Hygrometer

[Greg Newell]

Del,
         Thanks for the informative post about how the meters work. Since 
you don't use your Lignomat to directly check the wood, what meter are you 
using to check the air in the room? How big is this room? How is it built? 
I got a post recently from Roger Wheelock about his product and how they 
test them and they have found that their controlled room is more controlled 
after the addition of a heavy plastic lining the walls. Do you do this in 
this room of yours?

Greg

At 12:06 PM 8/31/2002, you wrote:

>----- Original Message -----
>From: "Farrell" <mfarrel2@tampabay.rr.com>
>To: <pianotech@ptg.org>
>Sent: August 30, 2002 4:34 PM
>Subject: Re: Hygrometer
>
>
> > Hi Greg. I am not trying to directly measure moisture content (MC) of the
>board. Intruments for measuring wood MC only go down to 5 or 6% MC. When you
>are down at the extreme of most any instrument like this, the inaccuracy
>goes way up. Del has mentioned that they do not work well at these low MCs.
>---------------------------
>
>
>The general rule around here--and around here there are folks who measure
>wood moisture content for a living--is, "they don't work below 6%." In
>reality, though, they begin to get erratic and unreliable some above that.
>It's inherent in their nature.
>
>All wood moisture meters work on the principle of measuring the electrical
>resistance of the wood in some way. This resistance varies with the species
>of wood and with the amount of water bound in the wood. This is typically
>done in one of two ways. The most common is to insert two pins into the wood
>and measuring it directly by passing a current through it at some known
>voltage and comparing its resistance to some known standard. The other,
>still less common but growing in popularity, is to expose the wood to an
>alternating electromagnetic field and measuring the effect the wood has on
>that field. With either type of moisture meter, the closer you get to
>oven-dry the more inaccurate they become.
>
>We have a very nice--very expensive--Lignomat moisture meter that spends
>most of its miserable life in the bottom drawer of the tool cabinet. We rely
>on checking the temperature and humidity of our conditioning room every day
>and comparing those two readings to a chart which tells us the equilibrium
>moisture content of wood at that temperature and humidity. We then slightly
>adjust the temperature of the room accordingly.
>
>Del

Greg Newell
mailto:gnewell@ameritech.net