Patent Number: 
Section: claims

1. A method of detecting errors in control and shutdown rod position during operation of a nuclear power plant using a diagnostic system for a digital rod position indication (DRPI) system that monitors in real time DRPI signals generated by a plurality of detector coils of the DRPI system while the nuclear power plant is operating, the diagnostic system comprising a digital diagnostic unit having inputs configured to receive DRPI signals communicated between a DRPI display cabinet and a redundant pair of DRPI A and B data cabinets, a coil diagnostic unit configured to receive voltage signals from each one of the detector coils, a plurality of data acquisition modules configured to receive digital rod position signals for each detector coil from the DRPI A and B data cabinets, at least one address input/output module configured to drive rod addresses of the digital rod position signals to the DRPI A and B data cabinets, and a gate array module configured to acquire the digital DRPI signals from the data acquisition and address input/output modules, the gate array module having an interface connected with a controller to monitor the digital rod position signals from the DRPI A and B data cabinets for each coil, the method comprising:connecting the inputs of the digital diagnostic unit in parallel between the DRPI display cabinet and the DRPI A and DRPI B data cabinets of the DRPI system;communicating the DRPI signals between the DRPI display cabinet and the DRPI A and B data cabinets;receiving voltage signals from each one of the detector coils in the coil diagnostic unit;receiving digital rod position signals for each detector coil from the DRPI A and B data cabinets in the plurality of data acquisition modules;driving the rod addresses from the at least one address input/output module to the DRPI A and B data cabinets;acquiring the digital rod position signals and the rod addresses from the data acquisition and address input/output modules in the gate array module;monitoring in the controller the digital rod position signals from the DRPI A and B data cabinets for each coil; andidentifying mismatches between the DRPI A rod position signal of the DRPI A data cabinet and the DRPI B rod position signal of the DRPI B data cabinet for each coil while the nuclear power plant is operating. 2. The method of claim 1, wherein the monitoring further comprises:processing the DRPI A rod position signal and the DRPI B rod position signal and identifying variations in a signal level and a signal timing of the digital rod position signals that indicate rod position errors of the DRPI system. 3. The method of claim 2, wherein the monitoring further comprises: detecting parity bit errors in the DRPI A rod position signal and the DRPI B rod position signal and identifying errors associated with the DRPI display cabinet and the DRPI A and DRPI B data cabinets using at least one of the signal level variation, the signal timing variation, and the parity bit error.