US3354388A - Method for measuring the moisture content of wood - Google Patents

Method for measuring the moisture content of wood Download PDF

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Publication number
US3354388A
US3354388A US248573A US24857362A US3354388A US 3354388 A US3354388 A US 3354388A US 248573 A US248573 A US 248573A US 24857362 A US24857362 A US 24857362A US 3354388 A US3354388 A US 3354388A
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US
United States
Prior art keywords
wood
electrodes
moisture
moisture content
capacitance
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US248573A
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English (en)
Inventor
William D Perry
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Weyerhaeuser Co
Original Assignee
Weyerhaeuser Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to NL302310D priority Critical patent/NL302310A/xx
Application filed by Weyerhaeuser Co filed Critical Weyerhaeuser Co
Priority to US248573A priority patent/US3354388A/en
Priority to GB49587/63A priority patent/GB1069100A/en
Priority to JP6791663A priority patent/JPS4630278B1/ja
Priority to SE14469/63A priority patent/SE302535B/xx
Priority to CH1597163A priority patent/CH417160A/de
Priority to FR959048A priority patent/FR1393329A/fr
Application granted granted Critical
Publication of US3354388A publication Critical patent/US3354388A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • G01N27/223—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/048—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

Definitions

  • This invention relates to a moisture detector for wood. Specifically, this invention relates to a capacitance-type moisture detector that rapidly measures the water concentration in wood employing a pair of electrodes that are not'in physical contact with the wood.
  • moisture detecting meters One type is the resistance meters which consist of probes driven into wood and a suitable readout electrical circuit. These meters are slow, not suitable for high speed scanning and leaves holes in the wood.
  • Another type is the power loss meters that consist of electrodes which contact the wood surface setting up an electrical field in the wood and a suitable readout electrical circuit therefor. These meters are sensitive to the degree of contact with the wood surface and to the wood thickness. Accordingly, greater thickness in the wood results in decreased accuracy.
  • Capacitance-type moisture meters have been devel oped that consist of two electrodes either in contact with or at a fixed distance to the wood. These meters are supposed to measure the increase in capacitance due to the presence of a dielectric other than air adjacent to the electrodes.
  • wood has a dielectric constant of about 2, water 80 and air 1. Consequently, the gauges or meters are dependent on wood density and thickness as Well as moisture content. They are also quite sensitive to the distance between the wood surface and the electrodes, which means that a wet pocket in the middle of a thick wood sample may not be detected. Accuracy is in doubt if the electrode-to-wood distance varies as is the case with rough sawn lumber.
  • An object of this invention is to provide a capacitancetype moisture detector that accurately determines the water content in wood regardless of the shape or size of the wood.
  • Another object of this invention is to provide a capacitance-type moisture detector that accurately determines the water content of Wood regardless of its distribution within the Wood.
  • Another object of this invention is to provide a capaci tance-type moisture detector that is provided with a pair of elecrodes that do not physically contact the wood and is suitable for accurately determining the water concentration in wood at a high speed scanning rate.
  • this invention consists of a pair of shielded electrodes mounted a fixed distance apart such that the wood to be measured can pass between them without touching them.
  • the electrodes are connected to any conventional electrical circuit that allows the increase of capacitance due to the presence of water in wood to be indicated as an output Voltage or current.
  • the two shielded electrodes are connected together electrically so that the volume between them is essentially a field-free region. As Wood containing water is moved into this volume, an electrical charge is induced in the wood. The amount of charge induced depends on the conductivity, and hence, the moisture content of the wood.
  • This invention allows moisture contents to be measured on rough or surfaced lumber, is relatively insensitive to wood position in the space between electrodes, is especially sensitive to non-uniform moisture distribution resulting in water concentrations inside a piece ice of lumber, and allows rapid measurement without physical contact with the lumber surface.
  • FIGURE 1 is a perspective View of the sensing head of the capacitance-type moisture meter embodying the present invention.
  • FIGURE 2 is a schematic illustration of the electrode assembly and electrical circuit analog therefor.
