Aerosol Photometer
Aerosol Photometer - 2i 18
How the Photometer Operates
Theory of Operation
When air or gas is drawn through the instrument,
particulate matter in the sample passes through the
focal point of the scattering chamber. Particulate
matter scatters light into the dark cone and onto the
photomultiplier tube, which converts the light into an
electrical signal. The signal is amplified and digitized,
then analyzed by a microprocessor to determine the
intensity of the light scattered by the signal. This
signal is then compared to a reference signal to
provide an output that is normalized by the reference
signal.
A photometer is ideally suited to detect particulate
matter in air or gas, reporting the mass concentrations
encountered on a display. Particles from less than
0.1 micron to approximately 600 microns can be
detected by the 2i. Since the photometer reports
concentration of particulate matter, many applications
are possible. By using a baseline of 100 micrograms
per liter of aerosol, it is possible to directly read the
concentrations of aerosols.
Sampling System
A vacuum pump in conjunction with a flow meter,
onboard sensors and closed feedback loop provides a
constant volumetric sample flow rate of 1 cfm (28.3
liters per minute). The 2i uses an oil-free, dual head,
diaphragm pump with a direct-coupled DC motor.
Solenoid actuated valving directs the airflow through
the sampling system to the scattering chamber from
three possible sources. The CLEAR position directs
clean air from an internal ULPA filter to the scattering
chamber for zeroing the instrument. The
UPSTREAM position permits sampling of the air
above the filter being challenged, and the
DOWNSTREAM position permits sampling of the air
that penetrates the filter.
Light Scattering Chamber (LSC)
The scattering chamber is not only an integral part of
the sampling system; it is a major component in itself.
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