Ecotech HiVol 3000

HiVol 3000 User manual 1.7 Introduction
7
1.4.3.1 Total Suspended Particulate (TSP) Sampling
TSP is the suspended particle fraction in the atmosphere that includes
particle sizes up to around 50µm diameter. Due to the simple inlet shape of
the TSP sampler the particle cut-point is not precise and may be influenced
by wind speed, wind direction and sampler flow-rates. The TSP inlet will
prevent unusually large particles and insects being collected on the filter.
Figure 1 Inlet hoods for HiVol
1.4.3.2 Size Selective Inlets: Sampling at PM
10
and PM
2.5
Ambient air is drawn into the size-selective inlet at a constant volumetric
flow-rate of 1.13m
3
/min (67.8m
3
/h) for both the PM
10
and PM
2.5
inlets. To
achieve this, the HiVol 3000 uses a true volumetric flow-rate controller (via
temperature and pressure compensation of a mass flow sensor.)
The size-selective inlet is of the impactor type. The particles in the air are
accelerated through multiple acceleration nozzles. Particles larger than the
specified 2.5 or 10 µm cut-point gain sufficient momentum to cause
impaction onto a greased collection shim where they are trapped. (The
collection shim should be periodically cleaned and re-greased.) The PM
10
or
PM
2.5
particles, however, are smaller and having less momentum, remain
entrained in the air-flow and pass to the filter, where they are collected.
The SSI cut-point is affected by airstream velocity / flow-rate, acceleration
nozzle diameter, and particle density, composition and shape.
The symmetrical design of the SSI overcomes the effect of wind direction
and the inlet design makes the collection efficiency independent of wind
speeds up to 36 kilometres per hour.