Design a sample system

What you will be able to do

• Choose a representative sample point
• Size tubing, flow and lag time
• Select filters, coolers and probes for the sample
• Keep condensate and dust out of the analyser
• Know which samples are out of scope

Follow these 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.The overview.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.Where to tap.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.Tubing and time delay.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.Dust and mist.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.Water in the sample.Intermediate3 min
6. Sample pressure, flow and fast bypass loopsAn analyser needs a steady sample at its specified pressure and flow.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.Hard samples.Intermediate3 min
8. Sampling cryogenic and liquefied gases: vaporisersA liquid sample must be vaporised completely before it reaches an analyser.Very cold samples.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.The limits.Intermediate3 min
10. Sample system troubleshooting: symptoms to causesMost analyser faults are sample system faults.When it goes wrong.Intermediate3 min

Stuck on a real problem while you learn? Ask an engineer. Every lesson is checked against the figures in our catalogues.