Online Gas Analyser

The CEM400 is an extractive online gas analyser dedicated to Continuous Emission Monitoring.

It is based on UV spectroscopy that brings a higher sensitivity than infra-red and gives the possibility to measure several gases simultaneously. A high selectivity is achieved by a fast Fourier transform (FFT) on the absorbance spectrum for all the gases having a periodic structure like NH3, SO2, NO and some others. All the internal gas circuit is heated at 190°C to admit directly hot and humid combustion gases. the CEM400 stand in a watertight wall mounted enclosure. This model may include a heated sampling pump as an option.

Main Method : UV Spectroscopy

  • everal gases can be measured simultaneously thanks to the UV spectroscopy method by using different wavelengths and algorithms. For gases with a periodic absorption spectrum such as NH3, SO2, NO, CS2, formaldehyde or acetylene, an algorithm based on FFT (Fast Fourier Transform) guarantees a very good selectivity of measurement. The solid-state design due to the UV spectroscopy gives a high reliability of the measuring system with quite no maintenance.
  • The UV lamp is a xenon flash lamp with a high lifetime and without thermal effect that may generate measurement drift.
  • The gas flow cell has two quartz windows to transmit the UV light throught the measured gas. The standard path length of the flow cell is 240 mm.
  • The spectrograph is based on a concave grating to minimize the optical parts and the spectrum is read on a 254 or 512 pixels diode array.
  • A zero is done automatically on zero air or nitrogen with an adjustable period (if possible every 2 or 4 hours but once per day remains acceptable).
  • The absorbance spectrum is calculated from the reference spectrum acquired during the zero step.

User-Friendly Interface

The colour touch screen and intuitive interface available in 8 different languages (Chinese, English, French, German, Italian, Portuguese, Spanish, Turkish) makes very easy to test or configure the analyser. Many test functions allows to test and troubleshoot each element of the analysers (light signal, pumps, solenoid valves, etc...) to setup quickly a maintenance diagnostic.



Recorded data and diagnostic files for each parameter can be downloaded to memory stick thanks to a USB port. This allows to collect easily these files on site without using a computer. The files are in text format and can be directly imported to Excel® for graphic charts.

No Interference with CO, CO2 and CH4

The major emission gases like CO, CO2, and CH4 have no UV absorption, therefore they don’t interfere with the measured gases. H2O has a weak absorption in the UV range but at different wavelengths than combustion gases like NH3, NO, NO2 or SO2. Consequently, H2O, with an usual concentration between 5% and 20%, is not disturbing the measurements.

Low Maintenance and High Reliability

The design has been specially oriented for low maintenance and high reliability on the measurements. The UV xenon lamp is specified for a lifetime of 109 flashes. Therefore, the lifetime is about 1 year with continuous measurements or 10 years with one measurement per minute. This reduces considerably the maintenance and the risk of wrong measurement due to aged lamps or its replacement.


Gas Circuit

Three gas connections are available on the rear panel of the analyser :

  • Inlet for the sample
  • Zero air or nitrogen
  • Outlet for sample or zero

Inlet and zero are connected on a 3 ways electric valve. When the automatic zero is activated, the solenoid valve switches the flow cell on zero air. A pressure sensor takes the pressure of measured gas to compensate it and to give a flow indication. All the gas circuit is in a heated compartment controlled within +/- 0.5 °C at an adjustable temperature between 60°C and 190°C. An optional pump may be included before the gas flow cell in order to pump the sample as well as the zero gas that may be ambiant air for most of the applications.


Multi-Gas Configuration

Several gases can be measured in a same analyser if the sample gas composition is compatible with the selected algorithms and wavelengths. The analyser gives high measurement selectivity thanks to the recognition of the specific UV absorption spectrum of gases by using proprietary algorithms.

Heated Version

The analyser is provided with an heating system for the gas circuit. The heating temperature can be adjusted up to 190°C. The high temperature evaporates any deposits on the windows.

Measuring Time

For process that requires fast measurement like motor bench application, the analyser is able to measure the sample concentration within 200 milliseconds thanks to an ultra fast electronics design based on high speed DSP (Digital Signal Processor). However, usual measurements on emission gases are performed within 5 seconds. A special auto averaging algorithm can be activated to improves the stability without affecting the response time.

