Abstract:
A module is described for acquiring geophysical signals. The module includes at least one casing which is individually linked to one track. Each casing houses a processor which operates to digitize the geophysical signals. The module further includes two cable sections associated with each casing. Each cable section includes at a first end, a connector suitable for being coupled up to a complementary connector, and at a second end, an adapted configured to be fixed to a casing and to effect an electrical link with the processor housed in the casing.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to systems deployed on-site on land or at sea for the acquisition of geophysical data. 
     2. Description of the Related Art 
     These systems use an assembly of sensors, linked by electrical cables to casings whose role is to process the data emanating from the sensors, in particular by digitizing the data and transmitting them to a central processing unit to which the casings are also linked by electrical cables. These casings can also comprise means making it possible to test the operation of the sensors and the digitizing of the data. 
     The known systems are generally designed according to one of the following two architectures, which will now be explained with reference to FIGS.  1  and  2 : 
     monotrack architecture (represented in FIG.  1 ), 
     multitrack architecture (represented in FIG.  2 ). 
     FIG. 1 is a diagram representing a monotrack architecture. In this diagram, the geophysical data acquisition system S comprises a plurality of tracks T(i), each of which consists of an assembly of geophysical sensors. 
     Such tracks T(i) are well known and conventionally consist of n identical modules which each link in series or in parallel m geophysical sensors such as geophones whose analog output signal characterizes the response of the subsurface strata to the signal emitted following the activation of one or more seismic sources. 
     The monotrack system S also comprises casings B(i) for digitizing the analog data emanating from the sensors of each track, and transmitting these data to storage means (not represented in the figure). Each track T(i) is thus linked to a respective casing B(i) by a cable  10  connected to a port P(i) of the casing, said cable conveying the analog data emanating from the sensors of the track T(i). 
     The casings B(i) comprise means for digitizing these analog signals, and for transmission to the storage means by way of a cable C which links the casings in series. 
     The cable C is composed of sections C(i) conveying the digital signals emanating from the casings B(i) as well as the electrical power supply required for the operation of these casings. Each section C(i) is furnished at each of its two ends with a connector  20  for coupling R with a casing. Each casing B(i) therefore comprises in addition to its port P(i) two connectors for cooperating with the connectors  20  of two cable sections. 
     The diagram of FIG. 2 represents a so-called “multitrack” or “N-track” system S′, according to the second type of architecture commonly employed. 
     The multitrack system S′ comprises casings B′(j) for digitizing and transmitting data, each casing being linked to N tracks T(i) (4 tracks for each casing in the instance of the system represented here, but N-track systems in which N is equal to 6 for example are also commonly used). Each track is for its part linked to a single casing, by way of a cable  10  conveying the analog data emanating from the sensors of the track. 
     An important difference as compared with the monotrack system S represented in FIG. 1 is that in the instance of the multitrack system, the cables  10  for transmitting analog data are linked to the casings B′(j) not directly by a port, but by way of a main cable C′ to which the casings are linked in series and to which the cables  10  are coupled by so-called take-outs E(i) as they are widely known in the art. 
     The cable C′ transmits, like the cable C of the monotrack system of FIG. 1, the digital data emanating from the casings to storage means, not represented in the figure. 
     An N-track system thus comprises N times fewer casings than tracks, each interval between two consecutive casings comprising N take-outs of which the first N/2 are linked to a first of the two casings, the other N/2 take-outs being linked to the second casing. 
     The cable C′ of the multitrack system S′ is more complex that the cable C of the monotrack system of FIG.  1 . This cable C′ thus comprises inside a single sheath: 
     the extensions of the cables  10  for routing the analog data emanating from the tracks of sensors to the corresponding casing, 
     conductors for transmitting digital data, 
     at least one conductor for supplying power to the casings. 
     The casings B′(j) are linked to the cable C′ by connectors of the casing cooperating with matching connectors  20 ′ of the cable C′ so as to constitute couplings R′. 
     In the two known architectures described hereinabove, the distance between two tracks T(i) is typically of the order of 50 meters. This distance is also that which separates two consecutive casings of a monotrack system, while the casings of an N-track system are separated by around (N×50) meters. 
     These two architectures each comprise advantages and drawbacks, which may be summarized as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Advantages of monotrack 
                 Advantages of multitrack 
               
