FR2788130A1 - Measuring concentration of solution comprises adding reactants and detecting color changes - Google Patents

Abstract

Before the measuring stage, there is a calibration stage in which the light intensity is controlled so the light detected by the photosensitive detector gives an output signal (Uc) equal to a reference signal (Up). An Independent claim is also included for an apparatus for the above process including a supply module (6), a light source (4), a photosensitive detector (5), a comparison module (7) or measuring module (8) and a display (9). Preferred Features: One or more specific reactants (2) is/are introduced in solution into a reservoir (3) containing a set dose of the sample which color the sample as a function of its concentration. The sample is then illuminated with a light source (4) and the light passing through the sample is measured using a photosensitive detector (5). The reference signal is calculated as a function of the coloration by the reactants and the response curve of the detector. The light source is supplied with current by a controlled source. The comparison module includes a chain of resistances R'0 to R'n between which are nodes U'0 to U'n. One end of the chain carries the detector and the other end an internal resistance Rp for the reference signal. It also includes comparators C'0 to C'n allowing the value at each node to be compared to Ug, the set voltage for the sample. The display is a series of electroluminescent diodes D'0 to D'n each of which lights up when the concentration threshold it represents is passed. It also includes logic circuits which only allow the diode corresponding to the last threshold passed to light up. The measuring device comprises a voltage bridge ABCDEF with two branches ABF and CDF, extended by a branch FG. The ABF branch carries the detector, a node B and a resistance Ri in series, and the CDF branch carries the reference value Rp, a node D and a resistance Ri in series. The BD branch carries a potentiometer P3 with a variable node E and the display module includes a branched voltage or amp display which is in parallel with B and E or in series with P3 depending on whether it is measuring voltage or intensity. The measuring module also includes a variable resistance Rv on the FG branch, which can increase or decrease the amplitude of values between B and D and which can make the display device coincide with the concentration unit. A selector button on the measuring device allows a variable resistance Rv to be selected simultaneously with an internal resistance Rp for the reference value and a potentiometer P1 controlling the intensity of the light source, to allow selection of a particular type of measurement. There is a light source in series with each potentiometer P1.

Description

The present invention relates to the field of methods and devices

  for measuring the solute content of a sample, and more particularly to processes and devices using specific chemical reagents responsible for

  color the sample according to the solute content.

  The invention makes it possible to measure the concentration of solute using an electronic device responsible for accurately interpreting changes in

  colors operated by the introduction of specific chemical reagents.

  The electronic device is of the type comprising a light source which emits light through the sample and comprising a photosensitive sensor

  located on the other side of the sample relative to the light source.

  The method according to the invention is a method for measuring the content of a sample of solute, of the type comprising a step of introducing one or more reagents specific for the solute into a reservoir containing a dose of sample determined in order to color the sample as a function of the solute content, and comprising a step of illuminating the sample by a light source and of measuring the light passing through said sample using a photosensitive sensor, characterized in that it includes a preliminary sampling step consisting in adjusting the light intensity of the light source so that the illumination perceived by said photosensitive sensor causes

  an output signal equal to a predetermined reference.

  The method and the device were developed for the analysis of nitrates and nitrites contained in sea water or fresh water and for the measurement of pH, but the operating principle can be extended to many other types measures, such as potassium or phosphate concentration measurements. The device according to the invention allows the implementation of the method. It is characterized in that it comprises a power supply module, a light source, a photosensitive sensor, a comparison module or a measurement module and

a display module.

  The prior art already knows devices for measuring the solute content of a sample by color comparison after reaction with a specific chemical reagent: there are test papers and kits of chemical reagents supplied with a color scale for interpreting the concentration depending on the color, but these devices often prove to be imprecise and cannot be used by

  people who don't see colors well.

  There are also colorimeters and spectrometers but these devices, intended for use in the laboratory, are very expensive and are not suitable for family use or for field measurements. The operation of colorimeters and spectrometers is based on the measurement of the colors of the sample or on the measurement of the emission spectra. These devices allow of course to reach great precision, but it is not

  necessarily what the user is looking for.

  o0 There are a number of applications o an accuracy of the order of 1 to 5

  % is enough, but no inexpensive device can do it.

