ANALOX 1371 MK 2 SURVEYOR CARBON DIOXIDE MONITOR
1371-810-03 User Manual, August 2007
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PRINCIPLE OF OPERATION
Most gases, when exposed to the Infra Red region of the electromagnetic spectrum, will
absorb energy and produce very specific resonant molecular vibrations. These characteristic
absorptions (vibrations) can then generally be used to identify individual gases.
The degree of absorption depends on the number of absorbing molecules (concentration) in an
Infra Red path length between an Infra Red source and Infra Red detector. (Beer-Lambert Law)
In practical terms, the path length is chosen for the degree of absorption necessary to determine
a particular band of concentration (range of measurement) and the gases can be identified by
use of narrow band interference filters, tuned to an appropriate characteristic absorption
wavelength.
The family of Transducers used in the ANALOX 1371 MK 2 range of Instruments are based
on a measurement and reference sensor principle, utilising sample path lengths of between 1mm
and 100mm in length, depending on the concentration to be measured, and wavelength selection
by a carefully specified narrow band interference filter. The source is pulsed at a regular frequency
to produce an Infra Red carrier signal which is attenuated by Carbon Dioxide absorption and a
detection system which converts this attenuation into an electrical output.
The electrical output from the transducer is then processed by additional electronic circuits to
provide indication of concentration on an LCD Display and monitoring for Alarm conditions.
