--- title: Learning Path: Specify a Gas Analyser | Sarvesh url: https://www.sarveshanalytics.com/learn/path-specify-an-analyser.html description: An eleven-lesson path for engineers writing a specification: datasheets, accuracy, technology choice, sampling, mounting, signals, cost and supplier questions. updated: 2026-11-03 source: html --- Learn ยท Learning path # Specify an analyser From a blank page to a specification any supplier can quote against. 12 lessons About 41 min For: Process, instrumentation and procurement engineers writing or reviewing a specification ## 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 datasheet** Read 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. Intermediate*5 min*](https://www.sarveshanalytics.com/learn/reading-a-gas-analyser-datasheet.html) 2. [ **How to specify a gas analyser: A practical checklist** A 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. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/how-to-specify-a-gas-analyser.html) 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. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/what-accuracy-do-you-really-need.html) 4. [ **Gas analysis technologies compared: which sensor for which gas** Each 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. Beginner*3 min*](https://www.sarveshanalytics.com/learn/gas-analysis-technologies-compared.html) 5. [ **Extractive vs In-Situ gas analysis** In-situ analysers measure the gas where it flows, with no sample line, and suit hot, dusty ducts. Decide where the measurement happens. Beginner*3 min*](https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html) 6. [ **Choosing the sample point for a gas analyser** Take 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. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html) 7. [ **What samples an analyser cannot take: know the limits** Standard 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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html) 8. [ **Where to mount a gas analyser: panel, shelter or field** Mount 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. Beginner*3 min*](https://www.sarveshanalytics.com/learn/where-to-mount-a-gas-analyser.html) 9. [ **Analyser outputs: 4-20 mA, relays and Modbus explained** A 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. Beginner*3 min*](https://www.sarveshanalytics.com/learn/analyser-outputs-4-20-ma-relays-and-modbus.html) 10. [ **Total cost of ownership of a gas analyser** The analyser is often a third or less of the cost of a working measurement. Count the whole cost. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/total-cost-of-ownership-of-a-gas-analyser.html) 11. [ **How to compare gas analyser quotes like for like** Put 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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/comparing-gas-analyser-quotes.html) 12. [ **Questions to ask a gas analyser supplier before you buy** Ask 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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/questions-to-ask-a-gas-analyser-supplier.html) Stuck on a real problem while you learn? [Ask an engineer](https://www.sarveshanalytics.com/contact.html#enquiry). Every lesson is checked against the figures in our catalogues.