Does anyone have an Extech MO280 pinless moisture meter?

[Sawdust=manglitter]

I already have a cheap Stanley 0-77-030 moisture meter, but obviously it doesn't account for species so isn't accurate and leaves pin holes, which is far from ideal.

I am therefore looking for a decent pinless moisture meter that is more accurate and accounts for wood species, and also one that won't break the bank. So I came across the Extech MO280, which appears to do what I need it to, obviously it won't have the accuracy of a Wagner but it's not too bad of a price.

http://www.extech.com/display/?id=14596

So with prices around the £100 mark, where's the catch? Does anyone own one or have any comments or reviews on it? Any alternative suggestions would be appreciated

 

[custard]

I use a Lignomat Combi Scan. I've checked it against Wagners and Brook Huits on several occasions and it's always given the exact same reading. I must have been using this one for nearly ten years and its never let me down.

http://scosarg.com/lignomat-combiscan-moisture-meter

 

[meccarroll]

Hi if you want a meter that gives the correct readings it should be able to make internal adjustments for both WOOD SPECIES and TEMPERATURE.
I don't think the Extech MO280, has a temperature correction facility, but you may want to check. I think you will still have to use a chart to set the meter for the band that the species of wood you are testing relates to so it's not really a whole lot different than using a chart with correction data with your existing meter.

You can download chart tables that give correction data for different species of wood and temperature differences, I have a cheap pin meter which is ok for what I need. So long as the wood is within 2-4% of what I require I am reasonably satisfied. Even if you get the wood to the exact moisture content you desire it will change as soon as the surrounding environment does and that happens quite a lot over time (winter to summer, rainy days, hot dry days, etc) so within 2-4% would seem fairly good to my way of thinking.

The Extech might be ok for what you need, but at five times more than your stanley is it that much better except for the pin holes? Might you be better throwing in the extra £130 for the Wagner? I don't know myself but I'm happy to read the charts and make any adjustment from the chart (basically same as reading a chart and adjusting your meter anyway).

Personally I'm sticking with my cheapy and charts for now (because they work), but when I want to make the upgrade I will possibly buy main brand (Wrangler etc) for long term reliability.

Mark

EDIT: Just read the above post and it seems to have the right spec and a good recommendation from the user so definitely worth checking out.

 

[Sawdust=manglitter]

I use a Lignomat Combi Scan. I've checked it against Wagners and Brook Huits on several occasions and it's always given the exact same reading. I must have been using this one for nearly ten years and its never let me down.

http://scosarg.com/lignomat-combiscan-moisture-meter

Thank you Custard, that seems like a perfect alternative, and a recomendation coming from you gives me the reassurance! How do you find it on sawn/rough wood that may not be perfectly flat?

Hi if you want a meter that gives the correct readings it should be able to make internal adjustments for both WOOD SPECIES and TEMPERATURE.
I don't think the Extech MO280, has a temperature correction facility, but you may want to check. I think you will still have to use a chart to set the meter for the band that the species of wood you are testing relates to so it's not really a whole lot different than using a chart with correction data with your existing meter.

Thanks for your reply Mark. I appreciate what you say about the charts I could use for the Stanley one I have, but I would still have holes to worry about, so won't feel comfortable checking moisture accross a board, only at wastage parts of the board. And also as you suggest above, I could do with something that accounts for the surrounding temperature too, so the one Custard suggests seems ideal for my uses!

 

[meccarroll]

The Lignomat sounds ok for the money especially as it's been tested by someone you trust. Electronics seem to be a bit of a lottery at times. The mainstream brands do tend to stand up well for long term professional use but I think the price tag for mainstream can be over the top for a light user.

Glad you found one to fit the budget, I'll put it on my list too, as a future possible upgrade.

Mark

 

[custard]

How do you find it on sawn/rough wood that may not be perfectly flat?

I haven't found that to be a problem, but I'm in the workshop today so I'll take some photos of it on a rough sawn/cupped board and let's see how the readings change after it's planed flat.

 

[custard]

Here's a rough sawn board of Sycamore. It may not look like Sycamore but that's because it's been thermo treated during kilning. Bit of an aside, it came from a flooring manufacturer who rejected this batch it because it has fiddleback/rippled figure! I pick up quite a lot of heavily figured timbers from flooring manufacturers, they just want the plainer boards that match the photographs in their brochures and therefore sell off all the gorgeous figured stuff.

As you can see it's rough sawn and also cupped,

The Lignomat Combi Scan comes with about thirty species of timber pre-loaded, but Sycamore isn't one of them. No problems, you find out the specific gravity of the timber species you want to measure and enter that. In this case I've guessed that Sycamore has a specific gravity of 0.50. The moisture reading of the rough sawn board was 9.9%.

