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Wood moisture meters - without knowing species?

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julianf

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I know very little about these, hence needing to ask -


The type of non-probe moisture meter - they work on density (or something?), right?

And you have to tell them the wood type, so they can calibrate their results?


For whatever reason, i rarely know the species of what i have. Does that mean these meters will be no good for me?
 

Sgian Dubh

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Wood has dielectric properties and pinless moisture meters use this to provide readings. The meter, placed against the wood, generates a radio frequency field extending a specific distance. In one version of this type of meter the moisture content of the wood registers via the power loss of the signal. In the other type the change in electrical capacitance according to the wood’s moisture content is measured.

The length of projection of the frequency field generated by the meter varies from model to model, but in an ideal world the field should project to about the centre of the board. The manufacturer fixes the field depth. This doesn't always suit the thickness of the board in the test, and a less accurate reading is the result. So, for example, if the field projection set by the manufacturer is ~13 mm, this is ideal for boards that are about 25 mm thick, but it's not optimal for say, 75 mm thick material. I think some of the more sophisticated meters may have a facility for the user to specify, i.e., adjust, the field depth to suit a particular need ... but I'm not 100% sure of that.

As to not knowing the wood species you're testing, that's a tricky one because, as you guess, these meters generally come with written instructions and guidance for making adjustments for wood species, as well as sometimes for things like air temperature. I guess all you can do is either improve your wood species identification skills, or perhaps you'll have to rely on WAG, ha, ha. Slainte.
 

Sgian Dubh

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julianf":3nv6kder said:
Any comments before i flick some money off into the void?
I've no experience with that brand, so can't help I'm afraid. I take it you're planning to buy that unit from North America or somewhere else that uses dollars as I note the prices are listed in that currency. Why not look for a UK supplier as I see you're based in Devon? Slainte.
 

Sgian Dubh

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Edited to delete the double posting. I'm not quite sure how that happened. Slainte.
 

Yojevol

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Julien, if you know so little about this subject, what are you going to do with the very accurate info when you've got it? Mostly you just need to get a feel of what the moisture content is. If I were you I would buy a cheap one. I just came up with 735 on ebay, purporting to be UK sourced, priced from £7. Get one and play with it. Take a piece of wood, take a reading, see how the reading changes with the species setting. I bet it won't change much form one timber to the next, especially between the common hardwoods we use.
I've got a probe type which I use infrequently. I usually take it along to my local timber auction and take a reading before putting in a bid. Recently I have been using it to monitor a batch of yew which I'm seasoning. In this case I'm not interested in the actual MC but the rate at which it drying out. Once it's down to about 14% I can start to think about using it. Can I use it now or should I put it into my kiln (aka spare bedroom) and try and get it down to something more like 8%.
Brian
 

julianf

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735? I did a search for 735 and meter, and 735 and moisture on eBay, but nothing that seemed sensible came up?

None of these things are made in the UK. If I buy from a UK retailer, I'll pay a bit of a premium for what, at the low end of things, will be a cheap Chinese unit.

All I'll be doing with a UK retailer is paying them to buy the unit from China on my behalf. It's not going to save the UK / world / whatever. I'd probably have to not buy it at all to do that, but that discussion will just confuse this thread, I think.

I guess I probably don't need an absolute at all, all I need is relative. As in when the numbers stop falling ill know it's acclimatised. Which is what I'm after - the actual number on the screen probably isn't of importance to me.
 

AndyT

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julianf":2vicquf2 said:
I guess I probably don't need an absolute at all, all I need is relative. As in when the numbers stop falling ill know it's acclimatised. Which is what I'm after - the actual number on the screen probably isn't of importance to me.
In that case, you could just periodically weigh each piece on your kitchen scales and keep a note so you can see when the weight loss (=moisture loss) has slowed down/stopped. Possibly more accurate.
 

MikeG.

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AndyT":2yktotxr said:
.......In that case, you could just periodically weigh each piece on your kitchen scales........
I'm fairly confident of how the conversation would go if my wife found me loading an 11 foot long plank of waney edged sawn oak onto her glass topped kitchen scale. :lol:
 

Yojevol

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I'm fairly confident of how the conversation would go if my wife found me loading an 11 foot long plank of waney edged sawn oak onto her glass topped kitchen scale.
You'll just have to invest in a bathroom scales - Chinese import of course!
 

Tim l

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Aldi have one for 9.99.go to the homepage and search in tools.I might get one it might be useful at that price.
 

julianf

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Tim l":34tmtqf7 said:
Aldi have one for 9.99.go to the homepage and search in tools.I might get one it might be useful at that price.
See that bit at the top -



Im almost certain that you pull that off to reveal pins...
 

Yojevol

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Just searched the net and came up with this article. It's a bit old but I'm sure the principles are still relevant.
My MM is one of these. It's a 30 year old design and, unbelievably, can still be bought via Amazon for £180, gulp. I'd certainly be tempted by the Aldi one if I were buying today.
The Comprotec site (above link) has a link to the MC correction factors for individual timbers - makes interesting reading. It indicates that my present yew reading should be corrected from 18% to 19.7%

Brian
 
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