Optical detection of a case opening

Abstract

Equipment (1) comprising a housing (2) in which are integrated a light signal emitter (21), a receiver (22) arranged to receive the light signals after they have been reflected off an internal wall (23) of the housing, and a processing unit (15) arranged to: control the emitter (21) so that it emits a detection light signal (S1); acquire a first electrical signal (V1) produced by the receiver (22) when it receives the detection light signal; detect, based on a first level of the first electrical signal, whether the housing (2) is open or closed. (Figure from the summary: Fig. 1)

Description

Title of the invention: Optical detection of the opening of a case

[0001] The invention relates to the field of detecting the opening of a housing of equipment (which may be a meter, but not necessarily).

[0002] BACKGROUND OF THE INVENTION

[0003] Some malicious people know techniques that allow them, after opening the casing of their meter, to manipulate it to reduce the measurement of their consumption. This can be any type of meter: electricity, water, gas, etc.

[0004] A number of devices are known for detecting the opening of a meter housing.

[0005] In the case of water and gas meters, the detection device must consume very little electrical energy, because these meters are generally powered by a battery.

[0006] A conventionally used detection device comprises an electromechanical contact whose state changes when the housing is opened. However, water and gas meters are frequently filled with gel at the end of their manufacture. When it polymerizes, this gel tends to block the electromechanical contact and thus renders the detection device inoperative.

[0007] SUBJECT OF THE INVENTION

[0008] The object of the invention is to effectively detect the opening of the housing of an item of equipment, without using electromechanical contact and while consuming very little electrical energy. Summary of the invention

[0009] With a view to achieving this aim, equipment is proposed comprising a housing in which are integrated: • a transmitter arranged to emit light signals; • a receiver arranged to receive the light signals after they have been reflected against an internal wall of the housing; • a processing unit designed for: • control the transmitter so that it emits a light detection signal; • acquire a first electrical signal produced by the receiver when it receives the light detection signal; • detect, based on a first level of the first electrical signal, whether the box is open or closed.

[0010] Detection, achieved via emission, internal reflection and signal capture light detection system, is effective, simple and inexpensive to implement. The invention works even when the housing is filled with gel. The components used consume very little electrical energy.

[0011] We further propose equipment as previously described, in which the processing unit is arranged to: acquire a second electrical signal produced by the receiver while the transmitter is off; carrying out the detection of the opening or closing of the housing as a function of a value representative of a difference or a ratio between the first level of the first electrical signal and a second level of the second electrical signal.

[0012] There is further provided equipment as previously described, in which the housing comprises a first housing part, which is removable, the inner wall being a wall of the first housing part, and in which the transmitter and the receiver are both positioned: opposite and close to the first part of the housing, or opposite and close to a second housing part of the housing, transparent or translucent to light signals, and positioned between the first housing part on the one hand, and the transmitter and the receiver on the other hand.

[0013] We further propose equipment as previously described, further comprising: a first optical guide positioned between the transmitter and the internal wall, and arranged to guide and concentrate the light signals towards the internal wall; a second optical guide positioned between the receiver and the internal wall, and arranged to guide and concentrate the light signals towards the receiver.

[0014] We further propose equipment as previously described, in which the first optical guide and the second optical guide are manufactured in a single piece.

[0015] We further propose equipment as previously described, further comprising a cover device comprising a first portion delimiting an internal space in which the receiver is positioned, and arranged to prevent parasitic light signals coming from inside or outside the housing from disturbing the receiver.

[0016] We further propose equipment as previously described, in which the hiding device also comprises a second portion located between the transmitter and the receiver, and arranged to prevent parasitic reflections, resulting from a reflection of the light signals emitted by the transmitter on the first optical guide or on the second optical guide, or lateral radiation from the transmitter, do not disturb the receiver.

[0017] There is further provided equipment as previously described, in which the inner wall is made of injected plastic with a mirror finish.

[0018] We further propose equipment as previously described, in which the internal wall has a concave reflector shape.

[0019] We further propose equipment as previously described, comprising a reflective material chemically deposited on the internal wall.

[0020] We further propose equipment as previously described, comprising a self-adhesive and reflective label, stuck on the internal wall.

[0021] We further propose equipment as previously described, in which the internal wall has a color having a wavelength XI such that:

[0022] XI = X2 ± 10%,

[0023] where X2 is a wavelength of the light signals.

