Using both UVDOAS and FTIR technology allows the Cerex UV-FTIR to be one of the most sensitive continuous emissions and stack monitoring solutions in the market


Cerex’s UV-FTIR is an FTIR continuous multi-gas analyzer, engineered specifically for low cost, high performance monitoring of cross process applications. Capable of simultaneous monitoring of more than 350 compounds in Cerex’s FTIR library, the FT-5000 provides continuous emissions monitoring without having to extract the gas samples from the stack.

Cerex has the capability to adapt analyzers to extractive, cross-stack, and insitu scenarios, whilst safely providing data in real-time. For extractive applications, heated tube bundles are available; for cross-stack applications, transmitters and reflectors are available; for in-situ applications, gas probes are available. The UV-FTIR can be customized to fit your specific application needs.

Offering true part-per-billion (ppb) detection limits in an easy to operate package, the Cerex UV-FTIR’s air-conditioned system can reliably deliver unattended, continuous real time monitoring of ultra low ppb concentrations of individual gas species with absorption features spanning the IR spectrum from 2 to 14 microns. There are no tedious ongoing calibrations, or additional costs for sample handling, wet chemistry, carrier gas, or sorbent filters. Results are immediate, and the raw data containing all the information necessary for gas identification and quantification is always saved.

How it WorksFTIR

Fourier transform infrared spectroscopy (FTIR) is the preferred technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, and gas.

The UV-FTIR operates by sending a beam of infrared light through a 20 meter sealed sample cell within the instrument. The IR beam is directed by a series of optics to an ultra-sensitive cryo-cooled MCT detector where minute changes in IR absorption are sensed due to trace concentrations of individual gases. A classical least squares regression analysis compares the measured absorption spectrum to calibrated reference absorption spectra files. Beer’s law is then used to determine gas concentrations (Beer-Lambert Law).

The result of coupling our proven detection system with a 20 meter internal optical sample path and CMS real time analytic software is an industry leading FTIR multi-gas analyzer.

How it WorksUVDOAS

UVDOAS (Ultraviolet Differential Optical Absorption Spectroscopy) is a monitoring technique which uses the absorbance of UV light to identify and quantify gases within a sample. Gases absorb unique wavelengths of light, creating a unique fingerprint of each compound within the absorbance spectrum; the amplitude of the absorbance wavelength is proportional to the concentration of the gas present in the sample (Beer-Lambert Law).

In addition to FTIR technology, the Cerex UV-FTIR uses a collimated beam of light and fiber optics to obtain these spectral fingerprints and then, using a pattern-matching classical least squares regression analysis, compare them to a vast library of stored references. The result is a real-time concentration number of the gases of interest.

Cerex’s UV-FTIR analyzers feature:

  • Dual Channel FTIR and UVDOAS continuous emissions monitoring
  • All criteria gases with one analyzer
  • Cross stack and parallel cell models
  • In situ stack monitoring, non contact
  • Outdoor model available
  • Operational range in ppb, ppm, and higher
  • Continuous, real time monitoring of over 400 individual gas species
  • Output options for alarm, data, and process control are available
  • Integrated Ethernet / WiFi
  • PC or Smartphone Remote Control
  • Automatic saved records of data
  • Customizable audible, visual and email alerts

UV-FTIR Applications

  • Mobile Laboratory Monitoring
  • Indoor Air Quality Monitoring
  • In situ Continuous Emissions Monitoring (CEMs)
  • In situ Process Monitoring
  • In situ Tailgas
  • In situ Ammonia Slip
  • In situ DeNOx/SCR and DeSOx/FGD
  • Zone Monitoring


Benefits of FTIR -

Extensive Library with Options for Customization

Cerex has over 385 compounds available for detection with the UV-FTIR. If your compound is not one of the compounds already available within our database, the UV-FTIR may import gas spectra from the numerous FTIR databases on the web (NIST, EPA, PNNL, etc.)

If you have a compound that is not available in a public database, we may be able to work with you to develop a custom spectrum. Detection limits are a function of the IR detector, installed path length, and site conditions. The detection limits shown have been empirically determined from bump tests of fielded instruments at full path-length.

Type Compound MDL PPB
Criteria Sulfur Dioxide 300
Volatile Organic Compounds Acrolein 15
1,3 Butadiene 4
Styrene 8
BTEX Benzene 30
Toluene 100
Ethylbenzene 25
m-Xylene 100
o-Xylene 300
p-Xylene 300
Alkanes Pentane C5 4
n-Hexane C6 3
TVOC Methane C1 3
NMHC Ethane C2 8
NMNEHC Butane C4 4
Propane C3 4
Formaldehyde 7
Propene (propylene) 6
Ethene (ethylene) 4
Acetylene 4
Acetaldehyde 5
Methanoic Acid 5
Methanol 4
Other Hydrogen Cyanide 10
Hydrogen Fluoride 4
Ammonia 3
Hydrogen Sulfide 450

Benefits of UVDOAS -

Low detection limits

All gas compounds absorb UV light energy at specific wavelengths. In addition to FTIR technology, The UV-FTIR detects gas compounds found present in a reflected UV light beam. For a gas compound to be detected by UV-FTIR analyzers, there must be enough UV energy present at the wavelength's point of absorption.

