Fluorescence is a long established measurement technique and the most widespread technique for measuring oil in water.
The measurement principle is based upon a physical characteristic of aromatic hydrocarbons. When exposed to UV or low blue light, the aromatic hydrocarbons absorb the energy from that light (excitation) and give off light of a different wavelength (emission). The amount of light emitted helps determine the amount of oil present in the water.
Relative measurement technique
Fluorescence is a relative measurement technique. There are many factors that affect the level of light emitted by the oil:
- Not all oils fluoresce- generally aromatics do and aliphatics don't.
- Different oils give different levels of emitted light for the same ppm of oil.
- Droplet size affects the level of emitted light.
- Some chemicals used also fluoresce.
- Oil florescence is not a simple linear equation.
In order to ensure that all Advanced Sensors analyzers are as accurate as possible each analyzer is calibrated to the expected ranges, with a sample of the customers own oil where provided. Pre-calibration with the customers own sample is particularly important for higher oil ranges. Advanced Sensors can provide measurement up to 20,000 ppm.
- Use of ultrasonics ensures that an homogenised sample is provided, giving a reference point should there be any fluctuation in oil droplet size, as well as keeping the sensor clean.
- Creation of customer specific oil curves for pre-defined ranges overcomes issues associated with different oil types and there relative strengths.
- Use of a spectrometer means that Advanced Sensors can detect a change in oil type or the presence of fluorescing chemicals and can adjust for them.
- As the emitted fluorescence is based upon the level of the excitation light it is critically important that the output of the light source remains constant , otherwise the analyzer will require periodic recalibration. Advanced Sensors uses a laser to provide a long life consistent light source I and the technique is often called LIF (Laser Induced Fluorescence).
Correlation to Lab Samples
Regardless of how well calibrated the analyzer is, it is important that any analyzer is cross checked with and correlated to the local regulatory technique. Advanced Sensors has an excellent record of continuous correlation to lab results with no additional calibration required.