[0024] We further propose equipment as previously described, the transmitter and the receiver being arranged to respectively transmit and receive light signals which are non-visible signals.

[0025] We further propose equipment as previously described, the equipment being a fluid meter.

[0026] A detection method is further proposed, implemented in the processing unit of equipment as previously described, and comprising a detection phase comprising the steps of: • control the transmitter so that it emits a light detection signal; • acquire a first electrical signal produced by the receiver when it receives the light detection signal; • detect, based on a first level of the first electrical signal, whether the box is open or closed.

[0027] We further propose a detection method as previously described, implemented in the processing unit of equipment as previously described, in which the detection phase further comprises the steps of: • acquire a second electrical signal produced by the receiver while the transmitter is deactivated; • detect the opening or closing of the housing based on a value representative of a difference or ratio between the first level of the first electrical signal and a second level of the second electrical signal.

[0028] We further propose a detection method as previously described, comprising the steps of: • repeat the detection phase; • when a detection phase is finished, set a random duration, and start a next detection phase after the random duration.

[0029] A computer program is further provided comprising instructions which cause the processing unit of the electrical equipment as previously described to execute the steps of the detection method as previously described.

[0030] A computer-readable recording medium is further provided, on which the computer program as previously described is recorded.

[0031] The invention will be better understood in light of the following description of particular non-limiting embodiments of the invention. Brief description of the drawings

[0032] Reference will be made to the attached drawings, among which:

[0033] [Fig-1] [Fig.l] represents a simplified sectional view, along a vertical plane, of a fluid meter;

[0034] [Fig.2] [Fig.2] represents steps of the detection method. DETAILED DESCRIPTION OF THE INVENTION

[0035] With reference to [Fig.l], a fluid meter 1 (for example water or gas) is intended to measure the fluid consumption of a user's (subscriber's) installation. The fluid is supplied to the installation by a distribution network.

[0036] The meter 1 comprises a housing 2 and an electrical card 3.

[0037] The housing 2 here comprises a first housing part 4, a second housing part case 5 and a chassis 6.

[0038] The chassis 6 comprises a lower face 7 which is also the lower face of the housing 2.

[0039] The first housing part 4 comprises an upper face 8 which is also the upper face of the housing 2, a first lateral face 9a and a second lateral face 9b. The first housing part 4 is removable. It can be removed by an operator who works for example for the fluid distributor or for the distribution network manager. The first housing part 4 is opaque to visible light (just like the chassis 6).

[0040] The second housing part 5 is transparent or translucent to visible light. It is mounted inside the housing 2, i.e. between the first housing part 4 and the inside of the meter 1. It comprises an upper face 10, a first lateral face 11a and a second lateral face 11b, which are positioned parallel to, facing and close to, respectively, the upper face 8, the first lateral face 9a and the second lateral face 9b of the first housing part 4.

[0041] The upper face 8 of the first housing part 4 has an opening 14. Light from the outside can therefore penetrate inside the meter 1 via this opening 14 and the second housing part 5.

[0042] The electrical card 3 of the meter 1 is positioned parallel to and close to the upper face 10 of the second housing part 5 (and therefore to the upper face 8 of the first housing part 4).

[0043] The electrical card 3 firstly comprises a processing unit 15.

[0044] The processing unit 15 comprises at least one processing component 16, which is for example a “generalist” processor, a processor specialized in signal processing (or DSP, for Digital Signal Processor), a microcontroller, or a programmable logic circuit such as an FPGA (for Field Programmable Gate Arrays) or an ASIC (for Application Specified Integrated Circuit). The processing component 16 is here a microcontroller.

[0045] The processing unit 15 further comprises one or more memories 17, connected to or integrated in the microcontroller 16. At least one of these memories 17 forms a computer-readable recording medium, on which is recorded at least one computer program comprising instructions which cause the microcontroller 16 to execute at least some of the steps of the detection method which will be described below.

[0046] The processing unit 15 further comprises an analog-to-digital converter (ADC) 18, possibly (but not necessarily) integrated into the microcontroller 17.

[0047] The electrical card 3 also includes an LCD screen 19, which is positioned opposite the opening 14, which allows the user to see the screen 19 through the opening 14 and the second housing part 5.

