Defect detector

The detectors are normally integrated into the tracks and often include sensors to detect several different kinds of problems that could occur.

Defect detectors were one of the inventions which enabled American railroads to eliminate the caboose at the rear of the train, as well as various station agents placed along active routes to detect unsafe conditions.

The detectors would transmit their data via wired links to remote read-outs in stations, offices or interlocking towers, where a stylus-and-cylinder gauge would record a reading for every axle; a defect would register a sharp spike on the graph and an alarm would sound or a visible signal would be given to the train crew.

The first computerized detectors had lights indicating the nature of defect and a numeric display of the associated axle number.

Later models allowed crews to interact with the detector using a touch tone function on their radios to recall the defect report.

Today, defect detectors are typically part of the general monitoring platforms keeping track of train status.

In the 2000s, defect detectors have increasingly incorporated computers to generate more detailed and accurate reports of train status.

Modern systems use computer programs to analyze photographs and identify potential errors for review by humans.

[2] One focus has been on reducing the number of false positives, which require trains to stop and be inspected, causing delays.

If a bearing reaches the maximum temperature for safe travel, the detector will flag and count it as a defect.

A shifted load detector is mainly found on railroads where double-stack trains are prevalent as the containers may become misaligned and present a hazard to bridge trusses or tunnel walls.

Typically, these systems utilize accelerometers, strain gauges, fiber optic methods, or the very latest wheel impact phase detector (WIPD).

These systems rely on an array of video devices in various locations between the rails and either side of the track, looking for particular bogie components (such as brake beam, springs, friction wedges, etc) and this data is then put through image analysis to determine if there are maintenance issues.

[5] Bogie performance detectors most often use optical methods, and are installed adjacent to the track with wheel sensors clamped to the rails.

These detectors either inject and monitor radio signals into the rail, or rely on electrical continuity of existing track-based circuits, to detect rail-line breaks.

The detectors are typically a mix of temperature sensors and strain gauges (so measure in degrees Celsius and kilonewtons force).