Sensors
The sensors installed at defect detector locations can include and are explained:
- Hotbox or hot bearing detectors
Two infrared eyes sit on each side of the tracks staring up at the trains bearings. As the train's bearings pass over the infrared eyes, the detector checks the temperature of them. If a bearing reaches the maximum temperature for safe travel, the detector will flag and count it as a defect.
- Dragging equipment detectors
A column of cones sits across the whole width of the railroad (just like a rail tie) attached to switches. Anything dragging from the train will hit this cone, thus pushing it back. Then it returns to its normal position to prepare for anything else that might be dragging under the train. The detector will register this action and flag it as a defect.
- High car or shifted load detectors
Two vertical white pads sit on each side of the train. Anything that is shifting over will be counted as a defect. It is mainly found on railroads where double-stack trains are prevalent, and where low vertical clearances, such as tunnels, are present.
- Wheel impact or sliding wheel detectors (often placed at the entrances of delicate high speed track like Amtrak's Northeast Corridor)
Wheel sensors along the tracks feel for flat spots on the trains wheels. Any flat wheel that becomes too dangerous to travel on (a big flat spot on the train wheel) will be counted as a defect.
- Weighing in Motion sensors for axle loads, imbalances or infracharging
- Wide-load detectors
A bridge spans over the railroad with two laser beams that shine down on each side of the passing train. Anything that cuts through the beam will be counted as a defect. This sensor may also be integrated into the high car detector.
- Structure gauge & loading gauge
- Hot-Wheel Detection (caused by sticking brake)
Read more about this topic: Defect Detector