Electronic module with improved moisture protection

Abstract

Electronic module comprising a protective casing defining an internal volume and an electronic board placed in the internal volume, the electronic module comprising: means, for detecting a predetermined environmental condition of the internal volume, means for generating a cool zone inside the internal volume, which means are arranged such that the cool zone is separated from the electronic board; a control unit that is linked to the means for detecting an environmental condition and to the means for generating a cool zone and arranged to trigger the means for generating a cool zone when the means for detecting a predetermined environmental condition in the internal volume detect an environmental condition that is liable to result in the moisture in the air contained in the internal volume condensing on the electronic board.

Claims

1. An electronic module configured for being mounted on an avionics rack, the electronic module including: a protective casing defining an internal volume, the protective casing being adapted to be received by the avionics rack; an electronic circuit board placed in the internal volume; means for detecting a predetermined environmental condition of the internal volume; means for generating a cold zone inside the internal volume such that the cold zone is separated from the electronic circuit board; a control unit that is connected to the means for detecting a predetermined environmental condition and to the means for generating a cold zone, the control unit being adapted to trigger the means for generating a cold zone when the means for detecting a predetermined environmental condition in the internal volume detect an environmental condition that is liable to result in the moisture in the air contained in the internal volume condensing on the electronic circuit board, wherein the means for detecting a predetermined environmental condition comprise a first temperature sensor fastened to the electronic circuit board and a second temperature sensor fastened to the protective casing, and wherein the control unit is adapted to trigger the means for generating a cold zone exclusively based on the analysis of a difference between a first temperature measured by the first temperature sensor and a second temperature measured by the second temperature sensor, the control unit being arranged to trigger the means for generating a cold zone when the first temperature is lower than the second temperature such that a moisture present in the internal volume is forced to condense in the cold zone.

2. The electronic module as claimed in claim 1, in which the control unit is adapted to trigger the means for generating a cold zone only if the temperature measured by the first temperature sensor is lower than a predetermined threshold temperature.

3. The electronic module as claimed in claim 1, in which the means for detecting a predetermined environmental condition comprise a third temperature sensor fastened to the electronic circuit board.

4. The electronic module as claimed in claim 1, in which the means for generating a cold zone comprise a Peltier effect cell that has a hot face and a cold face.

5. The electronic module as claimed in claim 4, in which the hot face of the Peltier effect cell is thermally connected to the protective casing or to a thermally conductive chassis of the electronic module.

6. The electronic module as claimed claim 1, in which the means for generating a cold zone are such that the condensates resulting from the condensation of the air contained in the internal volume are directed to a dedicated retention zone of the internal volume and/or to the exterior of the internal volume.

7. The electronic module as claimed in claim 6, in which the retention zone is coated with a protective resin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference will be made to the appended figures in which:

(2) FIG. 1 is a partly cutaway diagrammatic perspective view of an electronic module according to a first embodiment of the invention;

(3) FIG. 2 is a diagrammatic view of the module from FIG. 1 in section taken along the line II-II;

(4) FIG. 3 is a partly cutaway diagrammatic perspective view of an electronic module in accordance with a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring to FIGS. 1 and 2, the electronic module in accordance with the invention, generally designated 100, is here adapted to be mounted in an avionics rack 60 of an aircraft (not shown).

(6) The electronic module 100 comprises an electronic circuit board 10 fixed onto a base 20 of a protective casing 21. Electronic tracks 11 and 12 respectively connect the electronic circuit card 10 to a first or data connector 13 and to a second or power supply connector 14 both of which open onto an external surface of the protective casing 21.

(7) The protective casing 21 extends around the electronic circuit board 10 and defines an internal volume 22 of the electronic module 100. A first temperature sensor 30 and a second temperature sensor 31—both of resistive type—are respectively glued to the circuit board 10 and to an interior face 23 of the protective casing 21. A Peltier effect cell 50 having a hot surface 51 and a cold surface 52 has its hot surface 51 glued to an interior surface 24 of the base 20. A retention zone 53 vertically in line with the Peltier effect cell 50 when the electronic module 10 is plugged into the avionics rack 60 (FIG. 2) is covered with parylene. The retention zone 53 forms a cup at the center of which an orifice 54 provided with a valve 55 passes through the protective casing 21 and opens to the exterior of the latter.

(8) A processor 40 is connected to the first and second temperature sensors 30 and 31 and to the Peltier effect cell 50. The processor 40 is supplied with energy via the power supply connector 14 and exchanges data with the outside via the data connector 13.

(9) In operation, the processor 40 monitors and compares the temperatures T.sub.30 and T.sub.31 respectively measured by the first and second temperature sensors 30 and 31 in order to detect conditions liable to cause condensation of the moisture in the air contained in the internal volume 22 on the electronic circuit board 10. A situation of this kind may arise when the aircraft is started up after it has been subjected to a low temperature. The operation of one of the modules adjacent to the module 100 can heat the protective casing 21 and the air contained in the internal volume 24 before the electronic circuit board 10 has been activated and has been able to increase in temperature. The electronic circuit board 10 is then cooler than the air contained in the internal volume 24 and condensation is liable to be formed on the electronic circuit board 10. The temperature T.sub.30 measured by the first temperature sensor 30 is then lower than the temperature T.sub.31 measured by the second temperature sensor 31 and the processor 40 detects conditions liable to cause condensation of the moisture in the air contained in the internal volume 22 on the electronic circuit board 10. The processor 40 then triggers the operation of the Peltier effect cell 50. The cold surface 52 of the Peltier effect cell 50 then creates a cold zone the temperature T.sub.52 of which is lower than that of the electronic circuit card 10. This lower temperature of the cold face 52 causes condensation on the latter rather than on the electronic circuit board 10, protecting the electronic circuit board 10 from condensation. The condensates formed on the surface of the cold face 52 drop by gravity into the retention zone 53 and are evacuated to the orifice 54.

