Method and device for temperature evaluation and associated calibration method

Abstract

The invention relates to a method and device for evaluating the temperature of a medium in which an electronic device (14) is placed. The evaluation method implements the following steps: a) measuring a first internal temperature inside the electronic device, then b) after a given period of time, measuring a second internal temperature inside the electronic device, then c) estimating the temperature outside the electronic device, based on an estimate of a stabilized temperature inside the electronic device, according to the values ​​measured in steps a) and b). A calibration method is also proposed. Figure 2

Description

Title of the invention: Method and device for evaluating temperature and associated calibration method

[0001] Technical field to which the invention relates

[0002] The present invention relates to the technical field of thermometry. The present invention relates more particularly to a method and a device for evaluating the temperature of a medium, in which an electronic device is placed. The present invention also relates to a method for calibrating a temperature evaluation device, when it is present in an electronic device. Technological background

[0003] For certain electronic devices, knowledge of the temperature of the environment in which they are present is essential to enable them to function properly.

[0004] This is particularly the case for infrared sensors, evaluating the temperature on the surface of an object located at a distance, from the analysis of the infrared radiation of said object. To carry out qualitative measurements, it is necessary to first estimate the temperature of the environment in which the aforementioned object is located.

[0005] This is why this type of device requires the use of a separate device, namely a thermometer, to precisely measure the temperature of the environment in which the infrared sensor is located.

[0006] The need for a thermometer, separate from the infrared sensor, has the disadvantage of having to use and manipulate several devices to carry out a qualitative measurement.

[0007] According to another disadvantage, the temperature measurements taken by a thermometer must be transmitted to the infrared sensor manually or via a communication protocol that is complex and expensive to implement.

[0008] According to another disadvantage, the presence of a thermometer near the infrared sensor may not be possible, for example when said sensor is integrated into a trim part of a passenger compartment of a motor vehicle.

[0009] Object of the invention

[0010] The invention is remarkable in that the evaluation method implements the following steps:

[0011] a) measurement, inside the electronic device, of a first internal temperature, then

[0012] b) after a given period of time, measurement, inside the electronic device, of a second internal temperature, then

[0013] c) estimation of the temperature outside the electronic device, from an estimation of a stabilized temperature, inside the electronic device, as a function of the values ​​measured during steps a) and b).

[0014] By "stabilized temperature" is meant a temperature whose value does not vary significantly over a period of time equal to or greater than 30 minutes. For example, a temperature variation of less than 0.1°C is not considered to constitute a significant variation.

[0015] Advantageously, the evaluation method described above makes it possible to evaluate the temperature outside an electronic device, from measurements carried out inside the electronic device.

[0016] Therefore, when the electronic device requires knowledge of the temperature of the environment in which it is located, the method according to the invention can be carried out using an evaluation device as described below, integrated into the electronic device, in order to simplify the use of said electronic device.

[0017] Indeed, the invention allows the use of a single electronic device to perform functions that until now required two separate electronic devices, namely, the electronic device and a thermometer located outside said device. The invention thus allows easier integration of an electronic device requiring knowledge of the temperature of the environment in which it is located, because, thanks to the method described above, the thermometer can be integrated into the electronic device. This is particularly advantageous when the electronic device must be integrated into a confined environment, such as an element of a passenger compartment of a motor vehicle such as a dashboard.

[0018] According to another advantage, the invention makes it possible to avoid manual transfer of temperature measurements, carried out by a thermometer present outside the electronic device, because the invention makes it possible to estimate the temperature outside said device, from temperature measurements carried out from inside the electronic device. The invention therefore allows simpler and faster operation of an electronic device, requiring knowledge of the temperature of the environment in which it is located.

[0019] Preferably, during step b) described above, the predetermined time period is between 1 second and 120 seconds, preferably between 2 seconds and 60 seconds.

[0020] According to one possible embodiment, the estimation of the stabilized temperature is obtained from a calibration value, reflecting the thermal inertia of the interior of the electronic device. By "interior of the electronic device" is meant all components present in the space delimited by the electronic device.

[0021] The estimate of the stabilized temperature is for example obtained from the sum of the following terms:

[0022] - the value of the first internal temperature, and

[0023] - a product between the calibration value and the internal temperature variation of the electronic device, for the period of time (mentioned in step b)).

