NL2029084A - Electrical capacitance tomography sensor calibration method - Google Patents
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- NL2029084A NL2029084A NL2029084A NL2029084A NL2029084A NL 2029084 A NL2029084 A NL 2029084A NL 2029084 A NL2029084 A NL 2029084A NL 2029084 A NL2029084 A NL 2029084A NL 2029084 A NL2029084 A NL 2029084A
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- 238000000034 method Methods 0.000 title claims abstract description 51
- 238000003325 tomography Methods 0.000 title claims abstract description 10
- 239000004567 concrete Substances 0.000 claims abstract description 77
- 238000005259 measurement Methods 0.000 claims abstract description 32
- 238000012544 monitoring process Methods 0.000 claims abstract description 27
- 230000008569 process Effects 0.000 claims abstract description 22
- 230000005540 biological transmission Effects 0.000 claims abstract description 21
- 238000002360 preparation method Methods 0.000 claims abstract description 13
- 238000001035 drying Methods 0.000 claims abstract description 10
- 238000010606 normalization Methods 0.000 claims abstract description 10
- 238000003384 imaging method Methods 0.000 claims abstract description 9
- 229920006395 saturated elastomer Polymers 0.000 claims description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 11
- 238000005303 weighing Methods 0.000 claims description 7
- 230000005284 excitation Effects 0.000 claims description 4
- 238000012360 testing method Methods 0.000 claims description 3
- 239000011377 vacuum concrete Substances 0.000 claims description 3
- 238000005520 cutting process Methods 0.000 claims description 2
- 238000005266 casting Methods 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 13
- 239000004568 cement Substances 0.000 abstract description 9
- 230000005514 two-phase flow Effects 0.000 abstract description 8
- 239000007787 solid Substances 0.000 abstract description 6
- 230000000007 visual effect Effects 0.000 abstract description 4
- 239000000523 sample Substances 0.000 description 50
- 238000005516 engineering process Methods 0.000 description 10
- 239000000306 component Substances 0.000 description 7
- 238000011160 research Methods 0.000 description 7
- 230000008859 change Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000006731 degradation reaction Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000003518 caustics Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000010365 information processing Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000009545 invasion Effects 0.000 description 1
- 238000012886 linear function Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000009828 non-uniform distribution Methods 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000012800 visualization Methods 0.000 description 1
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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
- G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
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- 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; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
- G01N33/383—Concrete or cement
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Abstract
The present disclosure belongs to a technical field of monitoring of durability of concrete, and relates to an electrical capacitance tomography sensor calibration method. A process of the method includes five steps of preparation of concrete sample, equipment connection, preparation work, measurement of capacitance values and normalization. Two same ECT sensors are used to implement off—line calibration and on—line measurement; and the calibrated concrete samples are placed inside the ECT sensor for on—line calibration to visually monitor unsaturated moisture transmission inside the concrete samples. Compared with direct moisture calibration, the calibration of concrete samples with different saturation prepared through a blast drying oven, can more realistically simulate the moisture inside the concrete samples in a real environment; the calibration process is simple and fast, and can correct the normalized capacitance values in time, thereby improving the accuracy of ECT imaging, achieving accurate calibration of visual monitoring of unsaturated moisture transmission in a cement—based material, and overcoming the shortcoming that a conventional calibration method is not suitable for a monitoring process of liquid—solid two—phase flow of a cement—based material.
Description
P728/NLpd
TECHNICAL FIELD The present disclosure relates to a technical field of moni- toring of durability of concrete, in particular to an electrical capacitance tomography (ECT) sensor calibration method.
BACKGROUND The description of this part is merely intended to provide background information related to the present disclosure, and does not necessarily constitute the prior art.
At present, concrete structures have become one of the most widely used building structures in modern engineering construc- tion. However, the service lives of concrete structures cannot reach the designed service lives because the concrete structures will be affected by load and environment during an actual service process. There are many reasons for durability failure of con- crete, where existence and migration of moisture are important factors that cause degradation of concrete. On the one hand, mois- ture is a carrier for a corrosive substance to enter the concrete. On the other hand, moisture is also a necessary condition for an occurrence of a degradation reaction process. Therefore, it is of great significance to dynamically monitor and quantitatively ana- lyze a moisture transmission process based on a visualization technology.
