The current issue of trains magazine has a photo of a ‘slide fence’ The caption explains that if a rock strikes the fence, it will trip the track signal to red.
Can a rock trip the signal without actually breaking the wire? If so, What type of technology is being used?
Rich
Simple technology. A rock hits the fence and pulls it out of line; the fence stringers are connected to relay boxes; the relay is attached to the signal circuit. When the relay is tripped, the signal goes red.
I heard of one instance where a deer was trapped behind the fence; he tripped it and set the signals read.
Old Timer
How far are the signals apart?
Old timer- thanks for the info.
At 1st I thought that the wires had current in them. But what you are saying is that they are just ‘trip wires’ Is that correct?
Thanks again Rich
rluke: the wires can be trip wires or dc current in thin strand wires that breaks. Both are common in Colorado. (Application dependent)
China: the systems are usually wired into the regular CTC/ABS wayside signal system like high water detectors. On occasion, rotating beacons are mounted locally on posts as well (dark territory or slide prone areas)… The special instructions in the timetable will tell you what you are dealing with.
Thank you Mudchicken
Signal spacing varies. At one time signal were normally spaced approximately 2 miles apart(in the day when a 5000 foot train was considered BIG)…with todays bigger, heavier longer trains many railroads are respacing the signals to be 3 or 4 miles apart…todays trains are 9000 feet long and on some territories, longer.
when I was young , I couldn’t figure out how those little skinny wire could hold the rocks back in a rock slide. I thought that they were really “fences”. I took me a while to figure out that they were just sensors - whether wire break or trip sensors.
dd
[#offtopic] To give you example years ago PA tried to build fences to hold the rocks. Okay for little ones but not much good for bigger one. Between TN and NC there was a slide that covered I-40 and closed it for months. It was 2 lane for many more months. Took over ayear to fix. Lost half the moutain.[:O]
On the SP, the types used by MC were used and where the slides were slow earth movements, there were mercury tilt switches. The switches were fixed to posts driven into the greound that would tilt as the earth moved. All of the tilt switches that I know of were on the Siskiyou between Roberts Mountian and Drain.