<div dir="ltr"><br><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">---------- Forwarded message ---------<br>From: <strong class="gmail_sendername" dir="auto">David Witten</strong> <span dir="auto"><<a href="mailto:wittend@wwrinc.com">wittend@wwrinc.com</a>></span><br>Date: Thu, Aug 6, 2020 at 12:19 PM<br>Subject: Re: temperature tests<br>To: Julius Madey <<a href="mailto:hillfox@fairpoint.net">hillfox@fairpoint.net</a>><br></div><br><br><div dir="ltr">Jules,<div><br></div><div>I'm not certain that really specific parameters have been stipulated. The goal always seems to be "can useful science be done with this" and "is this the best we can afford". Neither goal has been entirely expressed in numbers. </div><div>But I do not see any real competitors on the horizon.</div><div><br></div><div>It is really a matter of squeezing all the performance out of what we have.</div><div><br></div><div>Dave</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Aug 6, 2020 at 12:07 PM Julius Madey <<a href="mailto:hillfox@fairpoint.net" target="_blank">hillfox@fairpoint.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<font face="Arial">Pink Flamingos are popular in some areas !
Garden gnome sounds like a more 'blend into the landscape' item
though !<br>
<br>
Something like aluminized mylar somewhere towards the outer shell
of the enclosure could help as a reflective barrier.<br>
<br>
I'm really curious to see how the vertical PVC pipe in soil works
out. <br>
<br>
If absolute accuracy of the mag measurements isn't needed and an
~1degree temperature change can be achieved over most of a 24 hour
period, that might be all that's necessary; do we know what
Hyomin's goal on measurements is?<br>
<br>
<br>
</font><br>
<div>On 8/6/2020 12:46 PM, David Witten
wrote:<br>
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<blockquote type="cite">
<div dir="ltr">Julius,
<div><br>
</div>
<div>Thanks for sharing that.</div>
<div><br>
</div>
<div>My plan for putting a device outside for testing looks very
similar. </div>
<div><br>
</div>
<div>I am planning to place the device in a piece of PVC pipe
nestled inside that amount of Pink foam. I have some stuff
that set designers and outdoor sculptors use to seal the Foam
material to waterproof it and make it hard. Then almost any
other paint/sealant can be applied. It can be buried or left
out in the weather. I also thought about wrapping it in
Tyvec.</div>
<div><br>
</div>
<div>The fact that I can make this stuff look like almost
anything (garden gnome?) should help with my neighborhood's
covenants.</div>
<div><br>
</div>
<div>Dave</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Thu, Aug 6, 2020 at 10:54
AM Julius Madey <<a href="mailto:hillfox@fairpoint.net" target="_blank">hillfox@fairpoint.net</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div> <font face="Arial">Dave,<br>
I've had a lot of experience with calibrating thermal
sensors, thermoelectric heat pump temperature chambers,
etc. This was a 'quick and dirty' test with a small,
essentially zero gradient temp chamber. <br>
<br>
Aluminum is about second to copper in heat conductivity.
A small 100 ohm wirewound resistor is a snug fit in a hole
bored through the aluminum block and filled with heat sink
compound in the photo. With the insulation provided by
the block of foam, the aluminum block is an isothermal
source in close contact with the assembly consisting of
your original small board and the plug in RM3100 module
above it. <br>
<br>
Placed in the cavity in the foam block and with relatively
slow temperature change, the cavity volume is for all
practical purposes, zero gradient. <br>
<br>
50 to 75mA of current (0.25 to 0.56 watts) into the
resistor produced up to 35-40 degrees above ambient within
the chamber with rise times slow enough to maintain
effectively zero temperature gradient within the
heater/board assembly.<br>
<br>
I guess +/- 0.5 to 1% per degree C tempco for a wide range
inexpensive 3 axis magnetometer isn't too bad for general
applications if in fact the data we're seeing so far is
real and not an artifact due to some unknown. But is it
adequate for the requirements of the HAMSCI project ? <br>
<br>
And, if temperature control of some sort is required,
what's the least expensive, most practical way to achieve
that?<br>
<br>
Regards,<br>
Jules<br>
<br>
<br>
<br>
</font><br>
<div>On 8/6/2020 10:12 AM, David Witten wrote:<br>
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<blockquote type="cite">
<div dir="ltr">Jules,
<div><br>
</div>
<div>Very interesting. How are tiy doing the heating?
Conventional oven?</div>
<div><br>
</div>
<div>Dave</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Thu, Aug 6, 2020 at
12:07 AM Julius Madey <<a href="mailto:hillfox@fairpoint.net" target="_blank">hillfox@fairpoint.net</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div> <font face="Arial">Dave,<br>
I made up a small insulated temperature chamber
from a 5 x 5 inch block of insulating foam board
then bored a 1.5 inch diameter hole to the
center. Heater is a small block of aluminum with
a 100 ohm resistor in a drilled hole in the block
filled with heat sink compound and connected to a
twisted pair leading out of the chamber, resulting
in a small area loop which creates a small but
constant local B field as noted in the attached
plots. Heater current typically 55mA for the
temperature spans noted. <br>
<br>
The RM3100 is mounted on your original small test
board which is glued to the Al block and with 18
inch i2c bus leads running to a SparkFun
differential i2c board that supplies the 3.3 volts
to the RM3100. Inner chamber is closed off with a
foam plug of the same material. <br>
<br>
Both the sense and the magnitude of the tempco for
the two RM3100s I have is different. One is
positive, the other negative. Z axis was the
hardest to evaluate probably due to the relatively
small magnitude changes and the likely larger
variation of the vertical field component during
the tests. <br>
<br>
A better characterization would require a lab
grade setting with mu-metal chamber, precision 3
axis Helmholtz coils and precision temperature
chamber. <br>
<br>
Assembling the simple in-ground unit I mentioned
in my last and will hopefully try this weekend. <br>
<br>
Haven't heard back from PNI yet.<br>
<br>
Regards,<br>
Jules<br>
<br>
<br>
<br>
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