Controlled current source of constant light intensity for particle size analyzer

摘要

It is often necessary in instruments using light source that the intensity of the light output remains constant throughout the measurement. To obtain constant light output, conventional techniques pass a constant current through the lamp. These techniques use either discrete components or 3-terminal regulator integrated circuits to meet the constant current requirements for the lamp. However, this method does not maintain the light intensity constant for unclean glass envelope, for browning of the lamp envelope due to carbon deposition, etc. It also does not correct for the aging of the lamp and the filament characteristics. A controlled current source for constant intensity light output has been developed for an instrument designed for measurement of particle size distribution of fine powders suspended in a liquid medium, The instrument uses Stokes' law sedimentation with light extinction method for measurement of particle size distribution. To obtain accurate and reproducible results, it is essential that the light intensity of the lamp remains highly stable.