Post on 24-Sep-2020
A New Pinless Moisture Meter
Do we still need pins?
Peter Garrahan
New England Kiln Drying Association
March 27-28, 2013.
West Lebanon, NH
A New Pinless Moisture Meter
Presentation Outline:
Part 1: A New Pinless Moisture Meter
• Presentation of new pinless meter on behalf of
Delmhorst
• Overview of the work done at FPInnovations to • Overview of the work done at FPInnovations to
support this technology
Part 2: Comparison of Moisture Meter Technologies
(pins vs. pinless)
• Factors that can potentially affect a reading
• Achieving the best accuracy possible
• Choosing which type of meter to use
• Impact of client demands/practices
Review of Basics
ASTM – D4444-08
Dielectric meters—Dielectric meters transmit
electromagnetic wave energy into the wood to detect
the influence of moisture in the wood on these waves
as an estimate of MC.as an estimate of MC.
Wave energy is most often in the radiofrequency range;
Hand-held meters commonly are placed directly on the
wood surface.
Review of Basics
ASTM – D4444-08
Hand-held meters provide a rapid means of sampling
MC of wood-based materials during and after
processing to maintain quality assurance and
compliance with standards.compliance with standards.
These measurements are influenced by actual MC, a
number of other wood variables, environmental
conditions, geometry of the measuring probe circuitry,
and design of the meter.
Review of Basics
Methods of Measuring Moisture Content
1. Direct
i. Oven-dry MC
ii. Distillation
2. In-direct
i. Moisture meters
• Conductance (DC-resistance)
• Dielectric (pinless)
Review of Basics
What is a Moisture Meter
A moisture meter is a device designed to measure an
electrical property of wood which is affected by (among electrical property of wood which is affected by (among
other variables) the amount of moisture present in the
wood.
Developing a Moisture Meter
16.0
18.0
Black Spruce
Typical scatter associated with a test for calibration of a moisture
meter under ideal test conditions.
6.0
8.0
10.0
12.0
14.0
6.0 11.0 16.0
Meter Reading
ODMC
A New Pinless Moisture Meter
TechScan• Targeted at restoration and
flooring sectors
• Two Scales:
Wood Scale: 5% - 30%
moisture range.
Reference Scale: Reads from 0 Reference Scale: Reads from 0
-100 on a relative basis for use
on non-wood materials such as
drywall and concrete
• Correction chart (species/SG)
• Available within the next two
weeks
A New Pinless Moisture Meter
ProScan• Targeted at secondary wood
manufacturing, flooring, etc.
• Digital readout (5 to 30%)
• Internal adjustments for
species (SG)
• Reference scale for non-• Reference scale for non-
wood materials
• Alarm to alert for high
readings
• Available in approx. 6 to 8
weeks
Developing a Moisture Meter
Developers of technology
Manufacturing
Support
Developing correction factors
Verification of operation over a wide
range of operating (sample)
conditions
Developing a Moisture Meter
LOTS of SAMPLES!
• Species
• Various EMC levels
• SG variations• SG variations
• Wood temperature
• Thickness
• Surface condition
• etc.
Developing a Moisture Meter
Sample preparation
Developing a Moisture Meter
Measurements under controlled conditions
Developing a Moisture Meter
Comparisons with pin readings
Developing a Moisture Meter
Oven-dry MC determination
Developing a Moisture Meter
Summary of Results
• SG is the primary factor affecting meter reading
• Correlations developed between SG, ODMC, & Meter
reading.
• Information has been integrated into meter versions • Information has been integrated into meter versions
that incorporate a correction factor.
Choosing a Meter
Part 2: Comparison of Moisture Meter Technologies
(pins vs. pinless)
• Factors that can potentially affect a reading
• Achieving the best accuracy possible• Achieving the best accuracy possible
• Choosing which type of meter to use
• Impact of client demands/practices
Choosing a Meter
Factors That can Potentially Affect a Meter Estimate of MC
1. Species
2. Specific gravity (density)
3. Wood temperature
4. MC Range4. MC Range
5. MC Gradient
6. Presence of wet pockets
7. Surface moisture
8. Sample size (width and thickness)
9. Surface quality
Choosing a Meter
Factor DC-Resistance Dielectric
Species
• Correction factor
required
• Regional differences • Species correction is a Species
• Regional differences
can be an issue
• Differences between
different sources
• Species correction is a
factor of SG
Choosing a Meter
Factor DC-Resistance Dielectric
• No separate correction
required.
