WO2002006805A1 - Spacer-inserted dissolved oxygen sensor - Google Patents

Spacer-inserted dissolved oxygen sensor Download PDF

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Publication number
WO2002006805A1
WO2002006805A1 PCT/KR2001/001186 KR0101186W WO0206805A1 WO 2002006805 A1 WO2002006805 A1 WO 2002006805A1 KR 0101186 W KR0101186 W KR 0101186W WO 0206805 A1 WO0206805 A1 WO 0206805A1
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WO
WIPO (PCT)
Prior art keywords
oxygen
spacer
sensor
membrane
dissolved oxygen
Prior art date
Application number
PCT/KR2001/001186
Other languages
French (fr)
Inventor
Bong-Il Ji
Young-Tae Kim
Original Assignee
Yuil Eginneering Corp
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 Yuil Eginneering Corp filed Critical Yuil Eginneering Corp
Priority to AU2001272795A priority Critical patent/AU2001272795A1/en
Publication of WO2002006805A1 publication Critical patent/WO2002006805A1/en

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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
    • 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
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/18—Water
    • G01N33/1806—Biological oxygen demand [BOD] or chemical oxygen demand [COD]

Definitions

  • the present invention pertains to a sensor for measuring dissolved oxygen (DO) by inserting a spacer therein, and more specifically, to a sensor and an apparatus for monitoring concentration of dissolved oxygen by inserting a spacer having a very closely spaced side structure between an electrode and a membrane, advantageous in terms of a decrease of side diffusion of oxygen, an improvement of a straight flow which is axially permeated to the electrode through a top portion of the spacer, and high resistance to span shift caused by impact.
  • DO dissolved oxygen
  • the interval between the membrane 1 and the electrode 2 is not constantly maintained, and also span shift behavior caused by the change of signal values from the sensor subjected to small impact is frequently generated, so that the dissolved oxygen sensor should be standardized before use.
  • a sensor is standardized at one point, at a randomly-chosen concentration of oxygen on the assumption that a sensor has a linear detection range. If the sensor does not have a linear detection range for oxygen concentration, such sensor has measurement errors and thus should be standardized at multiple points.
  • the senor has a linear detection range for oxygen concentration.
  • the sensor structure is composed of a miniaturized electrode 2 and a thickened membrane 1.
  • the signal is stronger at low oxygen concentration, and a stable and representative signal can be obtained upon measurement of oxygen concentration, but the signal is not linearly proportional to oxygen concentration under high partial pressure of oxygen due to OH accumulation, compared to the miniaturized electrode.
  • Diffusion paths in the dissolved oxygen sensor consist of axial inflow diffusion and side inflow diffusion.
  • the number of the reacted electrons according to accumulation of OH is decreased, thus lessening the signal value.
  • the interval between the membrane and the electrode should be broadened. Otherwise, the signal value from the sensor is decreased. If the membrane adheres loosely to the electrode, span shift occurs if the sensor is subjected to small impact, so the sensor does not function.
  • a dissolved oxygen sensor for use in measurement of concentration of dissolved oxygen made by inserting a spacer between a membrane for selectively permeating oxygen, suitable for use in an electrode capable of intensively absorbing dissolved oxygen, and a cathode for generating a current change depending on an amount of oxygen permeable through the membrane.
  • a dissolved oxygen sensor apparatus composed of a dissolved oxygen sensor for use in measurement of concentration of dissolved oxygen made by inserting a spacer between a membrane for selectively permeating oxygen and a cathode for generating a current change depending on an amount of oxygen permeable through the membrane.