               
                   
                 architecture (FIG. 1) 
                 architecture (FIG. 2) 
               
               
                   
                   
               
               
                   
                 Quality of the signal 
                 Reduction in the number of 
               
               
                   
                 transmitted: the analog 
                 man cable/casing couplings 
               
               
                   
                 lines (from the track to 
                 (divided by 4 in the example 
               
               
                   
                 the casing) are short and 
                 of FIG. 2; by N in the general 
               
               
                   
                 insulated from one 
                 instance of a system with 
               
               
                   
                 another. 
                 N tracks) and in the associated 
               
               
                   
                 Flexibility of deployment 
                 cost. 
               
               
                   
                 in the field (the cable C 
                 Reduction in the number of 
               
               
                   
                 is simple and lightweight 
                 casings and in the associated 
               
               
                   
                 to handle, and it is there- 
                 cost. 
               
               
                   
                 fore easy to tailor it to 
               
               
                   
                 the local topography (so 
               
               
                   
                 as to bypass obstacles for 
               
               
                   
                 example) 
               
               
                   
                 Simplicity of the main 
               
               
                   
                 cable 10, and of the 
               
               
                   
                 connectors of this cable 
               
               
                   
                 with the casings B(i). 
               
               
                   
                 Reduced size of the 
               
               
                   
                 casing B(i) and of the 
               
               
                   
                 cable C. 
               
               
                   
                   
               
               
                   
                 Drawbacks of monotrack 
                 Drawbacks of multitrack 
               
               
                   
                 architecture (FIG. 1) 
                 architecture (FIG. 2) 
               
               
                   
                   
               
               
                   
                 Large number of cable 
                 Lack of flexibility (system 
               
               
                   
                 C/casing couplings (2 
                 whose basic element is an 
               
               
                   
                 connections per track). 
                 assembly of N tracks). 
               
               
                   
                 Number of casings (1 per 
                 Weight and complexity of 
               
               
                   
                 track); associated costs 
                 the cable C′. 
               
               
                   
                 of equipment and handling. 
                 Problems regarding the 
               
               
                   
                   
                 quality of the analog 
               
               
                   
                   
                 signals received by the 
               
               
                   
                   
                 casings B′(j): several 
               
               
                   
                   
                 neighboring strands 
               
               
                   
                   
                 contained within the same 
               
               
                   
                   
                 sheath convey low-level 
               
               
                   
                   
                 detectable analog signals, 
               
               
                   
                   
                 this possibly giving rise 
               
               
                   
                   
                 to crosstalk. Moreover, 
               
               
                   
                   
                 the sensitive analog links 
               
               
                   
                   
                 between the sensors of a 
               
               
                   
                   
                 track and their associated 
               
               
                   
                   
                 casing may be lengthy (for 
               
               
                   
                   
                 example 125 meters for a 
               
               
                   
                   
                 6-track system). 
               
               
                   
                   
               
             
          
         
       