[0024] This sum, which takes into account the calibration value (corresponding to a time constant, calibrated as explained below), makes it possible to evaluate in a few seconds (without waiting for the physical stabilization of the system) at what temperature the interior of the electronic device will stabilize a few minutes (or even a few tens of minutes) later (if the current operating regime is maintained).

[0025] This thus advantageously makes it possible to estimate almost instantaneously the temperature outside an electronic device, from temperature measurements taken inside said device, even when the temperature of the electronic device is not stabilized. This is particularly the case when an electronic device is switched on, the heat that it generates increases its internal temperature until it reaches a stable or substantially stable value.

[0026] In other words, the evaluation method described here allows an estimation of the temperature outside the electronic device, before its temperature stabilizes. This advantageously makes it possible to estimate very quickly after switching on the electronic device, the temperature of the environment in which it is located. However, when this information is necessary for the proper functioning of the electronic device, the invention allows faster and more precise operation of the latter after it has been switched on.

[0027] According to one possible embodiment, the temperature outside the electronic device is estimated by subtracting, from the estimate of the stabilized temperature, a heat dissipation value, reflecting a dissipation phenomenon in the medium, of the heat generated by the electronic device.

[0028] According to a first possibility, this heat dissipation value can be constant (for example determined beforehand by tests on the electronic device concerned).

[0029] In other words, when the electronic device is characterized by a dissipative power that is invariable over time, the heat dissipation value is equal to a constant hereinafter referred to as the heat dissipation constant.

[0030] The heat dissipation constant may correspond to a temperature difference between the interior of the electronic device, after stabilization of said temperature, and the exterior of the electronic device, when said electronic device is operating at a reference activity level.

[0031] According to a second possibility, when the electronic device is characterized by a dissipative power changing over time, an activity level of the electronic device is measured during step a) or during step b), and the heat dissipation value is obtained from the sum of the following terms:

[0032] - a reference heat dissipation constant (corresponding here to a temperature difference between the inside of the electronic device, after stabilization of said temperature, and the outside of the electronic device, when said electronic device is operating at a reference activity level); and

[0033] - a product between a coefficient of variation of heat dissipation and a difference in activity between the measured activity level and the reference activity level.

[0034] By “activity level” is meant an operating regime of the electronic device.

[0035] Preferably, the activity level of the electronic device is measured from the electrical voltage and / or the electrical current, supplying the electronic device and / or a load of a component of the electronic device. The quantity representative of the activity level can be chosen according to the system concerned so that there is a sufficient linear relationship between this quantity and the thermal power dissipated by the electronic device, preferably throughout the range of variation of this quantity as expected in the normal use of the electronic device. For example, in an electronic device comprising a circuit for regulating the supply current, the current consumed is essentially constant, and there is therefore a linear relationship between the supply voltage and the dissipated power (equal to the product of the supply voltage by the supply current).

[0036] This embodiment allows a more precise estimation of the temperature outside the electronic device, when the activity level of said device varies.

[0037] Of course, the various characteristics, variants and embodiments mentioned above can be associated with each other, in various combinations, to the extent that they are not incompatible or exclusive of each other.

[0038] The invention also relates to a device for evaluating the temperature of an environment in which an electronic device is placed, the evaluation device comprising a storage unit and a temperature probe intended to be housed in the electronic device, the storage unit and the temperature probe being connected to a calculation unit.

[0039] The device is remarkable in that the storage unit comprises instructions capable of being implemented by the calculation unit, in order to carry out a method for evaluating the temperature of an environment in which said electronic device is placed, as described above.

[0040] According to another embodiment, the evaluation device comprises an activity probe making it possible to measure an activity level of the electronic device, and the activity probe is connected to the calculation unit, and the storage unit comprises instructions capable of being implemented by the calculation unit, in order to carry out a method for evaluating the temperature of an environment in which said electronic device is placed, as described above.

[0041] Preferably, the activity probe comprises at least one electrical voltage probe and / or one electrical current probe and / or means for measuring the internal activity of a logic component of the electronic device.

[0042] According to a non-limiting exemplary embodiment, the electronic device may be a thermal camera, located for example in an industrial premises whose temperature is neither stabilized nor known and / or measuring the temperature of production parts of known emissivity, and having to automatically compensate for the radiative temperature component reflected by the parts (likely to distort the measurement) by taking into account the ambient temperature of the premises. Without the present invention, such a camera may have an erroneous measurement for several minutes - or even tens of minutes - after its switching on, due to the error in estimating the ambient temperature. This requires its operator, for example, to switch on sufficiently long before starting the measurements, or to manually configure the ambient temperature in the camera before each series of measurements as well as at each change in ambient temperature.Thanks to the present invention, such a thermal camera will be able to provide precise measurements immediately after a cold start, and according to fluctuations in ambient temperature, or in power dissipated by its internal electronics.

