How often does the PUF need changing, and how will that need manifest itself or influence readings?
PUF’s are generally only designed for fairly short sample durations, as they will suffer partial blockage over time. This will affect the size selectivity characteristics. Our advice to users is to change the PUF filter after every sample run, up to a full continuous 24-hour period. Little is presently known of how PUF loading affects the particle size selection characteristics, although tests have shown that the D50 (50th percentile) of the PUF will gradually decrease as the particulate loading increases. We therefore recommend that the PUF foams are not reused and are transported carefully.