[0048] The counter 1 further comprises a device 20 for detecting the opening of the housing 1.

[0049] The detection device 20 here comprises the processing unit 15, and in particular the microcontroller 16 and the CAN 18. This does not prevent the processing unit 16 from having functions other than this one, and for example metrology functions (measurement of fluid consumption).

[0050] The detection device 20 further comprises a transmitter 21 and a receiver 22, mounted on the electrical card 3.

[0051] The transmitter 21 is arranged to emit light signals, and the receiver 22 is arranged to receive the light signals after they have been reflected against an internal wall 23 of the housing 1. By "internal" is meant on the inside of the meter 1.

[0052] This internal wall 23 is the internal wall of the upper face 8 of the first housing part 4. The light signals emitted by the transmitter 21 therefore pass through the second part of housing 5, are reflected by the internal wall 23, then captured by the receiver 22.

[0053] The transmitter 21 is here a light-emitting diode (LED) and the receiver 22 is here a phototransistor.

[0054] The LED 21 and the phototransistor 22 are here both positioned opposite and close to the upper face 10 of the second housing part 5 of the housing 2, which is therefore itself positioned between the first housing part 4 on the one hand, and the LED 21 and the phototransistor 22 on the other hand.

[0055] The portion of the upper face 10 of the second housing part 5, opposite which the LED 21 and the phototransistor 22 are positioned, is itself positioned opposite a portion of the first housing part 4 which is a “solid” portion (and not opposite the opening 14).

[0056] Here, the LED 21 and the phototransistor 22 are positioned 5 mm from each other, and at a distance of 1 cm from the internal wall 23 of the first housing part 4.

[0057] The principle of the invention is first explained. It aims to detect whether the housing 2 is open or closed and therefore here, more precisely, to detect whether the first housing part 4 has been opened (i.e. at least one of its ends has been moved away from the rest of the housing 2).

[0058] The detection is based on the measurement of the optical reflections of a light signal emitted by the LED 21 then reflected on the internal wall 23 of the housing 2, and finally captured by the phototransistor 22.

[0059] The absence or spacing of the first housing part 4 leads to a limitation of the optical reflections, which causes the signal level in the phototransistor 22 to drop. This drop can be detected.

[0060] The processing unit 15 is therefore arranged to:

[0061] - drive LED 21 (i.e. light it up) so that it emits a signal luminous detection Si;

[0062] - while the LED 21 is lit, acquire a first electrical signal produced by the phototransistor 22 when it receives the detection light signal Si;

[0063] - detect, as a function of a first level of the first electrical signal, whether the housing 2 is open or closed;

[0064] - turn off LED 21 (this step can be performed before the previous one).

[0065] It is noted that the emission of the detection light signal Si here consists simply of turn on the LED 21. The reception of the light detection signal Si is the capture by the phototransistor 22 of the light flux emitted by the LED 21 and reflected by the internal wall 23 (and possibly by other walls of the housing 2).

[0066] The first electrical signal is here a first voltage Vi produced by the phototransistor 22. The first level is the amplitude of the first voltage Vî.

[0067] The first voltage Vi is an analog voltage.

[0068] The first voltage Vi is digitized by the CAN 18 to produce a digital signal.

[0069] This configuration is not mandatory; the receiver could in particular be a “digital” sensor.

[0070] The microcontroller 16 detects, depending on the first voltage Visi, whether the housing 2 is open or closed.

[0071] In order to improve the detection performance, the light energy is measured while the LED 21 is lit (as just seen), then the light energy is measured without the LED 21 being lit.

[0072] The order used to make the two measurements is indifferent.

[0073] The processing unit 15 therefore acquires a second electrical signal produced by the phototransistor 22 while the LED 21 is off (i.e. it does not emit light), and detects the opening or closing of the housing 2 as a function not only of the first level of the first electrical signal (amplitude of the first voltage Vi), but as a function of a value representative of a difference or a ratio between the first level and a second level of the second electrical signal.

[0074] The second electrical signal is a second voltage V2 produced by the phototransistor 22. The second level is the amplitude of the second voltage V2.

[0075] The second voltage V2 is an analog voltage, digitized by the CAN 18.

