The vent line must be installed in a manner which will prevent dirt and water from accumulating within the line. It must return sample to atmospheric pressure. The vent line should be 1/4” diameter tubing or larger and be at least 24” long. This will help to prevent the back diffusion of O2 into the sample system.
3.5Sample System
The sample system used in the OT-3 Trace Oxygen Analyzer is a robust gas handling and conditioning system designed for low flow rate trace oxygen analysis in a natural gas or other low-oxygen gas environment. It uses stainless steel tubing and fittings throughout and a special 0-10 psig regulator designed to provide stable sample flow at low volumes over wide temperature extremes. The incoming sample gas is conditioned using a coalescing filter and an acid scrubber to remove moisture and contaminants which would otherwise interfere with the accurate trace analysis and/or reduce the lifetime of the sensor.
Refer to Figure 3-4 for the following discussion.
Note: Check the front of this manual for any additional information in the form of addenda that may apply to your custom system.
Sample gas enters the system at 5-2000 psig. A shut off valve is installed and is used to switch gas flow on or off. The sample gas is passed through a horizontal coalescing filter to remove moisture and debris. This filter is designed to handle inlet gas pressure up to 2000 psig. It is important to periodically drain the condensate by opening the drain valve. If appropriate, the drain line should be connected to a suitable receptacle for handling contaminated waste liquid.
A 0-10 psig pressure regulator is installed downstream from the filter and controls the sample pressure through the analyzer. In conjunction with the flowmeter, it provides a stable mass flow even at low volume over the rated temperature range of the instrument. Set the pressure regulator to provide a flow rate of 0.4 SCFH (approximately 4 psig).
A clear PVC acid gas scrubber is installed between the regulator and the sample/span gas selector switch. The clear housing permits a visual analysis regarding the condition of the scrubber medium and allows the user to predict service intervals.
A switching valve is provided to feed the analysis unit with either sample or span gas.
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