Optical detection of opening of a housing

Abstract

An apparatus (1) comprising a housing (2) in which there is incorporated a transmitter (21) emitting a light signal, a receiver (22) arranged to receive the light signal upon reflection of the light signal by an inner wall (23) of the housing (2), and a processing unit (15) arranged to: control the transmitter (21) such that it emits a detection light signal (S1); acquiring a first electrical signal (V1) generated by the receiver (22) when it receives the detection light signal; whether the housing (2) is open or closed is detected based on a first level of the first electrical signal.

Description

Technical Field

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

[0002] Some people with bad intentions know some techniques that allow them to open the casing of their meters and tamper with them to reduce the metering of their consumption. This can affect any type of meter, such as electricity meters, water meters, gas meters, etc.

[0003] A number of devices for detecting opening of a meter housing are known.

[0004] For water and gas meters, the detection equipment must consume very little power because these meters are usually powered by batteries.

[0005] Conventionally used detection devices include electromechanical contacts that change state when the housing is opened. However, water and gas meters are often filled with a gel at the end of the manufacturing process. When it polymerizes, this gel tends to block the electromechanical contacts, rendering the detection device inoperable.

[0006] The object of the invention is to effectively detect the opening of a housing of an equipment without the use of electromechanical contacts and with very low consumption of electrical energy. Summary of the invention

[0007] To achieve this goal, a device is proposed, which comprises a housing in which the following components are incorporated:

[0008] a transmitter arranged to transmit an optical signal;

[0009] a receiver arranged to receive the optical signals after they are reflected by an inner wall of the housing;

[0010] A processor unit, the processing unit being arranged to:

[0011] controlling the emitter so that it emits a detection light signal;

[0012] Acquiring a first electrical signal generated by the receiver when the receiver receives the detection light signal;

[0013] Whether the housing is opened or closed is detected based on the first level of the first electrical signal.

[0014] Detection by emission, internal reflection and capture of detection light signals is efficient, simple and cheap to implement. The invention works even when the housing is filled with gel. The components used consume very little electrical energy.

[0015] It is also proposed an apparatus as described above, wherein the processing unit is arranged to:

[0016] acquiring a second electrical signal generated by the receiver when the transmitter is turned off;

[0017] The opening or closing of the housing is detected based on a value representing a difference or a ratio between a first level of the first electrical signal and a second level of the second electrical signal.

[0018] It is also proposed an apparatus as described above, wherein the housing comprises a removable first housing part, the inner wall is a wall of the first housing part, and wherein the transmitter and the receiver are both located:

[0019] Opposite to and adjacent to the first housing portion; or

[0020] Opposite and adjacent to a second housing portion of the housing, the second housing portion is transparent or translucent to the optical signal and is located between the first housing portion and the transmitter and the receiver.

[0021] It is also proposed that the apparatus as described above further comprises:

[0022] a first light guide located between the emitter and the inner wall and arranged to direct and focus the optical signal to the inner wall;

[0023] A second light guide is located between the receiver and the inner wall and is arranged to guide and focus the optical signal to the receiver.

[0024] It is also proposed an arrangement as described above, wherein the first light guide and the second light guide are manufactured as a single component.

[0025] It is also proposed an apparatus as described above, further comprising a masking device comprising a first part defining an internal space in which the receiver is located and arranged to prevent stray light signals originating from inside or outside the housing from interfering with the receiver.

[0026] An apparatus as described above is also proposed, wherein the masking device also includes a second part, which is located between the transmitter and the receiver and is arranged to prevent stray reflections caused by reflection of the optical signal emitted by the transmitter on the first optical waveguide or the second optical waveguide or by lateral radiation originating from the transmitter from interfering with the receiver.

[0027] It is also proposed an arrangement as described above, wherein the inner wall is made of injection moulded plastic with a mirror finish.

[0028] It is also proposed an arrangement as described above, wherein the inner wall has the shape of a concave reflector.

[0029] It is also proposed an arrangement as described above, comprising a reflective material chemically deposited on the inner wall.

[0030] It is also proposed that a device as described above comprises a self-adhesive reflective label attached to the inner wall. It is also proposed that a device as described above wherein the color of the inner wall has a wavelength λ1 such that:

[0031] λ1=λ2±10%,

[0032] Where λ2 is the wavelength of the optical signal.

