performed. Reflectometry can also make it possible to locate detected hotspots.

[0020] According to a second aspect of the present invention, a system is proposed for detecting and locating hot spots in an electrical connection capable of forming a joint between a current conducting cable of a first electrical wire and a current conducting cable of a second electrical wire, the system comprising a connector arranged on the first electrical wire and carrying out the method according to the first aspect of the invention or one or more of its improvements, the system comprising: a thermal impedance module integrated into a connector comprising the electric wire at the connection part; a detection and location device including a reflectance measurement module configured to determine a physical property that is a function of the overall thermal impedance by measuring a reflection coefficient at a location remote from the connection, and a module for processing data from the reflectance measurement device to generate an alarm for detecting and locating hot spots in the connector when the determined physical property deviates from a predetermined reference value.

[0021] The detection and location device comprises at least: a unit for coupling to the power grid; an injection unit configured to generate a high frequency electrical signal, said signal being injected into said network via coupling means; an acquisition unit capable of receiving a return signal from the injected signal via the coupling means and digitizing the received signal; a data control and processing unit connected to at least the acquisition unit and adapted to analyze the digitized data provided by the acquisition unit; A communication unit connected to the control and processing unit and capable of issuing an alarm to detect and locate hotspots.

[0022] According to a third aspect of the present invention, a connector is proposed that is capable of forming a joint between a current conducting cable of a first electric wire and a current conducting cable of a second electric wire, the connector being arranged on the first electric wire and integrating a thermal impedance module, the connector being adapted to carry out the method according to the first aspect of the present invention or one or more of its improvements.

[0023] In a first embodiment, the connector incorporates a thermally conductive module of heat-sensitive resistive material disposed to at least partially surround the electrical wire when the electrical wire is electrically connected to the connector.

[0024] In a second embodiment, optionally compatible with the first embodiment, the connector incorporates a thermal resistance module with a dipole including a thermistor, said dipole intended to be attached to an electrical wire.

[0025] In a third embodiment, optionally compatible with the first and / or second embodiment, the connector incorporates a heat-sensitive capacitance module having a heat-sensitive stiffness.

[0026] According to a fourth aspect of the invention, a method for instrumenting an electric power network is proposed, characterized in that the method comprises connecting to said electric network a connector forming a junction between a current conducting cable of a first electric wire and a current conducting cable of a second electric wire of said electric network, the connector being according to the third aspect of the invention or one or more of its improvements. [Brief explanation of the drawings]

[0027] Other advantages and special features of the invention will become apparent from reading the detailed description of implementations and embodiments, which is by no means exhaustive, with reference to the attached drawings. [Figure 1] 1 shows a schematic block diagram of an embodiment of an apparatus according to the invention; [Figure 2] FIG. 2 is a schematic diagram illustrating one embodiment of a heat-sensitive conductive module of the device shown in FIG. 1. [Figure 3] 2 is a schematic diagram of another embodiment of the heat sensitive resistance module of the device shown in FIG. 1; [Figure 4] 2 is a schematic diagram of another embodiment of the heat-sensitive capacitance module of the device shown in FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0028] The embodiments described below are in no way limiting, and in particular it is possible to consider a variant of the invention that includes only a selection of the described features and then separate them from the other features described, provided that this selection of features provides a technical advantage or is sufficient to distinguish the invention from the prior art. This selection includes at least one feature, preferably functional, and does not include structural details, or only some of the structural details, if only some of the structural details provide a technical advantage or are sufficient to distinguish the invention from the prior art.

[0029] In the figures, elements that appear in several figures are labeled with the same reference numerals.

[0030] Next, with reference to FIG. 1, the fault detection module 1 will be described, as well as the method implemented in this system.

[0031] The fault detection module 1 is provided for detecting and locating faults in one or more connectors 2 arranged at the junction of an electrical wire 3 and another electrical wire (not shown).

[0032] The device for detecting and locating hot spots according to the invention comprises a heat-sensitive conductive module 4 arranged on the connector 2 and acting as a target, and a data processing module 1 remote from the connector 2 .

