FR3076905A1 - ELECTRIC RESISTIVITY MEASUREMENT PROBE OF A MEDIUM - Google Patents

Abstract

A resistivity measuring probe of a medium configured to be inserted into said medium, said probe comprising at least four electrodes spaced from each other and a support body of each electrode.

Description

ELECTRIC RESISTIVITY MEASUREMENT PROBE OF A MEDIUM

The subject of the invention is a probe for measuring the electrical resistivity of a medium.

The invention is particularly applicable to a measurement of electrical resistivity in a nozzle, preferably metallic.

A nozzle is a structure allowing the crossing of one lane by another, the lane crossed being for example a road or a watercourse.

A nozzle is generally a composite structure, comprising a metal wall of corrugated sheet and a certain volume of soil, or embankment, which surrounds it.

It is known that a nozzle can undergo corrosion of the metal wall and collapse, at least partially, which can generate sagging or collapse of the worn track, jeopardizing the safety of users.

Monitoring of the electrical resistivity of the embankment surrounding the nozzle is therefore necessary throughout its existence.

To do this, it is known to take a sample of the metal wall and of the fill of the nozzle and to carry out an electrical resistivity measurement in the laboratory.

However, such a method has the disadvantage that the result obtained is punctual since the quantity of material removed is small. The resistivity value obtained is then assigned to the entire structure, without considering variations in the probable physical properties along the nozzle, or even without considering the influence of a possible change in electrical resistivity between the state of the in situ material and its sample state.

The object of the invention is to at least partially remedy these drawbacks.

To this end, the subject of the invention is a probe for measuring the electrical resistivity of a medium, configured to be inserted in said medium, said probe comprising at least four electrodes spaced apart from each other and a support body for said electrodes.

Thus, thanks to the support body integral with the electrodes, it is possible to insert the probe into the nozzle directly, which makes it possible to carry out in situ measurements and in real time of the electrical resistivity of the nozzle, and this in several places of the nozzle.

Thanks to the present invention, it is possible to carry out a calibration of the resistivity probe using an associated device in order to guarantee the value of the resistivity measured in situ.

The present invention also makes it possible to make several series of measurements if necessary.

According to another characteristic of the invention, the measurement probe comprises eight electrodes integral with one another and spaced from each other.

According to another characteristic of the invention, each electrode has a general shape of a hollow cylinder.

According to another characteristic of the invention, the probe comprises a means for spacing the electrodes, said means for spacing the electrodes comprising a plurality of spacers, each spacer being disposed between two electrodes.

According to another characteristic of the invention, each spacer is a hollow cylinder.

According to another characteristic of the invention, each spacer is integral with the support body.

According to another characteristic of the invention, the support body has a generally cylindrical shape, each electrode and each spacer being mounted one after the other along an external wall of the support body.

According to another characteristic of the invention, the external wall of the support body is grooved.

According to another characteristic of the invention, the support body comprises a head for inserting the probe into the medium to be probed.

According to another characteristic of the invention, the probe comprises a handle.

According to another characteristic of the invention, the probe comprises a sleeve for driving the probe into the medium to be probed, said sleeve being integral with the support body.

The invention also relates to a device for measuring the electrical resistivity of a medium, comprising a probe as described above.

According to another characteristic of the invention, the device comprises an apparatus for injecting a current into certain electrodes and / or measuring a potential difference between two of the electrodes.

According to another characteristic of the invention, the device comprises a switch box, for switching some of the electrodes of the probe to the device.

According to another characteristic of the invention, the switching box comprises an input connected to each of the electrodes, a four-pole output, and a switching shaft between the input and the output for choosing different measurement positions and composing quadrupoles among the electrodes.

According to another characteristic of the invention, the device comprises a calculation unit.

The invention also relates to a method for measuring the electrical resistivity of a medium, comprising a step of inserting a probe as described above in said medium.

According to another characteristic of the invention, the method comprises a step of injecting current into two electrodes of the probe as described above.

