--- title: Learn Gas Analysis: Lessons, Calculators, Glossary | Sarvesh url: https://www.sarveshanalytics.com/learn/index.html description: 75 free lessons, 7 calculators and a 170-term glossary on online gas analysers, sampling, calibration, hazardous areas and buying, from Sarvesh Analytics. updated: 2026-11-03 source: html --- Learn # The practical guide to online gas analysis and sampling. 75 lessons, 7 calculators and a 170-term glossary, written by the engineers who build the analysers. Start with a learning path, browse by track, or search for the question you have. Start here ## Pick the path that matches your job. Each path is a short, ordered set of lessons with the reason for every step. [ 10 lessons · 32 min ### New to gas analysis Engineers, buyers and students meeting process gas analysis for the first time Start this path ](https://www.sarveshanalytics.com/learn/path-new-to-gas-analysis.html)[ 12 lessons · 41 min ### Specify an analyser Process, instrumentation and procurement engineers writing or reviewing a specification Start this path ](https://www.sarveshanalytics.com/learn/path-specify-an-analyser.html)[ 9 lessons · 28 min ### Keep analysers running Instrument technicians, maintenance planners and plant operators Start this path ](https://www.sarveshanalytics.com/learn/path-keep-analysers-running.html)[ 8 lessons · 25 min ### Safety and hazardous areas Safety engineers, project engineers and anyone installing analysers where gas can burn or explode Start this path ](https://www.sarveshanalytics.com/learn/path-safety-and-hazardous-areas.html)[ 10 lessons · 33 min ### Design a sample system Instrument and process engineers designing or fixing a sample line Start this path ](https://www.sarveshanalytics.com/learn/path-design-a-sample-system.html) Browse by track ## Eight topics, from first principles to the purchase order. From what a number on an analyser means, to the sample system that feeds it, to how it is certified, run and bought. [ Track 1 · 9 lessons ### Foundations What a number on an analyser really means: units, gas behaviour, accuracy and speed. Open the track ](https://www.sarveshanalytics.com/learn/track-foundations.html)[ Track 2 · 15 lessons ### Measurement principles How each technology works, where it fails, and how each common gas is measured. Open the track ](https://www.sarveshanalytics.com/learn/track-measurement-principles.html)[ Track 3 · 10 lessons ### Sampling and conditioning Getting a representative, clean, dry sample to the analyser, which decides most field problems. Open the track ](https://www.sarveshanalytics.com/learn/track-sampling.html)[ Track 4 · 6 lessons ### Installation and integration Mounting, signals, wiring, control-system integration and commissioning. Open the track ](https://www.sarveshanalytics.com/learn/track-installation.html)[ Track 5 · 8 lessons ### Calibration and maintenance Keeping the reading true: calibration, validation, troubleshooting, spares and records. Open the track ](https://www.sarveshanalytics.com/learn/track-calibration-and-maintenance.html)[ Track 6 · 8 lessons ### Safety and hazardous areas Flammability, inerting, hazardous areas, protection concepts, SIL and oxygen hazards. Open the track ](https://www.sarveshanalytics.com/learn/track-safety.html)[ Track 7 · 13 lessons ### Process primers How real processes use gas analysis, from boilers to biogas to glove boxes. Open the track ](https://www.sarveshanalytics.com/learn/track-process-primers.html)[ Track 8 · 6 lessons ### Choosing and buying Specifying, accuracy needs, total cost, comparing quotes and supplier questions. Open the track ](https://www.sarveshanalytics.com/learn/track-choosing-and-buying.html) Calculators ## Do the arithmetic without the spreadsheet. Each one states its formula and its assumptions. [ ### ppm to mg/m3 and percent gas converter Percent, ppm and ppb are volume fractions: 1 % equals 10,000 ppm and 1 ppm equals 1000 ppb. Open ](https://www.sarveshanalytics.com/calculators/unit-converter-ppm-percent-mg-per-m3.html)[ ### Dew point to ppm calculator for gases Water content in ppm by volume equals the saturation vapour pressure at the dew point divided by the total pressure, times a million. Open ](https://www.sarveshanalytics.com/calculators/dew-point-to-ppm-calculator.html)[ ### Excess air from flue gas oxygen calculator With complete combustion, excess air in percent equals O2 divided by (20.95 minus O2), times 100, using dry flue gas oxygen. Open ](https://www.sarveshanalytics.com/calculators/excess-air-calculator.html)[ ### Emission correction to reference oxygen Emission limits are stated at a reference oxygen level so that diluting the flue gas with extra air cannot hide pollution. Open ](https://www.sarveshanalytics.com/calculators/emission-o2-correction-calculator.html)[ ### Gas sample line lag time calculator Sample lag equals the gas volume in the line, at line pressure, divided by the flow measured at atmospheric pressure. Open ](https://www.sarveshanalytics.com/calculators/sample-lag-time-calculator.html)[ ### Pressure effect on oxygen reading calculator A sensor that responds to oxygen partial pressure reads in proportion to absolute pressure. Open ](https://www.sarveshanalytics.com/calculators/pressure-effect-on-oxygen-reading-calculator.html)[ ### Inerting purge time and volume calculator With ideal mixing, oxygen falls exponentially as inert gas is added: the number of vessel volumes needed is the natural log of the starting concentration divided by the target. Open ](https://www.sarveshanalytics.com/calculators/purge-time-calculator.html) ## Every lesson ### Foundations 1. [ **What is online gas analysis? A plain introduction** Online gas analysis measures the composition of a process gas continuously, as it flows, and sends the result to a display, an alarm or a control system. Beginner*3 min*](https://www.sarveshanalytics.com/learn/what-is-online-gas-analysis.html) 2. [ **Online vs laboratory vs portable gas analysis** Use an online analyser when the answer is needed continuously to control or protect a process. Beginner*3 min*](https://www.sarveshanalytics.com/learn/online-vs-laboratory-vs-portable-gas-analysis.html) 3. [ **How gases behave: pressure, temperature and partial pressure** In a gas mixture each component contributes a partial pressure equal to its fraction times the total pressure. Beginner*3 min*](https://www.sarveshanalytics.com/learn/how-gases-behave-pressure-temperature-and-partial-pressure.html) 4. [ **ppm, percent and ppb explained for gas analysis** Percent, ppm and ppb are volume fractions: 1 % equals 10,000 ppm, and 1 ppm equals 1000 ppb. Beginner*3 min*](https://www.sarveshanalytics.com/learn/ppm-percent-and-ppb-units-explained.html) 5. [ **ppm to mg/Nm3: volume vs mass concentration** Mass concentration in mg per cubic metre equals ppm times molar mass divided by molar volume, and the molar volume depends on temperature and pressure. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/volume-mass-and-mg-per-nm3-concentration-units.html) 6. [ **Dry basis vs wet basis in gas measurement** A wet-basis reading counts water vapour as part of the gas; a dry-basis reading removes it. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/dry-basis-vs-wet-basis-gas-measurement.html) 7. [ **Accuracy, precision, repeatability and drift in gas analysers** Accuracy is how close a reading is to the true value; precision or repeatability is how closely repeated readings agree; drift is how the reading moves over time. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/accuracy-precision-repeatability-and-drift.html) 8. [ **Response time, T90 and sample lag in gas analysis** T90 is the time an analyser takes to reach 90 % of a step change in concentration. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/response-time-t90-and-sample-lag.html) 9. [ **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). Intermediate*5 min*](https://www.sarveshanalytics.com/learn/reading-a-gas-analyser-datasheet.html) ### Measurement principles 1. [ **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. Beginner*3 min*](https://www.sarveshanalytics.com/learn/gas-analysis-technologies-compared.html) 2. [ **Electrochemical vs paramagnetic oxygen sensors** Electrochemical oxygen cells suit ppm and percent oxygen, are compact, and are consumed over time. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/electrochemical-vs-paramagnetic-oxygen-sensors.html) 3. [ **How a zirconia oxygen analyser works** A zirconia analyser measures oxygen with a heated ceramic cell. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/how-a-zirconia-oxygen-analyser-works.html) 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. Beginner*4 min*](https://www.sarveshanalytics.com/learn/what-is-an-ndir-gas-analyser.html) 5. [ **How thermal conductivity gas analysers (TCD) work** A thermal conductivity analyser heats a small element and measures how quickly the surrounding gas carries heat away. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/how-thermal-conductivity-gas-analysers-work.html) 6. [ **What is dew point and how is it measured?** Dew point is the temperature at which moisture in a gas begins to condense. Beginner*4 min*](https://www.sarveshanalytics.com/learn/what-is-dew-point-and-how-is-it-measured.html) 7. [ **Moisture measurement methods compared for dry gas** Online dry-gas moisture is usually measured with a ceramic or capacitive sensor that responds to adsorbed water. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/moisture-measurement-methods-compared.html) 8. [ **Cross-Sensitivity and interference in gas analysers** Cross-sensitivity is a sensor's response to gases other than its target. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/cross-sensitivity-and-interference-in-gas-analysers.html) 9. [ **Trace oxygen measurement and air ingress: ppm done right** Air is 209,500 ppm oxygen, so a leak of just 0.01 % air adds about 21 ppm to a sample. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/trace-oxygen-measurement-and-air-ingress.html) 10. [ **Measuring hydrogen: purity, mixtures and safety limits** Hydrogen purity and hydrogen in nitrogen or argon are measured by thermal conductivity, because hydrogen conducts heat about seven times better than most gases. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/measuring-hydrogen-purity-and-hydrogen-in-gas-mixtures.html) 11. [ **Measuring carbon monoxide and carbon dioxide online** Carbon dioxide is measured by NDIR over ppm to 100 % ranges. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/measuring-carbon-monoxide-and-carbon-dioxide.html) 12. [ **Measuring methane and biogas composition online** Methane and CO2 in biogas are measured by NDIR, separately or in one dual-channel analyser, and oxygen is measured to show air ingress. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/measuring-methane-and-biogas.html) 13. [ **Extractive vs In-Situ gas analysis** In-situ analysers measure the gas where it flows, with no sample line, and suit hot, dusty ducts. Beginner*3 min*](https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html) 14. [ **Choosing an oxygen analyser: trace, percent or purity** Choose by range. Beginner*3 min*](https://www.sarveshanalytics.com/learn/choosing-an-oxygen-analyser-trace-percent-or-purity.html) 15. [ **Why ambient pressure affects oxygen purity readings** Many oxygen sensors respond to the partial pressure of oxygen, which falls when barometric pressure falls even if the gas is unchanged. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/why-ambient-pressure-affects-oxygen-purity-readings.html) ### Sampling and conditioning 1. [ **How to design a gas sample handling system** A good sample handling system delivers a representative, clean, dry sample at constant pressure and flow. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/how-to-design-a-gas-sample-handling-system.html) 2. [ **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. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html) 3. [ **Sample lines: materials, length, diameter and lag** Use stainless steel tube for trace oxygen, moisture and reactive gases, because plastic lets oxygen and water in and out. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/sample-lines-materials-length-and-lag.html) 4. [ **Filters for gas analysers: dust, mist, membrane** Use 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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/filters-and-particulate-protection.html) 5. [ **Condensate, moisture and sample cooling for gas analysis** Wet samples must be cooled to a fixed, low dew point so that water leaves as condensate at a controlled place, not in the analyser. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/condensate-moisture-and-sample-cooling.html) 6. [ **Sample pressure, flow and fast bypass loops** An analyser needs a steady sample at its specified pressure and flow. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/sample-pressure-flow-and-bypass-loops.html) 7. [ **Probes and blowback for hot, dusty and tarry gas** Hot, 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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/hot-dusty-gas-probes-and-blowback.html) 8. [ **Sampling cryogenic and liquefied gases: vaporisers** A liquid sample must be vaporised completely before it reaches an analyser. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/sampling-cryogenic-and-liquefied-gases.html) 9. [ **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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html) 10. [ **Sample system troubleshooting: symptoms to causes** Most analyser faults are sample system faults. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/sample-system-troubleshooting.html) ### Installation and integration 1. [ **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. Beginner*3 min*](https://www.sarveshanalytics.com/learn/where-to-mount-a-gas-analyser.html) 2. [ **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. Beginner*3 min*](https://www.sarveshanalytics.com/learn/analyser-outputs-4-20-ma-relays-and-modbus.html) 3. [ **Wiring, grounding and electrical noise for gas analysers** Use shielded twisted-pair cable for signals, ground the shield at one end, keep signal cables away from power and motor cables, and avoid ground loops by giving the loop a single reference. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/wiring-grounding-and-electrical-noise.html) 4. [ **Connecting a gas analyser to PLC, DCS and SCADA** Scale the 4-20 mA input to the analyser range, alarm on out-of-range currents as a fault, and use the analyser's fault and calibration-in-progress signals to hold or flag the value. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/connecting-an-analyser-to-plc-dcs-and-scada.html) 5. [ **Site utilities checklist for gas analysers** An analyser installation needs more than a power connection: a clean, stable electrical supply, instrument air or nitrogen for blowback and purges, a calibration gas supply with regulators, a safe vent, a drain for condensate, and in some cases heating, cooling or ventilation for the enclosure. Beginner*3 min*](https://www.sarveshanalytics.com/learn/site-utilities-checklist-for-analysers.html) 6. [ **Commissioning an online gas analyser: A Step-by-Step guide** Commission in order: inspect and verify the installation, leak-test the sample system, power up, purge with sample or inert gas, set pressure and flow, calibrate with zero and span gas, test alarms and outputs end to end, run on process gas, and record a baseline of flow, pressure and readings. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/commissioning-an-online-gas-analyser.html) ### Calibration and maintenance 1. [ **How gas analyser calibration works: zero and span** Calibration compares the analyser's reading with a gas of known concentration and adjusts it to match. Beginner*4 min*](https://www.sarveshanalytics.com/learn/how-gas-analyser-calibration-works.html) 2. [ **Calibration gases: choosing, handling and certificates** Choose span gas near 70 to 90 % of the range in a balance gas that matches the sample, with a certificate stating concentration, uncertainty and expiry. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/calibration-gases-choosing-and-handling.html) 3. [ **How often should you calibrate a gas analyser?** Set the interval from three things: how much error the process can tolerate, how fast the analyser drifts, and what a wrong reading costs. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/how-often-to-calibrate-a-gas-analyser.html) 4. [ **Auto-Calibration and validation checks for gas analysers** Auto-calibration switches zero and span gas to the analyser by solenoid valves on a timer, keypad or Modbus command, and adjusts or records the result. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/auto-calibration-and-validation-checks.html) 5. [ **Troubleshooting gas analyser readings: high, low, noisy, slow** Apply known gas at the analyser inlet. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/troubleshooting-gas-analyser-readings.html) 6. [ **Maintenance schedule and spares for gas analysers** Maintain analysers by routine: a daily look at flow, pressure and condensate; a weekly check of filters and drain; a monthly calibration check; and an annual full calibration, sensor check and leak test. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/maintenance-schedule-and-spares-for-gas-analysers.html) 7. [ **Sensor life, poisoning and replacement in gas analysers** Electrochemical cells are consumed by the gas they measure and last months to years depending on exposure. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/sensor-life-poisoning-and-replacement.html) 8. [ **Records, audit trails and qualification for regulated plants** Regulated plants must show that an analyser was fit for purpose and stayed so: traceable calibration records, alarm and fault history, controlled access to settings, change control, and documented qualification (installation, operation and performance). Advanced*3 min*](https://www.sarveshanalytics.com/learn/records-audit-trails-and-qualification-for-regulated-plants.html) ### Safety and hazardous areas 1. [ **Flammability, explosive limits and gas safety basics** A flammable gas burns only when fuel, oxygen and an ignition source are present and the fuel-air mixture lies between the lower and upper explosive limits (LEL and UEL). Beginner*3 min*](https://www.sarveshanalytics.com/learn/flammability-explosive-limits-and-gas-safety-basics.html) 2. [ **What is limiting oxygen concentration (LOC)?** The limiting oxygen concentration (LOC) is the oxygen level below which a flammable vapour or dust cannot sustain a flame. Beginner*3 min*](https://www.sarveshanalytics.com/learn/what-is-limiting-oxygen-concentration.html) 3. [ **Inerting and purging: how they work and how to prove them** Inerting keeps a vessel's oxygen below the limiting oxygen concentration by filling it with nitrogen or another inert gas. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/inerting-and-purging-how-they-work.html) 4. [ **Hazardous area classification: zones, gas groups, T-Classes** Area classification says how likely an explosive atmosphere is (Zone 0, 1 or 2 for gas), what gas it could be (group IIA, IIB or IIC) and how hot equipment may get (T1 to T6, 450 to 85 C). Intermediate*3 min*](https://www.sarveshanalytics.com/learn/hazardous-area-classification-zones-gas-groups-temperature-classes.html) 5. [ **Hazardous area gas analysers explained** A hazardous area analyser is built so it cannot ignite flammable gas. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/hazardous-area-gas-analysers-explained.html) 6. [ **Protection concepts: flameproof, intrinsic safety, purging** Hazardous-area equipment avoids ignition in one of three ways: contain an explosion (flameproof, Ex d), prevent sparks and heat (increased safety Ex e, non-sparking Ex n or ec, encapsulation Ex m), or limit energy (intrinsic safety Ex i), or keep the gas out (pressurised or purged enclosures, Ex p). Advanced*3 min*](https://www.sarveshanalytics.com/learn/protection-concepts-flameproof-intrinsic-safety-and-purging.html) 7. [ **What SIL means for gas analysers, and what it does not** A safety integrity level (SIL 1 to 4) states how reliably a safety instrumented function does its job on demand. Advanced*3 min*](https://www.sarveshanalytics.com/learn/what-sil-means-for-gas-analysers.html) 8. [ **Oxygen enrichment and oxygen deficiency hazards** Too much oxygen makes materials ignite more easily and burn fiercely; above about 23.5 % is commonly treated as oxygen-enriched. Beginner*3 min*](https://www.sarveshanalytics.com/learn/oxygen-enrichment-and-oxygen-deficiency-hazards.html) ### Process