  To achieve this, a solution consists, not in measuring the color spectrum, but in simply measuring the darkening of the solution that one wishes to analyze, or on the contrary its lightening, thanks to the addition of reagents

i5 adequate chemicals.

  European patent application N EP 0 228 877 presents a colorimeter which makes it possible to compare simultaneously optical densities of two liquid samples, one of reference, the other of measurement, with reference values, but on the one hand this device requires permanently having a reference sample and on the other hand, the measurement is based on differences in optical densities; however the optical density is defined as the inverse logarithm of the transmission factor or the reflection factor which are functions of the wavelengths of the emitted rays

by the light source.

  The method according to the invention makes it possible to measure concentrations with sufficient precision for a number of applications, without taking into account the wavelengths of the rays emitted or received. This is a simplification

  very important of the prior art.

  The method according to the invention is also based on a single sampling principle: it does not require presenting a sample of

  reference, nor to redo the sampling with each new measurement.

  The device allowing the implementation of the method according to the invention has two variants: according to the first version, a series of light-emitting diodes (hereinafter LED) indicate when the solute concentration thresholds in the solution are lit which have been crossed and according to the second

  version, the concentration value is displayed on a digital screen.

  In a variant of this last version, the measuring device comprises a selection button which makes it possible to carry out several types of measurement in succession without reiterating the calibration of each of them before each measurement. The selection button thus makes it possible to measure, for example, first the nitrites, then by simple change of the sample and of the specific reagent (s),

measure nitrates or pH.

  The device makes it possible to reach concentration values ranging from 5 mg / liter to 5 mg / liter for the LED version and from 1 mg / liter to 1 mg / liter for the

  digital screen version with an accuracy of up to 1%.

  The device according to the invention has the important advantages of being

  simple and inexpensive to make.

  It considerably improves the reading accuracy of colored tests by remedying the manufacturing tolerances of electronic components

  as well as certain manufacturing defects.

  The invention will be better understood with the aid of the description given below.

  the invention for purely explanatory purposes with reference to the appended figures: - Figure 1 illustrates the block diagram of the method and the device according to the invention; - Figure 2 illustrates two response curves of a photosensitive sensor, one performed with a green light source and the other performed with a yellow light source; - Figure 3 illustrates a block diagram of the power supply module; - Figures 4a and 4b respectively illustrate the version of the LED concentration display device and the version of the digital display concentration display device; - Figure 5 illustrates a block diagram of the chain of nodes; - Figure 6 illustrates a block diagram of a comparison device; - Figure 7 illustrates a block diagram of the original voltage; - Figure 8 illustrates a block diagram of the logic circuit; - Figure 9 illustrates a block diagram of the measurement module; and - Figure 10 illustrates a block diagram of the power supply module of the

  version of the selector button device.

  The method according to the invention, illustrated in FIG. 1, is a method for measuring the content of a sample (1) in solute, of the type comprising a step of introduction of one or more reagents (2) specific for the solute in a tank (3) containing a determined sample dose in order to color the sample (1) as a function of the solute content, and comprising a step of illuminating the sample (1) by a light source (4 ) and for measuring the light passing through said sample (1) using a photosensitive sensor (5), characterized in that it includes a preliminary sampling step consisting in adjusting the light intensity of the light source (4 ) before the measurement step so that the illumination perceived by said photosensitive sensor (5) causes a signal

  output Uc equal to a predetermined reference Up.

  Said predetermined reference Up is calculated as a function of the coloring by the specific reagent (s) (2) and as a function of the response curve of the

photosensitive sensor (5).

  The predetermined reference Up is preferably chosen such that Rc, the internal resistance of the photosensitive sensor is located on a part of the response curve of the substantially rectilinear photosensitive sensor, as illustrated in FIG. 2, in order to minimize the errors. In FIG. 2, Rcj denotes an example of determination of the internal resistance of the photosensitive sensor (5) when the light source (4) is yellow in color and Rcv denotes an example of determination of the internal resistance of the photosensitive sensor (5) when the

  light source (4) is green.

