Electronic Defect Detectors have been installed at strategic positions along railways for many years. The purpose of these systems is to automatically detect potentially dangerous failures in passing trains. The detectors transmit a voice synthesized alarm message over the railroad radio frequency to inform the train crew of a defect. Reported failures/problems include:
These trackside detectors locate overheated journals on moving trains prior to bearing failure. Overheated journals, i.e., hot boxes, occur when inadequate wheel bearing lubrication or mechanical flaws cause significant increase in bearing friction which, in turn, causes the wheel bearing temperature to increase. When the bearing temperature rises to an abnormally high level, bearing failure results. Such failures are a major cause of derailments, endangering life, destroying property, and resulting in costly delays.
Hot box detectors use infrared sensors that are focused at the wheel axles on both rails. As the train passes the detector, the temperature of each wheel bearing is measured. If either the absolute temperature of a bearing, or the temperature difference between two bearings on the same axle, exceeds a preset threshold then a radio mounted in a track-side enclosure transmits a beep over the radio. After the train completely passes the sensor, a "talker" will annunciate a message over the radio to inform the train crew of the axle number of each defect. When a train passes without problem, the talker transmits a "no defect" message over the radio. Some detectors report additional information such as:
Number of axles
Total length of the train
After a hot box or equipment defect alarm is announced, the train crew will usually stop the train and perform an inspection to determine the cause of the problem. The crew will notify the dispatcher of the problem and how much delay they experienced.
Matt Snell's excellent page provides background on defect detectors and modeling them.
This is a link to a page in a 1989 safety manual for the John Galt Line Railroad Company containing interesting information about types of detectors, what crews are required to do during inspections, and actions they are expected to take after locating a defect.