Online Gas Analyser

The CEM500-L is an extractive online gas analyser for Continuous emission monitoring (CEMS).

It is specifically dedicated to the new low level emission Regulations known as 50/30/5/3 (50 mg/Nm3 NOx, 30 mg/Nm3 SO2, 5 mg/Nm3 particles, 5 μg/Nm3 mercury) and also to chemical processes requiring low values of H2S. This new model is based on a multi-path flow cell of 1200 mm coupled to a high resolution spectrograph (0.1 nm) using an ultra-sensitive 2048 pixels CCD (charge-coupled device). It gives a high sensitivity and a longer lamp life time (3 years). The uv spectroscopy brings a higher sensitivity than Infra-red spectroscopy and also gives the possibility to measure several gases simultaneously on the same Spectrograph.

Optical principle - Main method : UV spectoscopy

  • Several 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 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 1200 mm.
  • The spectrograph is based on a concave grating to minimize the optical parts and the spectrum is read on a 2048 pixel CCD with a resolution of 0.1nm.
  • 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-Ffriendly interface

A colour touch screen display interface allows the user to easily navigate through a number of screens that are used to set and check all of the operating conditions of the instrument. A protective film limits the risk to damage the surface of the touch screen, especially against solvent and corrosive liquid.



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.


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 40°C and 240°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.


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 3 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.

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 240°C. The high temperature evaporates any deposits on the windows.

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, CEM500-L - Parameter specification

ParameterRange* (ppm)Range* (mg/m3)Detection LimitRepeatability
0-10 ppm0 - 7 mg/Nm30.1 ppm0.01 PPM AT 10 PPM
Nitrogen Oxide
0-80 ppm0 - 100 mg/Nm30.5 ppm0.2 ppm at 40 ppm
Sulfur Dioxide
0-30 ppm0 - 100 mg/Nm30.05 ppm0.2 ppm at 30 ppm
Hydrogen Sulfide
0-200 ppm0 - 400 mg/Nm3  
Nitrogen Dioxide
0-200 ppm0 - 400 mg/Nm3  
Carbon Disulfide
0-20 ppm0 - 60 mg/Nm3  
0-20 ppm0 - 60 mg/Nm3  
0-5 ppm0 - 20 mg/Nm3  
0-5 ppm0 - 20 mg/Nm3  
Nitrogen Trichloride
0-20 ppm0 - 100 mg/Nm3  


Online gas analyzer, CEM500-L - General specification

Data storage5000 measurements for all parameters
InterfacesInternal WIFI and Internal Ethernet
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 640x480 pixels
Power supply110-240 VAC/ 1000 VA / 50-60 Hz
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
EnclosureStainless steel IP65 with coating
Dimensions345 x 525 x 260 mm
Weight25 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, CEM500-L - Accessories

Sampling pump
Product code: PUMP500

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: IN4-20-500

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

Input modules
Product code:LOGIC500

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:OUT4-20-500

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

Output modules
Product code:RELAY500

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

Product code:WIFI500

Wifi interface
Connection to wireless WIFI network
Standard IEEE 802.11b
Secured data transfer by WEP keys

Product code:ETHER500

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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