EP1718959A1

EP1718959A1 - Condensate detector and method for detecting condensate on a surface

Info

Publication number: EP1718959A1
Application number: EP05716705A
Authority: EP
Inventors: Adriana Bernardi
Original assignee: Consiglio Nazionale delle Richerche CNR
Current assignee: Consiglio Nazionale delle Richerche CNR
Priority date: 2004-02-16
Filing date: 2005-02-16
Publication date: 2006-11-08
Also published as: WO2005078421A1; ITMI20040249A1

Abstract

A condensate detector capable of detecting the condensate eventually present on a surface to be monitored (SM) comprises: - emission means (1, 2) for emitting a first light beam onto a surface to be monitored (SM) and a second light beam onto a calibration surface (ST); - receiving means (3, 4) for supplying a first output signal (SEI) depending on the lighting radiation reflected from the surface to be monitored (SM) as a function of the condensate present onto the same, and a second output signal (SE2) depending on lighting radiation reflected from the calibration surface (ST); and - condensate control means (5) capable of maintaining the condensate present onto the calibration surface (ST) at a certain predetermined level. The invention also concerns a method for detecting the condensate eventually present onto a surface to be monitored (SM).

Description

CONDENSATE DETECTOR AND METHOD FOR DETECTING CONDENSATE ON ASURFACE

Field of the invention

The present invention concerns a condensate detector and a method for detecting the condensate on a surface. State of the art

Different types of devices for detecting the presence or absence of a condensate on a surface to be monitored -whether be an aqueous or other substances condensate- are currently known. The article by Dario Camuffo and Sergio Valcher "A Dew Point Signaller for Conservation of Works of Art", Environmental Monitoring and Assessment 6, 1986, pages 165-170, describes a device for detecting the presence of condensate onto appropriate control surfaces, for the monitoring of art works such as paintings, frescoes, sculptures, and historical buildings. In such a device, a LED (Light Emitting Diode) emits a beam of infrared light toward a mirror surface applied onto the art work to be monitored, and a photodarlington is used to measure the intensity of infrared radiation re-emitted by the mirror surface, which varies as a function of the level of fogging of the mirror itself. This device proved to be poorly reliable, and the measurements obtained by the same have turned out to be notably imprecise and appreciably perturbed by a number of undesirable environmental factors, such as variations of room temperature and light over the measuring period, and the deposition of polluting particles on the mirror surface. The object of the invention is to provide an improved condensate detector with respect to the already known detector above described, and particularly with reference to imprecise measurements due to the varying of the room temperature or light. Brief description of the invention This object is achieved, according to a first aspect of the present invention, by a condensate detector capable of detecting the condensate eventually present on a surface to be monitored, said detector comprising: - light emission means for emitting at least a first beam of light onto a surface to be monitored;

- receiving means, capable of supplying at least a first output signal which depends on the light radiation coming from the surface to be monitored when the same is hit by the light beam, and depending on the condensate present on the surface to be monitored; the condensate detector is characterized in that the light emission means are capable of emitting at least a second beam of light onto a calibration surface, and in that the receiving means are capable of supplying a second output signal depending on the lighting radiation coming from the calibration surface when the same is hit by the second light beam, and further characterized in that it comprises condensate controlling means capable of maintaining the condensate present on the calibration surface at a preset level. According to a second aspect of the invention, this object is achieved by a method for detecting a condensate eventually present onto a surface to be monitored, comprising the following operations:

- projecting a first light beam onto the surface to be monitored, so that at least a part of said first light beam is reflected and/or diffused by the surface to be monitored; - detecting the reflected and/or diffused part of the first light beam and converting the same in to a first output signal; the method is characterized in that it comprises the following operations:

- projecting a second light beam onto a calibration surface, so that at least a part of said second light beam is reflected and/or diffused by the calibration surface, and

- detecting the reflected and/or diffused part of said second light beam, and converting the same into a second output signal; wherein the condensate on the calibration surface is maintained at a predetermined level.

By comparing -or by processing- the abovementioned first and second signals, it is possible to clean up the variations of the first signal coming from the receiving means and due to factors other than the variations of the fogging of the surface to be monitored, therefore obtaining considerably more precise, reliable and repeatable measurements.

According to a third aspect of the present invention, this object is achieved with a computer program which can be downloaded to the internal memory of a digital processor or other logical circuit, where such a program comprises parts of program codes enabling a detector as previously defined to perform the operations of a method as previously defined, when the program is run by the abovementioned processor or another logical circuit.