[0043] The invention also relates to a method for calibrating an evaluation device as described above, this calibration method comprising the following steps:

[0044] a) operating the electronic device at a first level of activity called reference, preferably at a nominal operating regime, in an environment where the temperature is stable and known, for a sufficient period of time so that the internal temperature of the electronic device is stable; then

[0045] b) measurement by means of the temperature probe of the internal temperature (thus stabilized) of the electronic device; then

[0046] c) for each of at least two activity levels of the electronic device, measurement by means of the temperature probe, of several internal temperatures and of an internal stabilization temperature then

[0047] d) estimation of a calibration value, reflecting the thermal inertia of the interior of the electronic device, from the internal temperature values ​​measured by the temperature probe during step c); then

[0048] e) estimation of the coefficient of variation of heat dissipation as a function of the internal temperature measured in step b), of the stabilization temperatures measured in step c) and of said at least two activity levels of the electronic device.

[0049] Indeed, as explained below, if we denote Vr as the reference activity level (corresponding for example to a reference voltage), VI and V2 as the two respective activity levels mentioned above (here voltages), Tr as the internal temperature measured in step b), Tl as the stabilization temperature measured in step c) for activity level VI and T2 as the stabilization temperature measured in step c) for activity level V2, we can use the following dissipation variation coefficient:

[0050] C = [(T2-Tr)-(T1-Tr)] / (V2-Vl) = (T2-T1) / (V2-V1).

[0051] Detailed description of an exemplary embodiment

[0052] The invention will be better understood, thanks to the following description, which relates to preferred embodiments, given as non-limiting examples, and explained with reference to the appended schematic drawings, in which:

[0053] [Fig.l] illustrates a schematic view of a non-limiting embodiment of a temperature evaluation device according to the invention;

[0054] [Fig.2] illustrates a schematic view of a non-limiting embodiment of a electronic apparatus comprising a temperature evaluation device shown in [Fig.l]; and

[0055] [Fig.3] illustrates a calibration curve of an electronic device represented by the [Fig.2],

[0056] As a reminder, the invention proposes a device for evaluating the temperature of an environment in which an electronic device is placed, without resorting to the use of a thermal probe located outside the electronic device.

[0057] [Fig.l] shows a non-limiting embodiment diagram of a device 2 for evaluating the temperature of this medium. This evaluation device 2 comprises a probe for measuring an activity level or activity probe (here an electrical voltage measuring probe 4) and a temperature probe 6, both connected to a calculation unit 8. The calculation unit is also connected to a storage unit 10.

[0058] The term "connected" means the possibility for two elements to exchange information, reciprocally or non-reciprocally. The elements described above are for example connected via tracks and / or wires 12 made from an electrically conductive material.

[0059] The storage unit 10 is for example a rewritable non-volatile memory (for example of the EEPROM type for "Electrically Erasable and Programmable Read Only Memory"). The storage unit comprises instructions capable of being implemented by the calculation unit, in order to carry out a method for evaluating the temperature temperature of a medium, as described below, or a calibration method as described below.

[0060] Preferably, the temperature probe 6 is capable of carrying out temperature measurements in a range comprising the entire ambient temperature domain in which the electronic device is intended to operate, here with an accuracy of the order of 0.1°C. The invention could, however, operate (possibly less precisely) if only part of the operating domain were covered by the measuring range.

[0061] According to the present example, the temperature probe comprises a thermistor. The temperature probe 6 is here a thermistor with a negative temperature coefficient marketed under the reference Murata NCU15WB473F60RC (accuracy + / -0.5%).

[0062] According to an alternative embodiment, the temperature probe 6 can be a thermal diode or a bipolar transistor (for example marketed under the reference MMBT3904), used as a diode, in association with electronic regulation and acquisition circuits. A thermal diode advantageously makes it possible to reconcile very low cost, high linearity over a wide temperature range, with known and inexpensive electronic polarization and amplification stages, and correct precision after adequate calibration. In addition, such a solution can be easily included in the matrix (or "die" of an integrated circuit), which makes it a solution with almost no additional cost in this type of technology.

