(-60°C - 110°C).
What type of gain setting resistor should I use to keep a constant gain.
The AD8221 includes some data for 125C operation however, it was only qualified
for -40 to +85C operation. I believe the additional data was included for those
who wanted to see behavior beyond its specified temperature rating. The AD8221
should work well at your temperatures, however as we don't spec this part above
85 degrees we can not provide any guarantees.
We would recommend you also look at the AD8228, which is very similar to the
AD8221, except that it has fixed gains of 10 and 100. Because the resistors
are all internal, your gain drift with the AD8228 is much better at these gains
than with a resistor programmable part like the AD8221.