Automatic Compensation

An internal measurement of temperature and pressure of the sample is performed. A ratio related to the ideal gas law is applied on the measured value to compensate the effects of temperature and pressure.

Online gas analyzer, CEM400 - Parameter Specification

ParameterRange* (ppm)Range* (mg/m3)Typical RepeatabilityDetection Limit
0-10 ppm
0-100 ppm
0-1000 ppm
0 - 7 mg/m3
0 - 70 mg/m3
0 - 700 mg/m3
0.05 ppm at 10 ppm
0.1 ppm at 100 ppm
0.5 ppm at 1000 ppm
0.1 ppm
Nitrogen Oxide
0-2000 ppm0 - 2500 mg/m31 ppm at 1000 ppm3 ppm
Sulfur Dioxide
0-1000 ppm0 - 3000 mg/m32 ppm at 1000 ppm0.5 ppm
Hydrogen Sulfide
0-500 ppm0 - 750 mg/m30.5 ppm at 500 ppm0.5 ppm
Nitrogen Dioxide
0-2000 ppm0 - 4000 mg/m3 10 ppm
Carbon Disulfide
0-100 ppm0 - 300 mg/m3  
0-100 ppm0 - 300 mg/m3  
0-30 ppm0 - 100 mg/m3  
0-30 ppm0 - 150 mg/m3  
Nitrogen Trichloride
0-100 ppm0 - 500 mg/m3  


Online gas analyzer, CEM400 - General Specification

Data storage5000 measurements for all parameters
InterfacesInterface RS232 (MODBUS, AK and http / html5 protocol)
USB port (for memory stick)
Internal WIFI interface IEEE 802.11 B (OPTION)
Internal Ethernet 10 BASE-T interface IEEE 802.3 (option)
Signals1 to 8 analog outputs 4-20 mA opto-isolated (option)
1 to 4 relay contacts programmable (option)
DisplayLCD colour screen (TFT) with LED backlight 320x240 pixels
Power supply90-264 VAC / 1000 VA / 50-60Hz
Operatings limits0 to 40 °C, less than 90% as relative humidity
CE standardsElectromagnetic compatibility and safety
EN 61010-1, IEC 61010-1 / EN 61326, IEC 61326
EnclosureWall mounting enclosure (IP65), Coated steel
Dimensions410 x 571 x 255 mm (H x W x D)
Weight27 kg
Sampling gasPressure : 0 – 2 Bar Absolute (0 – 2000 hPa Absolute)
Flow : 0.1 to 10 l/min
Temperature : ambiant to 400 C
Fittings : Swagelok, stainless steel 316 for tube OD ¼'' (6.4 mm)
Zero gasPressure : 0 – 2 Bar Absolute (0 – 2000 hPa Absolute)
Flow : 0.1 to 10 l/min
Fittings : Swagelok, stainless steel 316 for tube OD ¼'' (6.4 mm)


Online gas analyzer, CEM400 - ACCESSORIES

Sampling Pump
Product Code: PUMP400

Internal membrane pump with heated head
Built-in inside the enclosure
Flow about 6 l/min
Heated version at 190 °C

Input Modules
Product Code: MI4-20

4-20 mA input module
Isolated 4-20 mA input
Impedance: 100 Ohm

Input Modules
Product Code:MIL

Double logical inputs module
Input no 1 : external pulse command for measurement
Input no 2 : measurements inhibition
Isolated 0 –24 V DC inputs
Impedance: >10 Kohm

Output Modules
Product Code:MO4-20

4-20 mA output module
Isolated 4-20 mA output
Active output, Max load 500 Ohm

Output Modules
Product Code:MRELAY

4-20 mA output module
Contact rating: 2A/220V

Product Code:WIFI400

Wifi Interface
Connection to wireless WIFI network
300m nominal range (open space)
Secured data transfer (WEP key)

Product Code:ETHER400

Ethernet interface
Ethernet 10 base-T (IEEE 802.3)

Product Code:MTI133

Phone modem
Industrial modem 33,6 Kb/s V34+
DIN rail Mounting
Power supply 24V from the analyser

Product Code:GSM

GSM modem
Dual band (EGSM 900/1800 MHz)
Integral SIM card reader
R & TTE approved

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