Light scattering photometers are widely used for testing the efficiency or penetration of air filters, including respirator filters. A photometer measures light scattered from a cloud of particles that passes through a focused light beam. The signal from a photometer is a voltage that is proportional to particle concentration.
A typical photometer based filter testing system employs one or two photometers for sampling the challenge and filtered aerosol. In the TSI models 8130 and 8127 Automated Filter Testers, particle penetration through a filter is determined by dividing the downstream voltage by the upstream voltage. TSI’s photometers have recently been used in automated testing of filter cartridges with cycle times less than 10 seconds.
For a given particle size distribution, the response of a photometer is generally linear over a very large range of concentrations. Since filter testing is concerned with relative rather than absolute measurements, photometers do not necessarily need to be calibrated for the specific aerosol used. For high efficiency filters to have the most accurate penetration and efficiency measurements it is necessary for the photometers to have low background levels. The photometers described here, if used in a Model 8130 filter tester, can reliably measure filter efficiencies up to 99.9995%. The lower limit of concentration is limited by optical and electrical noise.
However, photometers and instrumentation that is used for detecting particles in air share a common issue in that some of the particles being detected do not pass cleanly through the optical system, instead ending up on the surfaces, e.g. the walls or lenses. As particles accumulate on internal surfaces they increase the background level until at some point the photometer must be returned to the manufacturer for cleaning.
This paper describes a new, user-serviceable photometer...
Session: G13 - Measurement Techniques
Day: 13 October 2016
Time: 10:45 - 12:00 h