[0033] The fault detection module 1 is configured to perform impedance measurements on the electrical line and generate an alarm to detect and locate hot spots in the connector if the measurements deviate from a reference value (if an impedance mismatch becomes detectable on the line).

[0034] According to one possibility, the fault detection module 1 operates according to the reflectometry principle, which is similar to that of radar. A generally high-frequency or broadband electrical signal is injected into one or more locations in the cable network where a fault is likely to be detected. The signal propagates along the network and, if it encounters an electrical discontinuity, i.e., a change in impedance, loses some of its energy. In the simplest case, the signal propagates along a two-wire power line, which requires at least two conductors for signal propagation. The present invention also applies to all other types of cables containing one or more wires, particularly triaxial cables, coaxial cables, or cables referenced to a ground plane. Electrical discontinuities can occur due to faults. By analyzing the signal returned to the injection point, it is possible to deduce information therefrom about the presence, nature, and location of these discontinuities and, consequently, about the presence, nature, and location of possible faults.

[0035] The fault detection module 1 used in the device according to the invention comprises blocks that make it possible to implement this principle of detection and localization by reflectometry. It therefore comprises an injection unit 11 and a coupling unit 12. The injection unit in particular comprises a generator that supplies a voltage forming the injection signal, also called the probe signal. The generator is for example programmable.

[0036] The injection unit 11 generates an injection signal which is injected into a point on the network 3 via the coupling means 12. For this purpose, the coupling means 12 is coupled to a point P on the network, which is the input point for the injection signal. The wires to which the system is coupled are two-wire, with one connection made at a first point on the conductor and the other connection made at a second point on the other conductor opposite the first point. In multi-conductor applications with a ground plane, the coupling can be realized by connecting one point on the conductor and the other connection on the ground plane.

[0037] The coupling means 12 have in particular the function of injecting a probe signal between two conductors of the line to be monitored and of receiving a probe signal between two conductors of the line to be monitored.

[0038] The coupling means 12 may also have the function of protecting the detection system from the native signals of the line, protecting the system from attacks related to the environment (such as lightning strikes), and directing the probe signal towards the line to be monitored, where the line to be monitored is part of a network formed by several lines and where directional coupling is involved.

[0039] The fault detection module 1 also includes an acquisition unit 13 that can receive signals returned by discontinuities encountered in the emitted injection signal. These returned signals are transmitted to the acquisition unit via the combination unit 12. The acquisition unit 13 includes, for example, one or more matched filters, one or more low-noise amplifiers, and one or more analog-to-digital converters.

[0040] The fault detection module 1 also includes a control unit and data processing unit 14, which is connected to the injection unit 11 and to the acquisition unit 13. In particular, it makes it possible to control the programmable generator of the injection block. It receives the digitized received signals provided by the acquisition unit 13. In particular, it carries out processing of these digital data to ascertain the presence and location of faults.

[0041] The fault detection module 1 further comprises a communication unit 15, which allows communication with other systems, for example a monitoring system. In particular, the communication means enable the control and data processing unit 14 to control the monitoring system if a fault is detected. The communication means may be of wireless type. A secondary cable may also be used as a communication line. The communication unit 15 may also receive information from other members, which allows the data control and processing unit 14 to take external factors into account in its decision-making. This can be used advantageously when a component on the protected line, for example a switch, changes state. The processing block then recognizes that this is a normal event in the system operation and not a fault.

[0042] The fault detection module 1 injects a signal into the network, the frequency spectrum of which complies with the frequency template specifically related to EMC requirements, without interfering with either useful signals present on the line or the network cable environment. The repetition period of the injected signal must be short enough to allow the fault detection module to detect the first faults that could potentially destroy the installation, and therefore may be less than 500 μs or even shorter. For this purpose, the injected signal can be advantageously generated, for example, using a multicarrier reflectometry method of the MCTDR type or another method with the same frequency characteristics. Due to the bandwidth constraints of the network lines 3, the signal uses a frequency between 100 kHz and 200 MHz, an amplitude of less than 1 volt, and a period of the order of 100 μs.

