Not all oils are the same
Advanced Sensors uses fluorescence as its principle technique for measuring oil in water. With a single oil type the measurement at a fixed wavelength can be used to represent the amount of oil in the water. The measurement device is typically a PMT (Photo Multiplier Tube) or similar piece of equipment that can measure a fixed wavelength.
As oils of different types emit light at different wavelengths and intensities, it is possible to differentiate these oils using a spectrograph. Given that different oil types do not fluoresce with the same intensity under the same excitation light levels, it is important to know which oil type is being monitored. Advanced Sensors uses spectral information to allow its analyzer to automatically switch between oil types, and therefore ensure that the appropriate oil curve is always used.