Moisture meters

[WFWales]

does anyone know whether the 2 pin type of moisture meters give their results on a wet or a dry basis?

 

Has anyone tried calibrating them and what did that entail?

 

Cheers

[Alycidon]

They dont calibrate, or at least the Morso ones I sell dont. Dont quite understand what your question means?. The meters give a reading, this reading is the percentage of moisture that is present between the pins. It is normal to get slightly differing readings off the same log. Typical reading could be 12% or 15.3% or 45% if sold by others !!.

 

A true reading would be to spilt a log and take it off the newly exposed face. Generally I demonstrate MC to a customer before tipping by just grabbing a few logs off the load and showing them. It prooves the wood was dry when you dropped it.

 

 

Hope that helps.

A

[WFWales]

Hi Alcidon.

 

Check this out - http://www.woode3.eu/documents/Conversion%20tables_english.pdf

 

I'll find some more info on monday!!!

 

Cheers

[WFWales]

http://www.epa.gov/burnwise/workshop2011/WoodCombustion-Curkeet.pdf

page 14 onwards!

 

M

[Fahrenheit]

When I was first looking at moisture meters I bought two. I bought one for around £15 and I bought another for around £150. The expensive one you could calibrate and it also took outside temperature and humidity into consideration when calculating the moisture content of something.

 

Basically though both moisture meters gave roughly the same reading when stabbed into a log so the moral of the story is don't waste your money and buy and expensive one!

[Jamiedownes]

And don't buy a really cheap one, I did and it's pants, stabbed it into the back of my kitchen unit door (birch) and it reads 40%!

[Farmer Tom]

Hey WFW,

that Curkeet document looks really useful . Good find. Thanks

[Pete Bannister]

I use moisture meters almost daily in my profession and have done so for over 25yrs . There are a few basic points to note that may be of help:

1.for timber, you will be best served by a two- pronged meter that measures electrical resistance ( conductivity).

2.Buy one that you can easily obtain replacement probes for because you will break or distort them.

3.Get one that measures % moisture content. ( ie gives a % read out). Almost all but the cheapest do this. Most of them are designed to a sensitivity of +/ - 2% ( ie 4%) overall and the 'top end' ones will be more sensitive than this, even though they still quote these parameters.

4. Self-calibrated meters are not such a good idea. The more expensive meters are supplied with a calibration check device ( a wire strip of know dielectric resistance). Checking reading by testing something of a know m.c ( e.g. dry, internal joinery in a heated dwelling will generally be between 4%-9% mc.) is a good habit.

5. Surface readings are not very helpful. For wood fuel you need the general moisture content. So, in a pile of logs you need to take a number of samples throughout the pile and calculate a mean average. You need readings from at least 50 mm below the surface of a piece. So split the logs, and you can take readings across and along the section to get a really precise overall value for any one sample. The more samples you take, the better picture you will obtain. Beware that a surface reading can be totally misleading either way.

6. The point previously made about the method of calculation of moisture content is important. However, in this context ( cut wood fuel,) you need to think about 'total' moisture content: ie wet weight divided by dry weight. Your moisture meter is calibrated to give a 'total' moisture content reading: it can't distinguish between what we call 'available moisture' and 'hygroscopic moisture' and this is not important as far as wood fuel goes

7. For firewood, info on ambient temperature (a.t.) or relative humidity ( r.h.) is not helpful. So I would not recommend using a multi -functional meter. Although, knowing the background r.h. of an indoor wood storage area might be useful, its not difficult to work it out by measuring the m.c of a piece of timber that has reached moisture equilibrium with its surroundings. Timber is a good 'barometer' of r.h. and some simple instruments actually use a piece of beech as the means of measuring r.h. fluctuation

8 finally and importantly.... electronic meters with prongs are measuring electrical current flow..they dont know if its flowing through wood, water, or metal! you have to figure that one out. You will get false (high) readings where salt is present ..so avoid measuring stuff in ground contact since mineral salts may be present. Carbon will always reads 'high', so dont measure burnt stuff. Heat affects the readings. A 2 deg C increase in temperature of the material will increase the m.c. reading by about 0.5% m.c. on most meters. So if you measure something that's say 50 deg C above the norm, you will find a huge inaccuracy in the reading, whilst the m.c. may have remained constant. You cant really get false ' low' readings from these meters unless your battery is dead!

 

Hope that helps.

[Pete Bannister]

i agree with Farmer Tom , the intertek document is useful. The point about moisture meters being inaccurate when wood is above fibre saturation is also partly true however,

Above 50 % m.c for most species and the reading it questionable. But you can obtain fairly accurate info in the range 28% ( the commonly accepted fibre saturation value) and the high 40%'s ime.

Another point, although its accepted that meter prongs should only be used perpendicular to the timber, I’ve never found any measurable difference when testing the parallel to grain. So I think this is one of those 'facts' that get repeated without being independently tested ..there's a lot of that!

[Michael C]

Pete, you obviously know your stuff, so could you recommend a good model/brand to buy?