CN112378982A - On-line detection method and device for water content of wood - Google Patents
On-line detection method and device for water content of wood Download PDFInfo
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- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/048—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance for determining moisture content of the material
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Abstract
The invention provides an online detection method and device for wood moisture content. The online detection method for the water content of the wood comprises the following steps: connecting a sample to be detected to a probe of an electrochemical workstation to form a closed loop; measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured; based on the resistance of the sample to be detected, and according to a standard curve that the moisture content changes along with the resistance of the wood sample, obtaining the moisture content of the sample to be detected; the density of the sample to be measured is approximately the same as that of the wood sample. The online detection method for the moisture content of the wood can realize online detection of each moisture content stage of the wood in the drying process, and has high detection precision.
Description
Technical Field
The invention belongs to the technical field of wood processing, relates to an online detection method and device for the moisture content of wood, and particularly relates to an online detection method and device for the moisture content in the process of drying the wood.
Background
The moisture content of wood is one of the most important parameters to be measured quickly and accurately in the drying process, because the control and adjustment of the drying environment conditions are greatly dependent on the moisture content of wood. The detection of the moisture content of the wood is of great significance in wood processing and utilization, and 75% of quality problems in wood products are caused by inaccurate control of the moisture content of raw materials used in wood processing. The moisture content of wood seriously affects the physical mechanical properties and the machining performance of the wood.
Fiber Saturation Point (FSP) is the percentage of water in the wood that is saturated only by adsorbed water in the cell walls, but not by free water in the cell cavities and interstitial spaces. When the moisture content of the wood is larger than the fiber saturation point, the moisture content of the wood is indicated to be saturated by absorbed water and have a certain amount of free water. In this case, the wood is only changed by free water if it is dried or moistened, so that it does not cause drying shrinkage and swelling. When the moisture content of the wood is less than the fiber saturation point, the adsorbed water of the wood is unsaturated, and no free water exists. In this case, the wood is dried or moistened, which causes the drying shrinkage and swelling of the wood, and has an influence on the strength and volume of the wood.
The traditional method for detecting the water content of the wood mainly adopts a weighing method and a resistance method. The weighing method is one of the most accurate methods for the water content of the wood, has higher precision, but has slow testing speed, and cannot carry out continuous online testing. The resistance method can realize the on-line detection of the moisture content of the wood, but the detection precision is greatly influenced by the temperature, the tree species, the depth of the probe inserted into the wood, the position of the probe and the distance between the probes, so that the detection precision is certain below the fiber saturation point (for example, the moisture content is lower than 30 percent), and the detection of the high moisture content stage above the fiber saturation point is limited.
In addition, with the development of measurement methods, non-destructive methods such as X-ray densitometry, X-ray microscopy, computed tomography and nuclear magnetic resonance are used to determine the moisture content of wood. Although the above advanced measurement method has the characteristics of high measurement speed, high accuracy and imaging, there are some limitations such as high cost, complicated operation, and limitation of use environment in industrial production.
Citation 2 discloses a method for detecting moisture content of wood by using temperature compensation of a wood core, which comprises the following steps: firstly, 6 wood moisture content detection points are selected in a wood drying kiln, and each detection point is provided with a temperature sensor and a wood moisture content sensor; then, detecting the water content of the core of the board by two probes of the wood water content sensor at each detection point, and detecting the core temperature of the board by using a temperature sensor; and finally, respectively using the temperature of the material core detected by each temperature sensor for temperature compensation of the water content of the plate material at the corresponding detection point. However, the detection accuracy of this method is greatly affected by the tree species, the depth of the probe inserted into the wood, the probe position, and the probe pitch.
Cited documents:
cited document 1: CN102072922A
Cited document 2: CN103822946A
Disclosure of Invention
Problems to be solved by the invention
The invention aims to overcome the defects of the prior art and provide an online detection method for the moisture content of wood, which can effectively solve the problems of low detection precision and the like of the moisture content of wood at a high moisture content stage above a fiber saturation point.
Furthermore, the invention also provides an online detection device for the moisture content of the wood, and the device can realize online detection of the moisture content of the wood and has high detection precision.
Means for solving the problems
The invention relates to an online detection method for the moisture content of wood, which comprises the following steps:
connecting a sample to be detected to a probe of an electrochemical workstation to form a closed loop;
measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured;
based on the resistance of the sample to be detected, and according to a standard curve that the moisture content changes along with the resistance of the wood sample, obtaining the moisture content of the sample to be detected;
the density of the sample to be measured is approximately the same as that of the wood sample.
According to the online detection method for the water content of the wood, the position of the sample to be detected, which is connected with the probe, is coated with a conductive material.
