•Electropolished 316L-type stainless steel components.
To eliminate oxygen absorption and desorption from the internal wetted surfaces of the sample system components, the sample system is fabricated from electropolished 316L-type stainless steel.
•Welding/Metal Gasket-Type Fittings.
All of the joints upstream of the Micro-Fuel Cell oxygen sensor are orbitally welded. Orbital welding is used in the sample system wherever feasible. Orbital welding fuses the electropolished 316L stainless steel components together, forming a smooth, clean internal (wetted) weld junction and eliminating small spaces around the weld junction where gases can get trapped or absorbed. All of the weld junctions in the entire assembly are purged using an inert gas during welding to ensure that there is no oxygen contamination.
Orbital welding is used where practical; otherwise, conventional precision welding is used. For example, conventional precision welding is used to fuse the tubes to the mounting blocks.
•Valves.
The analyzer sampling system utilizes three different types of valves. Each valve is selected to prevent oxygen contamination of the sample depending on its position and purpose in the circuit.
Air-Actuated Bellows Valves: These valves are normally closed in the sample system. They are used to control the delivery through the sample system of the sample or zero gas. The valve bodies are orbitally welded in the system and the valve bonnets make a metal-to-metal seal to the body. This valve system eliminates inboard and outboard gas leakage. The valves are activated (open/closed) by computer-controlled solenoid valves.
Metering Valve: The metering valve is used to manually control the gas flow rate to the sensor. The body of the metering valve is orbitally welded, and the bonnet is sealed to the body with metal O-rings. This type of valve eliminates inboard and outboard gas leakage.
Solenoid Valves: The solenoid valves control the air flow to the air- activated bellows valves. The solenoid valves are controlled by the microprocessor module. When de-energized, the valve outlet is open to ambient air, allowing the air-activated bellows valve to close.
•Scrubber (optional). See Appendix for details.
In systems with a scrubber, oxygen-trapping media is used to remove any trace oxygen from the sample gas. This occurs automatically in the zero menu, where the pneumatic valves leading to the scrubber are triggered by a certain menu sequence. This process enables sample gas
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