Analyser types which fall under the category of gas chromatographs (GC) can extend the ADI model further by defining Parameters and/or subtypes of ChromatographDeviceType, Accessory, AnalyserChannel and/or Stream.

In the simplest case, no subtypes of ChromatographDeviceType need to be defined and the Parameters can be exposed on existing ChromatographDeviceType Object or one of its components.

The following paragraphs provide an example of how a gas chromatograph device could extend the ADI Information Model by further refining definition of an Accessory and by defining new Parameters on ChromatographDeviceType.

The Figure 23 shows how a typical GC works:

Figure 23 – GC overview

• The sample is extracted from the process using a sampling system external to the GC itself. It is done in a way that minimizes the time between the sample extraction from the process and its injection into the separation column sets.
• Each separation column set is maintained at a precise temperature by an oven, and used to separate molecules of the sample based on their size and chemical Properties.
• The propagation time through a given set of columns for a given component, is based on its size and Properties and the column Properties.
• The detector at the end of a column set monitors the outlet stream from the column; It determines the amount of a given component at the outlet and the time it used to reach it. The resulting detector output is a XY plot of the detector level versus time, called chromatogram.
• A set of mathematical algorithms converts the chromatogram peaks into component concentration.