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 temperature evaluation and associated calibration method

[0001] Technical field to which the invention relates

[0002] The present invention relates to the technical field of thermometry. More particularly, the present invention relates to a method and a device for measuring the temperature of a medium in which an electronic device is placed. The present invention also relates to a method for calibrating a temperature measurement 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 allow them to function properly.

[0004] This is particularly the case for infrared sensors, which assess the temperature at the surface of a distant object by analyzing the infrared radiation emitted by that object. To perform 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 accurately measure the temperature of the medium in which the infrared sensor is located.

[0006] The need for a thermometer, separate from the infrared sensor, has the disadvantage of requiring the use and manipulation of several devices to perform a qualitative measurement.

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

[0008] According to another drawback, the presence of a thermometer near the infrared sensor may not be possible, for example when said sensor is integrated into a trim piece in the 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 estimate of a stabilized temperature inside the electronic device, based on 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 considered not 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 taken 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 previously required two separate electronic devices, namely, the electronic device and a thermometer located outside said device. The invention thus allows for easier integration of an electronic device requiring knowledge of the temperature of its environment, since, 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 space, such as a component of a motor vehicle's interior, like a dashboard.

[0018] According to another advantage, the invention eliminates the need for manual transfer of temperature measurements taken by a thermometer located outside the electronic device, since the invention allows the temperature outside the device to be estimated from temperature measurements taken inside the electronic device. The invention thus enables simpler and faster operation of an electronic device that requires knowledge of the temperature of its surrounding environment.

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

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

[0021] The estimate of the stabilized temperature is obtained, for example, 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, during 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 later), makes it possible to evaluate in a few seconds (without waiting for the physical stabilization of the system) at what temperature the inside 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 advantageously allows for the near-instantaneous estimation of the external temperature of an electronic device from temperature measurements taken inside said device, even when the temperature of the electronic device has not stabilized. This is particularly the case when an electronic device is switched on; the heat it generates causes its internal temperature to rise until it reaches a stable or substantially stable value.

[0026] In other words, the evaluation method described herein allows for an estimation of the temperature outside the electronic device before its temperature stabilizes. This advantageously enables a very rapid estimation, after the electronic device is switched on, of the temperature of its surrounding environment. Since this information is necessary for the proper functioning of the electronic device, the invention allows for faster and more precise operation of the device 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 referred to below as the heat dissipation constant.

[0030] The heat dissipation constant can correspond 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.

[0031] According to a second possibility, when the electronic device is characterized by a dissipative power that changes 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 said temperature has stabilized, 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" we mean an operating mode of the electronic device.

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

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

[0037] Of course, the different characteristics, variants and embodiments mentioned above can be combined with each other in various combinations, provided that they are not incompatible or mutually exclusive.

[0038] The invention also relates to a device for evaluating the temperature of a medium 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 computing unit.

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

[0040] According to another embodiment, the evaluation device includes an activity probe for measuring an activity level of the electronic device, and the activity probe is connected to the computing unit, and the storage unit includes instructions suitable for implementation by the computing unit, in order to carry out a method for evaluating the temperature of a medium in which said electronic device is placed, as described above.

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

[0042] According to a non-limiting embodiment, the electronic device may be a thermal imaging camera, located, for example, in an industrial space where the temperature is neither stable nor known, and / or measuring the temperature of production parts with known emissivity, and automatically compensating for the radiative temperature component reflected by the parts (which could distort the measurement) by taking into account the ambient temperature of the space. Without the present invention, such a camera may have an erroneous measurement for several minutes—or even tens of minutes—after being switched on, due to the error in estimating the ambient temperature. This obliges 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 and each time the ambient temperature changes.Thanks to the present invention, such a thermal camera will be able to provide accurate measurements immediately after a cold start, and according to fluctuations in ambient temperature, or 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) switching on the electronic device at a first activity level, called the reference level, preferably at nominal operating mode, 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, via 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, via the temperature probe, of several internal temperatures and 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), the stabilization temperatures measured in step c) and said at least two levels of activity 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 coefficient of variation of dissipation:

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

[0051] Detailed description of an example embodiment

[0052] The invention will be better understood from the following description, which relates to preferred embodiments, given by way of non-limiting examples, and explained with reference to the accompanying schematic drawings, in which:

[0053] [Fig.1] 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 device comprising a temperature evaluation device shown in [Fig. 1]; 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 a medium in which an electronic device is placed, without resorting to the use of a thermal probe located outside the electronic device.

[0057] Figure 1 shows a non-limiting embodiment of a device 2 for evaluating the temperature of this medium. This evaluation device 2 comprises an activity level measurement probe or activity probe (here an electrical voltage measurement probe 4) and a temperature probe 6, both connected to a computing unit 8. The computing unit is also connected to a storage unit 10.

