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TIDA-010941: Photodiode, EMITTER and LED Angle

Ankit Nandha
Prodigy 10 points
Part Number: TIDA-010941

Tool/software:

Hello Everyone,


I seen that in many design that all the three components are in specific angles. Can anyone explain this ? How to derive this angles and what are the things we need to make sure while selecting or placing this three components ??

  • 0
    TI__Prodigy 690 points

    Hello,

    The photoelectric sensor for smoke detection uses Mie-scattering physics as the underlying principle.  As compared with Rayleigh scattering, Mie scattering does not have a closed form mathematical solution.  Consequently, these angles are determined empirically through measurements using LED's of different wavelengths with corresponding photodiodes while also varying the half angles of these components.  Typically, once the set of optical components are chosen together with the optimum angle based on the measurement data collected, the optical chamber is designed once.

    There has been a large amount of research in this area over many years.  The typical online resources will have more detailed information on this topic.  Once such research paper on this topic can be found here.  nfpa.org also has a wealth of information on the subject.

    We typically see Forward scatter angles in the 140 to 160 degrees range and Backscatter angles in the 60 to 80 degrees range for commercially available products.  The angles for the TIDA-010941 are 125 degrees forward IR and 30 degrees back scatter Blue in order to maximize the SNR from both wavelengths specifically for smoke type analysis.

    Regards,

    David