[0076] It is therefore the analysis of the difference in lighting at the level of the receiver 22, and of the electrical signals (first voltage Viet second voltage V2) that it generates, which makes it possible to eliminate the disturbances that would produce:

[0077] - a light ray external to the counter 1 and coming to “simulate” the LED 21;

[0078] - a light ray outside the counter 1 and saturating the phototransistor 22.

[0079] In the nominal case, with the box 2 closed, the difference in brightness, measured by the pho totransistor 22 with LED 21 on and without LED 21 on, is high. Indeed, a very large part of the luminous flux emitted by LED 21 is captured by phototransistor 22.

[0080] On the other hand, if the housing 2 is open, the luminous flux is not reflected by the internal wall 23 of the first housing part 4, which has been removed. Thus, the difference between the two measurements is significantly smaller. Of course, if the housing 2 is not completely open and if the first housing part 4 is still present while being partially open, the luminous flux is still partially reflected by the internal wall 23 but to a lesser extent, which also makes it possible to detect this partial opening.

[0081] The invention works very efficiently regardless of the ambient light at outside of meter 1:

[0082] - either ambient light is present, and the difference between the two measurements is reduced due to the illumination of the phototransistor 22 by ambient light;

[0083] - either there is no ambient light, and it is the absence or reduction of the re flexions on the first part of the housing 4, now removed, which reduces this difference between the two measurements.

[0084] The detection method, which is implemented by the processing unit 15, is described more precisely with reference to [Fig.2].

[0085] The method begins with a start step: step E0.

[0086] The method comprises Ph detection phases, which are continuously repeated. since the initial power-up of meter 1.

[0087] When a detection phase is completed, the processing unit 15 defines a random duration, and waits for a time equal to the random duration: step EL

[0088] This random duration is “drawn at random” after each detection phase.

[0089] This ensures that it is impossible for a potential fraudster to predict the start of the Ph detection phases. This prevents an attempt at fraud consisting of emitting a light signal similar to that emitted by LED 21.

[0090] Here, the random duration is limited between a minimum duration, equal for example to 5 seconds, and a maximum duration, equal for example to 5 minutes.

[0091] The values ​​of the random duration are here distributed uniformly, but another distribution, for example Gaussian or log-normal, is possible.

[0092] Following step El, the detection phase Ph starts.

[0093] The processing unit 15 lights the LED 21 which emits a detection light signal Sp The processing unit 15 acquires the first voltage Vi produced by the phototransistor 22 when the latter receives the first light detection signal Si: step E2.

[0094] Then, the processing unit 15 turns off the LED 21, and acquires the second voltage V2 produced by the phototransistor 22: step E3.

[0095] As we have seen, the order of the two steps E2 and E3 can be reversed.

[0096] The processing unit 15 detects the opening or closing of the housing 2 as a function of a value representative of a difference or a ratio between the first level of the first electrical signal (VJ) and the second level of the second electrical signal (V2).

[0097] Here, the processing unit 15 checks whether:

[0098] V! - V2 > Vseuii

[0099] where Vi is the first voltage, V2 is the second voltage, and Vseuii is a predetermined voltage threshold (for example equal to 0.4V): step E4.

[0100] If this is the case, the processing unit 15 deduces that the housing 2 is properly closed. detection phase ends and the process returns to step E1.

[0101] If V! - V2 < Vseuil

[0102] the processing unit 15 detects an opening of the housing 2.

[0103] The processing unit 15 confirms this result by a second measurement (i.e. repeats steps E2, E3 and E4): step E5.

[0104] The processing unit 15 checks whether or not the detection of the opening of the housing 2 is confirmed: step E6.

[0105] If the detection of the opening of the housing 2 is not confirmed, the detection phase ends and the method returns to step EL

[0106] Otherwise, the processing unit 15 records the information that the box 2 is open, produces an alarm message and transmits it to the fluid distributor and / or the network manager: step E7.

[0107] It is possible to reuse previous measurements by filtering out non-standard measurements and averaging in order to change the predetermined voltage threshold Vseuii. The predetermined voltage threshold Vseuii is therefore a dynamic threshold.

[0108] The predetermined voltage threshold Vseuii is for example defined from the history of previous measurements.

[0109] For example, we have:

[0110] Vthreshold = (Moy.V! - Moy_V2) / 2,

[0111] where Moy_Vi is the average of the values ​​of Vi between the first and third quartiles and Avg_V2 is the average of the V2 values ​​between the first and third quartiles.