[0043] In a previous step, the parameterization of the fault detection module 1 is carried out by determining the detection threshold, which corresponds to a predetermined minimum variation (taken as absolute value) of the reflection coefficient. The reflection coefficient is a measurement obtained from a reflectometry experiment, which is the ratio of the reflected voltage along the line to the incident voltage. It is therefore a unitless quantity ranging from -1 (short circuit) to +1 (open circuit).

[0044] Any change in resistance, conductivity or capacitance will ultimately result in a change in the reflection coefficient, and in the examples below, the impedance-dependent physical property of the overall thermal impedance is the reflection coefficient obtained by reflectance measurements.

[0045] Advantageously, reflectance measurements allow obtaining the reflection coefficient as a function of the distance to the injection point. The impedance is not only a function of the distance to the injection point, but can also be optionally estimated by calculation.

[0046] The threshold that is set is therefore based solely on this reflection coefficient and is unitless. It can usually be set to + / - 10% (hence the threshold is 0.1 in absolute value). If the absolute value of the reflected signal resulting from encountering a discontinuity in the network is greater than this threshold, a fault is detected. This threshold may be variable.

[0047] Next, several embodiments of the heat-sensitive conductive module 4 will be described.

[0048] Heat-sensitive conductive material module 2, it is proposed to integrate a heat-sensitive conductive module 4a into a connector 2a having a connector base 2a1. The principle is to partially embed pins 5a suitable for cooperating with each line (not shown) or wire to be monitored in the heat-sensitive conductive material forming the module 4a.

[0049] Generally, it is possible to use eutectic salt type materials. At room temperature, these salts are solid and insulating. At elevated temperatures, these salts are liquid and conducting.

[0050] The connector is not limited to a pair of pins, but may be other connectors that cover the entire surface of the connector 2a.

[0051] This material is determined so that its insulating properties change with temperature, in particular its resistance ρ is a function of temperature, and therefore the conductivity between the pins 5a is a temperature-dependent function.

[0052]

number

[0053] At normal room temperature, T = T0, and therefore g = G0. By choosing G0 small enough (in any case G0 << 1 / Z c and Z c is a characteristic of the line), abnormal temperature rise disappears and the device operates transparently (as if it were not there).

[0054] As soon as the temperature increases, the conductivity increases and the impedance mismatch becomes detectable, but not enough to alter the behavior of the monitored system (e.g., in terms of conducted power).

[0055] This implementation of the invention clearly leads to the desired objective that if the temperature rises, a strong marker (impedance mismatch) allows for the fast detection and localization of the fault, but without worsening the impact on basic functionality. Furthermore, the mismatch allows for an estimation of the conductivity, and therefore an estimate of the temperature, to be deduced.

[0056] Electronic Module Referring to the left part of FIG. 3, it is proposed to integrate a heat sensitive resistance module 4b into a connector 2b having a connector base 2b1.

[0057] Referring to the right side of Figure 3, module 4b includes a thermistor 4b1 in series with a capacitor 4b2 and two electrodes connected at each junction to the power grid line. Typically, the thermistor has a value of 10 kilohms at room temperature and 1 ohm at high temperatures. Typically, the capacitor has a value of 100 nF.

[0058] A thermistor (e.g., with a negative temperature coefficient) is an electronic component whose resistance depends on temperature according to the following approximate law:

[0059]

number

[0060] At normal room temperature, T = T0, and therefore R = R0. By choosing R0 large enough (in any case, R0 >> Z c and Z C is a characteristic of the line), abnormal temperature rise disappears and the device operates transparently (as if it were not there).

[0061] As soon as the temperature rises, the resistance decreases and a capacitance C is placed in parallel with the line. The value of C is chosen so that the capacitor is perceived as a short circuit by high-frequency signals (how this is done is known to those skilled in the art), but is transparent to low frequencies.

[0062] Negative temperature coefficient thermistors can be used over a wide temperature range from -200 to +1000°C and are available in a variety of versions, including glass beads, discs, bars, pellets, washers, or chips. Nominal resistances range from a few ohms to 100 kilohms.

[0063] This implementation of the invention clearly leads to the desired goal that as the temperature rises, a strong marker (a drop in impedance) allows for the fault to be detected and located quickly, but without worsening the impact on basic functionality. Estimating the resistance also allows for an estimation of the temperature.