[0033] It is also proposed that an arrangement as described above, the transmitter and the receiver are arranged to transmit and receive, respectively, a light signal as the invisible signal.

[0034] It is also proposed that the device as described above is a fluid meter.

[0035] A detection method is also proposed, implemented in the processing unit of the device as described above, and comprising a detection phase, the detection phase comprising the following steps:

[0036] controlling the emitter so that it emits a detection light signal;

[0037] Acquiring a first electrical signal generated by the receiver when the receiver receives the detection light signal;

[0038] Whether the housing is opened or closed is detected based on the first level of the first electrical signal.

[0039] A detection method as described above is also proposed, implemented in the processing unit of the device as described above, wherein the detection stage further comprises the following steps:

[0040] acquiring a second electrical signal generated by the receiver when the transmitter is deactivated;

[0041] The opening or closing of the housing is detected based on a value representing a difference or a ratio between a first level of the first electrical signal and a second level of the second electrical signal.

[0042] A detection method as described above is also proposed, comprising the following steps:

[0043] Repeat this detection phase;

[0044] When a detection phase is completed, a random time period is defined, and a subsequent detection phase is started after the random time period.

[0045] A computer program is also provided, comprising instructions for causing a processing unit of the electrical equipment as described above to execute the steps of the detection method as described above.

[0046] A computer-readable storage medium is also proposed, on which the computer program as described above is stored.

[0047] The present invention will best be understood from the following description of specific non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Reference will be made to the accompanying drawings, in which:

[0049] [ Figure 1 ] Figure 1 A simplified cross-sectional view of the flow meter along a vertical plane is shown.

[0050] [ Figure 2 ] Figure 2 The steps of the detection method are shown. DETAILED DESCRIPTION

[0051] refer to Figure 1 , a flow meter 1 (for example a water meter or a gas meter) is intended to measure the consumption of a fluid by a user (customer) installation. The fluid is supplied to the installation via a distribution network.

[0052] The meter 1 includes a housing 2 and a printed circuit board 3 .

[0053] In this case, the housing 2 comprises a first housing part 4 , a second housing part 5 and a frame 6 .

[0054] The frame 6 includes a bottom surface 7 , which is also the bottom surface of the housing 2 .

[0055] The first housing part 4 comprises a top surface 8, a first side surface 9a and a second side surface 9b, the top surface 8 also being the top surface of the housing 2. The first housing part 4 is removable. It can be removed by an operator working, for example, for a manager of a fluid dispenser or a distribution network. The first housing part 4 is opaque to visible light (as is the frame 6).

[0056] The second housing part 5 is transparent or translucent to visible light. It is assembled in the housing 2, that is, between the first housing part 4 and the interior of the meter 1. It includes a top surface 10, a first side surface 11a and a second side surface 11b, which are parallel to, opposite to and near the top surface 8, the first side surface 9a and the second side surface 9b of the first housing part 4, respectively.

[0057] The top surface 8 of the first housing part 4 comprises an aperture 14. Thus, light from the outside can enter the interior of the meter 1 via the aperture 14 and the second housing part 5.

[0058] The printed circuit board 3 of the meter 1 is positioned parallel to and adjacent to the top surface 10 of the second housing portion 5 (and thus parallel to the top surface 8 of the first housing portion 4 ).

[0059] The printed circuit board 3 firstly comprises a processing unit 15 .

[0060] The processing unit 15 includes at least one processing component 16, which is, for example, a "general purpose" processor, a processor dedicated to signal processing (or a digital signal processor (DSP)), a microcontroller, or a programmable logic circuit (such as an FPGA (or field programmable gate array) or an ASIC (or application specific integrated circuit). In this example, the processing component 16 is a microcontroller.

[0061] The processor unit 15 further comprises one or more memories 17 connected to the microcontroller 16 or integrated into the microcontroller 16. At least one of these memories 17 forms a computer-readable storage medium on which is stored at least one computer program comprising instructions for causing the microcontroller 16 to perform at least some of the steps of the detection method described below.

[0062] The processing unit 15 also comprises an analog-to-digital converter (ADC) 18 , which may (but need not) be integrated into the microcontroller 17 .

[0063] The printed circuit board 3 further comprises an LCD screen 19 which is positioned facing the aperture 14 so that a user can see the screen 19 through the aperture 14 and the second housing part 5 .