Passed it over the planer and here's the board, flat and true,

And a fresh meter reading again gives us the same 9.9% moisture content.

 

[MusicMan]

Thanks Custard, very interesting and useful.

Just a note on specific gravity. The Wood Database gives the specific gravity of American Sycamore as "Basic 0.46, 12% moisture content 0.62".

The basic value is defined as the ratio between oven-dry weight and green volume, which is an impossible combination (minimum weight and maximum volume) but is a consistent scientific reference. The 12% MC is a "snapshot" for woodworkers and is a better value to use. But at 9.9% MC the specific gravity will be lower, so I am a bit puzzled how one can calibrate the Lignomat with just one number for specific gravity. It should ask for s.g. at a specified MC - does it?

For the present discussion this is irrelevant of course but I am always curious as to how instruments are calibrated!

Keith

 

[Sawdust=manglitter]

Yes, thank you Custard, very useful indeed! You've twisted my arm, I think I'll be getting myself the Lignomat

 

[meccarroll]

Thanks Custard, very interesting and useful.

Just a note on specific gravity. The Wood Database gives the specific gravity of American Sycamore as "Basic 0.46, 12% moisture content 0.62".

The basic value is defined as the ratio between oven-dry weight and green volume, which is an impossible combination (minimum weight and maximum volume) but is a consistent scientific reference. The 12% MC is a "snapshot" for woodworkers and is a better value to use. But at 9.9% MC the specific gravity will be lower, so I am a bit puzzled how one can calibrate the Lignomat with just one number for specific gravity. It should ask for s.g. at a specified MC - does it?

For the present discussion this is irrelevant of course but I am always curious as to how instruments are calibrated!

Keith

Keith I know you put this point to CUSTARD but I'm interested as to why you think specific gravity changes.

My understanding is that specific gravity of an object is related to that substance taken from a known set of values (a reference set of values of that substance) and does not change in relation to say a moisture meter reading.

I would think an example of why we use a specific gravity as reference is to have a guideline for that substance. Take any substance at the earths atmospheric pressure at sea level and again in space and the gravitational effect will be very different.

So if we measure the specific gravity of different species of wood using the same criteria we can establish certain values for each and categorise them into groups.

Denser woods tend to show a higher reading than lighter woods on a meter. So I assume that by putting woods into groups based on specific gravity we can use that group number to adjust the meter to the correct moisture reading.

I don't think the specific gravity of a wood species changes with moisture content but the weight and volume might change.

I too am interested in opinions related to this subject.

Everything is relative to where you live (altitude), temperature, wood species etc. It's all constantly changing, that's why I don't loose too much sleep over minor differences in moisture % readings.

Mark

The below link to a Utube video is quite good:
https://www.youtube.com/watch?v=KCcKmVJ2hKo

 

[custard]

Here's a practical example of how I use a moisture meter.

This is one of the beautiful signature pieces from the Barnsley Workshop, it uses solid burr for the panels, in fact the panels are shaped with a subtle curved face to signal that they are indeed cut from the solid rather than veneered.

I plan to do something similar. In 2014 I got a load of nice Elm burrs that were showing a moisture content of about 30%, way too high to use in furniture even for a floating panel. The burrs went into my wood store and the moisture content gets checked every six months or so, and the date and the reading gets chalked on the burr slabs. Today it's down to 17.1%.

When it gets below 15% it'll be ready for the cabinet that I have in mind. I've waited three years to build this so I can wait a bit longer.

What's the number one requirement for successful cabinet making?

Patience!

 

[MusicMan]

Thanks Custard, very interesting and useful.

Just a note on specific gravity. The Wood Database gives the specific gravity of American Sycamore as "Basic 0.46, 12% moisture content 0.62".

The basic value is defined as the ratio between oven-dry weight and green volume, which is an impossible combination (minimum weight and maximum volume) but is a consistent scientific reference. The 12% MC is a "snapshot" for woodworkers and is a better value to use. But at 9.9% MC the specific gravity will be lower, so I am a bit puzzled how one can calibrate the Lignomat with just one number for specific gravity. It should ask for s.g. at a specified MC - does it?

For the present discussion this is irrelevant of course but I am always curious as to how instruments are calibrated!

Keith

Keith I know you put this point to CUSTARD but I'm interested as to why you think specific gravity changes.

My understanding is that specific gravity of an object is related to that substance taken from a known set of values (a reference set of values of that substance) and does not change in relation to say a moisture meter reading.

I would think an example of why we use a specific gravity as reference is to have a guideline for that substance. Take any substance at the earths atmospheric pressure at sea level and again in space and the gravitational effect will be very different.

So if we measure the specific gravity of different species of wood using the same criteria we can establish certain values for each and categorise them into groups.

