Fluorescence is a special form of luminescence. Fluorescence is excited by radiation in an ultraviolet range. When the electrons of fluorescing molecules absorb photons, they attain a higher level of energy. This excited state is then energetically instable. The electrons quickly return to their initial condition, causing the previously absorbed energy to be released once again. This release of energy results in the emission of fluorescent light. Because some of the energy is transformed into heat, the emitted radiation has less energy, and therefore a longer wavelength.
Process parameter fluorescence for parts cleanliness inspection
Are the cleaned parts really clean? Or is there still a thin layer of oil?
Prove to your clients and suppliers that your products are “100% clean” by using robust and sensitive fluorescence measurement technology.
Measuring principle of SITA CleanoSpector & SITA clean line CI
The SITA CleanoSpector and the SITA clean line CI detect residual contamination by measuring the fluorescence, which is excited by ultraviolet light from a light emitting diode (LED). A photodiode in the device’s sensor head measures the intensity of the fluorescence. The measured results can be interpreted in the following way: the higher the measured value, the larger the amount of contamination will be, and thus, the lower the level of cleanliness will be.
Procedure for preparing a calibration (reference) sample
Before a cleanliness inspection can take place, the SITA CleanoSpector must be calibrated on an ideally clean reference part. Thereby, the fluorescence of the ideally clean surface without contamination will be taken into account. In a following measurement on the ideally clean reference part, the SITA CleanoSpector will indicate a cleanliness value of 100%. The calibration value is saved in the measuring device.
1. Intensive cleaning of reference part surface
The reference part is subjected to an intensive cleaning lasting approximately 15 minutes, during which the part is dipped into a fresh, and material-appropriate, aqueous cleaning solution. For steel and other similar materials, an alkaline cleaning agent is recommended. When removing contamination from materials like aluminum and zinc, neutral or mild alkaline cleaning agents should be used.
2. Thorough rinsing with distilled water
Rinsing the reference part with distilled water removes the cleaning agent residues from the surface of the calibration sample. Residues from cleaning agents or residues of solvents fluoresce and cause a false calibration value.
3. Drying the calibration sample
The surface of the calibration sample is dried by hot air (hair dryer) in a dust-free environment.
4. Calibration of the SITA CleanoSpector on the calibration sample
The SITA CleanoSpector can internally save calibration values for up to 20 different part surfaces. These calibration values are assigned to the parameter “surface”. The calibration should take place on at least five different measurement points on the sample; this avoids accidentally calibrating the device on a selective spot of contamination. The number of calibration points can be adjusted in the device menu. For metallic surfaces, the measured calibration value should be above 3950. A detailed description of essential technical specifications can be found in the STIA CleanoSpector operating instructions.