  • Fig. 1 is a cross sectional view of a spacer-inserted dissolved oxygen sensor of the present invention.
  • Fig. 2 is a cross sectional view of a conventional dissolved oxygen sensor.
  • Fig. 3 is a perspective view and enlarged section view of the spacer of the present invention.
  • Figs. 4a and 4b are graphs illustrating linear detection range of a conventional dissolved sensor and a spacer-inserted sensor of the present invention.
  • Fig. 5a is a graph showing sensor response to oxygen of a conventional dissolved sensor and a spacer-inserted sensor of the present invention
  • Fig. 5b is an enlarged graph of a certain portion in the graph of Fig. 5a.
  • Fig. 6 is a graph illustrating span shift of a conventional dissolved sensor and a spacer-inserted sensor of the present invention.
  • Fig. 7 is a graph illustrating signal changes from the present dissolved oxygen sensor, according to a size of electrode and a thickness of membrane.
  • the present invention concerns a dissolved oxygen sensor comprising a membrane 1 for selectively permeating oxygen, suitable for use in an electrode capable of intensively absorbing dissolved oxygen, a cathode 2 for producing a current change depending on an amount of oxygen permeable through the membrane, and a spacer 5 positioned between the membrane 1 and the cathode 2, and an apparatus thereof.
  • a top portion of the spacer is composed of a netting structure 7, and a side portion of the spacer consists of a structure 8 including minute axial openings 6.
  • the spacer 5 is about
  • the side portion of the spacer 5 has much higher density than its top portion, so that side diffusion of oxygen can be ignored. That is, the side portion of the spacer 5 is closely spaced and thus side diffusion can be effectively blocked. Additionally, through minute axial openings 6 in the spacer 5, oxygen molecules flow in an axial direction relative to the surface of the electrode.
  • usable materials of the spacer 5 comprise a filter made of compressed natural pulps or a cloth knitted sparsely made of chemical fibers.
  • non-spacer 5 attached sensor has a decreased linear detection range according to an increase of oxygen concentration (see, Fig. 4a), but the linear detection range of the spacer 5-attached sensor is so excellent that its correlation coefficient becomes about 1 (see, Fig. 4b).
  • Fig. 5b shows a partly enlarged view of Fig. 5a. Referring to Fig. 6, there is shown span shift caused when the spacer 5- attached sensor and the non-spacer attached sensor are subjected to a predetermined impact.
  • the signal is drastically increased and is not restored to an original state after a first impact, and also is again shifted to yet a different value when the sensor is subjected to a second impact (see, Fig. 6).
  • the spacer 5-attached sensor is highly resistant to span shift, in which the signal is increased momentarily when the sensor is subjected to impact, but is immediately restored to the original state.
  • the electrode having a large size (9 mm) has a decreased linear detection range for oxygen concentration where partial pressure of oxygen is high, due to accumulation of OH, compared to the electrode having a small size (1 mm).
  • the spacer 5 -inserted cathode 2 is increased in size to 9 mm, the linear detection range is maintained under oxygen of high concentration.
  • the dissolved oxygen sensor according to the present invention made by inserting a spacer having a very closely spaced side structure therein can decrease the side diffusion of oxygen and improve a straight flow which is axially permeated to a electrode, thereby precisely measuring the practical concentration of dissolved oxygen, restraining the span shift caused by impact, and stably performing a function as a dissolved oxygen sensor, so greatly improving a water environment.

