The signal is subsequently amplified by LF GAIN to a 

 level dependant on rope condition, for optimum fault 

 measurement. A band of COMPRESSION (+) may be selected 

 within which the signal is attenuated by a factor of 10 

 (eg. background noise). If "o" is selected the signal 

 is unaltered. After this stage the LF signal is made 

 available to the TAPE RECORDING circuitry, the LF 

 panel METER and the CHART RECORDER. 



5.1.2 FM 



The LMA and LF data can be recorded on magnetic tape for 

 future processing or playback. The FM section consists 

 of voltage to frequency converters for the LF and LMA 

 These converters produce frequencies above and below 

 their centre frequency of 3KHz in proportion to the 

 signal inputs. A third converter produces one of two 

 frequencies to correspond to its digital or 1 input 

 This Frequency Shift Keying (FSK) is used to code the* 

 Yard or meter marks from the Digital Section. 



These signals are recorded at a fixed amplitude on tape 

 and upon playback are decoded and reconstructed by two 

 frequency to voltage converters and a Phase Locked Loop 

 FSK demodulator. 



A digital panel indicator allows approximate relocation 

 of any point on a recorded cassette by counting in res- 

 ponse to spindle rotation. 



5.1.3 Digital/Sensor Head 



The tachometer located in the rope guide roller on the 

 Sensor Head, with a fixed rotation to length ratio pro- 

 duces two square waves with a + or - 90o phase relation- 

 ship. The signals are transmitted up the cable to the 

 Control Electronics. The Digital section sharpens these 

 pulse trains and decodes their phase relationship to in- 

 dicate one direction of travel or the other. These 

 pulses are counted and a mark for each yard or meter of 

 rope travel is produced. The polarity of the mark is 

 determined by the rope direction. 



These marks, whether in real time or decoded from taped 

 data are delivered to an event marker in the Chart 

 Recorder and are also counted to generate a combined 

 50 and 100 mark indicator which is fed to a second event 

 marker in the Chart Recorder. 



A-45 



