--- title: Gas Analyser Questions and Answers | Sarvesh url: https://www.sarveshanalytics.com/learn/questions.html description: 300 questions about online gas analysers, sampling, calibration, hazardous areas and buying, each answered briefly and linked to a full lesson. updated: 2026-11-02 source: html --- Learn ยท Questions # Every question, answered 300 questions customers and engineers ask about online gas analysis, grouped by track. Each answer links to the lesson that explains it properly. ## Foundations **What is the difference between a gas analyser and a gas detector?** An analyser measures a concentration accurately over a defined range for process control or quality. A detector is a safety device that warns when a gas reaches a hazardous level. They are different product classes. From the lesson [What is online gas analysis? A plain introduction](https://www.sarveshanalytics.com/learn/what-is-online-gas-analysis.html) **How fast is an online gas analyser?** From a few seconds to a few minutes, depending on the sensor, the gas and the sample line. See the lesson on response time. From the lesson [What is online gas analysis? A plain introduction](https://www.sarveshanalytics.com/learn/what-is-online-gas-analysis.html) **Do I need a sample line for every analyser?** No. In-situ analysers measure inside the duct or pipe. Most trace and multi-gas analysers do use a sample line. From the lesson [What is online gas analysis? A plain introduction](https://www.sarveshanalytics.com/learn/what-is-online-gas-analysis.html) **What does an online analyser output?** Typically a 4-20 mA signal, relay alarms and digital data such as Modbus, along with a display. From the lesson [What is online gas analysis? A plain introduction](https://www.sarveshanalytics.com/learn/what-is-online-gas-analysis.html) **Can portable analysers replace online analysers?** Not for control or protection. They give a snapshot, not a continuous reading, and need a person present. From the lesson [Online vs laboratory vs portable gas analysis](https://www.sarveshanalytics.com/learn/online-vs-laboratory-vs-portable-gas-analysis.html) **Why use a laboratory if I have an online analyser?** To verify the online instrument, to measure gases it does not cover, and to certify product to a standard. From the lesson [Online vs laboratory vs portable gas analysis](https://www.sarveshanalytics.com/learn/online-vs-laboratory-vs-portable-gas-analysis.html) **Is online analysis more accurate than laboratory analysis?** Usually not. The laboratory can be more accurate; online analysis is faster and continuous. From the lesson [Online vs laboratory vs portable gas analysis](https://www.sarveshanalytics.com/learn/online-vs-laboratory-vs-portable-gas-analysis.html) **Which is cheapest?** A portable instrument has the lowest outlay; online has the lowest cost per reading when you need continuous data. From the lesson [Online vs laboratory vs portable gas analysis](https://www.sarveshanalytics.com/learn/online-vs-laboratory-vs-portable-gas-analysis.html) **Why does gas composition not change when I compress it?** Compression squeezes all components equally, so each keeps its share of the molecules. From the lesson [How gases behave: pressure, temperature and partial pressure](https://www.sarveshanalytics.com/learn/how-gases-behave-pressure-temperature-and-partial-pressure.html) **What is absolute pressure?** Pressure measured from a perfect vacuum, as opposed to gauge pressure, which is measured from the surrounding atmosphere. From the lesson [How gases behave: pressure, temperature and partial pressure](https://www.sarveshanalytics.com/learn/how-gases-behave-pressure-temperature-and-partial-pressure.html) **Why do analysers need a pressure reading?** Some sensors respond to partial pressure, so the analyser measures ambient pressure to correct the reading. From the lesson [How gases behave: pressure, temperature and partial pressure](https://www.sarveshanalytics.com/learn/how-gases-behave-pressure-temperature-and-partial-pressure.html) **Is air really 21 % oxygen?** Dry air is 20.95 %, usually rounded to 21 % or 20.9 %. From the lesson [How gases behave: pressure, temperature and partial pressure](https://www.sarveshanalytics.com/learn/how-gases-behave-pressure-temperature-and-partial-pressure.html) **How many ppm is 1 %?** 10,000 ppm. From the lesson [ppm, percent and ppb explained for gas analysis](https://www.sarveshanalytics.com/learn/ppm-percent-and-ppb-units-explained.html) **Is ppm a mass or a volume ratio in gas analysis?** Volume, unless the specification says otherwise. From the lesson [ppm, percent and ppb explained for gas analysis](https://www.sarveshanalytics.com/learn/ppm-percent-and-ppb-units-explained.html) **What does 99.999 % purity mean in ppm of impurity?** Five nines means 10 ppm total impurity, since 100 minus 99.999 is 0.001 %. From the lesson [ppm, percent and ppb explained for gas analysis](https://www.sarveshanalytics.com/learn/ppm-percent-and-ppb-units-explained.html) **Why do some limits use mg/m3?** Environmental rules usually state mass per volume at reference conditions. See the converter. From the lesson [ppm, percent and ppb explained for gas analysis](https://www.sarveshanalytics.com/learn/ppm-percent-and-ppb-units-explained.html) **How do I convert ppm to mg/Nm3?** Multiply by the molar mass and divide by 22.414, for 0 C and 1013.25 hPa. From the lesson [ppm to mg/Nm3: volume vs mass concentration](https://www.sarveshanalytics.com/learn/volume-mass-and-mg-per-nm3-concentration-units.html) **What is the difference between Nm3 and Sm3?** Nm3 refers to normal conditions, usually 0 C; Sm3 to standard conditions, often 15 or 25 C. Always check the definition in the document. From the lesson [ppm to mg/Nm3: volume vs mass concentration](https://www.sarveshanalytics.com/learn/volume-mass-and-mg-per-nm3-concentration-units.html) **Is a wet or dry basis used for emission limits?** Usually dry, but the permit or standard decides. From the lesson [ppm to mg/Nm3: volume vs mass concentration](https://www.sarveshanalytics.com/learn/volume-mass-and-mg-per-nm3-concentration-units.html) **Does temperature change ppm?** No. ppm is a volume fraction. It changes mg/m3. From the lesson [ppm to mg/Nm3: volume vs mass concentration](https://www.sarveshanalytics.com/learn/volume-mass-and-mg-per-nm3-concentration-units.html) **Is oxygen higher or lower when measured wet?** Lower, because the water vapour takes up part of the volume. From the lesson [Dry basis vs wet basis in gas measurement](https://www.sarveshanalytics.com/learn/dry-basis-vs-wet-basis-gas-measurement.html) **How much water is in flue gas?** Commonly 5 to 20 % by volume depending on the fuel. Gas-fired plants carry more than coal-fired. From the lesson [Dry basis vs wet basis in gas measurement](https://www.sarveshanalytics.com/learn/dry-basis-vs-wet-basis-gas-measurement.html) **Do dry-gas analysers see water?** A cooled sample still holds water at the cooler's dew point, which is usually a few percent or less. From the lesson [Dry basis vs wet basis in gas measurement](https://www.sarveshanalytics.com/learn/dry-basis-vs-wet-basis-gas-measurement.html) **Can I measure moisture in the same sample?** Only if the sample is kept above its dew point, which is a different sample system from a cooled dry one. From the lesson [Dry basis vs wet basis in gas measurement](https://www.sarveshanalytics.com/learn/dry-basis-vs-wet-basis-gas-measurement.html) **What is the difference between accuracy and precision?** Accuracy is how close to the true value; precision is how close repeated readings are to each other. From the lesson [Accuracy, precision, repeatability and drift in gas analysers](https://www.sarveshanalytics.com/learn/accuracy-precision-repeatability-and-drift.html) **What does plus or minus 1 % of span mean?** The error can be up to 1 % of the full-scale value anywhere on the range. From the lesson [Accuracy, precision, repeatability and drift in gas analysers](https://www.sarveshanalytics.com/learn/accuracy-precision-repeatability-and-drift.html) **What is resolution?** The smallest step the instrument can display, which is not the same as its accuracy. From the lesson [Accuracy, precision, repeatability and drift in gas analysers](https://www.sarveshanalytics.com/learn/accuracy-precision-repeatability-and-drift.html) **Why does an analyser drift?** Sensor ageing and temperature effects on the sensor and electronics. From the lesson [Accuracy, precision, repeatability and drift in gas analysers](https://www.sarveshanalytics.com/learn/accuracy-precision-repeatability-and-drift.html) **What is a good T90 for a gas analyser?** It depends on the sensor and gas. Process control often needs seconds to a minute; ask for the T90 at your flow and range. From the lesson [Response time, T90 and sample lag in gas analysis](https://www.sarveshanalytics.com/learn/response-time-t90-and-sample-lag.html) **Is T90 the same as response time?** T90 is the usual way to quote response time. Some datasheets use T95 or T63 instead. From the lesson [Response time, T90 and sample lag in gas analysis](https://www.sarveshanalytics.com/learn/response-time-t90-and-sample-lag.html) **Why is my reading slower than the datasheet T90?** The datasheet describes the analyser alone. Your sample line adds lag in front of it. From the lesson [Response time, T90 and sample lag in gas analysis](https://www.sarveshanalytics.com/learn/response-time-t90-and-sample-lag.html) **Can software speed up a reading?** Not the physical delay. Filters in the control system make it smoother and slower, not faster. From the lesson [Response time, T90 and sample lag in gas analysis](https://www.sarveshanalytics.com/learn/response-time-t90-and-sample-lag.html) **What is the most important line on a gas analyser datasheet?** The sample conditions. An analyser outside them will not perform as stated. From the lesson [How to read a gas analyser datasheet](https://www.sarveshanalytics.com/learn/reading-a-gas-analyser-datasheet.html) **What does IP rating tell me?** How well the enclosure keeps out dust and water, for example IP65. From the lesson [How to read a gas analyser datasheet](https://www.sarveshanalytics.com/learn/reading-a-gas-analyser-datasheet.html) **Are datasheet figures guaranteed on my plant?** They apply under the stated conditions. Your sample and installation can change them, so ask. From the lesson [How to read a gas analyser datasheet](https://www.sarveshanalytics.com/learn/reading-a-gas-analyser-datasheet.html) **Where do I find the ACCURRA-S datasheet?