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  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Pathology (AREA)
  • Immunology (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Electrochemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Molecular Biology (AREA)
  • Engineering & Computer Science (AREA)
  • Biodiversity & Conservation Biology (AREA)
  • Biomedical Technology (AREA)
  • Emergency Medicine (AREA)
  • Food Science & Technology (AREA)
  • Medicinal Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

Disclosed are a spacer-inserted dissolved oxygen sensor and an apparatus thereof. The sensor comprises a membrane for selectively permeating oxygen without permeation of liquid components, an electrode for producing a current change depending on an amount of oxygen permeable through the membrane, and a spacer positioned between the membrane and the electrode for axially permeating oxygen to the electrode. The spacer has a very closely spaced side structure, thus effectively decreasing side diffusion and having high resistance to span shift caused by impact. In addition, minute axial openings in the spacer are responsible for inducing axial flux of oxygen to the electrode.

Description

SPACER-INSERTED DISSOLVED OXYGEN SENSOR
TECHNICAL FIELD
The present invention pertains to a sensor for measuring dissolved oxygen (DO) by inserting a spacer therein, and more specifically, to a sensor and an apparatus for monitoring concentration of dissolved oxygen by inserting a spacer having a very closely spaced side structure between an electrode and a membrane, advantageous in terms of a decrease of side diffusion of oxygen, an improvement of a straight flow which is axially permeated to the electrode through a top portion of the spacer, and high resistance to span shift caused by impact.
PRIOR ART
Conventionally, there has been proposed a diaphragm dissolved oxygen sensor by Clark in 1956, as shown in Fig. 2. Thereafter, a dissolved oxygen sensor further comprising a guard cathode has been devised to decrease side diffusion. However, in the conventional sensor structure of Fig. 2, when the interval between a membrane (Teflon) 1 and an electrode 2 is lengthened (10 μm or more), the side diffusion is increased. Meanwhile, when the interval between the membrane 1 and the electrode 2 (Pb) is shortened (10 μm or less), OH", reduced on the surface of the electrode, is accumulated and thus signal from the sensor is not linearly proportional to the concentration of dissolved oxygen. Thus, an oxygen- sensing function is decreased.
As stated above, the interval between the membrane 1 and the electrode 2 is not constantly maintained, and also span shift behavior caused by the change of signal values from the sensor subjected to small impact is frequently generated, so that the dissolved oxygen sensor should be standardized before use.
Generally, a sensor is standardized at one point, at a randomly-chosen concentration of oxygen on the assumption that a sensor has a linear detection range. If the sensor does not have a linear detection range for oxygen concentration, such sensor has measurement errors and thus should be standardized at multiple points.
Therefore, it is very important that the sensor has a linear detection range for oxygen concentration.
In order to improve the linear detection range of the sensor, the sensor structure is composed of a miniaturized electrode 2 and a thickened membrane 1.
However, the signal from such sensor, proportional to oxygen concentration to be measured, is decreased, and the side diffusion is increased, thus measurement errors becoming larger upon measuring the dissolved oxygen at low concentration.
In the case of large electrode, the signal is stronger at low oxygen concentration, and a stable and representative signal can be obtained upon measurement of oxygen concentration, but the signal is not linearly proportional to oxygen concentration under high partial pressure of oxygen due to OH accumulation, compared to the miniaturized electrode.
Diffusion paths in the dissolved oxygen sensor consist of axial inflow diffusion and side inflow diffusion.
In using a conventional sensor manufactured by Clark as a dissolved oxygen sensor, there are two assumptions made. First, if oxygen axially flows in the electrode, the amount of oxygen diffused from the side is theoretically very small and thus can be ignored. Second, a diffusion coefficient of an electrolyte film and a membrane is constant, irrespective of concentration, temperature, and time. In the first case, oxygen inflow by side diffusion is much smaller than that by axial diffusion, however, in practice, the amount cannot be ignored. In order to increase the signal in a common sensor, the membrane should be disposed very closely to the electrode. But, if the membrane is adjacent to an anode 3 (Pt, Au) at a distance of 5 μm or less, OH", resulting from the reduction of oxygen, does not diffuse away from the anode, but is dissolved in an electrolyte 4 (KCl), thus increasing the pH of the electrolyte. Accordingly, reduction of oxygen at the anode is decreased, so breaking the stoichiometric quantity of the chemical redox reaction taking place on the dissolved oxygen sensor, represented by the following reaction:
Reaction 1
O2 + 2H2O + 4e" → 4OH" (alkaline electrolyte)
The number of the reacted electrons according to accumulation of OH is decreased, thus lessening the signal value. In order to prevent the accumulation of OH, the interval between the membrane and the electrode should be broadened. Otherwise, the signal value from the sensor is decreased. If the membrane adheres loosely to the electrode, span shift occurs if the sensor is subjected to small impact, so the sensor does not function.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to alleviate said problems of the prior arts and to provide a dissolved oxygen sensor, which has advantages of a decrease of side diffusion of oxygen, an improvement of a straight flow by axial electrode permeation, and high resistance to span shift attributed to impact, by inserting a spacer having a very closely spaced side structure.
It is another object of the present invention to provide a dissolved oxygen sensor apparatus, suitable for use in measurement of concentration of dissolved oxygen. In an aspect of the present invention, there is provided a dissolved oxygen sensor for use in measurement of concentration of dissolved oxygen, made by inserting a spacer between a membrane for selectively permeating oxygen, suitable for use in an electrode capable of intensively absorbing dissolved oxygen, and a cathode for generating a current change depending on an amount of oxygen permeable through the membrane.
