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How does a time registration with photofinish exactly works?

Discussion in 'Electronic Basics' started by Ilse Backers, Sep 23, 2004.

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  1. Ilse Backers

    Ilse Backers Guest


    Can somebody tell me more about how does a time registration with
    photofinish (e.g. in a cycling race, in a speedskating race,...)
    exactly work?
    What is the accuracy of it? And what do you have to do if you want it
    as accurate as possible? Are there other influences on it???
    Can somebody tell me also how it, electronically seen, works?

    Thank you!!
  2. CFoley1064

    CFoley1064 Guest

    Subject: How does a time registration with photofinish exactly works?
    A good block diagram of a modern race timing system is shown on this website

    Timings to the nearest millisecond are typically obtainable with this method.

    Longer distance LED photosensors are typically modulated at an intermediate
    frequency for better receptivity. Faster response times can be obtained by
    increasing the modulating frequency of the LED emitter and phototransistor
    receptor bandpass filter, making response times less than 1 ms. Photosensor
    manufacturers catalogs have all kinds of information on this method.

    While accuracy better than 1 ms really isn't necessary (and the backup of a
    camera, typically CCD, provides a photo record in case of a "tie", anyway), you
    can improve on this by dropping the modulating frequency and just going off
    dramatic changes in photosensor output, which decreases your sensitivity to
    electrical noise. Another possible here is using a low power laser diode, and
    providing a point-to-point aim for sensing. The limiting factor then becomes
    phototransistor response times. These can be improved again by using a
    photodiode and amplifier. But at this point, we're way beyond any reasonable
    accuracy for race times (better than than 10 microsecond, or .01 millisecond

    I hope this has been of help.

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