** On the downloads page of this website. From the lesson [How to read a gas analyser datasheet](https://www.sarveshanalytics.com/learn/reading-a-gas-analyser-datasheet.html) ## Measurement principles **Which gas sensor is the most accurate?** It depends on the gas. Each technology is best for the gases it was built for; the right match matters more than the technology's reputation. From the lesson [Gas analysis technologies compared: which sensor for which gas](https://www.sarveshanalytics.com/learn/gas-analysis-technologies-compared.html) **Can one sensor measure all gases?** No. Each uses a physical property that only some gases have. From the lesson [Gas analysis technologies compared: which sensor for which gas](https://www.sarveshanalytics.com/learn/gas-analysis-technologies-compared.html) **What is the difference between a sensor and an analyser?** The sensor is the element that responds to the gas. The analyser is the whole instrument with electronics, display and outputs. From the lesson [Gas analysis technologies compared: which sensor for which gas](https://www.sarveshanalytics.com/learn/gas-analysis-technologies-compared.html) **Does Sarvesh make chromatographs or laser analysers?** No. The range covers electrochemical, paramagnetic, zirconia, NDIR, thermal conductivity and ceramic moisture sensing. From the lesson [Gas analysis technologies compared: which sensor for which gas](https://www.sarveshanalytics.com/learn/gas-analysis-technologies-compared.html) **Which sensor is best for ppm oxygen?** An electrochemical cell, such as ACCURRA-S 3015, which reads 0 to 1000 ppm with a minimum range of 0 to 100 ppm. From the lesson [Electrochemical vs paramagnetic oxygen sensors](https://www.sarveshanalytics.com/learn/electrochemical-vs-paramagnetic-oxygen-sensors.html) **Which sensor has the longest life?** Paramagnetic sensors have no consumed element. Electrochemical cells wear out; the catalogue gives more than 18 months to 2 years depending on model. From the lesson [Electrochemical vs paramagnetic oxygen sensors](https://www.sarveshanalytics.com/learn/electrochemical-vs-paramagnetic-oxygen-sensors.html) **Can a paramagnetic sensor measure trace oxygen?** Paramagnetic sensors are used for percent and purity measurement. Trace oxygen uses electrochemical cells. From the lesson [Electrochemical vs paramagnetic oxygen sensors](https://www.sarveshanalytics.com/learn/electrochemical-vs-paramagnetic-oxygen-sensors.html) **Which sensor for oxygen purity?** Models 3090 and 3190, both with ambient pressure and temperature compensation. 3090 is electrochemical over 0 to 100 %; 3190 is paramagnetic over 95 to 100 %. From the lesson [Electrochemical vs paramagnetic oxygen sensors](https://www.sarveshanalytics.com/learn/electrochemical-vs-paramagnetic-oxygen-sensors.html) **How does a zirconia oxygen sensor work?** A heated zirconia cell conducts oxygen ions and produces a voltage that depends on the oxygen difference between the flue gas and a reference air stream. From the lesson [How a zirconia oxygen analyser works](https://www.sarveshanalytics.com/learn/how-a-zirconia-oxygen-analyser-works.html) **Why does zirconia need heating?** Zirconia conducts oxygen ions only at high temperature, so the cell is heated to a controlled working temperature. From the lesson [How a zirconia oxygen analyser works](https://www.sarveshanalytics.com/learn/how-a-zirconia-oxygen-analyser-works.html) **Can a zirconia analyser read low if there is unburnt fuel?** Yes. Combustibles consume oxygen at the hot cell, so the reading is lower than the true oxygen content. From the lesson [How a zirconia oxygen analyser works](https://www.sarveshanalytics.com/learn/how-a-zirconia-oxygen-analyser-works.html) **How is ACCURRA-Zr calibrated?** With plain air at a single point. From the lesson [How a zirconia oxygen analyser works](https://www.sarveshanalytics.com/learn/how-a-zirconia-oxygen-analyser-works.html) **Can NDIR measure oxygen?** No. Oxygen does not absorb infrared at these wavelengths. Use electrochemical or paramagnetic sensors. From the lesson [What is an NDIR gas analyser?](https://www.sarveshanalytics.com/learn/what-is-an-ndir-gas-analyser.html) **Can NDIR measure hydrogen?** No. Hydrogen is measured by thermal conductivity, for example ACCURRA-TCD. From the lesson [What is an NDIR gas analyser?](https://www.sarveshanalytics.com/learn/what-is-an-ndir-gas-analyser.html) **Does NDIR need a reference gas?** Calibration uses zero and span gas. Normal operation does not consume gas. From the lesson [What is an NDIR gas analyser?](https://www.sarveshanalytics.com/learn/what-is-an-ndir-gas-analyser.html) **How long does an NDIR sensor last?** The ACCURRA-S catalogue gives more than five years for the NDIR models. From the lesson [What is an NDIR gas analyser?](https://www.sarveshanalytics.com/learn/what-is-an-ndir-gas-analyser.html) **Do thermal conductivity analysers need a reference gas?** ACCURRA-TCD does not, according to the catalogue. From the lesson [How thermal conductivity gas analysers (TCD) work](https://www.sarveshanalytics.com/learn/how-thermal-conductivity-gas-analysers-work.html) **Which gases can a thermal conductivity analyser measure?** Any binary mixture whose components differ in conductivity. The ACCURRA-TCD catalogue lists hydrogen, helium, argon, nitrogen, nitrous oxide, neon and krypton. From the lesson [How thermal conductivity gas analysers (TCD) work](https://www.sarveshanalytics.com/learn/how-thermal-conductivity-gas-analysers-work.html) **Can it measure oxygen?** Only in a binary background of a gas with very different conductivity, such as oxygen in hydrogen or in helium. From the lesson [How thermal conductivity gas analysers (TCD) work](https://www.sarveshanalytics.com/learn/how-thermal-conductivity-gas-analysers-work.html) **Why does moisture matter?** Water vapour has its own conductivity, so wet samples shift the reading. Dry the sample or hold its moisture constant. From the lesson [How thermal conductivity gas analysers (TCD) work](https://www.sarveshanalytics.com/learn/how-thermal-conductivity-gas-analysers-work.html) **What dew point is dry enough for nitrogen?** It depends on the use. Heat treatment and electronics lines often specify dew points well below minus 40 C. Your process specification sets the limit. From the lesson [What is dew point and how is it measured?](https://www.sarveshanalytics.com/learn/what-is-dew-point-and-how-is-it-measured.html) **Is a lower dew point always better?** A lower dew point is drier, but cost rises as you dry further. Specify the dew point the process needs. From the lesson [What is dew point and how is it measured?](https://www.sarveshanalytics.com/learn/what-is-dew-point-and-how-is-it-measured.html) **How do I convert dew point to ppm?** Use the saturation vapour pressure at the dew point divided by the total pressure. At atmospheric pressure, minus 60 C is about 11 ppm by volume. From the lesson [What is dew point and how is it measured?](https://www.sarveshanalytics.com/learn/what-is-dew-point-and-how-is-it-measured.html) **Can I calibrate dew point on site?** No. Field calibration is not possible on M015; ask us how the sensor is checked and recalibrated. From the lesson [What is dew point and how is it measured?](https://www.sarveshanalytics.com/learn/what-is-dew-point-and-how-is-it-measured.html) **What is the most accurate way to measure dew point?** A chilled mirror hygrometer is the usual reference, but it needs clean gas and skilled operation. From the lesson [Moisture measurement methods compared for dry gas](https://www.sarveshanalytics.com/learn/moisture-measurement-methods-compared.html) **Can I measure dew point with a humidity sensor?** Relative humidity sensors suit ambient air. Dry process gas needs a sensor made for low dew point. From the lesson [Moisture measurement methods compared for dry gas](https://www.sarveshanalytics.com/learn/moisture-measurement-methods-compared.html) **Why does my moisture reading drift after maintenance?** The tubing re-wets when opened to air and takes time to dry. Purge before reading. From the lesson [Moisture measurement methods compared for dry gas](https://www.sarveshanalytics.com/learn/moisture-measurement-methods-compared.html) **Which range does ACCURRA-S M015 cover?** Minus 80 to plus 20 C dew point with a ceramic sensor, per the datasheet. From the lesson [Moisture measurement methods compared for dry gas](https://www.sarveshanalytics.com/learn/moisture-measurement-methods-compared.html) **What is cross-sensitivity?** A sensor's response to gases other than its target. From the lesson [Cross-Sensitivity and interference in gas analysers](https://www.sarveshanalytics.com/learn/cross-sensitivity-and-interference-in-gas-analysers.html) **How do I find a sensor's interferences?** In the datasheet or the manufacturer's cross-sensitivity table; ask the supplier about every gas in your sample. From the lesson [Cross-Sensitivity and interference in gas analysers](https://www.sarveshanalytics.com/learn/cross-sensitivity-and-interference-in-gas-analysers.html) **Can software correct cross-sensitivity?** Only if the interfering gas is measured too. Otherwise the instrument cannot tell the two effects apart. From the lesson [Cross-Sensitivity and interference in gas analysers](https://www.sarveshanalytics.com/learn/cross-sensitivity-and-interference-in-gas-analysers.html) **Is interference the same as drift?** No. Drift changes with time at a constant gas. Interference changes with the presence of another gas. From the lesson [Cross-Sensitivity and interference in gas analysers](https://www.sarveshanalytics.com/learn/cross-sensitivity-and-interference-in-gas-analysers.html) **Why does my trace oxygen reading never reach the expected low value?** Usually a leak or permeation in the sample line, not the sensor. Leak-test and purge. From the lesson [Trace oxygen measurement and air ingress: ppm done right](https://www.sarveshanalytics.com/learn/trace-oxygen-measurement-and-air-ingress.html) **How long does a trace oxygen cell take to recover after air exposure?** It can take hours at ppm level, depending on the exposure and the cell. Isolate it during maintenance. From the lesson [Trace oxygen measurement and air ingress: ppm done right](https://www.sarveshanalytics.com/learn/trace-oxygen-measurement-and-air-ingress.html) **Which analyser measures trace oxygen?