What model is your Micrologix?
It should support the SCP instruction which can let you take the raw analog values and rescale and invert the slope all in one easy to understand instruction.
For use with a PID, I normally will use multiple SCP instructions. I will scale the raw signals to engineering units first, then SCP the engineering value to numbers scaled for PID in separate instructions. The range for PID values in a Micrologix is normally 0 to 16383 for the process variable, setpoint, and control variable. SO, the setpoint will be entered in engineering units and also scaled for PID with the SCP instruction and the control variable will be scaled from PID units to engineering units before being sent to another SCP block which scales it once again to match the requirements of an analog output card. This might seem like a lot of extra steps, and it is, but it is almost always useful (or necessary) to have the values available in the PLC in engineering units for other logic or for visualization.