[0063] Preferably, the electrical voltage measuring probe 4 is produced by means of a voltage divider bridge providing a voltage representative of the supply voltage, this representation voltage being able for example to be applied to the input of an analog-digital converter equipping the electronic device, possibly with the interposition of a low-pass filter.

[0064] [Fig. 2] now illustrates a non-limiting example of integration of an evaluation device 2 as described above, in an electronic device 14.

[0065] The electronic device 14 consists of a printed circuit board 16, serving as a support for a power supply connector 18 or an electrical voltage regulator. The electronic device 14 comprises various electronic components 20, held on the printed circuit board 16. The electronic components 20 are connected together so as to allow their power supply by the power supply connector 18, so that the electronic device 14 can perform different tasks.

[0066] The electronic device 14 also comprises a heat dissipation element, for example a finned heat sink 22, held against a first large face 24A of the printed circuit board 16. Several fins 26 of the heat sink are flush with, preferably protrude from, the outer surface of a protective housing 28 surrounding the various elements mentioned above of the electronic device. The finned radiator 22 is positioned on the printed circuit board 16 so as to evacuate from the protective housing 28 all or almost all of the heat produced by the electronic components 20, when the power supply connector 18 is connected to a power supply source.

[0067] By way of non-limiting examples, the electronic device 14 may be:

[0068] - an infrared measurement sensor;

[0069] - an industrial electrical switching module with intelligent strategies of power limitation according to ambient temperature (temperature of the environment in which this electronic device is placed);

[0070] - any electronic device implementing management strategies dependent on the internal temperature and ambient temperature (temperature of the environment in which this electronic device is placed).

[0071] As mentioned above, the electronic apparatus 14 comprises an evaluation device 2 such as that presented above with reference to [Fig.l]. More precisely, the electrical voltage measuring probe 4 of the evaluation device 2 is connected to the electrical power supply connector 18, so as to allow the calculation unit 8 to measure in real time the electrical voltage value V flowing through said connector.

[0072] The temperature probe 6 is positioned against a large face of the printed circuit board 16, as close as possible to the electronic components which dissipate the greatest quantity of heat. According to the present example, the temperature probe is held against a second large face 24B of the printed circuit board, so as to be as close as possible, preferably opposite, the finned radiator 22, held against the first large face 24A of said board. The calculation unit 8 and the storage unit 10 are also present in the protective housing 28.

[0073] Optionally, it may be considered that the calculation unit 8 and the storage unit are part of the electronic components 20 mentioned above, when said units are present in the electronic device 14.

[0074] The invention also relates to a method for calibrating an electronic device 14 as described above and illustrated by [Fig. 2], implementing a first step consisting of placing the electronic device 14 in an environment 30, the temperature of which is controlled. During this first calibration step, the electronic device 14 is at rest. By the term "at rest", it is meant that the electronic device 14 is not connected to any electrical power source.

[0075] The electronic device 14 is for example placed here in a room whose ambient temperature is 25°C, for a sufficient time for the TiO temperature, inside the protective casing 28 of the electronic device, recorded by the temperature probe 6, is identical to the ambient temperature in the room 30. This period of time may be equal to or greater than 60 minutes, preferably equal to or greater than 120 minutes. The value of the ambient temperature, hereinafter called the outside temperature Te at the electronic device, is then recorded.

[0076] By way of non-limiting example, the electronic device 14 may be integrated into a trim of a passenger compartment of a motor vehicle, not shown in [Fig. 2] in order to facilitate understanding of the invention. In this case, it is preferable to carry out the present calibration test when the electronic device 14 is present in the trim. The trim may be an element of a dashboard, a part of a roof lining, a ceiling light, etc.

[0077] According to a second step, the electronic device 14 is electrically powered, at a reference voltage Vr which corresponds for example to a nominal or usual operating mode of said device. In the present case, the reference voltage Vr of the electronic device is 12 Volts.

[0078] According to a third step, the internal temperature Ti inside the protective casing 28 of the electronic device 14 is recorded at regular time intervals, by known means, until the internal temperature Ti reaches a stabilized temperature Ts. The temperatures thus recorded are used in order to be able to produce a calibration curve 32A as represented in part A of the graph visible in [Fig. 3]. On this graph visible in [Fig. 3], the abscissas correspond to the time (t) and the ordinates to the temperature (T).