(10) There is therefore obtained an electronic module 100 the electronic circuit board 10 of which is protected by the protective casing 21 from dust, from exterior moisture, from smoke and mechanical attacks. The protective casing 21 may be demountable in order for the electronic circuit board 10 to be easily accessible and, requiring no varnish protection, therefore easily repairable. The Peltier effect cell 50 enables the electronic circuit board 10 to be protected from moisture contained in the internal volume 22.

(11) According to a second embodiment, the processor 40 triggers the operation of the Peltier effect cell 50 only after previously effecting a comparison between the temperature T.sub.30 measured by the first temperature sensor 30 and a threshold temperature T.sub.s10, here equal to twenty degrees Celsius. If the temperature T.sub.30 measured by the first temperature sensor 30 is higher than the threshold temperature T.sub.s10 the processor 40 does not trigger the operation of the Peltier effect cell 50. If the temperature T.sub.30 measured by the first temperature sensor 30 is lower than the threshold temperature T.sub.s10 the processor 40 triggers the operation of the Peltier effect cell 50 if the temperature T.sub.30 measured by the first temperature sensor 30 is lower than the temperature T.sub.31 measured by the second temperature sensor 31.

(12) In accordance with a third embodiment shown in FIG. 3, the electronic circuit board 10 includes a third temperature sensor 32 and a fourth temperature sensor 33. The third temperature sensor 32 and the fourth temperature sensor 33 are placed on the electronic circuit board 10 in areas determined as a function of the topology of the electronic circuit board 10 and its heat dissipation profile to measure the temperatures of the areas of the electronic circuit board 10 that may be at lower temperatures than the rest of the electronic circuit board. These areas may be situated in the vicinity of components having a high thermal inertia such as for example the metal masses of voltage transformers. The condition liable to cause condensation of the moisture in the air contained in the internal volume 22 on the electronic circuit board 10 is then detected in the following manner. The processor 40 compares the temperatures T.sub.30, T.sub.32 and T.sub.33 respectively measured by the first temperature sensor 30, the third temperature sensor 32 and the fourth temperature sensor 33 and retains the lowest temperature T.sub.min(30, 32, 33). This lowest temperature T.sub.min(30, 32, 33) can then be compared to the threshold temperature T.sub.s10. If the lowest temperature T.sub.min(30, 32, 33) is lower than the threshold temperature T.sub.s10, the processor 40 then compares the lowest temperature T.sub.min(30, 32, 33) with the temperature T.sub.31 measured by the second temperature sensor 31.

(13) If the lowest temperature T.sub.min(30, 32, 33) is lower than the temperature T.sub.31 measured by the second temperature sensor 31 the processor 40 detects conditions liable to cause condensation of the moisture in the air contained in the internal volume 22 on the electronic circuit board 10. The processor 40 then triggers the operation of the Peltier effect cell 50.

(14) Of course, the invention is not limited to the embodiments described but rather encompasses any variant falling within the scope of the invention as defined by the claims.

(15) In particular: although here the cold zone is generated by a Peltier effect cell, the invention applies equally to other means of generating a cold zone separated from the electronic circuit board such as for example an electrical tracer that heats the circuit board, which therefore implies that a cold zone is generated elsewhere than on the circuit board (for example on a shroud of the data or power supply connector); although the cold zone is generated by a Peltier effect cell, the invention applies equally to other means of generating a cold zone separate from the electronic circuit board such as for example a cryostat; although here the conditions liable to cause condensation of the moisture in the air contained in the internal volume are detected by two temperature sensors, the invention applies equally to other means of detecting a predetermined environmental condition such as for example a hygrometer, a single temperature sensor possibly coupled to a pressure sensor, a dew point detector, a condensation sensor; although here the temperature sensors are resistive sensors, the invention applies equally to other means of measuring temperatures such as for example infrared or capacitive sensors; although here the temperature sensors are stuck to the electronic circuit board or the protective casing, the invention applies equally to other means of fastening the sensors such as for example screwing or clipping means; although here the retention zone is in the form of a cup coated with a layer of parylene resin, the invention applies equally to a retention zone of different or plane shape, protected or not by a coating that may be different from parylene, such as for example paint, a synthetic material or metal insert; although here the retention zone is provided with an orifice opening to the exterior of the internal volume and provided with a valve, the invention applies equally to other configurations of the retention zone such as for example a retention zone the orifice of which has no valve or a retention zone that has no orifice; although here the hot face of the Peltier effect cell is connected to the protective casing, the invention applies equally to a connection of the hot face of the Peltier effect cell to other types of elements of the electronic module such as for example to a thermally conductive chassis of the electronic module; although here the electronic circuit board is fixed to a base of the protective casing, the invention applies equally to other configurations of the protective casing such as for example a protective casing the base of which consists of the electronic circuit card itself; although here the temperature sensors and the Peltier effects that are connected to a processor, the invention applies equally to other types of control unit such as for example a microcontroller or an FPGA; although here the threshold temperature is equal to twenty degrees Celsius, the invention applies equally to other predetermined threshold values that may in particular be chosen according to the specific operating conditions of the electronic module, such as for example a threshold temperature higher than or lower than twenty degrees Celsius; although here the electronic circuit board includes third and fourth temperature sensors, the invention applies equally to an electronic circuit board comprising a different number of temperature sensors such as for example two or more than three sensors.