Operating Instructions GM35
Probe Model
Product overview
8009389/07-2006 © SICK MAIHAK GmbH • Germany · All rights reserved 17
2.2 Operating principle
2.2.1 Opto-electronic in-situ measuring principle
The Probe Model GM35 is based on the in-situ technique using an opto-electronic direct
measurement. The measured values are recorded by means of a no-contact measurement
across the entire duct cross-Chapter (cross duct). Using the wavelength-specific light ab-
sorption by the gas mixture in the active measuring distance, the SR unit unit determines
the concentration of the gas components present.
Fig. 5 Optical components of the GM35
The light from the sender/receiver unit (SR unit) passes through the active measuring path
(see Fig. 7page 23) and is reflected by the reflector opposite. The reflected light is then di-
rected by the lens-splitting mirror through a filter or cell wheel to detectors that have been
optimally configured for measuring CO, CO
2
, and H
2
O. By filtering the light received into its
spectral components, the receiver elements record the absorption of the gas molecules at
characteristic points of the spectrum in the IR range of 1.6 to 4.9 μm. Cross-sensitivities
with gases other than those to be measured are avoided by selecting these evaluation rang-
es within the IR spectrum in conjunction with the evaluation algorithms used (see 2.2.2 „Sig-
nal evaluation“).
Measuring path in gas duct
Cell wheel and detector
for CO measurement
IR transmitter
lamp
Zero-point reflector
and dark aperture
CO detector Reflector
Reference filter for pivoted
motorized Chapter
Sight with opto-electronic alignment
Filter wheel and
detector
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