WO2001094921A2 - A pH SENSOR SYSTEM AND METHOD FOR USING SAME - Google Patents
A pH SENSOR SYSTEM AND METHOD FOR USING SAME Download PDFInfo
- Publication number
- WO2001094921A2 WO2001094921A2 PCT/US2001/018694 US0118694W WO0194921A2 WO 2001094921 A2 WO2001094921 A2 WO 2001094921A2 US 0118694 W US0118694 W US 0118694W WO 0194921 A2 WO0194921 A2 WO 0194921A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- sensor system
- level
- sensitive material
- sensing circuitry
- housing
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
- G01N17/02—Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
- G01N21/80—Indicating pH value
-
- 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
- G01N33/38—Concrete; ceramics; glass; bricks
Definitions
- the present disclosure relates generally to monitoring the pH level of a medium. More particularly, the present disclosure is directed to a pH sensor system and method for monitoring the pH level of a medium such as, for example, concrete, by embedding the sensor system within the medium.
- a problem which reduces the integrity of roadways, related structures and buildings is the corrosion of the contained reinforcing material by sources of chlorides, e.g., chloride-based deicers, seawater and other various sources of chlorides.
- the reinforcing material is typically a high resistance steel bar especially sensitive to deterioration through the effect of corrosion due to the action of oxygen.
- a “passivation” layer typically forms on the steel surface of the bar when it comes into contact with freshly prepared wet concrete to provide protection against corrosion of the reinforcement bars.
- the reinforcement bars are enveloped in a continuous sheath of PNC or, polyethylene, and more recently, epoxy. Locations where the polymer coating is damaged, broken and has a "holiday," the passivation layer forms on the steel, protecting it from corrosion.
- the formation of the passivation layer on steel reinforcement bars is related to the pH of concrete, which is an alkaline medium with a pH of around 13.
- the passivation layer is, in most part, comprised of the oxides of iron which is formed by the reaction between iron and the hydroxide ions in concrete. In principle, this protection against corrosion should be sufficient because it provides a barrier against further oxidation of steel.
- the oxide film (passivation layer) becomes unstable resulting in little to no protection to the steel.
- the steel surface is vulnerable to chloride (salt) attack, which causes pitting corrosion. This, in turn, causes the roadways and structures formed from the reinforced concrete to degrade and ultimately fail.
- the parameters that contribute to the change in the pH of concrete are environmental conditions such as, for example, acid rain and carbon dioxide. Note that the "buffer capacity" of freshly prepared concrete is high. Therefore, it will take several years of exposure of the concrete structure to these environmental conditions before the pH level of the concrete decreases from 13 to 12.
- NMR nuclear magnetic resonance
- Other programs are underway to construct miniature NMR (NMR-on-a-Chip) just for this purpose.
- NMR does not have the same types of limitations as the electrochemical sensors. Thus, it is far from being a mature technology that could be used in concrete structures.
- the lack of accurate in situ data on chloride ion concentration inside concrete complicates the prediction of pitting in steel. This limitation is further compounded by lack of pH data. It is arguable whether change in pH is more important to corrosion than chloride concentration.
- miniature pH sensor system will be valuable in monitoring the internal environment of concrete, as it changes from benign (pH>13) to corrosive (pH ⁇ 12).
- the senor Since the sensor is small and comparable to the aggregates in concrete, it can be embedded in large numbers in a distributed fashion across the entire structure. The ubiquitous presence of a pH sensor will provide valuable data virtually at every location of the structure. This will help predict locations within the structure that are more vulnerable to corrosion than others. One can use this information to plan repair schedules before corrosion begins, thus saving valuable time and resources. Due to the increasing need for good management practices, a large number of embeddable sensors are being developed by various organizations.
- An example of one of the more comparable suite of sensors is the embeddable microinstruments developed by the University of Virginia and the Virginia Transportation Research Council, which is described in their web-site www.vatechnologies.com.
