A New PinlessMoisture Meter Do we still need pins?Review of Basics ASTM –D4444-08 Dielectric...

A New Pinless Moisture Meter

Do we still need pins?

Peter Garrahan

New England Kiln Drying Association

March 27-28, 2013.

West Lebanon, NH


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


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


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


Developers of technology

Manufacturing

Support

Developing correction factors

Verification of operation over a wide

range of operating (sample)

conditions


LOTS of SAMPLES!

• Species

• Various EMC levels

• SG variations• SG variations

• Wood temperature

• Thickness

• Surface condition

• etc.


Sample preparation


Measurements under controlled conditions


Comparisons with pin readings


Oven-dry MC determination


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


• 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


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


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


• 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


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


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


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


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

Thank YouThank YouThank YouThank YouThank YouThank YouThank YouThank You

A New PinlessMoisture Meter Do we still need pins?Review of Basics ASTM –D4444-08 Dielectric...

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