We all know that water in our oil damages both the oil itself and the system components. When the moisture level reaches the saturation point for the system oil, free water forms. The saturation point moves with the temperature of the oil. Warm oil holds more water in suspension than cold oil. So how do we know how much moisture is in our oil?
There are two ways of measuring:
1) Absolute
2) Relative
1) The absolute technique is reported in ppm (parts per million) water in the oil. It does not take into account the temperature of the oil or type of oil (water bearing capacity varies with oil type, viscosity, age, contamination level).
2) Relative humidity reports percentage of saturation level at a given temperature (x% @ y degrees Celsius). This takes into account the type of oil, temperature, age, contamination level etc. It gives a good idea of how close the oil is to saturation. This tends to be a system that is easier for people to relate understand.