--- title: How to Design a Gas Sample Handling System url: https://www.sarveshanalytics.com/learn/how-to-design-a-gas-sample-handling-system.html description: A practical guide to gas sample handling: probe, heated line, cooler, pump and filters, common failure modes, and the sample limits of ACCURRA-S and i-Cons. updated: 2026-11-03 source: html --- Learn · Sampling and conditioning # How to design a gas sample handling system for an online analyser Most analyser trouble starts upstream of the analyser. The sample system is where accuracy is won or lost. Intermediate 4 min read Lesson 1 of 10[Sampling and conditioning](https://www.sarveshanalytics.com/learn/track-sampling.html) Helpful first: [Extractive vs In-Situ gas analysis](https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html), [Response time, T90 and sample lag in gas analysis](https://www.sarveshanalytics.com/learn/response-time-t90-and-sample-lag.html) Quick answer A good sample handling system delivers a representative, clean, dry sample at constant pressure and flow. Keep the sample above its dew point until the cooler, keep lines short, filter in stages, and supervise faults. ACCURRA-S expects a dry, non-corrosive, non-flammable sample at 2 to 10 psig and about 1 LPM. Updated 3 November 2026 · Figures from Sarvesh datasheets **After this lesson you can** - List the stages of a sample handling system in order - Apply the rules that keep a sample representative - State what an ACCURRA-S expects at its inlet ## The chain A typical extractive chain has a probe with a filter at the tip, a transport line, a cooler or vaporiser to condition the sample, a pump, fine filters and scrubbers, and then the analyser. Each stage has a job and a failure mode. Probe, heated line, cooler, pump, fine filter and analyser, with a controller supervising blowback, line temperature and pump interlock. ## Typical failure modes - A blocked probe filter reduces flow and the analyser reads stale gas - Condensate in the line absorbs soluble gases and floods the analyser - A leak lets air in; at ppm level it dominates the reading - A failed pump gives no flow, with no obvious sign - Dead volumes and long lines slow the response ## Supervision: let the system say when it is wrong A sample system fails quietly. The analyser keeps reading, but what it reads is no longer the process. Supervision turns each failure into an alarm: | Failure | What detects it | What should happen | |---|---|---| | Cooler warm | Cooler temperature | Pump stops; SGI-300 runs the external pump only when the sample is below 12 C and dry | | Water past the cooler | Condensate sensor | Pump stops, alarm, so the analyser is not flooded | | Probe filter blocking | Flow falls | Blowback, then alarm if flow does not recover | | Heated line cold | Pt100 on the hose | Alarm; readings flagged | | Calibration running | Digital inputs from the analyser | Outputs frozen, control system told | i-Cons reads these inputs and reports values, status and maintenance history over Modbus, so the control room sees the sample system's health, not just a number. ## Design rules - Keep the sample above its dew point, with a heated probe and line, until the cooler - Condition in one place: cool, drain and filter before the analyser - Keep lines short and small in volume, in stainless or PTFE as the gas requires - Filter in stages: probe filter, then coalescing or fine filter - Provide blowback for dusty gas, and make it automatic on flow failure - Measure flow and condensate, and trip the pump on a fault - Calibrate through the same path where possible ## A worked design: boiler flue gas to an extractive analyser Flue gas at 180 C with about 12 % water vapour and light dust. Oxygen and CO are to be measured dry. Walk the chain: 1. **Dew point.** 12 % water at atmospheric pressure is a vapour pressure of about 12.2 kPa, a dew point of about 50 C. Everything up to the cooler must stay well above 50 C. 2. **Probe.** SP-300 has a heated 10 micron SS316 sintered filter, for process gas from 120 to 500 C, dust up to 10 g/Nm3 and moisture up to 15 %. Blowback at 4 to 7 kg/cm2 clears the filter. 3. **Heated line.** i-Cons drives heated hose in lengths of 30 to 90 m at 40 W per metre. A 30 m hose draws 1.2 kW; set its temperature well above the 50 C dew point, with Pt100 feedback. 4. **Cooler.** The i-Cons Peltier cooler takes gas at up to 160 C with a dew point up to 65 C and holds the outlet at 5 C. Our gas fits both limits. 5. **What leaves the cooler.** At 5 C the gas keeps about 0.86 % water, so a dry 3.00 % oxygen reads about 2.97 %. Good enough for most control; correct for it in reporting if you need to. 6. **Pump and flow.** The i-Cons pump gives 5 LPM free flow with a fast loop valve. The analyser takes about 1 LPM; the rest keeps the line fresh. 7. **Lag.