     
     The two architectures described hereinabove have moreover common drawbacks: 
     Firstly, the number of couplings R or R′ is sizeable, even if this number is reduced in the instance of a multitrack system. Since the data acquisition installations can be moved in the field, one and the same piece of hardware comprising the tracks and the casings is successively deployed and gathered up at various locations, this involving very many operations for making and undoing the multiple couplings of the system. It is therefore understood that this large number of couplings is especially detrimental in terms of cost of labor and timescales. 
     Another drawback common to both types of system is that each of the casings which they employ comprises two connectors for coupling with a main cable. The presence of these connectors on the casing constitutes a sizeable obstacle to the miniaturization of the casing, while present-day technological developments make it possible to substantially reduce the bulkiness of the other components of the casing. It would nevertheless be advantageous to reduce the size of the casings, which at present constitute voluminous elements of the systems and may be an impediment to the laying and gathering operations. 
     A third drawback common to present-day systems stems from the fact that it is sometimes necessary to supplement the couplings between the main cable and the casings with load take-up devices, such as portions of tension cables, one end of which is fixed to a part of the electrical cable close to the casing and the other end of which is mounted, in a removable or nonremovable manner, on the casing itself. 
     This arrangement may be necessary when the assembly formed by the cables and the casings is subjected to tensile loads, for example when submerging the assembly in water traversed by a strong current. 
     Such load take-up devices increase the complexity and the time required for employing the system, since when mounting and demounting casings provided with removable load take-up devices, the connecting and disconnecting of the electrical cables and of the casings must be accompanied by the mechanical stowing and unstowing of said load take-up devices. 
     Moreover, the load take-up device (comprising means on the casing, such as for example rings secured to the casing) constitutes just like the connectors an obstacle to the miniaturization of the casings. 
     Furthermore in the two known types of architecture, it is necessary to handle two families of objects having very different dimensions: the casings and sections of the main cable on the other hand, with specific logistics suited to each family. 
     However, there is nowadays a desire to gradually move the operations for laying and gathering the acquisition systems toward greater automation, so as to cut the associated labor costs and reduce the duration of these operations. Such movement is made tricky nowadays by the fact of having to handle these two families of objects. 
     Finally, it has been seen that the two architectures each exhibited drawbacks. The operators must therefore determine, on the basis of the specifics of the geophysical data acquisition campaign to be carried out, the suitable architecture. This implies that in many instances no choice of architecture will be optimal, and that the operators must have access to the hardware required for implementing the chosen architecture, this leading to overequipment or to hiring which is detrimental in terms of costs. 
     SUMMARY 
     A purpose of the invention is to make it possible to produce systems for acquiring geophysical data which are economical to manufacture and utilize by virtue of the sizeable reduction in the number of connectors employed in these systems. 
     A second purpose of the invention is to facilitate the operations for laying and gathering the acquisition systems by harmonizing the format of their components (which at present comprise casings and cables, the formats of these two types of components being very different). 
     A third purpose of the invention is to make it possible to produce a system in which the casings are of substantially smaller dimensions than the dimensions of present-day casings. 
     Another purpose of the invention is to make it possible to produce systems according to the objectives hereinabove, in which the casings may be subjected to sizeable tensile loads (of the order of 500 Newtons for utilization on land, and of the order of 2 500 Newtons for utilization in a wet environment of the “shallow water” type to use the widespread terminology), while still having reduced dimensions (of the order of 200 cm 3 ) 
     In order to achieve these purposes, the invention proposes a module for acquiring geophysical signals, comprising: 
     at least one casing B″(i), B″, which houses processing means including means for digitizing the signals, 
     and two cable sections C″(i) each comprising: 
     at a first end, a connector suitable for being coupled up to a complementary connector, 
     at a second end, an adapter designed to be fixed to the casing and to effect an electrical link with the processing means housed in the casing. 
     Preferred but nonlimiting aspects of the system according to the invention are the following: 
     it comprises at least two casings, linked in series by cable segments, comprising at each end an adapter designed to be fixed to the casing and to effect an electrical link with the processing means housed in the casing. 
     each casing comprises a rigid member fixed on one face of the respective adapters secured to the respective cable sections or segments, so as to take up a sizeable part of the tensile loads exerted between these two cable sections or segments. 