  It is also sometimes necessary to correct the value of

  Rp depending on the specific reagents used and the colors produced.

  For the measurement of the solute content to be reliable, it is essential that said light source (4) is supplied with current by a regulated voltage source. Thus, the measurement of the variation of the illumination of the sensor

  photosensitive (5) is done at constant brightness.

  The device for measuring the content of a solute sample according to the invention allowing the implementation of the method illustrated in FIG. 1 is characterized in that it comprises a supply module (6), a light source (4) , a photosensitive sensor (5), a comparison module (7) or a

  measurement (8) and a display module (9).

  Said light source (4) is constituted by a monochromatic source

  or not, and it is preferably constituted by a light-emitting diode.

  The best results are obtained with regard to the analyzes of

  nitrates and nitrites, by yellow or green LEDs.

  The photosensitive sensor (5) is of the photoresist or photodiode I phototransistor type. In the examples described below, the light source (4) is a yellow high-brightness LED, the photosensitive sensor (5) is a photoresist and the reference signal is voltaic. In the examples described below, the value of Rp, the internal resistance of the predetermined reference is 10 kQ, and Rc, the internal resistance of the sensor is also 10 kQ for a concentration for example of nitrates of 0 mg / L The power supply module (6) illustrated in FIG. 3 comprises a battery (10) or a battery delivering, for example, a voltage of 9 Volts. It is preferably provided with a switch (11) and with an operating indicator (12) and with voltage control connected in series with a Zener diode Z1. The operating lamp goes out, for example at 7.9 V, when the supply voltage decreases but is

  still above the device's operating threshold.

  The power supply module (6) further comprises a voltage regulator (13), set, for example, at 6 V, so as to supply the light source at a voltage lower than that of the extinction threshold of the operating lamp. (12), in order to guarantee a supply value of the source

constant light.

  In the example illustrated in FIG. 3, the resistors RI, R2 and R3 have respective values: 2.2 kQ, 120 Q and 100 Q and the capacitor C3 has a

capacity of 22 nF.

  In order to allow the light intensity of the light source (4) to be adjusted before the measurement step so that the illumination perceived by said photosensitive sensor (5) causes an output signal Uc equal to the predetermined reference Up , the power supply module (6) also includes a device for adjusting the

  brightness by a potentiometer P1.

  The potentiometer P1 thus makes it possible to adjust the illumination of the sensor so that the value of the output signal Uc, for a colored concentration of titrated solute serving as the origin of the measurement, is at a level equal to a voltaic value or

  amperometric defined according to the nature of the photosensitive sensor.

  In our example, potentiometer P1 has an internal resistance

maximum of 1 kQ.

  The photosensitive sensor (5) can optionally include a

  potentiometer P2 to allow adjustment of its internal resistance.

  In our example, the potentiometer P2 has an internal resistance

maximum of 10 kQ.

  The display module (9) has two versions: a version with display of the concentration by light-emitting diodes indicating crossing of thresholds, illustrated in FIG. 4a, and a version with display of the digital concentration,

illustrated in Figure 4b.

  These two versions include a Vl screw intended to actuate the

potentiometer P1.

  These two versions are distinguished by the fact that on the one hand they do not have the same display module (9), and on the other hand, by the fact that the first includes a comparison module (7) while the other has a module

measure (8).

  According to the version with display of the concentration by light-emitting diodes, said comparison module (7) comprises a chain of resistors R'0 to R'n illustrated in FIG. 5 between which are arranged nodes U'0 to U'n, one end of the chain comprising the photosensitive sensor (5) and the other end comprising the internal resistance Rp of the predetermined reference and in that each value of the nodes is compared, using one or more comparators C'1 to C'n illustrated in FIG. 6, at Ug, the original voltage determined during sampling. In this version of the invention, said display module (9) consists of a series of light-emitting diodes D'0 to D'x which light up when the threshold

  of solute concentration they indicate is exceeded.