[0064] The meter 1 also comprises a detection device 20 for detecting the opening of the housing 1 .

[0065] In this example, the detection device 20 comprises a processing unit 15, and in particular a microcontroller 16 and an ADC 18. This does not prevent the processing unit 16 from having functions in addition thereto, such as a metering (fluid consumption metering) function.

[0066] The detection device 20 further includes a transmitter 21 and a receiver 22 mounted to the printed circuit board 3 .

[0067] The transmitter 21 is arranged to transmit light signals and the receiver 22 is arranged to receive these light signals after they have been reflected by an inner wall 23 of the housing 1 . “Inside” is understood to mean inside the meter 1 .

[0068] The inner wall 23 is the inner wall of the top surface 8 of the first housing part 4. Therefore, the optical signal emitted by the transmitter 21 passes through the second housing part 5, is reflected by the inner wall 23, and is then captured by the receiver 22.

[0069] The transmitter 21 is a light emitting diode (LED) in this example, and the receiver 22 is a phototransistor in this example.

[0070] In this example, both the LED 21 and the phototransistor 22 are positioned opposite and adjacent to the top surface 10 of the second housing portion 5 of the housing 2 , so that the second housing portion 5 itself is positioned between the first housing portion 4 and the LED 21 and the phototransistor 22 .

[0071] That portion of the top surface 10 of the second housing part 5 which is opposite to the light emitting diode 21 and the phototransistor 22 is itself positioned opposite to the portion of the first housing part 4 which is a “solid” portion (rather than opposite to the aperture 14 ).

[0072] In this example, the LED 21 and the phototransistor 22 are spaced 5 mm apart from each other and are at a distance of 1 cm from the inner wall 23 of the first housing part 4 .

[0073] First, the principle of the invention is explained. It is intended to detect whether the housing 2 is open or closed, and therefore, in this example, more specifically, whether the first housing part 4 has been opened (i.e., whether at least one end thereof has been removed from the rest of the housing 2).

[0074] This detection is based on measuring the optical reflection of a light signal emitted by the LED 21 and subsequently reflected on the inner wall 23 of the housing 2 and finally captured by the phototransistor 22 .

[0075] If the first housing part 4 is missing or has been separated, the optical reflection is limited, resulting in a drop in the signal level in the phototransistor 22. This drop can be detected.

[0076] Therefore, the processing unit 15 is arranged to:

[0077] controlling the LED 21 (i.e., turning it on) so that it emits a detection light signal S1;

[0078] When the LED 21 is turned on, a first electrical signal generated by the phototransistor 22 when it receives the detection light signal S1 is acquired;

[0079] Detecting whether the housing (2) is open or closed based on the first level of the first electrical signal;

[0080] Turn off LED 21 (this step may be performed before the previous step).

[0081] It should be noted that in this example, the emission of the detection light signal S1 merely comprises switching on the LED 21. The reception of the detection light signal S1 is the capture by the phototransistor 22 of the light flux emitted by the LED 21 and reflected by the inner wall 23 (and by other walls of the housing 2 if applicable).

[0082] In this example, the first electrical signal is a first voltage V1 generated by the phototransistor 22. The first level is the magnitude of the first voltage V1.

[0083] The first voltage V1 is an analog voltage.

[0084] The first voltage V1 is digitized by the ADC 18 to generate a digital signal.

[0085] This configuration is not mandatory; the receiver can in particular be a "digital" sensor.

[0086] The microcontroller 16 detects whether the housing 2 is open or closed based on the first voltage V1.

[0087] To improve detection performance, the light energy is measured when the LED 21 is turned on (as just described) and then the light energy is measured when the LED 21 is not turned on.

[0088] The order in which the two measurements are taken does not matter.

[0089] Therefore, the processing unit 15 obtains the second electrical signal generated by the phototransistor 22 when the LED 21 is turned off (i.e., it is not emitting light), and detects the opening or closing of the shell 2 based not only on the first level of the first electrical signal (the amplitude of the first voltage V1), but also on the difference or ratio between the first level and the second level of the second electrical signal.

[0090] The second electrical signal is a second voltage V2 generated by the phototransistor 22. The second level is the amplitude of the second voltage V2.

[0091] The second voltage V2 is an analog voltage, which is digitized by the ADC 18 .

