[volt-nuts] Some questions to zeners (thermoelectric effects)
mikes at flatsurface.com
Mon Jan 28 12:11:07 EST 2013
On 1/28/2013 8:48 AM, Tony Holt wrote:
> Could the sense wires be welded to
> the ADC pins between the solder connection to the PCB and the package to
> avoid the thermal EMFs of a solder joint?
I don't think welding would make the difference, unless the wire is made
of the same material as the pin.
I'm also not clear to me how low-EMF solder helps in most cases. Solder
joints tend to be small and local, and it's the temperature difference
between the terminals which brings the thermoelectric effect into play.
For example, two copper wires soldered together - you have a Cu-solder
joint, followed by a solder-Cu joint, in very close proximity. As long
as "close" is close, and/or there's good thermal mass/conductivity,
don't the thermocouples simply offset each other?
More realistically, take a device with common tinned brass terminals on
a PC board. You have brass/tin, tin/solder then solder/copper
thermocouples in very close proximity, essentially resulting in a
brass/copper thermocouple. It seems that the temperature difference
between that connection and the similar thermocouples at the far end
device connection would overwhelm the local effects due to solder, which
require a temperature gradient across some small fraction of a mm.
Even with much larger, hand soldered terminals, something similar would
seem to apply. Wouldn't thermally insulating the terminals (which by
nature have pretty good thermal conductivity) to ensure a consistent
temperature across them be as good or better than just low EMF solder?
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