>Investigate the ratiometric method.  A/D's these days are more and more
>likely to be capable of rigging the reference to an external voltage.
>If you skip the precision reference and link the reference to the bridge
>exite voltage, you get better tracking (really).

SNIP

>What kind of performance / resolution are you looking for?  I saw the
>new AD7730 sigma delta family in the Analog Devices book, and it blew me
>away.  Without pulling off a genuine miracle in layout teqcniques, you
>could probably do 16 bit resolution and skip all of the above.  See the
>data sheet and you will see what I mean.  BIG bucks, though.
>

I would fully agree. The AD7730 achieves a very high resolution (24 bits),
but there is also AD7715, 16 bit lower cost (~$5), with differential input
_and_ differential reference. You can do four wire connection without any
instrumentation amplifiers at all.

What is the required resolution of your readings ? It will influence lot of
other things.

Josef