Measured moisture level with multimeter

[MnDave]

I decided to use my multimeter vs buying a Moisture Meter. I found the following resistance table on hearth.com.

https://www.hearth.com/talk/attachments/resistance-mc-chart001-jpg.40607/

I measured a few pieces of red oak yesterday.

First I marked the sides with a magic marker indicating the sides I do not want to test. Then I split the pieces using a maul.

I then pounded a small nail into a split side about 1/2 inch deep. I measured 1 1/4 inch away and pounded a second nail. I did this on both pieces.

I set my multimeter to measure ohms. On one piece I measured 23 mega ohms and the other 25 mega ohms.

I went to the table for red oak and found that my pieces are between 14 and 15 % moisture content.

I just noticed that the table is for 80F. I could have been more accurate by bringing the pieces in the house and setting them by the stove for a little while. I measured them in the garage at around 20F.



MnDave

 

[schlot]

Very cool info. It would be fun to run a MM test at the same time as your multimeter test to compare information.

 

[MnDave]

Very cool info. It would be fun to run a MM test at the same time as your multimeter test to compare information.

I will probably buy a MM someday and do a correlation.

I wonder if the MM instructions say anything about what the temp of the wood should be. I also think that MM's could have a table with a correction factor for various species.

It was kind of cool to see that the two random pieces were so close. I plan to repeat this test at room temp in the next few days to get a more accurate reading. I plan to measure some birch and elm as well.

MnDave

 

[MnDave]

I am always surprised to see birch listed as a hardwood.

IMO it is kind of soft and the woodpeckers must think so to.

MnDave

 

[oldspark]

Cant wait for backwoods to see this post.

 

[XJma]

I am always surprised to see birch listed as a hardwood.

IMO it is kind of soft and the woodpeckers must think so to.

MnDave

Technically speaking I believe that the term hardwood is generally referring to any deciduous tree. In other words, there are many soft hardwoods!! In college we rented a house that had birchwood floors, which are definitely a soft hardwood!!

 

[basod]

I wonder what kind of readings I would get with my megger @5kV ????
Better yet a 10Amp Ductor

 

[Backwoods Savage]

Cant wait for backwoods to see this post.

Saw it and was just going to pass on it until I saw your post.

 

[clemsonfor]

Cant beleive that you had to mark the outside of the split and could not tell the diff once split?

 

[schlot]

Cant beleive that you had to mark the outside of the split and could not tell the diff once split?

Think he was just being thorough.

 

[MnDave]

Cant believe that you had to mark the outside of the split and could not tell the diff once split?

I split one without marking and it was a little hard to tell so I marked the next ones so I would not make a mistake.

This wood was cut last fall, split and stacked last spring. A lot of my wood is dead fall.

It seems like it takes at least a year after splitting before the wood turns grey.

I have some that has turned grey and I will check those for moisture content.

My wood burns fine but I know that it could burn even better so I am trying to get 3 years ahead. I am gathering 2015 now.

MnDave

 

[Jon1270]

If you've got an accurate scale that measures in small increments (e.g. grams), you can check your work by weighing a small sample before and after drying it out completely in the oven. A sample that weighs 100g at 15% MC will weigh about 87g when totally dried out.

You can speed up the process by microwaving the sample, but it's easy to get it too hot and ruin it. If you char it, some of the weight is lost to smoke and the test isn't valid.

Electrical MC tests are quick and easy, but relatively inaccurate.

 

[MnDave]

If you've got an accurate scale that measures in small increments (e.g. grams), you can check your work by weighing a small sample before and after drying it out completely in the oven. A sample that weighs 100g at 15% MC will weigh about 87g when totally dried out.

Interesting. I like the idea of measuring moisture content by weight vs conductivity.

MnDave

 

[Jon1270]

Weight is how MC is actually defined. Electronic meters don't really measure MC, they just make an educated guess based on electrical properties, which themselves vary for reasons other than actual moisture, like species and temperature. Going by weight is a lot more accurate, but it takes an inconveniently long time to do. Even drying out a sample on low power in the microwave can take a couple of hours, and doing it in a conventional oven is at least overnight.

 

[oldspark]

If you've got an accurate scale that measures in small increments (e.g. grams), you can check your work by weighing a small sample before and after drying it out completely in the oven. A sample that weighs 100g at 15% MC will weigh about 87g when totally dried out.

You can speed up the process by microwaving the sample, but it's easy to get it too hot and ruin it. If you char it, some of the weight is lost to smoke and the test isn't valid.

Electrical MC tests are quick and easy, but relatively inaccurate.

Cant remember the guys name but one of the members did some testing by weighing wood while drying and using his MM and the results were the MM was not that bad and that was a just a cheap HF one.

 

[Jon1270]

Cant remember the guys name but one of the members did some testing by weighing wood while drying and using his MM and the results were the MM was not that bad and that was a just a cheap HF one.

Yes, electronic meters are generally the way to go, for the sake of convenience, and are usually plenty accurate for our purposes. As a woodworker (which I've been for much longer than I've been a wood burner) I've found it handy to know how to do it by weight, especially when I'm skeptical of what the electronic meter is telling me.

 

[oldspark]

Yes, electronic meters are generally the way to go, for the sake of convenience, and are usually plenty accurate for our purposes. As a woodworker (which I've been for much longer than I've been a wood burner) I've found it handy to know how to do it by weight, especially when I'm skeptical of what the electronic meter is telling me.

Yea he was a wood worker also, cant remember how far off the meter was but he was more tham happy with his HF MM for firewood, I believe it was never more than 3% or so. He had very interesting posts and did a bunch of testing on firewood, he moved a little over a year ago and dont post much any more.

 

[PLAYS WITH FIRE]

Found this interesting:

http://woodgears.ca/lumber/moisture_meter.html

 

[Gark]

Doesn't the chart specify "two pairs of probes" spaced 1 1/4 apart? Wondering if two pairs would give a different megohm reading than the two nails you used... I'm guessing that "two pairs" separated by the 1 1/4 inch would yield a lower resistance, which means a higher MC.

 

[ScotO]

I really like the idea of measuring MC with resistance. I won't do it for my firewood, but I WILL use it for the lumber I cut from logs. I have a couple stacks of walnut and poplar drying in the garage, this would be a great way to accurately find out the MC in the wood.