industrial instrumentation basics

 How an NDIR Gas Analyzer Actually Works Walk past a CEMS cabinet or a CO/CO₂ analyzer skid in a cement plant and you'll usually find an NDIR analyzer doing the heavy lifting for gases like CO, CO₂, SO₂, or NOx. Unlike the zirconia cell, which measures oxygen through an electrochemical reaction, NDIR works on something completely different — light absorption. It's a beautifully simple idea once you see how the pieces fit together. The Core Idea: Gases Absorb Specific Colors of Infrared Light NDIR stands for Non-Dispersive Infrared. Every gas molecule made of two or more different atoms — CO, CO₂, SO₂, NO, CH₄, and so on — absorbs infrared light at very specific wavelengths, determined by how its molecular bonds stretch and bend. CO₂, for instance, strongly absorbs infrared light around 4.26 micrometers. CO absorbs strongly around 4.6 micrometers. Each gas has its own fingerprint. Symmetric diatomic gases like O₂ and N₂ don't have this property — their bonds don't create...

Infrared (IR) gas analysis is one of the most widely used techniques for measuring gas concentrations in industrial processes — from kiln inlet oxygen and CO monitoring in a cement plant to combustion efficiency checks on any fired process. This post covers how IR gas analyzers work, the two main analyzer types, and the physical layout of a typical sampling system. For the detailed working principle of the non-dispersive (NDIR) technique specifically, see the dedicated NDIR Gas Analyzer post; for oxygen measurement via zirconia cells, see Working Principle of Zirconia Gas Analyzer . How Infrared Gas Analysis Works An infrared gas analyzer measures the concentration of a specific gas in a sample by determining how much of an emitted infrared light source that gas absorbs. Different gas molecules absorb different, specific wavelengths of infrared light — so a sample with a higher concentration of a target gas absorbs more of that gas's characteristic wavelength, and the analyze...