Further advantages achievable with the present invention will become more evident to an expert of the branch of the art, from the following detailed description of a particular embodiment, given as a non-limiting example, as well as certain particular embodiments of the same, and making reference to the following figures.

List of the Figures Figure 1 schematically illustrates, in a prospective view, the arrangement of the two optical emitters and receivers according to a particular embodiment of a condensate detector of to the present invention;

Figure 2 schematically illustrates, in a side view, the arrangement of the two optical emitters and receivers of the condensate detector of Figure 1 ; Figure 3 illustrates a schematic top view, along a sectional plane parallel to the surface to be measured, of the condensate detector of Figure 1 ;

Figure 4 illustrates a schematic view along the sectional plane A-A of the condensate detector of Figure 1 ; and

Figure 5 schematically illustrates a part of the electrical and logical circuit for the acquisition of the signals of the optical receivers of the condensate detector of

Figure 1.

Detailed description

The attached Figures are related to an example of a particular embodiment of a condensate detector according to a first aspect of the present invention. Such a detector comprises means of emission which are in turn, in the present example of embodiment, comprising a first optical emitter 1 and a second optical emitter 2; the first optical emitter 1 , which if fitted with a light emitting diode (LED) 100 (Figure 5), is capable of projecting a first beam of light L1 (Figure 1 ) against a first part SM of a surface S - such as for instance a reflecting or poorly reflecting glass surface, or a stone surface, on which the level of deposited condensate is to be monitored; said first part of the surface SM is in the following indicated as "surface to be monitored"; the second optical emitter, which is fitted with a similar light emitting diode 200 (Figure 5), is capable of projecting a second beam of light L2 (Figure 1) against a second part ST of the surface S, whose fogging level is to be monitored. This second surface part is in the following indicated as "calibration surface". The condensate detector according to a first aspect of the invention is also fitted with receiving means capable of receiving the first and second beam of light L1 , L2 and of supplying a first signal depending on the lighting radiation coming from the surface to be monitored SM when the same is hit by the first beam of light L1 , and second signal depending on the lighting radiation coming from the calibration surface ST when the same is hit by the second light beam L2; in the present example of embodiment, the means of reception comprise a pair of photo- receivers 3, 4 (Figures 1 , 5), each of which is preferably fitted - as will be more evident in the following - with a photo-transistor 300, 400.

The intensity of the light beam reflected by the surface SM also depends on the fogging level of the surface itself: the Applicant holds that the reduced light intensity of the radiation received by the photo-transistors 300 and due to the fogging of the surface SM is caused by a diffusion phenomenon, instead of by absorption, as stated in the abovementioned article of Dario Camuffo and Sergio Valcher; moreover, the Applicant has observed that the frequency band of the beam L1, which best highlights the variations of the condensate present on a surface SM, in case of an aqueous condensate, is the infrared light band between about 800 and about 1,000 nanometers, but failed to notice any particular advantages when using a source of infrared beams for instance in a band of 1.400 - 1 ,500 nanometers, corresponding to a few of the absorption peaks of water. The frequency band of the means of emission 1 , 2 and of the means of reception 3, 4 is preferably that from 925 to 975 nanometers, which the Applicant has found to be particularly useful for detecting condensate phenomena on a surface. The sensors working with infrared light are preferable because the sensors operating in the band of visible light - for instance at wavelengths below 750 nanometers - produce strong lighting interferences due to the ambient light; however, sensors operating in artificially lighted ambiances may adopt operating bands other than those of the photo-emitting/photo-receiving couples.

The condensate detector according to a first aspect of the present invention is also fitted with means of fogging control, capable of keeping the condensate present on the calibration surface ST at a predetermined fogging level. In the example of embodiment of the Figures, the means of fogging control comprise a housing 5 (Figures 3, 4) that encloses the calibration surface ST so as to maintain a moisture level around it that is predetermined and essentially independent of the humidity level of the external ambient.