  • FIGURE 3 is a simplified wiring diagram used with the sensing head of the moisture meter.
  • the capacitance-type moisture detector 1 is generally rectangular in form and is comprised of four upright support members 2 formed of a suitable material, such as wood.
  • Upper and lower connecting side plates or boards 3 and 4 extend between the upright supports 2 as well as upper and lower end plates or shields 6 and 7 between the upright supports 2 to form a box-shaped housing for the moisture detector.
  • Top and bottom cover plates 5 and 5' are connected to the respective side and end plates to properly shield the electrodes 9 and 9' that are supported on a suitable non-conductor plate 8 connected to the upper side plates 3 and lower side plates 4.
  • the side connecting upper plates 3 and lower plates 4 are formed of a wood material or any other suitable structural material and the top cover plate and bottom cover plate 5 and 5 and also the upper and lower end plates 6, 7 are formed of aluminum, stainless steel, copper or other suitable conducting material.
  • the support member 8 is formed of glass, a resin sheet material such as Plexiglas or other suit able non-conducting material and the electrodes 9 and 9' are formed of aluminum, stainless steel, copper or other suitable conducting material.
  • the two electrodes 9 and 9 are connected together electrically. Also, the two shield members 5 and 5' are connected together electrically. In this manner, the two electrodes 9 and 9' become variable potential electrodes and the two shield members 5 and 5 become ground potential electrode members. The two sets of electrodes are then connected to the unknown terminals of a standard impedance bridge.
  • an electrode to ground capacitance C and C is created and an electrode to wood capacitance C and C is created. Since the shields 5 and 5' are connected together and the electrodes 9 and 9 are also connected together, the circuit then reduces to a total electrode to ground capacitance C that is equal to the sum of C and C and a total electrode to wood capacitance C that is equal to the sum of C and C As can be seen, the internal resistance R of the wood is connected in series with C which is connected to the signal-in lead 12 and grounded by lead 13.
  • the wood 10 is passed between the electrodes 9 and 9' on conveyor rollers 11 which are grounded. In this manner, an electrical charge is induced into the Wood 10. Due to the presence of moisture or water within the Wood, the flow of current between the electrode and wood will vary in accordance with the resistance of the wood. The flow of current between the electrode and wood can be readily measured by the impedance bridge, not shown, to indicate the quantity of moisture in the wood.
  • the size, shape and spacing of the electrodes 9 and 9" can be predetermined for successful operation.
  • the generator voltage and the frequency of the impedance bridge can be readily determined since the impedance bridge is driven by a 10 kilocycle per second signal and the output voltage is observed by an oscilloscope, a voltmeter or other similar voltage indicating device as is well-known in this art.
  • the invention set forth above places the electrode arrangement with the electrodes of the same potential spaced above and below the wood and the wood behaving as a semigrounded plate.
  • the relatively large wood-to-electrode spacing makes minor vari ations in lumber dimensions insignificant. Since the wood surface does not contact the electrodes 9 and 9, the moisture meter 1 is not influenced by surface dryness but is influenced by the moisture in the interior of the wood which is desired to be measured.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Measurement Of Resistance Or Impedance (AREA)
US248573A 1962-12-31 1962-12-31 Method for measuring the moisture content of wood Expired - Lifetime US3354388A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
NL302310D NL302310A (enrdf_load_stackoverflow) 1962-12-31
US248573A US3354388A (en) 1962-12-31 1962-12-31 Method for measuring the moisture content of wood
GB49587/63A GB1069100A (en) 1962-12-31 1963-12-16 Improvements in or relating to the detection of moisture in wood
JP6791663A JPS4630278B1 (enrdf_load_stackoverflow) 1962-12-31 1963-12-18
SE14469/63A SE302535B (enrdf_load_stackoverflow) 1962-12-31 1963-12-23
CH1597163A CH417160A (de) 1962-12-31 1963-12-27 Feuchtigkeitsmessgerät für Holz
FR959048A FR1393329A (fr) 1962-12-31 1963-12-31 Appareil détecteur de l'humidité du bois

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US248573A US3354388A (en) 1962-12-31 1962-12-31 Method for measuring the moisture content of wood

Publications (1)

Publication Number Publication Date
US3354388A true US3354388A (en) 1967-11-21

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ID=22939696

Family Applications (1)

Application Number Title Priority Date Filing Date
US248573A Expired - Lifetime US3354388A (en) 1962-12-31 1962-12-31 Method for measuring the moisture content of wood

Country Status (7)

