I am attempting to predict the change of saturation level of Hydraulic oil, with respect to temperature. I have a device that will give me the percentage saturation level over a thermal range of 10 - 70Cº but cannot as yet translate this into PPM.
No! 1% saturation is not necesarily 10,000 ppm. In many cases 100% water saturation occurs at only 200ppm at room temperature in hydraulic oil. The relationship between %saturation-water and ppm is different at varying temperatures. This is because oils (like air) can hold more water (ppm) at higher temperatures. Calculating the ppm from the %saturation usually requires a logarithmic formula with both temperature AND %saturation as variables. First, you have to know the saturation curve for your specific oil. Here's an example from the Hydac AquaSensor brochure:
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So now the question is how to determine that curve. I don't know the answer to that, but be warned: the curve will also change as the fluid and aditives begin to break down.