i try to use 0-100% (0.0000 to 1.0000) as all input and output of my pid and the rescale it to engeneer units...i feel it easier this way.
I did few analog cascade to on-off reverse controling to save analog card for motorised valves....A first pid determine the output needed to get the sp asked and than another pid control output pulses to open or close the valve according to position setpoint
be aware of your scan time VS where you put the subroutine....The doc and help file about it is very good for pid controler