4-8 Electrostatic Classifier Model 3082 and SMPS Spectrometer Model 3938
Sheath Flow Loop
The sheath flow loop is a leak-tight, closed loop for moving and
recirculating DMA sheath flow. The sheath flow loop consists of the
following components:
Sheath Flow
Loop Component
Single pump for moving sheath flow and controlling flow rate.
Routes air between blower and HEPA filters.
Upstream and downstream of blower; maintains clean flow.
Prevents temperature rise of sheath flow due to blower.
Pressure and relative humidity of the sheath flow are
measured. These sensors are located on the Sensor PCB
which is mounted to the main flow manifold.
Thermal mass flowmeter to measure temperature and flow
rate and provide feedback to blower for flow control. Flow rate
is converted to volumetric with the inclusion of pressure
measurement from sheath flow pressure sensor. The
flowmeter includes the sheath flow temperature sensor.
Top and bottom (main) flow manifolds route flow between
sheath flow loop components and DMA.
Circuit Boards
There are three to four printed circuit boards (PCB) inside the classifier,
depending on instrument configuration:
Contains circuitry associated with communications, blower
control, fan control, etc. The microprocessor daughter board
and SD Flash memory card are also mounted to the
main PCB.
Mounted on the bottom flow manifold behind the HEPA filters.
The sheath pressure sensor, case temperature sensor, and
impactor differential pressure sensors are located on the top of
the Sensor PCB. The back of the sensor PCB makes an O-ring
seal with the flow manifold as the sheath relative humidity
sensor is mounted to the back of the PCB and is exposed to
the sheath flow path.
Contains circuitry associated with the touch-screen display.
Installed only in units with the dual-polarity option to facilitate
switching between polarities.
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