** ACCURRA-S 3015 covers 0 to 1000 ppm with a minimum range of 0 to 100 ppm. From the lesson [Trace oxygen measurement and air ingress: ppm done right](https://www.sarveshanalytics.com/learn/trace-oxygen-measurement-and-air-ingress.html) **Can I use plastic tube if the line is short?** At ppm levels, no. Use stainless steel; it is a small cost against the error. From the lesson [Trace oxygen measurement and air ingress: ppm done right](https://www.sarveshanalytics.com/learn/trace-oxygen-measurement-and-air-ingress.html) **How do you measure hydrogen purity online?** With a thermal conductivity analyser, for a binary mixture. ACCURRA-TCD needs no reference gas. From the lesson [Measuring hydrogen: purity, mixtures and safety limits](https://www.sarveshanalytics.com/learn/measuring-hydrogen-purity-and-hydrogen-in-gas-mixtures.html) **Can hydrogen be measured next to methane?** Not reliably by thermal conductivity alone, since methane changes the reading. Ask an engineer about the composition. From the lesson [Measuring hydrogen: purity, mixtures and safety limits](https://www.sarveshanalytics.com/learn/measuring-hydrogen-purity-and-hydrogen-in-gas-mixtures.html) **What range of hydrogen can ACCURRA-TCD measure?** 0 to 100 % depending on the background gas, per the application notes. From the lesson [Measuring hydrogen: purity, mixtures and safety limits](https://www.sarveshanalytics.com/learn/measuring-hydrogen-purity-and-hydrogen-in-gas-mixtures.html) **Is ACCURRA-TCD suitable for hazardous areas?** Use ACCURRA-Hz for oxygen in hazardous areas. Tell us your area classification for other measurements. From the lesson [Measuring hydrogen: purity, mixtures and safety limits](https://www.sarveshanalytics.com/learn/measuring-hydrogen-purity-and-hydrogen-in-gas-mixtures.html) **Which ACCURRA-S models measure CO2?** 6030 (0 to 20 % or 0 to 100 %) and 6015 for ppm ranges, by NDIR. From the lesson [Measuring carbon monoxide and carbon dioxide online](https://www.sarveshanalytics.com/learn/measuring-carbon-monoxide-and-carbon-dioxide.html) **Which models measure CO?** 2015 for ppm ranges and 2030 for percent ranges. Confirm ranges against the datasheet. From the lesson [Measuring carbon monoxide and carbon dioxide online](https://www.sarveshanalytics.com/learn/measuring-carbon-monoxide-and-carbon-dioxide.html) **Can one analyser read both CO and CO2?** Yes, in a dual-channel enclosure from one sample. From the lesson [Measuring carbon monoxide and carbon dioxide online](https://www.sarveshanalytics.com/learn/measuring-carbon-monoxide-and-carbon-dioxide.html) **Why is the sample cooled before an NDIR analyser?** To remove condensing water that would disturb the optical path and the reading. From the lesson [Measuring carbon monoxide and carbon dioxide online](https://www.sarveshanalytics.com/learn/measuring-carbon-monoxide-and-carbon-dioxide.html) **How do you measure methane in biogas?** By NDIR on a conditioned sample, for example ACCURRA-S 4030. From the lesson [Measuring methane and biogas composition online](https://www.sarveshanalytics.com/learn/measuring-methane-and-biogas.html) **Can one analyser measure methane and CO2 together?** Yes, a dual-channel enclosure reads both from one sample. From the lesson [Measuring methane and biogas composition online](https://www.sarveshanalytics.com/learn/measuring-methane-and-biogas.html) **What does biogas contain besides methane?** CO2, water vapour, and traces of H2S, hydrogen, nitrogen and oxygen. From the lesson [Measuring methane and biogas composition online](https://www.sarveshanalytics.com/learn/measuring-methane-and-biogas.html) **Is a biogas analyser safe-area equipment?** The standard ACCURRA-S is for safe areas. For classified locations, tell us the zone and we will advise. From the lesson [Measuring methane and biogas composition online](https://www.sarveshanalytics.com/learn/measuring-methane-and-biogas.html) **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. From the lesson [Extractive vs In-Situ gas analysis](https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html) **Why do extractive systems fail?** Most failures are in the sample path: blocked filters, condensate and pump faults. From the lesson [Extractive vs In-Situ gas analysis](https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html) **Can I measure CO in situ?** Extractive measurement is the usual approach for CO in flue gas. From the lesson [Extractive vs In-Situ gas analysis](https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html) **Which Sarvesh product does extractive emission monitoring?** SGI-320, with a heated probe, heated line, conditioner and analysers. From the lesson [Extractive vs In-Situ gas analysis](https://www.sarveshanalytics.com/learn/extractive-vs-in-situ-gas-analysis.html) **Which analyser for 99.99 % nitrogen?** Trace model 3015. Residual oxygen up to 100 ppm is the measurement. From the lesson [Choosing an oxygen analyser: trace, percent or purity](https://www.sarveshanalytics.com/learn/choosing-an-oxygen-analyser-trace-percent-or-purity.html) **Which for PSA oxygen at 93 %?** The percentage models 3030 or 3130, which cover 0 to 100 %. The purity models start at 95 %. From the lesson [Choosing an oxygen analyser: trace, percent or purity](https://www.sarveshanalytics.com/learn/choosing-an-oxygen-analyser-trace-percent-or-purity.html) **Which for cryogenic oxygen at 99 %?** Purity model 3090 or 3190, with ambient pressure and temperature compensation. From the lesson [Choosing an oxygen analyser: trace, percent or purity](https://www.sarveshanalytics.com/learn/choosing-an-oxygen-analyser-trace-percent-or-purity.html) **Which for boiler flue gas?** ACCURRA-Zr, an in-situ zirconia analyser. From the lesson [Choosing an oxygen analyser: trace, percent or purity](https://www.sarveshanalytics.com/learn/choosing-an-oxygen-analyser-trace-percent-or-purity.html) **Why does barometric pressure affect oxygen analysers?** Many sensors respond to oxygen partial pressure, which scales with total pressure. A fall in pressure lowers the reading even though the gas is unchanged. From the lesson [Why ambient pressure affects oxygen purity readings](https://www.sarveshanalytics.com/learn/why-ambient-pressure-affects-oxygen-purity-readings.html) **How much error can pressure cause?** The ACCURRA-S catalogue states up to 10 % over a day and night swing in the 90 to 100 % range, without compensation. From the lesson [Why ambient pressure affects oxygen purity readings](https://www.sarveshanalytics.com/learn/why-ambient-pressure-affects-oxygen-purity-readings.html) **Which ACCURRA-S models compensate?** Purity models 3090 (electrochemical, 0 to 100 %) and 3190 (paramagnetic, 95 to 100 %). From the lesson [Why ambient pressure affects oxygen purity readings](https://www.sarveshanalytics.com/learn/why-ambient-pressure-affects-oxygen-purity-readings.html) **Does compensation remove the need for calibration?** No. Calibration is still needed, but compensation keeps the calibration valid across weather and seasons. From the lesson [Why ambient pressure affects oxygen purity readings](https://www.sarveshanalytics.com/learn/why-ambient-pressure-affects-oxygen-purity-readings.html) ## Sampling and conditioning **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. From the lesson [How to design a gas sample handling system](https://www.sarveshanalytics.com/learn/how-to-design-a-gas-sample-handling-system.html) **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. From the lesson [How to design a gas sample handling system](https://www.sarveshanalytics.com/learn/how-to-design-a-gas-sample-handling-system.html) **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. From the lesson [How to design a gas sample handling system](https://www.sarveshanalytics.com/learn/how-to-design-a-gas-sample-handling-system.html) **Can you design the system for me?** Yes. Send the sample temperature, pressure, dew point, dust level and distance to the analyser. From the lesson [How to design a gas sample handling system](https://www.sarveshanalytics.com/learn/how-to-design-a-gas-sample-handling-system.html) **Where should a sample point be?** At a well-mixed location, upstream of air leaks, at known process conditions and accessible for maintenance. From the lesson [Choosing the sample point for a gas analyser](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html) **How far downstream of a gas injection point should I sample?** Far enough for mixing, typically several pipe diameters of turbulent flow or a mixing element. Ask for advice for your case. From the lesson [Choosing the sample point for a gas analyser](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html) **Does the tapping affect response time?** Yes. A large or dead tapping volume adds lag. From the lesson [Choosing the sample point for a gas analyser](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html) **Can you advise on the sample point?** Yes. Send a drawing or photographs with the application data sheet. From the lesson [Choosing the sample point for a gas analyser](https://www.sarveshanalytics.com/learn/choosing-the-sample-point.html) **What tubing is best for gas analysis?** 316 stainless steel for most trace and reactive work. From the lesson [Sample lines: materials, length, diameter and lag](https://www.sarveshanalytics.com/learn/sample-lines-materials-length-and-lag.html) **How long can a sample line be?** As short as practical; the limit is the acceptable lag, which depends on bore, flow and pressure. From the lesson [Sample lines: materials, length, diameter and lag](https://www.sarveshanalytics.com/learn/sample-lines-materials-length-and-lag.html) **Can I use flexible hose?** For short connections to the analyser in non-critical percent measurements. Use metal for ppm and moisture. From the lesson [Sample lines: materials, length, diameter and lag](https://www.sarveshanalytics.com/learn/sample-lines-materials-length-and-lag.html) **Do I need a heated line?** If the sample is wet and hot, yes, until it reaches a cooler. Dry gases at ambient temperature do not. From the lesson [Sample lines: materials, length, diameter and lag](https://www.sarveshanalytics.com/learn/sample-lines-materials-length-and-lag.html) **How often should analyser filters be changed?