What happens if the photometer sample flow drops below its normal operating range of 28.3 lpm +/- 2.8?
Reduction of the photometer sample flow to a level below the lower tolerance limit, while using the internal reference settings for the 100% level, results in an increased displayed leakage value. This higher value is the result of an increase in residence time of the aerosol passing through the light scattering chamber’s area of observation. The longer residence time of the aerosol results in a more conservative evaluation of the filter under test. If an actual upstream aerosol sample was being used to establish a 100% point, the unit’s aerosol response is self correcting for the decreased flow rate and standard accuracy conditions would be maintained.
