Capelec EOBD, Руководство пользователя

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23/04/2019 Rev 3 17
N° Descriptions
1 IR detector
2 Sample cell
3 IR transmitter
4 O rings
5 Optical window
Principle of NDIR measurement:
The CAP3201 is based on non-dispersive infrared technology.
Instead of using a refractory prism to achieve the very high spectral definition of infrared light
(like those used in laboratory high performance equipment), the machine uses NDIR. NDIR devices
are generally used for measuring concentrations of a specific and limited set of gases in mixtures
having a known and limited collection of basic gases.
It is possible for example to take the measure of the CO
2
concentration from a basic gas such as
the exhaust gas coming from a car. Some gases might have an absorption spectrum masking CO
2
presence.
A specific collection of gases (CO
2
, C6H14, CO) is measured as follows: a unique range of
wavelengths in the infrared spectrum is selected for each gas in order to measure the point where
its absorption is high and where there is no other basic gas which is equally absorbent.
Optical filters transmitting only the given range of wavelengths are placed in front of the
thermocouple detector. When the set is full of gas, the infrared detector measures the reduction
in the infrared energy obtained for the range of wavelengths linked to each gas.
The signal processing electronics then determine the I/Io ratio.
I/Io = degree of absorption
I = signal received (sample) for each gas to be measured.
Io = signal for reference
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