** By experience at the site; start with a regular interval and shorten it if the pressure drop or flow shows blocking. From the lesson [Filters for gas analysers: dust, mist, membrane](https://www.sarveshanalytics.com/learn/filters-and-particulate-protection.html) **Can I clean and reuse a filter element?** Not reliably. Replace it. From the lesson [Filters for gas analysers: dust, mist, membrane](https://www.sarveshanalytics.com/learn/filters-and-particulate-protection.html) **What dust size can ACCURRA-S accept?** The catalogue specifies dust below 3 micron. From the lesson [Filters for gas analysers: dust, mist, membrane](https://www.sarveshanalytics.com/learn/filters-and-particulate-protection.html) **Who supplies the filters?** Sarvesh represents Headline Filters, UK, in India. From the lesson [Filters for gas analysers: dust, mist, membrane](https://www.sarveshanalytics.com/learn/filters-and-particulate-protection.html) **What temperature should a sample cooler run at?** Often 3 to 5 C, low enough to remove most water without freezing. Follow the cooler's specification. From the lesson [Condensate, moisture and sample cooling for gas analysis](https://www.sarveshanalytics.com/learn/condensate-moisture-and-sample-cooling.html) **What is the difference between SGI-300 and i-Cons?** SGI-300 is a Peltier cooler with pump, filter and condensate detector; i-Cons is a smart Peltier conditioner with diagnostics, auto blowback and Modbus in a compact 19 inch cabinet. From the lesson [Condensate, moisture and sample cooling for gas analysis](https://www.sarveshanalytics.com/learn/condensate-moisture-and-sample-cooling.html) **Can I measure moisture after a cooler?** Only to the cooler's dew point. If you need the process moisture, the sample must not be cooled. From the lesson [Condensate, moisture and sample cooling for gas analysis](https://www.sarveshanalytics.com/learn/condensate-moisture-and-sample-cooling.html) **Why does my CO2 reading differ before and after the cooler?** Soluble CO2 partly dissolves in condensate; the difference should be small and steady. From the lesson [Condensate, moisture and sample cooling for gas analysis](https://www.sarveshanalytics.com/learn/condensate-moisture-and-sample-cooling.html) **What flow does an ACCURRA-S need?** About 1 LPM, per the catalogue, with a regulated pressure of 2 to 10 psig. From the lesson [Sample pressure, flow and fast bypass loops](https://www.sarveshanalytics.com/learn/sample-pressure-flow-and-bypass-loops.html) **Do I need a pressure regulator?** Yes when the process pressure is higher than the analyser's range or varies. From the lesson [Sample pressure, flow and fast bypass loops](https://www.sarveshanalytics.com/learn/sample-pressure-flow-and-bypass-loops.html) **Where should the sample vent?** To a safe place suited to the gas; flammable or toxic samples go to a flare or recovery. From the lesson [Sample pressure, flow and fast bypass loops](https://www.sarveshanalytics.com/learn/sample-pressure-flow-and-bypass-loops.html) **What is a fast loop?** A bypass that circulates a large flow near the tapping so the analyser takes a quick, small slice. From the lesson [Sample pressure, flow and fast bypass loops](https://www.sarveshanalytics.com/learn/sample-pressure-flow-and-bypass-loops.html) **What material should a probe be?** SS316 for general duty, Inconel for higher temperature or corrosion, ceramic for the hottest duties. From the lesson [Probes and blowback for hot, dusty and tarry gas](https://www.sarveshanalytics.com/learn/hot-dusty-gas-probes-and-blowback.html) **How often should blowback run?** Set by the dust load; start frequent and relax once the probe stays clean. From the lesson [Probes and blowback for hot, dusty and tarry gas](https://www.sarveshanalytics.com/learn/hot-dusty-gas-probes-and-blowback.html) **Can I sample tarry gas?** Yes with a heated probe, heated line and conditioning matched to the tar, after review of the composition. From the lesson [Probes and blowback for hot, dusty and tarry gas](https://www.sarveshanalytics.com/learn/hot-dusty-gas-probes-and-blowback.html) **What is the difference between SP and SRP probes?** SP are fixed probes; SRP are retractable. From the lesson [Probes and blowback for hot, dusty and tarry gas](https://www.sarveshanalytics.com/learn/hot-dusty-gas-probes-and-blowback.html) **Why can't I analyse liquid oxygen directly?** Analysers measure gas. The liquid must be vaporised, and completely, to keep its composition. From the lesson [Sampling cryogenic and liquefied gases: vaporisers](https://www.sarveshanalytics.com/learn/sampling-cryogenic-and-liquefied-gases.html) **Which vaporiser does Sarvesh offer for cryogenic samples?** SV-200, with a bypass line; SV-400 is also available. From the lesson [Sampling cryogenic and liquefied gases: vaporisers](https://www.sarveshanalytics.com/learn/sampling-cryogenic-and-liquefied-gases.html) **Can I analyse LPG with ACCURRA-S?** Flammable samples are outside the standard ACCURRA-S sample specification; ask an engineer. From the lesson [Sampling cryogenic and liquefied gases: vaporisers](https://www.sarveshanalytics.com/learn/sampling-cryogenic-and-liquefied-gases.html) **How do I flush a vaporiser?** Use the bypass line, per the product instructions. From the lesson [Sampling cryogenic and liquefied gases: vaporisers](https://www.sarveshanalytics.com/learn/sampling-cryogenic-and-liquefied-gases.html) **Can ACCURRA-S measure corrosive gases?** Not in the standard configuration. Send the stream composition and we will advise. From the lesson [What samples an analyser cannot take: know the limits](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html) **Can you analyse H2S?** No; H2S is outside the ACCURRA-S gas list and the i-Cons and SGI-320 limits. From the lesson [What samples an analyser cannot take: know the limits](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html) **Can I put an analyser on raw biogas?** Only after conditioning; moisture and H2S must be dealt with first. From the lesson [What samples an analyser cannot take: know the limits](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html) **How do I find out if my sample is suitable?** Send the gas composition, pressure, temperature, dust and moisture with an application data sheet. From the lesson [What samples an analyser cannot take: know the limits](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html) **Why is my analyser reading wrong?** Check the sample first: flow, filters, leaks, condensate. Then apply a known gas. From the lesson [Sample system troubleshooting: symptoms to causes](https://www.sarveshanalytics.com/learn/sample-system-troubleshooting.html) **How do I find a leak?** Pressurise with inert gas and use a leak-detection fluid or a pressure-hold test. From the lesson [Sample system troubleshooting: symptoms to causes](https://www.sarveshanalytics.com/learn/sample-system-troubleshooting.html) **Why does water get into the analyser?** A failed cooler or blocked drain, or a line below the dew point. From the lesson [Sample system troubleshooting: symptoms to causes](https://www.sarveshanalytics.com/learn/sample-system-troubleshooting.html) **When should I call an engineer?** When known gas reads wrong, or after the sample checks are clean. From the lesson [Sample system troubleshooting: symptoms to causes](https://www.sarveshanalytics.com/learn/sample-system-troubleshooting.html) ## Installation and integration **Can an ACCURRA-S be field mounted?** It is built for panel or rack mounting. For field use, ask about an enclosure suited to the site. From the lesson [Where to mount a gas analyser: panel, shelter or field](https://www.sarveshanalytics.com/learn/where-to-mount-a-gas-analyser.html) **How far can the analyser be from the sample point?** As far as the acceptable lag allows; use a fast loop for long runs. From the lesson [Where to mount a gas analyser: panel, shelter or field](https://www.sarveshanalytics.com/learn/where-to-mount-a-gas-analyser.html) **Do analysers need heating in winter?** Ambient limits apply; in cold sites a heated shelter or enclosure avoids condensation. From the lesson [Where to mount a gas analyser: panel, shelter or field](https://www.sarveshanalytics.com/learn/where-to-mount-a-gas-analyser.html) **What IP rating do I need?** Choose by the dust and water exposure at the site; indoors IP20 to IP54 is common, outdoors IP65 or higher. From the lesson [Where to mount a gas analyser: panel, shelter or field](https://www.sarveshanalytics.com/learn/where-to-mount-a-gas-analyser.html) **What is a 4-20 mA signal?** A current that represents the reading, 4 mA at the bottom of the range and 20 mA at the top. From the lesson [Analyser outputs: 4-20 mA, relays and Modbus explained](https://www.sarveshanalytics.com/learn/analyser-outputs-4-20-ma-relays-and-modbus.html) **Which outputs does ACCURRA-S have?** Configurable 4-20 mA, relay alarms and Modbus RTU, according to the catalogue. From the lesson [Analyser outputs: 4-20 mA, relays and Modbus explained](https://www.sarveshanalytics.com/learn/analyser-outputs-4-20-ma-relays-and-modbus.html) **What is the maximum cable length for 4-20 mA?** Hundreds of metres, limited by the loop's compliance voltage and wire resistance. From the lesson [Analyser outputs: 4-20 mA, relays and Modbus explained](https://www.sarveshanalytics.com/learn/analyser-outputs-4-20-ma-relays-and-modbus.html) **Can Modbus start a calibration?** On models that support it; ask for the register map. From the lesson [Analyser outputs: 4-20 mA, relays and Modbus explained](https://www.sarveshanalytics.com/learn/analyser-outputs-4-20-ma-relays-and-modbus.html) **How far apart should power and signal cables run?** Use separate trays; a few tens of centimetres of separation is common, and follow your plant's standard. From the lesson [Wiring, grounding and electrical noise for gas analysers](https://www.sarveshanalytics.com/learn/wiring-grounding-and-electrical-noise.html) **Can I run Modbus beside power cables?** Avoid it; use shielded twisted pair and keep it separate. From the lesson [Wiring, grounding and electrical noise for gas analysers](https://www.sarveshanalytics.com/learn/wiring-grounding-and-electrical-noise.html) **What causes a noisy 4-20 mA signal?** Ground loops, unshielded cable, cables beside power, or a loose terminal. From the lesson [Wiring, grounding and electrical noise for gas analysers](https://www.sarveshanalytics.com/learn/wiring-grounding-and-electrical-noise.html) **Do I need surge protection?