Principles Of Operation; Sampling System; Inlet - Teledyne T640 User Manual

6.

PRINCIPLES OF OPERATION

6.1.

SAMPLING SYSTEM

6.1.1.

INLET

08354A DCN7303
The Model T640 PM Mass Monitor is an optical aerosol spectrometer that
converts optical measurements to mass measurements with sharp accuracy 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 with different-sized particles,
which are dried 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 and signal length are measured; the amplitude (height) 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.
There are several components that are part of drawing in and measuring aerosol
samples: the inlet, the Aerosol Sample Conditioner (ASC), an optical particle
sensor, a flow sensor, and pump.
The inlet for the T640 is designed to allow complete transmission of all particle
sizes.
The US EPA PM10 inlet used for the 640X Option samples at 16.67-LPM to
mechanically size-cut the aerosol intake for sampling particles at 10 microns and
under.
Teledyne API Model T640 PM Mass Monitor 63