WO2000055611A2 - Measuring cell and method for measuring the conductivity of liquids - Google Patents
Measuring cell and method for measuring the conductivity of liquids Download PDFInfo
- Publication number
- WO2000055611A2 WO2000055611A2 PCT/NL2000/000169 NL0000169W WO0055611A2 WO 2000055611 A2 WO2000055611 A2 WO 2000055611A2 NL 0000169 W NL0000169 W NL 0000169W WO 0055611 A2 WO0055611 A2 WO 0055611A2
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- WO
- WIPO (PCT)
- Prior art keywords
- measuring
- conductivity
- current
- measuring cell
- outer electrodes
- Prior art date
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Classifications
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- 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
- G01N27/07—Construction of measuring vessels; Electrodes therefor
Definitions
- Measuring cell for measuring the conductivity of liquids and method for measuring the conductivity of a liquid.
- the present invention relates to a measuring cell for measuring the conductivity of liquids, which measuring cell is provided with two opposite outer electrodes, with a first current source, with a reference electrode and with a voltmeter.
- Measurements of the conductivity are amongst other used in baths in which metal is cleansed, in the detection of leaks in heat exchangers, in "Cleaning in Place” (CIP) installations, in demineralisation installations, in liquid interface detection, concentration measurements of salts and other dissolved substances in cooling water, liquid separation in osmosis processes, the monitoring of boiler water, measurements in waste water, the saving on chemicals by measuring the overdose, concentration measurements of acids and bases, for the determination of the purity of water for applications in the preparation of pharmaceuticals and food, for the determination of pollution of ground water, etcetera.
- CIP Cosmetic in Place
- Such measurements are carried out by a so-called conductivity transformer comprising a universal measurement amplifier, a measuring cell having two electrodes connected to the measurement amplifier, and a reference resistance to which the resistance measured (conductivity) is compared.
- Said transformer can further be provided with a micro processor with which all necessary adjustments are automatically regulated.
- the conductivity values are indicated for a column liquid of 1 cm 3 , that is to say a column of 1 x 1 x 1 cm.
- the specific conductivity is found by multiplying the conductivity with the cell constant, defined as the distance between the electrodes divided by the surface of the electrodes.
- the measuring cell of the kind described above according to the invention is characterized in that the measuring cell is further provided with a perforated electrode movably placed between the two outer electrodes, with a second current source, the first and the second current source applying a first and a second current, respectively, between the outer electrodes and the perforated electrode, with displacement means for moving the perforated electrode to various positions, and with switching means for switching between the first and second current between the outer electrodes and the perforated electrode, the electrodes, the current sources, the voltmeter and the switching means being situated in a circuit.
- the present invention further relates to a method for measuring the conductivity of a cylinder of liquid which is situated between the outer electrodes, in which a measuring cell according to the invention is used, in which method four measurements are carried out, the position of the perforated electrodes in each of the measurements (ii) being X (ii) , in which in two of the four measurements the first current is applied and the reference electrode is at one side of the electric circuit, and in the other two measurements the second current is applied and the reference electrode (R ref ) is at the other side of the electric circuit, in each of the measurements the perforated electrode being positioned such so as to cause a zero voltage reading on the voltmeter, and the specific conductivity being determined by the formula:
- r is the radius of the cylinder.
- Figures 1 up to and including 4 each show a different measurement position of the measuring cell according to the present invention used for measuring the conductivity of a liquid.
- a measuring cell for measuring the conductivity of liquids according to the present invention is shown in four different measurement positions in the figures 1 up and including 4.
- the measuring cell contains two opposite outer electrodes 1 , 2.
- a reference electrode R ref and a voltmeter 3 are provided for determining the conductivity of a liquid column 4 to be measured which is situated between the outer electrodes 1 , 2.
- the cylinder has a radius r.
- the measuring cell further has a perforated electrode 5, which is movably placed between the two outer electrodes 1 , 2.
- the perforated electrode 5 divides the cylinder into two compartments that are in contact with each other.
- the first 6 and the second 7 current source are capable of applying a first and a second current, respectively, between the outer electrodes 1 , 2 and the perforated electrode 5.
- the voltmeter for instance a voltmeter of high accuracy, is used to determine a situation of a voltage difference of zero between the two compartments of the cylinder.
- the measuring cell comprises displacement means (not shown) for moving the perforated electrode 5 to various positions between the outer electrodes 1 ,2.
