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defect detectors
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[quote user="cacole"]<p>Out here in the desert, defect detectors are stretched out along about one mile of track, and involve quite a bit of equipment, so you would have to do a lot of selective compression to get one on a model railroad.</p><p>There's usually a hot box detector at each end, with a dragging equipment detector, axle counter, speed measuring detector, and IEC tag reader in between. One even has a wide load detector because of a narrow bridge across the San Pedro River at Benson, Arizona. In the middle is a large enclosure with the electronics and a radio relay tower, all surrounded with a chain link fence.</p><p>Along the Union Pacific Sunset Route, defect detectors are spaced about every 20 to 30 miles.</p><p> </p><p>[/quote]</p><p>That's a very unusual installation! </p><p>Almost all DEDs are less than 10' linear including the instrument house, and most HBDs are not any longer. AEI readers are not combined with them but may be co-located. Combined HBD-DEDs can stretch out over about 80 feet. </p><p>Typical modern railroad practice is to install a DED at every intermediate signal (8,000-foot to 10,000 foot apart) in concrete-tie territory, and 25,000-foot intervals in wood-tie territory. The closer spacing in concrete-tie territory is because concrete ties are much more vulnerable to fatal damage from dragging equipment whereas wood ties can take quite a bit of abuse.</p><p> Typical spacing of HBDs is 50,000 feet. DEDs and HBDs may be co-located and share the same instrument shelter, or have separate shelters -- depends on how the railroad wants to wire it. AEI (not IEC) readers are usually installed at either end of a terminal or important junction in order to generate an accurate trainlist of trains entering and leaving. There's seldom more than one or two every 100 miles. </p><p>High-Wide detectors are applied to protect major through bridges and tunnels, and are often found entering and leaving major terminals, about five-to-ten miles out of the terminal, giving a load enough time to shift but not so much time it runs into something like a highway overpass. They have nothing to do with the narrowness of the bridge -- by definition virtually all through bridges and highway overpasses are "narrow" -- but with achieving an acceptable reduction of risk. </p><p>An old-style HBD depending upon railroad, can use anything from a 48" instrument case up to an 8' x 8' instrument shelter. Typical practice today is an 8' x 8' or 8' x 10' instrument shelter. </p><p>Wheel-impact and broken-flange detectors are very rare by comparison. There might be all of two of them on an entire transcon route.</p><p>As always practices vary by railroads and over time </p><p>S. Hadid </p>
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