WO1994018528A1

WO1994018528A1 - Method for measuring at least one feature of a liquid solution and device therefor

Info

Publication number: WO1994018528A1
Application number: PCT/FR1994/000141
Authority: WO
Inventors: Jean Claude Diverrez
Original assignee: Jean Claude Diverrez
Priority date: 1993-02-15
Filing date: 1994-02-09
Publication date: 1994-08-18
Also published as: FR2701566A1; EP0683892A1; FR2701566B1

Abstract

A method for measuring at least one feature of a liquid solution by means of a measurement device including an elongate member (15) or gauge (15) extending into the solution along a predetermined axis and having a plurality of emitting (Ei) and receiving (Ri) electrode pairs along the longitudinal gauge axis (17), wherein, for each measurement, at least one value characterizing the received signal is extracted therefrom, the characteristic value is stored, and, for each electrode pair, the conductance related to each corresponding level is quantified.

Description

METHOD FOR MEASURING AT LEAST ONE CHARACTERISTIC OF A LIQUID SOLUTION AND MEANS FOR IMPLEMENTING SAID SOLUTION

The invention relates to a method for measuring at least one characteristic of a liquid solution, in particular with a view to determining its homogeneity and the level of the free surface of said solution.

It also relates to the means for implementing the method.

In particular for determining the level of a liquid solution flowing in a pipe or contained in any container, there are mainly known three families of methods which are cited here for information:

- hydrostatic methods with an electrical translator, such as the assembly of a float or a plunger and a dynamometric sensor or even differential pressure sensors,

- methods based on the electrical properties of the liquid, either conductimetric or capacitive,

- radiation methods using either the absorption phenomenon or the time interval separating the emission and reception of acoustic waves (ultrasound). The invention relates to methods and devices relating to methods based on the electrical properties of the liquid. To determine the level of a hydrocarbon contained in a tank, a device is known (US-A-3,911,744) comprising:

- an elongated element called a gauge on which are associated: a plurality of so-called emission electrodes distributed at a determined pitch along the longitudinal axis of the gauge, a so-called reception electrode which also extends parallel to the abovementioned longitudinal axis and is spaced from the emission electrodes by a predetermined distance,

means for successively applying to the emission electrodes an excitation voltage determined with respect to a fixed reference potential and for simultaneously indicating which electrodes are excited and,

- Detection means which provide an output signal indicative of the response to the excitation of the electrodes. These detection means essentially consist of a visual indication of the conduction detection carried out by a diode which lights up at the first immersed upper pads providing an approximate estimate of the level of the liquid. In addition, these detection means include a galvanometer which makes it possible to determine the degree of immersion of the last electrode subject to knowing precisely the nature of the liquid, which is not the case for measuring the level of a liquid. whose nature evolves over time and whose resistivity varies enormously. It will be remembered that the resistivity can vary in a ratio of a few thousand depending on the nature of the liquid. Furthermore, the electrodes are housed in a tube and therefore such a device is not suitable for operation in a charged environment.

This method requires the intervention of a manipulator and high voltages (two 15-volt batteries).

Also known (FR-A-2,368,521 and FR-A-2,657,691) are devices which consist of an elongated element called a gauge, made of electrically insulating material, according to which devices:

- one or more reception electrodes extend parallel to the longitudinal axis, - the emission electrodes distributed parallel to the reception electrode, according to a defined pitch, are separated from the previous ones in a direction perpendicular to the longitudinal axis by a predefined distance,

the metallic or metallized electrodes have an active surface flush with the external surface of said elongated element,

- pulse trains are sent per cycle to the different emission electrodes,

the electrical means then make it possible to detect the conduction or the non-conduction between the emission / reception electrodes; a binary and global count totals the number of pulses received in return and,

- the height is calculated based on the average obtained over different counting cycles.

These devices require the use of an exclusively pulse generator.

Binary information counting requires setting a prior filtering threshold.

It is an all-or-nothing detection principle and the amplitude of the return signal is not measured. Due to its definition, it does not take account of variations in resistivity and overcomes surface effects by setting a filtering threshold.

The precision of the result in discrete values depends on the number of electrodes, the pitch retained, the spacing and the thickness of the electrodes.

This precision may be low in certain cases but it may be advantageous to increase this precision without increasing the number of electrodes and therefore multiplying the number of connections and the complexity of the circuits.

The filtering threshold must be set according to the nature of the liquid which, as mentioned above, is not necessarily known.

