OELCHECK determines the phenolic inhibitor content for all turbine oils using infrared spectroscopy. Phenols exhibit a very characteristic absorption band in the range around the wave number of 3650 cm-1. The intensity of their signal is first determined by the IR instrument.
Using a calibration performed at OELCHECK using a pure additive, the absolute content of the inhibitor in the sample is then calculated from the signal intensity. If the oil type is known precisely and a fresh oil reference is available, the phenolic inhibitor content can also be given as a percentage compared to the fresh oil from these data. For practical purposes, it can be deduced to what extent the turbine oil can still counteract oxidation. Given a known initial situation and assuming that further use takes place under comparable conditions, it is thus possible to estimate how long the oil can still remain in service.