--- title: Sensor Life, Poisoning and Replacement in Gas Analysers url: https://www.sarveshanalytics.com/learn/sensor-life-poisoning-and-replacement.html description: How long gas sensors last, what poisons them, the signs of ageing, and how to plan replacement of electrochemical, zirconia and NDIR sensors. updated: 2026-11-02 source: html --- Learn · Calibration and maintenance # Sensor life, poisoning and replacement Sensors are the one part of an analyser that wears out by design. Knowing how and why lets you plan, not react. Intermediate 3 min read Lesson 7 of 8[Calibration and maintenance](https://www.sarveshanalytics.com/learn/track-calibration-and-maintenance.html) Helpful first: [Electrochemical vs paramagnetic oxygen sensors](https://www.sarveshanalytics.com/learn/electrochemical-vs-paramagnetic-oxygen-sensors.html) Quick answer Electrochemical cells are consumed by the gas they measure and last months to years depending on exposure. Paramagnetic and NDIR sensors have no consumed element and last much longer. Zirconia cells last years but are harmed by poisons in flue gas. Contaminants such as H2S, chlorine, silicones and acid gases can poison sensors early. Large span corrections and slow response signal the end of life. Updated 2 November 2026 · Figures from Sarvesh datasheets **After this lesson you can** - Explain why each sensor type ages - List common poisons and the sample conditions that cause early failure - Spot the signs of an ageing sensor - Plan replacement ## How each sensor ages | Sensor | How it ages | Life driver | |---|---|---| | Electrochemical O2 or CO cell | The reaction that generates the signal consumes the cell | Total oxygen or CO exposure; heat; contamination | | Paramagnetic | No consumed element; mechanical and contamination effects | Dirty sample coating the cell | | NDIR | Light source and optics age slowly; windows can fog or coat | Condensation and dirt | | Zirconia | Heater and ceramic wear; electrodes poisoned | Temperature cycling and poisons in the gas | | Ceramic moisture | Surface contamination and ageing | Contaminants and wetting | No figure is promised here; the life of a given sensor in your sample is best found from your own records and the supplier's guidance. ## What poisons sensors - **Sulphur compounds** such as H2S and SO2, **chlorine and halides**, and **silicones** attack many cells and catalytic surfaces. - **Acid gases and high CO2** can shorten life in some electrochemical cells. - **Oil, tar and condensate** coat optics and sensor surfaces. - **Heat** speeds the ageing of electrochemical cells. Most poisoning comes from sample conditions outside the specified envelope: [What samples an analyser cannot take: know the limits](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html). Conditioning and filtration are the first defence. ## Signs of an ageing sensor - Large corrections at each span check, and shrinking margin. - Slow response, longer than at commissioning. - A noisy or unstable zero that will not settle. - A diagnostic or low-sensitivity alarm on the analyser. - Falling output in a known gas. ## Planning replacement 1. Record the installation date and calibration history for each sensor. 2. Plan replacement from the trend, before the sensor fails, for safety and quality-critical points. 3. Keep a spare, and replace with the same type; recalibrate after fitting. 4. For trace oxygen, allow settling time after fitting: [Trace oxygen measurement and air ingress: ppm done right](https://www.sarveshanalytics.com/learn/trace-oxygen-measurement-and-air-ingress.html). 5. Record the cause when a sensor fails early; it points to a sample problem worth fixing. **In short** - Electrochemical cells are consumed; paramagnetic and NDIR sensors last longer. - Poisons such as sulphur, halides and silicones shorten life. - Large span corrections and slow response signal the end of life. - Plan replacement from the trend and keep a spare. ## Check your understanding Answer in your head or on paper first, then open the answer. Recalling an answer teaches more than rereading. **Why do electrochemical cells wear out?** The reaction that creates the signal consumes the cell. **Name two contaminants that shorten sensor life.** H2S or SO2 (sulphur compounds), and chlorine or silicones. **What signs show a sensor near its end?** Large span corrections, slow response and a noisy zero. ## Key terms - [Sensor life](https://www.sarveshanalytics.com/learn/glossary.html#t-sensor-life) - [Poisoning (sensor)](https://www.sarveshanalytics.com/learn/glossary.html#t-poisoning-sensor) - [Electrochemical cell](https://www.sarveshanalytics.com/learn/glossary.html#t-electrochemical-cell) - [Zirconia sensor](https://www.sarveshanalytics.com/learn/glossary.html#t-zirconia-sensor) ## Frequently asked questions **How long do gas sensors last?** It depends on the type and the sample. Electrochemical cells months to years; others longer. **Can a poisoned sensor recover?** Sometimes slowly if the exposure was brief; usually replace it. **Should I replace sensors on a schedule?** For critical points yes, informed by the calibration trend. **Does ACCURRA-S sensor choice affect life?** Yes: electrochemical cells are consumed; paramagnetic models have no consumed part. ## Related products [ ### ACCURRA-S Online analyser for trace, percent and purity O2, CO, CO2, CH4 and dew point; can measure two gases from one sample. View ACCURRA-S ](https://www.sarveshanalytics.com/safe-gas-analyser.html) ## Where this applies - [Nitrogen purity and trace oxygen](https://www.sarveshanalytics.com/applications/nitrogen-purity-trace-oxygen.html) ## Where to go next - [Maintenance schedule and spares for gas analysers](https://www.sarveshanalytics.com/learn/maintenance-schedule-and-spares-for-gas-analysers.html)