TSI Incorporated PORTACOUNT PRO+ 8038, Operation And Service Manual

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Theory of Operation 83
The PortaCount Pro sensor consists of a saturator, condenser, and
optical elements. The saturator is lined with an alcohol-soaked wick.
A thermoelectric device is mounted between the saturator and
condenser which cools the condenser and heats the saturator. After
passing through the saturator, the aerosol (now saturated with alcohol
vapor) enters the condenser tube. The alcohol vapor condenses on
the particles, causing them to grow into droplets. The droplets then
pass through the nozzle and into the sensing volume as depicted in
the schematic diagram below.
The focusing optics in the sensor consists of a laser diode and a
series of lenses that focus the laser light into a sensing volume just
above the nozzle. Each particle passing through the sensing volume
scatters light. The light is collected by the receiving optics and
focused onto a photodetector. The photodetector generates an
electrical pulse from the scattered light as each droplet passes
through the sensing volume. The particle count is determined by
counting the number of pulses generated during a given time period.
Knowing the particle count, time period and flow rate allows particle
concentration to be computed.