Hello,
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!!
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 resolution).
I hope this has been of help.
Chris
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