Specify an analyser

What you will be able to do

• Write a specification with the facts a supplier needs
• Decide how much accuracy the process really needs
• Choose between sensor technologies and between extractive and in-situ
• Check that the sample and the installation are covered
• Compare quotes on like-for-like terms

Follow these lessons in order

1. How to read a gas analyser datasheetRead a datasheet in four groups: what it measures (gas, range, minimum range), how well (accuracy, repeatability, drift, response), what it needs (sample conditions, power, utilities, ambient limits) and what it gives (outputs, approvals, options).Learn the vocabulary suppliers will use.Intermediate5 min
2. How to specify a gas analyser: A practical checklistA good specification states the question the number must answer, then the measurement (gas, range, accuracy, response), the sample (composition, pressure, temperature, dust, moisture), the site (area classification, ambient limits, utilities), the outputs and standards, and the support needed.The specification checklist.Intermediate4 min
3. What accuracy do you really need from a gas analyser?Start from the tolerance the process or product can bear, then build an error budget: sensor accuracy, calibration gas uncertainty, drift between calibrations, sample effects and pressure and temperature effects.Avoid paying for accuracy you cannot use.Intermediate4 min
4. 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.Match technology to gas.Beginner3 min
5. Extractive vs In-Situ gas analysisIn-situ analysers measure the gas where it flows, with no sample line, and suit hot, dusty ducts.Decide where the measurement happens.Beginner3 min
6. 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.A good analyser on a bad tapping reads badly.Intermediate4 min
7. 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.Find out the limits on paper.Intermediate3 min
8. Where to mount a gas analyser: panel, shelter or fieldMount an analyser as close to the sample point as practical, in a clean, temperature-stable, accessible place, out of vibration, direct sun and weather.Plan the installation.Beginner3 min
9. Analyser outputs: 4-20 mA, relays and Modbus explainedA 4-20 mA output sends the reading as a current, with 4 mA for the bottom of the range and 20 mA for the top; the live zero lets the system detect a broken wire.Plan the signals.Beginner3 min
10. Total cost of ownership of a gas analyserThe analyser is often a third or less of the cost of a working measurement.Count the whole cost.Intermediate3 min
11. How to compare gas analyser quotes like for likePut quotes side by side on the same scope: what is included in the sample system, what range and accuracy basis (span or reading), what response time and at what flow, certificates and documents, calibration gas and spares, commissioning and support, and what is excluded.Compare like with like.Intermediate3 min
12. Questions to ask a gas analyser supplier before you buyAsk about application experience on streams like yours, what the analyser cannot take, how the sample is handled, what certificates and documents come with it, how calibration works, what spares and service you can count on, and what the supplier does not claim.Choose a partner, not a box.Intermediate3 min

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