FIS Photocell Spec

jacunskimMember

Hi everyone.

I was recently reading the latest version of The Good Book (that would be the FIS Timing Booklet), and I noticed something odd. The technical specs for photo cells are listed on page 33. It states the following:

Triggering Object:

An 8 mm object moving with a speed of 10 km/h is not allowed to trigger the photocell (measured at a distance of 2 m from lens of the receiver).

A 100 mm object moving with a speed of 200 km/h must trigger the photocell (measured at a distance of 2 m from lens of the receiver).

Of course, the photocell doesn’t know anything about the object’s size or speed. It just knows for how long the beam was interrupted. But here's the thing:

an 8 mm object moving at 10 km/h will break the beam for 2.9 ms;

a 100 mm object moving at 200 km/h will break the beam for 1.8 ms.

How can a 1.8 ms break trigger the photocell, but a 2.9 ms break not? Am I missing something? Has FIS created an impossible spec?

Thanks for the insight.

-- Mark

12/24/147:18 AM

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