Sampling and conditioning

What this track covers

Most analyser complaints are sample problems, not analyser problems. A perfect sensor reads a bad sample perfectly. This track follows the sample from the process to the sensor, in the order things happen.

It also says clearly which samples an analyser cannot take, so that you find out on paper rather than at commissioning.

Lessons, in order

1. How to design a gas sample handling systemA good sample handling system delivers a representative, clean, dry sample at constant pressure and flow.Intermediate4 min
2. Choosing the sample point for a gas analyserTake the sample where the gas is well mixed, at process conditions you understand, upstream of any air leak, away from dead zones, and with a tapping that cannot fill with liquid or dust.Intermediate4 min
3. Sample lines: materials, length, diameter and lagUse stainless steel tube for trace oxygen, moisture and reactive gases, because plastic lets oxygen and water in and out.Intermediate4 min
4. Filters for gas analysers: dust, mist, membraneUse filtration in stages: a coarse filter or probe filter near the tapping for bulk dust, a finer filter after the cooler, a coalescing filter to remove liquid mist and oil aerosol, and a membrane filter as a final guard.Intermediate3 min
5. Condensate, moisture and sample cooling for gas analysisWet samples must be cooled to a fixed, low dew point so that water leaves as condensate at a controlled place, not in the analyser.Intermediate3 min
6. Sample pressure, flow and fast bypass loopsAn analyser needs a steady sample at its specified pressure and flow.Intermediate3 min
7. Probes and blowback for hot, dusty and tarry gasHot, dusty or tarry gas needs a probe that survives the temperature, a filter at the tip that keeps dust out, and a way to clear the filter, usually automatic blowback with clean air or gas.Intermediate3 min
8. Sampling cryogenic and liquefied gases: vaporisersA liquid sample must be vaporised completely before it reaches an analyser.Intermediate3 min
9. What samples an analyser cannot take: know the limitsStandard ACCURRA-S analysers expect a non-corrosive, non-toxic, non-flammable, non-condensing and dry sample, free of oil, at 2 to 10 psig and about 1 LPM, with dust below 3 micron.Intermediate3 min
10. Sample system troubleshooting: symptoms to causesMost analyser faults are sample system faults.Intermediate3 min

Next track: Installation and integration