[0079] According to the present example, the value of the time interval dt between two consecutive measurements is between 1 second and 5 seconds. For example, the temperature is considered to be stabilized when it does not vary more than 0.1°C during at least 5 consecutive measurements.

[0080] According to a fourth step, the difference cpr is determined between the stabilized temperature Ts inside the electronic device 14 (here 42°C), measured by the temperature probe 6, and the temperature outside Te of the electronic device (here 25°C). The difference thus determined is here 17°C.

[0081] According to a fifth step, the difference thus determined is saved in a database (hereinafter referred to as the calibration database) as a reference heat dissipation constant cpr (and thus corresponds to the temperature difference between the inside of the electronic device, after stabilization of said temperature, and the outside of the electronic device, when the electronic device is operating at the reference activity level, i.e. here at the reference voltage Vr).

[0082] According to a sixth step, the value of the voltage supplying the electronic device 14 is suddenly changed, in order to reach a new value VL. By "suddenly ", we mean an instantaneous or almost instantaneous change in the value of the electrical voltage supplying the electronic device 14. According to the present example, the new electrical voltage value VI is 16 Volts. As shown in part B of curve 32A, the internal temperature curve then describes an equation of the type

[0083] [Math.l] Ti = Te+$l(l-exp(~))

[0084] According to a seventh step, the successive values ​​of Ti are measured (by means of the temperature probe 6) and, when the temperature is stabilized (for example when it does not vary to within + / - 0.1 °C), the values ​​¢1 and r_l are determined.

[0085] The value of ¢1 is the difference between the temperature Ti inside the electronic device after stabilization (at the end of part B in [Fig.3]) and the ambient temperature Te, i.e. here 45.5°C - 25°C = 20.5°C.

[0086] The value of Ti is for example determined by looking, from the voltage step at the value VI (16V), for the duration for which 63.2% of the temperature increase is obtained during part B. Here we obtain L = 669 s.

[0087] According to an eighth step, the value of the voltage supplying the electronic device 14 is suddenly changed, in order to reach a new value V2. By "suddenly", we mean an instantaneous or almost instantaneous modification of the value of the electrical voltage supplying the electronic device 14. According to the present example, the new electrical voltage value V2 is 8 Volts. As shown in part C of curve 32A, the internal temperature curve then describes an equation of the type

[0088] [Math.2] Ti = Te+$2(1-exp(%))

[0089] According to a ninth step, the successive values ​​of Ti are measured (by means of the temperature probe 6) and, when the temperature is stabilized (for example when it does not vary to within + / - 0.1 °C), the values ​​¢2 and r2 are determined.

[0090] The value of ¢2 is the difference between the temperature Ti inside the electronic device after stabilization (at the end of part C in [Fig.3]) and the ambient temperature Te, i.e. here 38.5°C - 25°C = 13.5°C.

[0091] The value of r2 is for example determined by looking, from the voltage step at the value V2 (8V), for the duration for which 63.2% of the temperature increase is obtained during part B. Here we obtain r2 = 621 s.

[0092] As shown schematically in Figure 3, the previous steps can be repeated in order to obtain more T values ​​and <e>i.

[0093] According to a tenth step, an average value of calibration value T is calculated from the values ​​T, r2 calculated previously.

[0094] According to the present example, the average calibration value T is equal to 645 s.

[0095] This calibration value (here average) is representative of a time constant of the system, reflecting the thermal inertia of the interior of the electronic device 14.

[0096] In this tenth step, a coefficient of variation of heat dissipation C is also determined by the formula: C = (¢2 - <1> 1) / (V2 - VI).

[0097] This coefficient of variation of heat dissipation C therefore gives the ratio between a variation in temperature difference between the inside and the outside of the electronic device, and a variation in activity level (here a variation in voltage).

[0098] Indeed, in the system described here, it is considered that the electronic device consumes a constant current and that the power produced by the electronic device (entirely evacuated in steady state) is therefore proportional to the measured voltage. This evacuated power is also proportional to the temperature difference between the inside of the electronic device and the outside of the electronic device (by definition of the thermal resistance, here of the radiator 22), hence the linearity between the temperature difference and the activity (here represented by the measured voltage).

[0099] According to an eleventh step, the average value of calibration value T and the coefficient of variation of heat dissipation C determined in the previous step are stored in the calibration database (for example by programming the storage unit 10).

[0100] The invention also relates to a first method for evaluating the temperature of the environment in which the electronic device 14 described above is located, when the heat produced by said device is dissipated into its environment over time.

