EP4022250A1

EP4022250A1 - Apparatus and method for inductively measuring a representative variable or a variation in the perimeter of a deformable object, and use of the apparatus on a shutter, a pressure probe or for plethysmography

Info

Publication number: EP4022250A1
Application number: EP20764367.7A
Authority: EP
Inventors: Francis Cour
Original assignee: Calyf
Current assignee: Calyf
Priority date: 2019-08-29
Filing date: 2020-08-28
Publication date: 2022-07-06
Also published as: CN114340489A; WO2021038030A1; FR3100326A1; FR3100326B1; US20220304592A1

Abstract

The measurement apparatus (50) comprises at least one elastic hybrid cable (52) wound around the deformable object (22), and a measurement unit (54) capable of measuring the inductance of a wire of the elastic hybrid cable (52) comprising a conductive material between two reference points (58).

Description

APPARATUS AND METHOD FOR MEASURING BY INDUCTANCE OF A REPRESENTATIVE QUANTITY OR OF A VARIATION IN THE PERIMETER OF A DEFORMABLE OBJECT, AND USE OF THE APPARATUS ON A SHUTTER, A PRESSURE SENSOR OR FOR PLETHYSMOGRAPHY

The present invention generally relates to an inductive measuring device, suitable for measuring the perimeter or changes in the perimeter of a deformable object. It also relates to the application of this device for measuring the perimeter of an inflatable element of the type used in pressuremeter or dilatometric probes in the geotechnical field, for which the expansion rates can reach values from a few% to several hundreds of %, or an inflatable element of the inflatable shutter or inflatable packer type of the type used in the petroleum, geothermal or geotechnical fields.

More precisely, the invention relates, according to a first aspect, to an apparatus for measuring a quantity representative of a perimeter or of a variation of a perimeter of a deformable object, the measuring apparatus comprising a unit of measurement of inductance.

Pressuremeter and dilatometric tests are loading tests carried out in the subsoil, generally in a calibrated borehole, the analysis of which makes it possible to obtain mechanical properties of the subsoil, for example the EM pressuremeter module. In the case of the dilatometer, the measurement of the expansion is carried out by displacement sensors, in the case of the pressuremeter the measurement of the expansion is deduced from the volume of the fluid injected to fill the probe.

To perform this type of measurement, an object that can be deformed by expansion, here a deformable cell, is pressurized, in increasing pressure levels, by injecting the fluid from the fluid reservoir by means of the transfer member of the control unit. transfer. For each pressure level, the volume of fluid injected is measured.

In the case of the dilatometer the measurement of the expansion is carried out by displacement sensors, in the case of the pressuremeter the measurement of the expansion is deduced from the volume of the fluid injected to fill the probe.

However, such type of measuring devices do not make it possible to have precise measurements. Measurements made with a dilatometer are only precise on the contact points of the sensors, generally three in number, and on deformations and on deformations limited in expansion rate of a few tens of%, in a few punctual points which do not make it possible to characterize a ground, in particular when this one is heterogeneous (composed of layers of non-homogeneous materials).

One solution to such a problem is to measure the perimeter at different longitudinal heights of the deformable cell, the latter having a cross section whose perimeter varies depending on the type of material of the subsoil around, once the deformable cell is placed under. pressure and as it swells in stages. Thus, depending on the perimeter at the different longitudinal heights of the deformable cell and its pressure, it is possible to obtain precise measurements of the subsoil, taking into account in particular the vertical stratification of the subsoil.

It is possible to estimate the perimeter of a cylinder by measuring the inductance of a wire wrapped around it, by applying the formulas for calculating the inductance of a short solenoid or a simple conductive loop. However, such a perimeter calculation is only applicable for fixed perimeters and the use of a conductor wrapped around a probe positioned in the basement and the perimeter of which is likely to vary by a significant factor of l. The order of 1: 3 (ie expansion rate of 300%) is therefore not feasible, the conductors existing on the market not having sufficient expansion rates.

Regarding the measurement of a variable perimeter, the principle of a measurement of the perimeter via an inductance loop is used in the field of inductance plethysmography, to estimate a perimeter around a part of the body of an individual or animal or more commonly estimate the corresponding section. However, the sensors used in plethysmography are used for small deformation of the order of a few tens of% expansion rate and do not allow measurements to be performed on bodies that can reach perimeter expansion rates of 1: 3 ( coefficient of expansion of the diameter of 300%).

Document US 5913830 describes an apparatus for measuring the perimeter around a part of the body of an individual, by measuring the inductance of an electric wire attached to an elastic band, itself wound around the part of the body of an individual. the individual. However, such a device does not make it possible to have precise perimeter measurements. In addition, such a device does not allow measurements to be taken over a large expansion range, given that the precision of measurements with such a device decreases when the measured perimeter increases. Indeed the inductive bands used in inductance plethysmography (commonly called inductance plethysmography belts) associate for example by sewing or gluing an electric wire to an elastic band by making zig zags, sinusoid or other curved shapes. regular, flat over all or part of the length of the elastic band. The elastic band, stretching out when it is stretched, will drag the conductive wire and will therefore spread and flatten the curves formed by the conductive wire (figure 13).

Patent US4308872A discloses an inductance plethysmography apparatus using a helical electric wire fixed by regular points to an elastic band.

The present invention aims to provide an apparatus for measuring a perimeter or a variation in perimeter of a deformable object making it possible to accurately measure a variable perimeter without having to adjust it or reposition it between different measurements, and this for a wide range of coefficient of expansion of the perimeter, which can reach several hundred%.

To this end, the present invention relates according to a first aspect to a measuring device of the aforementioned type characterized in that it further comprises at least one elastic hybrid cable wound up and arranged to form at least one turn around the deformable object. , the or each elastic hybrid cable comprising a yarn of a first type and a yarn of a second type, for the or each elastic hybrid cable, the yarn of the first type having a lower degree of tenacity than that of the yarn of the second type , the yarn of the second type having a lower degree of elasticity than that of the yarn of the first type, the yarn of the second type comprising a conductive material, for the or each elastic hybrid cable, the yarn of the second type, when said elastic hybrid cable is at rest, being wound helically around the wire of the first type, the measurement unit comprising for the or each elastic hybrid cable a pair of measurement terminals electrically connected to two reference points of said hybrid cable elastic and being able to measure the inductance of the wire of the second type of said elastic hybrid cable between the two reference points of said elastic hybrid cable, the measuring apparatus further comprises a calculation unit electrically connected to the measuring unit and configured to calculate for the or each elastic hybrid cable, said characteristic quantity around said elastic hybrid cable, using the inductance of the wire of the second type of said measured elastic hybrid cable.