     each casing comprises means for attaching the adapters of the cables to the rigid member. 
     the means for attachment are rigid lugs, a part of which is embedded in the adapter, another part of each lug projecting from the adapter toward the rigid member and engaged in a respective orifice of the rigid member along a direction substantially perpendicular to the direction of the part of the cable sections or segments which is adjacent to the casing. 
     processing means integrated into the cable adapters comprise spark arresters. 
     the rigid member carries means for processing electrical signals. 
     each casing comprises leaktightness means. 
     the leaktightness means comprise a seal placed in a space circumscribed by the lugs. 
     at least one casing comprises a platen situated on a second face of the cables which is opposite the first face and is substantially parallel to the rigid member. 
     parts of the lugs which project toward the platen are engaged in orifices of said platen. 
     the cable section end connectors are mechanically and electrically hermaphrodite and are identical. 
     the adapter situated at the second end of each cable section is designed to be fixed in a removable manner to a casing. 
     the casings comprise a port for the connection of at least one geophysical sensor outside the casing. 
     Other aspects, purposes and advantages of the present invention will become more apparent from reading the following detailed description of a preferred embodiment thereof, given by way of example and with reference to FIGS. 3 to  6   b  of the appended drawings, in which drawings: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic representation of a geophysical data acquisition system according to a first known type of architecture, 
     FIG. 2 is a diagrammatic representation of a geophysical data acquisition system according to a second known type of architecture different from the type of FIG. 1, 
     FIG. 3 is a diagrammatic representation of a geophysical data acquisition system architecture according to the invention, 
     FIG. 4 is an exploded diagrammatic view of the main components of a first embodiment of a casing of a system according to the invention, 
     FIGS. 5 a  and  5   b  are two sectional diagrammatic views of two variants of a second embodiment of a casing of a system according to the invention, 
     FIGS. 6 a  and  6   b  are a perspective view and an exploded view of a third embodiment of a casing of a system according to the invention. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIG. 3, there is represented a geophysical data acquisition system S″ according to the invention. 
     Like the known systems, it comprises a plurality of tracks T(i) linked to data storage means (not represented) by way of a cable C″. 
     More precisely, like in the monotrack systems, each track T(i) is linked individually to a respective casing B″(i). 
     However, in contrast to the known systems represented in FIGS. 1 and 2, no connector for electrical linking with the central processing unit or the interlinking of the casings is fixed on the casings. In the system according to the invention, each casing B″(i) is associated with two cable sections C″(i) and C″(i+1) for electrical connection with the neighboring casings. 
     The two cable sections C″(i) and C″(i+1) are fixed on the casing B″(i), preferably being aligned on either side of the casing. The structure of the link between the cable sections and the casing will be described with reference to FIGS. 4,  5   a ,  5   b  and  6   b.    
     Each cable section C″(i) is furnished at a first end with means of coupling with a casing B″(i), the second end of the section C″(i) possibly being identical to the first and also being furnished with means of coupling with a casing, or else comprising an electrically and mechanically hermaphrodite connector  30  which can be connected to another identical connector. 
     The casings B″(i) are thus linked in series by way of the means of end coupling of the cable sections, to constitute modules  40  whose two ends are furnished with a connector  30  for coupling R″ with the neighboring module. 
     The module  40  represented in FIG. 3 comprises four casings B″(i) each linked to a track T(i). According to the invention, the number of casings of a module may be arbitrary, the module possibly comprising just a single casing, or several thereof. 
     It is therefore understood that: 
     on the one hand, the number of couplings R″ is divided by two as compared with the known systems comprise the fewest couplings (multitrack systems). Specifically, the implementation of an N-track multitrack system requires two couplings per casing, and hence 2/N couplings per track. In the system according to the invention, this ratio is still divided by two, to a value of 1/N coupling per track. 
     on the other hand, the casings B″(i) do not directly carry connectors, thereby making it possible to design them with reduced size, as will be seen with reference in particular to FIG.  4 . 
     With reference now to FIG. 4, there is represented an exploded view of a casing B″ of an acquisition system according to the invention with its two identical cable sections C″(i) and C″(i+1). 
     The section C″(i) comprises in its sheath  130  the assembly of electrical conductors required for coupling with the central processing unit or with other casings B″, so as to convey the data emanating from sensors linked to the casings of the acquisition system. 
     This section is furnished at a first end remote from the casing with a connector, not represented in the figure, which can be mechanically and electrically coupled with an identical connector secured to another casing or to a central processing unit. 
