2. 2
Thermometry Department
National Institute for Standards (NIS)
➢ NIS was established in 1963, the principle
function is the maintenance of national
primary standards, and giving technical
advice in measurements and calibration of
high precision measuring devices.
➢ One of functions of Thermometry
Department (NIS) is calibration of MC
meters.
3. 3
Checking calibration
Meter Manufacturing calibration
Property to be
measured
Sensitive
element
➢determination of the accuracy of an instrument,
➢ascertain necessary correction factors
A comparison between a meter under test and an established
standard
➢The comparison of transducer
signal outputs against the reference
standard to get calibration curve
Output Signal
What & Why Calibration?
4. 4
➢ MC is one of important technical
specification in wood, because the influence
it has on all the major properties that affect
the performance of wood in service.
➢ GATT, liberation of international trade, and
trade technical barriers.
➢ Quality control in industry and trade.
The Egyptian Need for MC meters
calibration
6. 6
Moisture content in wood
Moisture exists in wood either as
1- "bound" water that is held chemically
within the cell walls or as
2- "free" water that is stored in lumen of
cell cavities. As freshly cut or "green"
wood dries, the free water evaporates
first.
7. 7
This is a key concept in wood since
moisture affects the physical and
mechanical properties of wood differently
depending on whether the MC% is above
or below the FSP.
MC% above FSP: physical and
mechanical properties of wood remain
constant as MC% changes
MC% below FSP: physical and
mechanical properties of wood change as
MC% changes
The FSP varies for different species of
wood, but is typically around 30%.
28.5Spruce, Sitka
27.0Spruce, red
24.0Pine, red
25.5Pine, longleaf
21.0Pine, loblolly
28.0Larch, western
28.0Hemlock, western
26.0Douglas fir
27.0Birch, yellow
24.0Ash, white
FSP(%)Species
Fiber saturation point (FSP):
The moisture content at which all of the free water is removed - the cell
cavities are empty - but the cell walls are still completely saturated.
8. 8
when wood is no longer gaining or losing moisture. it has
reached an equilibrium with its environment.
Equilibrium Moisture Content
(EMC)
10. 10
Realizing NIS calibration system for MC in
wood meters and comparing between
Conductance and capacitance-type meters
Checking Calibration System for thermometers
Checking Calibration System for MC meters
High Homogenate media
with different fixed pointes
for comparison
Standard Vs. Calibrated meter
,Water bath, Oil bath
For each Wood type
Different EMC samples
Standard Meter or
method
to compare with
RTD (PT 100) or
Standard
Thermometer
Oven-Dry Method
ASTM D4442 & D4444
Client
thermometer to
Calibrated
Client Meter to
Calibrated
Client MC Meters to
Calibrated
Our missing part in NIS
11. 11
Oven-Drying
The ovendrying method is generally accepted as a
standard for calibrating other methods (ASTM
D4442). This method involves simply weighing the
specimen before and after ovendrying to constant
weight at 103°C.
Constant weight is defined as no further weight loss
when a specimen is weighed to an accuracy of ± 0.2
percent at 3-hour intervals.
12. Electric Moisture Meters for Wood
Meters based on the relationships between
an electrical property and the moisture on
wood below FSP (≈30%), the most
commercial used
1- Conductance type meters
Capacitance type meters -2
14. 14
Oven-Dry Method
ASTM D4442 & D4444
Client MC Meters to
Calibrated
Calibration System for MC meters
1. Oven (E. Schulz & Co.) 103 ± 2 o
C
2. Balance (METTLER TOLEDO) capacity
205 g readability 0.01 mg
3. Desiccators
1- Conductance type meters
Testo 606
2- Capacitance type meters
Humitest MC-100S
15. 15
1. Wood samples (Mosaky, Zan, Aro, and Mogna)
The most used in Egyptian market
2. Chambers at 25 o
C
3. Saturated Salt Solutions (ASTM D-4933)
Magnesium Chloride 33.9 %RH
Potassium Acetate 37.7 %RH
Potassium Carbonate 43.2 %RH
Potassium Sulphate 84.6 %RH
4. humidity and temperature sensors
Testo 625
6.2
7.7
8.5
17.4
EMC
Calibration System for MC meters
Conditioning for 60 days repeated meny times
For each Wood type
Different EMC samples
Our missing part in NIS
22. 22
Traceability
The traceability is: The property of the result of a measurement or the value of a
standard whereby it can be related to stated references, usually national or international
.standards, through an unbroken chain of comparisons all having stated uncertainties
➢The traceability of the instruments used in the measurement is as following
All the temperatures reading values were measured according to ITS’s-90 which
mean that the reading is traceable to the SI units.
➢hygrmoeters were calibrated by using Testo 650, which are transfer standard
traceable
to IMGC-Italy.