Such a device enables the perimeter or perimeter variations of a deformable object to be measured very precisely, over a wide range of expansion.

This is due in particular to the fact that the hybrid cable can undergo considerable extension while retaining the same general shape, and return to its initial position without residual deformation or elongation.

In particular, the wire of the second type, comprising the conductive material, remains arranged in the form of a solenoid, the solenoid retaining substantially the same diameter. The device enables measurements to be made over a range of diameter expansion up to a ratio of 1: 3, without degradation of accuracy or quality of measurement.

The measurement precision is less than a few hundred micrometers for the measurement of the perimeter of a deformable object when the latter has a circular section and has a diameter of the order of 10mm to 1000mm, that is to say a accuracy less than 0.1%.

Furthermore, the hybrid cable can undergo a large number of extension and retraction cycles, each cycle being able to be at diametral expansion rates of several hundred%, without damage, and in particular without the arrangement of the wire of the second type is disturbed. The yarn of the first type, relatively more elastic, returns the yarn of the second type in its original configuration, in an orderly manner, during retraction.

The measuring device therefore allows excellent repeatability of the measurement, without degrading the accuracy.

The device is extremely simple to use, in particular because it uses already existing technologies for measuring the inductance at the terminals of the hybrid cable, commonly called inductance meters.

In addition, the hybrid cable has low resistance to stretch. Strong resistance to extension would likely interfere with the measurement.

The inductive strip of US4308872A does not allow precise and large amplitude measurements to be made without degrading the geometry of the helical wire and therefore disturbing the repeated measurements. To date, this device is not in use.

In the invention, the geometry of this hybrid yarn at rest does not deteriorate after cyclic stress and this hybrid yarn does not need to be associated with an elastic band.

According to particular embodiments, the measuring device comprises one or more of the following characteristics, taken in isolation or in any technically possible combination:

- the deformable object comprises a cross section of substantially circular shape at the or each elastic hybrid cable, the computing unit is configured to calculate said characteristic quantity for an elastic hybrid cable using a linear relationship between the measured inductance by the unit of measurement and the said characteristic quantity;

- in full elongation, the hybrid cable is in a configuration where the wire of the first type is wound in a helix around the wire of the second type with a number of turns per linear meter of the hybrid cable between n _sE -15% and n _sE + 15%, n _sE being determined by function of the diameter of the wire of the first type, the diameter of the wire of the second type and a predetermined maximum elongation rate, from the following formula:

1000 .J ^K „x (k _^ + 200) n. - - -Forrotffe {F1) fp (y, + y _k K_ + 100 in which cp _e is the diameter in mm of the wire of the first type at rest, fk is the diameter in mm of the wire of the second type, and K _ma x is the predetermined maximum elongation rate, expressed in percent;

- the wire of the first type is twisted on itself with a specific number of clean turns, the clean turns winding in the opposite direction to the turns of the helix formed by the wire of the first type around the wire of the second type, the number of clean turns per linear meter of the hybrid cable at the maximum elongation rate being between n _sE and 3 xn _sE, preferably between n _sE and 2 xn _sE. ;

- each measurement has an accuracy of less than 0.1%;

- for the or each elastic hybrid cable, the reference points of said elastic hybrid cable are fixed with respect to each other.

According to a second aspect, the invention relates to a method for measuring a quantity representative of a perimeter or of a variation in a perimeter of a deformable object, the measurement method comprising the following steps:

- Arrangement of at least one elastic hybrid cable wound so as to form at least one turn around the deformable object, the or each elastic hybrid cable comprising a wire of a first type and a wire of a second type, for the or each elastic hybrid cord, the yarn of the first type having a lower degree of tenacity than that of the yarn of the second type, the yarn of the second type having a lower degree of elasticity than that of the yarn of the first type, the yarn of the second type comprising a conductive material, for the or each elastic hybrid cable, the yarn of the second type, when said elastic hybrid cable is at rest, being wound helically around the yarn of the first type,

- measurement of the inductance of the wire of the second type of said elastic hybrid cable between two reference points of said elastic hybrid cable,

- calculation for the or each elastic hybrid cable, of said representative quantity at the level of said elastic hybrid cable, using the inductance of the wire of the second type of said elastic hybrid cable measured.

According to particular embodiments, the measurement method comprises one or more of the following characteristics, taken in isolation or in any technically possible combination: the deformable object comprises a cross section of substantially circular shape at the level of the or each elastic hybrid cable, said characteristic quantity being calculated at the stage of calculation for the elastic hybrid cable using a linear relationship between the inductance measured by the unit of measurement and said characteristic quantity;

- for the or each elastic hybrid cable, each reference point of said elastic hybrid cable is maintained at a fixed position on the deformable object;

- the wire of the first type has a diameter at rest cp _e , the wire of the second type has a diameter fk _, the deformable object has a perimeter at rest Pe at the level of the or each elastic hybrid cable, and (cp _{e +} Fk ><Pe / (10 ^* TT).

According to a third aspect, the invention also relates to a device for measuring by pressurizing the subsoil comprising:

- at least one probe intended to be introduced into a subsoil borehole, said probe comprising a deformable cell, and

- a transfer unit configured to introduce a fluid inside the deformable cell, characterized in that it further comprises a device for measuring a quantity representative of a perimeter or a variation of a perimeter of the deformable cell, the measuring device having the above characteristics, the or each elastic hybrid cable of the measuring device being wound and forming at least one turn around the deformable cell of the probe.

According to particular embodiments, the measuring device comprises several elastic hybrid cables distributed over the deformable cell at different predefined longitudinal heights.

According to a fourth aspect, the invention also relates to the use of a measuring apparatus for measuring the perimeter of an inflatable obturator or packer or for controlling the expansion of said obturator or packer, the measuring apparatus having the above characteristics. , the or each elastic hybrid cable of the measuring device being wound and forming at least one turn around said shutter or said packer.

