Charge mode piezoelectric signal conditioning
You achieve the best shielding if you connect the shield to the case on both sides of the cable. 

Ground currents between device and sensor grounds produces voltage on the shield resistance/impedance. This voltage will add to your measurement, if you use shield as one of the wires.

Even if you isolate the coax ground from sensor ground it will have a slight capacitive coupling. 
All depends on your environment and requested accuracy.

Problems disappear for high frequencies (>1MHz for 10m cable), where coupling between shield and core acts as a common mode filter / transformer.

for best results:

low frequency - use twisted pair, shielded

high frequency - you may also use coax if low frequency is removed