** 30 m of 4 mm bore PTFE holds about 380 mL. At 4 LPM that is about 6 seconds; at 1 LPM it would be about 23. **Good to know** The SGI-300 and i-Cons datasheets limit the sample to SO2, NOx and CO below 1000 ppm and exclude HCl, HF, H2S and other highly corrosive, toxic or flammable gases. A sample outside that needs a different design. ## What the analyser expects The ACCURRA-S catalogue states the sample it expects: non-corrosive, non-toxic, non-flammable, non-condensing and dry, free from entrained oil, at 2 to 10 psig regulated externally, flow about 1 LPM, dust below 3 micron and a dew point at least 5 degrees below the lowest ambient temperature. Where your sample does not meet these, a conditioning system is designed around your application. ## When to use i-Cons or SGI-300 i-Cons packages the pump, cooler, filter, condensate and flow sensors, blowback and heated-hose control with diagnostics. Its cooler takes sample at up to 160 C with a dew point up to 65 C, and an SP-300 heated probe handles process gas from 120 to 500 C with dust up to 10 g per normal cubic metre. SGI-300 is the cooler with integrated drain pump, filter and condensate sensor for building your own panel. i-Cons and SGI-320 are not suitable for samples containing HCl, HF or H2S. ## Guidance and standards **API RP 555**, Process Analyzers, is the long-standing industry guide to analyser systems, including sample conditioning and analyser houses. **ISO 10715** gives sampling guidance for natural gas. For stack emission measurement, **EN 15259** covers the measurement site and plan, and **EN 14181** the quality assurance of automated measuring systems once installed: [Emission monitoring (CEMS) basics: what a system does](https://www.sarveshanalytics.com/learn/emission-monitoring-cems-basics.html). Lag and line size: [Sample lines: materials, length, diameter and lag](https://www.sarveshanalytics.com/learn/sample-lines-materials-length-and-lag.html). The tapping: [Choosing the sample point for a gas analyser](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html). **In short** - The goal is a representative, clean, dry sample at constant pressure and flow. - Keep the sample above its dew point until the cooler. - Filter in stages and keep lines short. - Supervise faults with flow and condensate alarms. ## Check your understanding Answer in your head or on paper first, then open the answer. Recalling an answer teaches more than rereading. **Why must the sample stay above its dew point until the cooler?** Condensation anywhere earlier in the line removes water-soluble gases and wets the line, which changes the sample before it is analysed. **What sample pressure and flow does an ACCURRA-S expect?** 2 to 10 psig regulated externally, and a flow of about 1 LPM. **A reading lags a process change by minutes. Which part of the sample system do you suspect?** Line volume and length: tube internal volume divided by flow is the transport delay. Shorten the line or raise the flow. ## Key terms - [Sample handling system](https://www.sarveshanalytics.com/learn/glossary.html#t-sample-handling-system) - [Fine filter](https://www.sarveshanalytics.com/learn/glossary.html#t-fine-filter) - [Condensate](https://www.sarveshanalytics.com/learn/glossary.html#t-condensate) - [Peltier cooler](https://www.sarveshanalytics.com/learn/glossary.html#t-peltier-cooler) ## Frequently asked questions **What is the most common sample system fault?** A blocked probe filter or condensate in the line. Both are addressed by blowback, heated lines and a condensate sensor with pump trip. **Why must the sample stay above its dew point?** Below it, water condenses and takes soluble gases with it, changing the sample before it reaches the analyser. **How far can the sample line be?** With i-Cons, up to 60 m with the standard pump and 60 to 90 m with the high-flow pump. **Can you design the system for me?** Yes. Send the sample temperature, pressure, dew point, dust level and distance to the analyser. ## Related products [ ### 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)[ ### SGI-300 / SGI-320 Peltier sample cooler with integrated pump, filter and condensate detector; SGI-320 for emission monitoring. View SGI-300 / SGI-320 ](https://www.sarveshanalytics.com/sample-coolers.html)[ ### SP and SRP sample probes Heated and non-heated probes with blowback, and retractable probes, in SS316, Inconel or ceramic. View SP and SRP sample probes ](https://www.sarveshanalytics.com/sample-probes.html) ## Where this applies - [Stack and emission monitoring](https://www.sarveshanalytics.com/applications/stack-and-emission-monitoring-system.html) - [Steel plant process gases](https://www.sarveshanalytics.com/applications/steel-plant-process-gas-analysis.html) - [Sampling components and systems](https://www.sarveshanalytics.com/sampling-components.html) - [Sample probes SP-100, SP-200 and SP-300](https://www.sarveshanalytics.com/sample-probes.html) ## Where to go next - [Sample lines: materials, length, diameter and lag](https://www.sarveshanalytics.com/learn/sample-lines-materials-length-and-lag.html)