Alge photocells in blowing snow

You did mention if you are using through beam configuration or reflector.

Through beam use reduces the threat of getting a false pulse.

ALGE PR1a and RLS1n photocells use the same frequency so you could upgrade just the transmitters or receivers and use your existing cells.

I must agree with FKP. Use through beams for anything that matters, especially scored races. Besides tolerance to blowing/falling snow you will also find an easier time getting more width for your finish or intermediate lines.

We were using reflectors for the race that caused this post. Issues included snow building up on the reflector as the wind changed direction.

My instinct has been that the old rectangular Alge photocells seemed to have a wider tolerance to horizontal/vertical movement, than the PR1a, I've often wondered if it's instinct or fact. Having used them for years, I've never really looked into how photocells work.

Do different types of photocells have different widths of beams, or use different amounts of power, which make them more or less reliable? Does using a C-cell battery vs TDC cable make any difference in PR1a performance?

In addition to using a through beam, are there any brands of photocell which have more tolerance to false finishes from things like dense snowflakes?

Actually the reflector type is the same. ALGE has used the same type of clear reflector for years. The round type used in the PR1a are the same as were used in the RLS1n. The ALGE cell with the glass lens projects quite a tight beam. The beam is only bouncing back from one of the reflector pyramids. That being said you have two possibilities for a beam break and an impulse with any reflector set. Out bound and in bound. Using through beam configuration drops the likelihood for such false impulses by 50%


The PR1a and RLS1n use the same frequency so you might want to try using them in tandem with a RLS1n as a transmitter and PR1a as a receiver. Make sure you turn the PR1a to RX after lining them up.

The simple and most reliable solution is to cut down on the distance between the photocells.
Less distance - less snow to interrupt the cells. Also make sure the mounts are 100% rigid.

Through beams is far better that reflector.

Use photocells with batteries, even when powered from the timer.

Filters may reduce some of the noise, but will not resolve your problem. Its nonsense from a technically point (filter on/off) but some proof in the pudding may be observed.

It is a straigt forward procedure to rebuild the old RLS1n (reflector) to RLS1n-TX (combi reflector/through beams). The innards are the same, just add a switch (tx/rx) to the correct cable.

I'm looking into the through beams. In very heavy snowfalls there will always be a risk of blocking the beam, but I imagine that depends on how tight or wide the beam is- that is, the size of the object required in order to trigger an impulse. I imagine some brands/models of beams will trigger with say a 2cm diameter object blocking the beam, whereas others might require say a 4cm diameter object?

"The ALGE cell with the glass lens projects quite a tight beam."

By a tight beam does that mean they have a narrower range for aligning, and are more susceptible to false finishes from vibration or snowflakes?

Do the older rectangular silver Alge photocells (from 15+ years ago) have a tigher or a wider beam?

Are there other brands that have wider beams, which are more forgiving?

"Use photocells with batteries, even when powered from the timer. "

Why is that?

Thanks for the info, it's interesting to understand the technology better.

+M

I am upgrading my Alge reflectors to thru beams this fall. The reflectors caked over with snow and I lost a few times at a Masters race. Pr1's have hoods on both TX & RX units to prevent snow cakeover. Have to use add on hoods with other brands.

Mouse,
Your questions about the tight beam, it does require a more precise alignment. This also means a more focused light that would be more tolerant to snow but less tolerant to vibrations. I have both tag and alge cells that I use regularly and find them both fairly equal with regards to performance. As mentioned before I use through beams for all USSA/FIS racing and rarely get a false finish for snow. I do see TAG reflector setups used regularly as I manage the NASTAR venue at the resort where I live and when it snows hard, we get false finishes, even with a finish width of only 12 meters. We had the old ALGE units that you speak of about 20 years ago but I do not recall their performance in snow.

Really there is not much to understand about photocells, use through beams with good brackets on solid posts (notched of course), align them well and check them between runs. If you are doing sanctioned races with two sets use the sync cable with the PR1a or HL-232 to prevent bleed from causing problems. If you do not want to spend the money for through beams have a good timer who is paying attention and sync your had watches so you can easily identify a correct impulse in blowing snow. Keeping the finish line narrower (within rule limits) helps too.

In order to meet FIS-specifications, the beams have to be thight, regardless of brand.

Size of beam is a part of FIS rules, and homologation. (timing booklet, p 26).

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).


The distance at finish is flexible in exceptional cases:

FIS Alpine Joint regulations:

615.2 The Finish Line and its Markings
"In Downhill and Super-G races, the finish must be no less than 15 metres wide and in Slalom and Giant Slalom no less than 10 metres wide. In exceptional cases, the Jury may decrease this distance on the spot for technical reasons or because of the terrain. "

Snow closing the photcells is such an "exceptional case". Organizers and TDs are eager to finish races if they can provide fair conditions for the racers. Visibilty for racers, gate-to-gate is the main safety concern. The distance of the finish line is not a concern under such circumstances.

This applies only to SL-races. No TD would accept scored GS, SG and DH under such conditions.

I have been down to 5 meter distance on the finish line at a SL FIS-race. However, the race was cancelled due to visibility for the athletes on course.

If you are not able to serve stable photocells at a 10m distance, just and fair conditions for athletes are most likely not present on the course.

If you experience cluttering at the photocells, ask the TD for permisson to reduce the distance at finish. "No timing - no race" is lingo acceptable to most TDs.


Mouse: Batteries in photocells provides you redundancy when powered from cable.

Once the race starts, it would be (should be) unacceptable to most TDs and Juries to move posts or narrow the finish line, just as it would be to move the wand to one side or the other, or up and down. You would be changing the length of the course for 2 reasons:
1. The width can impact the race's line, and hence the course length and
2. There is no way to guarantee you will move the photocells to the exact same plane/line as they were previously on.

Through beams are really the only reasonable solution.

Thanks for the comments & details, much appreciated.