Teledyne GC-Pro/TCD - Gas Chromatograph - Manual (Page 17)

GC-Pro TCD Introduction
Teledyne Analytical Instruments 3
1.2 Principle of Operation
The analyzer uses a sample valve which is a specialized electronic-
controlled valve responsible for extracting a precise volume of sample
and delivering it to the separation column. This valve uses four micro
cavities and rotates between two positions in a timed fashion controlled
by the timing function in the control section.
The gas separation column separates the component of interest in the
sample gas based on its retention time in the packed column. Using a
carrier gas and a microprocessor actuated switching valve, the eluted gas
is analyzed using a Thermal Conductivity Detector (TCD). After each
injection cycle the column is back flushed to accept the fresh sample in
the next cycle. The result is a series of peaks over time corresponding to
the detector output for each sample cycle. The integrated area under the
peak is directly related to concentration and after signal processing, this
result is displayed in the appropriate units on the screen. The screen is
updated after each cycle.
1.3 Analyzer Description
The standard analyzer is a rack mountable instrument designed to fit
into a standard 19” instrument rack. The front interface screen is
mounted on the left side of the panel. The right side of the panel
includes the gas controls, pressure gauges and flowmeter. The front
panel is shown in Figure 1-1.