ECT is a tomography technology based on a capacitance sensi- tive mechanism, which has advantages of no invasion, fast re- sponse, wide application range, low cost, no radiation, portabil- ity, etc. Therefore, it is widely applied to visual monitoring of gas-solid two-phase flow, gas-liquid two-phase flow, oil-water two-phase flow, liquid-solid two-phase flow and the like, and is the fastest growing and most mature tomography technology in pro- cess tomography. The ECT technology can be used to research the law of water transmission in a concrete structure, which accords with the research law of liguid-solid two-phase flow, and provides effective technical support for more objective and accurate evalu- ation of the durability of a concrete structure.
An ECT system consists of a capacitance sensor array, a data acquisition and information processing system and an imaging com- puter.
Even for an vacuum sensor, an inherent soft field charac- teristic of an ECT sensor causes extremely non-uniform distribu- tion of a sensitive field, which greatly affects the quality of image reconstruction; and the non-uniformity depends on structural parameters of a capacitance sensor, therefore, a design for the capacitance sensor array is one of the key and core technologies for the ECT system, and is an important precondition for realizing two-dimensional imaging of unsaturated moisture transmission in a cement-based material.
However, in a process of monitoring flowing of liquid-solid two-phase flow in moisture transmission in the concrete, the sys- tem acquires and processes a limited number of tiny capacitance values, which is very sensitive to measurement noise and interfer- ence.
In addition, image reconstruction, namely a solution process of an inverse problem, has the difficulties as follows: (1) under- determinedness due to a voltage measurement value being far lower than unknown variables of the equation; (2) the soft field charac- teristic caused by polarization of an dielectric medium in an electric field; and (3) ill-posedness caused by the insensitivity of a boundary measurement value to changes of a medium in a cen- tral area, which lead to a large error and low resolution in data acquisition and image reconstruction of the ECT system.
Thus in an image reconstruction process, the acquired capacitance data needs to be normalized to realize non-dimensionalization, so as to fa- cilitate calculations and reduce an influence of measurement er- rors.
Since concrete and water in a measured object field are dis- tributed in parallel, a normalized capacitarce value is obtained by using a parallel model: he Tbs ‚ where C, represents a measured capacitance value, C. represents an empty field capaci- tance value, Cr represents a full field capacitance value, and A represents a normalized capacitance value and has a linear rela- tionship with the measured capacitance value.
In the process of monitoring moisture transmission in the concrete by the ECT system, empty and full field capacitance val- ues, i.e. a maximum capacitance value and a minimum capacitance value acquired in an unsaturated moisture transmission process in a concrete component, need to be measured, to determine a func- tional relationship between medium distribution and a normalized capacitance value, and this process is considered as a calibration process of ECT imaging. Since different mix proportions and types of concrete components will lead to a change of mixed dielectric constant when the moisture enters, which causes a change of a nor- malized capacitance, and accordingly affects the accuracy of image reconstruction. Therefore, re-calibration is required when the concrete components are replaced with new ones.
