Instruction manual

Instruction Manual
760006-A
September 2001
2-8 Installation Rosemount Analytical Inc. A Division of Emerson Process Management
Model NGA 2000 Platform
application and the preferences of the individual
user.
Typical sample handling systems incorporate
such components as pumps, valves, needle
valves, flowmeters and filters in order to provide
a clean, dry sample to the Analyzer module.
There are some general sample handling issues
that must be addressed. It must be possible to
control the sample flow into the Analyzers, and
also this flow must in general not be made to
pass through Analyzers in succession, but
rather through them in parallel. The Analyzer
reading is sensitive to sample pressure
changes, so care must be taken to make sure
that such changes do not occur, and that the
span gas pressure is the same as the sample
pressure.
Excessive sample flow can destroy the flow
sensor within the Analyzer module; bring the
flow up from zero, rather than down from wide
open when starting them up.
Solenoid valves used for zero and span gas
control are prone to leaking. If they do so it will
be impossible to get good readings from the
system.
Sample systems must be designed to make it
impossible for water to get into the Analyzer.
Heated sample lines should be heated the en-
tire length, and care must be taken to make
sure that any water dropped out is drained from
the sample line. Unheated lines must slope
down to the Analyzer - water will collect in the
low points and be subsequently entrained in the
sample. The same is true of exhaust lines -
particularly for the FID Analyzers. It must be
impossible for condensate to freeze or flow back
into the Analyzer, or provide a slug of water
whose effect will be to provide pressure
changes as the bubbles go through it.
There are many such issues. Sample system
design is rather an arcane skill, and it is worth
having an experienced person or company de-
sign such a system. Most Analyzer problems
are in fact sample handling system problems.