- displacement means for moving the perforated electrode 5 to various positions between the outer electrodes 1 ,2.
- numerous displacement means available to the expert can be used.
- the measuring cell comprises switching means known per se for switching between the first and second current between the outer electrodes 1 , 2 and the perforated electrode 5.
- the electrodes 1 , 2, 5, the current sources, 6, 7, the voltmeter 3 and the switching means are situated in a circuit which is schematically shown in the figures.
- the present invention provides a main standard for the measuring of the conductivity of liquids, with an emphasis on a low uncertainty in the measurements, with which also low conductivities (e.g. ⁇ 25 ⁇ S/cm) can deducibly be measured.
- the measurement of the conductivity of the liquids is carried out by measuring the length L of a cylinder 4 of the liquid which has a resistance which can be derived form the reference resistance R ref , which preferably has a value with an uncertainty ⁇ 0.00001 %.
- the specific conductivity K of the liquid is then calculated from said resistance R and from the radius r of the cylinder, which with an uncertainty of 0.0005% can be known on the basis of the formula:
- a complete measurement consists of a series of four measurements, in which the current sources 6, 7 and the reference resistance R ref are repositioned on the left hand side and the right hand side of the circuit, as shown in figure 4.
- the central perforated electrode 5 is positioned so as to give a zero voltage reading, after which the position X , X 12 , X 21 , X 22 of the perforated electrode 5 is determined. The positions obtained are then used to calculate the specific conductivity of the liquid according to
- the uncertainty of the measurement according to the present invention in principle depends on the uncertainty in the zero voltage measurement necessary for comparing the liquid and the reference resistance and on the uncertainty in the length measurement itself. An uncertainty of 0.001 % can as a result be achieved, which in order of size is lower than the lowest known uncertainty.
- thermo stabilisation of the cylinder It is known per se to obtain the temperature stability necessary for performing the measurements by known thermo stabilisation of the cylinder and by placing the complete measurement system in an incubator with a temperature stability better than 0.004%. Such and other parts known for the operation of the measuring cell are not described here in detail in order to keep the description simple.
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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)
- Measurement Of Resistance Or Impedance (AREA)
Abstract
Measuring cell for measuring the conductivity of liquids. The measuring cell comprises two opposite outer electrodes, a first current source, a reference electrode and a voltmeter. The measuring cell further comprises a perforated electrode movably placed between the two outer electrodes, a second current source, the first and the second current source applying a first and a second current, respectively, between the outer electrodes and the perforated electrode, displacement means for moving the perforated electrode to various positions, and switching means for switching between the first and second current between the outer electrodes and the perforated electrode. The electrodes, the current sources, the voltmeter and the switching means are situated in a circuit. Method for measuring the conductivity of a liquid while using the measuring cell.
Description
Measuring cell for measuring the conductivity of liquids and method for measuring the conductivity of a liquid.
The present invention relates to a measuring cell for measuring the conductivity of liquids, which measuring cell is provided with two opposite outer electrodes, with a first current source, with a reference electrode and with a voltmeter.
Measurements of the conductivity are amongst other used in baths in which metal is cleansed, in the detection of leaks in heat exchangers, in "Cleaning in Place" (CIP) installations, in demineralisation installations, in liquid interface detection, concentration measurements of salts and other dissolved substances in cooling water, liquid separation in osmosis processes, the monitoring of boiler water, measurements in waste water, the saving on chemicals by measuring the overdose, concentration measurements of acids and bases, for the determination of the purity of water for applications in the preparation of pharmaceuticals and food, for the determination of pollution of ground water, etcetera. Such measurements are carried out by a so-called conductivity transformer comprising a universal measurement amplifier, a measuring cell having two electrodes connected to the measurement amplifier, and a reference resistance to which the resistance measured (conductivity) is compared. Said transformer can further be provided with a micro processor with which all necessary adjustments are automatically regulated.
Usually the conductivity values are indicated for a column liquid of 1 cm3, that is to say a column of 1 x 1 x 1 cm. The specific conductivity is found by multiplying the conductivity with the cell constant, defined as the
distance between the electrodes divided by the surface of the electrodes.
It is an object of the present invention to provide a measuring cell and measuring method for measuring the conductivity of liquids which in comparison to the known measuring cells and measuring principles, respectively, have a considerably lower uncertainty, with which also lower conductivities can be measured in a deducible manner.