➢Balance used in weighting process traceable to Mass, Pressure & Density
Department
of NIS
23. 23
Sources of Errors and Uncertainties for
Electric Moisture Meters
➢ Adequacy of sample
➢ Specimen characteristics
(species, density, moisture distribution,
thickness, and temperature)
➢ Electrode contact
➢ Grain direction
➢ Chemicals in the wood
➢ Weather conditions
➢ Skill of operator
➢ The maintenance of the meters.
27. 27
References
ASTM D 4442-92, 2002. Standard Test Methods for Direct Moisture
Content Measurement of Wood and Wood-Base Materials, ASTM
ASTM D 4444-92, 2002. Standard Test Methods for Use and
Calibration of Hand-Held Moisture Meters, ASTM
ASTM D 4933-99, 2002. Standard Guide for Moisture
Conditioning of Wood and Wood-Based Materials
ASTM E 104-85 2002. Standard Practice for Maintaining Constant
Relative Humidity by Means of Aqueous Solutions
Forest Products Laboratory 1999. Wood handbook: Wood as an
engineering material. Gen. Tech. Rep. FPLGTR113. Madison,
WI: U.S. Department of Agriculture, Forest Service, Forest
Products Laboratory.
Ullmann’S Encyclopedia of Industrial Chemistry 6Th Edition
2002. Electronic release, WILEY-VCH
Wood
28. 28
New calibration system to MC conductance meters
Manufacturing Calibration MC meters
Physical Model Equation
Sakuma Eq. from
.Plank Eq
!!!??
Standard pointes
to compare output
signal with
measured values
Fixed Points ITS90
For each Wood type
Different EMC samples
measured using
Oven-Dry Method
Optical Pyrometer
Obtain all range
Calibration
Curve
Conductance MC
Meters
Large number of
Different EMC samples
needed
To cover all range
Manufacturing Calibration thermometers
29. 29
Ionic Conduction theory for wood using
Anderson-Stuart model for ionic conduction
in amorphous materials
The electric conductance of wood increases as the temperature increases
charge carriers whose number or mobility is increased
.by thermal activity
Murphy [39] in an electrolysis experiment proved that conduction in dry
cellulose is ionic and probably protonic, and reached the same conclusion
.for humidified cellulose
Phenomena such as polarization and the dependence of conductivity on
voltage, the metal used for electrodes and the time of application of voltage
The chemical structure of wood is cellulose 40%, lignin 21%, hemicelluloses
.30%, and others materials, which are natural polymers
36. 36
New calibration system to MC conductance meters
Manufacturing Calibration MC meters
Physical Model Equation
Standard pointes
to compare output
signal with
measured values
Fixed Points ITS90
For each Wood type
Different EMC samples
measured using
Oven-Dry Method
e.g. PT thermometer
Optical Pyrometer
Obtain all range
Calibration
Curve
Conductance MC
Meters
Large number of
Different EMC samples
needed
To cover all range
Manufacturing Calibration thermometers
New
Equation
Sakuma Eq. from
.Plank Eq
37. 37
S.R. Elliott, 2nd ed., Longman Scientific & Technical, 1990
”Physics of Amorphous Materials"
Dekker, SOLID STATE PHYSICS ,
Chapter 7 Ionic conductivity and diffusion
Kittel, INTRODUCTION TO SOLID STATE PHYSICS
Chapter 18
Burns, SOLID STATE PHYSICS
References
The Feynman l e c t u r e s o n p h y s i c s,
Volume 1
James, William L, 1988. Electric moisture meters for wood, U.S.
Department of Agriculture, Forest Service, Forest Products
Laboratory.
Ullmann’S Encyclopedia of Industrial Chemistry 6Th Edition
2002. Electronic release, WILEY-VCH
Wood
38. 38
➢ NIS has been successful established
facilities for calibration of all moisture
meters types, by Egyptian market Wood
kinds.
➢ The conductance meters having many
advantages over capacitance meters.
(more cheap, easy to use and maintenance, less
Errors)
➢ capacitance meters desirable where
appearance is important.
Conclusion
39. 39
➢Anderson-Stuart model explain the D.C.
conductance on wood below FSP as a
function of MC.
➢Suggesting new calibration method
needs only three experimental EMC
values.
Short time, low cost; comparing the long time
and high cost in other method due to large
numbers of points needed
40. 40
➢ Using of conductance moisture meters for
their advantages
➢ The calibration for moisture meters should
be checked periodically using standards.
➢ The moisture meters manufactories should
the calibration of the meters to wood kinds
in Egyptian Market.
➢ Using new calibration method
Recommendations
41. 41
One of first Calibration Certificates issued by NIS to Egyptian Co.