  The original Ug voltage is determined by a divider bridge consisting of two resistors Rd and R'd, as illustrated in Figure 7. In our example, Rd = Rd 'and Ug

  is equal to the regulated voltage divided by two.

  The resistance R'0 is equal to the sum of the values of the resistances R'1 to R'n. The value of each resistance Rx is equal to the difference between on the one hand the value of the internal resistance Rcx of the branch comprising the photosensitive sensor (5) for a concentration Cx and on the other hand the value of the internal resistance Rcx1 of the branch comprising the photosensitive sensor (5) for a concentration Cx.1, divided by two, Cxjet Cx corresponding to the values of

  respective concentration which one wishes to display with the LEDs Dx41 and Dx.

  The sum of the resistances Rp + R'0 to R'x is also equal to the sum

  resistances R'x.1 to R'n + Rc for a concentration of solute Cx.

  The voltage at a given node U'x measured between point P and point U'x of

  the chain of nodes remains equal to the regulated voltage Ug.

  In a preferred version of the invention, the comparator has multiple inputs and is constituted by a power logic circuit (4049) which compares in

  internal the input voltage to the regulated voltage divided by two.

  In a variant of this version, said display module (9) comprises logic circuits, illustrated in FIG. 8, connected to the outputs SO to Sn of the comparators and loads to cause only the energizing of the light-emitting diode (D'0 , D'l, D'2, D'3, ...) corresponding to the last threshold of

concentration of solute crossed.

  This last variant makes it possible to reduce the energy consumption of the

  measuring device and thus increase its autonomy.

  According to the version with display of the concentration by digital screen, illustrated in FIG. 9, said measurement module (8) comprises a voltage divider bridge ABCDEF with two branches ABF and CDF, extended by a branch FG. The ABF branch is a voltage divider bridge consisting of: possibly the potentiometer P2 then the photosensitive sensor (5), a node B and a resistor Ri in series. The CDF branch is a voltage divider bridge consisting of: at least one internal resistance

  Rp of the predetermined reference, then a node D and a resistor Ri in series.

  In a simple version of the digital display version, the BD branch of the voltage divider bridge comprises a potentiometer P3 having a variable node E and said display module (9) comprises a connected voltaic or amperometric display (15), either by parallel between node B and variable node E of potentiometer P3, or in series with said potentiometer P3 in order to measure either the

voltage or intensity.

  The potentiometer P3 is optional as it is intended to allow presetting

  of the display (15). It can, for example, be operated with the V2 screw.

  The branch FG comprises at least one variable resistance Rv, disposed on the branch FG, which has the purpose of increasing or decreasing the magnitude of the values between the nodes B and D and which thus makes it possible to make the displayed unit coincide with

the unit of concentration.

  The variable resistors Rv are adjusted using the V3 screws.

  When you choose to measure the voltage, the voltmeter can, for example, be adjusted so that 1 V = 100 units to interpret the variation in voltage UBE. In a variant of this version, illustrated in FIG. 10, said measurement module (8) comprises a plurality of variable resistance Rv, a plurality of internal resistance Rp of predetermined reference, and a plurality of potentiometer

  o0 P1 preset light source intensity adjustment (4).

  Said measurement module (8) further comprises a selector button (14) which makes it possible to simultaneously select a variable resistance Rv, an internal resistance Rp of predetermined reference and a potentiometer P1 preset for adjusting the intensity of the light source (4 ), in order to select a type

particular measure.

  The color of the sample being a function of the chemical reagent introduced and the solute whose concentration is to be measured, it is preferable to provide, in series with each potentiometer P1, a particular light source (4) whose

  color is a function of the reaction color of the sample.

  Indeed, each set (Rv, Rp, P1, light source (4)) corresponds to

a particular solute.

  The variable resistors Rv, the internal resistors Rp of predetermined reference and the potentiometers P1 are of course always positioned in parallel. The resistors Ri have, in our example a resistance of 10 k.,

  and potentiometer P3 has a maximum resistance of 1 MQ.