In the present example of a particular embodiment, the housing 5 consists of a Plexiglas box which is glued or at any rate sealed onto a part ST of the surface S to be monitored, and inside which an appropriately absorbing material is placed so as to render the atmosphere inside the housing 5 anhydrous, or at any rate adequately dry to permanently prevent the formation of condensate on the surface ST. On the contrary, the surface^to be monitored SM is left exposed to the various factors whereon the formation of condensate depends - in the example of the Figures 3, 4, the surface SM is exposed to the atmosphere outside the condensate detector. In this manner the variations of the output signal of the second photo-transistor 400 depend on the same factors on which the output of the first photo-transistor 300 depends - factors such as for instance the ambient light and that emitted by the respective photo-emitter 200 or 100, the ambient temperature and that of the various elements, the reflection factor on the surfaces ST and SM, respectively - but not the quantity of condensate on the surface SM. By comparing - or any rate by processing - the information supplied by the two output signals SE1 and SE2 of the two photo-transistors 100, 200 - known as first SE1 and second SE2 output signal, respectively - it is possible to obtain a cleaned-out signal whose variations - for instance in time - depend solely on the variations of the fogging level of the surface SM and not on the other disturbance factors mentioned above.

It is thus possible to produce a condensate detector with greater precision, repeatability and reliability than the detector described in the article by Dario Camuffo and Sergio Valcher mentioned above.

Clearly, the more the first couple of emitter 1 / receiver 3, and the second couple of emitter 2 / receiver 4 have constructive characteristics similar to each other - characteristics such as for instance type, brand and model of electrical and electronic components, circuital and mechanical arrangements, geometry, emplacement and conditions of installation, thermal capacity of the electronic and mechanical elements and thermal drift of the signals with changing temperature - the more the difference between the first and second signal of the receivers 3, 4 will faithfully reflect the sole fogging effect of the surface to be monitored SM. In the example of Figure 5, the two signals SE1 and SE2, which are emitted as emitter voltages by the photo-transistors 300, 400, respectively, are subtracted one from the other in a subtraction block 7 - for instance in an operational amplifier - thus obtaining an SES signal that reflects the variations at the output of the photo-receiver 3, which are solely due to the variations of the fogging of the surface SM; or solely to the state of fogging of the surface SM. with greater precision.

It is at any rate possible to clean up the signal SE1 from any undesirable noises and drifts by using other types of processing operations, carried out for instance by using the means of comparison 7. Advantageously, the carcass 6 (Figures 3, 4) that emplaces and sustains the two couples of emitters and transmitters 1 , 2, 3, 4, or the housing 5, is produced so as to reduce the lighting differences between the two receivers 3, 4 to a minimum - for instance the differences due to the shadows projected by the same carcass on the two receivers 3, 4 - and to consequently reduce the measuring errors of the photo-receivers 3, 4; the carcass 6, for instance may be produced of Plexiglas or other material transparent to visible light or the entire spectrum of light, including the infrared radiation band, or it may appropriately be produced as a reticular structure of thin elements such as rods, sticks or other thread-like elements. Advantageously, at least the housing 5, or even the entire carcass 6, is produced to also be permeable to infrared radiation, so as to avoid an undesirable hothouse effect inside the housing 5, which would differentiate the temperature of the surface ST from that of the surface SM; for this purpose the housing may for instance be produced of Lupolene (low density polyethylene), or other material permeable to infrared radiation. It is possible to further reduce the output noises of the receivers 3, 4 due to ambient lighting, by heading each of the two receivers 3, 4 with a monochrome optical filter having a narrow passing band; a few appropriate values of amplitude of the passing band may be 50 nanometer or less, for instance 10 nanometer; in general, the more restricted the filter passing band, the less ambient lighting disturbs the output signals of the photo-transistors 300, 400.

The angle of the light beam emitted by the LEDs must be sufficiently narrow to allow it to hit a surface representative of the phenomenon, but not so broad as to reduce the sensitivity of the receiver.

The Applicant has also noted that when simple photo-transistors 300, 400 are used as photo-receivers instead of photo-Darlingtons, as described in the article of Dario Camuffo and Sergio Valcher mentioned above, better detecting precision is achieved? this means that it is preferable to use some photo-transistors as photo- receivers, whose voltage output does not pilot another transistor.

The couples of photo-emitter / photo-receiver are preferably of a high efficiency type, for instance characterized by a relatively high CTR, for instance equal to 0.4 - 0.5, where CTR means "Current Transfer Ratio", defined as CTR = IC IF, where lc indicates the current output of the collector of the photo-transistors 300, 400 and IF indicates the direct polarization current of the LEDs 100, 200; in the linear operating area of the photo-transistors, the CTR may be assumed to be about constant.