- the current version of this unit is encased in plastic and needs external wire connections for power and measurement.
- the same web-site also describes a concept for a wireless version; it has a rechargeable battery which will need periodic recharging during the lifetime of the sensor and is expected to carry an RF link for communication.
- the Virginia sensor suite does not yet have telemetry, requires a battery or an external power source, and is much bigger in size than the aggregates found in concrete.
- Wires and their associated connectors is a common source of reliability problems in field instrumentation. From an operational perspective, hanging wires are not desirable characters in structures such as bridges. Therefore, in its present form and purpose, the University of Virginia sensor may not be useful to monitor corrosion in bridge decks.
- sensors are the fiberoptics-based chloride sensors developed by the Vermont DOT, the University of Vermont (Laser Focus World, March 1998, p. 47) and Ontario, Canada (Ontario Ministry of Transportation and Communication, 1986) that measure changes in chloride concentration in concrete. Initial testing in concrete has shown that the chloride sensing elements need further improvement for long term stability. Furthermore, they depend upon external fiberoptic cables for communication.
- the pH sensor system includes at least a housing having at least one transparent surface; a light sensitive circuitry, e.g., a circuitry having at least a LED and photo-detector, enclosed within the housing; and, a chromatic pH sensitive material overlaying at least a portion of the transparent surface having the characteristic of becoming saturated with hydrogen ions when an ambient pH level reaches a predetermined level, wherein the light sensitive circuitry detects a different intensity of incident light when the chromatic pH sensitive material is saturated than when the chromatic pH sensitive material is not saturated.
- a light sensitive circuitry e.g., a circuitry having at least a LED and photo-detector
- the pH sensor system monitors the pH level of the surrounding medium by way of the pH sensitive material on the transparent surface. As the pH level of the medium steadily decreases, the pH sensitive material on the transparent surface of the housing will gradually be saturated with hydrogen ions such that the pH sensitive material becomes colorless. Upon the pH sensitive material becoming saturated with hydrogen ions and therefore reaching a colorless state, the material is unable to absorb any light emitted from the LED such that the light is reflected back to the photo-detector.
- the monitoring process entails embedding the pH sensor system in the medium, e.g., concrete, storage tanks, etc., to be monitored.
- the medium e.g., concrete, storage tanks, etc.
- the pH sensitive material is saturated with hydrogen ions and becomes colorless. It is advantageous to monitor the pH level so that the medium does not prematurely degrade to the point that preventive measures may not be implemented.
- FIG.1 is a schematic representation of a pH sensor system in accordance with the present disclosure
- FIG. 2 is a circuit diagram of a pH sensor system according to the present invention.
- FIG. 3 shows the configuration of the setup of sol-gel on a glass slide
- FIG. 4 shows the glass slide containing the sol-gel in conjunction with a
- FIG. 5 shows the glass slide containing the sol-gel with cement thereon.
- pH sensor system 10 of the present disclosure includes at least housing 12 having at least one transparent surface 14, light sensing circuitry 15 enclosed within housing 12 and having at least a light emitting diode (LED) 16 and photo-detector 18, e.g., a semiconductor pin photodiode or avalanche photodiode, and a chromatic pH sensitive material 20 overlaying at least a portion of the transparent surface 14.
- housing 12 will be formed from conventional materials known in the art. Suitable materials for use herein include, but are not limited to, ceramic materials, e.g., alumina, macor, etc.; plastic materials; nylon; concrete; epoxy and the like.
- housing 12 can vary accordingly and can be determined on a case by case basis.
- Housing 12 will have at least one surface 14 that is optically transparent. That surface is transparent to light having a wavelength of from about 300 to about 500 nm, which is the wavelength of light emitted by the LED 16.
- Useful materials for transparent surface 14 include, but are not limited to, glass, sapphire and the like.
- a pH sensitive material 20 will be applied on at least a portion of the (the part that is exposed to the medium) transparent surface 14 of housing 12.