     The second end of the section C″(i) is coupled electrically to means of processing the signals fixed on a rigid plastic insert (the insert and its processing means not being represented). These processing means can in particular comprise overvoltage limiters (which may use spark arresters). 
     The sheath of the section C″(i) is also engaged in a conduit of the insert in which the section C″(i) follows an “S” route so as to bypass baffles inside the conduit. Thus the section C″(i) and the insert are also mechanically secured (the baffles of the conduit defining passages whose width is scarcely greater than the diameter of the sheath of the cable section), their mechanical link being able to withstand a tension of the order of 500 Newtons. 
     An overmolding of a semi-rigid plastic identical to that of the sheath of the cable is produced around the cable section C″(i), around the insert and around its processing means. This overmolding unites into a single member a part  131  surrounding the part of the section C″(i) which is adjacent to the insert, and an adapter of generally flattened form  140   a  which constitutes the part of the overmolding which is most remote from the section C″(i). The material of this overmolding can for example be polyurethane. 
     The ribbed geometry of the part  131  renders it sufficiently flexible to allow certain deformations of the cable section which it surrounds, but sufficiently rigid to limit these deformations to the interior of a specified angular cone. 
     By thus limiting the curvature of the cable section located in proximity to the casing, the overmolding part  131  maintains the link between the cable section and the casing of shearing loads which may damage this link. 
     This overmolding, which covers the end of the cable section and the means of processing of the insert, also comprises a conduit  142   a  directed perpendicularly to the section C″(i), affording access from outside to the means of processing of the insert. 
     This conduit emerges outside the overmolding on an essentially plane face of the adapter  140   a , said face being the so-called upper one. It constitutes the only point affording access to the interior of the overmolding, the sheath of the cable section having reacted thermally with the plastic of the overmolding to constitute an otherwise leaktight assembly. 
     Two variant embodiments of the invention, corresponding to two respective solutions for electrically linking the elements of the casing, are brought together in the exploded view of FIG.  4 : 
     in the left part of the figure, conducting wires  141   a  are connected to the processing means of the insert and exit the adapter  140   a  via the conduit  142   a,    
     in a preferred variant represented in the right part of the figure, the conduit  142   b  of a second adapter  140   b , otherwise identical to the first adapter, is extended upwards by a duct  140   b . The second adapter  140   b  lies within an overmolding surrounding a second cable section C″(i+1)) identical to C″(i) and a second insert identical to that of the adapter  140   a.    
     Two rigid lugs  143  project perpendicularly from the upper face of the adapter  140   a . The lower part of these lugs, which is embedded in the rigid insert, is fairly sizeable so that the anchoring of the lugs in the insert can withstand without damage shearing loads of the order of 2 550 Newtons applied parallel to the upper face of the adapter on the projecting part of the lugs. 
     In the diagram of FIG. 4, the two adapters  140   a  and  140   b  are in the position of mounting of the casings. In this position, the adapters are placed in such a way that their respective upper faces are adjacent and define a single plane, and the sections C″(i) and C″(i+1) are aligned. The faces of mutual contact of the two adapters are generally plane and perpendicular to the axis of the sections C″(i) and C″(i+1). 
     Represented above the adapters thus assembled is a platen  150  whose surface corresponds to the uniting of the two upper faces of the adapters. 
     This platen is made from a rigid metallic material such as steel, and is drilled with four holes  153  located opposite the lugs of the two adapters when the latter are in contact in the position of mounting of the casing. These holes  153  have a diameter corresponding to that of the lugs. 
     A second platen  160  is fixed on the upper face of the platen  150 , remote from the adapters  140   a  and  140   b . This second platen also carries means for processing the signals which may be produced in the form of a printed circuit placed for example on the lower face of the platen  160  and linked: 
     to the conductors  141   a  of the adapter  140   a  in the variant in the left part of the figure, 
     two connection pins  141   b  which can be engaged in the duct  1420   b  for connecting with the processing means of the adapter  140   b  in the preferred variant in the right part of the figure. 
     Whatever variant embodiment is chosen, the conductors  141   a  and the pins  141   b  each pass through an orifice of the platen  150  (not visible in the figure) for connection with the processing means of the adapters. 
     When the casing is mounted, the platen  150  sits on the adapters  140   a  and  140   b , each of the lugs  143  being engaged in one of the four orifices  153  of the platen so as to guarantee the anchoring of the two adapters in the directions parallel to their upper faces. 
