polymorph:
Well, if the PLC already has an ADC, why convert it back to analog? If you do that, you lose four times. The first ADC, then scaling, then DAC, then the Arduino's ADC, then scaling again.Let the DAQ do the ADC and scaling, then send the corrected digital data to the Arduino for logging. The great thing about digital is that, barring catastrophe, a 1 is a 1, a 0 is a 0.
Im confuzzled 
You're saying use the already scaled digital values and send those to the arduino, So it'd look like this?
Sensor -> ADC -> PLC (scaled here) -> PLC Digital Output ->Tee-off this line to the arduino -> DAC -> Analog Signal -> Valve input
On a side note, The HMI communicates with the PLC via profibus, so I'd like to have a button on the HMI to start the logging, I'm presuming I could easily grab another output off the PLC to the Arduino that triggers the Ardiuno to start logging when that input is live?