To re-run a test from tape the following procedure is 

 used: 



i) Connect the Chart Recorder Section to the Electronic 

 Control Section, 

 ii) Turn the Electronic Control Section on and set the 

 chart recorder to the desired chart speed or propor- 

 tional drive setting (see sections 4o3 & 4.5.4). 

 iii) Set the Record/Play switch to the 'Play' mode and 

 insert the cassette, 

 iv) Zero the chart recorder channels as at the beginning 

 of a rope test, 

 v) Use the tape transport controls to locate the area 

 of interest and start the recorder with the 'Tape 

 Run' button. 



The zero references for the LMA and LF Channels may re- 

 quire repositioning with the chart recorder controls . 



Note - High quality recording tape should be used, 

 TDK type AD is recommended. 



4.7 Rope Magnetization 



The strong magnetic field within the Magnograph sensing 

 head will leave remnant magnetism in the rope. This 

 remnant magnetism decreases somewhat with time and work- 

 ing of the rope in use. The presence of remnant mag- 

 netism in the rope causes a shift in the LMA zero as a 

 result of a redistribution of the magnetic flux from the 

 auxiliary field outside the sensing head to the field 

 inside the sensing head. 



The effect of the presence of remnant magnetism on the 

 LMA readings can compromise the readings of the LMA 

 channel if not properly accounted for. 



In Fig. 4.12 the sensor head and its associated magnetic 

 fields are shown for a rope with no remnant magnetism in 

 it. (There may be small amounts* of remnant magnetism in 

 the cable due to the earth's magnetic field but these will 

 be insignificant) . 



A-36 



