Quoting Mike Hord <mike.hord@gmail.com>:

> I've been asked for a thumbnail model of how the
> thermocouple I've superglued to the common lead
> of a laser diode to measure its temperature rise is
> impacting the measurement.
>
> Obviously, gluing a largish thermocouple to a
> small lead is rather like taking a voltage reading
> of a high-impedance source with a lower impedance
> meter.
>
> This is just a rough estimate, but my
> thermodynamics skillset is pretty limited.  Can
> anyone give me a clue on how to start?  My first
> visit in the meantime is going to be wikipedia-
> maybe I can come up with something there.
>
Hi, Mike:-

You can use your electronic skill set. R= rho * L/A
works for thermal resistance as well as electrical
resistance. You can look up the thermal conductivity
of the wires and estimate the effect of the thermal
"shunt" to room temperature. Obviously you want to use
the smallest gage wire possible (the only disadavantages
of fine wires are fragility and electrical resistance,
and the latter isn't really a problem). A thermocouple
is the best way to do this, IMHO. I would suggest taking
a measurement with the power just removed to confirm that
no DC is finding its way into the T/C measurement.

Best regards,
Spehro Pefhany


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