- Material 20 will advantageously be formed from an inert material and a pH indicator. If prepared according to the procedure prescribed later in this document, material 20 will absorb at least some part of light that is within the range of about 300 to about 500 nm.
- pH sensitive material 20 formed from at least the pH indicator with the inert material and suitable catalyst on the transparent surface the color of the pH sensitive material 20 will change from a color state to a colorless state as material 20 becomes saturated with hydrogen ions. In essence, the color of the pH sensitive material 20 changes as a function of pH immobilized within the material on the basis of a waveguide.
- any changes in pH of the medium being monitored will be reflected in a color change in the pH indicator in the inert material as the pH sensitive material becomes saturated with hydrogen ions.
- the pH sensitive material When the chromatic pH sensitive material 20 is substantially saturated with hydrogen ions, the pH sensitive material will be colorless. This, in turn, results in the light emitted from the LED to reflect off of pH sensitive material 20 which increases the voltage output of the photo-detector.
- the actual level of voltage depends upon the details of the electronics (e.g., amplifier and A/D converter) employed to measure the voltage. It also depends upon the wavelength of the light (of the LED source).
- the wavelength of the light is about 355 ⁇ 20 nm
- the voltage of the photo-diode reaches a certain level, e.g., to about 500% of its original value
- the pH of the medium reaches a predetermined level different from the original ambient pH of the medium thereby indicating that the medium has turned corrosive, as discussed hereinbelow.
- the wavelength of the light is about 425 ⁇ 20 nm
- an increase of, for example, 120% increase in the output voltage of the photo-diode indicates that the pH of the medium reaches a predetermined level different from the original ambient pH of the medium.
- the light sensitive circuitry 15 can measure the change of color in the material 20.
- Suitable inert materials for use herein include any inert material known to one skilled in the art. Suitable inert materials include, but are not limited to, cellulose, cellulose acetates and sol-gels, e.g., silica-based gel such as, e.g., methyltriethoxysilane (MTEOS)). A preferred inert material for use herein is MTEOS.
- the pH indicators are those that will advantageously reflect a change in the pH level of the material being monitored. Suitable pH indicators for use herein are indicators that respond to pH changes in the range of from about 12 to about 14. A preferred pH indicator for use herein is trinitrobenzene sulfonic acid (TNBS).
- the inert material with the pH indicator in the presence of a catalyst such as, e.g., NaOH or KOH, and water, form pH sensitive material 20.
- a catalyst such as, e.g., NaOH or KOH
- the catalyst can be first mixed with the inert material (MTEOS) to form a first solution and then further mixed with the pH indicator.
- the catalyst can be mixed with the pH indicator and then the inert material can be added thereto to form the solution.
- the components of the mixture are ordinarily mixed for a time period ranging from about 1 hour to about several (3) days.
- the amount of the individual components (e.g., H 2 O, MTEOS, KOH and TNBS) used to make the material 20 can vary over a wide range, e.g., a molar ratio of H 2 O: MTEOS:KOH:TNBS ranging from about 3:1:0.000001:0.000001 to about 6:1:0.1:0.1 can be advantageously employed.
- a molar ratio of H 2 O: MTEOS:KOH:TNBS ranging from about 3:1:0.000001:0.000001 to about 6:1:0.1:0.1 can be advantageously employed.
- the pH sensitive material is formed, the material is then deposited on at least a portion of the transparent surface 14 of housing 12. Techniques for depositing the pH sensitive material 20 on the transparent surface 14 are within the purview of one skilled in the art, e.g., by manual application using an applicator, or automated/semi- automated processes such as dip-coating and/or spin coating.
- the pH sensitive material is' generally deposited on the transparent surface at a thickness ranging from about 0.1 mm to about 2 mm and preferably from about 0.5 mm to about 1 mm.
- the pH sensitive material is then allowed to dry under, for example, ambient temperature in an atmosphere saturated with ethanol, methanol or isopropyl alcohol for a time period of at least 1 day to about 7 days.