[0092] Therefore, analyzing the difference in illumination at the receiver 22 and the electrical signals (the first voltage V1 and the second voltage V2) generated by it makes it possible to eliminate interference that would be generated by:

[0093] light from an “analog” LED 21 on the outside of the meter 1;

[0094] Light from outside the meter 1 saturates the phototransistor 22 .

[0095] In a nominal situation, with the housing 2 closed, the difference in brightness measured by the phototransistor 22 with the LED 21 turned on and with the LED 21 not turned on is high. In fact, a large part of the luminous flux emitted by the LED 21 is captured by the phototransistor 22.

[0096] However, if the housing 2 is open, the luminous flux is not reflected by the inner wall 23 (which has been removed) of the first housing part 4. Therefore, the difference between the two measurements is obviously smaller. Of course, if the housing 2 is not completely open and if the first housing part 4 is still present (partially open), the luminous flux is still partially reflected by the inner wall 23, but to a lesser extent, which means that this partial opening can also be detected.

[0097] The invention works very effectively regardless of the ambient light outside the meter 1:

[0098] Ambient light is present, and the difference between the two measurements decreases because the phototransistor 22 is illuminated by the ambient light;

[0099] Or there is no ambient light and the reflection on the now removed first housing part 4 is absent or reduced, which reduces the difference between the two measurements.

[0100] Reference now Figure 2 The detection method implemented by the processing unit 15 is described in more detail.

[0101] The method begins with a start step: step E0.

[0102] The method comprises a detection phase Ph which is continuously repeated from the time the meter 1 is initially powered on.

[0103] When a detection phase is completed, the processing unit 15 defines a random time period and waits for a time equal to the random time period: step E1.

[0104] This random time period is “randomly drawn” after each detection phase.

[0105] This ensures that it is impossible for a potential fraudster to predict the start of the detection phase Ph. In this way, attempts to deceive the system by emitting a light signal similar to that emitted by the LED 21 are prevented.

[0106] In this example, the random time period is constrained between a minimum time period (e.g., equal to 5 seconds) and a maximum time period (e.g., equal to 5 minutes).

[0107] In this example, the values ​​of the random time segments are distributed in a uniform manner, but another distribution (eg Gaussian or log-normal) is also possible.

[0108] After step E1 , the detection phase Ph begins.

[0109] The processing unit 15 turns on the LED 21, and the LED 21 emits the detection light signal S1. The processing unit 15 obtains the first voltage V1 generated by the phototransistor 22 when it receives the first detection light signal S1: step E2.

[0110] Next, the processing unit 15 turns off the LED 21 and obtains the second voltage V2 generated by the phototransistor 22: step E3.

[0111] As mentioned above, the order of the two steps E2 and E3 can be exchanged.

[0112] The processing unit 15 detects the opening or closing of the housing 2 based on a value representing a difference or a ratio between a first level of the first electrical signal ( V1 ) and a second level of the second electrical signal ( V2 ).

[0113] In this example, the processing unit 15 checks whether the following is true:

[0114] V1-V2>V 阈值

[0115] Where V1 is the first voltage, V2 is the second voltage, V 阈值 is a predetermined voltage threshold (eg equal to 0.4 V): step E4.

[0116] If this is the case, the processing unit 15 concludes that the housing 2 is indeed closed. The detection phase ends and the method returns to step E1.

[0117] If V1-V2≤V 阈值

[0118] The processing unit 15 then detects that the housing 2 is opened.

[0119] The processing unit 15 confirms this result by taking a second measurement (ie it repeats steps E2 , E3 and E4 ): step E5 .

[0120] The processing unit 15 checks whether the detection of the opening of the housing 2 is confirmed: step E6.

[0121] If the detection of the opening of the housing 2 is not confirmed, the detection phase ends and the method returns to step E1 .

[0122] Otherwise, the processing unit 15 records the opening of the housing 2 , generates an alarm message and transmits it to the fluid dispenser and / or the network manager: step E7 .

[0123] Previous measurements can be reused by filtering out non-standard measurements and averaging to change the predetermined voltage threshold V 阈值Therefore, the predetermined voltage threshold V 阈值 is the dynamic threshold.

[0124] For example, a predetermined voltage threshold V is defined based on the history of previous measurements. 阈值 .

