Convert Dew point Deg. C t0 PPM or PPB. How?

Does anyone know how to calculate Parts Per Million (or Billion) given Dew point in Degrees C?

This would be for Heated Nitrogen. Are there any other variables required (Flow Rate or Pressure?)

Ideally, I would like to do this with either a ControlLogix or a CompactLogix PLC using Ladder instructions.

Thanks

Figure 2 in this document might be helpful:
http://www.ge-mcs.com/download/moisture-humidity/916-064B.pdf

Flowrate will not be a factor but pressure definitely is.
If you're happy with the nomograph above, I'd choose some values off it that bound/contain your application and put them in a function generator block.

Thanks jamesau,

I will have a look. Appreciate the help.

Cheers!