Such a device does not make it possible to measure layers of non-homogeneous liquids.

On the other hand, if any electrode malfunctions, for example, when it is covered by paper or any material, the amplitude of the pulse corresponding will be weakened and will be eliminated due to the previously fixed threshold and, therefore, will not be counted hence an error in estimation of the liquid height. The result of this operating mode is an inability to detect the operating incident.

In all these devices, the electrodes are metallic, therefore very sensitive to corrosion.

Many liquids whose level is sought to transport or contain a multitude of corrosive substances with regard to all metals (waste water, for example).

These devices are also subjected to the effect of electrolysis and polarization over time, inevitable in direct current, creates an electromotive force which can bring the conductivity below an arbitrarily fixed threshold.

One of the results that the invention aims to obtain is to remedy in particular the aforementioned problems. To this end, the subject of the invention is a method for measuring at least one characteristic of a solution of charged or uncharged liquid, in particular with a view to determining its homogeneity, which method uses a measuring device comprising an elongated element called a dipstick immersed in the solution along a predetermined axis, which dipstick carries a plurality of pairs of so-called emission and reception electrodes distributed along the longitudinal axis of the dipstick, each of the electrodes having an active face of geometry predetermined parallel to the longitudinal axis of the gauge, the said active faces of the same pair being spaced from each other in a direction perpendicular to the longitudinal axis of the gauge by a predefined distance, in which method , for the measurement of at least one characteristic of a solution:

- a predetermined pair of electrodes is selected. an electrical signal is sent to the selected transmission electrode of which at least one characteristic is known, such as its amplitude,

the electrical response to the aforementioned transmitted signal is collected simultaneously on the reception electrode, and

the above operations are repeated for at least some of the other pairs of electrodes remaining until these pairs are completely scanned, this method being characterized in that, for each measurement:

- at least one value characterizing the said received signal is extracted from the collected signal,

- this characterizing value is memorized then

- the conductance relative to each corresponding level is quantified for each pair of electrodes using at least one function FI (k. Cm, Ss), F2 (, Cm):

FI which is a correlation function relating the immersed surface of an electrode of a given type to the variation in conductance and F2 which is a correlation function which links the variation in conductance on the surface electrode as a function of distance from a reference point of this electrode to the free surface of liquid.

The invention will be clearly understood with the aid of the description below given by way of nonlimiting example with regard to the attached drawing which schematically represents:

- Figure 1: a measuring device shown in the form of a block diagram, - Figure 2: a gauge,

- Figure 3: a detail of the gauge,

- Figure 4: a sectional view along IV-IV of the figure

3,

FIG. 5: a graphic representation of the FI function,

- Figure 6: a graphical representation of the functions FI + F2 for various liquids. Referring to the drawing, there is seen a device 14 for measuring at least one characteristic of any liquid solution 5 which comprises an elongated element 15, called a gauge 15, immersed in the solution along a predetermined axis, which gauge carries a plurality of pairs of electrodes called emission Ei and reception Ri distributed along the longitudinal axis 17 of the gauge, each of the electrodes having an active face 16 of predetermined geometry parallel to the longitudinal axis of the gauge, said faces active of the same couple being spaced from each other in a direction perpendicular to the longitudinal axis of the gauge by a predefined distance.

For the measurement of at least one characteristic of a solution: - a predetermined pair of electrodes is selected,

an electrical signal is sent to the selected emission electrode of which at least one characteristic is known, such as its amplitude,

- The above operations are repeated for at least some of the other pairs of electrodes remaining until the complete scanning of these pairs.

According to the invention, for each measurement: - at least one value characterizing the received signal is extracted from the collected signal,

- this characterizing value is memorized, then

- the conductance relative to each corresponding level is quantified for each pair of electrodes using at least one function FI (k, Cm, Ss), F2 (k, Cm):

FI which is a correlation function linking the immersed surface of an electrode of a given type to the variation in conductance and

F2 which is a correlation function which links the variation in conductance on the surface electrode as a function of the distance from a reference point of this electrode to the free surface of liquid. It is not a specific conductivity but a value representative of the conductance.

To facilitate understanding, this representative value will be called conductance. To quantify the conductance, the ratio between the known characteristic of the transmitted signal and the characterizing value of the response is calculated.

You can visualize these different conductances and plot the variation thereof as a function of the measurement level.

