Rome Navigation Innovations 2/7/06 1 Show By Example How Evaluation of Data Performance in General Will Be Carried out Showcase Geometry Data Alignment Techniques as A Solution to Many Problems. Evaluation of Geometry Data Error Performance on A Geometry Car Using Geometry Data Alignment Techniques H. James Rome Rome Navigation Innovations,Inc 27 Old County Rd, Gloucester, MA Purpose of the Presentation

Rome Navigation Innovations 2/7/06 2 Presentation Concentrates on a case Study: Comparison of “Alternate” and Standard Gage Example of Performance Analysis Investigate Repeatability and stability of two measures of gage.

Rome Navigation Innovations 2/7/06 3 What’s This Geometry Data Alignment Package? Lines up data from several runs to data on Reference Run. Can align data to an Accuracy ~ 1 ft Used For: –Trend Analysis –Repeatability and Error Analysis Example Follows

Rome Navigation Innovations 2/7/ Left Profile Lined up with GPS to about 2 meters x Distance along track, ftX10 4 -> Profile, Inch,-> Plot.vs.time at ft location37825 time back from reference run, months Profile, Inch,-> Example …Before Data Alignment:

Rome Navigation Innovations 2/7/ Plots after Data Alignment up with With Package, x Profile, Inch,-> Distance along track, ftX10 4 -> Plot.vs.time at ft location37825 time back from reference run, months Profile, Inch,-> Trend Apparent

Rome Navigation Innovations 2/7/06 6 Use of Alignment for Error Analysis Approach can be used to Evaluate Repeatability Errors. –If Data is Taken Close Enough in time, Differences in Aligned Data imply the sum of the errors in Both measurements.. examples follow

Rome Navigation Innovations 2/7/06 7 NOTE! This alignment can be carried out over 10’s or even 100’s of miles with the click of a mouse. Thus no need to constrain evaluations to a several thousand ft “Test Track”. Occasional rare events, long term error error trends, and Data Reliability can be evaluated.

Rome Navigation Innovations 2/7/06 8 Example Comparison of Alternate and Standard Gage Both Measures were available on the Same Car Two Runs over the same 70 mi of track were used for the Study Each Is Analyzed as if the other did not exist From an FRA Car ~ 2006

Rome Navigation Innovations 2/7/06 9 Snippet Aligned Alternate Gage, and Standard Gage Alternate Gage Standard Gage “Standard” Gage Is Noisier! 1000 Pt mean subracted

Rome Navigation Innovations 2/7/06 10 x X+1000 Take Difference of Two Curves Find Root Mean Square of Difference,RMS Plot RMS vs. X What We Do Next

Rome Navigation Innovations 2/7/ x plot of 1000 pt rms alt gage differences standard gage differences Plot of Running 1000 Pt. RMS differences vs. Distance for Both Gages RMS’s ~ 40 % Less for Alternate Gage RMS (Units) Record # along track 

Rome Navigation Innovations 2/7/06 12 Note There is usually a Calibration Error in Gage Measurement Is the Calibration Stable During the Run?

Rome Navigation Innovations 2/7/06 13 Sample of Gage Aligned with ( 1000 pt) Bias Removed the Bias Distance along track,ft Gage, Inches

Rome Navigation Innovations 2/7/06 14 Sample of Gage Aligned gage..NOTE here Bias is not removed! Is this “Bias” stable? Distance along track,ft Gage, Inches

Rome Navigation Innovations 2/7/ x plot of 1000 pt mean vs distance alt gage standard gage Plot of 1000 pt Mean difference of same Paramter: for Alternate and Standard Gages Vs. Distance Typical Max Shift… Standard,.1” Alternative:.06” Record # along track 

Rome Navigation Innovations 2/7/ FRACTION ACTUAL DIFFERENCES LESS THAN X, mean subtrated alt gage standard gage From Histogram of All Differences, Find Cumulative Distribution Alternative Gage: 70% of error<.05’’ Standard Gage: ~ 70% of errors <.08’’ Error Limits, (Units)  X

Rome Navigation Innovations 2/7/ hisotragm of 1000 pt. RMS differences, mean subtrated alt gage standard gage Histogram of 1000 pt RMS errors For Both Gages. Most Likely Value Alternative ~.055 Noise Floor Most Likely Value Standard ~.075 Noise Floor Fraction in Bin Bin Value , Linear Units Less than ½ # Outliers!

Rome Navigation Innovations 2/7/ Period ~39 units Frequency, 1/( Unit record)  Frequency, 1/ (Unit Record)  Lots of High Frequency Noise. Power Spectra, vs Frquency from Both Gages Alternative Gage Standard Gage Note error power is about Double for Standard Gage

Rome Navigation Innovations 2/7/06 19 Conclusions Comparing Standard and Alternative Gages Alternative Gage has significantly: –Lower RMS errors –Fewer large Errors –More Bias Stability –Less high Frequency Noise Bottom Line: From the Point of View of Repeatability,Alternative Gage is Just Better!

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Rome Navigation Innovations 2/7/06 21 NOTE! Most of this Quality Information could not be obtained from a short stretch of Data With Automated Data Alignment, No test track required. Track of Opportunity can be used Simply Run over same ( say mile) length of track twice within a few days or weeks.

Rome Navigation Innovations 2/7/06 22 Other Uses Compare Results of GRMS Vehicles without having them Coordinate their Runs..and over a long distance. Compare Geometry measurement Equipment Find Fraction of time when there are data outages

Rome Navigation Innovations 2/7/06 23 What About Other Parameters The Key is the the ability to Align Massive amounts of Geometry car Data. It puts an Entirely new spin on how extensive and how inexpensive Quality Evaluation can be! Similar studies can be carried out on Any measurement taken on the Geometry car And That includes GPS