According to a fifth aspect, the invention also relates to the use of the measuring apparatus presented above in the field of inductance plethysmography for measuring the perimeter of a part of the body of an individual or of a living being. or the variation of the perimeter of said part of the body, characterized in that the measuring device has the above characteristics, the or each elastic hybrid cable of the measuring device being wound and forming at least one turn around said part of the body, said part of the body being for example the torso or the abdomen. Other characteristics and advantages of the invention will emerge from the detailed description which is given below, by way of indication and in no way limiting, with reference to the appended figures, among which:

- [Fig 1] Figure 1 is a simplified schematic representation of the measuring device of the invention, mounted around a deformable object;

- [Fig 2] Figure 2 is a representation similar to that of Figure 1, after expansion of the deformable object;

- [Fig 3] Figure 3 is a schematic longitudinal sectional view of an elastic hybrid cable of the measuring device of Figure 1 at rest,

- [Fig 4] Figures 4 is a side view and in schematic longitudinal section of the elastic hybrid cable of Figure 3 at a maximum elongation rate K _max ,

- [Fig 5 to 8] Figures 5 to 8 are graphical representations of the inductance of an elastic hybrid cable measured by the measurement unit of Figure 1 as a function of the diameter of the deformable object of Figure 1 , under different test conditions;

- [Fig 9] Figure 9 is a schematic representation of a dilatometric probe equipped with the measuring device of Figure 1;

- [Fig 10] Figure 10 is a schematic representation illustrating the use of a measuring device according to the invention in the field of inductance plethysmography;

- [Fig 11] Figure 11 shows a device for measuring by compression of a sample of soil or rock comprising in particular a measuring device according to the invention;

- [Fig 12] Figure 12 is a schematic representation illustrating the use of a measuring device according to the invention to measure the perimeter of an inflatable shutter or packer; and

- [Fig 13] Figure 13 illustrates the at rest and the stretched state of two inductance plethysmography belts of the state of the art, one with a sinusoidal conductive wire and the other with a wire zig-zag conductor.

The measuring device 50 shown in Figures 1 to 4 is intended to measure the perimeter or the change in perimeter (expansion) of a deformable object 22.

It is well suited to be used in a measuring device 10 by pressurizing the subsoil 15, of the type shown schematically in FIG. 9.

It is further adapted to be used to measure the perimeter of an inflatable obturator or packer or to control the expansion of said obturator or packer, as illustrated in FIG. 12. It can also be used in any other field, to measure the perimeter or the expansion of any other deformable object.

For example, it is well suited for use in the field of inductance plethysmography, as illustrated in Figure 10, for example to measure the perimeter or dilation of a part of the body of an individual or an animal. . This part of the body is for example the torso, an arm, a thigh, etc.

Likewise, it is suitable for use for measurements on single or triaxial compression tests of a soil or rock sample, as shown in Figure 11.

By deformable object is meant here any body, inert or living, whose perimeter is liable to change, spontaneously or under the effect of an external force.

The measuring device 50 is more particularly intended to measure a quantity representative of the perimeter of the deformable object 22. This quantity is for example directly the perimeter of the deformable object. As a variant, it is intended to measure its diameter or its radius, in the case of an object of circular section. According to another variant, it measures a quantity representative of the variation in the perimeter of the deformable object 22, that is to say the expansion of the deformable object 22. The device then measures the variation in the perimeter, in the diameter, or the radius of this object.

The measuring device 50 comprises at least one elastic hybrid cable 52 of a predetermined length wound and forming at least one turn around the deformable object 22, at a predefined longitudinal height.

The or each elastic hybrid cable 52 makes a number of turns around the deformable object 22, typically 1 to 10, but this number could exceed 10.

The accuracy of the measurement increases with the number of turns, and increases when the turns are tight, that is to say contiguous.

In Figures 1 and 2, the deformable object 22 has a cylindrical shape. As a variant, it has any other suitable shape so that the hybrid cable can be wound around the object 22.

The measuring device 50, according to the invention, further comprises an inductance measuring unit 54 electrically connected by one or more pairs of measuring terminals 56 to a pair of reference points 58 of each elastic hybrid cable 52, and a calculation unit 60 electrically connected to the measurement unit 54.

For example, the reference points 58 of an elastic hybrid cable 52 correspond to the ends of the elastic hybrid cable 52.

Preferably, the reference points 58 of each elastic hybrid cable 52 have a fixed position on the deformable object 22. The reference points 58 of said hybrid cable elastic are fixed relative to each other. In other words, the distance between the reference points 58 of each elastic hybrid cable 52 is not likely to change appreciably when the deformable object 22 is deformed.

Figure 3 is a schematic longitudinal sectional view of an elastic hybrid cable 52 at rest, as included in the measuring device 50.

The elastic hybrid cable 52 comprises a yarn of a first type 64, said to be of high elasticity, and a yarn of a second type 66, said of high tenacity.

The high tenacity yarn 64 has a lower degree of tenacity than the high tenacity yarn 66, and the high tenacity yarn 66 has a lower degree of elasticity than the high tenacity yarn 64.

In Figures 1 to 4, the sections of the wires 64 and 66 are not to scale with respect to the dimensions of the deformable bodies.

When the elastic hybrid cable is at rest, the high tenacity yarn 66 is wound helically around the high elasticity yarn 64, as shown in Figure 3. As the elastic hybrid cable 52 elongates, the elastic hybrid cable 52 is stretched. relative positions of the two yarns 64 and 66 are reversed, to result in a configuration where from a maximum elongation rate K _max , the high elasticity yarn 64 is wound in a spiral around the taut high tenacity yarn 66, as shown in figure 4.

Thus, at rest, the high tenacity wire 66 forms a circular toric solenoid with a longitudinal axis. As the lengthening, the turns of the solenoid are more and more apart and the radius of the turns decreases.

The yarn 64 of high elasticity can be chosen from among the yarns of the following group: elastomer yarns such as polyurethane yarns, elastane yarns, or a combination of these yarns.

The high tenacity yarn 66 comprises a conductive material.

For example, the high tenacity wire 66 consists of enamelled wires of a conductive material.

As a variant, the high tenacity thread 66 consists of enameled threads of conductive material lined with a thread chosen from among the threads of the following group: threads of natural fibers, such as cotton, linen or hemp, glass threads, carbon threads , yarns of organic fibers such as aramid, para-aramid, polyester, polypropylene, polyamide, aramid or a combination of these yarns. The chosen wire and the enameled wires are wound around each other in a double helix, forming the high tenacity wire 66.

Preferably, the high tenacity yarn 66 and the high elasticity yarn 64 have a ratio of their elastic moduli greater than or equal to 10,000. According to a particular embodiment of the invention, the high elasticity yarn 64 consists of a yarn whose longitudinal modulus of elasticity is equal to approximately 2 MPa. The high tenacity wire 66 consists of enameled copper wires lined with an aramid wire of 1600 dT ex, marketed under the brand Kevlar ^® , for example, whose longitudinal modulus of elasticity is equal to approximately 30,000 MPa.

The elastic hybrid cable 52 is for example of the type described in application WO 2013/110731.

According to this example, in full elongation, the hybrid cable is in a configuration where the high elasticity wire is wound helically around the high tenacity wire with a number of turns per linear meter of the hybrid cable between n _sE -15% and n _sE + 15%. n _sE is determined based on the diameter of the high elasticity wire, the diameter of the high tenacity wire and a predetermined maximum elongation rate, from the following formula: where cp _e is the diameter in mm of the high tensile yarn at rest, fk is the diameter in mm of the high tenacity yarn, and K _ma x is the predetermined maximum elongation rate, expressed in percent.