To that end the measuring cell of the kind described above according to the invention is characterized in that the measuring cell is further provided with a perforated electrode movably placed between the two outer electrodes, with a second current source, the first and the second current source applying a first and a second current, respectively, between the outer electrodes and the perforated electrode, with displacement means for moving the perforated electrode to various positions, and with switching means for switching between the first and second current between the outer electrodes and the perforated electrode, the electrodes, the current sources, the voltmeter and the switching means being situated in a circuit.
The present invention further relates to a method for measuring the conductivity of a cylinder of liquid which is situated between the outer electrodes, in which a measuring cell according to the invention is used, in which method four measurements are carried out, the position of the perforated electrodes in each of the measurements (ii) being X(ii), in which in two of the four measurements the first current is applied and the reference electrode is at one side of the electric circuit, and in the other two measurements the second current is applied and the reference electrode (Rref) is at the other side of the electric circuit, in each of the measurements the perforated electrode being positioned such so as to cause a zero voltage reading on the voltmeter, and the specific conductivity being determined by the formula:
in which r is the radius of the cylinder.
As a result of the inventive measuring cell and the inventive method sources of uncertainty such as polarisation and electrode pollution can be eliminated.
Other sources of measurement inaccuracy, such as electric currents, electric field lines in the cylinder not being parallel and the influences of external fields are minimised or eliminated by using a mechanical concept having a very high axial and radial symmetry, shielding of the cylinder in order to obtain a Faraday cage and the use of two very stable current sources with currents that are equal to each other within 0.1 %.
Some embodiments of the measuring cell and a method for measuring the conductivity of a liquid according to the present invention will be described below by way of example on the basis of the drawing, in which:
Figures 1 up to and including 4 each show a different measurement position of the measuring cell according to the present invention used for measuring the conductivity of a liquid.
A measuring cell for measuring the conductivity of liquids according to the present invention is shown in four different measurement positions in the figures 1 up and including 4. The measuring cell contains two opposite outer electrodes 1 , 2. A reference electrode Rref and a voltmeter 3 are provided for determining the conductivity of a liquid column 4 to be measured which is situated between the outer electrodes 1 , 2. The cylinder has a radius r.
The measuring cell further has a perforated electrode 5, which is movably placed between the two outer electrodes 1 , 2. The perforated electrode 5 divides the cylinder into two compartments that are in contact with each other. The first 6 and the second 7 current source are capable of applying a first and a second current, respectively, between the outer electrodes 1 , 2 and the perforated electrode 5. The voltmeter, for instance a voltmeter of high accuracy, is used to determine a situation of a voltage difference of zero between the two compartments of the cylinder.
Furthermore the measuring cell comprises displacement means (not shown) for moving the perforated electrode 5 to various positions between the outer electrodes 1 ,2. For said displacement means numerous displacement means available to the expert can be used. Furthermore the measuring cell comprises switching means known per se for switching between the first and second current between the outer electrodes 1 , 2 and the perforated electrode 5.
The electrodes 1 , 2, 5, the current sources, 6, 7, the voltmeter 3 and the switching means are situated in a circuit which is schematically shown in the figures.
The present invention provides a main standard for the measuring of the conductivity of liquids, with an emphasis on a low uncertainty in the measurements, with which also low conductivities (e.g. < 25μS/cm) can deducibly be measured.
The measurement of the conductivity of the liquids is carried out by measuring the length L of a cylinder 4 of the liquid which has a resistance which can be derived form the reference resistance Rref, which preferably has a value with an uncertainty ~ 0.00001 %. The specific conductivity K of the liquid is then calculated from said resistance R and from the radius r of the cylinder, which with an uncertainty of 0.0005% can be known on
the basis of the formula:
κ=-
R.π.r2
A complete measurement consists of a series of four measurements, in which the current sources 6, 7 and the reference resistance Rref are repositioned on the left hand side and the right hand side of the circuit, as shown in figure 4. In each of the measurements the central perforated electrode 5 is positioned so as to give a zero voltage reading, after which the position X , X12, X21 , X22 of the perforated electrode 5 is determined. The positions obtained are then used to calculate the specific conductivity of the liquid according to
In this manner the sources of uncertainty such as polarisation and electrode pollution are eliminated.
The uncertainty of the measurement according to the present invention in principle depends on the uncertainty in the zero voltage measurement necessary for comparing the liquid and the reference resistance and on the uncertainty in the length measurement itself. An uncertainty of 0.001 % can as a result be achieved, which in order of size is lower than the lowest known uncertainty.
