Moisture Meter

[Yonak Hawkins]

Thank you, John. I guess I'm thick-headed. I still don't understand.

..So I have a piece in a plastic bag which maintains the original MC. I have a piece out of the oven which has reached equilibrium MC. Measuring them will naturally display different measurements as long as the original board was not completely dry. If I knew the MC of the "dry" piece, I could use that as a base line to set up the meter for the "wet" piece.

You refer to "calculated value" in your fourth bullet. What are you meaning by that ? How do you calculate the MC of the oven dried sample ? Otherwise, it seems to me you are saying to measure the two pieces and, if they measure differently, adjust the SC value until they measure the same, but the MC of the two pieces is not the same.

[John K Jordan]

Thank you, John. I guess I'm thick-headed. I still don't understand.

..So I have a piece in a plastic bag which maintains the original MC. I have a piece out of the oven which has reached equilibrium MC. Measuring them will naturally display different measurements as long as the original board was not completely dry. If I knew the MC of the "dry" piece, I could use that as a base line to set up the meter for the "wet" piece.
You refer to "calculated value" in your fourth bullet. What are you meaning by that ? How do you calculate the MC of the oven dried sample ? Otherwise, it seems to me you are saying to measure the two pieces and, if they measure differently, adjust the SC value until they measure the same, but the MC of the two pieces is not the same.

No, you never have to measure the dry piece with the moisture meter. You know by definition it's is at 0% MC by way of the oven-drying process. (I haven't tried it by I imagine a pinless meter might give an invalid reading.) The only purpose of drying that sample piece is to calculate the MC in the "wet" board. Once you use the dry piece to calculate the MC by the formula then you know what the MC is in the "wet" piece and can fine tune the meter for that species.

You calculate the MC in the board after drying the sample by weighing it before and after the drying and using the formula

MC - (InitialWeight - OvenDryWeight) * 100% / OvenDryWeight

For a good explanation you can google something like oven-dry moisture content for wood. This PDF came up first, probably as good as any:
https://ir.library.oregonstate.edu/downloads/jm214q048

Besides the oven, you do need a good scale. The smaller the sample size the more precision you need in the scale but small scales are cheap, even those that can weigh in 1/100s of a gram. I have a laboratory triple-beam balance scale (which is overkill) and keep these in my shop for various weighing. The first two are tiny, excellent for small things. The third one is a general purpose scale but the 1g resolution would not be as useful for small wood samples but you can use a larger sample.
https://www.amazon.com/gp/product/B0012LOQUQ
https://www.amazon.com/gp/product/B002SC3LLS
https://www.amazon.com/gp/product/B002UEZ2FC
I've tested these with a set of precision calibrated weights and they are all very close. For oven-dry MC tests you really only need the relative weight, not the absolute, so as long as a scale has sufficient resolution and is reasonably linear over the range it will work fine.

(OK, I admit I may be a scale and test instrument nut. I have other digital scales and two good to 600 lbs I use to weigh llamas and mini-donkeys. )

Hey, an easier method: drive up this way with your meter for a visit - we can oven-dry and weigh wood, compare meters, and play in the shop! I have plenty of air-dried boards willing to sacrifice themselves for science.

JKJ

[Yonak Hawkins]

John, thank you for your help and for your time to write all your notes and links. Now it's up to me. I'll have to put on my lab coat, muss up what little hair I have, install the pocket protector and get to work. If you need me I'll be in the lab. Thank's so much.