1-8
Model 3090/3090AK Engine Exhaust Particle Sizer
TM
Spectrometer
Particles then enter the sizing region through an annular gap, where they
meet a stream of particle free sheath air. The sizing region is formed by the
space between two concentric cylinders. The outer cylinder is built from a
stack of sensing electrode rings that are electrically insulated from each
other. The electrodes are connected to a very sensitive charge amplifier,
also called an electrometer, with an input near ground potential.
The inner cylinder is connected to a positive high voltage supply, which
forms the high voltage electrode. This creates an electric field between the
two cylinders. While the positive charged particles stream with the sheath
air from the top to the bottom of the sizing region, they are also repelled
from the high voltage electrode and travel towards the sensing electrodes.
Particles, which land on the sensing electrodes transfer their charge. The
generated current is amplified by the electrometers, digitized, and read by
a microcontroller. The data are processed in real time to obtain 10 particle
size distributions per second. The entire system is automated and data
analysis is performed using a computer system with customized EEPS
software. The software collects and stores sample data. Data is displayed
in graphs and tables and can be exported to other applications.
For information on the theory of instrument operation, refer to
Appendix B
.
