For those interested in overdamped geophones, this paper:
http://www.ub.uib.no/elpub/2002/h/406002/hovedoppgave.pdf
describes in detail one such design. It includes a in-depth analysis of geophones, with particular attention to noise, and a technique for temperature compensation.

Mike Price


On 11/19/2012 8:13 AM, GMVoeth GM wrote:
> On 11/17/2012 4:26 AM, Brett Nordgren wrote:
>> Geoff,
>>
>> The formulas were derived. I just assumed a simple linear relation
>> between resistance and temperature, which is a decent approximation at
>> normal temperatures. My formula came from (RT2-RT1)=0.00393*(T2-T1).
>> At very low (cryogenic) temperatures, you need a more complex formula.
>> I should have mentioned that the temperatures are Celsius or Kelvin. As
>> you point out, since you are taking a difference, which one you use
>> doesn't matter.
>>
>> You can find more than you'd ever want to know if you do a Google search
>> on copper temperature coefficient. That's what I did.
>>
>> Regards,
>> Brett
>>
>> At 10:41 PM 11/16/2012, you wrote:
>>
>>> mucho gracious, yes, carbon has a reverse coeff.
>>> too bad they are not identical or you might somehow
>>> get a hybrid resistor which will stay the same
>>> as temp changes. i shall assume T = kelvin or rankin
>>> which are absolute but then as deltas that may not be
>>> important.
>>> are these formulas within the crc handbook ?
>>> geoff
>>
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> +0.393 percent per degree C
>
> It gotta be Centegrade or Kelvin or it wont work.
> just like me, it gotta be electronics or i dont work :-)
>
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