Principles Of Operation; Definitions And Conversion Factors - Teledyne T640 Standard Operating Procedure

3.1 Principles of Operation

The Model T640 PM Mass Monitor is an optical aerosol spectrometer that converts optical
measurements to mass measurements by determining sampled particle size via scattered light at
the single particle level according to Lorenz-Mie Theory. Briefly, the sampling head draws in
ambient air, which are dried (i.e., brought below 35% RH) with the Aerosol Sample Conditioner
(ASC) and moved into the optical particle sensor where scattered light intensity is measured to
determine particle size diameter. The particles move separately into the T-aperture through an
optically differentiated measurement volume that is homogeneously illuminated with
polychromatic light. The polychromatic light source, an LED, combined with a 90° scattered
light detection, achieves a precise and unambiguous calibration curve in the Mie range,
resulting in a large size resolution.
Each particle generates a scattered light impulse that is detected at an 85° to 95° angle where
amplitude (height) and signal length are measured; the amplitude of the scattered light impulse
is directly related to the particle size diameter. The T-aperture and simultaneous signal length
measurements eliminate border zone error, which is characterized by the partial illumination of
particles at the border of the measurement range.
The T640 operates at 5.0 lpm with a TSP inlet. This configuration is approved as an FEM for
PM2.5; however, it also provides data (not approved as an FEM) for PM10 and PM10-2.5.
Sample volume is reported in actual conditions by using the instruments ambient temperature
and barometric sensor data. Specific component operation is described in Section 6 of the T640
User Manual, which can be found at
api.com/manuals/T640_User_Manual.pdf

4.0 DEFINITIONS AND CONVERSION FACTORS

PM2.5 is particulate matter with an aerodynamic diameter less than or equal to a nominal 2.5
µm.
Most technical terms in this SOP are defined as they are introduced. A few important definitions
are provided in Table 1.
http://www.teledyne-
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DEP 03-21
Revision No. 0
November 2017