Relative humidity & saturation curve

Test control unit at OELCHECK:


Sample quantity:

ca. 125ml




Determined values:

Relative humidity in % for specified temperatures between 30 and 80°C;

Saturation curve stating the saturation content of water in ppm from 30 to 80°C

Analysis for:


Short description:

A humidity sensor of the type LubCos H20 from Argo Hytos is installed in a vessel which protects the oil sample from humidity. A heating block holds this sample bottle together with the build-on sensor. A magnetic stirrer ensures the homogeneity and uniform temperature distribution of the oil sample after the start of the test. During a predetermined heating program, the relative humidity of the oil is recorded at different temperatures. A water saturation curve is generated from the results obtained in this process and the measurement of the absolute water content using Karl Fischer titration.


If only the relative humidity in percent of the oil that is to be analyzed at a certain temperature is of interest, the measurement is limited to this one target temperature.


The absolute water content in mg/kg is determined using the Karl Fischer titration. However, depending on the composition and the operating conditions (especially temperature), oils can absorb different amounts of water before turbidity or, with further increasing water content, phase separation occurs. Therefore, users oftentimes are not only interested in finding out the absolute water content, but they also want to receive information regarding the water absorption capacity of the oil.

Underlying test standard:

OELCHECK test method OPM 022