A conventional calibration method includes the following steps: removing an ECT sensor, acquiring capacitance values under an empty tube state and a full tube state to obtain a maximum val- ue and a minimum value in a monitoring process to complete the calibration. Herein, it is assumed that a capacitance value be- tween the maximum value and the minimum value has a linear rela- tionship with a moisture content; however, in an actual measure- ment process, a relative dielectric constant (about 80) of water is much larger than a relative dielectric constant (6-8) of dry concrete, so that the relative dielectric constant will have a great change after mediums are mixed, and thus the calibration method in which a linear relationship is assumed will cause larger errors; and moreover, the ECT sensor needs to be removed and re- calibrated every time a new concrete component is monitored. Fur- thermore, the removal and installation of the ECT sensor will cause unnecessary errors and be time-consuming and labor- intensive. In recent 30 years, the ECT technology has developed rapidly, becomes one of the fastest growing tomography technolo- gies in a process tomography technology; and has made a variety of achievements in the fields such as pneumatic transmission, fluid- ized bed, petroleum and chemical industry. However, there are few related reports on the ECT technology in the field of cement-based materials, and there are also no patent documents about ECT sensor calibration methods in the field of the cement-based materials. Based on interdisciplinary researches, the ECT technology is applied to the field of the cement-based materials; an electrode sensor array for monitoring moisture transmission in the cement- based materials based on capacitance measurement is developed; a more accurate sensor calibration method is explored; advanced ECT sensors and calibration methods are used to give priority to a du- rability research of the cement-based materials in laboratories; the research is carried out from the aspects of moisture monitor- ing; crack monitoring, rebar position monitoring and harmful ion monitoring in the cement-based materials; in addition, with con- tinuous technological innovation and equipment improvement, it can be predicted that the advanced ECT sensors and calibration methods can be applied to real-time nondestructive monitoring of internal medium distribution in large concrete projects such as roads, bridges, subway tunnels and dams in the future, thereby knowing the dynamic distribution of the moisture in the concrete in time, and providing new research concepts and means for the research of the durability of concrete structures; and in this way, better evaluation of material transmission performances of concrete structures is achieved, and accurate prediction of structural du- rability is achieved as well.
SUMMARY The present disclosure intends to overcome the shortcomings of the conventional art and seeks to design an ECT sensor calibra- tion method, which provides a theoretical basis for accurately monitoring unsaturated moisture transmission in a concrete compo- nent and can calibrate a relationship between a moisture content and a capacitance response value in moisture transmission in the concrete component. In order to achieve the above effects, a specific process of the ECT sensor calibration method of the present disclosure in- cludes five steps of preparation of concrete sample, equipment connection, preparation work, measurement of capacitance value and normalization;
(1) preparation of concrete sample: preparing a concrete sam- ple with a cylindrical structure; removing a mold 24 hours after pouring; placing the concrete sample in a constant-temperature and constant-humidity standard curing room for 7 days; taking out the 5 concrete sample and symmetrically cutting off two ends of the con- crete sample to eliminate influences of the ends and rinse off; and forming a test sample by using the remaining middle 5 cm of the concrete sample; (2) equipment connection: taking one of two ECT sensors as an ECT sensor for off-line calibration connected with a digital elec- tric bridge, and another of the two ECT sensors is taken as an ECT sensor for on-line measurement connected with an imaging computer through a data acguisition box; (3) preparation work: drying the concrete sample in a blast drying oven at 105 °C to be constant in weight; taking out and weighing the concrete sample to record mass of the concrete sample as m,; placing the concrete sample in an intelligent vacuum con- crete water saturator to conduct water saturation for 22 hours to form a water-saturated sample with saturation of 100%; taking out and weighing the water-saturated sample to record mass of the wa- ter-saturated sample as m; and then fixedly placing the water- saturated sample inside the ECT sensor for off-line calibration; (4) measurement of capacitance values: sequentially measuring capacitance values between electrode pairs of the water-saturated sample according to an above measurement mode, wherein a number of N= £2 _ zis) the measured electrode pairs is > = ; after measure- ment is completed, removing the water-saturated sample and drying it in the blast drying oven at 105 °C; obtaining real-time mass m, of the sample by using a staged weighing method; calculating satu- ration of the sample by adopting a dynamic monitoring method ac- = By” Me x HK cording to a formula: a = Mg ; repeating above steps to sequentially prepare samples with saturation of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% and 10% respectively; saving capacitance values corresponding to saturation of the samples; and (5) normalization: deriving capacitance value data from the digital electric bridge; normalizing the capacitance values ac- cording to a capacitance normalization parallel model; taking an ECT sensor with a dry concrete sample as an empty tube which is normalized to be “0%; taking an ECT sensor with a water-saturated sample as a full tube which is normalized to be “1”; and determin- ing a functional relationship of a moisture content and a normal- ized capacitance value according to a total of 11 capacitance val- ues (one for every 10%) corresponding to the saturation 0-100% to complete calibration.