According to another characteristic of the invention, the method comprises a step of measuring a potential difference between two other electrodes of the probe as described above.

According to another characteristic of the invention, the method comprises a step of determining the electrical resistivity of the medium from a measurement result obtained during the measurement step.

Other characteristics and advantages of the invention will appear on reading the description which follows. This is purely illustrative and should be read in conjunction with the accompanying drawings in which:

- Figure 1 illustrates a perspective view of a probe of an electrical resistivity measurement device according to the present invention, before assembly;

- Figure 2 illustrates a perspective view of the probe of Figure 1, after assembly;

- Figure 3 illustrates a top view of a support body of the device of Figures 1 and 2;

- Figure 4 illustrates a perspective view of an electrode of the device of Figures 1 and 2;

- Figure 5 illustrates a perspective view of a spacer of the device of Figures 1 and 2;

- Figures 6a and 6b illustrate a switch box associated with the probe of Figures 1 and 2;

- Figure 7 illustrates a timing diagram of a resistivity measurement method according to the present invention;

- Figure 8 illustrates a perspective view of the probe of Figure 2 installed in a nozzle during an implementation of the method of Figure 7; and

- Figure 9 illustrates a schematic summary view of connection of a measuring device to the probe of Figure 2 during the implementation of the method of Figure 7 according to different positions.

Electrical resistivity measuring device and electrical resistivity measuring probe

The subject of the invention is a device for measuring the electrical resistivity of a medium M.

The measuring device is referenced 1 in the figures.

As shown in FIGS. 1 and 2, the device 1 comprises a probe 14.

The probe 14 will now be described in detail.

The probe 14 comprises at least four electrodes 2 integral with each other and spaced from each other.

In the illustrated embodiment, the device 1 comprises eight electrodes 2.

Preferably, each electrode 2 is a ring in the form of a hollow cylinder.

Advantageously, the electrodes 2 are all identical.

Each of the electrodes 2 constitutes a circuit independent of the other electrodes.

The device 1 also includes a means for spacing the electrodes, referenced 3.

The spacer 3 includes a plurality of spacers 4, each spacer 4 being disposed between two electrodes.

Preferably, each spacer 4 is a hollow cylinder.

Advantageously, all of the spacers 4 are identical.

Preferably, the spacers 4 have an outside diameter identical to the outside diameter of the electrodes 2.

As can be seen in the figures, the measuring device also comprises a support body 5 secured to each electrode 2.

Preferably, each spacer 4 is also integral with the support body 5.

As can be seen from the figures, the support body 5, otherwise called the internal structure, has a generally cylindrical shape, each electrode and each spacer being mounted one after the other along an external wall 6 of the internal structure 5 .

Thus, the hollow cylinders forming the electrodes 2 and the spacers 4 are fitted onto the external wall 6.

The external wall 6 advantageously comprises at least one groove 7.

The groove (s) allow (tent) a passage of electric cables along the device 1.

The internal structure 5 also includes a head 8 for inserting the device 1 into the medium M.

The head 8 forms the free end of the external wall 6.

In the illustrated embodiment, the head 8 is a point, of conical shape, which facilitates the introduction of the device 1 into the medium M.

The device 1 also includes a sleeve 9 to allow threshing of the device 1 in the medium M.

The sleeve 9 is fitted on the external wall 6 of the internal structure 5 to an opposite end 10 of the head 8.

The sleeve 9 is provided with a handle 11.

The handle 11 is for example made up of two bars 12 arranged opposite one another, on either side of the sleeve 9, and extending transversely to a longitudinal axis L of the internal structure 5.

The electrodes 2 are made from an electrically conductive material, such as, for example, stainless steel.

The spacers 4, the internal structure 5 and the sleeve 9 are made from an electrically insulating material, and having mechanical characteristics compatible with the use of the device 1 to measure the resistivity of the medium M, in particular in terms of resistance to sinking and stiffness.

For example, the material is a mixture of plastic reinforced with glass fibers.