A high CTR value indicates a good reading of the photo-transistor 300, 400 in the presence of low currents in the LEDs 100, 200, meaning with beams L1 of lesser energy, which therefore cause a lesser disturbance to the conditions of condensation on the surface SM. To complete the description, data are given on a following numerical example. Numerical example In the example of the embodiment of the Figures, the Applicant used two HONEYWELL LEDs SE 5455 with the following characteristics as emitters 100, 200:

The Applicant used two photo-transistors HONEYWELL SD 5443 with the following characteristics as photo-receivers:

The CTR factor of such a LED/photo-transistor couple was about 0.4 - 0.5. The LEDs and the photo-transistors had been arranged so as to have an incident beam angle α and emerging beams of 45° (Figure 2 jT In order to detect the condensate on samples of transparent or semi-transparent glass — not mirror glasses - of various colors, the minimum emitting power needed to enable detection was about 16 mA; this minimum power may however be lower for mirror surfaces, and greater (for instance 100 mA) for non-reflecting surfaces. In this manner and using the constructive data just mentioned, the Applicant had succeeded in detecting and measuring the condensate, with good reliability and precision, even on non-mirror surfaces such as semi-transparent glass and non mirror-polished marble and metallic surfaces, while projecting the two light beams L1, L2 directly upon them, whereas the detector of the known type described in the article of Dario Camuffo and Sergio Walcher mentioned above could achieve acceptably reliable condensate measurements only on mirror surfaces, and detecting the presence of condensate on a surface of different type - such as for instance semi-transparent glass, plastered, painted or marble-coated building wall - required gluing a platelet of mirror glass or mirror-polished metal onto such a surface, whereon a beam of infrared LED could be projected; this introduced considerable inaccuracies of measurement, due to the fact that the temperature of the applied platelet was often appreciably different from that of the underlying surface, and the condensate formed only on the applied platelet and not on the wall of actual interest for a condensate detection, or vice-versa. The detector of the numerical example outlined above works in a reliable manner even when the two receivers 3, 4 are invested by direct light (for instance in full sunlight), without needing particular shields or protections, beyond the mentioned monochrome filters; the total drift of the output signal of such a sensor proved to be equal to 2-5% of the full scale of the output signal.

Moreover, the low power levels of the emitted beam fail to appreciably heat up the surface to be monitored SM, and do not essentially falsify the condensate forming conditions on the same; only the designer and user may therefore select the detector's operating cycle in relatively broad freedom, it is for instance possible to irradiate the SM and ST surfaces for the few seconds needed for a measurement at irregular intervals in the order of minutes or hours (thus achieving duty cycles in the on/off cycle with values ranging for instance from 0.2 to 0.08), without needing an additional pilot system based'On alternate current (with a square wave, for example), at an increased frequency during the few seconds of measuring time. An expert of the branch will also be able to identify various other constructive and usage arrangements to further improve on the precision of the measurements, for instance by selecting two surfaces SM and ST and having them impinged upon by the two beams from the emitters 1 , 2, as closely similar as possible, (for instance as regards their characteristics of opacity, material, surface structure, ambient lighting, orientation and position with respect to the two emitters/receivers, and temperature during the measurements): it is in practice preferable, whenever possible, to select the surface SM to be monitored and the calibration surface ST as two different areas of a single surface S having adequately uniform characteristics. In the example of embodiment of the Figures 3, 4, attention is called to the fact that that apart from the condensate, some other particles or substances may also deposit on the surface SM exposed to the external environment, such as for instance fine dust, droplets of grease or other soiling materials capable of varying the reflective capacity of the surface SM itself, while said substances do not deposit on the surface ST, which is protected by the housing 5; a method and a sensor variant capable of eliminating or at least reducing this imprecision of measurement.

In a particular form of embodiment, the condensate sensor may comprise or at any rate be connected to an appropriate logical unit, such as for instance a programmable microcontroller that implements the following calibration procedure: periodically - for instance once, twice, four times per year or whenever required, the logical unit compares the signals SE1 and SE2, at a specific instant characterized by missing or very weak ambient light - for instance by night - and under temperature and humidity conditions such as excluding the presence of condensate on the surface SM. Under such conditions, the difference between the two signals SE1 and SE2 is attributed to differences in the degree of soiling - or at any rate of fogging - of the surfaces SM and ST which cannot be attributed to condensation phenomena; the difference is memorized and utilized as a constant calibration value, by removing it from the subsequent readings of the signal SE1, or by processing it in a different manner, so as to correct the values of the signal SE1 acquired during normal operation.

