Measurement principles

What this track covers

No single sensor suits every gas. This track explains each principle in plain terms, compares them fairly, and then goes gas by gas so you can pick the right method for oxygen, hydrogen, carbon monoxide, carbon dioxide, methane and moisture.

It ends with the choice every project faces: sample the gas and analyse it outside the pipe, or measure in place.

Lessons, in order

1. Gas analysis technologies compared: which sensor for which gasEach gas analysis technology works only on gases with the right physical property: electrochemical and paramagnetic sensors for oxygen, zirconia for hot oxygen, NDIR for gases that absorb infrared (CO, CO2, methane), thermal conductivity for binary mixtures such as hydrogen in nitrogen, ceramic or chilled-mirror sensors for moisture.Beginner3 min
2. Electrochemical vs paramagnetic oxygen sensorsElectrochemical oxygen cells suit ppm and percent oxygen, are compact, and are consumed over time.Intermediate4 min
3. How a zirconia oxygen analyser worksA zirconia analyser measures oxygen with a heated ceramic cell.Intermediate4 min
4. What is an NDIR gas analyser?An NDIR (non-dispersive infrared) analyser shines infrared light through a sample and measures how much a target gas absorbs.Beginner4 min
5. How thermal conductivity gas analysers (TCD) workA thermal conductivity analyser heats a small element and measures how quickly the surrounding gas carries heat away.Intermediate4 min
6. What is dew point and how is it measured?Dew point is the temperature at which moisture in a gas begins to condense.Beginner4 min
7. Moisture measurement methods compared for dry gasOnline dry-gas moisture is usually measured with a ceramic or capacitive sensor that responds to adsorbed water.Intermediate3 min
8. Cross-Sensitivity and interference in gas analysersCross-sensitivity is a sensor's response to gases other than its target.Intermediate3 min
9. Trace oxygen measurement and air ingress: ppm done rightAir is 209,500 ppm oxygen, so a leak of just 0.01 % air adds about 21 ppm to a sample.Intermediate4 min
10. Measuring hydrogen: purity, mixtures and safety limitsHydrogen purity and hydrogen in nitrogen or argon are measured by thermal conductivity, because hydrogen conducts heat about seven times better than most gases.Intermediate3 min
11. Measuring carbon monoxide and carbon dioxide onlineCarbon dioxide is measured by NDIR over ppm to 100 % ranges.Intermediate3 min
12. Measuring methane and biogas composition onlineMethane and CO2 in biogas are measured by NDIR, separately or in one dual-channel analyser, and oxygen is measured to show air ingress.Intermediate3 min
13. Extractive vs In-Situ gas analysisIn-situ analysers measure the gas where it flows, with no sample line, and suit hot, dusty ducts.Beginner3 min
14. Choosing an oxygen analyser: trace, percent or purityChoose by range.Beginner3 min
15. Why ambient pressure affects oxygen purity readingsMany oxygen sensors respond to the partial pressure of oxygen, which falls when barometric pressure falls even if the gas is unchanged.Intermediate4 min

Next track: Sampling and conditioning