[0058] The term "connected" refers to 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 non-volatile rewritable memory (for example, of the EEPROM type for "Electrically Erasable and Programmable Read Only Memory"). The storage unit includes instructions suitable for implementation by the processing unit, in order to carry out a method for evaluating the temperature of a medium, as described below, or a calibration method as described below.

[0060] Preferably, the temperature probe 6 is capable of performing temperature measurements over a range encompassing the entire ambient temperature range in which the electronic device is intended to operate, here with an accuracy on the order of 0.1 °C. However, the invention could still function (possibly with less accuracy) if only a portion of the operating range were covered by the measurement range.

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

[0062] According to one 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 conjunction with electronic regulation and acquisition circuits. A thermal diode advantageously combines very low cost, high linearity over a wide temperature range, with known and inexpensive electronic biasing and amplification stages, and acceptable accuracy after proper calibration. Furthermore, such a solution can be easily included in the die of an integrated circuit, making it a solution with virtually no additional cost in this type of technology.

[0063] Preferably, the electrical voltage measurement probe 4 is made by means of a voltage divider bridge providing a voltage representative of the supply voltage, this representative voltage being able for example to be applied to the input of an analog-to-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 the integration of an evaluation device 2 as described above into an electronic device 14.

[0065] The electronic device 14 consists of a printed circuit board 16, which serves as a support for a power connector 18 or a voltage regulator. The electronic device 14 includes various electronic components 20, held on the printed circuit board 16. The electronic components 20 are connected to each other in such a way as to allow them to be powered by the power supply connector 18, so that the electronic device 14 can perform various tasks.

[0066] The electronic device 14 also includes 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, or preferably protrude beyond, the outer surface of a protective housing 28 surrounding the various aforementioned elements of the electronic device. The finned heat sink 22 is positioned on the printed circuit board 16 so as to dissipate from the protective housing 28 all or almost all of the heat produced by the electronic components 20 when the power connector 18 is connected to a power supply.

[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 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 device 14 includes an evaluation device 2 such as that shown above with reference to [Fig. 1]. More specifically, the electrical voltage measuring probe 4 of the evaluation device 2 is connected to the electrical power connector 18, so as to allow the computing unit 8 to measure in real time the value of the electrical voltage 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 that dissipate the most heat. In this 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, to the finned heatsink 22, which is held against the first large face 24A of said board. The processing unit 8 and the storage unit 10 are also present in the protective housing 28.

[0073] Possibly, the calculation unit 8 and the memory unit may be considered as 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 in [Fig. 2], implementing a first step consisting of placing the electronic device 14 in an environment 30, of which The temperature is controlled. During this first calibration step, the electronic device 14 is at rest. By "at rest," we mean that the electronic device 14 is not connected to any power source.

[0075] The electronic device 14 is, for example, placed in a room with an ambient temperature of 25°C for a sufficient period of time so that the temperature TiO₂ inside the protective housing 28 of the electronic device, as measured 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 referred to as the external temperature Te of the electronic device, is then recorded.

[0076] By way of non-limiting example, the electronic device 14 may be integrated into the interior trim of a motor vehicle, not shown in [Fig. 2] to facilitate understanding of the invention. In this case, it is preferable to perform the present calibration test when the electronic device 14 is present in the trim. The trim may be a component of a dashboard, part of a headliner, a dome light, etc.

[0077] According to a second step, the electronic device 14 is 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 housing 28 of the electronic device 14 is recorded at regular time intervals, using known means, until the internal temperature Ti reaches a stabilized temperature Ts. The temperatures thus recorded are used to create a calibration curve 32A as shown in part A of the graph visible in [Fig. 3]. In this graph, the abscissa corresponds to time (t) and the ordinate to 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 by 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 the electronic device Te (here 25 °C). The difference thus determined is 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 the reference heat dissipation constant cpr (and thus corresponds to the difference 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 to reach a new value VI. By "suddenly," we mean an instantaneous or near-instantaneous change in the value of the electrical voltage supplying the electronic device 14. In the present example, the new value of electrical voltage 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+0\( ï-exp(r} ) )

[0084] According to a seventh step, the successive values ​​of Ti are measured (using the temperature probe 6) and, when the temperature is stabilized (for example when it does not vary 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 on [Fig.3]) and the ambient temperature Te, i.e. here 45.5°C - 25°C = 20.5 °C.

