Teledyne GC-Pro/FID - Gas Chromatograph - Manual (Page 22)

Operational Theory GC-Pro FID
Teledyne Analytical Instruments 8
2.2 Modes of Operation
The analyzer has 2 modes of operation depending on the position of
the GC Sampling Valve (See Piping Diagram in Figure 2-2). They are:
Sample Mode (position A) and Analysis Mode (position B).
1. Valve Position A—Sampling Mode
In this mode the analyzer configures the operational valve to
back flush the column and charge the sample loop. The Sample
Mode is programmed to continue for a 7 minute period by
factory default; however, it is usually modified to match the
needs of a particular process. The specific timing interval for
your system is listed in the Addendum and Testing Results
section of Appendix C. It is possible to set the Sample Mode
duration up to 25 minutes.
2. Valve Position B—Analysis Mode
In this mode the analyzer configures the sampling valve to feed
the gas in the sample loop through the column and to the
detector. The eluted sample from the column is fed to the FID
for the analysis of the compound of interest in the hydrocarbon
stream. If configured to do so, the analyzer may read the detector
for a programmed 5 second period at some point within this
mode cycle to obtain a baseline reading for further calculation.
This mode is usually programmed to continue until the
compound of interest is fully eluted from the column. It is
possible to set it up to 25 minutes.
During the Analysis Mode, a ‘Peak Detect’ period is programmed at
which time the analyzer reads the detector output. The analyzer
integrates the peak area during this time in conjunction with the baseline
settings to calculate the concentration of the compound of interest. The
calculation is performed at the end of the ‘Peak Detector’ period and the
result is displayed at the end of Analysis Mode.
2.3 Analyzer Subsystems
The Model Analyzer is composed of three subsystems:
1. Sample System
2. Detector Cell
3. Electronic Signal Processing, Display and Control