The online detection method for the water content of the wood comprises the step of detecting the water content of the wood, wherein the conductive material comprises one or a combination of more than two of conductive metal paint, graphite conductive adhesive and carbon material conductive adhesive.
The online detection method for the water content of the wood is characterized in that the coating thickness of the conductive material is 0.05-0.15 mm.
The online detection method for the water content of the wood is characterized in that the potential setting range of the electrochemical workstation is-10V; the current setting range of the electrochemical workstation is-250 mA; the lower limit of the battery measurement of the electrochemical workstation is below 50 pA.
The method for detecting the water content of the wood on line comprises the step of measuring the current of the closed loop by utilizing a linear sweep voltammetry method.
According to the online detection method for the water content of the wood, disclosed by the invention, when the current of the closed loop is measured, the electrochemical workstation adopts a current-time curve for testing, and the parameters are set as follows: the potential is 0.5-1.5V, the sampling interval is 0.01-1 s, and the total sampling time is 200-300 s.
The method for detecting the water content of the wood on line comprises the following steps:
drying the wood sample at the same temperature, and measuring the water content of the wood sample corresponding to different drying times by adopting a weighing method;
measuring the current of the wood samples corresponding to different drying times by adopting the electrochemical workstation, and obtaining the resistance of the wood samples corresponding to different drying times;
and obtaining the standard curve according to the moisture content and the resistance of the wood sample corresponding to the different drying times.
The online detection method for the water content of the wood is characterized in that the drying temperature is 10-120 ℃.
The invention also provides an on-line detection device for the moisture content of the wood for implementing the on-line detection method, which comprises an electrochemical workstation and a data acquisition device which are connected; wherein, the electrochemical workstation is connected with a probe by a lead.
ADVANTAGEOUS EFFECTS OF INVENTION
The online detection method for the moisture content of the wood can realize online detection of each moisture content stage of the wood in the drying process, and has high detection precision.
The online detection device for the moisture content of the wood has the advantages of simple connection operation, convenient use and high detection precision.
Drawings
FIG. 1 shows a schematic diagram of an on-line moisture content detection apparatus of the present invention;
wherein, 1 is an electrochemical workstation; 2 is a data acquisition device; 3 is a lead;
4 is a probe; and 5 is a sample to be detected.
FIG. 2 shows the current (a) and resistance (b) at an initial potential of 1V for measuring the change in moisture content of wood with time according to example 1 of the present invention;
fig. 3 shows a fitted curve of the moisture content of wood and the resistance of example 1 of the present invention.
Detailed Description
The present invention will be described in detail below. The technical features described below are explained based on typical embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:
in the present specification, the numerical range represented by "numerical value a to numerical value B" means a range including the end point numerical value A, B.
In the present specification, "plural" in "plural", and the like means a numerical value of 2 or more unless otherwise specified.
In this specification, the terms "substantially", "substantially" or "substantially" mean an error of 5% or less, or 3% or less or 1% or less, compared to the relevant perfect or theoretical standard.
In the present specification, "%" denotes mass% unless otherwise specified.
In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.
In the present specification, when "normal temperature" or "room temperature" is used, the temperature may be 10 to 40 ℃.
In the present specification, the "water" used may be tap water, distilled water, deionized water, ion-exchanged water, high purity water, purified water, or the like, which is available in the art, unless otherwise specified.
In this specification, "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
In the present specification, reference to "some particular/preferred embodiments," "other particular/preferred embodiments," "embodiments," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.
First aspect
The invention provides an online detection method for the moisture content of wood, which comprises the following steps:
connecting a sample to be detected to a probe of an electrochemical workstation to form a closed loop;
measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured;
based on the resistance of the sample to be detected, and according to a standard curve that the moisture content changes along with the resistance of the wood sample, obtaining the moisture content of the sample to be detected;
the density of the sample to be measured is approximately the same as that of the wood sample.
According to the invention, the relationship between the resistance and the moisture content of the wood is established according to the fact that the resistance of the wood is continuously changed along with the difference of the moisture content, so that the moisture content change in the drying process of the wood is obtained according to the change of an electric signal. The online detection method for the moisture content of the wood can realize online detection of each moisture content stage of the wood in the drying process, and has high detection precision.
Sample to be tested
The sample to be tested can be any available wood, such as eucalyptus, oak, acacia melanoxylon, pinus radiata and the like. In general, in the test, wood needs to be subjected to pretreatment such as sawing. Specifically, wood is sawn into feasible sizes for testing as samples to be tested. The size of the sample to be measured is not particularly limited in the present invention, and may be, for example, a chordal cutting plate of 10 to 150mm (chordal direction) × 10 to 150mm (radial direction) × 10 to 1000mm (longitudinal direction), and the sawn test material has no visible defects as much as possible.
