I am receiving conflicting opinions on using an Alge and a Heuer side by side for finish timing.

Is there anything written definitively on the subject?

The cells should stacked rather than side by side. Each cell and reflector should be mounted on it's own seperate post. You should keep the beams of the cells as close to the 20cm (8 inch) mark as you can. ALGE cells are physically larger than the TAG units. You may wish to place the TAG lower as primary and the ALGE above. Proper set up will make sure that the beams are parallel. With each cell dialed in on it's own reflector there should be no interference. We like to have a second person "walk the line" and check the cells at three places; Near , center, and far side. Start in the center and place your glove on the snow and then raise it until the primary cell triggers. That point should approximate the top of the boot. Then come down from the top and trigger the backup. That point should be approximately 20cm higher than the primary beam. Be on the lookout for swales or other issues that would cause the primary beam to be mounted too high and let racers slip under it.

The FIS timing booklet from May 2005 does not mention anything about using cells from different manufacturers. It does not mention anything about using through beam (transmitter-receiver) cells and reflector cells at the same time either.

Common sense and operational evidence should be your guide. Discard any equipment not on the FIS homologation list and then use what you have in a configuration that works for your situation.

This message has been edited. Last edited by: FKP,

I've had issues with using a Tag photosensor next to a Alge sensor when running duals. Both sensors are the reflactor type. From what I can tell, the Tag transmitter sends out a less focused beam, effectively flooding the area. Easier to aim by far, but harder to keep from flooding over to other reflectors. My solution was to use hoods (or in my case tubes) over the Teg unit and stagger the placement of the sensors.

The observation is correct. Using the TAG cell for primary works best.

Is there a regulation issue with isolation between finish cells? If one bleeds over to the other, is the backup invalid?

In this situation, running afoul of regulations is the least of your problems.

If both TX's reach one or both RX's with sufficient strength, they will cancel each other out, and you will get no impulses at all.

TX's emit a sine wave. The RX keys on this sine wave, and when it drops away for a given interval, you get a circuit closure. Two TX's with sufficient strength will cancel each other's sine wave, and the RX will behave as if there is no TX at all (misaligned). You'll get diddly squat.

The real BITCH of this situation is that TX's usually drift relative to each other. So you can set up a pair and they seem fine, but as the sine waves drift slightly and get increasing out of phase, they will cause a gradual cancellation. So suddenly, in the middle of the race, you get ZIP from your finish cells.

So set up your cells well ahead of time and let them burn in for a while. Check the RX meters periodically - if the TX's start to drift and cause a cancellation, you'll see a low-frequency oscillation in one or both RX meters. That's when you know you need to either move them further apart or shield them better from each other, using Pringles cans or something similar.