| OCR Text |
Show ii) Velocity Discrimination The signals from the photodetector of the system contain all the information about the velocity and size of the particles. The signal processing system can only however, give one the information on the velocities of these particles without distinguishing whether they represent the gas phase or, either one of the two distinct particle groups in the solid phase. A flourescence-dye technique is to be employed to permit discrimination between the two phases and also between the solid phase particles in the flow. The principle of the technique is as follows. The flourescence emission from Rhodamine 6G dye is at wavelenghts longer than the Argon-ion laser wavelength, Fig. 7. If one of the particle groups, for example wood particles, is dyed with Rhadamine 6G, the photodetector, Fig. 8, will detect both direct scattered light from the tracer and sand particles along with the flourescent emission from wood particles. The scattered light from undyed particles is eliminated by placing an optical filter between the receiving assembly and photodetector pinhole which blocks the scattered light at the laser wavelength but allows the longer wavelength signals from the flourescent particles to enter the photomultiplier tube. Thus, only the velocity information will be detected from one group of particles although the other solids are actually present in the flow. Other particle types can be dyed in order to measure their velocities in the presence of all the other undyed particles. 2.3.11 |