In some specific embodiments, the sample to be tested is coated with a conductive material at the position where the probe is connected. The conductive material acts as a conductive contact to enhance the conductivity between the wood and the electrode.
Further, the conductive material of the present invention is not particularly limited, and may be some conductive materials that can be coated, which are commonly used in the art, such as: the conductive material comprises one or the combination of more than two of conductive metallic paint, graphite conductive adhesive and carbon material conductive adhesive. For electrically conductive metallic lacquers, for example: can be conductive silver paint, conductive copper paint, etc.
The present invention is not particularly limited as to the thickness of the coating, as long as the application is uniform. Specifically, in the present invention, the coating thickness of the conductive material is 0.05mm to 0.15 mm.
Further, the application position and the application range are not particularly limited in the present invention as long as the connecting position of the probe and the sample to be measured has a conductive material.
Electrochemical workstation
The electrochemical method is a simple, convenient, rapid, accurate and sensitive characterization method, and plays an important role in scientific research and production all the time. The method is mainly characterized in that the relation between the electric parameters and the measured substances is established according to the electrochemical properties and the change rule of the substances in the solution, and then the qualitative and quantitative analysis is carried out on the components. The invention utilizes the electrochemical workstation to establish the relationship between the electrical parameters and the measured substances, thereby measuring the water content of the sample to be measured.
Specifically, the electrochemical workstation of the invention comprises a rapid digital signal generator, a direct digital signal synthesizer for high-frequency alternating-current impedance measurement, a dual-channel high-speed data acquisition system, a potential current signal filter, a multi-stage signal gain, an iR drop compensation circuit, a double potentiostat and a galvanostat. Specifically, the potential range is-10V to 10V. The current range is-250 mA, the potential resolution is 0.1mV, the lower limit of the current measurement is lower than 50pA, and the sensitivity is 1e-6A/V is higher than the others.
The external part of the electrochemical workstation is connected with a lead, and the end part of the lead is provided with a probe. And connecting the sample to be detected to a probe of the electrochemical workstation to form a closed loop, and then carrying out determination. Specifically, the current of the closed loop is measured by the electrochemical workstation, so that the resistance of the sample to be measured can be obtained.
In the present invention, the current of the closed loop is measured by linear sweep voltammetry. Linear sweep voltammetry is a method in which a linearly varying voltage is applied to an electrode, i.e., the electrode potential is a method in which the electrolytic current on the working electrode is recorded as the voltage applied changes. The invention can accurately measure the current of the closed loop by utilizing the linear sweep voltammetry, thereby obtaining the resistance of the sample to be measured.
The present invention is not particularly limited as long as an accurate test result can be obtained, with respect to specific test conditions. Specifically, in the present invention, when measuring the current of the closed loop, the electrochemical workstation performs a test using a current-time curve whose parameters are set as: the constant potential is 0.5-1.5V, the sampling interval is 0.01-1 s, and the total sampling time is 200-300 s.
Standard curve
The water content of the sample to be detected is obtained according to the standard curve of the water content along with the resistance change of the wood sample based on the resistance of the sample to be detected. For a wood sample, the density of the wood sample is about the same as that of a sample to be detected, and then more accurate moisture content can be obtained.
In the invention, the moisture content of the wood sample corresponding to different drying times can be measured by using a weighing method, so as to obtain a standard curve. Specifically, the method for manufacturing the standard curve comprises the following steps:
drying the wood sample at the same temperature, and measuring the water content of the wood sample corresponding to different drying times by adopting a weighing method;
measuring the current of the wood samples corresponding to different drying times by adopting the electrochemical workstation, and obtaining the resistance of the wood samples corresponding to different drying times;
and obtaining the standard curve according to the moisture content and the resistance of the wood sample corresponding to the different drying times.
In the present invention, the standard curve is a relationship curve between the resistance and the moisture content obtained by using the moisture content of the wood sample corresponding to different drying times and the resistance of the wood sample corresponding to different drying times, wherein the same temperature means that the drying temperature is almost unchanged in the whole drying process.
For the weighing method, the wood sample can be placed in a drying oven for drying, then the weight of the wood sample corresponding to different drying time is obtained, and the moisture content of the wood sample corresponding to different drying time is calculated through the weighing method. In general, the wood sample used at this time is preferably subjected to a weighing test on the same wood sample.
Specifically, the calculation formula of the different drying times of the weighing method corresponding to the water content of the wood sample is as follows:
wherein: MC is the water content of the wood sample;
m is the weight of the wood sample corresponding to different drying times;
M0is the oven dried weight of the wood sample.