primers 1. [ **Combustion, excess air and flue gas oxygen explained** Burners need slightly more air than the exact amount that burns the fuel, so that combustion is complete. Beginner*3 min*](https://www.sarveshanalytics.com/learn/combustion-excess-air-and-flue-gas-oxygen.html) 2. [ **How an air separation plant works and what is measured** An air separation unit compresses air, removes water and CO2, cools it until it liquefies and distils the liquid into oxygen, nitrogen and argon, which boil at different temperatures. Beginner*3 min*](https://www.sarveshanalytics.com/learn/how-an-air-separation-plant-works.html) 3. [ **PSA, VPSA and membrane gas generators explained** PSA nitrogen generators use carbon molecular sieve to adsorb oxygen from compressed air, giving nitrogen with ppm to percent residual oxygen. Beginner*3 min*](https://www.sarveshanalytics.com/learn/nitrogen-and-oxygen-generators-psa-vpsa-and-membrane.html) 4. [ **Heat treatment furnace atmospheres explained** A furnace atmosphere protects the metal from oxidation or adds carbon to its surface. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/heat-treatment-furnace-atmospheres-explained.html) 5. [ **Hydrogen electrolysers and gas analysis: what to measure** An electrolyser splits water into hydrogen at one electrode and oxygen at the other. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/hydrogen-electrolysers-and-gas-analysis.html) 6. [ **Biogas, landfill gas and digesters explained** Anaerobic digestion converts organic waste into biogas: methane, CO2, water vapour and traces of H2S. Beginner*3 min*](https://www.sarveshanalytics.com/learn/biogas-landfill-gas-and-digesters-explained.html) 7. [ **Controlled-Atmosphere fruit storage explained** Fruit keeps breathing after harvest, consuming oxygen and releasing CO2. Beginner*3 min*](https://www.sarveshanalytics.com/learn/controlled-atmosphere-fruit-storage-explained.html) 8. [ **Cement kiln gas analysis explained: O2, CO and safety** A cement kiln burns fuel to heat raw meal to about 1450 C. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/cement-kiln-gas-analysis-explained.html) 9. [ **Steel plant gases: coke oven, blast furnace, converter** Integrated steelworks make three main by-product fuel gases: coke oven gas, rich in hydrogen and methane; blast furnace gas, lean and mostly CO, CO2 and nitrogen; and converter gas, rich in CO. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/steel-plant-gases-explained.html) 10. [ **Emission monitoring (CEMS) basics: what a system does** A continuous emission monitoring system measures pollutants and oxygen in stack gas and reports concentrations corrected to a reference oxygen and dry basis. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/emission-monitoring-cems-basics.html) 11. [ **Compressed air quality and dew point (ISO 8573-1)** ISO 8573-1 classifies compressed air purity by particles, water and oil. Beginner*3 min*](https://www.sarveshanalytics.com/learn/compressed-air-quality-and-dew-point.html) 12. [ **Inert gas blanketing in pharma and chemical plants** Blanketing fills the space above a liquid or powder with nitrogen so that oxygen stays below the limit at which a flame can spread. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/inert-gas-blanketing-in-pharma-and-chemical-plants.html) 13. [ **Glove boxes and Controlled-Atmosphere chambers explained** A glove box is a sealed chamber filled with nitrogen or argon in which oxygen and moisture are held at very low levels, often through a circulating purifier that removes both. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/glove-boxes-and-controlled-atmosphere-chambers.html) ### Choosing and buying 1. [ **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. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/how-to-specify-a-gas-analyser.html) 2. [ **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. Intermediate*4 min*](https://www.sarveshanalytics.com/learn/what-accuracy-do-you-really-need.html) 3. [ **Total cost of ownership of a gas analyser** The analyser is often a third or less of the cost of a working measurement. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/total-cost-of-ownership-of-a-gas-analyser.html) 4. [ **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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/comparing-gas-analyser-quotes.html) 5. [ **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. Intermediate*3 min*](https://www.sarveshanalytics.com/learn/questions-to-ask-a-gas-analyser-supplier.html) 6. [ **The application data sheet: what to send Sarvesh** The application data sheet collects the pre-order design inputs an engineer needs: the measurement points and gases, ranges, sample pressure, temperature and dew point, dust and corrosives, area classification, utilities, outputs and calibration approach. Beginner*3 min*](https://www.sarveshanalytics.com/learn/the-application-data-sheet-and-what-to-send-us.html) ## Still not sure which analyser fits? Send us the gas, the range and the process. We reply with a recommendation, not a brochure. [Talk to an engineer](https://www.sarveshanalytics.com/contact.html#enquiry)