Concept:

Gas samples destined for GC analysis often require heating to ensure heavier sample constituents are returned to the gas phase when captured in a cold metal sample cylinder. Without heating, heavier sample constituents will condense, or just adhere to the inside walls of the sample cylinder and not be vented out of the cylinder during the sample purge process. This results in the heavier constituents being underrepresented in the sample and subsequently underreported in the GC analysis.

Overview:

The SAS 100 is a heated sample oven plus a heated sample bridge that ports the sample purging from the sample cylinder to the GC. Note that the GC must have a heated gas sample valve (GSV) and that this GSV must be automated and under the control of the GC attached to the sampler.

The SAS 100 heats the sample cylinder, and its contents, to a user selected temperature, for a user selected duration, then purges the sample to the GC, then triggers the Remote Start on the GC. Additionally, if the GC is equipped with a split inlet that must be brought to ready, the Prep Run on the GC is triggered via cabling prior to sample purge, then the Remote Start input is triggered on the GC sending the GC into its analytical run. Signaling between the SAS and the GC is done by cables, not by software.

Method Execution:

The SAS 100 has an intelligent controller that controls temperatures, valve actuations such as purge flow and calibration blend port selection and signaling between the sampler and the GC. The sampler stores up to six “Methods” as well as the Standby Temperature. When the sampler is not in use the oven, and heated bridge to the GC, are maintained at the Standby Temperature.

When needed, the user places the sample cylinder in the SAS oven, makes the one connection to the tubing, and opens the hand valve on the sample cylinder. No sample flows from the sample cylinder as the flow valve is in the closed position. The sample lid is closed.

Next, at the touch screen, the user selects one of six methods that the user has predefined. Each method contains a Start Temperature, a Start Time, High Temperature, a High Temperature Hold Time, and a sample purge time, expressed in seconds. Each method has a number as well as a short user defined text that identifies the method for easy selection.

The user then keys Start, and the sampler heats the sample to the Start Temperature, and holds it there for the duration of the Start Time. At the end of the Start Time the sampler then heats the sample to the High Temperature and holds it there for the duration of the High Temperature Hold Time.

When the High Temperature Hold Time has elapsed, the sampler checks the status of GC Ready via cabling. If the GC shows ready then the sampler’s purge valve is opened letting the sample purge to the GC’s GSV; the purge time, in seconds, is part of the user defined Method. The sample purge stops, and time is given for the sample pressure in the GSV to equilibrate to atmospheric pressure. If the GC then requires a Prep Run signal, such as to shift from Gas Saver to Split Active mode, that signal is supplied and then the sampler waits for the next GC Ready indication. With the GC Ready indication, the GC is started on its analytical run via the remote Start signal. If the GC run time is programmed into the sampler method the sampler will provide an audible beep when the GC has finished its analytical run. Once the sample is purged to the GC, and the GC sent to run, the oven in the sampler will cool to the Start Temperature of the Method.

It should be noted a Method does not require a heating to High Temperature. A Method can be configured to simply hold at the Standy Temperature for some amount of time and then go to the sample purge routine. Also, the Start Time can be configured to zero so that the Method moves to High Temperature immediately upon Method start.

When a sample cylinder is heated, it typically takes about 15 minutes at temperature to come to thermal equilibrium.

A warning sign can be programmed into the controller to caution users when the sampler oven is above a user selected temperature.