The likelihood of this difference may also be compared with the value (SE1 - SE2) acquired during the previous calibration, for instance 3 or 6 months earlier. The present example of embodiment is susceptible of numerous modifications and variants without abandoning the scope of protection of the present invention; the means of emission may for example, instead of from a pair of emitters 1, 2, be produced from a single photo-emitter associated with an appropriate optical system that splits the single beam emitted by the emitter, through prisms, mirrors, lenses or optical fibers into two light beams, and directs each of the two beams against a different surface SM or ST; the sensor may be produced as an entirely analogical circuit or it may be governed by an appropriate digital micro-controller an appropriate software has been downloaded to. The condensate detector according to this invention may be used both for generating an analogical signal (the condensate level on the surface to be monitored) and a digital signal (the presence or absence of condensate), and may for instance be utilized in the following fields: - conservation of artistic or cultural assets, in particular the conservation of glass or stone surfaces, frescoed or painted walls (in particular of hypogea, grottoes or crypts) or other types of walls of historical monuments;

- road signalization and security, to monitor for instance the formation of ice or hoarfrost on a road surface; - automotive equipment, to monitor the conditions of visibility in a car passenger compartment - the sensor is in this case appropriately miniaturized;

- transport of goods and materials that deteriorate in the presence of humidity;

- food and canning industry, and the building trade in general.

It is understood that any modification or variant that falls within the meaning and the scope of the claims is included in the same.

Claims

1) A condensate detector capable of detecting the condensate eventually present on a surface to be monitored (SM), where said detector comprises: - light emission means (1 , 2) capable of emitting at least a first beam of light against said surface to be monitored (SM); - receiving means (3, 4) capable of supplying at least an output signal (SE1 ) depending on the lighting radiation coming from said surface to be monitored (SM) when the same is hit by said first beam of light, and depending on the condensate present onto said surface to be monitored (SM), characterized in that said light emission means (1 , 2) are capable of emitting at least a second beam of light onto a calibration surface (ST), where said receiving means (3, 4) are capable of supplying a second output signal (SE2) which depends on the lighting radiation coming from said calibration surface (ST) when the same is hit by said second beam of light; and further characterized in that it comprises condensate control means (5), which are capable of maintaining the condensate present onto said calibration surface (ST) at a predetermined level. 2) A detector according to claim 1, characterized in that it also comprises means (7) for comparing said first output signal (SE1) and second output signal (SE2) so as to detect changes of said first output signal (SE1) due to at least temperature and/or lighting variations of said condensate detector and/or of said surface to be monitored (SM), from changes of said first output signal due to the variations of the condensate present on said surface to be monitored (SM).

3) A detector according to claim 2, characterized in that said means for comparing (7) are capable of comparing said first output signal (SE1) from said second output signal (SE2) by subtracting said second output signal from said first output signal or vice-versa.

4) A detector according to one or more of claims from 1 to 3, characterized in that said fogging control means comprises a housing (5) which encloses said calibration surface (ST) so as to maintain a preset humidity level around it which is predetermined and substantially independent from the humidity level of the external environment.

5) A detector according to claim 4, characterized in that said condensate control means (5) are capable of maintaining said calibration surface (ST) substantially free of condensate.

6) A detector according to claims 4 or 5, characterized in that said receiving means (3, 4) comprises a first photo-receiver (3) capable of supplying said first output signal (SE1) and a second photo-receiver (4) capable of supplying said second output signal (SE2), and in that said housing (5) is at least partially transparent to at least visible light, so as to reduce the differences of shading and/or of lighting between said first (3) and said second photo-receiver (4), and/or the differences of shading and/or of lighting between said surface to be monitored (SM) and said calibration surface (ST).

7) A detector according to one or more of the claims from 4 to 6, characterized in that said housing (5) is at least partially transparent to at least infrared light radiation, so as to favour the transmission of infrared light radiation from the inside of said housing (5) to the outside; and vice-versa. 8) A detector according to one or more of the claims from 1 to 7, characterized in that said emission means (1 , 2) and said receiving means (3, 4) are capable of emitting and receiving infrared light, respectively.