The oven-dry weight of the wood sample can be determined by placing the sample in a drying oven at 100-105 ℃, drying for more than 6 hours, then weighing and recording every 2 hours, and determining that the oven-dry weight is reached when the difference between the two weighed masses is less than 0.02 g. The weight of the wood sample at this time is the oven dry weight of the wood sample.
Meanwhile, after the moisture content of the wood sample is measured by adopting a weighing method every time, the resistance of the wood sample at the moment is measured by adopting an electrochemical workstation, so that a relation curve between different resistances and different moisture contents is obtained, and the relation curve is a standard curve. The method for measuring the resistance of the wood sample by using the electrochemical workstation is the same as or similar to the sample to be measured.
Further, as for the temperature of drying, the present invention is not particularly limited, and may be a temperature conventional in the art, for example: 10 to 120 ℃. The drying time can be set as required, for example: the interval between the two weighing times can be 10 min-360 min.
Second aspect of the invention
The second aspect of the invention provides a device for realizing the online detection method of the moisture content of the wood of the first aspect of the invention, which comprises an electrochemical workstation 1 and a data acquisition device 2 which are connected; wherein, a probe 4 is connected on the electrochemical workstation 1 by a lead 3.
The electrochemical workstation 1 of the present invention is the main body site of the signal acquisition and processing analysis. According to the invention, the data and the image measured by the electrochemical workstation 1 can be displayed on the data acquisition device 2, the resistance value is further obtained through the data acquisition device 2, and then the water content of the sample 5 to be measured can be obtained according to the standard curve. In the present invention, the probe 4 may be an alligator clip, and the probe 4 and the lead 3 are used for realizing the connection of the circuit.
Examples
Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Examples wood moisture content was measured using a CHI760E electrochemical workstation test system (shanghai chenhua instruments ltd). Wherein the potential range is-10V, the potential resolution is 0.1mV, the current range is-250 mA, and the lower limit of the current measurement is lower than 50 pA. The computer is used for data acquisition, storage and processing. The test equipment is shown in fig. 1.
Example 1
Preparation of Standard Curve
The test material was Eucalyptus (Eucalyptus exserta) collected from Gao Zhou city, Guangdong province, China. A slit board without visible defects having dimensions of 120 mm (chord wise) x 25 mm (radial) x 900 mm (longitudinal) was sawn from a eucalyptus log having an initial moisture content of 42%.
Wood samples having dimensions of 120 mm (chordwise) x 25 mm (radial) x 10mm (longitudinal) were sawn from the above string-cut panels for resistance and moisture content measurements, and standard curves were made.
First, an initial weight of a wood sample is obtained, and the wood sample is subjected to an electrochemical test. Thereafter, the wood samples were dried in a model DKN611 drying cabinet (japan major and scientific) at a constant temperature of 60 ℃ to obtain different water contents. The wood samples were taken out of the drying oven at 30 minutes, 60 minutes, 90 minutes, 120 minutes, 180 minutes and 240 minutes, respectively, and after the wood samples were weighed, the wood samples were electrochemically tested, respectively, to obtain the current for each test, and the specific test results are shown in table 1 below. And drying the wood sample after all tests are finished, and obtaining the oven-dried weight of the wood sample. The method specifically comprises the steps of putting a wood sample into an oven at 103 +/-2 ℃, drying for more than 6 hours, weighing every 2 hours and recording in table 1, and when the mass difference between the two times of weighing is less than 0.02g, determining that the wood sample is absolutely dry, so that the absolute dry weight of the wood sample is 27.9 g.
Wherein: the electrochemical test is as follows: the current and the resistance are measured by an electrochemical workstation, and the parameters of the electrochemical workstation are set as follows: the potential is constant at 1V, the sampling interval is 0.1s, the running time is 240s, and the sensitivity is 0.01A/V. Before testing, the wood samples were sprayed with a conductive silver paint as a conductive coating at both ends, with a thickness of 0.1 mm.
TABLE 1
Then, the water contents of the wood samples corresponding to different drying times were obtained according to the following calculation formula, and the results are shown in table 2 below:
wherein: MC is the water content of the wood sample corresponding to different drying time;
m is the weight of the wood sample corresponding to different drying times;
M0is the oven dried weight of the wood sample.
The resistance of the wood samples for different drying times was obtained according to the following calculation formula, and the results are shown in table 2 below:
R′＝U/I
wherein R' is the resistance of the wood sample corresponding to different drying times;
u is a constant voltage;
i is the current for the wood samples at different drying times.
TABLE 2
Then, a standard curve between the moisture content and the resistance is obtained according to the moisture content and the resistance in table 2, specifically as shown in fig. 3, and the formula of the standard curve is shown in the following formula (a).