Denser woods tend to show a higher reading than lighter woods on a meter. So I assume that by putting woods into groups based on specific gravity we can use that group number to adjust the meter to the correct moisture reading.

I don't think the specific gravity of a wood species changes with moisture content but the weight and volume might change.

I too am interested in opinions related to this subject.

Everything is relative to where you live (altitude), temperature, wood species etc. It's all constantly changing, that's why I don't loose too much sleep over minor differences in moisture % readings.

Mark

The below link to a Utube video is quite good:
https://www.youtube.com/watch?v=KCcKmVJ2hKo

Mark,

The specific gravity, or density, is defined as the ratio of weight to volume of a piece of material. It most certainly changes with moisture content. For a reference, see http://www.wood-database.com/wood-artic ... c-gravity/, which is based on US Department of Agriculture data. The reason is that wood is a combination of several substances of different densities: water, lignin, cellulose etc and if the proportions of these change then the average density of the whole changes. As Archimedes famously realised in his bath. Beech, for example, changes from around 1.0 when green to about 0.5 - 0.6 when seasoned.

The parameter that wood scientists define as "basic specific gravity", which I explained in my post, is carefully defined so as to be independent of moisture content, and can be used to compare species. But it does not correspond to wood in any actual condition. It divides the fully dry weight by the fully wet volume. Maybe it is this value that is expected by the moisture meters, but I haven't seen any of their technical literature so cannot say.

You would quite be hard pressed to measure the effect of Earth's gravity or atmospheric pressure on density (specific gravity) of wood. Temperature effects are more measurable. Wood species has a major effect of course. And you are right that density is constantly changing, but the main reason for that is the absorption or desorption of water as the wood attempts to get in equilibrium with the moisture in its environment.

Matthias Wandel's video is quite a nice introduction though he does not go into the density changes with moisture content.

I do agree that minor changes are unimportant for woodworkers!

Keith

 

[meccarroll]

Hi Keith,

I took a look at Eric Meier post on the Specific Gravity of wood. Personally, I think he has overcomplicated the term for woodworkers. As he put it himself, his introduction is as clear as mud.

The specific gravity of wood, for the woodwork industry, is a constant. If the water content of wood increases, the MC% also increases but the specific gravity of the wood does not change, it is a constant value.

So if you just take the set of values given with the moisture meter that is all you need. If the water content in the wood being tested increases it will show as a MC% rise and if the water content decreases the moisture meter will show a MC% decrease, it is that simple. No need to overcomplicate things.

The moisture meter is testing MC% based on a specific gravity value of the wood, not the other way around.

That is my take on specific gravity for woodwork.

I may of course have this completely wrong in which case, I don't mind being corrected.

Mark

 

[garethharvey]

How do these meters work without prongs?

I am completely baffled!!

 

[MusicMan]

Mark

"The specific gravity of wood, for the woodwork industry, is a constant. If the water content of wood increases, the MC% also increases but the specific gravity of the wood does not change, it is a constant value."

I was trying to be tactful, but I just have to say that this is plain wrong!

It is possible to find woods that will sink in water when they are freshly felled, but float when they dry out. Clearly the density is changing. I think beech may be one of these but I haven't tried it.

Keith

 

[MusicMan]

How do these meters work without prongs?

I am completely baffled!!

By using an AC field and measuring either the capacitance change, or the power loss. Both these depend on the dielectric strength, which depend on the moisture content (and a few other things including the density).

In a lot of detail:

http://www.dpi.nsw.gov.au/__data/assets ... f-Wood.pdf

Essentially, the same way that a metal detector works without prongs!

 

[MusicMan]

Here's another useful reference, which says much the same thing as the Wood Database reference, but perhaps more clearly.
http://www.ripublication.com/IJAER/ijaarv5n5_3.pdf


The relevant bit is as follows:

"The most important factor affecting shrinkage is wood density, because wood shrinks by an amount that is proportional to the moisture lost from the cell wall [5]. Wood specific gravity, the ratio of oven-dry weight of a given volume of wood to the weight of an equal volume of water [2], is considered to be a good indicator of wood quality, because it is correlated with strength properties of lumber and to wood pulping properties [3]; [4]. Wood density, the weight of wood per unit volume, is another measure of the amount of wood material in a tree and the two are often used interchangeably. Wood density, however, should be reported at certain moisture content, so it is only equal to specific gravity at 0% moisture content. Wood density (specific gravity) is the product of several other traits within a tree including cell diameter, cell wall thickness, and the amount of latewood produced by the tree [2]."

Because of all the variables, it is indeed a confusing topic.

Keith

 

[meccarroll]

How do these meters work without prongs?

I am completely baffled!!