[0125] For example:

[0126] V 阈值 =(Moy_V1-Moy_V2) / 2,

[0127] where Moy_V1 is the average of the V1 values ​​of the first and third quartiles, and Moy_V2 is the average of the V2 values ​​of the first and third quartiles.

[0128] Advantageously, one or more light guides 30 are added in the housing 2 to keep the light beam focused and allow its overall reflection on the housing 2 .

[0129] In this example, the meter 1 includes a first light guide 30a, which is positioned between the LED 21 and the inner wall 23 and is arranged to guide and focus the light signal to the inner wall 23. The meter 1 also includes a second light guide 30b, which is positioned between the phototransistor 22 and the inner wall 23 and is arranged to guide and focus the light signal to the phototransistor 22.

[0130] The first light guide 30a is in the form of a cylinder, with its axis X a Extends vertically from the LED 21 relative to the board 3. Axis X a Perpendicular to the printed circuit board 3 , the top surface 10 of the second housing part 5 and the top surface 8 of the first housing part 4 .

[0131] The second light guide 30b is in the form of a cylinder, with its axis X b The axis X extends vertically from the phototransistor 22 relative to the plate 3. b Perpendicular to the printed circuit board 3 , the top surface 10 of the second housing part 5 and the top surface 8 of the first housing part 4 .

[0132] The first light guide 30 a and the second light guide 30 b extend vertically and perpendicularly from the inner wall 31 of the top surface 10 of the second housing portion 5 .

[0133] In this example, the first light guide 30a and the second light guide 30b are manufactured as a single component.

[0134] It should be noted that the meter 1 also comprises a guiding device (not shown) which guides the light beam from the outlet of the first light guide 30a to the inlet of the second light guide 30b.

[0135] The meter 1 also comprises a masking device 32 .

[0136] The masking device 32 comprises a first part 32a and a second part 32b.

[0137] The first portion 32a defines an interior space 33 in which the receiver 22 (or at least a sensitive unit thereof) is positioned. The first portion 32a prevents stray light signals from inside or outside the housing 2 from interfering with the receiver 22.

[0138] The first portion 32 a is in the form of a cylinder and has an axis X perpendicular to the printed circuit board 3 , the top surface 10 of the second housing portion 5 and the top surface 8 of the first housing portion 4 . c In this example, the axis X c Passing through a point located in the middle of the segment connecting the LED 21 and the phototransistor 22 .

[0139] The first portion 32 a extends vertically and perpendicularly from the inner wall 31 of the top surface 10 of the second housing portion 5 .

[0140] The free end of the first portion 32 a is very close to (or even in contact with) the printed circuit board 3 .

[0141] The masking device 32 further comprises a second portion 32b.

[0142] The second portion 32b is located between the transmitter 21 and the receiver 22. It prevents the reflection of the optical signal emitted by the transmitter 21 on the first light guide 30a or the second light guide 30b or the stray reflection caused by the lateral radiation originating from the transmitter 21 from interfering with the receiver 22.

[0143] The second portion 32b is a straight spacer extending vertically and perpendicularly from the printed circuit board 3. The height of the spacer is along the axis X. c Extends so that the top of the partition is along the axis X c Positioned close to (or even above) the free ends of the light guides 30a, 30b.

[0144] The transmitter 21 and the receiver 22 may be arranged to transmit and receive, respectively, an optical signal as an invisible signal, ie an optical signal generated by transmitting light having a wavelength in the invisible spectrum.

[0145] This prevents a potential fraudster from seeing that the detection method is implemented in the meter 1 , even if the housing 1 comprises a face (such as the second housing part 5 ) which is transparent or translucent to visible light, through which the light signal emitted by the LED 21 can pass.

[0146] Furthermore, the light may be chosen to have a wavelength different from the light normally present in the vicinity of the meter 1 so as not to interfere with the detection device 20. Thus, the light is, for example, infrared light.

[0147] It is also possible to choose a light that is more difficult for potential fraudsters to reproduce, such as blue light.

[0148] The meter 1 may also comprise a plurality of emitters 21 generating light of different wavelengths, which emitters 21 are activated alternately to ensure that the source cannot be reproduced by a potential fraudster.

[0149] The inner wall 23 of the first housing part 4 can be designed to improve reflection.

[0150] The inner wall 23 may be shaped like a concave reflector.