[0101] In this method, according to a first step, a first internal temperature Til is measured, via the temperature probe 6, inside the electronic device 14.

[0102] According to a second step, a second internal temperature Ti2 is measured, via the temperature probe 6, inside the electronic device 14, after a period of time dt (relative to the measurement of the first internal temperature Til).

[0103] According to a third step, the temperature outside Te of the electronic device is estimated from an estimate of a stabilized temperature Ts, inside the electronic device, as a function of the internal temperature values ​​Til, Ti2 measured during the first step and the second step; here, the temperature Te outside the electronic device 13 is estimated from the following equation:

[0104] [Math.3] Te—Ts-AT

[0105] where, Ts denotes the stabilized temperature inside the electronic device, estimated here from the following equation:

[0106] [Math.4] (Ti2-TiY) Ts = Tzl + r ——-

[0107] where the calibration value T comes from the calibration database, obtained from the calibration method described above.

[0108] The term AT mentioned in equation [Math. 3] corresponds here to a heat dissipation constant determined by experiment, for example from a calibration method of the type described above. This heat dissipation constant AT can be stored in the storage unit 10.

[0109] This first evaluation method is suitable for the case where the system has a constant dissipative power and where the temperature difference AT therefore does not depend (or not significantly) on the activity level of the electronic device 14.

[0110] This first evaluation method therefore does not use an activity probe.

[0111] The invention also proposes a second method for evaluating the temperature of the environment in which the electronic device 14 described above is located, when the heat produced by said device is dissipated in its environment in a non-homogeneous manner over time.

[0112] This second evaluation method implements a first step consisting of recording the value of the electrical voltage V, supplying the electronic device 14, via the electrical voltage measuring probe 4, as well as the value of the temperature Til inside the electronic device 14, via the temperature probe 6.

[0113] According to a second step, a second internal temperature Ti2 is measured, via the temperature probe 6, inside the electronic device 14, after a period of time dt (relative to the measurement of the first internal temperature Til).

[0114] According to a third step, from the calibration database obtained from the calibration method described above, the calibration value (average calibration value) T specific to the electronic device 14 is read.

[0115] According to a fourth step, the stabilized temperature Ts inside the electronic device 14 is determined, from the equation [Math. 4] mentioned above.

[0116] According to a fifth step, a heat dissipation value cp is calculated by summing the following terms:

[0117] - the reference heat dissipation constant cpr, read from the database calibration and corresponding to a temperature difference between the interior of the electronic device, after stabilization of said temperature, and the exterior of the electronic device, when said electronic device operates at the level reference activity (here at the reference voltage Vr); and

[0118] - a product between the coefficient of variation of heat dissipation (also read in the calibration database) and a difference in activity between the measured activity level (here the measured voltage V during the first step of this method) and the reference activity level (here the reference voltage Vr).

[0119] The heat dissipation value cp is therefore here:

[0120] [Math.5]

[0121] Due to the calibration performed, this heat dissipation value <p correspond à un écart de température estimé, entre la l’intérieur l’appareil électronique, après stabilisation ladite température, lorsque le dispositif d’évaluation est alimenté par tension électrique v, mesurée sonde 4, et l’extérieur dudit électronique 14.

[0122] As explained above, the linearity between the temperature difference <p et la tension mesurée v vient des propriétés suivantes :

[0123] - in the example described here, the thermal power produced by the electrical device tronic 14 is proportional to the measured voltage V (operation at quasi-constant current);

[0124] - in steady state, all the thermal power produced is dissipated towards the outside;

[0125] - the dissipated thermal power is proportional to the temperature difference <p (par definition of the thermal resistance of the heat sink).

[0126] In other systems, the thermal power produced by the electronic device 14 may in practice be proportional to another operating parameter (or activity measurement) of the electronic device 14, for example the supply current, in which case it is this other parameter which will be used to evaluate the activity level (instead of the voltage in formula 5, the calibration then being adapted to this situation).

[0127] According to a sixth step, the temperature outside Te of the electronic device 14 is estimated by subtracting, from the estimate of the stabilized temperature Ts inside the electronic device 14, the heat dissipation value cp determined in the fifth step.

[0128] It is clear from the various embodiments of the invention described above that the invention advantageously makes it possible to estimate the temperature outside an electronic device, without having to resort to using a temperature probe positioned outside said device.