** For long outdoor cables, yes. From the lesson [Wiring, grounding and electrical noise for gas analysers](https://www.sarveshanalytics.com/learn/wiring-grounding-and-electrical-noise.html) **How do I scale a 4-20 mA input?** Set 4 mA to the low end and 20 mA to the high end of the analyser range, in the same units. From the lesson [Connecting a gas analyser to PLC, DCS and SCADA](https://www.sarveshanalytics.com/learn/connecting-an-analyser-to-plc-dcs-and-scada.html) **What should happen when the analyser fails?** That is a process decision: hold, switch to manual, alarm or trip. Decide it in advance. From the lesson [Connecting a gas analyser to PLC, DCS and SCADA](https://www.sarveshanalytics.com/learn/connecting-an-analyser-to-plc-dcs-and-scada.html) **Can the control system start an analyser calibration?** Where the analyser supports it by Modbus or a digital input. From the lesson [Connecting a gas analyser to PLC, DCS and SCADA](https://www.sarveshanalytics.com/learn/connecting-an-analyser-to-plc-dcs-and-scada.html) **How do I avoid nuisance alarms?** Use a deadband and a short delay, and separate warning from trip levels. From the lesson [Connecting a gas analyser to PLC, DCS and SCADA](https://www.sarveshanalytics.com/learn/connecting-an-analyser-to-plc-dcs-and-scada.html) **What power does an analyser need?** Check the model datasheet for voltage and consumption; use a clean supply. From the lesson [Site utilities checklist for gas analysers](https://www.sarveshanalytics.com/learn/site-utilities-checklist-for-analysers.html) **Do I need instrument air for every analyser?** Only for functions such as blowback or air purges, and for some probes. From the lesson [Site utilities checklist for gas analysers](https://www.sarveshanalytics.com/learn/site-utilities-checklist-for-analysers.html) **Where do I store calibration cylinders?** In a ventilated, secured place, with cylinders restrained, away from heat and incompatible gases. From the lesson [Site utilities checklist for gas analysers](https://www.sarveshanalytics.com/learn/site-utilities-checklist-for-analysers.html) **Can I vent to the room?** Only if the sample is harmless in the quantity vented; follow your site safety rules. From the lesson [Site utilities checklist for gas analysers](https://www.sarveshanalytics.com/learn/site-utilities-checklist-for-analysers.html) **How long does commissioning take?** From a few hours for a simple rack analyser to days for a system with probes and heated lines. From the lesson [Commissioning an online gas analyser: A Step-by-Step guide](https://www.sarveshanalytics.com/learn/commissioning-an-online-gas-analyser.html) **Should I calibrate before or after purging?** After purging and leak-testing, so the calibration reflects a clean system. From the lesson [Commissioning an online gas analyser: A Step-by-Step guide](https://www.sarveshanalytics.com/learn/commissioning-an-online-gas-analyser.html) **What documents do I need at hand-over?** Drawings, register map, calibration record, spares and maintenance intervals. From the lesson [Commissioning an online gas analyser: A Step-by-Step guide](https://www.sarveshanalytics.com/learn/commissioning-an-online-gas-analyser.html) **Can you commission for me?** Ask us about service support for your site. From the lesson [Commissioning an online gas analyser: A Step-by-Step guide](https://www.sarveshanalytics.com/learn/commissioning-an-online-gas-analyser.html) ## Calibration and maintenance **What is the difference between calibration and a calibration check?** A check compares and records; a calibration also adjusts the instrument. From the lesson [How gas analyser calibration works: zero and span](https://www.sarveshanalytics.com/learn/how-gas-analyser-calibration-works.html) **What span gas concentration should I use?** Typically 70 to 90 % of the range, in a background similar to the sample, with a certificate. From the lesson [How gas analyser calibration works: zero and span](https://www.sarveshanalytics.com/learn/how-gas-analyser-calibration-works.html) **Can I calibrate oxygen with air?** Yes for percent ranges, using clean dry air at 20.9 %; not for trace ranges. From the lesson [How gas analyser calibration works: zero and span](https://www.sarveshanalytics.com/learn/how-gas-analyser-calibration-works.html) **How do I know calibration worked?** Re-apply the gas and confirm the reading; then confirm the process reading returns. From the lesson [How gas analyser calibration works: zero and span](https://www.sarveshanalytics.com/learn/how-gas-analyser-calibration-works.html) **What calibration gas do I need for ACCURRA-S 3015?** A zero gas with very low oxygen and a span gas in nitrogen near the top of your range, with a certificate. From the lesson [Calibration gases: choosing, handling and certificates](https://www.sarveshanalytics.com/learn/calibration-gases-choosing-and-handling.html) **How long does a calibration cylinder last?** Until the expiry on the certificate, and until pressure falls to the cylinder maker's minimum. From the lesson [Calibration gases: choosing, handling and certificates](https://www.sarveshanalytics.com/learn/calibration-gases-choosing-and-handling.html) **Can I make my own calibration gas?** Not for a measurement that matters. Certified gas gives a traceable result. From the lesson [Calibration gases: choosing, handling and certificates](https://www.sarveshanalytics.com/learn/calibration-gases-choosing-and-handling.html) **Do I need different gas for each analyser?** Only if the ranges, gases or backgrounds differ. From the lesson [Calibration gases: choosing, handling and certificates](https://www.sarveshanalytics.com/learn/calibration-gases-choosing-and-handling.html) **How often should an oxygen analyser be calibrated?** Start monthly and adjust with as-found data; safety and purity measurements may justify more often. From the lesson [How often should you calibrate a gas analyser?](https://www.sarveshanalytics.com/learn/how-often-to-calibrate-a-gas-analyser.html) **Is annual calibration enough?** Only if drift records show it, and the consequence of error is small. From the lesson [How often should you calibrate a gas analyser?](https://www.sarveshanalytics.com/learn/how-often-to-calibrate-a-gas-analyser.html) **Does auto-calibration replace manual calibration?** It can reduce manual work, but you still verify with certified gas and review the results. From the lesson [How often should you calibrate a gas analyser?](https://www.sarveshanalytics.com/learn/how-often-to-calibrate-a-gas-analyser.html) **Who sets the interval?** You do, from your tolerance and records, unless a standard or quality system specifies one. From the lesson [How often should you calibrate a gas analyser?](https://www.sarveshanalytics.com/learn/how-often-to-calibrate-a-gas-analyser.html) **Is auto-calibration available on all ACCURRA-S models?** It is optional on most; 3015 and M015 do not have it. From the lesson [Auto-Calibration and validation checks for gas analysers](https://www.sarveshanalytics.com/learn/auto-calibration-and-validation-checks.html) **How often should auto-calibration run?** Daily or weekly is a common start; adjust to your drift records. From the lesson [Auto-Calibration and validation checks for gas analysers](https://www.sarveshanalytics.com/learn/auto-calibration-and-validation-checks.html) **Does auto-calibration reduce the need for cylinders?** No, it needs certified gas connected to the analyser. From the lesson [Auto-Calibration and validation checks for gas analysers](https://www.sarveshanalytics.com/learn/auto-calibration-and-validation-checks.html) **Can it start from the control system?** Via Modbus command on models that support it. From the lesson [Auto-Calibration and validation checks for gas analysers](https://www.sarveshanalytics.com/learn/auto-calibration-and-validation-checks.html) **Why is my analyser reading zero?** Check the output scaling, fault state, sensor and valve positions; then apply span gas. From the lesson [Troubleshooting gas analyser readings: high, low, noisy, slow](https://www.sarveshanalytics.com/learn/troubleshooting-gas-analyser-readings.html) **Why does the reading drift upward?** Temperature change, a leak, calibration gas exhausted or sensor ageing. From the lesson [Troubleshooting gas analyser readings: high, low, noisy, slow](https://www.sarveshanalytics.com/learn/troubleshooting-gas-analyser-readings.html) **How do I know if the sensor is dead?** Large span corrections, slow response or a zero that will not settle. From the lesson [Troubleshooting gas analyser readings: high, low, noisy, slow](https://www.sarveshanalytics.com/learn/troubleshooting-gas-analyser-readings.html) **Where are the alarm and calibration records?** ACCURRA-S saves calibration with deviation values and alarm history in the analyser. From the lesson [Troubleshooting gas analyser readings: high, low, noisy, slow](https://www.sarveshanalytics.com/learn/troubleshooting-gas-analyser-readings.html) **How often should an analyser be serviced?** A routine of daily, weekly, monthly and annual tasks, adjusted from your records. From the lesson [Maintenance schedule and spares for gas analysers](https://www.sarveshanalytics.com/learn/maintenance-schedule-and-spares-for-gas-analysers.html) **Which spares are essential?** Filter elements, fittings, calibration gas and, for critical analysers, a spare sensor. From the lesson [Maintenance schedule and spares for gas analysers](https://www.sarveshanalytics.com/learn/maintenance-schedule-and-spares-for-gas-analysers.html) **Can Sarvesh service my analyser?** Contact us with the model and site; support is part of how we work. From the lesson [Maintenance schedule and spares for gas analysers](https://www.sarveshanalytics.com/learn/maintenance-schedule-and-spares-for-gas-analysers.html) **Who should maintain analysers?** Trained instrument technicians following the manual. From the lesson [Maintenance schedule and spares for gas analysers](https://www.sarveshanalytics.com/learn/maintenance-schedule-and-spares-for-gas-analysers.html) **How long do gas sensors last?** It depends on the type and the sample. Electrochemical cells months to years; others longer. From the lesson [Sensor life, poisoning and replacement in gas analysers](https://www.sarveshanalytics.com/learn/sensor-life-poisoning-and-replacement.html) **Can a poisoned sensor recover?