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         that the wire rope 12 moves at constant speed between suc-  measurements.  On  the  other  hand,  visual  markers  could
         cessive  incremental pulses  24.  Then,
 Sea  Link  Wooden  Shelldistance ratios are
                                                              become covered with grease and not be detectable, or they
 Construction  &  Fishing  Blocks                             could wear off.
         equivalent to time ratios between pulses. This equivalence
                                                               Therefore, according to other embodiments of the inven-
         can be used for interpolation.
           By calculating a value for d, the distance calibrator 40 has   tion,  magnetic absolute distance markers  14 can  be used.
         established calibration parameters by which  the distance
 S Siinnggllees  •  Ds  •  Doouubblleess • •   T Trriipplleess • •   R Reegguullaar  ar  annd  Hd  Heeaavvy  Wy  Wooooddeen  Bn  Blloocckkss produce a   One advantage of magnetic markers is that they are not af-
         calibration and measurement apparatus 10 can
                                                              fected by grease and dirt on the rope surface. Therefore, this
         calibrated distance measurement corresponding to any val-  approach promises to be robust and reliable.
         ue of the incremental rope distance signal 22. Various types   For example, a “test wire” 14 can be utilized for in-service
         of distance markers 14 can be utilized. For example, it is   in situ calibration of an LMA (loss of metallic cross-sectional
         possible according to certain embodiments of the invention   area) signal trace (as produced by a magnetic NDE sensor
         to attach absolute visual markers 14, such as paint or plastic   head) to establish a certain position along the length of a
         strips that are spaced apart at known distances along the   wire rope  12 as a reference for correlation with the LMA
         wire rope 12, in which case an optical sensor head 30 could   trace. Figures 18-20 illustrate by way of examples LMA trac-
         be used. Commercially available wear-resistant paints and   es (test wire signals) 60, 70, 80, each of which includes test
         tapes  would be suitable. Plastic markers  14—for example   wire detection 52.
         made from UHMWPE—also could be molded onto the wire   Essentially, this technique uses test wires that are per-
         rope  12. These indicators could be optically detected  by a   manently  or  temporarily  attached to  the  wire  rope  12  for
         simple machine vision system and used for absolute distance   inspection. Besides serving as a rope cross-section reference,
                                                              the test wire  also establishes a distance marker  14 along
                                                              the length of the rope. This helps to locate the positions of
                                                              anomalies along the rope and to correlate them with corre-
 All  Material  Factory  Certified                            sponding indications on the chart recording.
                                                               It is conceivable for wire rope manufacturers to embed test
 Wooden  Shell  Blocks  3”  to  16”                           wires (or other steel objects) at certain predetermined dis-
                                                              tances (say 100 m or 1 km) in the rope. These markers could
 For  more  Associated  Wire  Rope  &  Rigging,  Inc. Waterman  Supply  Co.,  Inc.
 information,  8125  Saran  Drive,  Playa  Del  Rey,  CA  90293  910  Mahar  Ave.,  Wilmington,  CA  90748  then be used for absolute distance measurements. The incre-
 contact:  Ph:  1-800-901-1135  Fax:  310-448-5446  Ph:  1-800-322-3131  Fax:  310-522-1043  mental measurements from a distance counter wheel could
                                                              then be refined and calibrated by this absolute information.
 Email:  awrrinc@earthlink.net  Email:  waterman@bigplanet.com  Of course, the above method may be problematic and/or
                                                              not accepted by wire rope manufacturers and users. Never-
         Figure 19: Second exemplary loss of metallic cross-sectional  area
         (“LMA”) traces.                                                                       continued on next page
 Wire  Rope  News  &  Sling  Technology          August  2006  37  Wire Rope News & Sling Technology   April 2018  65
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