     A cover  170  covering the two platens  150  and  160  from above comprises a port P for the connecting of a measurement point, not represented in the figure. The plugs of this port are linked to the processing means of the platen  160  by pins or conductors, also not represented in the figure for the sake of clarity. 
     When the casing B″ is closed, the inserts of the two adapters, the platen  150  and the cover  170  are fixed together by s crews passing through orifices of the platen  150  and make it possible as will be seen to construct a completely leaktight assembly. 
     The casing B″ of the acquisition system according to the invention does therefore not comprise on its main body (materialized by the two adapters and the cover) any connector for coupling with other casings, the hermaphrodite connectors for such coupling possibly being shifted to the extremity of the cable sections C″(i) and C″(+1). 
     An advantageous consequence thereof is that this casing B″ may be of especially reduced dimensions—of the order of 200 cm 3 , while the casings of present-day systems have a volume which commonly reaches several liters. 
     Moreover, the take-up of load by the lugs  143  makes it possible to dispense with the additional devices for taking up loads alluded to hereinabove, which were not integrated into existing casings. 
     Specifically, in the system according to the invention the tensile loads between the cables interlinking the casings or linking them to a central processing unit are taken up by the succession of the following elements: 
     sheath of the cable (and possibly additional armor of the cable made of Kevlar (registered trademark) in the case of a reinforced link) which is linked to a first side of the casing, 
     link between the end of the c able and a first insert of the adapter. This link is as has been seen effected by engaging the sheath of the cable between baffles of the insert, but may also as will be seen more particularly with reference to FIG. 5 b , employ the clamping of the end of a Kevlar (registered trademark) armor in the case of a reinforced link, 
     lugs projecting from the first insert and from the first associated adapter, 
     platen in which the projecting lugs are engaged (and possibly second platen as described later with reference to FIG. 5 b ), 
     lugs of the second adapter of the casing, 
     insert of the second adapter, 
     sheath of the second cable section linked to a second side of the casing. 
     By dispensing with the conventional load take-up devices it is thus also possible to eliminate the drawbacks cited above and related to the conventional load take-up devices. 
     FIG. 5 a  is a longitudinal sectional view diagrammatically representing a second embodiment of a casing B″ according to the invention, and intended to be employed on land, said casing now being assembled. The two variant embodiments already represented in FIG. 4 are found again in the right and left parts of this figure respectively. 
     Found again in this figure are the two cable sections C″(i) and C″(i+1) which are aligned on either side of the casing. The end adapter  140   a  of the section C″(i) is in contact with the end adapter  140   b  of the section C″(i+1). The platen  150  is fixed (by conventional means not represented such as screws, which also hold the cover  170  on the plane upper faces of the two adjacent adapters, and on its upper face carries the platen  160  which comprises means for processing the signals, said signals being conveyed by: 
     the electrical conductors  141   a  which pass through the conduit  142   a  of the adapter  140   a  so as to be in electrical contact with the processing means contained inside this adapter (variant in the left part of the figure), 
     the pins  141   b  engaged in the duct  1420   b  (which extends inside the adapter  140   b  up to the processing means through another conduit), and connected with the processing means contained inside the adapter  140   b  (variant in the right part of the figure). 
     In both instances, the conductors  141   a  and the pins  141   b  each pass through a respective conduit of the platen  150 . 
     FIG. 5 b  illustrates a different configuration of the lugs  143   a  and  143   b  of the respective adapters  140   a  and  140   b . Here, as in FIG. 4, the lugs are partially embedded in the insert  145   a ,  145   b  of their associated adapter, but project perpendicularly from the two faces (upper and lower) of said adapter. 
     Their projecting upper part is engaged just like,that of the lugs  143  of FIG. 4 in an orifice of the platen  150 , their projecting lower part being moreover engaged in an orifice of an additional platen  180  sitting on and screwed to the plane lower face of the two adapters  140   a  and  140   b  which are then “sandwiched” between the two platens  150  and  180 . 
     This variant embodiment—second load take-up platen  180  and lugs likewise projecting downwards so as to anchor the adapters to this second platen—is advantageous in the instance where the two sections of cable of the casing may be subjected to a sizeable tension (of the order of 2 500 Newtons). It thus constitutes a preferred variant embodiment when employing the casing at sea or in wet surroundings of the “shallow water” type. 
     In practice, such a device is designed to withstand tensions of the order of 2 500 Newtons, while the first embodiment involving only upward projecting lugs as represented in FIG. 4 permits longitudinal loads of the order of 500 Newtons. 