** Sometimes slowly if the exposure was brief; usually replace it. From the lesson [Sensor life, poisoning and replacement in gas analysers](https://www.sarveshanalytics.com/learn/sensor-life-poisoning-and-replacement.html) **Should I replace sensors on a schedule?** For critical points yes, informed by the calibration trend. From the lesson [Sensor life, poisoning and replacement in gas analysers](https://www.sarveshanalytics.com/learn/sensor-life-poisoning-and-replacement.html) **Does ACCURRA-S sensor choice affect life?** Yes: electrochemical cells are consumed; paramagnetic models have no consumed part. From the lesson [Sensor life, poisoning and replacement in gas analysers](https://www.sarveshanalytics.com/learn/sensor-life-poisoning-and-replacement.html) **Does ACCURRA-S support audit trails?** It stores calibration with deviation values and alarm history, and password-protects set-up. Tell us your exact requirements. From the lesson [Records, audit trails and qualification for regulated plants](https://www.sarveshanalytics.com/learn/records-audit-trails-and-qualification-for-regulated-plants.html) **Is ACCURRA-S compliant with a specific regulation?** We make no such claim; ask for a point-by-point answer for your requirement. From the lesson [Records, audit trails and qualification for regulated plants](https://www.sarveshanalytics.com/learn/records-audit-trails-and-qualification-for-regulated-plants.html) **Who writes the qualification documents?** Your quality team, with documents and data from the supplier. From the lesson [Records, audit trails and qualification for regulated plants](https://www.sarveshanalytics.com/learn/records-audit-trails-and-qualification-for-regulated-plants.html) **Can records be archived electronically?** Via the analyser's digital outputs into your own system. From the lesson [Records, audit trails and qualification for regulated plants](https://www.sarveshanalytics.com/learn/records-audit-trails-and-qualification-for-regulated-plants.html) ## Safety and hazardous areas **What is the explosive range of hydrogen?** About 4 to 75 % by volume in air. From the lesson [Flammability, explosive limits and gas safety basics](https://www.sarveshanalytics.com/learn/flammability-explosive-limits-and-gas-safety-basics.html) **Is a process analyser a safety device?** It can be part of a protection scheme, but it is not a personal gas detector and carries no SIL claim from us. From the lesson [Flammability, explosive limits and gas safety basics](https://www.sarveshanalytics.com/learn/flammability-explosive-limits-and-gas-safety-basics.html) **What does LEL stand for?** Lower explosive limit, also called lower flammable limit. From the lesson [Flammability, explosive limits and gas safety basics](https://www.sarveshanalytics.com/learn/flammability-explosive-limits-and-gas-safety-basics.html) **Does pressure change the explosive limits?** Yes; the range widens with pressure and temperature. Use design data for your conditions. From the lesson [Flammability, explosive limits and gas safety basics](https://www.sarveshanalytics.com/learn/flammability-explosive-limits-and-gas-safety-basics.html) **What is a typical LOC?** For many organic vapours in nitrogen, roughly 8 to 12 % oxygen; for hydrogen in nitrogen, near 5 %. Use values for your own materials. From the lesson [What is limiting oxygen concentration (LOC)?](https://www.sarveshanalytics.com/learn/what-is-limiting-oxygen-concentration.html) **What oxygen alarm should I set?** The value comes from your hazard study, as a margin below the LOC. The analyser alarm points are configurable. From the lesson [What is limiting oxygen concentration (LOC)?](https://www.sarveshanalytics.com/learn/what-is-limiting-oxygen-concentration.html) **Which analyser for a blanketed tank?** ACCURRA-S 3015 for ppm, 3030 or 3130 for percent, and ACCURRA-Hz or INFINITY-Tx in hazardous areas. From the lesson [What is limiting oxygen concentration (LOC)?](https://www.sarveshanalytics.com/learn/what-is-limiting-oxygen-concentration.html) **Does nitrogen blanketing need continuous monitoring?** Continuous monitoring is the usual way to demonstrate the barrier holds, and it permits a smaller margin under common guidance. From the lesson [What is limiting oxygen concentration (LOC)?](https://www.sarveshanalytics.com/learn/what-is-limiting-oxygen-concentration.html) **How do you purge a tank with nitrogen?** By sweep-through or dilution to a target oxygen, then confirm with an analyser. From the lesson [Inerting and purging: how they work and how to prove them](https://www.sarveshanalytics.com/learn/inerting-and-purging-how-they-work.html) **How much nitrogen do I need to purge a vessel?** About three vessel volumes for 1 % oxygen if well mixed, more in practice. From the lesson [Inerting and purging: how they work and how to prove them](https://www.sarveshanalytics.com/learn/inerting-and-purging-how-they-work.html) **Which standard sets inerting margins?** Standards such as NFPA 69 give guidance; follow the one that applies to your site. From the lesson [Inerting and purging: how they work and how to prove them](https://www.sarveshanalytics.com/learn/inerting-and-purging-how-they-work.html) **What oxygen alarm should I set?** Below the LOC by the margin your safety assessment requires. From the lesson [Inerting and purging: how they work and how to prove them](https://www.sarveshanalytics.com/learn/inerting-and-purging-how-they-work.html) **What does Zone 2 mean?** An area where an explosive gas atmosphere is not likely in normal operation and, if it occurs, lasts only briefly. From the lesson [Hazardous area classification: zones, gas groups, T-Classes](https://www.sarveshanalytics.com/learn/hazardous-area-classification-zones-gas-groups-temperature-classes.html) **Is IIC better than IIB?** IIC equipment is suitable for a wider range of gases, since it meets a more demanding test. From the lesson [Hazardous area classification: zones, gas groups, T-Classes](https://www.sarveshanalytics.com/learn/hazardous-area-classification-zones-gas-groups-temperature-classes.html) **What does T6 mean?** The equipment's surface will not exceed 85 C. From the lesson [Hazardous area classification: zones, gas groups, T-Classes](https://www.sarveshanalytics.com/learn/hazardous-area-classification-zones-gas-groups-temperature-classes.html) **Who decides the zone?** The plant owner or its consultant, documented on the area classification drawings. From the lesson [Hazardous area classification: zones, gas groups, T-Classes](https://www.sarveshanalytics.com/learn/hazardous-area-classification-zones-gas-groups-temperature-classes.html) **What does Gas Group IIC mean?** The most demanding gas group, which includes hydrogen and acetylene. IIC-certified equipment also suits IIA and IIB gases. From the lesson [Hazardous area gas analysers explained](https://www.sarveshanalytics.com/learn/hazardous-area-gas-analysers-explained.html) **What does T6 mean?** A maximum surface temperature of 85 C. From the lesson [Hazardous area gas analysers explained](https://www.sarveshanalytics.com/learn/hazardous-area-gas-analysers-explained.html) **What is a flameproof enclosure?** An Ex d enclosure that withstands an internal explosion and prevents it igniting the outside atmosphere. From the lesson [Hazardous area gas analysers explained](https://www.sarveshanalytics.com/learn/hazardous-area-gas-analysers-explained.html) **Is ACCURRA-Hz SIL rated?** We make no SIL claim. If your project requires SIL-rated devices, tell us at the start. From the lesson [Hazardous area gas analysers explained](https://www.sarveshanalytics.com/learn/hazardous-area-gas-analysers-explained.html) **What does Ex d mean?** Flameproof: the enclosure contains an internal explosion and prevents it igniting the outside atmosphere. From the lesson [Protection concepts: flameproof, intrinsic safety, purging](https://www.sarveshanalytics.com/learn/protection-concepts-flameproof-intrinsic-safety-and-purging.html) **What is intrinsic safety?** A concept that limits electrical energy so no spark or heat can ignite gas. From the lesson [Protection concepts: flameproof, intrinsic safety, purging](https://www.sarveshanalytics.com/learn/protection-concepts-flameproof-intrinsic-safety-and-purging.html) **Can I open a flameproof analyser in a hazardous area?** Only following the manufacturer's rules; ACCURRA-Hz allows calibration without opening the covers. From the lesson [Protection concepts: flameproof, intrinsic safety, purging](https://www.sarveshanalytics.com/learn/protection-concepts-flameproof-intrinsic-safety-and-purging.html) **Do I need a barrier for INFINITY-Tx?** Check the certificate and the loop's entity parameters; ask us for the installation requirements. From the lesson [Protection concepts: flameproof, intrinsic safety, purging](https://www.sarveshanalytics.com/learn/protection-concepts-flameproof-intrinsic-safety-and-purging.html) **Are ACCURRA analysers SIL rated?** We make no SIL claim. Tell us your requirement and we will respond point by point. From the lesson [What SIL means for gas analysers, and what it does not](https://www.sarveshanalytics.com/learn/what-sil-means-for-gas-analysers.html) **What is the difference between SIL and Ex certification?** Ex certification addresses ignition of explosive atmospheres; SIL addresses the reliability of a safety function. From the lesson [What SIL means for gas analysers, and what it does not](https://www.sarveshanalytics.com/learn/what-sil-means-for-gas-analysers.html) **Can a gas analyser be part of a safety loop?** Yes, with a proper safety design, but it needs careful treatment of sample, drift and response time. From the lesson [What SIL means for gas analysers, and what it does not](https://www.sarveshanalytics.com/learn/what-sil-means-for-gas-analysers.html) **What is proof testing?** A periodic test that reveals hidden failures in a safety function. From the lesson [What SIL means for gas analysers, and what it does not](https://www.sarveshanalytics.com/learn/what-sil-means-for-gas-analysers.html) **What oxygen level is safe to breathe?** Normal air is 20.95 %; below about 19.5 % is generally treated as deficient and above about 23.5 % as enriched. From the lesson [Oxygen enrichment and oxygen deficiency hazards](https://www.sarveshanalytics.com/learn/oxygen-enrichment-and-oxygen-deficiency-hazards.html) **Is nitrogen toxic?