It is known per se to obtain the temperature stability necessary for performing the measurements by known thermo stabilisation of the cylinder and by placing the complete measurement system in an incubator with a
temperature stability better than 0.004%. Such and other parts known for the operation of the measuring cell are not described here in detail in order to keep the description simple.
(AS/NG 1317)
Claims
1 . Measuring cell for measuring the conductivity of liquids, which measuring cell is provided with two opposite outer electrodes, with a first current source, with a reference electrode and with a voltmeter, characterized in that the measuring cell is further provided with a perforated electrode movably placed between the two outer electrodes, with a second current source, the first and the second current source applying a first and a second current, respectively, between the outer electrodes and the perforated electrode, with displacement means for moving the perforated electrode to various positions, and with switching means for switching between the first and second current between the outer electrodes and the perforated electrode, the electrodes, the current sources, the voltmeter and the switching means being situated in a circuit.
2. Method for measuring the conductivity of a cylinder of liquid which is situated between the outer electrodes, in which a measuring cell according to claim 1 is used, in which method four measurements are carried out, the position of the perforated electrodes in each of the measurements (ii) being X(ii), in which in two of the four measurements the first current is applied and the reference electrode is at one side of the electric circuit, and in the other two measurements the second current is applied and the reference electrode (Rref) is at the other side of the electric circuit, in each of the measurements the perforated electrode being positioned such so as to cause a zero voltage reading on the voltmeter, and the specific conductivity being determined by the formula: 
in which r is the radius of the cylinder.
(AS/NG 270)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL1011540A NL1011540C2 (en) | 1999-03-12 | 1999-03-12 | Measuring cell for measuring the conductivity of liquids and method for measuring the conductivity of a liquid. |
| NL1011540 | 1999-03-12 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| WO2000055611A2 true WO2000055611A2 (en) | 2000-09-21 |
| WO2000055611A3 WO2000055611A3 (en) | 2001-04-05 |
Family
ID=19768827
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/NL2000/000169 WO2000055611A2 (en) | 1999-03-12 | 2000-03-13 | Measuring cell and method for measuring the conductivity of liquids |
Country Status (2)
| Country | Link |
|---|---|
| NL (1) | NL1011540C2 (en) |
| WO (1) | WO2000055611A2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8342775B2 (en) * | 2004-06-30 | 2013-01-01 | Agri Drain Corporation | Groundwater control system with purity sensor and method |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB982290A (en) * | 1960-03-16 | 1965-02-03 | Wayne Kerr Lab Ltd | Improvements in or relating to apparatus for measuring the electrical conductivity of liquids |
| NL7509233A (en) * | 1974-08-02 | 1976-02-04 | Kent Ltd G | MEASURING CELL FOR MEASURING THE ELECTRICAL CONDUCTIVITY OF LIQUIDS. |
| US5138264A (en) * | 1988-12-29 | 1992-08-11 | Hitachi, Ltd. | Apparatus for measuring electrical conductivity |
| WO1997016726A1 (en) * | 1995-11-02 | 1997-05-09 | Chiron Diagnostics Corporation | Planar hematocrit sensor incorporating a seven-electrode conductivity measurement cell |
-
1999
- 1999-03-12 NL NL1011540A patent/NL1011540C2/en not_active IP Right Cessation
-
2000
- 2000-03-13 WO PCT/NL2000/000169 patent/WO2000055611A2/en active Application Filing
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB982290A (en) * | 1960-03-16 | 1965-02-03 | Wayne Kerr Lab Ltd | Improvements in or relating to apparatus for measuring the electrical conductivity of liquids |
| NL7509233A (en) * | 1974-08-02 | 1976-02-04 | Kent Ltd G | MEASURING CELL FOR MEASURING THE ELECTRICAL CONDUCTIVITY OF LIQUIDS. |
| US5138264A (en) * | 1988-12-29 | 1992-08-11 | Hitachi, Ltd. | Apparatus for measuring electrical conductivity |
| WO1997016726A1 (en) * | 1995-11-02 | 1997-05-09 | Chiron Diagnostics Corporation | Planar hematocrit sensor incorporating a seven-electrode conductivity measurement cell |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8342775B2 (en) * | 2004-06-30 | 2013-01-01 | Agri Drain Corporation | Groundwater control system with purity sensor and method |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2000055611A3 (en) | 2001-04-05 |
| NL1011540C2 (en) | 2000-10-03 |
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