[0086] The value of T1 is for example determined by finding, from the voltage step to the value VI (16V), the time for which 63.2% of the temperature increase during part B is obtained. Here we obtain T| = 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 near-instantaneous change in the value of the electrical voltage supplying the electronic device 14. In the present example, the new value of electrical voltage 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( l-exp(^ ) )

[0089] According to a ninth step, successive values ​​of Ti are measured (using the temperature probe 6) and, when the temperature is stabilized (for example when it does not vary within + / - 0.1 °C), the values ​​¢2 and '2 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 on [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 finding, from the voltage step to the value V2 (8V), the time for which 63.2% of the temperature increase during part B is obtained. Here we obtain r2 = 621 s.

[0092] As schematically represented in Figure 3, the preceding steps can be repeated in order to obtain more r' values ​​and <e>i.

[0093] According to a tenth step, an average calibration value is calculated from the previously calculated T2 values.

[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 outside of the electronic device, and a variation in activity level (here a variation in voltage).

[0098] Indeed, in the system described here, the electronic device is considered to consume a constant current, and the power produced by the electronic device (entirely dissipated in steady state) is therefore proportional to the measured voltage. This dissipated power is also proportional to the temperature difference between the inside and outside of the electronic device (by definition of the thermal resistance, here of the heat sink 22), hence the linear relationship between the temperature difference and the activity (here represented by the measured voltage).

[0099] According to an eleventh step, the average value of the 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 medium 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 process, 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 time lapse 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 and second steps; here, the temperature Te outside the electronic device 13 is estimated from the following equation:

[0104] [Math.3] Te=Ts-M

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

[0106] [Math.4]

[0107] where the calibration value r is taken from the calibration database, obtained from the calibration process described above.

[0108] The term AT mentioned in equation [Math. 3] here corresponds to a heat dissipation constant determined experimentally, for example from a calibration procedure 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 level of activity 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 into its environment in a non-homogeneous way 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 time lapse 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 process 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 O is calculated by summing the following terms:

[0117] - the reference heat dissipation constant, read from the database calibration and corresponding 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 the reference activity level (here at the reference voltage Vr); and

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

[0119] The heat dissipation value 0 is therefore:

[0120] [Math.5] = + C*(V-Vr)

[0121] Due to the calibration performed, this heat dissipation value O corresponds to an estimated temperature difference, between the temperature inside the electronic device, after stabilization of said temperature, when the evaluation device is powered by the electrical voltage V, measured by the electrical voltage probe 4, and the temperature outside said electronic device 14.

[0122] As explained above, the linearity between the temperature difference O and the measured voltage V arises from the following properties:

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

[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 O (by 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 parameter) 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 level of activity (in place 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 value of heat dissipation cp determined in the fifth step.

[0128] It is apparent from the various examples of embodiment of the invention described above that the invention advantageously allows the temperature outside of an electronic device to be estimated without having to use 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 of its environment to perform 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 according to the temperature of the medium where the thermal camera and the observed target are located (ambient temperature), this temperature of the medium (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] T = zc

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

Claims

Demands

1. A method for evaluating the temperature of a medium in which an electronic device (14) is placed, the electronic device (14) being capable of dissipating at least part of the heat it generates into the medium, characterized in that the evaluation method implements the following steps: a) measuring, inside the electronic device (14), a first internal temperature, then b) after a given period of time, measuring, inside the electronic device (14), a second internal temperature, then c) estimating the temperature outside the electronic device (14), from an estimate of a stabilized temperature inside the electronic device (14), based on the values ​​measured during steps a) and b), in that the estimate of the stabilized temperature is obtained from a calibration value, reflecting the thermal inertia of the inside of the electronic device (14),The estimate 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 time period, and in that the temperature outside the electronic device is estimated by subtracting, from the estimate 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).

2. An evaluation method according to claim 1, 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 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 - 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.

3. Evaluation method according to claim 2, characterized in that the activity level of the electronic device (14) is measured from the electrical voltage or electrical current supplying the electronic device (14), or from a load of a component of the electronic device (14).

4. A device for evaluating the temperature of a medium 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 a medium in which said electronic device is placed according to any one of claims 1 to 3.

5. Evaluation device according to claim 4, characterized in that it comprises an activity probe (4) for measuring an activity level of the electronic device (14), and in that the activity probe (4) is connected to the computing unit (8), and in that the storage unit (10) includes instructions suitable for implementation by the computing unit (8), in order to carry out a method for evaluating the temperature of a medium in which said electronic device is placed according to claim 2.

6. Evaluation device according to claim 5, characterized in that the activity probe comprises at least one electrical voltage probe or one electrical current probe.

7. A method for calibrating an evaluation device according to claim 5 or 6, characterized in that this calibration method comprises the following steps: a) switching on the electronic device (14) at a first activity level, referred to as the reference level, 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) measurement via the temperature probe (6) of the internal temperature of the electronic device (14), then (c) for each of at least two activity levels of the electronic device, measurement via the temperature probe (6) of several internal temperatures and 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 levels of activity of the electronic device (14).

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