Hi gareth......, I took this from the interweb: The two main types of hand held moisture meters are resistance type and the dielectric type. Resistance type meters use penetrating electrodes that measure the resistance between the two pins. Dielectric-type moisture meters use surface electrodes to generate a radio frequency field into the wood. The meter measures the resulting difference in electrical field conditions.

For general woodwork (the type of meter we'd buy) I don't think there is really that much difference in accuracy between the two as, in general, they both measure near the surface (app 12-20mm max).

Mark

 

[meccarroll]

Here's another useful reference, which says much the same thing as the Wood Database reference, but perhaps more clearly.
http://www.ripublication.com/IJAER/ijaarv5n5_3.pdf


The relevant bit is as follows:

"The most important factor affecting shrinkage is wood density, because wood shrinks by an amount that is proportional to the moisture lost from the cell wall [5]. Wood specific gravity, the ratio of oven-dry weight of a given volume of wood to the weight of an equal volume of water [2], is considered to be a good indicator of wood quality, because it is correlated with strength properties of lumber and to wood pulping properties [3]; [4]. Wood density, the weight of wood per unit volume, is another measure of the amount of wood material in a tree and the two are often used interchangeably. Wood density, however, should be reported at certain moisture content, so it is only equal to specific gravity at 0% moisture content. Wood density (specific gravity) is the product of several other traits within a tree including cell diameter, cell wall thickness, and the amount of latewood produced by the tree [2]."

Because of all the variables, it is indeed a confusing topic.

Keith

Hi Keith, please don't trouble yourself being tactful, you can be as bold as you like with your comment, so long as they are pertinent to the subject I can take them....LOL. I mean that in good humour.

The above quote is much better and a great deal less muddy than the initial link to Eric Meier's introduction to specific gravity. thank you for posting it, I assume you may have this book to hand?

Instead of Weight we should be using the term MASS /VOLUME = DENSITY, though, rather than using the term WEIGHT.

To contunue:
I think you may be misinterpreting moisture content in wood, with the density of wood, and in doing so also confusing this with the Specific Gravity of wood (which I think is more correctly termed as Relative Gravity).

To clarify this I will quote your source above:

Wood specific gravity, the ratio of oven-dry weight of a given volume of wood to the weight of an equal volume of water

.

Here is a direct quote from your reference giving their formula:

Specific gravity
The specific gravity of wood core was determined by the maximum moisture content method [7]
Specificgravity=1/(((Mm −Mo)/MO)+1/Gso) (1)
Where, M m = green weight of the sample having maximum moisture
M o = oven dried constant weight of the sample Gso= average density of wood substances; constant having value of 1.53.

When simplified equates to: The dry weight

I look forward to your comments Keith.

Regards Mark

EDIT: I had to edit this to remove Eric Meier's name from your source of reference. It appears this is from another source and not Eric Meier.

 

[MusicMan]

Thanks, Mark.

Yes, Eric Meier took his data from the USDA tables and sources. I don't have the book but I have very frequently used the online equivalent (and several other books on wood science) in my research on historical woodwind instruments, including how they change with age and drying.

The problem is that there are several definitions and loose usages.

General definitions (see e.g. wikipedia)

"Specific gravity is the ratio of the density of a substance to the density of a reference substance; equivalently, it is the ratio of the mass of a substance to the mass of a reference substance for the same given volume. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water at its densest (4°C) for liquids; for gases it is air at room temperature (21°C). "

Density is always defined as mass/volume for a given actual piece of material.

Since the density of water is very nearly 1 g/cc, the s.g. referenced to water is virtually the same as the density in c.g.s units. (The tiny difference is because of the way that the length and mass units are defined). In SI units of course the density is 1000 kg/ cubic metre but the s.g. is still 1.

Both density and specific gravity of a particular piece of wood depend on its water content.

For purposes of comparison between woods, we have come up with a couple of definitions that do not depend on water content.

One is the one quoted by Eric Meier, as "basic specific gravity", being the ratio of completely dry weight to completely wet volume. This has the disadvantage that it is a constructed parameter which cannot exist in any piece of wood.

The other is the one you quote, the "wood specific gravity", which is the oven-dry density. While this can be achieved obviously by oven-drying, it is not a condition in which we use wood.

The equation that you cite is yet another usage, the "specific gravity of wood core". It does not equate to the dry weight, since it is a dimensionless equation (no units, just ratios). It is comparing the average dry specific gravity to the specific gravity of the "wood substances" (that's lignin, cellulose, extractives such as resins etc) to find out something about the structural compactness of the wood.

It may well be the oven-dry specific gravity that should be used in the calibration tables. But I haven't seen the manuals so I don't know that.

And no, I am not confusing the definitions of the terms weight, density and moisture content .

cheers, Keith