12
Exhaust
Mass Flow Controller
Cyclone
Filter
Inlet
Vacuum
Pump
“Vac”
Pressure
Transducer
Tap
2.5.1
Cyclone and Inlet
The ambient air enters through a screened inlet on top of the stack. The screened inlet removes bugs,
rain, and particles larger than approximately 15 µm. The air stream then passes through a cyclone that
removes particles larger than 2.5 µm. The cyclone is located inside the module, as shown on the
previous page. The cyclone is 50% efficient at removing particles with aerodynamic diameters larger
than 2.5 m at the nominal flow rate of 22.0 Lpm. It is volumetric flow controlled using a mass flow
controller and corrections are made for temperature and barometric pressure variations. A temperature
probe is inserted in the inlet tee of the Module C. The temperature probe is situated in the air stream just
prior to the cyclone. The temperature is measured and the average temperature is recorded on the
CompactFlash memory card.
μ
2.5.2 Mass
Flow
Controller
The Mass Flow Controller is used to maintain a constant flow rate during a sampling period. It is located
within the Pump Enclosure, near the base of the stand. For service/removal instructions, see Section 9.5.
2.5.3
Filter Cassettes and Cartridges
The filter cassettes and cartridges are manufactured specifically for the URG-3000N sampler. They are
made of acetyl homopolymer with stainless steel screens. The two halves of the cassette snap together
and are sealed with an o-ring. A special tool is required to separate and assemble the two halves. The
individual cassettes are always installed in cartridges, with four cassettes per cartridge. Most cassettes
are secured in the cartridges by a snap ring and cannot be removed easily. Each cartridge has a center
hole and a small alignment hole. When the cartridge is placed on the cyclone manifold, alignment pins on
the manifold prevent the cartridge from being installed incorrectly.