- the pH sensor systems of the present disclosure are particularly useful for monitoring the pH level of a medium which is susceptible to degradation when the pH level of the medium reaches a predetermined level.
- the mediums to be monitored herein are those which possess an ambient pH level in the range of from about 12 to about 14. Examples of these mediums include, but are not limited to, concrete, soil, storage tanks for chemical reagents, e.g., NaOH, KOH, etc., biological mediums and the like.
- the pH sensor system is first embedded in the medium to be monitored.
- the LED and the light sensitive circuitry are powered by a power source 30 such as, for example, a rechargeable nickel-cadmium or lithium-ion battery or a super capacitor.
- the power source can be internal to the sensor housing when the sensor is embedded in concrete or soil, and external to the sensor housing, when the sensor is immersed in a fluid inside a chemical container or a tank.
- Power source 30 is linked to an external power source such as a battery for recharging the power source 30.
- the link can be either through an inductive coupling or direct wire contacts.
- power source 30 can be placed outside housing 12.
- Power source 30 is connected to a relay 32 and a resistor R.
- Relay 32 and resister R provide overcurrent protection to LED 16, as known in the art.
- LED 16 constantly emits light upon being powered by power source 30. The light is preferably directed toward transparent surface 14 where it is gradually reflected back as incident light by pH sensitive material 20 as material 20 becomes increasingly saturated with hydrogen ions therefore indicating that the pH of the medium being monitored is decreasing.
- a voltmeter/A-D converter or lock-in amplifier/A-D converter 34 connected in parallel to photo-detector 18 measures the voltage across photo-detector 18. The measured voltage is outputted via a data link 36 to a processor, e.g., a processor within a laptop computer.
- the power source 30 powers the LED 16, photo-detector 18, voltmeter/A-
- D converter or lock-in amplifier/A-D converter 34 and data link 36 D converter or lock-in amplifier/A-D converter 34 and data link 36.
- the dye absorbs less and less light. Therefore, the amount of incident light reflected back and detected by the photo-detector 18 is greater than when the pH sensitive material 20 is not saturated. As a result, the voltage across the photo-detector 18 increases as is known in the art. Accordingly, voltmeter/A-D converter 34 outputs this voltage via data link 36 which enables an operator to determine that pH sensitive material 20 is becoming saturated due to a decrease in the ambient pH level.
- the operator can determine the ambient pH level by relating the measured voltage across the photo-detector 18 with the corresponding pH level using a chart or table that relates voltage to pH level.
- the actual level of voltage depends upon the details of the electronics (such as amplifier and A/D converter) employed to measure the voltage. It also depends upon the wavelength of the light (of the LED source). For example, if the wavelength of the light is about 355 ⁇ 20 nm, then if the voltage of the photo-diode reaches about 500% of its original value, the pH of the medium reaches a predetermined level different from the original ambient pH of the medium thereby indicating that the medium has turned corrosive, as discussed herein.
- sol-gel on which each of the films is based was prepared using a 6: 1 molar ratio of water to methytriethoxysilane (MTEOS) to ensure more complete hydrolysis and formation of siloxane bonds and allowing for more pH indicator to be incorporated into the film.
- MTEOS methytriethoxysilane
- the pH indicator used for these experiments was trinitrobenzene sulfonic acid, a colorimetric dye, that responds to pH changes in the pH 12-14 range with an absorbance maximum at 355 nm.
- a 9.34 mM solution of TNBS in distilled water was prepared and substituted for the water component in the preparation of a sol-gel thin film.
- several solutions of the sol-gel-TNBS composite were prepared as follows. A 6:1 ratio of TNBS solution and MTEOS were combined and stirred for 48-52 hours to allow for homogenization of the precursor solution. A catalyst in the form of 0.5-2.0 ⁇ L of a 10 M solution of potassium hydroxide in water was added to some samples and the solution was stirred for 30-60 seconds before casting the film while another sample remained uncatalyzed and films were prepared without further modification of the precursor solution.
