3 . Operating Theory 



The intent of this section is to familiarize the user 

 with the basis on which measurements of rope condition 

 are made with the Magnograph . It touches on the magne- 

 tic principles involved and how they are applied to pro- 

 duce these readings. By necessity the analysis is sim- 

 plified to stress the major considerations and effects 

 of the principles involved. 



3 . 1 The H a ll Principle 



The Hall Principle states that an electric potential will 

 exist across a flat conductor carrying current if the 

 conductor is subjected to a magnetic field. (refer to 

 Fig. 3.1) 



Vh is proportional to; 

 I.B 



1 - is the current 

 B - is the magnetic 

 flux density 



Fig. 3.1 Hall Principle. 



The Magnograph uses this princif)le to measure metallic 

 area and localized faults . The semi conductor Hall 

 Effect Sensors used provide quite large and stable hall 

 voltages and allow very small changes in flux density (B) 

 to be measured whether they are static or dynamic in 

 nature. The magnetic circuit and the placement of the 

 Hall devices is shown in a cross-sectional view of the 

 Magnograph in Fig. 3.2. 



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