MC＝47.59-1.17R+0.013R2-4.8×10-5R3 (A)
In the formula (A): MC is the water content of the wood sample;
r is 10 of the resistance (R') of the wood sample-6And (4) doubling.
Detection of sample to be tested
The sample to be tested was Eucalyptus (Eucalyptus exserta) collected from Gaozhou, Guangdong province in China, and the sample used in the standard curve was taken from a different tree strain. A slit board without visible defects having dimensions of 120 mm (chord wise) x 25 mm (radial) x 900 mm (longitudinal) was sawn from eucalyptus logs with an initial moisture content of 45%.
Samples to be measured having dimensions of 120 mm (chord direction) × 25 mm (radial direction) × 10mm (longitudinal direction) were sawn from the above chord-cut plate for resistance measurement.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: the initial potential was 1V, the sampling interval was 0.1s, the run time was 240s, and the sensitivity was 0.01A/V. Before testing, conductive silver paint is sprayed on two ends of a sample to be tested to serve as a conductive coating, and the thickness of the coating is 0.1 mm.
The sample to be tested was dried in DKN611 type drying oven (japan major and scientific company) at a constant temperature of 60 ℃, taken out of the drying oven at 60 minutes, 120 minutes and 180 minutes, weighed and electrochemically tested, respectively, to obtain the current for each test, and the corresponding resistance was calculated, with the specific test results shown in table 3 below.
And drying the sample to be tested after all tests are finished, and obtaining the absolute dry weight of the sample to be tested. The method specifically comprises the steps of putting a sample to be detected in an oven at 103 +/-2 ℃, drying for more than 6 hours, weighing every 2 hours and recording in table 3, and when the mass difference between the two times of weighing is less than 0.02g, determining that the sample reaches absolute dryness, so that the absolute dryness weight of the sample to be detected is 27.96g, and using the absolute dryness weight to calculate the water content by a weighing method.
TABLE 3
And substituting the resistance value into the standard curve to obtain the water content of the sample to be detected, wherein the specific result is shown in the following table 4. In addition, the inventors measured the water content of the sample to be measured by a weighing method, and the results are shown in table 4 below.
TABLE 4
As can be seen from Table 4, the water content of the sample to be measured in the drying process measured by the method of the present invention is substantially the same as the water content measured by the weighing method. Therefore, the online detection method for the water content of the wood can realize online detection of each water content stage of the wood in the drying process, and has high detection precision.
Example 2
The test sample in example 1 was replaced with Eucalyptus (Eucalyptus exserta) of high city, Guangdong province, China, but the test samples used for the standard curve were taken from different tree plants and were different from the Eucalyptus in example 1. A slit board without visible defects having dimensions of 120 mm (chord wise) x 25 mm (radial) x 900 mm (longitudinal) was sawn from eucalyptus logs with an initial moisture content of 45%.
Samples to be measured having dimensions of 120 mm (chord direction) × 25 mm (radial direction) × 10mm (longitudinal direction) were sawn from the above chord-cut plate for resistance measurement.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: the initial potential was 1V, the sampling interval was 0.1s, the run time was 240s, and the sensitivity was 0.01A/V. Before testing, conductive silver paint is sprayed on two ends of a sample to be tested to serve as a conductive coating, and the thickness of the coating is 0.1 mm.
The sample to be tested was dried in DKN611 type drying oven (japan major and scientific company) at a constant temperature of 60 ℃, taken out of the drying oven at 60 minutes, 120 minutes and 180 minutes, weighed and electrochemically tested, respectively, to obtain the current for each test, and the corresponding resistance was calculated, with the specific test results shown in table 5 below.
And drying the sample to be tested after all tests are finished, and obtaining the absolute dry weight of the sample to be tested. The method specifically comprises the steps of putting a sample to be detected in an oven at 103 +/-2 ℃, drying for more than 6 hours, weighing every 2 hours and recording in table 5, and when the mass difference between the two times of weighing is less than 0.02g, determining that the sample reaches the absolute dry state, so that the absolute dry weight of the sample to be detected is 22.43g, and using the absolute dry weight to calculate the water content by a weighing method.
TABLE 5
And substituting the resistance value into the standard curve to obtain the water content of the sample to be detected, wherein the specific result is shown in the following table 6.
TABLE 6
As can be seen from Table 6, the water content of the sample to be measured in the drying process measured by the method of the present invention is substantially the same as the water content measured by the weighing method. Therefore, the online detection method for the water content of the wood can realize online detection of each water content stage of the wood in the drying process, and has high detection precision.
