TSI Instruments 3775 User Manual

Technical Description 5-5
Currently, six CPCs (Models 3772, 3775, 3776, 3782, 3785, and
3786) are also commonly used with submicron size-distribution
measurement systems such as the Scanning Mobility Particle
Sizer
TM
(SMPS
TM
) Spectrometers (TSI Model 3936).
Design of the CPC
The basic instrument consists of three major subsystems: the
sensor, the microprocessor-based signal-processing electronics,
and the flow system. The sensor and the flow system are described
below.
Sensor
The sensor is made up of saturator, condenser, and optical
detector, shown schematically in
Figure 5-1. The sensor grows the
sampled aerosol particles into larger droplets and detects them
optically. The aerosol enters the saturator section and passes
through a heated, liquid-soaked cylindrical wick. To remain wetted,
the wick dips into the liquid reservoir and continually absorbs
liquid. The liquid butanol evaporates and saturates the aerosol
stream with butanol vapor. Butanol is replenished from a reservoir
and a fill bottle.
The vapor-saturated aerosol then passes into a vertical condenser
tube which is cooled by a thermoelectric device. The cooled vapor
becomes supersaturated and begins to condense on to the particles
(condensation nuclei) to form larger droplets. The droplets pass
from the condenser tube through a nozzle into the optical detector.
Liquid that condenses on the walls of the condenser tube runs back
down and is removed by the water removal system into the drain
bottle when the system is ON. Otherwise, the liquid goes back into
the saturator and is absorbed into the wick for reuse.
The sensor’s optical detector is comprised of a laser diode,
collimating lens, cylindrical lens, collection lenses, and photodiode
detector. The laser and collimating lens form a horizontal ribbon of
laser light above the aerosol exit nozzle. The collection lenses and
detector incorporate a pair of aspheric lenses that collect the light
scattered by the droplets at 90° angle (side scatter) and focus the
light onto a low-noise photodiode. The main beam is blocked by a
light-stop in the rear of the sensing chamber. A reference
photodiode is used to maintain constant laser power output. The
surface temperature of the optics housing is maintained at a higher
level than the saturator to avoid condensation on the lens surfaces.

TSI Instruments 3775 Specifications

General

Brand	TSI Instruments
Model	3775
Category	Laboratory Equipment
Language	English