4.5.3 Use of the Compression Band Switch 



The compression band switch controls the amplification 

 of the LF signal in a manner that will reduce signals 

 with an amplitude below a certain number of divisions 

 on the chart but will leave the gain unchanged for 

 signals over this number. As an example, a setting of 

 4 on the Compression Band Switch will reduce signals of 

 + 4 small chart divisions by a factor of 10 but will 

 leave signals above + 4 divisions with their original 

 gain. This feature is used to accentuate the higher 

 amplitude LF signals . Caution is required in the use 

 of the compression control and it should only be used 

 when familiar with the instrument and the rope under 

 test. The compression control works only in the 

 'Record' mode and the 'compressed' LF signal will be 

 recorded on the tape. If uncertainty exists on what 

 compression setting will be most valuable for a parti- 

 cular rope the compression switch should be left at 

 zero as LF signals which are of interest but which 

 have been 'compressed' are not retrievable from the 

 tape recording of the rope. 



4.5.4 Use of Proportional Drive Chart Control 



The chart can be advanced proportionally with rope 

 speed during a test or tape replay. To do this select 

 a proportional drive setting on the Chart Recorder 

 Section and depress the 50mm/sec . chart speed button. 

 The chart will advance and 'sync' itself to the rope 

 speed . 



The proportional drive requires a few yards (meters) to 

 lock into the rope speed and initial rope speeds will 

 not be accurately represented. 



4.5.5 Distance Markers on Chart Recorder 



There are 2 event markers on the chart recorder which 

 indicate distance travelled along the rope. The lower 

 event markers (on the side of the LF trace) marks every 

 yard or meter. The upper event marker (on the side of 

 the LMA trace) marks every 50 and 100 yards or meters . 

 The 50 y/m marks are short pulses and the 100 y/m 

 marks are long pulses. The 50 and 100 y/m marks will 

 only be indicated when the rope measured length counter 

 is counting up. The y/m marks have 2 polarities as 

 shown in Fig. 4.11. 



A-34 



