Laboratory testing of track signaling system susceptibility to electrical interference

The safe operation of track signaling systems is being threatened by the increasingly complex electrical noise conducted by track systems. The wide range of signaling system types and functions, along with a diversity of electrical noise sources, further complicates the assurance of system compatibility. Of particular concern is the track-conducted EMI created by new developments in DC and AC traction systems and the influence of such interference on the safe operations of new microprocessor-based highway grade-crossing systems. Two factors are recognized as being important for assuring adequate compatibility margins for operating systems. First, the magnitude and other relevant characteristics of the interfering signal must be known by measurement or prediction for worst case system operating conditions. Second, the susceptibility threshold of the signaling system to the interference must be measured as the system performs its range of operating functions. The authors have developed a track simulator for laboratory interference susceptibility testing that provides considerable flexibility in the types of test signaling systems, the interference characteristics, and the track-system operating conditions. Detailed test procedures have been developed and evaluated for some equipments and interference conditions of interest. The paper illustrates the field and laboratory fixtures and test procedures that have been used to define operating track-signaling system interference-susceptibility thresholds and compatibility margins for specific systems of concern.