Patent Number: 
Section: claims

1. A method of locating a garter spring external to a pressure tube, said method comprising:receiving, from a measurement device in said pressure tube, a plurality of data points, where said receiving includes receiving a data point representative of a diameter of said pressure tube at each of a plurality of angular offsets for a first range of axial positions in said pressure tube;fitting a shape to said plurality of data points;determining an integrated residual error between said data points and said shape;associating said integrated residual error with said first range of axial positions;repeating said receiving, fitting, determining and associating for a further plurality of axial positions, thereby producing a plurality of integrated residual errors;applying a digital filter to said plurality of integrated residual errors, thereby producing a plurality of filtered integrated residual errors; andindicating, as a location of said garter spring, an axial position associated with a local maximum filtered integrated residual error among said plurality of filtered integrated residual errors. 2. The method of claim 1 wherein said digital filter comprises a three-stage digital filter. 3. The method of claim 2 wherein a first stage of said three-stage digital filter comprises a 6th order infinite impulse response Butterworth low pass filter, with a 3 dB cut off at 18 mm. 4. The method of claim 2 wherein a second stage of said three-stage digital filter comprises a 4th order finite impulse response derivative filter. 5. The method of claim 2 wherein a third stage of said three-stage digital filter comprises an order 40 finite impulse response step change cross correlation filter. 6. The method of claim 1 wherein said shape is a circle. 7. The method of claim 1 wherein said shape is an ellipse. 8. A device comprising:a processor adapted to:receive, from a measurement device in said pressure tube, a plurality of data points, where said processor is adapted to receive a data point representative of a diameter of a pressure tube at each of a plurality of angular offsets for a first range of axial positions in said pressure tube;fit a shape to said plurality of data points;determine an integrated residual error between said data points and said shape;associate said integrated residual error with said first range of axial positions;repeat said receiving, fitting, determining and associating for a further plurality of axial positions, thereby producing a plurality of integrated residual errors;digitally filter said plurality of integrated residual errors to, thereby, produce a plurality of filtered integrated residual errors; andindicate, as a location of a garter spring, an axial position associated with a local maximum filtered integrated residual error among said plurality of filtered integrated residual errors. 9. A computer readable medium containing computer-executable instructions that, when performed by a processor, cause said processor to:receive a plurality of data points, where said instructions cause said processor to receive a data point representative of a diameter of said pressure tube at each of a plurality of angular offsets for a first range of axial positions in said pressure tube;fit a shape to said plurality of data points;determine an integrated residual error between said data points and said shape;associate said integrated residual error with said first range of axial positions;repeat said receiving, fitting, determining and associating for a further plurality of axial positions, thereby producing a plurality of integrated residual errors;digitally filter said plurality of integrated residual errors to, thereby, produce a plurality of filtered integrated residual errors; andindicate, as a location of a garter spring, an axial position associated with a local maximum filtered integrated residual error among said plurality of filtered integrated residual errors.