In addition, the high elasticity wire is twisted on itself - in other words twisted - with a specific number of clean turns, the clean turns winding in the opposite direction of the turns of the helix formed by the wire of high elasticity around the high tenacity yarn, promotes winding of the high tenacity yarn around the high elasticity yarn as the hybrid cable returns from its full extension configuration to its resting configuration.

The number of clean turns per linear meter of the cable at the maximum elongation rate is between n _sE and 3 xn _sE, preferably between n _sE and 2 xn _sE.

The spiral shape of the high elasticity wire, and its deformation when the hybrid cable relaxes to its resting configuration, guides the high tenacity wire and allows it to tidy up around the high elasticity wire.

By respecting the above specifications on the number of clean turns of the high elasticity wire and the number of turns of the high elasticity wire in full elongation of the hybrid cable, a hybrid cable can be manufactured having a good behavior for a range of rates. elongation ranging from 0 to several hundred%. The predetermined maximum elongation rate of the hybrid cable is for example between 100% and 400%. The upper limit is for example defined by the number of contiguous turns of the high tenacity yarn that it is possible to place on the high elasticity yarn at rest. Advantageously, the wire of the first type has a diameter at rest cp _e and the wire of the second type has a diameter fk such that (f _{q +} fk) <Pe / (10 ^* TT), where Pe is the perimeter at rest of l deformable object at the or each elastic hybrid cable. The inventor believes that such a size ratio contributes to obtaining high measurement precision.

In other words, the ratio between the diameter of the elastic hybrid cable and the perimeter of the deformable object is less than 10 ^* TT.

Perimeter at rest is understood to mean the minimum perimeter of the deformable object in the measurement range considered.

As a variant, the elastic hybrid cable 52 is not of the type described in application WO 2013/110731, but is of any other suitable type.

The measurement unit 54 is able to measure for each elastic hybrid cable 52, the inductance of the high tenacity wire 66 of said elastic hybrid cable 52 between the two reference points 58 of said elastic hybrid cable 52.

For example, the measurement unit 54 is, for example, an inductance meter as known to those skilled in the art.

The inductance meter is for example a commercial multimeter, of the "Keysight U1733C" or "Siborg LCR Reader" type, or any other equivalent model.

The measurement unit 54 is also able to transmit each measured inductance to the calculation unit 60.

The calculation unit 60 is configured to calculate for each elastic hybrid cable 52, the magnitude representative of the perimeter or of the variation in the perimeter of the deformable object 22, at the predefined height of said elastic hybrid cable 52, using the inductance of the high tenacity yarn 66 of said measured elastic hybrid cable.

The tests carried out have demonstrated the fact that the inductance of the high tenacity wire 66 of said elastic hybrid cable 52, and more precisely, the inductance measured by the measurement unit 54 between the reference points 58 of said elastic hybrid cable 52, is proportional to the perimeter of the deformable object 22 to the longitudinal height of an elastic hybrid cable 52. More precisely, it varies linearly with the perimeter of the deformable object 22 to the longitudinal height of an elastic hybrid cable 52 This is illustrated in Figures 5 to 8.

The curve of FIG. 5 was obtained for measurements with a measuring device 50 comprising a single elastic hybrid cable 52 wound up and forming three turns around a deformable cell 22 of cylindrical shape. The inductance measurements were carried out for a diameter of the deformable cell 22 varying between 65 millimeters and 95 millimeters. The curves of FIG. 6 were obtained for measurements with a measuring device 50 comprising three elastic hybrid cables 52 (curves L1, L2 and L3), each wound and forming three turns around a deformable cell 22 of cylindrical shape. The towers are contiguous. The hybrid cables were arranged axially at three different levels of the cell.

The diameter at rest cp _e of the wire of the first type (high elasticity wire) is 0.63mm. The diameter fk of the wire of the second type (high tenacity wire) is 0.4mm. This wire is a multi-stranded copper wire, consisting of 9 strands. The predetermined maximum elongation rate K _max is 170%. The number n _sE of turns at rest of the wire of the second type around the wire of the first type per linear meter is 750 turns / m.

The inductance measurements were carried out for a perimeter of the deformable cell 22 varying between 19 centimeters and 29 centimeters, ie an expansion rate of 150%. The test was performed by expanding and then retracting the deformable cell.

The curve in Figure 7 was obtained for measurements with a measuring device 50 comprising a single elastic hybrid cable 52 wound and forming three turns around a deformable cell 22 of cylindrical shape. The towers are contiguous.

The diameter at rest cp _e of the wire of the first type (high elasticity wire) is 0.63mm. The diameter fk of the wire of the second type (high tenacity wire) is 0.4mm. This wire is a multi-stranded copper wire, consisting of 9 strands. The predetermined maximum elongation rate K _max is 300%. The number n _sE of turns at rest of the wire of the second type around the wire of the first type per linear meter is 1200 turns / m.

The inductance measurements were made for a perimeter of the deformable cell 22 varying between 35 centimeters and 98 centimeters, ie an expansion rate of 277%. The curve in figure 8 was obtained for measurements with a measuring device

50 comprising a single elastic hybrid cable 52 wound and forming nine turns around a deformable cell 22 of cylindrical shape. The inductance measurements were carried out for a perimeter of the deformable cell 22 varying between approximately 19 centimeters and 26 centimeters, ie an expansion rate of 137%. The towers are contiguous. The diameter at rest cp _e of the wire of the first type (high elasticity wire) is 0.63mm.

The diameter fk of the wire of the second type (high tenacity wire) is 0.4mm. This wire is a multi-stranded copper wire, consisting of 9 strands. The predetermined maximum elongation rate K _max is 170%. The number n _sE of turns at rest of the wire of the second type around the wire of the first type per linear meter is 750 turns / m. In all cases, a linear relationship is observed between the measured inductance and the perimeter of the deformable cell. The coefficient of determination R ² is always greater than 99.98%.

Similarly, the inductance measured by the measurement unit 54 between the reference points 58 of said elastic hybrid cable 52 varies linearly with the diameter of the deformable object 22, when the latter has a cross section of substantially circular shape. at the preset height.

It is proportional to the inductance of the high tenacity wire 66 of said elastic hybrid cable 52, and more precisely, to the inductance measured by the measurement unit 54 between the reference points 58 of said elastic hybrid cable 52.

Therefore, the calculation unit 60 is then configured to calculate, for each elastic hybrid cable 52, the characteristic quantity using a linear relationship between the inductance measured by the measurement unit 54 and said characteristic quantity. This linear relationship corresponds to a predetermined line characteristic of said elastic hybrid cable 52. The characteristic line corresponds to the line representative of the inductance measured as a function of the perimeter.