Example 3
Preparation of Standard Curve
The cork oak wood is collected from the ecological protection center of Tan Jiahe in the Nanwan forest farm of Xinyang city in Henan province, the altitude of the sampling place is 200m, the east longitude is 113 degrees and 55 degrees, and the north latitude is 31 degrees and 52 degrees. The tree ages are all 60 years, and the average breast diameter of the cork oak is 38 cm. The sample was sawed into several pieces of 900 mm (length) x 120 mm (width) x 25 mm (thickness), and the initial water content of the sample was 50%. A piece of chord cutting plate without visible defects is selected and sawn into a wood sample with the size of 120 mm (chord direction) multiplied by 25 mm (radial direction) multiplied by 10mm (longitudinal direction) for resistance and moisture content measurement, and then a standard curve is manufactured.
First, an initial weight of a wood sample is obtained, and the wood sample is subjected to an electrochemical test. Thereafter, the wood samples were dried in a model DKN611 drying cabinet (japan major and scientific) at a constant temperature of 60 ℃ to obtain different water contents. The wood samples were taken out of the drying oven at 30 minutes, 60 minutes, 90 minutes, 120 minutes, 180 minutes and 240 minutes, respectively, and after the wood samples were weighed, the wood samples were electrochemically tested, respectively, to obtain the current for each test, and the specific test results are shown in table 7 below.
And drying the wood sample after all tests are finished, and obtaining the oven-dried weight of the wood sample. The method specifically comprises the steps of putting a wood sample into an oven at 103 +/-2 ℃, drying for more than 6 hours, weighing every 2 hours and recording in table 7, and when the mass difference between the two times of weighing is less than 0.02g, determining that the wood sample is absolutely dry, so that the absolute dry weight of the wood sample is 30.92 g.
Wherein: the electrochemical test is as follows: the current and the resistance are measured by an electrochemical workstation, and the parameters of the electrochemical workstation are set as follows: the potential is constant at 1V, the sampling interval is 0.1s, the running time is 240s, and the sensitivity is 0.01A/V. Before testing, the wood samples were sprayed with a conductive silver paint as a conductive coating at both ends, with a thickness of 0.1 mm.
TABLE 7
Then, the water contents of the wood samples corresponding to different drying times were obtained according to the following calculation formula, and the results are shown in table 8 below:
wherein: MC is the water content of the wood sample corresponding to different drying time;
m is the weight of the wood sample corresponding to different drying times;
M0is the oven dried weight of the wood sample.
The resistance of the wood samples for different drying times was obtained according to the following calculation formula, and the results are shown in table 8 below:
R′＝U/I
wherein R is the resistance of the wood sample corresponding to different drying times;
u is a constant voltage;
i is the current for the wood samples at different drying times.
TABLE 8
Then, a standard curve between the moisture content and the resistance was obtained according to the moisture content and the resistance in table 8, which is specifically shown in the following formula.
MC＝51.84-1.49R+0.02R2-9.0×10-5R3 (A)
In the formula (A):
MC is the water content of the wood sample;
r is 10 of the resistance (R') of the wood sample-6And (4) doubling.
Detection of sample to be tested
The sample to be tested is collected from the ecological protection center of Tan domestic river in the forest farm of southern Bay in Xinyang city of Henan province, the altitude of the sampling site is 200m, the east longitude is 113 degrees and 55 degrees, and the north latitude is 31 degrees and 52 degrees. The tree ages are all 60 years, and the average breast diameter of the cork oak is 38 cm. Samples used for comparison to the standard curve were taken from different trees. The sample was sawed into several pieces of 900 mm (length) x 120 mm (width) x 25 mm (thickness), and the initial water content of the sample was 50%.
Samples to be measured having dimensions of 120 mm (chord direction) × 25 mm (radial direction) × 10mm (longitudinal direction) were sawn from the above chord-cut plate for resistance measurement.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: the initial potential was 1V, the sampling interval was 0.1s, the run time was 240s, and the sensitivity was 0.01A/V. Before testing, conductive silver paint is sprayed on two ends of a sample to be tested to serve as a conductive coating, and the thickness of the coating is 0.1 mm.
The samples to be tested were dried in DKN611 type drying oven (japan big and scientific company) at a constant temperature of 60 ℃, taken out of the drying oven at 60 minutes, 120 minutes and 180 minutes, weighed and electrochemically tested for each sample to be tested, to obtain the current for each test, and the corresponding resistance was calculated, and the specific test results are shown in table 9 below.
And drying the sample to be tested after all tests are finished, and obtaining the absolute dry weight of the sample to be tested. The method specifically comprises the steps of putting a sample to be detected in an oven at 103 +/-2 ℃, drying for more than 6 hours, weighing every 2 hours and recording in a table 9, and when the mass difference between the two times of weighing is less than 0.02g, determining that the sample reaches the absolute dry state, so that the absolute dry weight of the sample to be detected is 30.43g, and the absolute dry weight is used for calculating the water content by a weighing method.