The method according to the invention refers to a measurement of conductance between an emission electrode and a reception electrode and the response of which is a function of the signal emitted and the conductance of the liquid which is in particular proportional to the surface of the perpendicular section. to the deflection of the current and inversely proportional to the distance separating two electrodes.

The invention does not seek to establish the specific conductivity value but it endeavors to establish in particular the variations of the conductance according to the level of immersion and, by analysis of the results obtained, to indicate if the solution is a liquid of composition homogeneous or if there are different layers of fluids.

The result of the conductance of each layer is provided on a scale which can be very wide, for example, from alcohol to ammonia through demineralized water, rain water, tap water, sewage, etc.

It is not necessary to know a priori the conductivity of the liquid.

As a first approximation of the distribution of the strata of liquids of different conductivity, we compare step by step the representative values of the measured conductance, we determine, in particular according to determined comparison criteria, the number of levels having the same conductance then we deduces the thickness of each layer of liquid of a different nature, taking into account the pitch between two pairs of electrodes. In particular in the case of a so-called homogeneous solution, the level of the free surface is calculated relative to a reference frame Z, such as the bottom of the gauge or the bottom of a tank, and for this: - the number of pairs of electrodes called reference couples whose conductance is substantially identical,

- the conductance value called the reference value is extracted at least from the last highest reference torque,

- this reference value is compared to the conductance value of the pair of so-called surface electrodes located at least immediately above the last pair of aforementioned reference electrodes, - at least one correlation function FI is applied to said comparison (K, Cm, Ss), F2 (k, Cm) predetermined linking the conductance variations due both to the immersed fraction of the surface of the so-called surface electrode and to the distance separating a reference point from this electrode of surface of the free surface of the liquid and,

- the total height of the liquid is calculated according to the different results of these comparisons and determination as well as the construction parameters of the gauge, such as the distance separating the bottom of the pair of electrodes located lowest and the pitch separating each pair d 'electrodes.

For the calculation of this liquid height, we can ι thus apply a formula of the type: H = Ho + Fo (Cm, n) + FI (k, Cm, Ss) + F2 (k, Cm) where:

H represents the height of total liquid, Ho represents the height of the bottom of the lower pair of electrodes relative to a reference frame of level o, Cm represents the conductance recorded on the pairs of so-called reference electrodes,

Fo is equal to the step P multiplied by the number n of reference couples having an identical conductance Cm, Ss is equal to the submerged surface of the pair of surface electrodes, k is the ratio between the conductance recorded on the pair of surface electrodes and the conductance Cm, FI is a correlation function linking the submerged surface of a electrode of a type given to the variation in conductance,

F2 is a correlation function which links the change in conductance on the surface electrode as a function of the distance from a reference point of this electrode to the liquid free surface.

FI and F2 are expressed initially from the geometric parameters of implantation of the electrodes as well as the shape of their section and their active surface. It has thus been shown that, if in a measurement domain the conductance ratio evolves in a range from zero to a few hundred, the functions depend, as a first approximation, only on k.

We choose the gap between P between two electrodes such that it is at most equal to the value of F2 (Cm, k) for k = 1.

According to the invention, at least the conductances are corrected as a function of the temperature of the liquid.

The measurement accuracy, for homogeneous solutions, is greater than the construction pitch and is determined by the functions FI (k, Cm, Ss) and F2 (k, Cm).

It is possible to place the active surfaces 16 of the emission electrodes in a plane intersecting that in which the active faces of the reception electrodes are placed.

For implementing the method, the means further comprise:

- means for selecting a predetermined pair of electrodes, - means for sending an electrical signal of which at least one characteristic is known, such as its amplitude, to the selected emission electrode. - Means for simultaneously collecting on the reception electrode the electrical response to the aforementioned transmitted signal.

According to the invention, these means further comprise: - means for extracting from the signal received at least one value characterizing the said signal received,

- means for memorizing this characterizing value,

- Means for renewing the above operations for at least some of the other pairs of electrodes remaining until these pairs are completely scanned, then, means for quantifying for each pair of electrodes the conductance relative to each level corresponding to the aid at least one function FI (k. Cm, Ss) and F2 (k, Cm).

In the present device, the electrodes made of stainless or carbon / graphic material are, for example, arranged equidistantly, preferably, along a bar of electrically neutral material on the surface of which they are flush.

