SERVO
PRO NANOCHROME Gas Analyser
10
04416001A / Revision 7
1.3.2 Plasma Emission Detector (PED)
The plasma emission detector (PED) is based on a spectroscopic emission cell,
which is an established technique to measure impurities from the ppb to ppm
level. The characteristics which make the plasma system stable and selective are
the frequency, intensity, regulation, the coupling technique and the focusing
(stabilising) electrodes.
The carrier gas flows at atmospheric pressure through a proprietary pure quartz
cell. The cell is submitted to a high frequency high intensity electromagnetic
field. This ionizes the carrier gas which becomes the centre of a luminous
phenomenon (electroluminescence), a collection of charged particles called the
plasma.
Once the carrier gas is ionized many spectral lines are emitted. Excitation
results mostly from electron or ion collision; that is, the kinetic energy of
electrons or ions accelerated in an electric field in which the atoms or molecules
of a gas are subjected to, which cause the emission of light.
The presence of the impurities in the sample gas to be analysed will alter the
spectrum of emitted lines. Characteristic emission spectra can be obtained for
carrier gas and each substance in it.
1.3.3 Signal conditioning
The signal conditioning module offers very high gain with minimum drift and
noise. A special design low noise high stability analogue power supply is used.
The signal conditioning board can accept signals from up to 7 detectors. The
various signals can be monitored from the diagnostic menu. The signal
conditioning module has its own microcontroller to communicate with the main
PC.
1.3.4 Main PC and graphic display
The main PC board manages all User Interface I/O and sends the information to
the I/O board and the Signal Conditioning board via RS-485. The keypad and
colour graphic display are directly connected to it.