TABLE 9
The water content of the sample to be tested can be obtained by substituting the resistance value into the standard curve, and the specific results are shown in the following table 10.
Watch 10
As can be seen from Table 10, the water content of the sample to be measured in the drying process measured by the method of the present invention is substantially the same as the water content measured by the weighing method. Therefore, the online detection method for the water content of the wood can realize online detection of each water content stage of the wood in the drying process, and has high detection precision.
Example 4
Preparation of Standard Curve
The test wood is black wood Acacia wood (Acacia melanoxylon) collected from a estuary forest farm in Shaoshaguan City of Guangdong province in China. A cord cut board without visible defects having dimensions of 120 mm (chord wise) x 25 mm (radial) x 900 mm (longitudinal) was sawn from one log, which had an initial moisture content of 42%.
Wood samples having dimensions of 120 mm (chordwise) x 25 mm (radial) x 8 mm (longitudinal) were sawn from the above string-cut panels for resistance and moisture content measurements, and standard curves were made.
First, an initial weight of a wood sample is obtained, and the wood sample is subjected to an electrochemical test. Thereafter, the wood samples were dried in a model DKN611 drying cabinet (japan major and scientific) at a constant temperature of 60 ℃ to obtain different water contents. The wood samples were taken out of the drying oven at 30 minutes, 60 minutes, 90 minutes, 120 minutes and 180 minutes, respectively, and after the wood samples were weighed, the wood samples were electrochemically tested, respectively, to obtain the current for each test, and the specific test results are shown in table 11 below.
And drying the wood sample after all tests are finished, and obtaining the oven-dried weight of the wood sample. The method specifically comprises the steps of putting a wood sample into an oven at 103 +/-2 ℃, drying for more than 6 hours, weighing every 2 hours and recording in a table 11, and when the mass difference between the two times of weighing is less than 0.02g, determining that the wood sample is absolutely dry, so that the absolute dry weight of the wood sample is 22.48 g.
Wherein: the electrochemical test is as follows: the current and the resistance are measured by an electrochemical workstation, and the parameters of the electrochemical workstation are set as follows: the potential is constant at 1V, the sampling interval is 0.1s, the running time is 240s, and the sensitivity is 0.01A/V. Before testing, the wood samples were sprayed with a conductive silver paint as a conductive coating at both ends, with a thickness of 0.1 mm.
TABLE 11
Then, the water contents of the wood samples corresponding to different drying times were obtained according to the following calculation formula, and the results are shown in table 12 below:
wherein: MC is the water content of the wood sample corresponding to different drying time;
m is the weight of the wood sample corresponding to different drying times;
M0is the oven dried weight of the wood sample.
The resistance of the wood samples for different drying times was obtained according to the following calculation formula, and the results are shown in table 12 below:
R′＝U/I
wherein R' is the resistance of the wood sample corresponding to different drying times;
u is a constant voltage;
i is the current for the wood samples at different drying times.
TABLE 12
Then, a standard curve between the moisture content and the resistance was obtained according to the moisture content and the resistance in table 12, which is specifically shown in the following formula.
MC＝49.48-1.1R+0.01R2-3.0×10-5R3 (A)
In the formula (A):
MC is the water content of the wood sample;
r is 10 of the resistance (R') of the wood sample-6And (4) doubling.
Detection of sample to be tested
The sample to be tested is black wood Acacia wood (Acacia melanoxylon) which is collected from China forest at the mouth of China, Guangdong province, Shaoyuan city, and the sample used in the standard curve is taken from different trees. The cut chordal boards without visible defects were sawn from the logs to dimensions 120 mm (chordal) x 25 mm (radial) x 900 mm (longitudinal) with an initial moisture content of 45%.
Samples to be measured having dimensions of 120 mm (chord direction) × 25 mm (radial direction) × 10mm (longitudinal direction) were sawn from the above chord-cut plate for resistance measurement.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: the initial potential was 1V, the sampling interval was 0.1s, the run time was 240s, and the sensitivity was 0.01A/V. Before testing, conductive silver paint is sprayed on two ends of a sample to be tested to serve as a conductive coating, and the thickness of the coating is 0.1 mm.
The sample to be tested was dried in DKN611 type drying oven (japan major and scientific company) at a constant temperature of 60 ℃, taken out of the drying oven at 60 minutes, 120 minutes and 180 minutes, weighed and electrochemically tested, respectively, to obtain the current for each test, and the corresponding resistance was calculated, and the specific test results are shown in table 13 below.