** No, but it displaces oxygen and can cause asphyxiation in closed spaces. From the lesson [Oxygen enrichment and oxygen deficiency hazards](https://www.sarveshanalytics.com/learn/oxygen-enrichment-and-oxygen-deficiency-hazards.html) **Can a process oxygen analyser be used as a personal monitor?** No; use a device built and certified for personal or area monitoring. From the lesson [Oxygen enrichment and oxygen deficiency hazards](https://www.sarveshanalytics.com/learn/oxygen-enrichment-and-oxygen-deficiency-hazards.html) **How should an oxygen analyser vent?** To a safe place suited to the gas, away from people and ignition sources. From the lesson [Oxygen enrichment and oxygen deficiency hazards](https://www.sarveshanalytics.com/learn/oxygen-enrichment-and-oxygen-deficiency-hazards.html) ## Process primers **What oxygen level should a boiler run at?** It depends on fuel and burner; take the target from the burner supplier and your commissioning, and trim to just above the CO breakpoint. From the lesson [Combustion, excess air and flue gas oxygen explained](https://www.sarveshanalytics.com/learn/combustion-excess-air-and-flue-gas-oxygen.html) **Why is oxygen measured in flue gas?** It is the simplest indicator of excess air and therefore of fuel efficiency. From the lesson [Combustion, excess air and flue gas oxygen explained](https://www.sarveshanalytics.com/learn/combustion-excess-air-and-flue-gas-oxygen.html) **Why measure CO too?** To make sure that reducing excess air does not cause incomplete combustion. From the lesson [Combustion, excess air and flue gas oxygen explained](https://www.sarveshanalytics.com/learn/combustion-excess-air-and-flue-gas-oxygen.html) **Which Sarvesh product measures flue gas oxygen?** ACCURRA-Zr, an in-situ zirconia analyser. From the lesson [Combustion, excess air and flue gas oxygen explained](https://www.sarveshanalytics.com/learn/combustion-excess-air-and-flue-gas-oxygen.html) **What are the products of an air separation plant?** Oxygen, nitrogen and argon, as gas and liquid, often with instrument air. From the lesson [How an air separation plant works and what is measured](https://www.sarveshanalytics.com/learn/how-an-air-separation-plant-works.html) **Which measurements matter most in an ASU?** Oxygen purity, trace oxygen in nitrogen and argon, and moisture. From the lesson [How an air separation plant works and what is measured](https://www.sarveshanalytics.com/learn/how-an-air-separation-plant-works.html) **Why measure CO2 at the purifier?** A rising CO2 shows the adsorber is exhausted and CO2 could freeze downstream. From the lesson [How an air separation plant works and what is measured](https://www.sarveshanalytics.com/learn/how-an-air-separation-plant-works.html) **Do you supply analysers for ASUs?** Yes; see the industrial gas plant pages. From the lesson [How an air separation plant works and what is measured](https://www.sarveshanalytics.com/learn/how-an-air-separation-plant-works.html) **What is PSA?** Pressure swing adsorption: beds of adsorbent separate gases at pressure and are regenerated by lowering pressure. From the lesson [PSA, VPSA and membrane gas generators explained](https://www.sarveshanalytics.com/learn/nitrogen-and-oxygen-generators-psa-vpsa-and-membrane.html) **How pure is PSA nitrogen?** From about 95 % to 99.999 % nitrogen, depending on design and flow. From the lesson [PSA, VPSA and membrane gas generators explained](https://www.sarveshanalytics.com/learn/nitrogen-and-oxygen-generators-psa-vpsa-and-membrane.html) **How pure is PSA oxygen?** Typically 90 to 95 %. From the lesson [PSA, VPSA and membrane gas generators explained](https://www.sarveshanalytics.com/learn/nitrogen-and-oxygen-generators-psa-vpsa-and-membrane.html) **Do I need an analyser on a generator?** If purity matters, yes. It shows when output drifts out of specification. From the lesson [PSA, VPSA and membrane gas generators explained](https://www.sarveshanalytics.com/learn/nitrogen-and-oxygen-generators-psa-vpsa-and-membrane.html) **What is carbon potential?** The carbon content steel would reach at equilibrium with the furnace gas. From the lesson [Heat treatment furnace atmospheres explained](https://www.sarveshanalytics.com/learn/heat-treatment-furnace-atmospheres-explained.html) **What analyser measures hydrogen in nitrogen?** ACCURRA-TCD, by thermal conductivity. From the lesson [Heat treatment furnace atmospheres explained](https://www.sarveshanalytics.com/learn/heat-treatment-furnace-atmospheres-explained.html) **How do you protect against air leaks in a furnace?** Measure trace oxygen and alarm on a rise; maintain seals and positive pressure. From the lesson [Heat treatment furnace atmospheres explained](https://www.sarveshanalytics.com/learn/heat-treatment-furnace-atmospheres-explained.html) **What does the dew point tell you?** How much water is in the atmosphere, which affects oxidising or reducing behaviour. From the lesson [Heat treatment furnace atmospheres explained](https://www.sarveshanalytics.com/learn/heat-treatment-furnace-atmospheres-explained.html) **What gases do I measure around an electrolyser?** Hydrogen in oxygen, oxygen in hydrogen, hydrogen purity and moisture. From the lesson [Hydrogen electrolysers and gas analysis: what to measure](https://www.sarveshanalytics.com/learn/hydrogen-electrolysers-and-gas-analysis.html) **What alarm level for hydrogen in oxygen?** Set by the manufacturer and your safety study, far below 4 %. From the lesson [Hydrogen electrolysers and gas analysis: what to measure](https://www.sarveshanalytics.com/learn/hydrogen-electrolysers-and-gas-analysis.html) **Are ACCURRA-Hz analysers suitable for electrolyser areas?** They are certified for Gas Group IIC, Zone 1 and 2, T6; confirm your zone and requirements. From the lesson [Hydrogen electrolysers and gas analysis: what to measure](https://www.sarveshanalytics.com/learn/hydrogen-electrolysers-and-gas-analysis.html) **Do your analysers have SIL?** We make no SIL claim. From the lesson [Hydrogen electrolysers and gas analysis: what to measure](https://www.sarveshanalytics.com/learn/hydrogen-electrolysers-and-gas-analysis.html) **What is biogas made of?** Mostly methane and CO2, with water vapour and traces of H2S. From the lesson [Biogas, landfill gas and digesters explained](https://www.sarveshanalytics.com/learn/biogas-landfill-gas-and-digesters-explained.html) **What is CBG?** Compressed biogas: biogas upgraded to high methane content and compressed for use as fuel. From the lesson [Biogas, landfill gas and digesters explained](https://www.sarveshanalytics.com/learn/biogas-landfill-gas-and-digesters-explained.html) **Why is H2S a problem?** It is corrosive and toxic and damages sensors and engines. From the lesson [Biogas, landfill gas and digesters explained](https://www.sarveshanalytics.com/learn/biogas-landfill-gas-and-digesters-explained.html) **Which analyser measures biogas methane?** ACCURRA-S 4030, by NDIR, on a conditioned sample. From the lesson [Biogas, landfill gas and digesters explained](https://www.sarveshanalytics.com/learn/biogas-landfill-gas-and-digesters-explained.html) **What oxygen level is used in ULO storage?** Around 1 to 2 % or lower, depending on the fruit; follow your guideline. From the lesson [Controlled-Atmosphere fruit storage explained](https://www.sarveshanalytics.com/learn/controlled-atmosphere-fruit-storage-explained.html) **Which analyser measures CA store gas?** ACCURRA-S 3030 for oxygen and 6030 for CO2; confirm range and accuracy for ULO. From the lesson [Controlled-Atmosphere fruit storage explained](https://www.sarveshanalytics.com/learn/controlled-atmosphere-fruit-storage-explained.html) **Can one analyser serve several rooms?** With a sampling manifold that switches rooms in turn; discuss the arrangement. From the lesson [Controlled-Atmosphere fruit storage explained](https://www.sarveshanalytics.com/learn/controlled-atmosphere-fruit-storage-explained.html) **Why measure CO2 as well as oxygen?** Because the combination sets the preservation, and the ratio shows respiration. From the lesson [Controlled-Atmosphere fruit storage explained](https://www.sarveshanalytics.com/learn/controlled-atmosphere-fruit-storage-explained.html) **Where in a cement plant is oxygen measured?** At the kiln inlet, the precalciner and preheater outlets, and at the stack. From the lesson [Cement kiln gas analysis explained: O2, CO and safety](https://www.sarveshanalytics.com/learn/cement-kiln-gas-analysis-explained.html) **Can your analyser trip an ESP on CO?** We make no SIL claim and need your response and integrity requirements first. From the lesson [Cement kiln gas analysis explained: O2, CO and safety](https://www.sarveshanalytics.com/learn/cement-kiln-gas-analysis-explained.html) **Can the probe survive kiln dust?** With the right probe material, filter and blowback, yes; tell us the dust load and temperature. From the lesson [Cement kiln gas analysis explained: O2, CO and safety](https://www.sarveshanalytics.com/learn/cement-kiln-gas-analysis-explained.html) **Do you supply cement plants?** JK Cement is among our customers. From the lesson [Cement kiln gas analysis explained: O2, CO and safety](https://www.sarveshanalytics.com/learn/cement-kiln-gas-analysis-explained.html) **What is in blast furnace gas?** Mostly nitrogen, CO and CO2 with a little hydrogen, and heavy dust. From the lesson [Steel plant gases: coke oven, blast furnace, converter](https://www.sarveshanalytics.com/learn/steel-plant-gases-explained.html) **Why is converter gas recovered only sometimes?** Its composition changes during the blow; it is recovered when CO is high enough and oxygen is low. From the lesson [Steel plant gases: coke oven, blast furnace, converter](https://www.sarveshanalytics.com/learn/steel-plant-gases-explained.html) **Can you analyse coke oven gas?** Send the composition; tar and ammonia need review and a suitable sample system. From the lesson [Steel plant gases: coke oven, blast furnace, converter](https://www.sarveshanalytics.com/learn/steel-plant-gases-explained.html) **Which analysers are used in steelworks?** NDIR for CO and CO2, thermal conductivity for hydrogen in binary cases, and oxygen analysers, with probes for hot dusty gas. From the lesson [Steel plant gases: coke oven, blast furnace, converter](https://www.sarveshanalytics.com/learn/steel-plant-gases-explained.html) **What is a CEMS?** A continuous emission monitoring system that measures stack gases and reports them corrected to regulatory conditions. From the lesson [Emission monitoring (CEMS) basics: what a system does](https://www.sarveshanalytics.com/learn/emission-monitoring-cems-basics.html) **Is SGI-320 approved by regulators?