This characteristic line is determined during a preliminary calibration step, using tubes of calibrated sections. This contributes to obtaining very good measurement accuracy.

Advantageously, when the deformable object 22 is of substantially circular shape at the predefined height, the calculation unit 60 is configured to calculate for each elastic hybrid cable 52, a diameter of the deformable object 22, as a function of the inductance of the high tenacity wire 66 of said elastic hybrid cable 52 measured, for example via a predefined characteristic straight line representative of the inductance measured as a function of the diameter.

In Figure 1, the deformable object 22 has a first perimeter. The elastic hybrid cable 52 has a first elongation. The high tenacity wire 66 has a closed contour solenoid shape with a perimeter equal to the perimeter of the deformable object. It forms turns having a first spacing between them.

In Figure 2, the deformable object 22 has undergone expansion. The elastic hybrid cable 52 has a second elongation, greater than the first. The high tenacity wire 66 always has a closed contour solenoid shape with a perimeter equal to the perimeter of the deformable object. The turns of the wire have a second spacing between them, greater than the first spacing.

Thus, the elongation of an elastic hybrid cable 52 of the measuring device 50 varies as a function of the perimeter of the deformable object 22 at the predefined longitudinal height of said object. elastic hybrid cable 52. The shape of the high tenacity wire 66 also varies depending on the perimeter of the deformable cell 22. The diameter of the toric solenoid formed by the high tenacity wire 66 increases with the perimeter of the deformable object 22. This is allowed by the fact that the turns move away from each other. The inductance of the high tenacity wire 66 is essentially a function of the perimeter of the solenoid, which follows the perimeter of the deformable cell 22.

Because the elastic hybrid cable has a very high elongation capacity, it is possible to make measurements over a wide range of expansion values, up to at least a factor of 1: 3 of the perimeter without loss of measurement accuracy. Measuring sensors currently marketed for inductance plethysmography (commonly called plethysmography belts) only operate over a much smaller range of expansion values, typically 15 to 40% elongation and repeated cyclic stresses at higher levels. elongation rates are liable to degrade the sensors and therefore the quality of the measurement.

Indeed, the hybrid cable used in the present invention behaves like an elastic whose elasticity is constant up to a predetermined maximum elongation and beyond, when said predetermined elongation is reached, then behaves like a high tenacity yarn, with very low elongation and high strength before breaking.

The hybrid cable used in the present invention, wound and forming at least one turn around the deformable object, is therefore designed and chosen so that it works only in its elastic range, thus offering very low resistance over the entire range. target measurement, thus avoiding creating resistance to expansion of the deformable object. For this purpose, it will suffice for the hybrid cable to be designed such that its maximum elongation capacity is greater than the maximum expansion factor of the deformable object to be measured; this is possible for expansion factors of the deformable object of up to 1: 3 or more.

In one of the experimental implementations on an inflatable body having a section at rest that is substantially circular, with a diameter of 200 mm, it has been observed that the uncertainty on the perimeter measurement comes mainly from that of the measurement unit. 54 inductance. Thus, when the measurement unit 54 is able to provide inductance measurements with an accuracy of less than 10 nanohenri, we have been able to obtain that each diameter measurement carried out by the measuring device 50 has an accuracy of less than 100 micrometers.

These measurements are repeatable without degradation of precision. On the curve of FIG. 5, a measurement error of 10 nanohenri corresponds to a measurement error on the perimeter of 225 micrometers, or a measurement error on the diameter of 75 micrometers.

Without being bound by this theory, the inventor believes that the following elements contribute to this excellent precision:

- the fact that the hybrid cable can undergo many cycles of elongation / retraction, without the ordering of the high tenacity yarn, that is to say of the conductive yarn, being degraded;

- the fact that the hybrid cable works in its area of very low resistance to elongation, where the conductive wire is not subjected to significant mechanical stresses;

- the fact that the inductance of the hybrid cable is strictly a function of the perimeter of the torus formed by the conductive wire, which follows very precisely the perimeter of the deformable object;

- the fact that the diameter of the conductor cable (or the sum of the diameters of the wire of the first type and the diameter of the wire of the second type) is chosen to be much smaller than the diameter of the deformable object;

- the fact that the reference points are fixed with respect to each other, in order to avoid a variable parasitic inductance, specific to the loop formed by the terminals of the measurement unit itself (inductance meter);

- the fact that the relationship between the inductance and the perimeter remains linear whatever the number of turns of the hybrid cable, for a low number of turns of the hybrid cable around the deformable object, the maximum number of turns being chosen as that the longitudinal distance (along the deformable object), between the first and the last turn of the wound hybrid cable remains less than the diameter at rest of the deformable object;

- the fact that the value of the inductance measured at the reference points 58 is independent of the number of turns (of the wire of the second type around the wire of the first type) per linear meter of hybrid cable.

The measuring device 50 is particularly easy to use, and this on all kinds of deformable object 22.

Although this implementation is not essential, the hybrid cables can also be mounted on an elastic sleeve which is then threaded around the deformable object. In this case, it is not necessary to secure the hybrid cables and the elastic sheath with glue or by stitching.

Several applications will now be described, with reference to Figures 9 to

12.

The measuring device 10 shown in FIG. 9 is a dilatometric measuring device or a pressuremeter measuring device intended to respectively carry out a dilatometric test or a pressuremeter test. For example, the device 10 is a pressuremeter measuring device of the Ménard type, in accordance with standard NFP 94-110-1.

The measuring device 10 comprises a probe 20 intended to be introduced into a longitudinal borehole 18 in the basement 15. In the example of FIG. 9, said probe 20 comprises a cell 22 which can be deformed by injection of fluid, in the form of a tube. longitudinal central axis. The deformable cell constitutes a deformable object within the meaning of the present invention.

The probe is for example a pressuremeter probe.

For this application, the hybrid cables can advantageously be covered with a protective sheath, for example made of elastomer, in order to avoid direct contact with the ground.

For example, the basement 15 comprises a layer 28 of a first type of material between two layers 26 of a second type of material.

For example, the probe 20 of the device 10 according to the invention is a Ménard probe conforming to the NFP 91-110-1 standard, advantageously an FC 60 Francis COUR probe with flexible sheath.

The FC 60 Francis COUR probe is for example described in patents FR 3 009 841 and FR 2 910 047 of the Applicant

The device 10 also includes a transfer unit 34 such as a pump, configured to introduce a fluid inside the deformable cell 22.

The fluid is typically an incompressible fluid, for example water. Alternatively, the fluid is a gas.

