<div dir="ltr">To group.<div><br></div><div>Dave<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 11:46 AM<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">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>
</div>
<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>
</font> </div>
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