- Sample 1 contains no TNBS and is outside the scope of this disclosure.
- Samples 2 and 3 contain TNBS, which is within the scope of this disclosure, and were prepared using a 9.34 mM solution of TNBS in distilled water.
- Thin films of each of the samples were prepared by spreading approximately 0.8 mL of the pH sensitive solution over an approximately one inch square area of prepared glass microscope slide.
- the surfaces were prepared by rinsing with warm tap water and Mr. Clean brand cleaning solution (containing sodium hydroxide). The surfaces were then rinsed twice with distilled water and hung to dry in a covered beaker. Surfaces were cleaned no more than 12 hours prior to application of the pH sensitive solution. Once the films were applied they were allowed to cure flat under an inverted beaker at ambient temperature for at least one week before any tests were conducted.
- sol-gel-TNBS pH sensitive films were first characterized using a spectrometer. Absorbance spectra in the 200-600 nm range were taken of each film. For this purpose, a baseline for absorbance was established using two films of identical composition without TNBS (Sample 1). Next, two films of both Samples 2 and 3 (films containing TNBS) were used to obtain spectra of the TNBS relative to that of a blank sol-gel film.
- Figure 3 shows the LED/Glas-Slide/Photo-diode arrangement.
- a paper screen blocks the scattered light from the LED from reaching the photodiode directly without passing first through the sample.
- the first set of experiments consisted of calibration of the pH sensitive material, with and without TNBS, using the experimental setup shown in Figure 4. The results of the experiments are set forth below in Table II.
- the pH sensitive films containing TNBS i.e., samples 2 and 3
- the films used appear to be durable, maintaining the same physical and optical properties after being immersed in a pH environment of about 13 for several days, thus providing a viable platform for a long-term embedded sensor in concrete.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2001275436A AU2001275436A1 (en) | 2000-06-09 | 2001-06-08 | A ph sensor system and method for using same |
EP01942145A EP1290429A2 (en) | 2000-06-09 | 2001-06-08 | A pH SENSOR SYSTEM AND METHOD FOR USING SAME |
US10/311,169 US20030211011A1 (en) | 2001-06-08 | 2001-06-08 | Ph sensor system and method for using same |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US21054700P | 2000-06-09 | 2000-06-09 | |
US60/210,547 | 2000-06-09 |
Publications (2)
Publication Number | Publication Date |
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WO2001094921A2 true WO2001094921A2 (en) | 2001-12-13 |
WO2001094921A3 WO2001094921A3 (en) | 2002-04-18 |
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Family Applications (1)
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PCT/US2001/018694 WO2001094921A2 (en) | 2000-06-09 | 2001-06-08 | A pH SENSOR SYSTEM AND METHOD FOR USING SAME |
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EP (1) | EP1290429A2 (en) |
AU (1) | AU2001275436A1 (en) |
WO (1) | WO2001094921A2 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2004027403A1 (en) * | 2002-09-20 | 2004-04-01 | Mitsubishi Denki Kabushiki Kaisha | Chemochromic sensor and method for sensing a chemochromic reagent and test material |
US7723120B2 (en) | 2005-10-26 | 2010-05-25 | General Electric Company | Optical sensor array system and method for parallel processing of chemical and biochemical information |
US7883898B2 (en) | 2007-05-07 | 2011-02-08 | General Electric Company | Method and apparatus for measuring pH of low alkalinity solutions |
US8133741B2 (en) | 2005-10-26 | 2012-03-13 | General Electric Company | Methods and systems for delivery of fluidic samples to sensor arrays |
CN107860771A (en) * | 2017-12-26 | 2018-03-30 | 常州大学 | A kind of sodium hydroxide solution calibration facility of nearly zero flow velocity |
