Patent Number: 
Section: claims

1. A diagnostic system for a digital rod position indication (DRPI) system of a nuclear power plant to monitor 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 connected in parallel between a DRPI display cabinet and redundant pair of DRPI A and DRPI B data cabinets, the digital diagnostic unit having:inputs configured to receive DRPI signals communicated between the DRPI display cabinet and the 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 to the DRPI A and B data cabinets; anda gate array module configured to acquire the DRPI signals from the data acquisition and address input/output modules, the gate array module having an interface connected with a controller configured to monitor the digital rod position signals from the DRPI A and B data cabinets for each coil and identify mismatches between a DRPI A rod position of the DRPI A data cabinet and a DRPI B rod position of the DRPI B data cabinet for each coil while the nuclear power plant is operating. 2. The system of claim 1, wherein the digital rod position signals include rod address signals and rod position data signals, and wherein the rod position errors are determined based on signal level variation and/or signal timing variation of the rod address signals and the rod position data signals. 3. The diagnostic system of claim 1, wherein the digital diagnostic unit further detects parity bit errors in the digital rod position signals between the DRPI display cabinet and the DRPI data cabinet. 4. The diagnostic system of claim 3, wherein the digital diagnostic unit stores measured voltages of the digital rod position signals when a rod position error or a parity bit error is detected. 5. The diagnostic system of claim 3, wherein the digital diagnostic unit monitors at least one of the signal level variation, the signal timing variation, and the parity bit error of the digital rod position signals to identify the component that is the source of the error. 6. The diagnostic system of claim 5, wherein the digital diagnostic unit monitors variations in the digital rod position signals while the nuclear power plant is operating. 7. The diagnostic system of claim 5, wherein the digital diagnostic unit monitors variations in the digital rod position signals to identify errors of a particular card, cable, or control rod. 8. The diagnostic system of claim 1, wherein the diagnostic unit monitors Gray code rod drop signals of the digital rod position signals.