The means for selecting the electrodes and transmitting signals to the emission electrodes include, for example:

a decoding module 1 for the commands presented on a bus 13,

- a signal generator 2,

- an addressing module 3 which controls a series of analog switches 4, 6 for electrically connecting the signal generator to the different electrodes Ei. The signals received on the reception electrode Ri are sent to a response analyzer 8 which quantifies the conductance of the liquid 5 and this is either converted into digital value 10 and transferred to a computer via a bus 13, or transmitted in analog form.

The response of the temperature probe 7 is transmitted to a correction module 9 and to a converter analog / digital (not shown) then transferred to bus 13.

The stainless electrodes are then formed by bars of rectangular or cylindrical section, the surface of which is flush with the resin body.

The present invention differs from other conductimeters or limnigraphs by the use of graphite carbon studs and not by the use of metal electrodes which are strongly subjected to oxidation and whose lifetime is limited or the use of metals, such as gold or platinum whose cost becomes prohibitive.

The connection of the carbon electrodes to the electrical circuit cannot be carried out by welding.

According to the invention, the electrodes of the same type are electrically connected by a connection means 18 comprising:

a plate 19 of insulating material pierced with holes 20 of section complementary to the section of the electrodes and,

the internal face of these holes is covered with a layer 21 of electrically conductive material connected to an electric line 22 itself constituted by a layer of electrically conductive material thus forming a printed circuit board and each electrode is partially engaged in the holes. Advantageously, the active faces 16 of the reception electrodes are in a plane intersecting the plane in which the active faces of the emission electrodes extend.

The edge 23 where these planes then intersect makes it possible to eliminate or reduce the remanence introduced by a sudden decrease in the level of the electrolyte.

Indeed, the film of the liquid which remains in deposit for a certain time will cause a low conductance to appear at high level.

For an electrolyte of homogeneous concentration, the conductance recorded on the non-immersed electrodes will decrease very strongly until disappearance, after a few seconds at most. This phenomenon (decrease in conductance on high level electrodes) allows, for close measurements, to trace the movement of the liquid and in particular vortices or waves. This arrangement also makes it possible to measure projections of liquid on the gauge even if the latter is not completely submerged.

The analysis of the conductance measurement does not require a juxtaposition of the facing electrodes or their placement on the same face.

These can be placed on two opposite or contiguous faces of an epoxy resin bar immersed in the solution to be analyzed.

In practice and to facilitate industrial manufacture, it is generally simpler to take electrodes of the same surface and to arrange them at an equivalent distance vertically.

All the reception electrodes Ri can be electrically connected or advantageously replaced by a single continuous bar arranged vertically over the entire height of the gauge.

The associated electronics are embedded in a waterproof non-conductive resin resistant to chemical attack by the products to be measured. The junction of the electronics with the external environment and in particular the connections with a central control unit or a computer as well as the power supply are made using a waterproof connector (not shown).

For a correction of the conductance as a function of the temperature, the gauge includes a temperature sensor which will be placed at the low level of the gauge.

The measurement is unique and instantaneous (a few milliseconds).

Analysis of the received signal makes it possible to determine the conductance at each level.

This results in the total number of immersed electrodes, the range heights on immiscible liquids. For a homogeneous liquid, the interpolation carried out on the partial immersion of the last electrode and on the result obtained by the surface effect makes it possible to continuously determine the height between the bottom of the last immersed electrode and the actual level.

In FIG. 5, the variation of the measurement made on an electrode with a radius of three millimeters is shown as a function of the level of the fluid which evolves between the bottom of the electrode and the top of the latter. In FIG. 6, the variation of the conductivity linked to the functions FI, F2 in various electrolytes is shown alongside two electrodes measured on the highest level electrode.

The measurement then becomes continuous and no longer discreet. In general, the device is independent of the intrinsic conductance of the liquid.

However, several operational amplifiers of different gains (not shown), associated with one or more analog / digital converters (not shown) make it possible to obtain refined precision.

For some applications, it is possible to establish the relationship between conductance and intrinsic conductivity at the same time as the level. The industrial uses of the present invention are manifold.

The device is equally suitable for laboratory measurements, determination of levels in a tank or container, in a river, a pond, a well, in a water pipe, in a storm overflow, etc. .

In a wastewater pipe, it makes it possible to determine the height or even the flow from other parameters, such as the speed, or by application of the height / flow transformation formulas and the variations in conductance over time, deduces the quality of discharged water such as rain, polluted water, etc.