The measuring device 10 according to the invention further comprises the measuring device 50. The latter is configured to measure a quantity representative of the perimeter or of a variation in the perimeter of the deformable object 22, here the deformable cell, at at least one predefined longitudinal height of the deformable object 22.

Advantageously, the measuring device 50 is configured to measure said representative quantity at different predefined longitudinal heights of the deformable object 22, here the deformable cell.

In this case, the measuring device 50 comprises for the or each predefined longitudinal height, an elastic hybrid cable 52 wound and forming at least one turn around the deformable object 22 at said predefined longitudinal height.

By way of example, the measuring apparatus 50 of FIG. 9 comprises two elastic hybrid cables 52.

According to other variant embodiments, the measuring device 50 comprises three or four elastic hybrid cables 52, or more than four cables 52. The pairs of reference points 58 of each elastic hybrid cable 52 are electrically connected to the inductance measurement unit 54.

Each elastic hybrid cable makes a number of turns around the deformable object, typically 1 to 10, but this number could exceed 10.

The conductors used to constitute the son of the second type can also advantageously be chosen such that they are flexible, for example enamelled stranded conductors.

This sheath is a sleeve threaded around the deformable cell 22, and covering at least the entire section of the cell on which the hybrid cable is pressed.

Each hybrid cable is connected to an electronic box located near the probe, which measures the inductance of each conductor wire simultaneously or advantageously one by one, and transmits the measured inductance values to the surface (via a wireless link, via an electric cable or via an optical fiber). The measurements are displayed and / or recorded on the surface.

The probe can be protected by a flexible sheath, for example made of elastomer (not shown) preventing direct contact of the hybrid cables with the ground, in order to avoid damaging them.

The probe is also equipped with a pressure sensor (not shown) which measures the pressure directly in the deformable cell or in the pipe which supplies this deformable cell from the surface. A recording and display system then makes it possible to plot the curve linking the measured pressure and the diameter of the probe on each of the levels.

The operation of a measuring device 10 in the example of a test by pressurizing the subsoil will now be described.

The probe 20 is first introduced into a borehole 18 in the basement 15 so as to position the probe 20 at a defined depth (measuring station).

The pressuremeter or dilatometric tests are typically carried out at different depths along the borehole 18.

The deformable cell 22 is pressurized in increasing pressure steps by introducing fluid by means of the transfer unit 34.

The pressurization is carried out for example by successive increasing stages.

The pressure inside the deformable cell 22 varies, for example, from 1 bar to 500 bars.

The diameter of the deformable cell 22 varies depending on the pressure level and the type of material of the subsoil 15. The elongation of each elastic hybrid cable 52 of the measuring apparatus 50 varies as a function of the perimeter of the deformable cell 22 at the predefined longitudinal height of said elastic hybrid cable 52. The inductance of the high tenacity wire 66 varies as a function of the perimeter of the deformable cell 22.

Next, the measurement unit 54 measures the inductance of the high tenacity wires 66 of each elastic hybrid cable 52 and transmits it to the computing unit 60, then the computing unit 60 calculates the characteristic quantity for the hybrid cable. elastic 52 as a function of the inductance of its high tenacity wire 66 measured, for example via a characteristic straight line of the elastic hybrid cable 52.

The relationship between the inductance of each of the hybrid cables and the desired characteristic quantity, which has been established beforehand by calibration for each of the hybrid cables, makes it possible to display in real time (and to record if necessary) the evolution of the diameter of the cable. the deformable cell in each of its levels as it expands and retracts.

The steps described above are repeated successively for each pressure stage.

In the case of the pressuremeter test, a pressuremeter curve, or expansion curve, is then obtained by plotting the pressure measured in the deformable cell 22 on the abscissa and the variation in diameter during the pressuremeter test on the ordinate.

This curve is then analyzed in order to determine the mechanical properties of the subsoil 15.

Typically, the probe 20 is then moved vertically in the borehole 18 to be positioned at the level of the next measuring station and the process steps are repeated.

Advantageously, the invention comprises a step of calibrating the calculation unit 60, preliminary to the introduction of the probe 20 into the borehole 18. During this step, the transfer unit 36 introduces fluid from the storage tank. fluid 30 inside the deformable cell 22 until the deformable cell 22 has a predefined diameter. The measurement unit 54 then measures the corresponding inductance for each elastic hybrid cable 52.

This operation is carried out for different diameter bearings. For each elastic hybrid cable 52, a curve of a characteristic of said elastic hybrid cable 52 is obtained by plotting on the abscissa the characteristic quantity, for example the diameter of the deformable cell 22, and on the ordinate the measured inductance. Such a curve is represented in FIG. 5. The calculation unit 60 performs, for example, for each elastic hybrid cable 52, a linear regression in order to obtain the characteristic straight line of said. elastic hybrid cable 52 making it possible to calculate the corresponding characteristic quantity as a function of a measured inductance.

The advantage of measuring a characteristic quantity such as the diameter of the probe at different levels during its swelling is to detect inhomogeneous swelling that would result from a heterogeneous soil, with layers offering different resistances at different heights.

The probes currently on the market do not allow such measurements at different levels and are therefore liable to deteriorate during swelling in a highly heterogeneous soil or to give an erroneous measurement of the resistance of the soil.

For example, the probe 20 of Figure 1 is positioned at a depth where one of the layers 26 and the layer 28 overlap. The deformable cell 22 of the probe 20 then comprises a part in contact with one of the layers 26 and another part in contact with the layer 28. A first of the two hybrid electric cables 52 of the measuring device 50 is wound around the deformable cell 22 at its part in contact with layer 26 and a second of the two hybrid electric cables 52 is wound around deformable cell 22 at its part in contact with layer 28.

In the example of FIG. 1, the part of the deformable cell 22 in contact with the layer 26 has a smaller diameter than the part of the deformable cell 22 in contact with the layer 28. The inductance measured for the first of the two hybrid electric cables 52 will then be lower than the inductance measured for the second of the two hybrid electric cables 52, which reflects different physical properties for the layers 26 and 28.

It is then understood that by increasing the number of elastic hybrid cables 52 of the measuring device 50 distributed over the deformable cell 22, it is possible to obtain a better knowledge of the physical properties of the subsoil 15 in contact with the cell. deformable 22, in particular when the basement 15 comprises several layers of different type of material.

Thus, the measuring device 50 according to the invention makes it possible to measure a characteristic quantity such as the perimeter or the diameter of the deformable cell 22 at different longitudinal heights in a precise and simple manner, this characteristic quantity being variable as a function of the quantity. of fluid introduced into the deformable cell 22.

