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.
I agree with what PeterH said. I thought the Arduino was only logging the data, and you were asking how to send it to the Arduino.
So... where is the Arduino in this? What is the purpose of the Arduino?
I need to record liquid level, temperature, valve position, heater status, level setpoint and temperature setpoint, and of course a time-stamp for each, so 6 inputs and a time stamp.
That's a good starting point but it's lacking a lot of detail.
Where abouts are these data present in your system, and in what format? (I assume that some of these data will be present in multiple places in different formats.)