Exhaust Gas Analyzers


Bridge Analyzers has developed a series of Exhaust Gas Analyzers to assist in diagnosing engine emission problems.  Our 4 & 5 gas analyzers are designed to provide a cost effective method for measuring exhaust emissions so engines can be tested and repaired to maintain maximum engine performance and identify compliance issues. CO or CO/H-C gas analyzers cannot measure O2 & CO2 in the exhaust gas stream that could be caused by an extraneous air leak (See included technical support note). The Bridge 4 & 5 gas models measure both O2 and CO2 in addition to CO and H-C. Bridge manufactures exhaust gas analyzers that give you peace of mind that your readings will be accurate, quick and reliable and meet emissions compliance testing

Bridge Exhaust Gas Analyzers use two measurement methods for exhaust gas analysis:  NDIR for CO, CO2, and Hydrocarbons, and Chemical Sensors for O2 and NO.  These technologies are approved for use in exhaust gas analyzers by Federal, International, State/Provincial and local agencies.


2 Gas Analyzer – CO/HC – Model 9003

2 gas exhaust emissions analyzer
4 Gas Analyzer – CO/CO2/HC/O2 – Model 9004

4 gas exhaust emissions analyzer
5 Gas Analyzer – CO/CO2/HC/O2/NOx – Model 9005

5 gas exhaust emissions analyzer

NDIR Definition:

NDIR stands for Non-Dispersive InfraRed.  This technology is used to measure the concentration of a gas (actually, the number of molecules in the optical path) by determining how much infrared energy is absorbed at a select wavelength band that corresponds to a resonant mode spectrum of the molecule being analyzed.

For example, the CO2 molecule has a strong resonance at a frequency relating to the 4.26 micron electromagnetic wavelength – near infrared.  So – CO2 will strongly absorb infrared energy at this select wavelength.  The more CO2 molecules there are in the optical path – the more energy gets absorbed – although this is a highly non-linear function.

The gas analyzer determines how much energy is absorbed (the infrared absorption) at a specific molecular resonance of a particular gas, and then relates this absorption to gas concentration – the characteristic instrument curve for the gas being analyzed.

This technique is very specific to the particular resonance of each gas molecule being measured, so it works well to measure certain gases in mixes of other gases – providing that appropriate absorption bands unique to each gas can be isolated.

In general, it is the technique of choice for measuring such common gases as CO (Carbon Monoxide), CO2 (Carbon Dioxide), SO2 (Sulfur Dioxide), NO2 (Nitrous Oxide Anesthetic Gas) and a variety of Hydrocarbons (generally the Alkane group – looking at the H-C stretch resonance) – but other hydrocarbons are readily measurable as well – for example fluorinated hydrocarbon anaesthetic agents.

This technology is cost effective, robust, stable, well proven, and by far the most popular method for measuring the gases above – with 100,000’s of installations operating worldwide, from CEM to Anesthesia Machines, to Exhaust Gas Analyzers, and a variety of industrial applications.

EPA Method Compliance:

The NDIR gas measurement technology is generally recognized as one of the technologies of choice for analyzing emission gases.  The NDIR method is specified as an appropriate measurement technology by the EPA for several gases in official EPA-Defined test methods – given below:

EPA Method 3A:  NDIR for measuring CO2 emissions from Stationary Sources

EPA Method 6C:  NDIR for measuring SO2 emissions from Stationary Sources

EPA Method 10:  NDIR for measuring CO emissions from Stationary Sources

EPA Method 21:  NDIR for measuring VOC Leaks

EPA Method 25B:  NDIR for measuring VOCs.

In addition, NDUV (same approach as NDIR, but at an Ultra-Violet wavelength) is an EPA specified measurement method in:

EPA Method 7B:  NDUV for measuring NOx from Stationary Sources.

Mobile Emissions Source Test Compliance:

All Domestic and International Federal and State mobile emission programs (e. g. BAR-74, BAR-80, BAR-84, BAR-90, BAR-97, ASM, IM-240, FTP, etc) specify NDIR as the gas measurement technology of choice for measuring CO, CO2, HC (measuring gasoline vapor, C4 – C10 as Hexane) in the exhaust streams of internal combustion engines.

In addition, NDUV is recognized as one of the measurement technologies of choice for NOx emission measurement from the same sources.

NDIR has also been the analytical technology of choice for the measurement of C1 – C20 (Methane and above) in a variety of applications, from wasteful site emission measurements to VOC elimination or recovery installations. 

NDIR Instrument Utility and Costs:

NDIR-based analytical equipment is available in a variety of styles, from hand-held portables to bench-top commercial and laboratory-grade analyzers to complete CEM installations.  This equipment is relatively low cost, robust, stable, and easy to operate – lending itself to a variety of commercial applications.  It does not require frequent recalibration to remain accurate, and has demonstrated stability and longevity – with many instruments providing decades of use in the field.