Magnet in Car Fries Finish Line Electronics
Posted: Wed Apr 17, 2013 11:20 am
A recent emailer related a problem encountered at a race he attended: A car containing a magnet "fried" (permanently damaged) the finish line electronics.
I have not been able to acquire details as to the type of magnet, the length of the aluminum track, nor the brand and model of the electronics.
Finish line electronics typically have a pair of wires serving each (photodiode) sensor positioned just below the underside of the track and running perpendicular to the lanes. If the wires are not shielded adequately, a sufficiently powerful magnet in a car moving at typical PWD car speeds across the finish line should be able to induce a current in those wires which then creates a voltage in the sensitive input circuits sufficient to "fry" low power components. Protection circuitry (e.g. clamping diodes) is common in some circuits, especially if the input is from external (uncontrolled) sources, but I don't know if it is typical in commercial finish line equipment.
I know that there are some small but very powerful magnets that can be easily salvaged from scrapped personal computers.
I wonder if one of these magnets were used in the suspect car in hopes of getting a "kick start" from the start gate when it opens. Commercial start gates use stainless steel which is only lightly magnetic, so an ordinary magnet would probably not provide a meaningful effect.
Our district race inspection procedure includes a test using a pair of (steel) paper clips dangled in the front of the car to detect magnets, but I don't know for sure that it is applied consistently. The procedure would miss a magnet placed in rear of the car by someone who was deliverately aiming for damage rather than advantage. Lack of detection places the electronics in the tracks (which we borrow) at risk.
Has anyone encountered this problem? What do you do to enforce the usual "no magnets" rule? Does anyone have inspection gear to detect magnets?
I have not been able to acquire details as to the type of magnet, the length of the aluminum track, nor the brand and model of the electronics.
Finish line electronics typically have a pair of wires serving each (photodiode) sensor positioned just below the underside of the track and running perpendicular to the lanes. If the wires are not shielded adequately, a sufficiently powerful magnet in a car moving at typical PWD car speeds across the finish line should be able to induce a current in those wires which then creates a voltage in the sensitive input circuits sufficient to "fry" low power components. Protection circuitry (e.g. clamping diodes) is common in some circuits, especially if the input is from external (uncontrolled) sources, but I don't know if it is typical in commercial finish line equipment.
I know that there are some small but very powerful magnets that can be easily salvaged from scrapped personal computers.
I wonder if one of these magnets were used in the suspect car in hopes of getting a "kick start" from the start gate when it opens. Commercial start gates use stainless steel which is only lightly magnetic, so an ordinary magnet would probably not provide a meaningful effect.
Our district race inspection procedure includes a test using a pair of (steel) paper clips dangled in the front of the car to detect magnets, but I don't know for sure that it is applied consistently. The procedure would miss a magnet placed in rear of the car by someone who was deliverately aiming for damage rather than advantage. Lack of detection places the electronics in the tracks (which we borrow) at risk.
Has anyone encountered this problem? What do you do to enforce the usual "no magnets" rule? Does anyone have inspection gear to detect magnets?