LMA accuracy was determined by adding individual wires to a wire 

 rope so that the known actual change in percent LMA could be compared to 

 the recorded change in percent LMA. 



Test Setup 



A test track (Figure 1), designed to accommodate a 100-foot loop of 

 wire rope, was constructed to conduct tests on running wire ropes of 

 various diameters and constructions. Wire rope speed was infinitely 

 variable by means of a variable speed transmission powered by a 1-3/4-hp 

 electric motor. Rope speeds are variable from to over 800 fpm. 



Each end support consists of three 1-foot-diameter sheaves that 

 simulate a 4-foot-diameter sheave. The larger sheave diameter was 

 needed to supply the larger wire ropes with an acceptable bend radius. 



DISCUSSION 



Gap Configuration 



A broken wire can have various shaped ends that produce gaps of 

 different configurations. A fatigue break gives square ends, while a 

 tensile break causes the ends to neckdown. Another condition occurs 

 when a wire is bent and pushed to the side (Figure 2d). A series of 

 tests was conducted on different gap configurations (Figure 2) to 

 determine the effective gap size. The results indicated that the signal 

 size depended on the clear air gap size in the longitudinal direction. 

 Hence, wires that are pushed sideways and are grossly displaced produce 

 a signal size that is dependent mainly on the longitudinal gap size. 



Gap Orientation 



Gap orientation refers to the location of a wire break in relation 

 to the four Hall-effect devices that were located 90 degrees apart in 

 the sensor head. In these tests a wire break could be directly under a 

 Hall-effect device, while at other times a break could be oriented up to 

 45 degrees from the device. 



The test to determine the effect of gap orientation used a 1-1/2- 

 inch-diameter wire rope with two manmade wire breaks approximately 4 

 yards apart (A and B of Figure 2). Break A was a broken crown wire, and 

 Break B was a broken filler wire. On the test stand, a break appeared 

 at the same orientation after each complete loop. Hence, for this test 

 the sensor head was rotated from through 90 degrees in 22.5-degree 

 increments. The LF data were compared to observe any changes in the 

 signal size. 



Figure 3 shows that the signal size changed considerably: between 

 the maximum and minimum signal, a 40% decrease for each wire break 

 signal was noted. The test was not designed to determine the orienta- 

 tion of the break in relation to the Hall-effect devices; however, the 

 data from break A revealed that for the minimum signal size, the probable 

 break orientation was 45 degrees from a Hall-effect sensor because the 

 signal size changed only once for the five readings. Surprisingly, the 



