5.0 MAINTENANCE AND TROUBLE SHOOTING 



The purpose of this section is to provide: an under- 

 Standing of the operation of the circuitry at a "block" 

 level; a schedule for regular maintenance to ensure 

 serviceability of the equipment for many years to come; 

 and a means of identifying faulty blocks, should a 

 problem arise. 



5 .1 Block Description 



The "FUNCTIONAL BLOCK DIAGRAM" of Fig. 5-1 shows the 

 major divisions in the signal conditioning circuit 

 paths; Sensor Head, Analogue , FM , Digital 

 and Chart Recorder. 



5.1.1 Analogue/Sensor Head 



The analogue signals, LMA (proportional to cross- 

 sectional area of the rope) and LF (indicative of 

 irregularities in the tope) are derived in the SENSOR 

 HEAD by 8 LMA HALL SENSORS and 4 LF HALL SENSORS. These 

 sensors are excited by DC constant current supplies in the 

 ANALOGUE section of the Control Electronics. The signals 

 are summed, temperature corrected and amplified by two 

 preamplifier boards, one in each half of the SENSOR HEAD, 

 and transmitted up the cable to the Control Electronics . 



The LMA signal is summed with LMA ZERO which cancels the 

 1007o rope proportional signal and amplified by means of 

 LMA GAIN to normalize signal changes that they may be 

 expressed in percentage change. This normalized signal 

 is smoothed by a Low Pass Filter and made available to 

 the TAPE RECORDING circuitry, LMA panel METER, and 

 through additional LPF to the CHART RECORDER. At this 

 point the capability of inserting a fixed 7o OFFSET is 

 offered so that large area changes, up to 257o, may be 

 offset on the chart thus allowing use of optimum sensi- 

 tivity . 



The LF signal is summed with LF ZERO to eliminate any DC 

 levels due to additive DC field components, then Low 

 Pass Filtered to eliminate high frequency transients. 

 (Note: LF ZERO is disabled in the DYNAMIC MODE of 

 operation) . 



A-44 



