Hi Math,
In your schematic, R2 seems quite large at 511 KΩ. What is your VTR (voltage transfer ratio)? Are you planning to use a low sensitivity LVDT or is the full-scale displacement very small?
Is there a potential at Va and Vb, or are these nodes shorted and left floating? I recommend setting a potential at these inputs within the specified allowable range.
I also suggest you measure multiple input and corresponding output values, and do a linear regression analysis to find the true offset of the system.
What do you have the AD698 output driving?
Thanks and Best Regards,
Chris