An optical particle counting system has been developed for testing industrial pulse-cleaned cartridge dust collectors. The system is applied to measure fractional penetration of a full scale dust collector and to study its short term and long term dynamic behavior. Results show collector efficiencies for dust loadings of 23 g/m**3 exceeding 99. 999% over the particle size range from 0. 5 to 10 mu m, with a minimum fractional penetration occurring at approximately 2 mu m. The measurement system is shown to be capable of providing particle size and/or concentration measurements on time scales, ranging from 100 ms to many hours. Phenomena from details of individual cleaning pulses to overall collector life and efficiency are demonstrated.