Root Causes of Factors Affecting the Measurement of Oxygen Detectors
During oxygen content analysis, especially trace oxygen analysis, the oxygen concentration in ambient air is as high as 21% O₂. Improper operation will easily cause contamination and interference to samples and lead to incorrect analytical results, mainly due to improper operation of oxygen detectors. Several major factors affecting measurement are discussed as follows:
① Simplification and cleanliness of the gas circuit system of the oxygen detector.
Trace analysis requires effective elimination of sample gas contamination caused by dead spaces in various pipe fittings, valves, gauge heads and other components on the gas circuit. Therefore, the gas circuit system shall be simplified as much as possible, and connectors with minimal dead volume shall be selected. Water seals, oil seals, wax seals and similar devices shall be avoided to prevent contamination from escaped dissolved oxygen. It is also prohibited to add easily contaminated purification equipment on the pipeline between the sample gas outlet and the inlet of the oxygen analyzer. Only in this way can a clean system and accurate measurement data be guaranteed.
② Contamination of the oxygen detector.
Before reusing the oxygen detector, check whether air enters during sampling pipeline connection. Any infiltrated air must be thoroughly purged. Excessive oxygen passing through the sensor shall be avoided to extend the sensor service life. To shorten pipeline purification time, alternating high-pressure venting and low-flow purging is commonly adopted for rapid pipeline cleaning.
③ Selection of pipeline materials.
Pipeline material and surface roughness will affect the oxygen content in sample gas. Plastic tubes, rubber hoses and similar pipelines are generally not recommended. Copper tubes or stainless steel tubes are commonly used. Electropolished stainless steel tubes are mandatory for ultra-trace analysis (<0.1 ppm).
④ Leakage issues of the oxygen detector.
Strict leak detection must be performed before the first use of the oxygen detector. Accurate measurement results can only be obtained when the oxygen analyzer is completely airtight. Poor sealing at joints, welding points, valves and other positions will cause back-permeation of atmospheric oxygen into pipelines and the analyzer, resulting in excessively high oxygen readings.
