Zero 



jC~: 



2 -3 of rope 



Chart Dir. 





Fig. 4.13 LMA chart record showing zero increase 

 with rope magnetization 



This increase in the zero due to magnetization results in 

 a calibration error of the original gain setting by the 

 amount of the increase, ie . a YU shift in the LMA zero 

 due to the rope being magnetized will mean that the LMA 

 gain setting is off by 17o. This may not be of concern 

 to the user and LMA zero shift due to magnetization on 

 smaller ropes is quite small. Larger ropes (2" plus) 

 may have a shift of 2-3%. With this amount of shift 

 recalibration for the new zero is advisable. 



This can be accomplished in the following manner: 



i) Set up the instrument as described in section 4.4.3 

 with the sensor head on good section of the rope, 

 ii) Advance the rope by 3 feet so that the zero increase 

 due to magnetization is seen on the chart, 

 iii) Rezero the chart with the LMA Zero Potentiometer 



and adjust the gain as per the LMA calibration chart, 

 iv) Start the test. 



A-38 