The entire internal structure on which the electrodes 2, the spacers 4 and the sleeve 9 are mounted forms the probe 14.

The probe 14 is therefore a monolithic element, that is to say that a user has only one piece to handle and to insert into the medium M, as will be detailed later.

As shown in FIGS. 6a and 6b, the device 1 also comprises a switching box 15, for switching some of the electrodes 2 of the device 1 to a quadrupole measuring device 21.

The switch box 15 includes an input 16 connected to an eight-pole plug 17 bringing together a series of eight cables each connected to one of the electrodes 2.

The switch box 15 comprises a four-pole output 18, connected to the quadrupole measuring device of the device 1.

The switching box 15 also comprises between the input 16 and the output 18 a switching shaft 19 making it possible to choose different measurement positions and to mechanically compose the quadrupoles corresponding to the measurement positions, as will be detailed later.

The measurement box is provided with a control button 20 making it possible to choose one from seven measurement positions, as will be detailed later.

The device 1 also includes a calculation unit, making it possible to determine the electrical resistivity of the medium M from measurements taken by the probe 14, as will be detailed later.

The measuring device 21, illustrated in FIG. 8, makes it possible to inject a current into certain electrodes and / or measure a potential difference between two of the electrodes.

The measuring device 21 is preferably quadrupole.

The measuring device 21 comprises a first current injection pole and a second current injection pole.

The first and second poles are able to be connected to each of the electrodes 2.

The measuring device also includes a third and fourth pole, each of the third and fourth poles allowing a measurement of potential difference between two electrodes.

Note that the connection between the electrodes 2 and the poles of the measuring device 21 is made via the switch box 15 allowing the selection of the electrodes actually connected to the first, second, third and poles, and controlled by the control button 20.

Method for measuring the electrical resistivity of the medium M

The invention also relates to a method for measuring the electrical resistivity of the medium M, referenced 70.

It is recalled that the electrical resistivity of a medium M is the physical property which determines the capacity of this medium to oppose the passage of an electric current.

The resistivity p is expressed for example by the formula:

p = k.U / l with k

(c ₁ D ₁ C ₂ D · ^) (ciD ₂ C2D2)

Ci and C ₂ : the current injection electrodes,

Di and D ₂ : the electrodes for measuring the potential difference,

C ₂ Di, CiD ₂ , C ₂ Diet C ₂ D ₂ : the spacings between the axes of the electrodes,

U: potential difference between the electrodes D1 and D ₂ (in volts),

I: current injected between the electrodes Ci and C ₂ (in amperes), p: the electrical resistivity measured (in ohm-meter), and k: the geometric factor (in meters).

The method will be described when applied to a metal nozzle on which an embankment rests.

A nozzle is a work allowing the crossing of a way by another.

A nozzle is generally a composite structure, comprising a metal wall of corrugated sheet and a certain volume of soil, or embankment, which surrounds it.

The measurement method 70 includes a step 71 of inserting the probe 14 into the medium M.

The insertion step 71 is preceded by a preparation step 72.

The preparation step 72 comprises a coring step 73 of the corrugated sheet then a step of drilling the embankment 74.

The drilling is preferably carried out perpendicular to a generator of the nozzle.

For example, drilling is carried out to a depth of around 55 cm.

The diameter of the drilled hole is advantageously less than the diameter of the probe.

For example, the diameter of the drilled hole is between 16 mm and 18 mm, for a probe diameter of 20 mm.

This dimensioning ensures good contact between the probe 14, once inserted in the drilled hole, and the soil which surrounds it.

The insertion step 71 then comprises a step of force-fitting, by threshing, the sleeve 9 of the probe 14 into the drilled hole.

Once the probe is installed in the desired position, the method comprises a step 75 of measuring the electrical resistivity of the medium M.

For example, measurement step 75 is based on a known method of quadrupole measurement known as Wenner, according to which a current is injected at a pair of two electrodes among the eight electrodes and the resistance is measured between two other electrodes.