Finally, the measuring device 50 according to the invention makes it possible to obtain measurements of said characteristic quantity of the deformable cell 22 without having to adjust it or reposition it between different measurements. A second example of application of the measuring device 50 will now be described, with reference to FIG. 10.

According to this example, the measuring apparatus 50 is used in the field of inductance plethysmography, to measure the perimeter of a part of the body of an individual 70 or of any other living being. The measuring device 50 is for example used to measure a perimeter around the torso of the individual 70, as shown in Figure 10.

According to this example of use, the measuring device 50 is as described above. The deformable object 22 corresponds to the part of the body of the individual 70. The measuring device 50 then comprises at least one elastic hybrid cable 52 wound up and forming at least one turn around the torso of the individual 70 to at least a predefined height.

By way of example, the measuring apparatus 50 of FIG. 10 comprises two elastic hybrid cables 52. For example, one of the elastic hybrid cables 52 is placed at the level of the rib cage of the individual 70, and the other is placed at the level of his abdomen.

When using the measuring device 50 in this way, the measuring unit 54 measures the inductance of the high tenacity wires 66 of each elastic hybrid cable 52 and transmits it to the computing unit 60, then the Calculation unit 60 calculates the perimeter of the torso of the individual 70 at each elastic hybrid cable 52 using the corresponding measured inductance.

In a variant not shown, the measuring apparatus 50 is used to measure a perimeter of an arm or a leg.

The measuring device 50 then makes it possible to have precise temporal monitoring of the perimeter of a part of an individual's body, without having to adjust it or reposition it between different measurements.

The measuring device 50 then makes it possible to obtain precise measurements of the perimeter of a part of an individual's body, and over large perimeter ranges, and for large diameters.

A third example of application of the measuring device 50 will now be described, with reference to FIG. 11.

According to this example, the measuring apparatus 50 is used for measurements on single or triaxial compression tests of a sample 105 of soil or rock, to measure a perimeter of the sample 105 of soil or rock.

FIG. 11 represents a device for measuring by compression 100 of the triaxial sample 105.

The compression measuring device 100 comprises an enclosure 110 capable of containing a fluid 115, the sample 105 being positioned in the enclosure 110. Advantageously, the compression measurement device 100 comprises a membrane 120 positioned in the enclosure 110 and containing the sample 105.

The compression measuring device 100 further includes a piston 125 configured to exert an axial force on the sample 105 at a defined pressure.

The compression measuring device 100 further comprises a measuring apparatus 50 configured to measure the perimeter of the sample 105.

According to this example of use, the measuring device 50 is as described above. The deformable object 22 corresponds to the sample 105. The measuring device 50 then comprises at least one elastic hybrid cable 52 wound and forming at least one turn around the sample 105 at at least a predefined height. By way of example, it comprises three elastic hybrid cables 52.

When the compression measuring device 100 comprises a membrane 120, at least one elastic hybrid cable 52 is wound around said membrane 120.

For the sake of clarity, in Figure 11 only the elastic hybrid cables 52 of the measuring device 50 have been shown.

Advantageously, the sample 105 is cylindrical in shape, with at least one elastic hybrid cable 52 being wound around the axis of the sample 105.

The enclosure 110 is, for example of cylindrical shape, the axis of the sample 105 then being aligned with the axis of the enclosure 110, and the piston 125 is configured to exert the axial force along the axis of the sample 105.

The perimeter measurements around the sample 105 are carried out for different levels of defined pressure exerted by the piston 125 on the sample 105, in order to obtain a pressuremeter curve of the compression of the sample 105 as a function of the defined pressure exerted on the sample 105. This curve is then analyzed in order to determine the mechanical properties of the sample 105.

A fourth example of application of the measuring device 50 will now be described, with reference to FIG. 12.

According to this example, the measuring device 50 is used to measure the perimeter of an inflatable obturator or packer 130 or to control the expansion of said obturator or packer 130.

The inflatable shutter 130 has the same general structure as the pressuremeter probe 20 described above. It is typically used in the petroleum, geothermal or geotechnical field, to plug a well or a borehole 28.

The inflatable shutter 130 comprises a cell 132 which can be deformed by injection of fluid, in the form of a tube with a longitudinal central axis. The deformable cell constitutes a deformable object within the meaning of the present invention. The measuring device 50 is of the type described above. It comprises at least one elastic hybrid cable 52 wound around the inflatable obturator 130. Typically, it comprises a plurality of elastic hybrid cables 52 wound and forming at least one turn around the deformable cell 132, at different predefined longitudinal heights.

The control of the expansion of said inflatable obturator or packer serves in particular to prevent bursting linked to excessive expansion of said obturator or packer.

The invention also relates to a method for measuring a quantity representative of a perimeter or of a variation in a perimeter of a deformable object 22, the measuring method comprising the following steps:

- Arrangement of at least one elastic hybrid cable 52 wound so as to form at least one turn around the deformable object 22, the or each elastic hybrid cable 52 comprising a wire of a first type 64 and a wire of a second type 66, for the or each elastic hybrid cord 52, the yarn of the first type 64 exhibiting a lower degree of tenacity than that of the yarn of the second type 66, the yarn of the second type 66 having a lower degree of elasticity than that of the yarn of the first type 64, the yarn of the second type 66 comprising a conductive material, for the or each elastic hybrid cable 52, the yarn of the second type 66, when said elastic hybrid cable 52 is at rest, being wound helically around the yarn of the first type 64,

- measurement of the inductance of the wire of the second type 66 of said elastic hybrid cable 52 between two reference points (58) of said elastic hybrid cable 52,

- calculation for the or each elastic hybrid cable 52, of said representative quantity at the level of said elastic hybrid cable 52, using the inductance of the wire of the second type 66 of said elastic hybrid cable 52 measured.

The method is specially adapted to be implemented with the measuring device described above. Conversely, the measuring device is specially designed for the implementation of the method.

The method is applicable in particular to the four application cases described above: measurement by pressurizing the subsoil, measurement of the perimeter of an inflatable or packer shutter, inductance plethysmography, simple or triaxial compression tests of a sample. soil or rock.

The characteristic quantity measured is as described above.

The elastic hybrid cable is as described above.

In particular, the wire of the first type has a diameter at rest cp _e and the wire of the second type has a diameter fk such that (f _{e +} fk) <Rb / (10 ^* tt), Pe being the perimeter at rest of the object deformable at the or each elastic hybrid cable 52.

The inductance measurement is carried out as described above. The deformable object is as described above.

In particular, when the deformable object 22 comprises a cross section of substantially circular shape at the or each elastic hybrid cable 52, said characteristic quantity being calculated at the step of calculating for the elastic hybrid cable 52 using a linear relationship between inductance measured by measurement unit 54 and said characteristic quantity.

