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[Anonymous]

Can someone please tell me how a FRED (Flashing Rear End Device) works?

[csxengineer98]

FRED.... a battery turns on the light and it blinks
now an EOT with telemitry uses batterys, or the newest ones have some kind of air powerd generator as well as batterys....but they have 2 way radio signal that is sent from the EOT to the head end of the train that gives information on if the marker light is on or not..rear end brake pipe pressure..and also if the rear end is moving... also...the HTD box on the locomtive can send a signal to the EOT to dump the train from the rear end... (place in emergancy)
for the emergancy function to work..the HTD had to be armed to the EOT number...
csx engineer

[ndbprr]

An excellent description however I am at a loss as to how it determines it is moving since the only connection is to the air line. The only ways I can figure are either a vibration detector or an infrared detector to monitor the ground of some sort.

[csxengineer98]

i think thier is a miget in them that pushes a button when the train is moving... they look out the little window where the red marker flasher is...lol
i think thier is a motion censor in them....kind like the ones they use on outdoor lighting..the oens that come on when someone or something passes infront of them
csx engineer

[pmsteamman]

There is a motion sensor, but as csx engineer can vouch for they can't always tell if they are going fwd or rev.