How does the sensor know the saturation point of a given oil, since different oils can dissolve different amounts of water?

​When adding water to dry oil, the water vapor pressure increases until the oil is saturated with water. This point is called the saturation point and the corresponding pressure is called the saturated water vapor pressure. The oil cannot dissolve any more water. When this point is exceeded, free or emulsified water is the result.
Although different oils can dissolve different amounts of water (in ppm) at the saturation point, the saturated water vapor pressure has the same value for all oil types at a given temperature. By definition, at this point the saturation level is 100%.