WO2007010320A1 - Procédé et dispositif destinés à la mesure de la conductivité d’un liquide - Google Patents

Procédé et dispositif destinés à la mesure de la conductivité d’un liquide Download PDF

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Publication number
WO2007010320A1
WO2007010320A1 PCT/IB2005/002156 IB2005002156W WO2007010320A1 WO 2007010320 A1 WO2007010320 A1 WO 2007010320A1 IB 2005002156 W IB2005002156 W IB 2005002156W WO 2007010320 A1 WO2007010320 A1 WO 2007010320A1
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WO
WIPO (PCT)
Prior art keywords
electrodes
measuring
fronts
sloping
fluid
Prior art date
Application number
PCT/IB2005/002156
Other languages
English (en)
Inventor
Andrea Scozzari
Original Assignee
Cnr Consiglio Nazionale Delle Ricerche
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cnr Consiglio Nazionale Delle Ricerche filed Critical Cnr Consiglio Nazionale Delle Ricerche
Priority to PCT/IB2005/002156 priority Critical patent/WO2007010320A1/fr
Publication of WO2007010320A1 publication Critical patent/WO2007010320A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/06—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a liquid

Definitions

  • the present invention relates to a method for liquid conductivity measurement.
  • EP0288099 measures the conductivity of a liquid carrying out, in three different instants, at least three samplings of the voltage or current passing through two electrodes immersed in the liquid.
  • the used pulses are rectangular waves. From the three sampled values a complex exponential function is obtained, from whose trend the resistivity and the capacity are estimated.
  • US5519323 describes a conductivity-measuring device with two electrodes that apply current according to rectangular wave pulses and at the same time measure the voltage drop.
  • a measuring circuit comprising a condenser, a differential amplifier having a feedback condenser in parallel, and a switch by which, in an alternated way responsive to the trend of the current rectangular wave, the two ends of the measuring condenser are connected to measuring electrodes and to the differential amplifier.
  • the current supply is carried out through condensers.
  • US4119909 describes the measuring • conductivity of a solution sending a sharp pulse of direct current in a measuring cell where the liquid is present.
  • the voltage is sampled in the cell both before sending the pulse and in a predetermined moment during the application of the current. This way a ⁇ V is obtained that is proportional to the conductivity of the liquid.
  • the excitation pulses are of rectangular shape and a pause is required between adjacent pulses to avoid the polarization of the electrolyte; this requires measuring the voltage without excitation for subtracting the starting polarization voltage.
  • sampling instants are directly upstream and downstream of said sloping up and down fronts.
  • said time function of the current through said electrodes is substantially a rectangular wave.
  • the succession of said sampling instants is a programmable succession on a semiconductor memory.
  • said electric current is generated by a voltage generator with a known resistance in series.
  • a device for measuring the conductivity of fluids comprises:
  • a semiconductor memory is provided for memorizing a programmable succession of said sampling instants in said memory and for memorizing their temporal relationship with said fronts.
  • said memory is a flash memory.
  • said means for generating said electric current comprises a voltage generator with known resistance arranged in series.
  • FIG. 1 shows a known electric model of a conductivity measuring cell
  • FIG. 2 shows a known measuring system consisting of a circuit comprising an ideal voltage generator, a known resistance and a measuring cell, of impedance Z x ;
  • FIG. 3 shows a diagrammatical view of the measuring method according to the invention
  • - figure 4 shows the generation of an excitation signal divided into two measuring chains
  • — figure 5 shows the trend time of the drive signals necessary to provide the succession of operations for carrying out the method according to the invention
  • FIG. 6 shows a possible temporization of the drive signals in case of aqueous solutions of strong electrolytes up to high values of conductivity, for example for measuring a solution of KCl up to its saturation.
  • Description of a preferred exemplary embodiment With reference to figure 1, an electric model of a conductivity measuring cell, known in literature, indicates how an impedance Z x , indicated as 10, is seen at the ends of two electrodes (not shown) immersed in a liquid to measure according to the concerned physical quantities and phenomena.
  • the measuring system of figure 2 is shown as a circuit 20 comprising: a generator 21 of an ideal voltage in the form of an voltage excitation signal of value E(t), of alternating type +V E -V E and of rectangular shape; a known resistance 22; and the measuring cell, seen as an impedance 10 of value Z x .
  • the excitation models for carrying out the measure provide the application to a cell, which is seen as an impedance 10 in the way shown in figure 1, either an current excitation signal of alternating type and of rectangular shape, or a voltage excitation signal always of alternating type and of rectangular shape.
  • the current excitation signal is easy to reproduce with precision even in case of variation of temperature, and the model is of easy construction with integrated electronics.
  • a requirement of quality of the generated current signal is needed related to its duty cycle, which has to be ideally 50% with jitter zero and steep fronts ideally with infinite slope.