  Thus, when Uc = Up, then UBE = 0, which corresponds to a concentration of the solution equal to zero and when Uc> Up, then UBE> 0 and the voltmeter displays the value corresponding to the voltage UBE, it is say the value of the concentration in

solute.

Claims (8)

  1- Method for measuring the content of a sample (1) in solute, of the type comprising a step of introducing one or more reagents (2) specific for the solute into a reservoir (3) containing a dose of sample determined in order to color the sample (1) as a function of the solute content, and comprising a step 1o of illuminating the sample (1) by a light source (4) and of measuring the light passing through said sample (1) thanks to a photosensitive sensor (5), characterized in that it comprises a preliminary sampling step consisting in adjusting the light intensity of the light source (4) before the measurement step so as to what the illumination perceived by said photosensitive sensor (5)   causes an output signal Uc equal to a predetermined reference Up.   2- A method of measuring the content of a solute sample according to claim 1, characterized in that said predetermined reference is calculated according to the coloring by the specific reagent (s) (2) and according to the   response curve of the photosensitive sensor (5).   3- Method for measuring the content of a solute sample according to one   any of claims 1 or 2, characterized in that said source   light (4) is supplied with current by a regulated voltage source 4- Device for measuring the content of a solute sample allowing the   implementation of the method according to any one of claims 1 to 3,   characterized in that it comprises a power supply module (6), a light source (4), a photosensitive sensor (5), a comparison module (7) or a   measurement module (8) and a display module (9).   - Device for measuring the content of a solute sample according to claim 4, characterized in that said comparison module (7) comprises a chain of resistors R'0 to R'n between which are arranged nodes U'0 at U'n, one end of the chain comprising the photosensitive sensor (5) and the other end comprising the internal resistance Rp of the predetermined reference and in that it comprises one or more comparators C'0 to C'n allowing to compare each value of the nodes U'O to U'n, to Ug, the original voltage determined during sampling.   6- A device for measuring the content of a solute sample according to claim 5, characterized in that said display module (9) consists of a series of light-emitting diodes D'0 to D'n which light up when the threshold of   solute concentration that they indicate is exceeded.   7- Device for measuring the content of a solute sample according to claim 6, characterized in that said display module (9) comprises logic circuits responsible for causing only the energization of the light-emitting diode (D '0, D'1 ,, D'2, D'3 ...) corresponding to the last threshold of concentration of solute crossed.   8- Device for measuring the content of a solute sample according to claim 4, characterized in that said measurement module (8) comprises a voltage divider bridge ABCDEF with two branches ABF and CDF, extended by a branch FG, the branch ABF comprising the photosensitive sensor (5), then a node B and a resistor Ri in series and the branch CDF comprising the reference   predetermined Rp, then a node D and a resistor Ri in series.   9- Device for measuring the content of a solute sample according to claim 8, characterized in that the branch BD of the voltage divider bridge comprises a potentiometer P3 having a variable node E and in that said display module ( 9) has a voltaic or amperometric display (15) connected, either in parallel between node B and the variable node, or in series with   said potentiometer P3 in order to measure either the voltage or the intensity.   - Device for measuring the content of a solute sample according to claim 8 or claim 9, characterized in that said measurement module (8) comprises at least one variable resistance Rv, arranged on the branch FG, which has for aim of increasing or decreasing the magnitude of the values between nodes B and D and which thus makes it possible to make the displayed unit coincide with the concentration unit. 11- Device for measuring the content of a solute sample according to claim 10, characterized in that said measurement module (8) comprises a selector button (14) which makes it possible to simultaneously select a variable resistance Rv, an internal resistance Rp of the predetermined reference and a potentiometer P1 preset for adjusting the intensity of the light source (4), so   allow you to select a particular type of measurement.   12- Device for measuring the content of a solute sample according to claim 11, characterized in that it comprises a light source (4) in   series with each potentiometer P1.