[0129] As a result, the invention allows for faster, simpler and more economical operation of an electronic device requiring knowledge of the temperature. temperature of its environment to carry out measurements and / or actions.

[0130] In the case mentioned above where the electronic device 14 is a thermal camera (or a thermal sensor), the measured temperature (detected by a pixel) can for example be corrected as a function of the temperature of the environment where the thermal camera and the observed target are located (ambient temperature), this temperature of the environment (ambient temperature) being evaluated here according to one of the methods described above.

[0131] The corrected temperature Tc is for example determined as follows:

[0132] [Math.6]

[0133] where Te is the ambient temperature evaluated according to one of the methods described above, T m is the temperature measured by the thermal sensor (or a pixel of the thermal camera) and e is a constant. < / e>

Claims

Claims

1. Method for evaluating the temperature of an environment in which an electronic device (14) is placed, the electronic device (14) being capable of dissipating into the environment at least part of the heat that it generates, characterized in that the evaluation method implements the following steps: a) measurement, inside the electronic device (14), of a first internal temperature, then b) after a given period of time, measurement, inside the electronic device (14), of a second internal temperature, then c) estimation of the temperature outside the electronic device (14), from an estimation of a stabilized temperature, inside the electronic device (14), as a function of the values ​​measured during steps a) and b).

2. Evaluation method according to claim 1, characterized in that the estimation of the stabilized temperature is obtained from a calibration value, reflecting the thermal inertia of the interior of the electronic device (14).

3. Evaluation method according to claim 2, characterized in that the estimation of the stabilized temperature is obtained from the sum of the following terms: - the value of the first internal temperature (Til), and - a product between the calibration value and the variation in internal temperature of the electronic device (14), during the period of time.

4. Evaluation method according to one of claims 1 to 3, characterized in that the temperature outside the electronic device is estimated by subtracting, from the estimation of the stabilized temperature, a heat dissipation value reflecting a phenomenon of dissipation, in the medium, of the heat generated by the electronic device (14).

5. Evaluation method according to claim 4, characterized in that, during step a) or during step b), an activity level of the electronic device (14) is measured, and in that the heat dissipation value is obtained from the sum of the following terms: - a reference heat dissipation constant, corresponding to a temperature difference between the interior of the electronic device, after stabilization of said temperature, and the exterior of the electronic device, when said electronic device is operating at a reference activity level; and - a product between a coefficient of variation of heat dissipation and a difference in activity between the measured activity level and the reference activity level.

6. Evaluation method according to claim 5, characterized in that the activity level of the electronic device (14) is measured from the electrical voltage or the electrical current, supplying the electronic device (14), or from a load of a component of the electronic device (14).

7. Device for evaluating the temperature of an environment in which an electronic device is placed, the evaluation device comprising a storage unit (10) and a temperature probe (6) intended to be housed in the electronic device (14), the storage unit (10) and the temperature probe (6) being connected to a calculation unit (8), characterized in that the storage unit (10) comprises instructions capable of being implemented by the calculation unit (8), in order to carry out a method for evaluating the temperature of an environment in which said electronic device is placed according to one of claims 1 to 6.

8. Evaluation device according to claim 7, characterized in that it comprises an activity probe (4) making it possible to measure an activity level of the electronic device (14), and in that the activity probe (4) is connected to the calculation unit (8), and in that the storage unit (10) comprises instructions capable of being implemented by the calculation unit (8), in order to carry out a method for evaluating the temperature of an environment in which said electronic device is placed according to claim 5.

9. Evaluation device according to claim 8, characterized in that the activity probe comprises at least one electrical voltage probe or one electrical current probe.

10. Method for calibrating an evaluation device according to claim 8 or 9, characterized in that this calibration method comprises the following steps: a) operating the electronic device (14) at a first level of activity called reference, in an environment where the temperature is stable and known, for a sufficient period of time so that the internal temperature of the electronic device is stable, then b) measuring by means of the temperature probe (6) the tem- internal temperature of the electronic device (14), then (c) for each of at least two activity levels of the electronic device, measurement by means of the temperature probe (6), of several internal temperatures and of an internal stabilization temperature, then d) estimation of a calibration value, reflecting the thermal inertia of the interior of the electronic device (14), from the internal temperature values ​​measured by the temperature probe during step c), e) estimation of the coefficient of variation of heat dissipation as a function of the internal temperature measured in step b), the stabilization temperatures measured in step c) and said at least two activity levels of the electronic device (14).

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