During calibration of the ECT sensor calibration method re- lated to the present disclosure, an electrode pair measurement mode is consistent with an on-line monitoring electrode pair meas- urement mode and comprises an excitation mode, a measurement mode and a grounding mode; in a process of monitoring unsaturated mois- ture transmission in the concrete sample on line, an accurate cor- respondence among the moisture content, the normalized capacitance value, a relative dielectric constant value and an image gray val- ue of the concrete sample is achieved.
The ECT sensor related to the present disclosure is an ECT sensor disclosed in Chinese Patent No. 201910904259.1 for monitor- ing moisture transmission in a concrete component.
Compared with the conventional art, according to the ECT sen- sor calibration method of the present disclosure, two same ECT sensors are used to implement off-line calibration and on-line measurement, and a digital electric bridge is used to implement the off-line calibration, and thus errors caused by under- determinedness, ill-posedness and soft field characteristics of image reconstruction in on-line calibration are avoided; a high speed and a high accuracy are achieved by conducting calibration using original data; and the calibrated concrete samples are placed in the ECT sensor for on-line calibration to visually moni- tor the unsaturated moisture transmission inside the concrete sam- ples, thereby saving complicated steps of removing and mounting the sensor in a conventional calibration method and avoiding er- rors caused by removing and mounting the sensor. Compared with di- rect moisture calibration, the calibration by preparing the con- crete samples with different saturation through a blast drying ov-
en can more realistically simulate the moisture in the concrete samples in a real environment, has a simple and fast calibration process, can correct the normalized capacitance values in time, and improves the accuracy of ECT imaging. The present disclosure optimizes a calibration method for an assumed linear function of a conventional sensor, more accurately reflects a functional rela- tionship between capacitance, a relative dielectric constant and the moisture by adopting a plurality of values during the process, achieves accurate calibration of visual monitoring of unsaturated moisture transmission in a cement-based material, overcomes the shortcoming that a conventional calibration method is not suitable for a monitoring process of liquid-solid two-phase flow of a ce- ment-based material, and provides a theoretical basis for visual monitoring of unsaturated moisture transmission in the cement- based material.
BRIEF DESCRIPTION OF THE DRAWINGS As a part of the present disclosure, accompanying drawings of the description provide further understanding of the present dis- closure. The schematic embodiments of the present disclosure and description thereof are intended to explain the present disclosure and are not intended to constitute an improper limitation to the present disclosure. FIG. 1 is a schematic diagram showing a connection of an ECT sensor for off-line calibration and a digital electric bridge in the step (2) of the present disclosure. FIG. 2 is a schematic diagram showing a connection of an ECT sensor for on-line measurement and an imaging computer in the step (2) of the present disclosure. FIG. 3 is a cycle diagram showing the operation of sequen- tially measuring samples with different saturation.
DETAILED DESCRIPTION OF THE EMBODIMENTS The present disclosure will be further described below through embodiments. Embodiment 1 A specific process of the ECT sensor calibration method re-
lated to this embodiment includes five steps, namely preparation of concrete sample, equipment connection, preparation work, meas-
urement of capacitance value and normalization as follows:
(1) preparation of concrete sample: a concrete sample with a cylindrical structure with a diameter of 15 cm and a height of 10 cm is prepared, a mold is removed 24 hours after pouring, and then the concrete sample is placed in a standard curing room with hu-
midity of 95% and temperature of 20+/-2°C for 7 days; then the concrete sample is taken out and two ends of the concrete sample are symmetrically cut off by 2.5 cm so as to eliminate influences of the ends and rinse off; and a remaining middle part of 5 cm of the concrete sample is made as a test sample;
(2) equipment connection: one of two ECT sensors, as an ECT sensor for off-line calibration, is connected with a digital elec-
tric bridge, where an excitation electrode is connected to an H terminal, a detection electrode is connected to an L terminal, and the rest electrodes and a housing are connected to a shielding port; a switch of the digital electric bridge is turned on and a parameter is adjusted to Cs-X (a parallel capacitor); a set meas-
urement voltage and a set measurement frequency are selected for heating for 30 minutes; a measurement circuit is corrected via a CAL key; and the digital electric bridge is connected with a com- puter via a USB interface so as to save data via a SAVE key after measurement is completed and upload the data to the computer for data integration.
