[TangerineSDR] Fwd: temperature tests

[David Witten]

To group.

Dave

---------- Forwarded message ---------
From: David Witten <wittend at wwrinc.com>
Date: Thu, Aug 6, 2020 at 11:46 AM
Subject: Re: temperature tests
To: Julius Madey <hillfox at fairpoint.net>


Julius,

Thanks for sharing that.

My plan for putting a device outside for testing looks very similar.

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.

The fact that I can make this stuff look like almost anything (garden
gnome?) should help with my neighborhood's covenants.

Dave



On Thu, Aug 6, 2020 at 10:54 AM Julius Madey <hillfox at fairpoint.net> wrote:

> Dave,
> 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.
>
> 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.
>
> Placed in the cavity in the foam block and with relatively slow
> temperature change, the cavity volume is for all practical purposes, zero
> gradient.
>
> 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.
>
> 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 ?
>
> And, if temperature control of some sort is required, what's the least
> expensive, most practical way to achieve that?
>
> Regards,
> Jules
>
>
>
>
> On 8/6/2020 10:12 AM, David Witten wrote:
>
> Jules,
>
> Very interesting.  How are tiy doing the heating?  Conventional oven?
>
> Dave
>
> On Thu, Aug 6, 2020 at 12:07 AM Julius Madey <hillfox at fairpoint.net>
> wrote:
>
>> Dave,
>> 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.
>>
>> 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.
>>
>> 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.
>>
>> A better characterization would require a lab grade setting with mu-metal
>> chamber, precision 3 axis Helmholtz coils and precision temperature
>> chamber.
>>
>> Assembling the simple in-ground unit I mentioned in my last and will
>> hopefully try this weekend.
>>
>> Haven't heard back from PNI yet.
>>
>> Regards,
>> Jules
>>
>>
>>
>>
>
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