Joshna,
There are a number of factors which can influence the stability and resolution of your signal. First, the resolution of the LVDT itself comes into play. If it can't resolve down to 0.000001 V, then it's not practical to expect to get this type of resolution.
Second, if you're inputting this signal to a 9215 (which has a resolution of 16 bits), you're not going to get six digit resolution. The range of the 9215 is -10 to 10 V and which is split up into 2^16 levels (65536). This comes to roughly 3275 levels per volt or an absolute resolution of around 0.0003 V. This is without any external noise you will encounter, and you're not using any signal conditioning, so it's not surprising that you're seeing these results.
Depending on the frequency of your signal, it's not uncommon to implement a low-pass filter in your FPGA code. Also, for signal stability, you may want to oversample and average. For example, if you wanted to acquire at 1kHz, you could actually acquire at 10 kHz and average your last ten samples. However, note that this does not improve accuracy, it just improves stability.
Regards,
Craig D
Applications Engineer
National Instruments