  • a signal with these features is peculiar to this measuring technique and reduces the effects due to the polarization of the electrolyte.
  • a signal of this type is of easy embodiment by a skilled person. Furthermore, with respect to a sinusoidal signal, such signal is much easier to generate in a highly reproducible way and it has not low distortion requirements .
  • the voltage signal is not a perfect square wave, but it has ascending and descending vertical portions 30 and 32, for transition of the excitation signal -V E +V E and vice-versa, with a slope that is given by C D , and horizontal portions 31 and 33 relative to the actual +V E and -V E , with a slope that is given by C D .
  • the slopes are exaggerated, with respect to the scale of figure 3, and the influence of C P is much less than the influence of C D .
  • the voltage at the ends of the cell 10 is sampled at instants 34,35 and 36,37, which are close respectively to each transition 30 and 32 of the excitation signal -V E +V E and vice-versa, distanced a predetermined time from each front 30 and 32.
  • the voltage sample V E taken in advance with respect to each transition of signal 30 or 32, can be centred on instants 34 and 36, as close to them as the respective transitions 30 or 32. Instead, the voltage sample taken later at the same transitions 30 or 32, respectively at instants 35 or 37, has to be delayed of a time sufficient to end the charging transient of inter-electrodic capacity C P , but close enough to the front to load in a negligible way the double layer capacity C D .
  • the difference between the samples bridging each transition 30 and 32 of the excitation signal V E depends solely from the real part of the cell impedance, and more precisely is: K x + K 1n
  • a technological problem is that of reducing at most the effects of the variation of the excitation voltage generator (V E ) and of its equivalent Thevenin resistance (Rm) .
  • FIG. 4 An electric diagram of a measuring device according to the invention is given in figure 4.
  • the commutating device 21 is a couple of complementary Mosfets, tested in an operating prototype not described in more detail.
  • another desired type of commutating device can be used, always taking into account criteria of high commutation speed and minimum losses.
  • the excitation signal thus generated is divided into two measuring chains, one of which is dedicated to the measure operated on the fluid, whereas the other is dedicated to provide a normalization signal proportional to an excitation voltage of the open circuit cell, determined through a network whose equivalent Thevenin resistance and whose partition factor reproduce the chain that concerns the cell in the best way possible.
  • Such arrangement is diagrammatically shown in fig. 5.
  • Such arrangement allows obtaining a high absolute precision as well as a repeatability of the measure; this is achieved by normalizing the voltage at the outlet of the fluid measuring chain with respect to the voltage that would be determined on a cell without fluid (a open circuit) .
  • Vm and Vr are respectively the "measurement” voltage, relative to the real cell, and the “reference” voltage, relative to the simulated cell at the outlet of the two measuring chains.
  • Each of them comprises a couple of sampling and holding devices, each of which is dedicated to sampling respectively the "high” and "low” half-period of the excitation signal; the resulting sampled signals are sent to a differential amplifier, at whose outlet a signal is given equal to the difference between the samples, which represents the desired ⁇ V.
  • the signals ⁇ + and ⁇ ⁇ pilot respectively the higher branch and the lower branch of the complementary commutation devices and are activated each in advance of a half-period corresponding to the respective sign of the generated half-wave.
  • the signals e m (t) and e r (t) represent an example of the wave forms respectively present at the ends of the cell and at the input of the chain of reference; it should be noted that for the signal e r (t) the wave is shown as perfectly rectangular, omitting the effect of the capacity Cp, whose presence is optional and is provided only for generalization.
  • the drive signals of the sampling and holding operations are considered at the high logical level for the sampling step and at the low logical level for operating the holding step.
  • the sampling time has to be long enough to allow the correct acquisition of the new sampled value.
  • the shape of the signal e m (t) in the reality may have an exponential trend more marked in each half-period with respect to what reported. This effect is intentionally at a minimum in the diagram in figure 6, owing to a disproportion between the waiting time before each sampling and the signal period, in order to appreciate it in the graphic representation.
  • the time indicated in the diagram of figure 7 is suitable for aqueous solutions of strong electrolytes up to high values of conductivity, for example for measuring a solution of KCl up to its saturation.
  • the apparatus proposed in the present invention uses a semi-permanent programmable memory (in the specific case a flash memory) as a generator of sequences; at its input
  • sampling logic for example sampling only the sloping up and down fronts
  • Vm and Vr are the output voltages (supposed constant with respect to the duration of a measurement step) for each two chains.
  • the conductivity is obtained from the conductance (G x ) determined from the cell constant that characterizes the used measuring cell.
  • equation (5) is used for reconstruction of the conductance of the cell.
  • a two points calibration can be effected using two solutions of known conductivity and tracing a line passing through the points (G x i,l/ri) and (G X2 ,l/r2).