Country Link
US (1) US3354388A (enrdf_load_stackoverflow)
JP (1) JPS4630278B1 (enrdf_load_stackoverflow)
CH (1) CH417160A (enrdf_load_stackoverflow)
FR (1) FR1393329A (enrdf_load_stackoverflow)
GB (1) GB1069100A (enrdf_load_stackoverflow)
NL (1) NL302310A (enrdf_load_stackoverflow)
SE (1) SE302535B (enrdf_load_stackoverflow)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3523246A (en) * 1965-04-27 1970-08-04 Brian Reginald Hall Method of and apparatus for testing a laminar material for irregularities of thickness
US3535631A (en) * 1966-05-13 1970-10-20 Agfa Gevaert Nv Apparatus for determining thickness variations across electrically conductive material
US4377783A (en) * 1979-10-15 1983-03-22 Wagner Delmer W Moisture detector
WO1984001220A1 (en) * 1982-09-22 1984-03-29 Weyerhaeuser Co Method of measuring moisture content of dielectric materials
US4881025A (en) * 1988-09-26 1989-11-14 Trustees Of The Diotec Trust Frequency dependent identification of materials
US5334942A (en) * 1992-12-02 1994-08-02 The Curators Of The University Of Missouri Of Columbia, Missouri Method of, and device for use in monitoring leaf wetness by conductivity/resistivity mesurement
US5585732A (en) * 1995-06-07 1996-12-17 Mississippi State University Detector for heterogeneous materials
US20080243444A1 (en) * 2007-03-27 2008-10-02 Francis John Babineau Method of predicting and communicating the performance of an installed building component based on the transient hygrothermal behavior of the component
CN106940338A (zh) * 2017-05-12 2017-07-11 成都凡米科技有限公司 一种新型水分含量测量装置及方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1924087A (en) * 1931-09-29 1933-08-29 Atlantic Prec Instr Company Method and means for measuring and indicating properties of conductors
US1984166A (en) * 1930-04-26 1934-12-11 Siemens Ag Method and device for determining the properties of stratified or fibrillated materials
US2574261A (en) * 1949-07-05 1951-11-06 California Cedar Prod Moisture detecting apparatus
US2782367A (en) * 1952-11-03 1957-02-19 Plywood Res Foundation Electronic device responsive to variable electrical conductances and capacitances of material, such as moisture content in lignocellulose materials
US3031617A (en) * 1958-08-13 1962-04-24 Donald R Paquette Linear capacitive probe detecting device
US3209247A (en) * 1960-10-19 1965-09-28 Moisture Register Company Dielectric loss type moisture measurement system with its output compared against a reference level

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1984166A (en) * 1930-04-26 1934-12-11 Siemens Ag Method and device for determining the properties of stratified or fibrillated materials
US1924087A (en) * 1931-09-29 1933-08-29 Atlantic Prec Instr Company Method and means for measuring and indicating properties of conductors
US2574261A (en) * 1949-07-05 1951-11-06 California Cedar Prod Moisture detecting apparatus
US2782367A (en) * 1952-11-03 1957-02-19 Plywood Res Foundation Electronic device responsive to variable electrical conductances and capacitances of material, such as moisture content in lignocellulose materials
US3031617A (en) * 1958-08-13 1962-04-24 Donald R Paquette Linear capacitive probe detecting device
US3209247A (en) * 1960-10-19 1965-09-28 Moisture Register Company Dielectric loss type moisture measurement system with its output compared against a reference level

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3523246A (en) * 1965-04-27 1970-08-04 Brian Reginald Hall Method of and apparatus for testing a laminar material for irregularities of thickness
US3535631A (en) * 1966-05-13 1970-10-20 Agfa Gevaert Nv Apparatus for determining thickness variations across electrically conductive material
US4377783A (en) * 1979-10-15 1983-03-22 Wagner Delmer W Moisture detector
WO1984001220A1 (en) * 1982-09-22 1984-03-29 Weyerhaeuser Co Method of measuring moisture content of dielectric materials
US4580233A (en) * 1982-09-22 1986-04-01 Weyerhaeuser Company Method of measuring moisture content of dielectric materials
US4881025A (en) * 1988-09-26 1989-11-14 Trustees Of The Diotec Trust Frequency dependent identification of materials
US5334942A (en) * 1992-12-02 1994-08-02 The Curators Of The University Of Missouri Of Columbia, Missouri Method of, and device for use in monitoring leaf wetness by conductivity/resistivity mesurement
US5585732A (en) * 1995-06-07 1996-12-17 Mississippi State University Detector for heterogeneous materials
US20080243444A1 (en) * 2007-03-27 2008-10-02 Francis John Babineau Method of predicting and communicating the performance of an installed building component based on the transient hygrothermal behavior of the component
US7899655B2 (en) 2007-03-27 2011-03-01 Johns Manville Method of predicting and communicating the performance of an installed building component based on the transient hygrothermal behavior of the component
CN106940338A (zh) * 2017-05-12 2017-07-11 成都凡米科技有限公司 一种新型水分含量测量装置及方法

Also Published As

Publication number Publication date
FR1393329A (fr) 1965-03-26
SE302535B (enrdf_load_stackoverflow) 1968-07-22
GB1069100A (en) 1967-05-17
CH417160A (de) 1966-07-15
JPS4630278B1 (enrdf_load_stackoverflow) 1971-09-02
NL302310A (enrdf_load_stackoverflow)

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