Thermo Scientific 5028i Instruction Manual page 31

Introduction
Principle of Operation
A clean filter spot is introduced by an automatic filter change to the
combined sampling and detection chamber at least every 24 hours,
usually centered at midnight. However, the official filter tape change
frequency for U.S. EPA testing for both PM and PM is every 8
2.5 10
hours. The automatic filter changes are controlled by the instrument
firmware which halts the 3-way valves operation, lowers the vacuum
chamber plate, advances the filter tape a fixed length, raises the vacuum
chamber plate, and initiates the 3-way valve of the channel operation
and a zeroing of the sample spot. Immediately after a filter change, a
new measurement cycle is initiated with an automatic zero adjustment
of the mass signal. The filter change interval and time of day can be user
adjusted. Additionally, automatic filter changes will occur if the mass on
the filter exceeds 1,500 µg since the last filter change or if the flow rate
through the filter tape is reduced by more than 5% due to potentially
restrictive particle deposition.
An example for sampler configuration, Channel A (Channel 1) of
Model 5028i is used to measure PM concentration with the specified
2.5
10-micron EPA PM inlet, ambient air is drawn into the 10 micron
10
(µm) size selective inlet which discriminates against particles with an
equivalent aerodynamic diameter above 10 µm. It has been approved
previously through prior U.S. EPA designations (RFPS-0699-130, 131,
and 132) and is also listed within 40 CFR Part 50, Appendix L as a
10-MICRON INLET (including model SA246b). PM BGI Inc. Very
2.5
Sharp Cut Cyclone (VSCC™) particle size separator is using for PM
2.5
selection. Meanwhile, Channel B (Channel 2) of Model 5028i use to
measure PM concentration only with the specified 10-micron EPA
10
PM inlet.
10
The volumetric flow rate at both inlet entrances are 16.67 liters per
3
minute (1 m /hour). In addition, the ambient temperature and relative
humidity is measured via a naturally aspirated radiation shield and
standard sensor as part of the volumetric flow control and dynamic
heating system.
Note Further particle discrimination would be achieved by inserting
a PM or PM cyclone between the 10-micron inlet and sample tube.
2.5 1
TSP inlets and European-style inlets are also available with the 5028i.
s
The ambient particulate is then drawn down a vertically mounted
heated sample tube on each channel. The heat applied to the sampe
is adjustable to either a fixed temperature or a RH-threshold at the
filter spot by independent controlling for each channel. The purpose
of heating the sample is to reduce particle bound water and to decrease
the relative humidity (RH) of the sample stream. This is done to reduce
positive artifact measurement that can potentially occur as a result of
condensation on the filter tape or conditions of elevated humidity. The
heaters are controlled by the CPU and the power applied is proportional
to the conditions.
Thermo Fisher Scientific Model 5028i Instruction Manual 1-5