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<font face="Arial">Dave,<br>
Fully understand; just wanted to share my results with you. <br>
<br>
I'm more comfortable now with relatively simple low cost
techniques to do some sort of calibration; the single axis
Helmholz pair I built in 1990 cost about $10 in material plus a
simple regulated power supply and the NOAA geomag model for a
specific lat/long/elevation is pretty good. <br>
<br>
Your test code has been EXTREMELY USEFUL in my experiments and let
me get this thing up and running quickly without spending time
doing my own coding; the output is consistent which allows
comparison to known field values. <br>
<br>
Would also have taken me a lot longer to get up and running
without your assistance with the adapter board and the Spark Fun
items.<br>
<br>
Best regards, <br>
<br>
Jules Madey K2KGJ<br>
<br>
</font><br>
<div class="moz-cite-prefix">On 4/25/2020 11:59 PM, David Witten
wrote:<br>
</div>
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cite="mid:CABJ3BVPMzE1VMpF8N4i1pX0NdFE=3L-RRmXXA=NS_mNi05wfLA@mail.gmail.com">
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<div dir="ltr">Julius (and anyone else),
<div><br>
</div>
<div>Please realize that you are running far ahead of what this
code was intended to do. It was meant to illustrate the
general technique used to interact with the device. It was
never intended to give meaningful results. I had thought that
I conveyed that it is only intended to show that these boards
work in a physical sense.</div>
<div><br>
</div>
<div>At the least, I know that all the vectors in this code
require a correction for gain. This is not my current
development repository, </div>
<div><br>
</div>
<div>I sent Frankie Bonte and her father a much more expensive
PNI demonstration board. It was my hope that they would use it
to explore the relationship between the values from this code
and the values that PNI's own code produces. They seem to
have chosen to go in some other direction that I do not
understand. I never received any feedback so I had to
purchase another Demo board and I have not gotten around to
using it because I have no usable Windows machines.</div>
<div><br>
</div>
<div>Again, do not expect the code in this github repo to give
meaningful results. These results have ALWAYS looked wrong to
me.</div>
<div><br>
</div>
<div>I have another private repo that I have been working on for
months, and I will only make it available when it seems ready
to me.</div>
<div><br>
</div>
<div>Davei Witten, KD0EAG</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Apr 25, 2020 at 10:18
PM Julius Madey <<a href="mailto:hillfox@fairpoint.net"
moz-do-not-send="true">hillfox@fairpoint.net</a>> wrote:<br>
</div>
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0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div> <font face="Arial">Dave,<br>
Made several runs with X,Y and Z sensors interchanges in
different orientations.<br>
<br>
Y and Z have equal sensitivities<br>
X sensitivity is significantly higher<br>
<br>
Using the NOAA model values for my Lat, Long and Altitude,
multiplying X by 0.056 and Y and Z values by 13 gives
results quite close to the predicted model values with the
resulting LSDs equal to 1nT. Close enough to get a much
better idea of noise level.<br>
<br>
Looking at the Helmholtz pair test data again, the
multiplication values are twice those quoted above......a
factor of 2 difference between the two methods. Given
that the NOAA model values are probably very close to what
the measured values should be, and since (ambient + test
field) - (a,bient - test field) = 2 x test field, the
calculated value for the Helmholz field is probably off by
a factor of two .... back to my notes on the coil field
....<br>
<br>
I don't see anything in the setup instructions for the
3100 registers to suggest such a difference and I haven't
dug into the code yet.<br>
<br>
I don't want to post anything on the repository until the
calibration results check out.<br>
<br>
Regards and stay well ...<br>
<br>
Jules K2KGJ<br>
<br>
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