•Species corrections most
• Meter readings must be
corrected for effect of SG
• SG variations within a
Specific Gravity
•Species corrections most
likely incorporate effect of
SG as well as chemical
differences between
species.
• SG variations within a
species can be a concern
• SG values in literature
are variable (regional
differences)
Choosing a Meter
Factor DC-Resistance Dielectric
Wood Temperature
• Meter readings affected
by wood temperature and
must be considered
under conditions other
• Meter readings are
affected but not to the
same extent as DC-
resistance.Wood Temperature under conditions other
than testing at normal
indoor ambient
conditions.
resistance.
• Still need to correct if
testing at extremes of
temperature
Choosing a Meter
Factor DC-Resistance Dielectric
MC Range
• Useful results within 6
to 25% range (below FSP)
• Readings outside this
• Useful results below
FSP
• Readings down to 5%MC Range• Readings outside this
range are an indication of
MC
• Readings down to 5%
• More stable at low MC
than DC-resistance
Choosing a Meter
Factor DC-Resistance Dielectric
• Meter can be used to
test for presence of a MC
gradient.
• Meter cannot detect
presence of a gradient
but is affected by it.
MC Gradient
gradient.
•Affects estimate of MC
obtained.
• Need to be aware and
pin at appropriate depth
• Good estimate of
average still possible (i.e.
pin at 1/5th depth)
but is affected by it.
• Produces an estimate of
the average to a certain
depth.
•More heavily influenced
by moisture at surface.
• Depth of penetration
varies by meter make and
model
Choosing a Meter
Factor DC-Resistance Dielectric
Presence of Wet Pockets
• Hitting a wet pocket will
cause over-estimate
• Need to probe a lot to
find wet pockets
• Easy to scan over surface of
board to find wet pockets
• Reading is not as heavily
influenced when you find one
(averaging effect)
• Larger wet pockets will have • Larger wet pockets will have
more pronounced effect than
very small ones.
Choosing a Meter
Factor DC-Resistance Dielectric
Surface Moisture
• Will not affect reading if
insulated pins are used
and in good condition.
• Has an influence on MC
estimates obtainedSurface Moisture
and in good condition.
• Can still detect for
presence of wet surface
by touching pins
estimates obtained
•May cause to over-
estimate average MC
Choosing a Meter
Factor DC-Resistance Dielectric
Sample Size Width• Meter readings not
affected by sample size
• Board needs to be as
wide or wider than sensor
plate.affected by sample size
• Meter reading is very
specific to wood between
tips of pins
• Thickness compensated
for by pinning depth
plate.
Thickness
•Meters have depth of
penetration limit.
• Thin material need to
be conscious of material
behind sample.
• Thick material (over 2-
inches) may not
penetrate to core.
Choosing a Meter
Factor DC-Resistance Dielectric
Surface Quality • Not affected by surface
• Rough surfaces reduce
the contact between
sensor and wood and Surface Quality
(rough vs. smooth)
• Not affected by surface
quality
sensor and wood and
tend to reduce the
reading.
• Can be compensated
for.
Choosing a Meter
Achieving the best accuracy possible
• Being aware of and compensate for or avoid the
various factors that can affect the readingvarious factors that can affect the reading
• The greatest strength of any meter is being able to
collect many readings from many boards.
• Using statistics on groups of samples will be more
meaningful than trying to interpret individual
readings.
Choosing a Meter
Choosing which type of meter to use
• Depends upon the various factors listed and which
meter will provide the most reliable and consistent
results.results.
• Type of material and extent of sampling required.
• May also be influenced by what your customer(s)
are doing.
Choosing a Meter
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