The Importance of Ambient Air Pressure Compensation in NDIR Gas Sensors

Accurate gas detection is critical in applications where safety, regulatory compliance, or process control are at stake. While factors like calibration, temperature stability, and cross-sensitivity are often highlighted, ambient air pressure is frequently overlooked. Yet, without pressure compensation, even small changes in pressure can cause significant measurement errors.

Many non-dispersive infrared (NDIR) gas sensors do not include automatic pressure compensation, shifting the responsibility to end users and increasing the risk of inaccurate data. This document explains why ambient pressure compensation is essential for reliable gas measurement. It also exa-mines how sensors with built-in pressure compensation - such as those from Micro-Hybrid - maintain accuracy under changing environmental conditions. Finally, we compare Micro-Hybrid’s solution with other leading manufacturers that sometimes omit this feature, and quantify the risks of uncorrected deviations.

NDIR sensors determine gas concentration based on the number of gas molecules in a fixed volume. According to the ideal gas law:

First and most crucially, ambient air pressure varies greatly with elevation. Consider this table:

As a rule of thumb, air pressure drops by roughly 1 hPa for every 8 meters of elevation gain, up to about 100 meters, though the rate slows at higher altitudes. Some leading manufacturers pre-calibrate their sensors for a fixed reference pressure, often assu-ming standard sea-level conditions, about 1013 hPa. Without an integrated pressure compensation component, the responsibility falls on the end user to supply this data, often leading to a decrease inmeasurement accuracy.  altitude with improper manual adjustment. For example, the city of Chengdu sits at an average elevation of 499 meters, where atmospheric pressure is typically around 950 hPa. Imagine an NDIR gas sensor installed in an incubator there, but still calibrated for sea-level pressure (1013 hPa).

The resulting measurement error is estimated as follows:

(1013 hPa - 950 hPa) × 0.0073 Vol.-%/hPa = 0.459 Vol.-%

That level of deviation is far beyond acceptable tolerances for precision gas monitoring, which often demand accuracy within ±0.2 Vol.-%.

Even at a fixed location, ambient air pressure varies. Let’s consider the air pressure variation in this forecast for Beijing on July 16, 2025:

Daily Variation in Beijing (July 16, 2025)

• Minimum pressure: 998.7 hPa
• Maximum pressure: 1004.75 hPa
• Difference: 6.05 hPa

For a 5 Vol.-% target, the error would be:

6.05 hPa × 0.0073 Vol.-%/hPa = 0.044 Vol.-%

Even without changing location, the gas reading could deviate by over 0.04 Vol.-% in a single day, exceeding tolerance for many applications.

A Two-Week Variation in Beijing, July 2025

• Minimum: 994.7 hPa (July 15, 11:00)
• Maximum: 1011.62 hPa (July 17, 03:00)
• Range: 16.92 hPa

This is equivalent to an error of 16.92 × 0.0073 = 0.1235 Vol.-% and is not appropriate for critical use ca-ses. These routine fluctuations show that when NDIR gas sensors that are not automatically calibrated for ambient pressure they can easily drift out of spec, even without changes in altitude.

To stay within a ±0.2 Vol.-% accuracy window at 5 Vol.-%, the maximum allowable pressure deviation is:

0.2 / 0.0073 ≈ 27 hPa deviation

This threshold is easily exceeded in daily weather cycles, particularly during storms, or when reloca-ting equipment between sites. Even moderate pressure changes can cause readings to fall outside specifications.

All Micro-Hybrid NDIR sensors feature integrated pressure sensors, enabling real-time compensation without user intervention. Key benefits include accurate readings regardless of installation altitude, automatic correction for daily and seasonal pressure fluctuations, with no manual pressure entry or recalibration needed, and consistent readings across multiple locations and environments.