Random pictures of LabVIEW code are useless to troubleshoot the problem. If the PID control is not stable, it means that the tuning parameters are way off or the code is not designed right.
Tell us about your hardware interface (seems to be FPGA based). You seem to be doing the PID calculations on the host only once every 100ms. That seems slow to me. What are your requirements? What are the reponse characteristics of your system?
Aren't there tools to run the PID control directly on the FPGA instead?