Another of the two ECT sensors, as an ECT sensor for on-line measurement, is connected with an imaging computer through a data acquisition box, and monitors unsaturated moisture transmission in the concrete sample after the calibration of the concrete sample is completed;
(3) preparation work: the concrete sample is placed in a blast drying oven at 105 °C and dried to be constant in weight; the concrete sample is taken out and weighed to record mass there- of as my; subsequently the concrete sample is placed in an intelli- gent vacuum concrete water saturator; a set amount of deionized water is added, and water saturation is conducted for 22 hours to form a water-saturated sample with saturation of 100%; the water- saturated sample is taken out and surfaces of the water-saturated sample are wiped with a semi-dry cloth, and then the water- saturated sample is weighed to record the mass thereof as my; and subsequently the water-saturated sample is fixedly placed inside the ECT sensor for calibration;
(4) measurement of capacitance values: firstly, a capacitance value between No.l electrode and No.2 electrode is measured; the No.l electrode is taken as an excitation electrode; the No.2 elec- trode is taken as a measuring electrode; the rest electrodes are in a grounded mode; the capacitance values between No.l and No.3 electrodes, No.l and No.4 electrodes, ..., No.2 and No.3 elec- trodes, No.2 and No.4 electrodes, ... are sequentially measured until the capacitance values between all electrode pairs are meas- ured; the number of the measuring electrode pairs is N= 2 = Ht)
= ; after measurement is completed, the water-
saturated sample is removed and dried in the blast drying oven at 105 °C; real-time mass m, of the sample is obtained by using a staged weighing method; the saturation of the sample is calculated by adopting a dynamic monitoring method according to a formula:
& = Pe ig x 180% Wip Ty ; samples with saturation of 90%, 80%, 70%, 60%,
50%, 40%, 30%, 20% and 10% respectively are sequentially prepared according to the above steps; the capacitance values corresponding to saturation of the samples are saved; and
(5) normalization: capacitance value data are derived from the digital electric bridge; the capacitance values are normalized according to a capacitance normalization parallel model; an ECT sensor with a dry concrete sample is taken as an empty tube which is normalized to be “0”; an ECT sensor with a water-saturated sam- ple is taken as a full tube which is normalized to be “17; a func- tional relationship of a moisture content and a normalized capaci-
tance value is determined according to a total of 11 capacitance values (one for every 10%) corresponding to the saturation 0-100% to complete the calibration; and in a process of monitoring un- saturated moisture transmission in the concrete sample on line, an accurate correspondence among the moisture content, the normalized capacitance value, a relative dielectric constant value and an im-
age gray value of the concrete sample can be achieved.
The above description is merely a preferred embodiment of the present disclosure and is not intended to limit the present dis- closure, and various changes and modifications may be made by those skilled in the art. Any modifications, equivalent substitu- tions and improvements made within the spirit and principle of the present disclosure should fall within the scope of the present disclosure.
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| NL2029084A NL2029084B1 (en) | 2021-08-31 | 2021-08-31 | Electrical capacitance tomography sensor calibration method |
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| NL2029084B1 NL2029084B1 (en) | 2022-03-04 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115264407A (en) * | 2022-06-14 | 2022-11-01 | 昆明理工大学 | Intelligent pipeline imaging detector based on tomography measurement and detection method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115264407A (en) * | 2022-06-14 | 2022-11-01 | 昆明理工大学 | Intelligent pipeline imaging detector based on tomography measurement and detection method |
| CN115264407B (en) * | 2022-06-14 | 2024-05-14 | 昆明理工大学 | Pipeline intelligent imaging detector and detection method based on tomography measurement |
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