Patent Number: 
Section: claims

1. A high resolution digital rod position indication system for determining an axial position of a control rod within a reactor, the control rod being coupled to a drive rod that is moved by predetermined increments spaced apart along a range of motion, said high resolution digital rod position indication system comprising:a plurality of detection coils spaced apart at predetermined intervals, the spacing of the predetermined intervals being greater than the spacing of the predetermined increments, adapted to be excited by a low voltage ac source, each of said plurality of detection coils adapted to sense the presence of the drive rod, each of said plurality of detection coils adapted to produce an output signal, said output signals having fluctuations corresponding to each incremental movement of the drive rod;a data acquisition unit adapted to be placed in electrical communication with each detection coil of the plurality of the detection coils, said data acquisition unit sampling said output signals from the plurality of the detection coils;a processing unit in communication with said data acquisition unit, said processing unit deriving the axial position of the control rod, relative to each predetermined increment, based on said fluctuations corresponding to the incremental movements. 2. The high resolution digital rod position indication system of claim 1 wherein said processing unit derives a root-mean-square voltage signal from said sampled data and said fluctuations being a measurable change in said root-mean-square voltage signal. 3. The high resolution digital rod position indication system of claim 2 wherein said processing unit begins with a known position and tracks occurrences of said fluctuations to update said axial position. 4. The high resolution digital rod position indication system of claim 2 wherein said axial position is determined from the amplitude of said root-mean-square voltage signal. 5. The high resolution digital rod position indication system of claim 4 wherein a set of reference values relating said amplitude of said root-mean-square voltage signal to a rod position is obtained by moving said control rod through a full range of motion, said processing unit comparing subsequently measured fluctuations to said set of reference values to determine said axial position. 6. The high resolution digital rod position indication system of claim 1 wherein said processing unit derives a dc voltage signal from said sampled data and said fluctuations being a fluctuation of the dc voltage. 7. The high resolution digital rod position indication system of claim 6 wherein said processing unit begins with a known position and tracks occurrences of said fluctuations to update said axial position. 8. A system for determining an axial position of a control rod within a reactor, the control rod being coupled to a drive rod that is moved by predetermined increments spaced apart within a housing, the housing being encircled by a plurality of detection coils spaced apart at predetermined intervals, the spacing of the predetermined intervals being greater than the spacing of the predetermined increments, capable of magnetically sensing the presence of the drive rod when the detection coils are energized by an ac current, said system comprising:a data acquisition unit adapted to be placed in electrical communication with each coil of the plurality of detection coils, said data acquisition unit collecting sampled data from each coil of the plurality of the detection coils, said sampled data representing the electrical signals produced by each coil of the plurality of the detection coils; anda processing unit in communication with said data acquisition unit, said processing unit receiving said sampled data from said data acquisition unit, said processing unit evaluating said sampled data for fluctuations corresponding to each incremental movement of the control rod said processing unit deriving the axial position relative to each predetermined increment according to said fluctuations. 9. The system of claim 8 wherein said processing unit derives a root-mean-square voltage signal from said sampled data and said fluctuations being a measurable change in said root-mean-square voltage signal. 10. The system of claim 9 wherein said processing unit begins with a known position and tracks occurrences of said fluctuations to update said axial position. 11. The system of claim 9 wherein said axial position is determined from the amplitude of said root-mean-square voltage signal. 12. The system of claim 11 wherein a set of reference values relating said amplitude of said root-mean-square voltage signal to a rod position is obtained by moving said control rod through a full range of motion, said processing unit comparing subsequently measured fluctuations to said set of reference values to determine said axial position. 13. The system of claim 8 wherein said processing unit derives a dc voltage signal from said sampled data and said fluctuations being a fluctuation of the dc voltage. 14. The system of claim 13 wherein said processing unit begins with a known position and tracks occurrences of said fluctuations to update said axial position.