[GSBN] Calibration of Balemaster probe

Sun Nov 8 14:33:38 UTC 2009

Thanks for sharing this wonderful data, Jim.  Your figures brought up 
a question for me about variation between measurements of the same 
straw at the same density and moisture content.  I'm guessing that 
the figures that you show are averages of some sort.  I'd like to 
hear more about that.  I'm thinking that you probably didn't insert 
the probe one time at each density, and move on to other densities.

I have observed that it is normal to get some variation in the 
Protimeter readings, when inserting the probe into the same bale at 
about the same spot in the bale, to similar depth.  I haven't done 
careful recording of this variation, but when I want to test a bale, 
I insert the probe three or four times and do a quick mental 
averaging.  I haven't tested that many bales, but I remember seeing a 
variation of two or three percent, sometimes more, between the 
different Protimeter readings.  Some of that variation could come 
from actual variation in the moisture levels at slightly different 
spots in the bale.  But I think most of it is from differences in how 
the straw interfaces with the probe.

What variations did you see, Jim, between one measurement and 
another, in your test bale at the same density?  Can anyone else on 
this list indicate the variations you have seen, in probing nearby 
spots in the same bale?

Your figures indicate that we can be pretty confident about the 
values that we get from a moisture probe.  That is good news.  Thanks 
again for sharing this information.

Derelict

PS.  One concern that I have about GSBN is highlighted by your 
request at the end of your message.  You ask that we keep the results 
to ourselves, since you are considering academic publication of this 
information.  That's an explicit, valid, and valuable statement ,that 
you are not yet ready to share this information with the entire 
world.  It tells me that you are not aware, or not remembering, that 
any message sent to GSBN is already available on Google to anyone, 
anywhere, even before it hits my mailbox.

I think there is a danger in the fact that our GSBN archives are set 
up that way.  It means that either people like Jim will be hesitant 
to share valuable preliminary work, or that they will forget that 
GSBN is not in any way private, except in who can post, and will 
share their research, and regret the consequences.  (Often, there 
will be no negative consequences, but the more research that we 
discuss here, the more likely that there will be negative fallout.)

Either way, I think the current archiving approach does more harm 
than good.  I think there is value in GSBN being a safe sandbox, in 
which to discuss ideas that we aren't ready to share with the world. 
The last time that this was discussed, my viewpoint was in the 
minority.  Jim, I would appreciate it if you would comment on how our 
instantly-open archives will affect your willingness to post 
information.

I deeply respect the  people who have expressed a different viewpoint 
on this archiving question, and I am not arguing for closing the 
archives forever.  I don't have a specific proposal for how the 
archiving should be structured.  I would just like to honor a request 
like Jim's, that we all exercise a little human discretion with his 
experimental data.  It bothers me that, even before any of us read 
it, his request has been violated via our automation.

Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek at unm.edu

--On Sunday, November 8, 2009 11:58 AM +0000 Jim Carfrae 
<jim.carfrae at plymouth.ac.uk> wrote:

> Hello All
>
> There have been a couple of threads here about the accuracy of
> straw bale moisture probes like the Protimeter 'Balemaster'. The
> big question on probes of this sort (that measure the electrical
> resistance of the straw at the tip, and translate this into a
> figure for moisture content) is how far the accuracy is affected by
> the density of the straw. David Eisenberg has described how, if you
> take a handful of straw and wrap it around the tip of the probe,
> the moisture reading goes up and down as you press the straw
> against the probe, which indicates a potential problem! I decided
> to set up an experiment to try and find out how much of a problem
> this actually is, and here is the methodology (for those who care
> to know).
>
> First I built a box with a lid that could be pressed into it.
> I then measured the internal volume of the box, and weighed out
> some straw that if compressed to the density of a typical bale
> (110Kg/m3) would fill the box exactly. The straw was taken from a
> bale that had been at the back of my garage for some time, in a
> reasonably stable environment, with wood stored next to the bale
> measuring (with a Protimeter 'Timbermaster') 16.1% moisture content
> The straw weighed out to go in the box was loosely restrung from
> the bigger bale, and before I placed it in the box I calculated the
> volume, then measured it with the Balemaster. I then placed the
> straw in the box and gradually screwed the lid down, stopping at
> pre-determined intervals to probe the straw through holes drilled
> in all sides of the box. After the lid had been screwed down as
> tight as it would go (at which point the straw was too dense to
> easily insert the Balemaster), I took the straw out, re-weighed it,
> and then dried it in a fan oven until it had lost all it's moisture.
>
> Results.
> Loosely retied straw; density 68.5Kg/m3, Balemaster reading 12.2%
> Straw in box; density 95Kg/m3, Balemaster reading 14.7%
> Straw in box; density 108Kg/m3, Balemaster reading 15.8%
> Straw in box; density 118Kg/m3, Balemaster reading 16.0%
> Straw in box; density 129Kg/m3, Balemaster reading 16.3%
> Straw in box; density 142Kg/m3, Balemaster reading 16.6%
>
> Actual moisture content of straw, determined by  gravimetric
> analysis (weighing, drying, weighing again) 16.2%
>
> This was a very encouraging result; wood next to the straw was
> 16.1%, Balemaster readings at the sort of densities found in a
> typical wall ranged from 15.8 to 16.3%, and the straw was actually
> 16.2%
>
> An observation: I've surveyed many straw buildings with a
> Balemaster, and the Balemaster will give you an impression of how
> dense the bales in the wall are according to the resistance as you
> insert it. This was borne out when using the Balemaster to probe
> the straw in the box, with the straw at 95Kg/m3 feeling slightly
> loose, and the resistance gradually increasing with 129Kg/m3
> feeling as tight as almost any building in my experience, and at
> 142Kg/m3 it was almost impossible to insert the Balemaster.
>
> I hope this will be of interest, but I would ask you to keep these
> results to yourselves, as I hope to publish them as part of an
> academic article soon.
>
> Regards
>
> Jim
>
> Jim Carfrae
> PhD Research Student
>
> Room 119, Reynolds Building
> University of Plymouth
> Drake Circus
> Plymouth
> PL4 8AA
>
> jim.carfrae at plymouth.ac.uk
> 07880 551922
> 01803 862369
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Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek at unm.edu