Cerex offers two UV bulb types for the UV-FTIR - Deuterium and Xenon. The primary reason to select one bulb type over the other is to have sufficient energy for analysis for your compounds of interest.

Each UV source bulb has a unique list of benefits and limitations. The spectral curves produced by each bulb can be seen in the chart above


  • Monitor distances up to 225m in a mono-static configuration or 450m in a bi-static configuration
  • More energy below 240nm
  • Required to detect 1,3-Butadiene (C4H6), ammonia (NH3), nitric oxide (NO), and others


  • Measuring longer distances, 1km or more, with a single instrument
  • Easier to align at longer distances due to the high visible component of light

UV-FTIR Specifications

General Parameters
Part Number Shepherd FTIR
Analyzer Type Multi-gas portable point analyzer
Technology Fourier Transform InfraRed (FTIR) Differential Optical Absorption Spectroscopy (DOAS)
Performance Available with standard HAP (385 compound & 62 Compound), Criteria, Hospital and custom gas detection libraries.
Data Output Rate User selectable from 5 seconds and up
Typical output rates are 30s, 60s, 120s, or 300s
Time weighted average available for user defined periods (8 hour, 12 hour, 24 hour)
Measurement Principle Beer-Lambert Law
Measurement Technique Classical Least Squares (CLS) regression analysis; optional Partial Least Squares (PLS)
Operating Temperature 0°C to 35°C (Optional Air Cooled Model)


Storage Temperature -40C° to 60C°
Power Supply 100 to 130V or 200 to 240VAC/50-60Hz
Power Consumption 240W MAX
Instrument Cooling Air Cooled
Installation Fixed mount or tripod mount (open path analyzer mode)
Bench-top (point analyzer mode)
Dimensions 42.1" x 21.9" x 23.3" (107cm x 55.7cm x 59.1cm)
Weight 85 lbs (38.6Kg)
Measuring Parameters
Concentration measurement accuracy ±5 % Reading TYP
Concentration measurement precision ±5 % Reading TYP
Interferent Mitigation Real time spectral subtraction and residual subtraction, multi-peak analysis.
Zero point calibration Simultaneous dual mode natural zero and/or synthetic zero on gas by gas basis. Automated compound specific background selection.
Real Time Operating Software Cerex Continuous Monitoring Software (CMS)
Operating System Windows 10 Pro
Post Collection Analysis Software Cerex Data Processor
Operating System Windows 7, 8, 10
Apodized Resolution User selectable: 0.5 cm-1, 1 cm-1, 2 cm-1, 4 cm-1, 8 cm-1, 16 cm-1, 32 cm-1
Scan frequency 6 scans/s @ 32 cm-1
Detector Stirling Cooled MCT (standard)
TE Cooled MCT (application dependent)
Detector temperature 77 K (Stirling cooled MCT)
Source SiC, 1550K
Beamsplitter ZnSe (standard)
Window material ZnSe (standard)
Wavenumber range 600-4200 cm-1 
Temperature stability < 1% per C⁰
Frequency repeatability  < 0.001 cm-1 @ 1918cm-1
Frequency accuracy < 0.06 cm-1 @ 1918cm-1
Short term stability < 0.09%
Maximum signal to noise ratio 50,000: 1 (RMS, 60s, 4 cm-1, at peak response)
Signal sampling 24-bit ADC
Quality Assurance Hardware
Type Internal linear multi-pass cell permanently mounted in beam path. External window removable.
Calibration gas inlet Quick Connect QA Adapter: 1/4" Swagelok
Calibration gas outlet Screw-in Exhaust Adapter: 3/8" Swagelok
Path Length 19.2 m
Volume 3.4 L
Maximum sample pressure 1 PSI
Pressure and temperature measurement Integrated pressure and temperature sensor
HMI Touchscreen (standard model)
Digital Interface RJ45 Ethernet LAN Port for local or internet based remote data and access using MODBUS TCP, VNC, and remote desktop.  Spectral data may be stored locally, on a NAS, or disabled. Industrial external wireless option available. Type A USB for data retrieval and peripheral accessories.
Power Connection Environmentally sealed circular Amphenol bayonet connector.
Integrated Computer Embedded industrial PC
Integrated Wind Mapping Three dimesnional ultrasonic anemometer with temperature measurement. Data integrated into CMS data tables and available via MODBUS.
Integrated Data Acqusition External ports with data integration for particulate or ancillary co-located analyzers (TDLAS laser, electrochemical, etc.).
Data Output MODBUS over RS-232, RS-485.  MODBUS over TCP-IP is standard.
Analog Output 8 channel configurable 0-24mA (4-20mA with extended range)

Discuss your project with our application specialists

Our engineers have decades of experience in creating custom solutions to meet your monitoring challenges

Contact Us