Troubleshooting Automatic Train Stop (ATS) systems requires a systematic approach because ATS must reliably stop a train during specific unsafe conditions. The troubleshooting method depends on whether the system is mechanical, inductive, or electronic.
In a mechanical trip ATS system, one common problem is failure to engage. This may occur if the trackside trip arm does not rise properly or if the onboard trip cock does not contact the trip arm as required.
If the trackside trip arm fails to operate, the maintainer should inspect the mechanism for obstructions, damage, binding, incorrect adjustment, or misalignment. The control system that raises and lowers the trip arm must also be checked.
Onboard mechanical problems may include a damaged trip cock, incorrect height adjustment, loose mounting, restricted movement, or binding in the trip mechanism.
Unintended mechanical engagement can cause unexpected brake applications. This may be caused by obstructions near the trackside trip arm, improper trip arm position, or an onboard trip cock that is loose, overly sensitive, or incorrectly adjusted.
If the ATS brake application is weak or ineffective, the maintainer should inspect the connection between the trip cock and the brake valve. The brake valve itself must also be tested for proper operation.
In an inductive ATS system, loss of signal reception is a common problem. Trackside inductors, cables, power supplies, and transmitters should be inspected for damage, loss of power, or failed signal transmission.
Onboard reception problems may involve a damaged antenna, misaligned receiver, loose cable, failed processing unit, or poor connection between the receiver and onboard ATS equipment.
If the system receives incorrect data, technicians should verify trackside encoding, signal status inputs, speed limit data, onboard software configuration, and how the onboard system interprets the received data.
Overspeed enforcement problems may be caused by inaccurate speed sensors, incorrect speed threshold settings, wrong speed limit data, or onboard calibration errors.
False brake applications may be caused by signal interference, faulty speed sensor readings, onboard processor faults, receiver problems, or incorrect system configuration.
System manuals, diagnostic tools, status indicators, event logs, and approved troubleshooting procedures are essential when working on ATS. Because ATS interacts with the train braking system, all troubleshooting must follow railway safety rules and be performed by qualified personnel.