--- title: Extractive vs In-Situ Gas Analysis | Sarvesh url: https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html description: Extractive and in-situ gas analysis compared: how each works, advantages, limits and when to choose each for boilers, process gas and stacks. updated: 2026-11-03 source: html --- Learn · Measurement principles # Extractive vs in-situ gas analysis: how to choose This is the first decision in any analyser project. It shapes the cost, the maintenance and what can go wrong. Beginner 3 min read Lesson 13 of 15[Measurement principles](https://www.sarveshanalytics.com/learn/track-measurement-principles.html) Helpful first: [What is online gas analysis? A plain introduction](https://www.sarveshanalytics.com/learn/what-is-online-gas-analysis.html) Quick answer In-situ analysers measure the gas where it flows, with no sample line, and suit hot, dusty ducts. Extractive analysers pull a sample to a conditioned analyser, and suit trace measurements and multiple gases. Extractive systems are only as good as their sample handling. Updated 3 November 2026 · Figures from Sarvesh datasheets **After this lesson you can** - Define in-situ and extractive analysis - Match each approach to a typical application - Say why extractive systems depend on sample handling ## In-situ An in-situ analyser puts the sensor in the process, usually in a duct or stack. There is no sample line, no conditioning, and almost no delay. ACCURRA-Zr is an example, measuring oxygen with a zirconia cell in hot flue gas. In-situ works best for one measurement in a hot, dusty gas where a sample would be hard to condition. ## Extractive An extractive analyser draws a sample through a probe and a line to an analyser, usually after cooling and drying. This lets the analyser sit in a clean location, allows trace-level and multiple measurements, and makes calibration with span gas simple. The price is a sample handling system that must be designed, built and maintained. A typical extractive sample path. A supervising controller manages blowback, line temperature and the pump, and raises an alarm on a fault. ## Comparison - In-situ: fast response, no sample line, limited to what the in-situ sensor can measure, harder to calibrate with span gas - Extractive: many gases and trace levels, analyser in a clean location, calibration with span gas, depends on sample conditioning - In-situ suits flue gas oxygen. Extractive suits trace oxygen, CO, CO2, methane, moisture, hydrogen and multi-gas emission systems ## Where Sarvesh products fit ACCURRA-Zr is in-situ for flue gas oxygen. ACCURRA-S, ACCURRA-TCD and ACCURRA-Hz are extractive. For hot, wet or dusty samples, probes, i-Cons and SGI-300 condition the gas, and SGI-320 packages the whole extractive chain for emission monitoring. ## Rule of thumb If you need oxygen only, in a hot duct, and want minimal maintenance, choose in-situ. If you need trace levels, other gases, or a clean calibration, choose extractive and invest in the sample system. The sample handling system between the process and the analyser decides how many years of trouble-free measurement you get. **In short** - In-situ measures in the duct with no sample line. - Extractive pulls a sample to a conditioned analyser and suits trace and multi-gas work. - An extractive system is only as good as its sample handling. - Many plants use both. ## Check your understanding Answer in your head or on paper first, then open the answer. Recalling an answer teaches more than rereading. **Name one advantage of in-situ analysis.** No sample line to block or lag, and a fast response, which suits hot dusty ducts. **Why do extractive systems suit trace oxygen in a clean gas?** A clean sample can be conditioned to constant pressure and flow, so a sensitive analyser can be used outside the pipe. **Where do extractive systems most often fail?** In the sample handling: blocked filters, condensation, leaks and long lag times, not the analyser itself. ## Key terms - [Extractive analysis](https://www.sarveshanalytics.com/learn/glossary.html#t-extractive-analysis) - [In-situ analysis](https://www.sarveshanalytics.com/learn/glossary.html#t-in-situ-analysis) - [Sample handling system](https://www.sarveshanalytics.com/learn/glossary.html#t-sample-handling-system) - [Probe](https://www.sarveshanalytics.com/learn/glossary.html#t-probe) ## Frequently asked questions **Is in-situ or extractive better?** Neither is better in general. In-situ suits hot flue gas oxygen; extractive suits trace and multi-gas measurements. **Why do extractive systems fail?** Most failures are in the sample path: blocked filters, condensate and pump faults. **Can I measure CO in situ?** Extractive measurement is the usual approach for CO in flue gas. **Which Sarvesh product does extractive emission monitoring?** SGI-320, with a heated probe, heated line, conditioner and analysers. ## Related products [ ### ACCURRA-Zr Zirconia percent O2 analyser for furnaces and boilers, single-point air calibration, options to 1400 C. View ACCURRA-Zr ](https://www.sarveshanalytics.com/flue-gas-analysers.html)[ ### i-Cons Smart Peltier sample conditioner with diagnostics, auto blowback and Modbus, in a compact 19 inch cabinet. View i-Cons ](https://www.sarveshanalytics.com/smart-systems-for-gas-analyser.html) ## Where this applies - [Boiler and furnace oxygen (flue gas)](https://www.sarveshanalytics.com/applications/boiler-and-furnace-oxygen-flue-gas.html) - [Stack and emission monitoring](https://www.sarveshanalytics.com/applications/stack-and-emission-monitoring-system.html) - [ACCURRA-Zr](https://www.sarveshanalytics.com/flue-gas-analysers.html) - [Sampling components and systems](https://www.sarveshanalytics.com/sampling-components.html) ## Where to go next - [How to design a gas sample handling system](https://www.sarveshanalytics.com/learn/how-to-design-a-gas-sample-handling-system.html) - [Choosing the sample point for a gas analyser](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html)