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EP0416469A2 (en) * | 1989-09-05 | 1991-03-13 | Pacesetter, Inc. | Oxygen content pacemaker sensor and method |
WO1998037802A1 (en) * | 1997-02-27 | 1998-09-03 | Minnesota Mining And Manufacturing Company | Blood parameter measurement device |
US5925572A (en) * | 1996-08-07 | 1999-07-20 | University Of South Florida | Apparatus and method for in situ pH measurement of aqueous medium |
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US6113858A (en) * | 1998-01-26 | 2000-09-05 | Tang; Ruey-Long | Monitor with in-situ optical probe for continuous concentration measurements |
Family Cites Families (1)
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JPS63191045A (en) * | 1987-02-04 | 1988-08-08 | Onoda:Kk | Apparatus and method for measuring neutralization depth for concrete layer |
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2001
- 2001-06-08 WO PCT/US2001/018694 patent/WO2001094921A2/en not_active Application Discontinuation
- 2001-06-08 AU AU2001275436A patent/AU2001275436A1/en not_active Abandoned
- 2001-06-08 EP EP01942145A patent/EP1290429A2/en not_active Withdrawn
Patent Citations (5)
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EP0416469A2 (en) * | 1989-09-05 | 1991-03-13 | Pacesetter, Inc. | Oxygen content pacemaker sensor and method |
US5925572A (en) * | 1996-08-07 | 1999-07-20 | University Of South Florida | Apparatus and method for in situ pH measurement of aqueous medium |
WO1998037802A1 (en) * | 1997-02-27 | 1998-09-03 | Minnesota Mining And Manufacturing Company | Blood parameter measurement device |
US6113858A (en) * | 1998-01-26 | 2000-09-05 | Tang; Ruey-Long | Monitor with in-situ optical probe for continuous concentration measurements |
WO2000029832A1 (en) * | 1998-11-16 | 2000-05-25 | Tufts University | Fiber optic sensor for long-term analyte measurements in fluids |
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Title |
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Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2004027403A1 (en) * | 2002-09-20 | 2004-04-01 | Mitsubishi Denki Kabushiki Kaisha | Chemochromic sensor and method for sensing a chemochromic reagent and test material |
CN100465623C (en) * | 2002-09-20 | 2009-03-04 | 三菱电机株式会社 | Chemochromic sensor and method for sensing a chemochromic reagent and test material |
US7723120B2 (en) | 2005-10-26 | 2010-05-25 | General Electric Company | Optical sensor array system and method for parallel processing of chemical and biochemical information |
US8105552B2 (en) | 2005-10-26 | 2012-01-31 | General Electric Company | Optical sensor array system for parallel processing of chemical and biochemical information |
US8133741B2 (en) | 2005-10-26 | 2012-03-13 | General Electric Company | Methods and systems for delivery of fluidic samples to sensor arrays |
US8420025B2 (en) | 2005-10-26 | 2013-04-16 | General Electric Company | Methods and systems for delivery of fluidic samples to sensor arrays |
US7883898B2 (en) | 2007-05-07 | 2011-02-08 | General Electric Company | Method and apparatus for measuring pH of low alkalinity solutions |
US8076153B2 (en) | 2007-05-07 | 2011-12-13 | General Electric Company | Method and apparatus for measuring pH of low alkalinity solutions |
US8148166B2 (en) | 2007-05-07 | 2012-04-03 | General Electric Company | Method and apparatus for measuring pH of low alkalinity solutions |
TWI449896B (en) * | 2007-05-07 | 2014-08-21 | Gen Electric | Method and apparatus for measuring ph of low alkalinity solutions |
CN107860771A (en) * | 2017-12-26 | 2018-03-30 | 常州大学 | A kind of sodium hydroxide solution calibration facility of nearly zero flow velocity |
Also Published As
Publication number | Publication date |
---|---|
AU2001275436A1 (en) | 2001-12-17 |
WO2001094921A3 (en) | 2002-04-18 |
EP1290429A2 (en) | 2003-03-12 |
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