** We make no statutory approval claim; send your regulatory requirement. From the lesson [Emission monitoring (CEMS) basics: what a system does](https://www.sarveshanalytics.com/learn/emission-monitoring-cems-basics.html) **What is the difference between hot-wet and cold-dry?** Hot-wet keeps the sample hot and wet to the analyser; cold-dry dries it first. From the lesson [Emission monitoring (CEMS) basics: what a system does](https://www.sarveshanalytics.com/learn/emission-monitoring-cems-basics.html) **Do I need to measure oxygen?** Yes, normally, for reference oxygen correction. From the lesson [Emission monitoring (CEMS) basics: what a system does](https://www.sarveshanalytics.com/learn/emission-monitoring-cems-basics.html) **What dew point is instrument air?** Often class 2, minus 40 C pressure dew point or lower, depending on the application and climate. From the lesson [Compressed air quality and dew point (ISO 8573-1)](https://www.sarveshanalytics.com/learn/compressed-air-quality-and-dew-point.html) **What is the difference between refrigerant and desiccant dryers?** Refrigerant dryers cool to about 3 C; desiccant dryers adsorb water to reach minus 40 C or lower. From the lesson [Compressed air quality and dew point (ISO 8573-1)](https://www.sarveshanalytics.com/learn/compressed-air-quality-and-dew-point.html) **Which analyser measures compressed air dew point?** ACCURRA-S M015, minus 80 to plus 20 C. From the lesson [Compressed air quality and dew point (ISO 8573-1)](https://www.sarveshanalytics.com/learn/compressed-air-quality-and-dew-point.html) **Does ISO 8573-1 cover CO and CO2?** Gaseous contaminants are handled in other parts of the standard; medical and breathing air have their own specifications. From the lesson [Compressed air quality and dew point (ISO 8573-1)](https://www.sarveshanalytics.com/learn/compressed-air-quality-and-dew-point.html) **What oxygen level is safe for blanketing?** Below the LOC of your material by the margin your safety assessment requires. From the lesson [Inert gas blanketing in pharma and chemical plants](https://www.sarveshanalytics.com/learn/inert-gas-blanketing-in-pharma-and-chemical-plants.html) **What gas is used for blanketing?** Usually nitrogen; argon or CO2 in some cases. From the lesson [Inert gas blanketing in pharma and chemical plants](https://www.sarveshanalytics.com/learn/inert-gas-blanketing-in-pharma-and-chemical-plants.html) **Does blanketing need continuous oxygen monitoring?** It is common and often required; follow your safety assessment and standards. From the lesson [Inert gas blanketing in pharma and chemical plants](https://www.sarveshanalytics.com/learn/inert-gas-blanketing-in-pharma-and-chemical-plants.html) **Can ACCURRA-S be used in a solvent area?** Not in a classified area; use ACCURRA-Hz or INFINITY-Tx. From the lesson [Inert gas blanketing in pharma and chemical plants](https://www.sarveshanalytics.com/learn/inert-gas-blanketing-in-pharma-and-chemical-plants.html) **What oxygen level does a glove box hold?** From a few ppm to below 1 ppm, depending on the box and use. From the lesson [Glove boxes and Controlled-Atmosphere chambers explained](https://www.sarveshanalytics.com/learn/glove-boxes-and-controlled-atmosphere-chambers.html) **Can ACCURRA-S 3015 measure 0.1 ppm?** Its minimum range is 0 to 100 ppm; sub-ppm needs other sensors. Tell us your target. From the lesson [Glove boxes and Controlled-Atmosphere chambers explained](https://www.sarveshanalytics.com/learn/glove-boxes-and-controlled-atmosphere-chambers.html) **How do I avoid draining the box atmosphere?** Return the sample or limit the flow. From the lesson [Glove boxes and Controlled-Atmosphere chambers explained](https://www.sarveshanalytics.com/learn/glove-boxes-and-controlled-atmosphere-chambers.html) **Can one analyser read oxygen and moisture?** A dual-channel ACCURRA-S can read both from one sample. From the lesson [Glove boxes and Controlled-Atmosphere chambers explained](https://www.sarveshanalytics.com/learn/glove-boxes-and-controlled-atmosphere-chambers.html) ## Choosing and buying **What should a gas analyser specification include?** Purpose, measurement, sample, tapping, site, utilities, outputs, calibration, standards and support. From the lesson [How to specify a gas analyser: A practical checklist](https://www.sarveshanalytics.com/learn/how-to-specify-a-gas-analyser.html) **Do I need to know the exact accuracy?** State what the process needs; see the accuracy lesson. From the lesson [How to specify a gas analyser: A practical checklist](https://www.sarveshanalytics.com/learn/how-to-specify-a-gas-analyser.html) **Can I send a partial specification?** Yes. Send what you have and we will ask for the rest. From the lesson [How to specify a gas analyser: A practical checklist](https://www.sarveshanalytics.com/learn/how-to-specify-a-gas-analyser.html) **What if the sample composition is unknown?** Say so, send typical analyses, and we will propose how to confirm it. From the lesson [How to specify a gas analyser: A practical checklist](https://www.sarveshanalytics.com/learn/how-to-specify-a-gas-analyser.html) **What accuracy do I need for oxygen trim?** Usually a few tenths of a percent of oxygen is adequate; control needs repeatability more than absolute accuracy. From the lesson [What accuracy do you really need from a gas analyser?](https://www.sarveshanalytics.com/learn/what-accuracy-do-you-really-need.html) **Is plus or minus 1 % of span good enough?** It depends on the tolerance and where on the range the process runs. From the lesson [What accuracy do you really need from a gas analyser?](https://www.sarveshanalytics.com/learn/what-accuracy-do-you-really-need.html) **How does calibration gas uncertainty affect accuracy?** It sets a floor: the reading cannot be known better than the reference. From the lesson [What accuracy do you really need from a gas analyser?](https://www.sarveshanalytics.com/learn/what-accuracy-do-you-really-need.html) **Should I pay for the best accuracy?** Only if the decision needs it and the sample and calibration can support it. From the lesson [What accuracy do you really need from a gas analyser?](https://www.sarveshanalytics.com/learn/what-accuracy-do-you-really-need.html) **How much does an online gas analyser cost to run?** It depends on the sample and the analyser; count calibration gas, filters, sensors and labour. From the lesson [Total cost of ownership of a gas analyser](https://www.sarveshanalytics.com/learn/total-cost-of-ownership-of-a-gas-analyser.html) **Is the cheapest quote the best?** Rarely. Compare scope and lifetime cost. From the lesson [Total cost of ownership of a gas analyser](https://www.sarveshanalytics.com/learn/total-cost-of-ownership-of-a-gas-analyser.html) **How do I lower running costs?** Good sampling, a routine, auto-calibration and spares. From the lesson [Total cost of ownership of a gas analyser](https://www.sarveshanalytics.com/learn/total-cost-of-ownership-of-a-gas-analyser.html) **Should I include downtime in the comparison?** Yes, for critical measurements. From the lesson [Total cost of ownership of a gas analyser](https://www.sarveshanalytics.com/learn/total-cost-of-ownership-of-a-gas-analyser.html) **How do I compare gas analyser quotes?** On the same scope and basis, with exclusions and running costs listed. From the lesson [How to compare gas analyser quotes like for like](https://www.sarveshanalytics.com/learn/comparing-gas-analyser-quotes.html) **What should every quote include?** Scope, performance, certificates, documents, calibration, commissioning and support. From the lesson [How to compare gas analyser quotes like for like](https://www.sarveshanalytics.com/learn/comparing-gas-analyser-quotes.html) **Is a lower price a warning sign?** Check what is missing. From the lesson [How to compare gas analyser quotes like for like](https://www.sarveshanalytics.com/learn/comparing-gas-analyser-quotes.html) **Can you quote against my specification?** Yes. Send it with the application data sheet. From the lesson [How to compare gas analyser quotes like for like](https://www.sarveshanalytics.com/learn/comparing-gas-analyser-quotes.html) **What should I ask an analyser supplier?** About experience on similar streams, sample limits, certification, calibration, spares and service. From the lesson [Questions to ask a gas analyser supplier before you buy](https://www.sarveshanalytics.com/learn/questions-to-ask-a-gas-analyser-supplier.html) **How do I judge whether a supplier's claims hold?** Ask what they cannot do, and check that the answer is specific. From the lesson [Questions to ask a gas analyser supplier before you buy](https://www.sarveshanalytics.com/learn/questions-to-ask-a-gas-analyser-supplier.html) **Do you provide training?** Ask us about training and service for your site. From the lesson [Questions to ask a gas analyser supplier before you buy](https://www.sarveshanalytics.com/learn/questions-to-ask-a-gas-analyser-supplier.html) **Who do I call for support?** Sales +91 94 2300 4179 and support +91 94 2300 4178. From the lesson [Questions to ask a gas analyser supplier before you buy](https://www.sarveshanalytics.com/learn/questions-to-ask-a-gas-analyser-supplier.html) **What is the application data sheet?** An online form for the pre-order design inputs we need to recommend an analyser. From the lesson [The application data sheet: what to send Sarvesh](https://www.sarveshanalytics.com/learn/the-application-data-sheet-and-what-to-send-us.html) **Is it free?** Yes. From the lesson [The application data sheet: what to send Sarvesh](https://www.sarveshanalytics.com/learn/the-application-data-sheet-and-what-to-send-us.html) **Can I attach files?** Yes, up to a total size noted on the form. From the lesson [The application data sheet: what to send Sarvesh](https://www.sarveshanalytics.com/learn/the-application-data-sheet-and-what-to-send-us.html) **How soon will I hear back?** An applications engineer will reply by email or phone; for urgent cases call sales on +91 94 2300 4179. From the lesson [The application data sheet: what to send Sarvesh](https://www.sarveshanalytics.com/learn/the-application-data-sheet-and-what-to-send-us.html) Your question is not here? [Ask an engineer](https://www.sarveshanalytics.com/contact.html#enquiry); we add the good ones.