In order to have deterministic control, you should do all of your PID calculations inside of one loop in a VI set to time critical priority. A good rule thumb for LabVIEW RT programs that need determinism is to do all of your deterministic coding inside of one VI set to time critical priority with only one loop inside. You can do multiple parallel PID calculations inside of that one loop. There is an example that ships with LabVIEW RT in ~\labview\examples\rt\RT control (7030).llb\Two Channel PID - RT Engine.vi