[0151] Therefore, the surface of the inner wall 23 is adapted to fit therein (for example during plastic injection molding) a concave reflector which concentrates the light rays coming from the LED 21 and reflects them to the phototransistor 22 .

[0152] The inner wall 23 may be made of an injection-molded plastic with a mirror finish (surface state) in order to reflect the light signal emitted by the LED 21 as effectively as possible.

[0153] It is possible to chemically deposit the reflective material on the inner wall 23 while manufacturing the first housing part 4 , for example by screen printing, inkjetting or painting.

[0154] The first housing portion 4 may include a self-adhesive reflective label affixed to the inner wall 23. The self-adhesive label is chosen for its reflective properties and durability.

[0155] The color of the inner wall 23 may have a wavelength close to the wavelength of light of the internal light source (eg, green in the case where the light source is green).

[0156] For example, the color of the inner wall 23 has a wavelength λ1 such that:

[0157] λ1=λ2±10%,

[0158] Where λ2 is the wavelength of the optical signal transmitted by the transmitter 21 (ie, the light generated by the transmitter 21).

[0159] The measurements without and with light (ie steps E2 and E3) can also be performed closer in time to avoid being affected by the ambient lighting (50 or 60 Hz) of the compact fluorescent tubes.

[0160] The present invention provides many advantages.

[0161] It works both when there is a transparent resin or gel in the meter 1 and when there is no transparent resin or gel: as described above, unlike the device comprising electromechanical contacts, the present invention works effectively even when a resin or gel is present.

[0162] The detection device 20 consumes very little electrical energy. The device 20 consumes very little current because it is activated for very short periods of time and turned off for much longer random periods of time. This limits the possible degradation of the reliability of the optical components. The device 20 is ideally suited for battery-powered equipment (e.g., meter 1).

[0163] The power consumption of the device 20 (LED 21, phototransistor 22, ADC 18 and microcontroller 16) is about 0.5 mA on average for 1 ms, ie 0.5 μA second. Since the duration of the detection phase Ph is at least 5 seconds, the power consumption is 0.1 μA second and is therefore completely negligible.

[0164] The device 20 is very simple and cheap to implement. The components used (eg LED 21 and phototransistor 22) are standard components which do not need to be high speed or sensitive.

[0165] The device 20 is easily adaptable and can be installed on existing products without modification.

[0166] The device 20 is very sensitive. The device 20 is able to detect the smallest opening of the housing 2. It can even detect water penetration between the housing 2 and the potting compound or between the first housing part 4 and the second housing part 5 due to the influence of water on the light.

[0167] The device 20 is robust to electronic interference, making it difficult for fraudsters to interfere with it, and enabling its use in complex electromagnetic environments.

[0168] The device 20 allows taking all necessary measures, such as deleting the key, sounding an alarm and / or transmitting the alarm to a monitoring network.

[0169] It is a simple, low-energy solution that can be easily adapted to the mechanical dimensions of all products.

[0170] The device 20 helps to overcome fraud attempts. Thus, it is able to thwart attempts to open the product in a brightly lit room or in complete darkness.

[0171] Naturally, the invention is not limited to the embodiments described but covers any variant coming within the ambit of the invention as defined by the claims.

[0172] The equipment implementing the present invention is not necessarily a flow meter. It can be any type of instrument, and even more generally any type of equipment.

[0173] The emitter does not have to be an LED, but can be any type of photoelectric emitter, such as a laser diode.

[0174] The receiver does not have to be a phototransistor, but can be any type of photoreceiver, such as a photodiode.

[0175] The electrical architecture used can differ from that described in this article. For example, the transmitter and receiver can be integrated into the same component, directly into the housing part, etc. Not all electrical components have to be mounted on the same board.

[0176] The housing may be different from that described herein. The second housing portion is optional. In addition, the housing does not necessarily include a removable housing portion (such as the first housing portion), and the detection device can detect that the housing has been opened by destroying the housing.

[0177] If the housing does not include a second housing portion, the transmitter and receiver may be positioned opposite and adjacent to the first housing portion.

[0178] In this example, detection is performed based on a value representing the difference or ratio between a first level of the first electrical signal and a second level of the second electrical signal. Therefore, the value is not necessarily equal to the difference between the first level of the first electrical signal and the second level of the second electrical signal. For example, it can be the difference between the second level and the first level, or the ratio between the first level and the second level, or the ratio between the second level and the first level, etc.