And drying the sample to be tested after all tests are finished, and obtaining the absolute dry weight of the sample to be tested. The method specifically comprises the steps of putting a sample to be detected in an oven at 103 +/-2 ℃, drying for more than 6 hours, weighing every 2 hours, recording, and determining that the sample reaches the oven dryness when the mass difference between the two times of weighing is less than 0.02g, so that the oven dryness weight of the sample to be detected is 22.43g, and the sample to be detected is used for calculating the water content by a weighing method.
Watch 13
The water content of the sample to be tested can be obtained by substituting the resistance value into the standard curve, and the specific results are shown in the following table 14.
TABLE 14
As can be seen from Table 14, the water content of the sample to be measured in the drying process measured by the method of the present invention was substantially the same as the water content measured by the weighing method. Therefore, the online detection method for the water content of the wood can realize online detection of each water content stage of the wood in the drying process, and has high detection precision.
Comparative example 1
The test material is a cross-cut tree disc of 22-year-old white birch taken from forest area of lesser Khingan of Heilongzhou province, the average diameter is 23cm, the thickness is 30mm, the initial water content is more than 60%, the material is uniform, and no visible defects exist.
The method comprises the steps of testing the moisture content of a test material by using a HYD-B type wood moisture content detector, and using 220V and 50HZ alternating-current voltage of a power supply at the use temperature of 10-60 ℃. During testing, wood is drilled, probes are inserted into the wood, the distances among the probes are respectively set to be 20mm, 30mm and 40mm, and the depths of the probes are respectively set to be 10mm, 15mm and 20 mm. The CFBLS tension-compression type resistance strain type pressure sensor is adopted for online weighing, the measuring range is 0-5 kg, the output sensitivity is 1.995mV/V, the using environment temperature is-20 ℃ to +60 ℃, and the excitation voltage is 10 VDC; the GDS-100 constant temperature and humidity drying box is adopted for drying test, and test data of different stages are obtained. The test results are shown in table 15.
Watch 15
As can be seen from table 15, the result accuracy of detecting the sample by using the HYD-B type wood moisture content detector is poor, and the online detection of the wood moisture content cannot be satisfied.
It should be noted that, although the technical solutions of the present invention are described by specific examples, those skilled in the art can understand that the present invention should not be limited thereto.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
Claims (10)
1. The method for detecting the water content of the wood on line is characterized by comprising the following steps of:
connecting a sample to be detected to a probe of an electrochemical workstation to form a closed loop;
measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured;
based on the resistance of the sample to be detected, and according to a standard curve that the moisture content changes along with the resistance of the wood sample, obtaining the moisture content of the sample to be detected;
the density of the sample to be measured is approximately the same as that of the wood sample.
2. The method for on-line detection of the moisture content of the wood according to claim 1, wherein a position of the sample to be detected, which is connected with the probe, is coated with a conductive material.
3. The method for on-line detection of the moisture content of the wood according to claim 2, wherein the conductive material comprises one or a combination of more than two of conductive metal paint, graphite conductive adhesive and carbon material conductive adhesive.
4. The online detection method of the moisture content of the wood according to claim 2 or 3, characterized in that the coating thickness of the conductive material is 0.05mm to 0.15 mm.
5. The method for detecting the water content of the wood according to any one of claims 1 to 4, wherein the potential setting range of the electrochemical workstation is-10V to 10V; the current setting range of the electrochemical workstation is-250 mA; the lower limit of the battery measurement of the electrochemical workstation is below 50 pA.
6. The method for detecting the water content of the wood according to claim 5, wherein the closed loop current is measured by using a linear sweep voltammetry method.
7. The method for detecting the moisture content of the wood according to claim 6, wherein when the current of the closed loop is measured, the electrochemical workstation adopts a current-time curve for testing, and the parameters are set as follows: the potential is 0.5-1.5V, the sampling interval is 0.01-1 s, and the total sampling time is 200-300 s.
8. The method for detecting the water content of the wood according to any one of claims 1 to 7, wherein the method for making the standard curve comprises the following steps:
drying the wood sample at the same temperature, and measuring the water content of the wood sample corresponding to different drying times by adopting a weighing method;
measuring the current of the wood samples corresponding to different drying times by adopting the electrochemical workstation, and obtaining the resistance of the wood samples corresponding to different drying times;
and obtaining the standard curve according to the moisture content and the resistance of the wood sample corresponding to the different drying times.
9. The method for detecting the water content of the wood according to claim 8, wherein the drying temperature is 10-120 ℃.
10. An on-line detection device for the moisture content of wood for implementing the on-line detection method of any one of claims 1 to 9, which is characterized by comprising an electrochemical workstation and a data acquisition device which are connected; wherein, the electrochemical workstation is connected with a probe by a lead.
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