[0064] Mechanical Module Referring to the left part of FIG. 4, it is proposed to integrate a heat-sensitive capacitance module 4c into a connector 2c having a connector base 4c1.

[0065] In this implementation, the idea is to use a bottom part of the connector 4c1 that is not completely rigid but is sufficiently deformable so that expansion under the influence of temperature rise will cause local movement of each track being monitored, as shown by the two circles 4c1 and 4c2 indicating movement in the left part of Figure 4. A person skilled in the art will know how to select such a material.

[0066] Of course, the connection is not limited to a pair of conductors, and other connectors may exist within the same connector.

[0067] Although the connector is shown as a single block, it may actually be made of different materials.

[0068] The higher the temperature, the greater the movement and the greater the change in capacitance. It may be advantageous to favor a direction of movement that tends to increase the spacing, thereby decreasing the capacitance.

[0069] A change in the spacing e=f(T) results in a dependence of the capacitance as a function of temperature.

[0070]

number

[0071] At normal room temperature, T = T0, and therefore C = C0. By choosing C0 close to the linear capacitance of the line (to minimize impedance mismatch in the connector in either case), abnormal temperature rise will disappear and the device will operate transparently (as if it were not there).

[0072] As soon as the temperature rises, the capacitance changes (decreasing as the lines move apart), and the impedance mismatch becomes detectable, but not enough to change the behavior of the monitored system (e.g., in terms of conducted power).

[0073] To a first approximation, capacitance changes at the same rate as mechanical movement. A typical movement of 10% of the nominal spacing will result in a 10% decrease in capacitance. A 10% decrease in capacitance will again result in an arbitrary unit (percentage) change in the reflection coefficient.

[0074] In this embodiment, the detection threshold can be set typically to ±5% (thus the threshold is 0.05 in absolute value). If the absolute value of the reflected signal resulting from encountering a discontinuity in the network is greater than this threshold, a fault is detected. This threshold may be variable.

[0075] This implementation of the invention clearly leads to the desired objective that if the temperature rises, a strong marker (impedance mismatch) allows for fast detection and localization of the fault, but without worsening the impact on basic functionality. Furthermore, the mismatch allows for an estimation of the capacitance, and therefore of the temperature, from which it is possible to deduce.

[0076] Several embodiments of the device according to the invention are possible.

[0077] It is also possible to separate the coupling means 12 from the other components of the detection system 1. This embodiment is particularly suitable for protecting high-voltage lines. The coupling means is therefore placed as close to the line as possible while being separated from the rest of the detection system. The connection between the coupling means and the detection system is made via a uniform, controlled impedance connection, for example a twisted pair of wires or a 50 ohm coaxial cable. In another embodiment, the coupling may be wireless.

[0078] Advantageously, the coupling can be directional, as indicated above. In this case, the device detects faults in only one direction, and this direction is predetermined. This coupling mode is particularly suitable when multiple lines to be protected are connected to a busbar and the power current circulates from the busbar through the lines to the load. Because the busbar has a low impedance relative to the lines, the probe signal naturally travels toward the busbar. Directional coupling allows the probe signal to be directed downstream, i.e., toward the load. Directional coupling can be implemented in several ways. For example, upstream self-inductance can be inserted while adjusting the frequency of the probe signal to increase the upstream impedance. Advantageously, the device according to the present invention makes it possible to detect and quickly respond to, or even predict, several types of faults. Measurements from the reflectometer, in particular changes in impedance or propagation velocity, can be used to establish connector diagnostics. The control and processing unit can therefore be programmed to establish such diagnostics, for example, based on predefined signatures characteristic of connector parameters, thresholds, events, or connector states.

[0079] The invention can also be applied to protect connectors from telecommunications or power networks in which carrier currents circulate. Advantageously, the reflectometry method does not interfere with data transfer within the network, provided that an appropriate frequency band or other method is selected for the probe signal emitted within the network to distinguish the signals.

[0080] Also advantageously, the device according to the invention can operate when the network is unpowered, unlike conventional current and voltage analysis solutions that require the network to be powered, which makes it possible to monitor the network especially before it is powered on.

[0081] Advantageously, reflectometry detection systems can provide information regarding the location of electrical faults, which information can be utilized by maintenance services.

