Specifications

748414-A
August 1999
6
Heated Flame Ionization Detector Analyzer Module
Rosemount Analytical NGA 2000
2
INSTALLATION
2.4 GASES
2.4.1 O
VERVIEW
During normal operation, the Analyzer Module requires fuel and air to maintain the burner
flame as well as suitable standard gases for calibration and instrument air for purge
requirements. In addition, instrument air for regulated air in is required to control the sample
pressure at the sample capillary. Criteria for selection of these gases follow in section 2.4.3.
After initial startup or after startup following a prolonged shutdown, the analyzer may display
baseline drift for a considerable period of time, particularly on the most sensitive range.
Commonly, the drift is caused by small amounts of hydrocarbons in the inner walls of the
tubing in both the internal flow system and the external gas supply system. Drift results from
any factor influencing the equilibrium of these absorbed hydrocarbons, such as temperature
or pressure.
Note that this type of drift occurs only when the flame is burning. If drift occurs when the
flame is extinguished, the electronic circuitry is at fault. To minimize drift, use clean fuel and
air, keep the analyzer clean, and locate the gas cylinders in an area of relatively constant
ambient temperature.
The cylinders supplying all gases each should be equipped with a clean, hydrocarbon-free,
two-stage regulator and a shutoff valve.
All new external gas tubing (except for PURGE IN/OUT and SAMPLE BYPASS) is strongly
recommended, preferably pre-cleaned, stainless steel, gas chromatograph-grade tubing.
Thoroughly clean before use (if a hydrocarbon-based cleaning solvent such as acetone is
used, purge tubing with dry nitrogen or helium for several minutes before using.)
Gas line connections are compression fittings. Do not use pipe thread tape.
Since the oxidation of hydrogen is accompanied by the formation of water vapor, the
Exhaust tubing always should be slanted downward at least 6 degrees from horizontal.
Otherwise, water may accumulate in the line, causing back pressure and noisy readings, or
may back up in the line and flood the burner. Depending on the percent of water vapor in
the sample, the sample bypass out connection may have condensation. Proper drainage
may be required.
If the sample is toxic or noxious, or is to be reclaimed, connect the Bypass outlet to a
suitable disposal system. Do not use any device that may cause back pressure in the line.
Purge air and burner air should be supplied from separate sources.