Table of Contents
Advertisement
Chapter 3
Advanced software features: Vari-flow
Some materials, such as metal flakes, may form structures when they are circulated
through the flow cell at normal pump speeds. These structures cause a secondary
diffraction pattern that is incorrectly interpreted as a small peak at 1000 microns.
Vari-flow (accessed by selecting the Advanced button in the Sampler Settings
dialogue) allows these materials to be dispersed in the tank in the normal way. The
pump is then briefly turned off or its speed reduced before measurement of the
sample. When the pump is turned off, the structures in the sample are randomised
and the measurement can be made without the occurrence of the secondary dif-
fraction pattern.
When the flake material is suspended in a volatile solvent such as white spirit, vari-
flow is even more useful since it assists the rapid thermal stabilisation of the disper-
sant. When the sample tank is filled with fresh solvent, very high backgrounds are
often observed. These arise from thermal gradients in the solvent causing steering
of the laser beam onto the inner rings of the detector array. As the temperature
equilibrates, the background falls to normal levels (80-100) and measurement can
proceed. Pausing the pump after the solvent has had a chance to thoroughly dis-
perse through the system will accelerate the fall of the background to normal levels.
What is the sequence of events?
The Vari-flow cycle is as follows:
1.
Page 3-8
The pump is operated at normal speed (set in the SOP) for an initial period to
allow the dispersant to be thoroughly mixed and become thermally homoge-
nous. This initial period, the Dispersant equilibration period, can be set in
this dialogue:
Software features
MAN 0385
Hide quick links:
Advertisement
Table of Contents