[0082] Advantageously, the device according to the invention can be parameterized to protect one or more track areas, and thus one or more connectors on the track. The detection parameters can also be set depending on the type of load or track area, in particular the sensitivity of the detection. As an example, to protect connectors at a certain distance from the device (for example 10 meters), detection is performed in an area between 9.5 meters and 10.5 meters. In this case, the processing means only processes the changes in impedance detected at connectors in the area to be protected.

[0083] In an alternative embodiment of the device according to the invention, the communication unit 15, the data control and processing unit 14, the injection unit 11 and the acquisition unit 13 can be shared, i.e. shared between several lines (and thus connectors), by inserting one or more multiplexers between the injection unit 11, the acquisition unit 13 and a coupling unit 12 specific to each line. In other words, a coupling unit 12 is assigned to each line and connector, and the connection between the coupling unit and the injection and acquisition units is ensured by one or more multiplexers.

[0084] Of course, the invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. Furthermore, different features, forms, variations and embodiments of the invention can be associated with one another in various combinations, unless they are mutually incompatible or exclusive.

[0085] Other physical characteristics of the impedance of the overall thermal impedance can be used.

[0086] This may be, for example, a conductivity measurement, for example, in connection with the implementation of the fault detection module described with reference to FIG.

[0087] This may be, for example, a resistance measurement, for example, in connection with the implementation of the fault detection module described with reference to FIG.

[0088] This may be, for example, a capacitance measurement, for example, in connection with the implementation of the fault detection module described with reference to FIG.

[0089] To perform such measurements, those skilled in the art have several well-known devices, such as RLC meters, which will not be described further.

[0090] It is therefore possible to instrument an electrical network including the connector without adding additional electrical circuitry.

[0091] In the situation of an existing electrical network, the connectors of the electrical network or only parts thereof are replaced by the connector according to the invention, ie the connector integrating the thermal impedance module.

[0092] In the context of the installation of an electrical network, it is possible to instrument the electrical network by placing such connectors at the time of installation.

[0093] Furthermore, analysis of spatiotemporal changes in physical properties not only detects hot spots in connectors, but also monitors electrical networks by detecting short circuits, closed circuits, or soft faults on electrical cables, such as clamped, damaged cables, or shunts.

[0094] In particular, the present invention can be extended to any application where hotspot detection and location is required, for example, in industrial environments such as monitoring pressurized tanks and steam ducts in nuclear power plants.

Claims

1. 1. A system for detecting and locating hot spots in an electrical connection that can form a joint between a current-conducting cable of a first electrical wire and a current-conducting cable of a second electrical wire, the joint being disposed on the first electrical wire; The system comprises: a thermal impedance module (4, 4a, 4b, 4c) integrated into a connector with the electric wire at the connection, the electric wire and the thermal impedance module having an overall thermal impedance; a detection and location device at a location remote from the connection, comprising: a reflectance measurement module configured to determine a physical property that is a function of the overall thermal impedance by measuring a reflection coefficient; a module for processing data coming from said reflectance measurement module in order to generate an alarm for detecting and locating hot spots in said connector if the determined physical property deviates from a predetermined reference value; a detection and location device including: Including, The detection and location device comprises at least: a. a coupling unit (12) for coupling to a power grid; b. an injection unit (11) configured to generate a high frequency electrical signal, said signal being injected into said first network of electrical wires via said coupling unit (12); c) an acquisition unit (13) capable of receiving a return signal from the signal injected via the coupling unit (12) and digitizing the received signal to acquire digitized data; d. a data control and processing unit (14) connected to at least said acquisition unit (13) and adapted to analyze the digitized data provided by said acquisition unit; e) a communication unit (15) connected to said data control and processing unit (14) and capable of issuing an alarm regarding the detection and location of hot spots.

2. The system described in claim 1, wherein the system estimates a temperature in the thermal impedance module (4) determined from the determined physical properties.

3. 3. The system of claim 1, wherein the determined physical property is a reflection coefficient obtained by reflectometry.

4. The system of claim 3 , wherein the reflectivity measurement uses a signal whose autocorrelation function is a Dirac pulse.

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