This linear relationship is as described above.

Advantageously, for the or each elastic hybrid cable 52, each reference point 58 of said elastic hybrid cable is maintained at a fixed position on the deformable object 22.

Claims

1 Apparatus (50) for measuring a quantity representative of a perimeter or of a variation in a perimeter of a deformable object (22), the measuring apparatus (50) comprising an inductance measurement unit (54), characterized in that it further comprises at least one elastic hybrid cable (52) wound and arranged to form at least one turn around the deformable object (22), the or each elastic hybrid cable (52) comprising a yarn of a first type (64) and a yarn of a second type (66), for the or each elastic hybrid cable (52), the yarn of the first type (64) having a lower degree of tenacity than that yarn of the second type (66), the yarn of the second type (66) having a lower degree of elasticity than that of the yarn of the first type (64), the yarn of the second type (66) comprising a conductive material, for the or each elastic hybrid cable (52), the yarn of the second type (66), when said elastic hybrid cable (52) is at rest, being wound helically around the yarn of the first type (64), the measuring unit (54) comprising for the or each elastic hybrid cable (52) a pair of measuring terminals (56) electrically connected to two reference points (58) of said elastic hybrid cable (52) and being adapted to measure the inductance of the wire of the second type (66) of said elastic hybrid cable (52) between the two reference points (58) of said elastic hybrid cable (52), the apparatus further comprising a calculation unit ( 60) electrically connected to the measurement unit (54) and configured to calculate for the or each elastic hybrid cable (52), said representative quantity around said elastic hybrid cable (52), using the inductance of the wire of the second type (66) of said elastic hybrid cable (52) measured.

2.- Apparatus (50) according to claim 2, wherein the deformable object (22) comprises a cross section of substantially circular shape at the or each elastic hybrid cable (52), the computing unit (60) is configured to calculate said characteristic quantity for an elastic hybrid cable (52) using a linear relationship between the inductance measured by the measurement unit (54) and said characteristic quantity.

3.- Apparatus (50) according to claim 1 or 2, wherein, at full elongation, the hybrid cable (52) is in a configuration where the wire of the first type (64) is wound helically around the wire of the second type. (66) with a number of turns per linear meter of the hybrid cable (52) between n _sE -15% and n _sE + 15%. n _sE being determined according to the diameter of the wire of the first type (64), the diameter of the wire of the second type (66) and a predetermined maximum elongation rate, from the following formula:

1000 .J ^K „x (k _^ + 200) n. - - -Forrotffe {F1) fp (y, + y _k + 100 in which cp _e is the diameter in mm of the wire of the first type (64) at rest, fk is the diameter in mm of the wire of the second type (66) , and K _ma x is the predetermined maximum elongation rate, expressed in percent.

4.- Apparatus (50) according to claim 3, wherein the wire of the first type (64) is twisted on itself with a specific number of clean turns, the clean turns winding in the opposite direction of the turns of the. helix formed by the wire of the first type (64) around the wire of the second type (66), the number of clean turns per linear meter of the hybrid cable at the maximum elongation rate being between n _sE and 3 xn _sE, preferably between n _sE and 2 xn _sE. .

5.- Apparatus (50) according to any preceding claim, wherein each measurement has an accuracy of less than 0.1%

6. Apparatus (50) according to any preceding claim, wherein, for the or each elastic hybrid cable (52), the reference points (58) of said elastic hybrid cable are fixed with respect to one another. 'other.

7.- Method for measuring a quantity representative of a perimeter or a variation of a perimeter of a deformable object (22), the measuring method comprising the following steps:

- Arrangement of at least one elastic hybrid cable (52) wound so as to form at least one turn around the deformable object (22), the or each elastic hybrid cable (52) comprising a wire of a first type ( 64) and a yarn of a second type (66), for the or each elastic hybrid cable (52), the yarn of the first type (64) having a lower degree of tenacity than that of the yarn of the second type (66), the yarn of the second type (66) having a lower degree of elasticity than that of the yarn of the first type (64), the yarn of the second type (66) comprising a conductive material, for the or each elastic hybrid cable (52), the yarn of the second type (66), when said elastic hybrid cable (52) is at rest, being wound helically around the yarn of the first type (64),

- measurement of the inductance of the wire of the second type (66) of said elastic hybrid cable (52) between two reference points (58) of said elastic hybrid cable (52), - Calculation for the or each elastic hybrid cable (52), of said representative quantity at the level of said elastic hybrid cable (52), using the inductance of the wire of the second type (66) of said elastic hybrid cable (52) measured.

8. A measurement method according to claim 7, wherein the deformable object (22) comprises a cross section of substantially circular shape at the or each elastic hybrid cable (52), said characteristic quantity being calculated in step calculation for the elastic hybrid cable (52) using a linear relationship between the inductance measured by the measurement unit (54) and said characteristic quantity.

9. A method according to any one of claims 7 or 8, wherein, for the or each elastic hybrid cable (52), each reference point (58) of said elastic hybrid cable is maintained at a fixed position on the object. deformable (22).

10. A method according to any one of claims 7 to 9, wherein the wire of the first type has a diameter at rest cp _e and the wire of the second type has a diameter fk, the deformable object has a perimeter at rest Pe at the level of the or each elastic hybrid cable (52), such that (f _{q +} fk) <Pe / (10 ^* p)

11 .- Device (10) for measuring by pressurizing the subsoil (15) comprising:

- at least one probe (20) intended to be introduced into a borehole (18) of the subsoil (15), said probe (20) comprising a deformable cell, and

- a transfer unit (34) configured to introduce a fluid inside the deformable cell, characterized in that it further comprises an apparatus (50) for measuring a quantity representative of a perimeter or of a variation of a perimeter of the deformable cell, the measuring device (50) being according to any one of claims 1 to 6, the or each elastic hybrid cable (52) of the measuring device (50) being wound and forming at least one turn around the deformable cell of the pressuremeter probe (20).

12.- Use of a measuring device (50) in the field of inductance plethysmography to measure the perimeter of a part of the body of an individual (70) or of a living being or of a variation of the perimeter of said body part (70), characterized in that the measuring apparatus (50) is according to any one of claims 1 to 6, the or each elastic hybrid cable (52) of the apparatus (50) measuring device being wound and forming at least a turn around said part of the body, said part of the body being for example the torso or the abdomen.

13.- Use of a measuring device (50) for measuring the perimeter of an inflatable obturator or packer (130) or controlling the expansion of said obturator or packer (130), characterized in that the device (50) of The measurement is according to any one of claims 1 to 6, the or each elastic hybrid cable (52) of the measuring apparatus (50) being wound and forming at least one turn around said shutter or said packer (130).