Hygrometer

[Farrell]

I sent the following post to Greg Newell privately because it had an attachment. If anyone wants the attachment, email me.

Post:

Here is a pdf of Chapter 3 from the Wood Handbook. Ron N. had given me the URL for it a while back. It is a government publication. My recollection is that Chapter 3 is the section most pertinent to our interests. The chart on page 7 is the magic chart. You can see that you can reach whatever MC target you have under a variety of RHs and temperatures. I was somewhat surprised that with my shop at 75 degrees F and 40% RH, I can easily achieve an equilibrium MC (EMC) of 6.5 by only heating the hot box (a warm box actually!) up to about 95 degrees F. I had been thinking that I would have to bake the little rascal at 250 degrees F for a few days!

I don't recall which meter Dave Porritt suggested. It seems there are three levels of gauges under $1,000. The under $100 jobs have an accuracy of plus/minus 5% - which should get you to within 7% EMC. The $100 to $200 jobs have an accuracy of plus/minus 3% (but some state that at RHs below 30% accuracy drops to plus/minus 5%) - which should get you to within about 4-7% EMC. I have found several around $300 that claim to have 2% RH accuracy from 5% to 95% RH - that should get me within 3% EMC. I tend to think this is the way I will go. These units have a remote probe so that you can place the probe inside the hot box and have the meter on the outside to check RH. I will hook up several Dampp Chaser rods (I'll experiment to see how many I need - I suspect I will only need one or two) to a thermostatic controller commonly used for fish tanks or reptiles (will drive up to 600 watts) - it also has a remote probe to place inside the hot box. That way I will control RH and temp by simply setting the thermostat. The unit is cheap $30 or $50 (I think) and works very well, turning your heat source on and off to maintain a constant temperature. I have used these units in my fish and turtle and reptile tanks for years and they keep the water/air at a very constant temperature.

I am currently building my box. I installed the box frame yesterday. It is permanently mounted on a wall. It measures 6' x 8' and will be about 8" or so thick. It will have two 6' x 4' doors on the front. I will insulate it with sheet foam. I will have a 5' tall rack in the back area for ribs (much like a gun rack you see in pick-up trucks - lots of those down here) and the board will sit on its long (bass) edge in the box. I will put a false floor a few inches up in the bottom for the board to sit on and have the DC rods below that. I might put a really small fan in it to provide a bit of circulation to ensure even heating. I will also likely put a aperture-controllable hole near the top and bottom to allow moisture to escape.

Those are my thoughts. Sorry you asked now? Take care and good luck!

Terry Farrell

  
----- Original Message ----- 
From: "Greg Newell" <gnewell@ameritech.net>
To: <pianotech@ptg.org>
Sent: Friday, August 30, 2002 10:19 PM
Subject: Re: Hygrometer


> Terry,
>          Glad to see your still in the thick of it. I've been stumbling a 
> bit in my own efforts of late. I'm spending a great deal of time trying to 
> get my house ready to sell. I'm not sure I'll be moving but i have found a 
> possibility that I just can't afford to ignore. Most all our efforts are 
> going in that direction right now.
>          Any idea where I could find one of these charts? Seems that Dave 
> Porritt's gauge looks pretty good for the task. I like the idea of the air 
> fully circulating around the board and therefore will have to build a hot 
> box. Where do you keep yours? I've been daydreaming of hanging it from the 
> ceiling vented above. Any thoughts?
> 
> Greg Newell
> 
> 
> 
> At 07:34 PM 8/30/2002, you wrote:
> >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.
> >
> >I am trying to measure temperature and relative humidity (RH) of the air 
> >in a hot box. There are reliable charts that provide values of wood MC for 
> >various combinations of temp and RH.
> >
> >Terry Farrell
> >
> >----- Original Message -----
> >From: "Greg Newell" <gnewell@ameritech.net>
> >To: <pianotech@ptg.org>
> >Sent: Friday, August 30, 2002 3:18 PM
> >Subject: Re: Hygrometer
> >
> >
> > > Dave,
> > >          What am I missing here? Is this not, as other sling hygrometers,
> > > measuring the air and not the board? Isn't Terry trying to judge the
> > > moisture content of the board and not necessarily the air around it?
> > >
> > > Greg Newell
> > >
> > >
> > > At 10:05 AM 8/30/2002, you wrote:
> > > >Terry:
> > > >
> > > >I have an Amprob THWD-1 that I've used for several years.  I got it for
> > > >about $105.00 from a local industrial supply co.  Since I'm not cooking
> > > >sounding boards I've found it to be quite good.  Check it out.
> > > >
> > > ><http://www.testmart.com/advice/advicetmp.cfm/v/001~~%2E%2E%2Fsearch%2F 
> > archivespec%2Ecfm~~TEMP~~AMPROB~~THWD%2D1~~%20~~%20%7C1.html>http://www.testmart.com/advice/advicetmp.cfm/v/001~~%2E%2E%2Fsearch%2Farchivespec%2Ecfm~~TEMP~~AMPROB~~THWD%2D1~~%20~~%20%7C1.html
> > > >
> > > >dave
> > > >
> > > >
> > > >_____________________________
> > > >David M. Porritt
> > > >dporritt@mail.smu.edu
> > > >Meadows School of the Arts
> > > >Southern Methodist University
> > > >Dallas, TX 75275
> > > >_____________________________
> > >
> > > Greg Newell
> > > mailto:gnewell@ameritech.net
> 
> Greg Newell
> mailto:gnewell@ameritech.net
>