CEM400 Online Gas Analyser

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Remote Cloud Monitoring

CEM400 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

  • 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, 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.


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