---
title: Pressure Effect on Oxygen Reading Calculator
url: https://www.sarveshanalytics.com/calculators/pressure-effect-on-oxygen-reading-calculator.html
description: See how much an uncompensated oxygen sensor reads low or high when ambient pressure differs from the pressure it was calibrated at. For purity analysers.
updated: 2026-11-02
source: html
---

Learn · Calculator

# How barometric pressure shifts an oxygen reading

Enter the true purity, the pressure at the sensor now and the pressure at calibration. The calculator shows what an uncompensated partial-pressure sensor would display.

 Quick answer

A sensor that responds to oxygen partial pressure reads in proportion to absolute pressure. A true 99.5 % oxygen stream reads about 97.2 % when the air pressure falls from 1013.25 hPa to 990 hPa on an uncompensated sensor. Pressure and temperature compensation removes most of this error.

Updated 2 November 2026 · Figures from Sarvesh datasheets

Applies to sensors that respond to partial pressure. A sensor with built-in pressure and temperature compensation, such as ACCURRA-S 3090 and 3190, corrects for this effect.

## How it is calculated

Many oxygen sensors respond to the partial pressure of oxygen at the sensing surface: the oxygen fraction multiplied by the absolute pressure. If the pressure at the sensor differs from the pressure at calibration, the signal scales by the ratio of the two.

Displayed = True x P_now / P_calibration

## Worked example

**Worked example**

Calibrated at 1013.25 hPa. A weather front drops the pressure to 990 hPa. A true 99.5 % stream reads 99.5 x 990 / 1013.25 = 97.2 %, an error of minus 2.3 points.

The plant sees a quality failure that never happened. A day and night swing in barometric pressure can create a similar error twice a day.

Compensated purity analysers measure ambient pressure and temperature and correct the reading. The catalogue gives a residual error below 0.5 % for 3090 and 3190.

## Limits

- Only partial-pressure sensors show this effect. A thermal conductivity or NDIR reading responds differently to pressure.
- Sample pressure at the sensor, not only the weather, matters: a sample vented to atmosphere sees atmospheric pressure.
- Temperature has its own effect on top of this.

## Frequently asked questions

**Why does my oxygen reading change with the weather?**

Because the sensor responds to partial pressure, and barometric pressure changes the partial pressure of oxygen even when the gas is unchanged.

**How much can pressure change an oxygen purity reading?**

About 1 % for each 1 % change in absolute pressure on an uncompensated sensor; day and night swings can reach several percent.

**Is the effect the same at altitude?**

A site at altitude has lower pressure. If you calibrate on site at that pressure, only changes from it matter; otherwise the offset is large.

**Which analysers compensate for pressure?**

ACCURRA-S 3090 and 3190 measure ambient pressure and temperature and correct the reading.

## Related lessons

- [Why ambient pressure affects oxygen purity readings](https://www.sarveshanalytics.com/learn/why-ambient-pressure-affects-oxygen-purity-readings.html)
- [How gases behave: pressure, temperature and partial pressure](https://www.sarveshanalytics.com/learn/how-gases-behave-pressure-temperature-and-partial-pressure.html)
- [Choosing an oxygen analyser: trace, percent or purity](https://www.sarveshanalytics.com/learn/choosing-an-oxygen-analyser-trace-percent-or-purity.html)