|Home | Products | Contact/Order | Mail List ||
|FL5000 > Performance with Magnetic Particles > Particle Test Procedure|
This page describes the measurement procedure used to quantify the performance of the BlueLine NDT FL5000 inspection light with various fluorescent magnetic particles. The measurement procedure addresses both the fluorescence excitation and emission.
Excitation - These measurements determine how efficiently energy is transferred from the light to the particles.
Interpreting the results:
Emission - this addresses how the fluorescence emission observed with blue light excitation compares with emission observed with ultraviolet light excitation.
In general, the fluorescence emission spectrum of any material is independent of the wavelength of light that stimulated the fluorescence. This is only true when there is a single fluorescing pigment present. If a mixture of pigments contributes to the fluorescence, their excitation spectra are likely to be different, so putting in light at different wavelengths may excite the pigments by different amounts. The measurements in steps 1 and 2 determine if this is occurring, so we can report this to users.
Step 3 above is necessary to ensure that the fluorescence emission is not being significantly reduced in its passage through the yellow filter glasses. The yellow filter material has been carefully selected to block the reflected blue light effectively while transmitting fluorescence with high efficiency, but this needs to be verified for each particle before BlueLine will certify its suitability for use with the blue light inspection system. (While it is possible that there are other yellow glasses out there that may work with the BlueLine lights, we can only certify the glasses that we supply.)
Before and after each set of excitation measurements we measure the excitation spectrum for a particular particle that has broad excitation through the ultraviolet and blue range. This provides a repeatability check to ensure that the spectrofluorometer is providing consistent results. We also measure the spectrum of the laboratory room fluorescent lights. Low pressure mercury vapor lamps have well known spectral lines, so this provides a check of the wavelength calibration of the instrument.
For each particle being tested we measure the excitation spectrum three times, using a separate sample from the particle batch for each measurement. If there are significant differences between the measurements this is indicative of a problem either with the instrument or with the particle batch, and this measurement set is not used. We then measure the background signal by directing the measurement probe at a non-fluorescent surface. In post-processing the background signal is subtracted from each of the excitation spectrum measurements and the results are then normalized and averaged. The resulting corrected excitation spectrum is what is used for the calculations described above.