[0112] Advantageously, one or more optical guides 30 are added to the housing 2 to keep the light beam concentrated and allow it to be fully reflected on the housing 2.

[0113] The counter 1 here comprises a first optical guide 30a positioned between the LED 21 and the internal wall 23, and arranged to guide and concentrate the light signals towards the internal wall 23. The counter 1 also comprises a second optical guide 30b positioned between the phototransistor 22 and the internal wall 23, and arranged to guide and concentrate the light signals towards the phototransistor 22.

[0114] The first optical guide 30a has a cylindrical shape whose axis Xa extends vertically relative to the card 3 from the LED 21. The axis Xa is perpendicular to the electrical card 3, to the upper face 10 of the second housing part 5 and to the upper face 8 of the first housing part 4.

[0115] The second optical guide 30b has a cylindrical shape whose axis Xb extends vertically relative to the card 3 from the phototransistor 22. The axis Xb is perpendicular to the electrical card 3, to the upper face 10 of the second housing part 5 and to the upper face 8 of the first housing part 4.

[0116] The first optical guide 30a and the second optical guide 30b extend vertically wedged and perpendicularly from the inner wall 31 of the upper face 10 of the second housing part 5.

[0117] Here, the first optical guide 30a and the second optical guide 30b are manufactured in a single piece.

[0118] It is noted that the counter 1 also comprises a guiding device, not shown, which makes it possible to direct the light beam from the exit of the first optical guide 30a towards the entrance of the second optical guide 30b.

[0119] The counter 1 also includes a cache device 32.

[0120] The cache device 32 comprises a first portion 32a and a second portion 32b.

[0121] The first portion 32a delimits an internal space 33 in which the receiver 22 (or at least its sensitive cell) is positioned. The first portion 32a makes it possible to prevent parasitic light signals, coming from inside or outside the housing 2, from disturbing the receiver 22.

[0122] The first portion 32a has a cylindrical shape and has as its axis an axis Xc, perpendicular to the electrical card 3, to the upper face 10 of the second housing part 5 and to the upper face 8 of the first housing part 4. The axis Xc here passes through a point located in the middle of the segment connecting the LED 21 and the phototransistor 22.

[0123] The first portion 32a extends vertically and perpendicularly from the internal wall 31 of the upper face 10 of the second housing part 5.

[0124] The free end of the first portion 32a is very close to the card 3 (or even in contact with it).

[0125] The cache device 32 also comprises a second portion 32b.

[0126] The second portion 32b is located between the transmitter 21 and the receiver 22. It makes it possible to prevent parasitic reflections, resulting from a reflection of the light signals emitted by the transmitter 21 on the first optical guide 30a or on the second optical guide 30b, or from lateral radiation coming from the transmitter 21, from disturbing the receiver 22.

[0127] The second portion 32b is a straight partition which extends vertically and perpendicularly from the electrical card 3. The height of this partition extends along the axis Xc, and is such that the top of the partition is positioned along the axis Xc close to (or even above) the free end of the optical guides 30a, 30b.

[0128] The transmitter 21 and the receiver 22 may be arranged to respectively transmit and receive light signals which are non-visible signals, i.e. which are produced by emitting light having a wavelength included in the non-visible spectrum.

[0129] This prevents a potential fraudster from noticing that the detection method is implemented in the meter 1, even if the housing 1 has a face transparent or translucent to visible light (like the second housing part 5) which could be crossed by light signals emitted by the LED 21.

[0130] Furthermore, it is possible to choose a light having a wavelength different from that of the lights normally present in the environment of the meter 1, to avoid disturbing the detection device 20. The light is thus, for example, an infrared light.

[0131] It is also possible to choose a light that is more difficult for a potential fraudster to reproduce, for example a blue light.

[0132] The counter 1 may also comprise a plurality of emitters 21, generating lights of different wavelengths, which are activated alternately to ensure that there is no reproduction of the source by a potential fraudster.

[0133] The inner wall 23 of the first housing part 4 may be designed to improve reflections.

[0134] The inner wall 23 may have a concave reflector shape.

