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PFP7/REV C/01-08
Section 8
Service Information
8.1
Sample system description
Figure 8.1.1
: Sample system
The sample is taken up by a concentric type nebuliser unit. Air, at a constant pressure, is
passed around the end of a small capillary tube forming a partial vacuum inside the capillary
tube and drawing sample into it via the nebuliser inlet tubing. The sample leaves the end of the
capillary as a fine aerosol. The volume and droplet size of the aerosol is controlled by varying
the position of the capillary tube and air jet with respect to each other. This adjustment is the
most important single factor affecting the linearity, stability and reproducibility of the instrument
and is factory set and sealed.
The aspirated sample is passed into the mixing chamber where the fuel gas is introduced. The
sample aerosol then strikes the PTFE impact bead which further breaks up any large particles in
the spray. The fuel/air/sample mixture is then swirled around two PTFE baffles. The majority of
sample strikes these baffles and runs out of the mixing chamber, via the drain trap to waste.
The remaining sample, consisting of only the smallest droplets mixed uniformly with the fuel,
reaches the modified Meker type burner where the mixture burns in a tall, round flame situated
in a double skin chimney.
Burner
Nebuliser
Fuel in
Drain
Air in
Restrictor screw
NB remove before using
natural gas
Capillary
Inlet tubing
Impact bead
Baffles
Burner
Nebuliser
Fuel in
Drain
Air in
Restrictor screw
NB remove before using
natural gas
Capillary
Inlet tubing
Impact bead
Baffles