In another aspect of the present invention, there is provided a dissolved oxygen sensor apparatus, composed of a dissolved oxygen sensor for use in measurement of concentration of dissolved oxygen made by inserting a spacer between a membrane for selectively permeating oxygen and a cathode for generating a current change depending on an amount of oxygen permeable through the membrane.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Fig. 1 is a cross sectional view of a spacer-inserted dissolved oxygen sensor of the present invention.
Fig. 2 is a cross sectional view of a conventional dissolved oxygen sensor.
Fig. 3 is a perspective view and enlarged section view of the spacer of the present invention.
Figs. 4a and 4b are graphs illustrating linear detection range of a conventional dissolved sensor and a spacer-inserted sensor of the present invention.
Fig. 5a is a graph showing sensor response to oxygen of a conventional dissolved sensor and a spacer-inserted sensor of the present invention, and Fig. 5b is an enlarged graph of a certain portion in the graph of Fig. 5a.
Fig. 6 is a graph illustrating span shift of a conventional dissolved sensor and a spacer-inserted sensor of the present invention.
Fig. 7 is a graph illustrating signal changes from the present dissolved oxygen sensor, according to a size of electrode and a thickness of membrane.
BEST MODES FOR CARRYING OUT THE INVENTION
As shown in Fig. 1, the present invention concerns a dissolved oxygen sensor comprising a membrane 1 for selectively permeating oxygen, suitable for use in an electrode capable of intensively absorbing dissolved oxygen, a cathode 2 for producing a current change depending on an amount of oxygen permeable through the membrane, and a spacer 5 positioned between the membrane 1 and the cathode 2, and an apparatus thereof.
In the enlarged view of the spacer 5 illustrated in Fig. 3, a top portion of the spacer is composed of a netting structure 7, and a side portion of the spacer consists of a structure 8 including minute axial openings 6. The spacer 5 is about
20-90 μm thick, and is responsible for artificially broadening the interval between the electrode and the membrane by a predetermined distance.
The side portion of the spacer 5 has much higher density than its top portion, so that side diffusion of oxygen can be ignored. That is, the side portion of the spacer 5 is closely spaced and thus side diffusion can be effectively blocked. Additionally, through minute axial openings 6 in the spacer 5, oxygen molecules flow in an axial direction relative to the surface of the electrode.
As such, usable materials of the spacer 5 comprise a filter made of compressed natural pulps or a cloth knitted sparsely made of chemical fibers.
A detailed description will be given of linear detection range, side diffusion, span shift and size effect of electrode, below.
As best seen in Figs. 4a and 4b, non-spacer 5 attached sensor has a decreased linear detection range according to an increase of oxygen concentration (see, Fig. 4a), but the linear detection range of the spacer 5-attached sensor is so excellent that its correlation coefficient becomes about 1 (see, Fig. 4b).
As apparent from the result shown in Fig. 5 a, it can be seen that the sensitivity of the spacer 5-attached sensor to oxygen is drastically decreased and is close to zero, from the experiment to find whether the spacer 5-attached sensor is in response to zero reaction when the sensor is immersed in a zero solution
(N SO3) free completely of dissolved oxygen.
Also, the extent of the side diffusion relative to the axial diffusion in the spacer 5-attached sensor is much less than that of non-spacer 5 attached sensor. Hence, it can be seen that the spacer 5-attached sensor can further restrain the side diffusion than non-spacer attached sensor. Fig. 5b shows a partly enlarged view of Fig. 5a. Referring to Fig. 6, there is shown span shift caused when the spacer 5- attached sensor and the non-spacer attached sensor are subjected to a predetermined impact.
In the non-spacer 5 attached sensor, the signal is drastically increased and is not restored to an original state after a first impact, and also is again shifted to yet a different value when the sensor is subjected to a second impact (see, Fig. 6).
To obtain a uniform signal, every value must be standardized after the sensor is subjected to impact. However, this manner is not preferable. The spacer 5-attached sensor is highly resistant to span shift, in which the signal is increased momentarily when the sensor is subjected to impact, but is immediately restored to the original state.
Additionally, insertion of the spacer 5 results in a drastic decrease of noise signal level (see, Fig. 6).
These results show that the spacer-inserted sensor is very stable and is not affected by external factors, compared with the non-spacer 5 attached sensor.
As seen in Fig. 7, the electrode having a large size (9 mm) has a decreased linear detection range for oxygen concentration where partial pressure of oxygen is high, due to accumulation of OH, compared to the electrode having a small size (1 mm). However, when the spacer 5 -inserted cathode 2 is increased in size to 9 mm, the linear detection range is maintained under oxygen of high concentration.
In addition, even though the membrane 1 is positioned closely to the cathode 2 and the sensor is subjected to impact, span shift is not caused because the predetermined interval is maintained by the spacer. Likewise, the accumulation of OH" is significantly decreased under oxygen of high concentration. The minute axial openings 6 in the spacer 5 enhance the axial diffusion of oxygen to accord with a first diffusion model, which is a theoretical basis of an oxygen sensor.
INDUSTRIAL APPLICABILITY As stated above, the dissolved oxygen sensor according to the present invention made by inserting a spacer having a very closely spaced side structure therein can decrease the side diffusion of oxygen and improve a straight flow which is axially permeated to a electrode, thereby precisely measuring the practical concentration of dissolved oxygen, restraining the span shift caused by impact, and stably performing a function as a dissolved oxygen sensor, so greatly improving a water environment.
The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims

1. A dissolved oxygen sensor for use in measurement of concentration of dissolved oxygen, made by inserting a spacer between a membrane for selectively permeating oxygen, suitable for use in an electrode capable of intensively absorbing dissolved oxygen, and a cathode for generating a current change depending on an amount of oxygen permeable through the membrane.
2. The sensor as defined in claim 1, wherein the spacer has a very closely spaced side structure for decreasing side diffusion of oxygen, and minute axial openings for axially inducing flux of oxygen to an electrode.
3. The sensor as defined in claim 1 or 2, wherein the spacer comprises a filter made of compressed natural pulps or a cloth knitted sparsely with chemical fibers, and is 20-90 μm thick.
4. A dissolved oxygen sensor apparatus, comprising a dissolved oxygen sensor for use in measurement of concentration of dissolved oxygen made by inserting a spacer between a membrane for selectively permeating oxygen and a cathode for generating a current change depending on an amount of oxygen permeable through the membrane.
PCT/KR2001/001186 2000-07-13 2001-07-11 Spacer-inserted dissolved oxygen sensor WO2002006805A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001272795A AU2001272795A1 (en) 2000-07-13 2001-07-11 Spacer-inserted dissolved oxygen sensor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR10-2000-0040137A KR100382315B1 (en) 2000-07-13 2000-07-13 The DO Sensor Inserted The Spacer
KR2000/40137 2000-07-13

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WO2002006805A1 true WO2002006805A1 (en) 2002-01-24

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Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6360595B1 (en) * 2001-03-16 2002-03-26 Ethicon Endo-Surgery, Inc. Liquid measuring device and method of using

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4376681A (en) * 1979-01-08 1983-03-15 Oriental Yeast Co., Ltd. Method of measuring carbon dioxide in a liquid or gas
JPH0363560A (en) * 1989-08-02 1991-03-19 Hitachi Ltd Dissolved oxygen sensor
JPH06242057A (en) * 1993-02-17 1994-09-02 Yokogawa Electric Corp Dissolved oxygen sensor
JPH09127045A (en) * 1995-10-26 1997-05-16 Nok Corp Dissolved oxygen sensor

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5431160A (en) * 1989-07-19 1995-07-11 University Of New Mexico Miniature implantable refillable glucose sensor and material therefor

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4376681A (en) * 1979-01-08 1983-03-15 Oriental Yeast Co., Ltd. Method of measuring carbon dioxide in a liquid or gas
US4460451A (en) * 1979-01-08 1984-07-17 Oriental Yeast Co. Ltd. Steam-sterilizable carbon dioxide sensor
JPH0363560A (en) * 1989-08-02 1991-03-19 Hitachi Ltd Dissolved oxygen sensor
JPH06242057A (en) * 1993-02-17 1994-09-02 Yokogawa Electric Corp Dissolved oxygen sensor
JPH09127045A (en) * 1995-10-26 1997-05-16 Nok Corp Dissolved oxygen sensor

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KR20000072042A (en) 2000-12-05
KR100382315B1 (en) 2003-05-01
AU2001272795A1 (en) 2002-01-30

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