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

La présente invention concerne un procédé permettant de mesurer la conductivité électrique d’un fluide dans lequel une paire d’électrodes est immergée et par laquelle passe un courant électrique en tenant compte d’une fonction de temps périodique sensiblement similaire à une onde rectangulaire de valeur moyenne nulle caractérisée par une inclinaison vers le haut et/ou des fronts inférieurs (30, 32) présentant une pente sensiblement infinie. Aux extrémités desdites électrodes, la tension est déterminée à des instants d’échantillonnage (34, 35 et 36, 37) immédiatement à proximité de ladite inclinaison vers le haut et/ou des fronts inférieurs, et en particulier, directement en amont et en aval de la dite inclinaison vers le haut et des fronts inférieurs. La succession d’instants d’échantillonnage (34, 35 et 36, 37) est une succession de plages d’une durée finie, programmables sur une mémoire à semi-conducteurs.
PCT/IB2005/002156 2005-07-21 2005-07-21 Procédé et dispositif destinés à la mesure de la conductivité d’un liquide WO2007010320A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/IB2005/002156 WO2007010320A1 (fr) 2005-07-21 2005-07-21 Procédé et dispositif destinés à la mesure de la conductivité d’un liquide

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IB2005/002156 WO2007010320A1 (fr) 2005-07-21 2005-07-21 Procédé et dispositif destinés à la mesure de la conductivité d’un liquide

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WO2007010320A1 true WO2007010320A1 (fr) 2007-01-25

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104330635A (zh) * 2014-11-17 2015-02-04 中国科学院大学 基于测量电磁转矩变化检测物体电导率的方法
RU175423U1 (ru) * 2017-07-11 2017-12-04 Общество с ограниченной ответственностью "ЭНЕРГИЯ ННО" Устройство для измерения удельной электропроводности водных растворов с расширенным динамическим диапазоном
CN112305026A (zh) * 2019-07-26 2021-02-02 佛山市顺德区美的饮水机制造有限公司 检测装置、检测方法、水质检测设备和净水装置

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0336615A1 (fr) * 1988-03-29 1989-10-11 Aichi Tokei Denki Co., Ltd. Débitmètre électromagnétique capable pour la mesure simultanée du débit et de la conductivité d'un fluide
EP0580326A1 (fr) * 1992-07-14 1994-01-26 Anatel Corporation Méthodes et circuits pour mesurer la conductibilité de solutions

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0336615A1 (fr) * 1988-03-29 1989-10-11 Aichi Tokei Denki Co., Ltd. Débitmètre électromagnétique capable pour la mesure simultanée du débit et de la conductivité d'un fluide
EP0580326A1 (fr) * 1992-07-14 1994-01-26 Anatel Corporation Méthodes et circuits pour mesurer la conductibilité de solutions

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104330635A (zh) * 2014-11-17 2015-02-04 中国科学院大学 基于测量电磁转矩变化检测物体电导率的方法
RU175423U1 (ru) * 2017-07-11 2017-12-04 Общество с ограниченной ответственностью "ЭНЕРГИЯ ННО" Устройство для измерения удельной электропроводности водных растворов с расширенным динамическим диапазоном
CN112305026A (zh) * 2019-07-26 2021-02-02 佛山市顺德区美的饮水机制造有限公司 检测装置、检测方法、水质检测设备和净水装置

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