9) A detector according to claim 8, characterized in that said emission means (1, 2) and said receiving means (3, 4) are capable of emitting and receiving, an infrared radiation with wavelengths comprised between 800 and 1 ,000 nanometers, respectively.

10) A detector according to claim 9, characterized in that said receiving means (3, 4) are capable of receiving infrared light radiation limited to a band of wave lengths comprised between 925 and 975 nanometers. 11) A detector according to one or more of the claims from 1 to 10, characterized in that said receiving means (3, 4) are capable of detecting the lighting radiation limited to a frequency band width of substantially 50 nanometers.

12) A detector according to one or more of the claims from 1 to 11 , characterized in that said receiving means (3, 4) comprises at least a photo- transistor (300, 400), whose output is not connected to control another transistor.

13) A detector according to one or more of the claims from 1 to 12, characterized in that said emission means (1, 2) are capable of emitting said first and/or second light beam at an angle of incidence (α) comprised between 45° ± 15° with respect to said surface to be monitored (SM) and said calibration surface (ST), respectively.

14) A detector according claim 12, characterized in that said emission means (1, 2) comprises at least one light emitting diode (100, 200) whose light, reflected and/or diffused from a surface (SM, ST), can be received by said at least one photo-transistor (300, 400), and in that the ratio (CTR) between the output current (lc) of the collector of said at least one photo-transistor (300, 400) and the direct polarization current (Ir) of said at least one light emitting diode (100, 200) is comprised between 0.4 and 0.5.

15) A method of detecting the condensate eventually present onto a surface to be monitored (SM) comprising the following operations: - projecting a first light beam onto said surface to be monitored (SM), so that at least part of said first light beam is reflected and/or diffused by said surface to be monitored (SM); - detecting the reflected and/or diffused part of said first light beam, and converting it into a first output signal (SE1 ); characterized in that it also comprises the following operations: - projecting a second light beam onto a calibration surface (ST) so that at least part of said second light beam is reflected and/or diffused by said calibration surface (ST), - detecting the reflected and/or diffused part of said second light beam, and converting it into a second output signal, while the condensate present on said calibration surface (ST) is maintained at a predetermined level. 16) A method according to claim 15, characterized in that by reading said second output signal (SE2), a comparison between changes of said first output signal (SE1), due to variations of condensate on said surface to be monitored (SM), and changes of said first output signal (SE1), due to at least the variations of temperature and/or of lighting of said condensate detector and/or of said surface to be monitored (SM), is made.

17) A method according to claim 15 and/or 16, characterized in that said surface to be monitored (SM) and said calibration surface (ST) are selected to be capable of reaching a thermal balance by exchanging heat with each other.

18) A method according to one or more of the claims from 15 to 17, characterized in that said calibration surface (ST) is kept free of condensate.

19) A method according to one or more of the claims from 15 to 18, characterized in that said calibration surface (ST) is selected to have one or more of the following characteristics sufficiently similar to those of said surface to be monitored (SM): surface structure, chemical composition, thermal and optical characteristics, temperature, lighting, and position with respect to said emission means (1 , 2) and receiving means (3, 4). 20) A method according to one or more of the claims from 15 to 19, characterized in that it comprises the following operations: - acquiring said first (SE1 ) and said second output signal (SE2), when there is likely no condensate on said surface to be monitored (SM); and - utilising the calibration values of said first (SE1) and second output signal (SE2) acquired to clean up the subsequent readings of said first (SE1 ) and second output signal (SE2) from the differences between said signals due to at least the differences of fogging level between said surface to be monitored (SM) and said calibration surface (ST) which are not attributable to condensate. 21) A method according to one or more of the claims from 15 to 21 , characterized in that at least one between said first and said second light beam is intermittently projected, with a utilization factor of less than 0.5, directly onto said surface to be monitored (SM) and onto said calibration surface (ST), respectively.

22) A detector according to one or more of the claims from 1 to 14, characterized in that it comprises means capable of implementing the method according to claim 20.

23) A computer program off-loadable to the internal memory of a digital computer or logical circuit, wherein said program comprises parts of program codes capable of inducing a detector according to one or more of the claims from 1 to 14 to perform the operations of a method according to one or more of the claims from 15 to 21 , when said program is run by said processor or said logical circuit.

24) A computer program according to claim 23, memorized on a memory support that can be read by a digital processor or other logical circuit.