The micro oxygen analyzer may also experience certain malfunctions during use due to environmental and operational issues, which may affect the normal use of the instrument. Therefore, special attention should be paid during use.
1. Pipeline material
Basically, copper or stainless steel pipelines are preferred, followed by polytetrafluoroethylene pipes. It is prohibited to choose pipes such as milk tubes and white tubes, as their airtightness and material impermeability are too poor, and the measurement error of trace oxygen is too large under standard measurement pressure. We usually choose a pipeline outer diameter of 6 millimeters or 1/4 inch, or 3 millimeters or 1/8 inch. In short, stainless steel pipes should be cleaned, degreased, and kept smooth and clean on the inner wall. For the analysis of trace level (<1PPMV) oxygen, stainless steel pipes with polished inner walls should be selected. The selected valves and fittings should have a minimum dead volume.
2. Sample
The moisture in the sample condenses and condenses on the pipe wall, causing the dissolution and absorption of trace oxygen. Insulation or heat tracing measures should be taken for the sampling pipeline according to the situation. When detecting trace amounts of oxygen in liquid nitrogen, special attention should be paid to heating measures. Otherwise, due to the boiling point of oxygen being 13 degrees lower than that of nitrogen, the sample gas will vaporize unevenly, resulting in significantly lower measurement values.
The sample gas should not contain oil components or solid particles to avoid membrane blockage and contamination.
The sample gas should not contain sulfides, phosphides, or acidic gas components. These components can pose a threat to fuel cells, especially alkaline fuel cells.
3. The supporting pipeline of the analyzer
The supporting pipelines of the analyzer should be sealed, as even small leaks can cause oxygen in the ambient air to diffuse in, resulting in higher measurement values.
Although the sample gas pressure is greater than the ambient pressure in the measurement, the oxygen in the sample gas is in trace amounts. According to Ferrari's law, the partial pressure of oxygen is proportional to its volume content. The atmosphere contains about 21% oxygen, which is about ten thousand times lower than the partial pressure of oxygen in the sample gas calculated in PPM. Therefore, the partial pressure of trace oxygen in the gas sample is much lower than that in the atmosphere. When a leak occurs, oxygen in the atmosphere will quickly diffuse from the leak site.
Also, the sampling pipeline should be as short as possible, with as few joints as possible, to ensure good sealing of joints and valves. After the pipeline is connected, an air tightness check should be conducted.
Requirements for air tightness inspection: Under a test pressure of 0.25MPAm for 30 minutes, the pressure drop should not exceed 0.01MPA.
4. Principles
The measuring position of the trace oxygen analyzer should be as close as possible to the measuring unit to avoid long pipelines and excessive uncertainties that may affect the reliability of the measurement data.