The LMA zero increase caused by the magnetized rope 

 leaving one end of the machine will also occur as the 

 magnetized rope leaves the other end of the machine. 



Once a test is completed the rope which has been run 

 through the machine will be magnetized. If the rope is 

 then run in the opposite direction an LMA zero shift 

 will occur. This is as a result of magnetized rope 

 leaving end B of the machine (see Fig. 4.12) and the 

 Internal magnetic field B increasing. No change occurs 

 in the field A as magnetized material is now entering 

 the head at end A and the zero shift in the LMA due to 

 this field redistributing has already occurred at end A 

 on the previous test. If recalibration of the LMA gain 

 is again desired it can be done by first advancing the 

 rope by 3 feet on this 're-run' and adjusting zero and 

 gain as previously described. 



The LMA zero shift due to magnetization has a more im- 

 portant effect on measurements than calibration. 



Rope tests are often carried out in two parts due to 

 accessibility of the working length of the rope. Once 

 one section of the rope has been tested care must be 

 taken in testing the rest of the rope as the sensing 

 head will ultimately meet the end of the first test 

 and see the magnetic 'signature' created by the magneti- 

 zation induced in the rope by the first test. An 

 example is in order to explain this further. 



Figo 4.14 shows the working length of a rope as if it 

 were completely stretched out. The first test was con- 

 ducted between dl and d2 . To test from to dl the 

 head should be installed with the same orientation on 

 the rope as the first test. As dl is approached and 

 passed the sensing head will see a changing magnetic 

 condition from unmagnetized rope entering it to mag- 

 netized rope entering it. This will create an LMA 

 chart record as in Fig. 4.15. 



A-39 



