Gas Sensors Sampling
Particulates and Cut-Point
EVM Series User Manual
Particulates and Cut-Point
In consideration of how the size of particulates affect the human body, it is important to select a
particulate size cut-point. Essentially, the particle size selector on the EVM is a top-mounted rotary
impactor. Based on your setting, it will filter out all particulates at or above the selected size. The
instrument has four settings which include 2.5 ฮผm, 4 ฮผm, 10 ฮผm, or none (100 ฮผm). (This is explained in
more detail in Chapter 4.)
Collecting/Sensing the Particulates
Once the impactor setting is selected, the EVM collects (or measures) real-time aerosol/dust
concentration using a 90ยบ optical light scattering photometer to determine the total mass concentration
(in units of mg / m
3
) of particulate matter. Additionally, gravimetric sampling, a more accurate method, is
also used to determine the mass of particulates.
Gravimetric Sampling
Gravimetric sampling is a type of filtering process in which the
particulates are collected and filtered into the gravimetric
cassette after the dust passes through the optical engine of the
EVM. A user supplied sealed gravimetric cassette can be used
in place of the cassette provided by TSI. The sealed cassette
can be sent to a laboratory for analysis. This testing is typically
used to measure personal exposure to inhalable dust
concentrations.
Pump
The pump is used in the particulate sampling process as a source of air movement so the particulates
are aspirated (or suctioned out) and collected for measurement. The flow rate is 1.67 Liter per minute.
The pump is typically calibrated before each gravimetric sampling.
Gas Sensors Sampling
The EVM uses a unique smart sensor technology includes automatic sensor recognition and measures
up to three gases simultaneously: a selection of optional nine toxic gases, Carbon Dioxide, combustible
gases, and VOCs.
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