Claims

1. A device (1), comprising a housing (2), wherein the housing (2) contains the following components: a transmitter (21) arranged to transmit an optical signal; a receiver (22) arranged to receive the light signal after the light signal is reflected by an inner wall (23) of the housing; A processing unit (15), the processing unit (15) being arranged to: Controlling the emitter (21) so that it emits a detection light signal (S1); Acquiring a first electrical signal (V1) generated by the receiver (22) when the receiver (22) receives the detection light signal; detecting whether the housing (2) is open or closed based on the first level of the first electrical signal, The processing unit (15) is further arranged to: acquiring a second electrical signal (V2) generated by the receiver when the transmitter is turned off; The opening or closing of the housing is detected based on a value representing a difference or a ratio between a first level of the first electrical signal (V1) and a second level of the second electrical signal (V2).

2. The device according to claim 1, wherein the housing (2) comprises a removable first housing part (4), the inner wall (23) being a wall of the first housing part, and wherein the transmitter and the receiver are both located: Opposite to and adjacent to the first housing portion; or Opposite and adjacent to the second housing part (5) of the housing, the second housing part is transparent or translucent to the optical signal and is located between the first housing part and the transmitter and the receiver.

3. The apparatus according to any one of the preceding claims, further comprising: a first light guide (30a) located between the emitter (21) and the inner wall (23) and arranged to guide and focus the optical signal to the inner wall; A second light guide (30b) is located between the receiver (22) and the inner wall and is arranged to guide and focus the optical signal to the receiver.

4. The apparatus according to claim 3, wherein the first light guide (30a) and the second light guide (30b) are made as a single component.

5. The equipment according to any of the preceding claims, further comprises a masking device (32), the masking device (32) comprising a first part (32a), the first part (32a) defining an internal space in which the receiver (22) is located and arranged to prevent stray light signals originating from inside or outside the housing (2) from interfering with the receiver.

6. Equipment according to claims 3 and 5, wherein the masking device (32) also includes a second part (32b), which is located between the transmitter (21) and the receiver (22) and is arranged to prevent stray reflections caused by reflection of the optical signal emitted by the transmitter (21) on the first optical guide (30a) or the second optical guide (30b) or by lateral radiation originating from the transmitter (21) from interfering with the receiver (22).

7. An arrangement according to any one of the preceding claims, wherein the inner wall (23) is made of injection moulded plastic with a mirror finish.

8. The apparatus according to any one of the preceding claims, wherein the inner wall (23) has the shape of a concave reflector.

9. A device according to any one of the preceding claims, comprising a reflective material chemically deposited on the inner wall (23).

10. A kit according to any one of the preceding claims, comprising a self-adhesive reflective label affixed to the inner wall (23).

11. The device according to any of the preceding claims, wherein the color of the inner wall (23) has a wavelength λ1 such that: λ1=λ2±10%, Where λ2 is the wavelength of the optical signal.

12. Apparatus according to any preceding claim, the transmitter and the receiver being arranged to transmit and receive, respectively, an optical signal as an invisible signal.

13. Equipment according to any of the preceding claims, which is a flow meter (1).

14. A detection method implemented in the processing unit of the device according to any one of the preceding claims and comprising a detection phase (Ph) comprising the following steps: Controlling the emitter (21) so that it emits a detection light signal (S1); Acquiring a first electrical signal (V1) generated by the receiver when the receiver receives the detection light signal; Whether the housing (2) is open or closed is detected based on the first level of the first electrical signal.

15. The detection method according to claim 14, wherein the detection stage further comprises the following steps: acquiring a second electrical signal (V2) generated by the receiver when the transmitter is deactivated; The opening or closing of the housing is detected based on a value representing a difference or a ratio between a first level of the first electrical signal (V1) and a second level of the second electrical signal (V2).

16. The detection method according to any one of claims 14 or 15, comprising the following steps: repeating the detection phase; When a detection phase is completed, a random time period is defined, and a subsequent detection phase is started after the random time period. 17 . A computer-readable storage medium storing a computer program including instructions for causing the processing unit of the electrical equipment according to claim 1 to execute the steps of the detection method according to claim 14 .

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