a rope speed of 200 ft/min; raw data are shown in Figure 16. Several 

 large LF signals indicate broken wires, but the intermediate-sized 

 LF signals take more experience to define. 



The first 36 feet of the rope were disassembled for a detailed 

 study. Three crown wire breaks and five filler wire breaks were found 

 (see Figure 17). As can be seen, several filler wire break signals were 

 the same size as the background-noise signals. It appears that inex- 

 perienced inspectors would have a difficult task distinguishing between 

 these types of signals. 



Rope Speed 



The Hall-effect devices, which detect broken wires by picking up a 

 magnetic flux leakage field created by a discontinuity in the wire rope, 

 are not dependent on rope speed to generate a signal." It has been 

 demonstrated that the Magnograph unit detected broken wires when the 

 sensor head was moved slowly over breaks on wires. The LF signal remained 

 even when the sensor head was at a standstill over the broken wire. 

 However, it was noted during field tests that the LF signal size varied 

 to a limited degree with rope speed, which led to further investigation. 



A test was conducted on a 1-1/8-inch-diameter, 6x25 regular-right- 

 lay, fiber-core rope to observe the effect of rope speed on LF signal 

 size; break gap spacing was about 1/8 inch. Figure 18 shows that as the 

 rope speed changed from 50 to 800 ft/min, the signal-to-noise ratio 

 ranged from a maximum of 7 to a minimum of 2. As the rope speed increased, 

 the background noise became larger, so the signal-to-noise ratio decreased. 

 The manufacturer recommends testing at rope speeds of 50 to 600 ft/min, 

 which is acceptable, but higher rope speeds are also acceptable. 



Rope Guides 



The Magnograph unit's sensor head can be used for wire ropes with 

 diameters varying from 1/2 to 2-1/2 inches by using different-sized rope 

 guides and adaptor tubes. The equipment uses five different rope guides 

 to accommodate all wire rope diameters (see Appendix, Figure 4.3): four 

 adaptor tubes handle ropes from 1/2 to 2 inches in diameter, and the 

 larger rope diameters of 2 to 2-1/2 inches are handled without an adaptor 

 tube. 



Tight and loose fit were investigated for the effect on LF signal- 

 to-noise ratio of a rope traveling through the sensor head. The manu- 

 facturer recommends rope guide C for wire ropes of 1-1/8 to 1-9/16 

 ihches in diameter, and rope guide D for 1-9/16 to 2 inches in diameter. 

 The 1-1/2-inch-diameter wire rope used in the test had a tight fit in 

 rope guide C, but a loose fit in rope guide D. The LF signal-to-noise 

 ratio for rope guide C was about 10 and for rope guide D about 6. When 

 going from the tight to loose fit, the LF signal size decreased slightly 

 and the background noise increased substantially. Consequently, the 

 rope guide with a tight fit is recommended. 



'Conventional DC-type wire rope testers are dependent on rope speed to 

 generate a signal. 



