Patent No.:   US 6,588,710                                      Date of Patent: July 8, 2003

Patent No.: Canadian 2,480,013                              Date of Patent: April 19, 2011   

This invention relates generally to railroad trackwork switches, and particularly concerns sensor apparatus useful for detecting and indicating whethere or not the switch point of a railroad trackwork switch is satisfactorily positioned with respect to the switch stock rail.