[0135] The surface of the internal wall 23 is therefore adapted to create a concave reflector (during plastic injection, for example) which will concentrate the light rays from the LED 21 by reflecting them towards the phototransistor 22.

[0136] The internal wall 23 can be made of injected plastic with a mirror finish (surface condition) in order to best reflect the light signals emitted by the LED 21.

[0137] It is possible, during the manufacture of the first housing part 4, to chemically deposit a reflective material on the internal wall 23, for example by screen printing, ink spray or paint spray.

[0138] The first housing part 4 may comprise a self-adhesive and reflective label, stuck on the internal wall 23. The self-adhesive label is selected for its reflective power and its durability over time.

[0139] The internal wall 23 may have a color having a wavelength close to the light wavelength of the internal light source (for example green if the light source is green).

[0140] The internal wall 23 has for example a color having a wavelength XI such that:

[0141] M = X2±10%,

[0142] where / .2 is a wavelength of the light signals emitted by the emitter 21 (i.e., the light produced by the emitter 21).

[0143] The measurements can also be taken closer in time, without and with the light source (i.e. steps E2 and E3), so as not to be affected by the ambient lighting (50 or 60Hz) of the compact fluorescent tubes.

[0144] The invention has a large number of advantages.

[0145] It works both in the presence of resin or transparent gel in the meter 1, but also without resin or gel: as we have seen, unlike the devices comprising an electromechanical contact, the invention works efficiently even in the presence of resin or gel.

[0146] The electrical energy consumption of the detection device 20 is very low. The device 20 consumes little current because it is activated for a very short time and switched off for random and much longer periods. This makes it possible to limit the possible reliability drift of the optical components. The device 20 fits perfectly into battery-powered equipment (such as the meter 1).

[0147] The consumption of the device 20 (LED 21, phototransistor 22, CAN 18 and microcontroller 16) is approximately 0.5 mA average for 1 ms, or 0.5 pAsec. The duration of a Ph detection phase being at least 5 seconds, the consumption is 0.1 pAsec and therefore totally negligible.

[0148] The device 20 is very simple to implement and has a low cost. The components used (for example the LED 21 and the phototransistor 22) are standard components which do not need to be fast or sensitive.

[0149] The device 20 is easily adaptable and can be installed on existing products, without modification.

[0150] The device 20 is very sensitive. The device 20 is capable of detecting a very slight opening of the housing 2. It can even detect water infiltration between the housing 2 and the potting gel or between the first housing part 4 and the second housing part 5 due to the effect of the water on the light rays.

[0151] The device 20 is robust to electronic interference, making disruption by counterfeiters difficult, and making it possible to use it in complex electromagnetic environments.

[0152] The device 20 makes it possible to take all necessary measures, such as erasing keys, raising an alarm and / or transmitting this alarm to the monitoring network.

[0153] This solution is simple, energy-efficient, and can easily be adapted to the mechanical dimensions of all products.

[0154] The device 20 makes it possible to overcome fraud attempts. It is thus capable of thwarting openings of the product in a lit room or in absolute darkness.

[0155] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0156] The equipment in which the invention is implemented is not necessarily a fluid meter. It can be any type of meter and even, more generally, any type of equipment.

[0157] The emitter is not necessarily an LED, but could be any type of pho- transmitter, and for example a laser diode.

[0158] The receiver is not necessarily a phototransistor, but could be any type of photoreceptor, and for example a photodiode.

[0159] The electrical architecture presented could be different from that described here. For example, the transmitter and the receiver could be integrated into the same component, directly into a housing part, etc. All the electrical components are not necessarily mounted on the same board.

[0160] The housing may be different from that shown here. The second housing part is optional. The housing does not necessarily include a removable housing part (such as the first housing part), and the detection device could detect an opening of the housing consisting of breaking it.

[0161] If the housing does not include the second housing part, the transmitter and receiver may be positioned opposite and in proximity to the first housing part.

[0162] The detection is here carried out as a function of a value representative of a difference or a ratio between the first level of the first electrical signal and the second level of the second electrical signal. This value is therefore not necessarily equal to the difference between the first level of the first electrical signal and the second level of the second electrical signal. It could be for example a difference between the second level and the first level, or a ratio between the first level and the second level, or a ratio between the second level and the first level, etc.

