So in searching around....LTC, TI, ADI and a various set of obsure vendors...
   
  Seems that the AS7793 is the chip of choice...built in current source, seems to be the perfect interface to a 3 wire RTD.  Anyone used these before?  Seems pretty straight forward to use.
   
  Now if the RTD cable has a ground shield, not terminated at the transmitter end, assume tying to the analog ground plane is what we want.  I am assuming that there is a ground shield...havent seen it yet.

       
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