How does sample flow effect photometer response?
A reduction of the sample flow to a level below the lower tolerance limit, while using the internal reference settings for 100% levels, 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 (LSC) area of observation. The longer residence time of the aerosol results in a more conservative evaluation of the filter under test. An increase in sample flow, however uncommon, results in the opposite effect. A shorter residence time decreases the displayed leakage value and results in a liberal assessment of the filter performance and the potential for passing a “bad” filter. These effects are the reason for the ±10% limits paced upon the sample flow requirements in aerosol photometer testing protocols. If an actual upstream aerosol sample was being used to establish a 100% point, the units aerosol response is self correcting for the change in flow rate and standard unit le