     FIG. 5 b  also illustrates a variant embodiment of the mechanical link between the sections C″(i), C″(i+1) and the respective inserts  145   a ,  145   b  of the respective adapters  140   a ,  140   b . To withstand sizeable tensions, each cable section can be reinforced with an additional sheath  190   a ,  190   b  made of Kevlar (registered trademark) whose end adjacent to the corresponding adapter  140   a ,  140   b  exhibits a thickening  1900   a ,  1900   b  clamped in a respective conical nut mechanism  191   a ,  191   b  embedded in the overmolding of the respective adapter. 
     The geometrical configuration of the casing represented in FIGS. 5 a  and  5   b  is a little different from that of the casing of FIG.  4 . Specifically, in this instance, the port P for connecting a measurement point is not situated perpendicularly to the upper face of the cover  170  of the casing, but is slanted. This characteristic in no way modifies the functionalities of the casing. 
     Also represented in FIGS. 5 a  and  5   b  are the means making it possible to guarantee the leaktightness of the device which may be exposed to aggressive surroundings involving for example dust or water liable to penetrate the casing and damage its components. 
     Accordingly, there is provided an O-ring seal  1100  disposed in a bore of the cover  170  and intended to guarantee the leaktightness between the cover  170  and the platen  150 . There is also provided an O-ring seal  1101   a  housed in a circular cavity flush with the upper face of the adapter  140   a  and surrounding the orifice made in the platen  150  which faces the conduit  142   a  for the passage of the conductors  141   a  when the platen  150  is sitting on the adapter. 
     This seal  1101   a  thus guarantees the leaktightness of the passage of the conductors  141   a . Likewise, an O-ring seal  1101   b  is provided in a circular cavity emerging on the upper face of the adapter  140   b  so as to guarantee the leaktightness of the passage of the pin  141   b.    
     FIGS. 6 a  and  6   b  depict a third embodiment of a casing B″. 
     FIG. 6 b  reveals two adapters  140   a  and  140   b  intended to be assembled by way of the lugs  143  and the platen  150 . 
     This figure also shows two electrically conducting plates  1400   a  and  1400   b  housed in respective recesses of the upper faces of the two adapters in such a way as to lie along the extension of said upper faces. 
     These two plates are made in one piece each with two axes which cannot be seen in the figure, housed in conduits which pass through the upper wall of the adapter so as to place each plate in electrical communication with the circuit carrying the means of processing the signals of the insert of the associated adapter. 
     FIG. 6 b  also shows a metallic and electrically conducting strap  1401  intended to be mounted on the lower face of the casing, the bent-back ends of its two branches (of which only branch  1402  is visible in the figure) being engaged in cavities  171  of the lid  170  when the casing is mounted, so as to further improve the cohesion of the assembly. 
     In FIG. 6 b  it will be observed that the adapters  140   a  and  140   b  define when they are assembled a central well  1403  which passes right through the assemblage formed by the two adapters and emerges toward the bottom of the casing on the strap  1401 . 
     This strap  1401  also comprises an orifice  1404  aligned with the well  1403  when the strap is mounted on the casing. 
     A metal finger  1405  visible in FIG. 6 b  is engaged, when the device is mounted, in the orifice  1404  and the well  1403  in such a way as to come into contact with the plates  1400   a  and  1400   b . This finger is electrically conducting and thus allows the strap  1401  to be linked electrically to the circuits of the inserts of the two adapters carrying the means of processing the signals, by way of the finger  1404  and of the plates  1400   a  and  1400   b.    
     The finger  1405  can be secured with a spike (not represented), also electrically conducting and intended to be driven into the ground, said spike then simultaneously ensuring: 
     the securing of the casing B″ to the ground when used on land, 
     and the earthing of the circuits of the inserts carrying the means of processing the signals by way of the strap  1401  which thus constitutes an earth strap. 
     When employed at sea, the device does not comprise any spike associated with the finger  1405  which is in contact with the water as well as the strap  1401 , these two elements thus also effecting the earthing of the circuits of the inserts. 
     It will be observed that the casing B″ described hereinabove is easily dismountable, the cable sections C″(i) and C″(i+1) each being able to abut at their end remote from the casing either with an adapter of a neighboring casing, or with a connector terminating a module  40  such as represented in FIG. 3, comprising several casings linked in series. 
     In a variant embodiment not represented in the figures, it is also possible to overmold the assembly which can then no longer be dismounted but whose robustness is increased through said overmolding. 
     It is thus apparent that the system according to the invention makes it possible: 
     to make substantial manufacturing savings by at most halving the number of connectors employed between the modules, 
     to make the system reliable by reducing the number of connections, 
     to standardize the format of the components of the system and thus to facilitate their handling, 
     to facilitate the handling of the system by virtue of the miniaturization of the casings and the integration into the body of the casings of the load take-up means, 
     simply and rapidly to deploy “clusters” consisting of casings mounted in series, it being possible for example for said clusters to be wound around a reel by virtue of the reduced volume of the casings.