Teledyne 360E I = Io e-Lc

Model 360E Instruction Manual THEORY OF OPERATION

The Model 360E Gas Filter Correlation Carbon Dioxide Analyzer is a microprocessor-controlled analyzer that

determines the concentration of carbon dioxide (CO2) in a sample gas drawn through the instrument. It requires

that sample and calibration gasses be supplied at ambient atmospheric pressure in order to establish a stable

gas flow through the sample chamber where the gases ability to absorb infrared radiation is measured.

Calibration of the instrument is performed in software and does not require physical adjustments to the

instrument. During calibration the microprocessor measures the current state of the IR Sensor output and

various other physical parameters of the instrument and stores them in memory.

The microprocessor uses these calibration values, the IR absorption measurements made on the sample gas

along with data regarding the current temperature and pressure of the gas to calculate a final co2 concentration.

This concentration value and the original information from which it was calculated are stored in one of the unit’s

internal data acquisition system (iDAS - See Sections 6.7) as well as reported to the user via a vacuum

florescent display or a variety of digital and analog signal outputs.

The basic principle by which the analyzer works is called Beer’s Law. It defines the how light of a specific

wavelength is absorbed by a particular gas molecule over a certain distance. The mathematical relationship

between these three parameters is:

I = Io e-αLc

Where:

Io is the intensity of the light if there was no absorption.

I is the intensity with absorption.

L is the absorption path, or the distance the light travels as it is being absorbed.

C is the concentration of the absorbing gas. In the case of the Model 360E, carbon dioxide (CO2).

α is the absorption coefficient that tells how well CO2 absorbs light at the specific wavelength of

interest.

In the most basic terms, the Model 360E uses a high energy heated element to generate a beam of broad-band

IR light with a known intensity (measured during Instrument calibration. This beam is directed through

multi-pass cell filled with sample gas. The sample cell uses mirrors at each end to reflect the IR beam back and

forth through the sample gas to generate a 2.5 meter absorption path (see Figure 10–1). This length was

chosen to give the analyzer maximum sensitivity to fluctuations in CO2 density.

05232 Rev B3 163