Claims

Claims

1. Equipment (1) comprising a housing (2) in which are integrated: • a transmitter (21) arranged to emit light signals; • a receiver (22) arranged to receive the light signals after they have been reflected against an internal wall (23) of the housing; • a processing unit (15) arranged to: • control the transmitter (21) so that it emits a detection light signal (SI); • acquire a first electrical signal (Vi) produced by the receiver (22) when the latter receives the detection light signal; • detect, as a function of a first level of the first electrical signal, whether the housing (2) is open or closed.

2. Equipment according to claim 1, in which the processing unit (15) is arranged to: • acquire a second electrical signal (V2) produced by the receiver while the transmitter is switched off; • carry out the detection of the opening or closing of the housing as a function of a value representative of a difference or a ratio between the first level of the first electrical signal (VJ and a second level of the second electrical signal (V2).

3. Equipment according to one of the preceding claims, wherein the housing (2) comprises a first housing part (4), which is removable, the internal wall (23) being a wall of the first housing part, and wherein the transmitter and the receiver are both positioned: • opposite and close to the first housing part, or • opposite and close to a second housing part (5) of the housing, transparent or translucent to light signals, and positioned between the first housing part on the one hand, and the transmitter and the receiver on the other hand.

4. Equipment according to one of the preceding claims, further comprising: • a first optical guide (30a) positioned between the emitter (21) and the internal wall (23), and arranged to guide and concentrate the light signals towards the internal wall; • a second optical guide (30b) positioned between the receiver (22) and the internal wall, and arranged to guide and concentrate the light signals towards the receiver.

5. Equipment according to claim 4, wherein the first optical guide (30a) and the second optical guide (30b) are manufactured in a single piece.

6. Equipment according to one of the preceding claims, further comprising a hiding device (32) comprising a first portion (32a) delimiting an internal space in which the receiver (22) is positioned, and arranged to prevent parasitic light signals coming from inside or outside the housing (2) from disturbing the receiver.

7. Equipment according to claims 4 and 6, wherein the hiding device (32) also comprises a second portion (32b) located between the transmitter (21) and the receiver (22), and arranged to prevent parasitic reflections, resulting from a reflection of the light signals emitted by the transmitter (21) on the first optical guide (30a) or on the second optical guide (30b), or from lateral radiation coming from the transmitter (21), from disturbing the receiver (22).

8. Equipment according to one of the preceding claims, in which the internal wall (23) is made of injected plastic with a mirror finish.

9. Equipment according to one of the preceding claims, in which the internal wall (23) has a concave reflector shape.

10. Equipment according to one of the preceding claims, comprising a reflective material chemically deposited on the internal wall (23).

11. Equipment according to one of the preceding claims, comprising a self-adhesive and reflective label, stuck on the internal wall (23).

12. Equipment according to one of the preceding claims, in which the internal wall (23) has a color having a wavelength XI such that: XI = X2 ± 10%, where / .2 is a wavelength of light signals.

13. Equipment according to one of the preceding claims, the transmitter and the receiver being arranged to respectively transmit and receive light signals which are non-visible signals.

14. Equipment according to one of the preceding claims, the equipment being a fluid meter (1).

15. Detection method, implemented in the processing unit of equipment according to one of the preceding claims, and comprising a detection phase (Ph) comprising the steps of: • controlling the transmitter (21) so that it emits a detection light signal (SJ; • acquiring a first electrical signal (Vi) produced by the receiver when the latter receives the detection light signal; • detecting, as a function of a first level of the first electrical signal, whether the housing (2) is open or closed.

16. Detection method according to claim 15, implemented in the processing unit (15) of equipment according to claim 2, in which the detection phase further comprises the steps of: • acquiring a second electrical signal (V2) produced by the receiver while the transmitter is deactivated; • carrying out the detection of the opening or closing of the housing as a function of a value representative of a difference or a ratio between the first level of the first electrical signal (Vi) and a second level of the second electrical signal (V2).

17. Detection method according to one of claims 15 or 16, comprising the steps of: • repeating the detection phase; • when a detection phase is finished, defining a random duration, and starting a next detection phase after the random duration.

18. A computer program comprising instructions that conduct the processing unit of the electrical equipment according to claim 1 to perform the steps of the detection method according to claim 15.

19. A computer-readable recording medium on which the computer program according to claim 18 is recorded.

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