For non-scored races, the USSA currently allows a wireless connection between the start-gate and timer, but not between the finish eyes and timer. Allowing wireless finish connections seems like a natural next step, especially since the distance is so much shorter. It is my hope that this will be allowed in the near future.
The purpose of this experiment is to determine the accuracy of a wireless finish compared with that of a wired finish for an alpine ski race.
A single Alge PR1aW photocell was used at the finish. It was connected to two timers. It was (a) hard-wired to an Alge Timy-PXE; and (b) connected wirelessly over the Alge WTN to a Timy3-WP. Channel 0 of both timers were shorted together and hard-wired to the start gate.
This experiment took place at the U8/U10 Town Meeting Day Slalom at Cochran's Ski Area, VT on March 1, 2016.
In this section, SysA is the hard-wired system, and SysB is the wireless system.
The plots below shows two curves: the difference between start times recorded by each timer and the difference between the net run run times for each system. We note a few things.
- Over the 65 minutes that it took to complete run 1, the timers drifted by almost 0.002s. This is evident from the start time difference. Note that this drift will not have any significant impact on the net run times.
- The wireless net run times are usually within 0.0005s of the wired times, and never more than 0.0007s. This is well within the requirements for alpine ski races at all levels. Note that, by comparing net run times, we have removed the effect of timer drift.
- Run 2 results are similar, if somewhat better. Over a similar amount of time, the timers drifted only about 0.001s, and the net run times were always within 0.0005s.
As an aside, it's interesting to note that timer drift seems to be affected by actually receiving timing impulses. I note this since simply leaving the timers running overnight (without any impulses) results in less than 0.0002s of drift.