During method 70, seven measurements are notably possible, depending on the electrodes selected for current injection and resistance measurement, as summarized in the table below, given by way of example:

Position First pole Second pole Third pole Fourth pole P1 E1 E2 E3 E4 P2 E2 E3 E4 E5 P3 E3 E4 E5 E6 P4 E4 E5 E6 E7 P5 E5 E6 E7 E8 P6 E1 E3 E5 E7 P7 E1 E4 E6 E8

The positions P1 to P7 are also illustrated in FIG. 8.

io The terms E1 to E7 refer to the electrodes 2.

The column "first pole" and the column "second pole" refer to the connection of the current injection poles of the measuring device 21 to the selected electrodes.

The column "third pole" and the column "fourth pole" refer to the connection of the measuring poles of the measuring device to the selected electrodes.

The calculation unit, on the basis of the measurements taken in positions P1 to P7 and of a model known to those skilled in the art, taking into account the spacing of the electrodes, the geometry of the nozzle, the temperature of the medium M, the material of the metal wall and the embankment, then determines the resistivity of medium M.

Benefits

As already indicated, the probe 14 has the advantage of being suitable for insertion into the medium whose electrical resistivity is tested, which allows measurements in situ and in real time.

Claims (20)

1. A probe for measuring the electrical resistivity of a medium, configured to be inserted into said medium (M), said probe (14) comprising at least four electrodes (2) spaced from each other and a support body (5) said electrodes (2). 2. Measuring probe according to claim 1, comprising eight electrodes (2) integral with each other and spaced from each other. 3. Measuring probe according to one of claims 1 or 2, wherein each electrode (2) has the general shape of a hollow cylinder. 4. Measuring probe according to any one of the preceding claims, comprising a means for spacing (3) the electrodes (2), said means for spacing (3) the electrodes (2) comprising a plurality of spacers (4 ), each spacer (4) being arranged between two electrodes (2). 5. Measuring probe according to the preceding claim, wherein each spacer (4) is a hollow cylinder. 6. Measuring probe according to one of claims 4 or 5, wherein each spacer (4) is integral with the support body (5). 7. Measuring probe according to the preceding claim, wherein the support body (5) has a generally cylindrical shape, each electrode (2) and each spacer (4) being mounted one after the other along a outer wall (6) of the support body (5). 8. Measuring probe according to the preceding claim, wherein the outer wall (6) of the support body is grooved. 9. Measuring probe according to one of the preceding claims, in which the support body (5) comprises a head (8) for inserting the probe (14) into the medium to be probed (M). 10. Measuring probe according to one of the preceding claims, comprising a handle (11). 11. Measuring probe according to one of the preceding claims, comprising a sleeve (9) for driving the probe (14) into the medium to be probed, said sleeve (9) being integral with the support body (5). 12. Device for measuring the electrical resistivity of a medium, comprising a probe (14) according to one of the preceding claims. 13. Measuring device according to the preceding claim, comprising an apparatus (21), said measuring apparatus, for injecting a current into certain electrodes and / or measuring a potential difference between two of the electrodes. 14. Measuring device according to the preceding claim, comprising a switching box (15), for switching some of the electrodes of the probe to the device. 15. Measuring device according to the preceding claim, wherein the switch box (15) comprises an input (16) connected to each of the electrodes, an output (18) with four poles, and a switching shaft (19) between the input (16) and output (18) to choose different measurement positions and compose quadrupoles among the electrodes. 16. Measuring device according to one of claims 12 to 15, comprising a calculation unit. 17. A method of measuring the electrical resistivity of a medium, comprising a step of inserting (71) a probe according to one of claims 1 to 11 in said medium. 18. Measuring method according to the preceding claim, comprising a step of injecting current into two electrodes of the probe according to one of claims 1 to 11. 19. Measuring method according to the preceding claim, comprising a step of measuring (15) of a potential difference between two other electrodes of the probe according to one of claims 1 to 11. 5 20. A measurement method according to the preceding claim, comprising a step of determining the electrical resistivity of the medium from a measurement result obtained during the measurement step.