Claims

1. Method for measuring at least one characteristic of a liquid solution (5), which method uses a measuring device (14) which comprises an elongated element (15), called a gauge (15), immersed in the solution along a predetermined axis, which gauge carries a plurality of pairs of electrodes called emission (Ei) and reception (Ri) distributed along the longitudinal axis (17) of the gauge, each of the electrodes having an active face ( 16) of predetermined geometry parallel to the longitudinal axis of the gauge, the said active faces of the same pair being spaced from one another in a direction perpendicular to the longitudinal axis of the gauge by a predefined distance , for the measurement of at least one characteristic of a solution:

- a predetermined pair of electrodes is selected,

an electrical signal is sent to the selected transmitting electrode of which at least one characteristic is known, the electrical response to the aforementioned transmitted signal is simultaneously collected on the receiving electrode, and

the above-mentioned operations are repeated for at least some of the other pairs of electrodes remaining until the complete scanning of these pairs, this process being CHARACTERIZED in that, for each measurement:

- at least one value characterizing the received signal is extracted from the collected signal,

- this characterizing value is memorized, then

- the conductance relative to each corresponding level is quantified for each pair of electrodes using at least one function FI (k, Cm, Ss), F2 (k, Cm): FI which is a binding correlation function the submerged surface of an electrode of a type given to the variation in conductance and F2 which is a correlation function which links the variation in conductance on the surface electrode as a function of the distance from a reference point of this electrode to the free surface of liquid.

2. Method according to claim 1 characterized in that we compare step by step the values representative of the measured conductance, we determine the number of levels having the same conductance then we deduce the thickness of each layer of liquids of nature taking into account the pitch between two pairs of electrodes.

3. Method according to claim 1 characterized in that, in the case of a so-called homogeneous solution, the level of the free surface is calculated relative to a zero frame of reference, such as the bottom of the gauge, and for this:

the number of pairs of electrodes known as reference couples whose conductance is substantially identical is determined,

this reference value is compared with the conductance value of the pair of so-called surface electrodes located at least immediately above the last pair of aforementioned reference electrodes,

- applying to said comparison at least one correlation function FI (k, Cm, Ss), F2 (k, Cm) predetermined linking the conductance variations due both to the immersed fraction of the surface of the so-called surface electrode that at the distance separating a reference point of this surface electrode from the free surface of the liquid and,

4. Method according to claim 1 or 3 characterized in that at least some of the correlation functions are established as a function of the geometric parameters of implantation of the electrodes.

5. Method according to any one of claimsl to 4 characterized in that one chooses the spacing between two electrodes such that it is at most equal to the value of F2 (k, Cm) for k = 1.

6. Method according to any one of claims 1 to 5 characterized in that at least the conductances are corrected as a function of the temperature of the liquid.

7. Method according to claim 1 characterized in that the active surfaces of the emission electrodes are placed in a plane intersecting that in which the reception electrodes are placed.

8. Means for implementing the method according to any one of claims 1 to 7, which method implements a measuring device (14) which comprises an elongated element (15), called a gauge (15), immersed in the solution along a predetermined axis, which gauge carries a plurality of pairs of electrodes called emission (Ei) and reception (Ri) distributed along the longitudinal axis (17) of the gauge, each of the electrodes having an active face (16) of predetermined geometry parallel to the longitudinal axis of the gauge, said active faces of the same pair being spaced from one another in a direction perpendicular to the longitudinal axis of the gauge by a distance predefined, further comprising:

means for selecting a predetermined pair of electrodes,

- Means for sending an electrical signal to the selected transmission electrode of which at least one characteristic is known, such as its amplitude, means for simultaneously collecting on the reception electrode the electrical response to the aforementioned transmitted signal, these means being characterized in that they include: - means for extracting from the collected signal at least one value characterizing the received signal, means for memorizing this characterizing value, - means for renewing the above operations for each of the other pairs of electrodes remaining until the complete scanning of these pairs then, means for quantifying for each pair of electrodes the conductance relative to each corresponding level using at least one function FI (k, Cm, Ss) and F2 (k, Cm).

9. Means according to claim 8 characterized in that the electrodes of the same type are electrically connected by a connection means (18) comprising: - a plate (19) of insulating material pierced with holes

(20) of complementary section to the section of the electrodes and,

- The internal face of these holes is covered with a layer (21) of electrically conductive material connected to an electric line (22) itself constituted by a layer of electrically conductive material thus forming a printed circuit board.

10. Means according to claim 8 characterized in that the active faces of the receiving electrodes are in a plane intersecting the plane in which extend the active faces of the emission electrodes.