Table 6 shows the results of the reliability tests. No failures in over 107 hours of 

 operation were observed, demonstrating a reliability greater than 90 percent with 90 percent 

 confidence for a MTBF of 42 hours. The test was interrupted only once a day for replacement 

 of batteries. 



Two items requiring minor modification were identified during these tests: the sensitivity 

 switch and the low battery indicator system. The sensitivity switch is a "break before make" 

 type diat sometimes turns the output volume off when changing sensitivity levels. Since this 

 does not affect completion of the mission (the operator simply readjusts the volume), this item 

 was not categorized as a failure. However, a more suitable switch will be used on the 

 preproduction models. 



The low battery indicator system monitors the battery voltage and provides early warning 

 to the operator when the battery is getting low. During the initial part of these tests, the indicator 

 system was only providing about 2 to 3 minutes warning before the system would quit working. 



Table 6. Reliability Summary 



Incident 



Test Hours 

 Completed 



Description 



1 



11.2 



Volume level sometimes affected by changing sensitivity levels. 



2 



20.6 



Battery voltage low. Low battery indicator not yet lit. Battery 

 test functioning and shows a low battery condition. 



3 



20.6 



New batteries installed. 



4 



64.5 



Battery voltage low. Low battery indicator not yet lit. 



5 



64.5 



New batteries installed. Battery life was 43.9 hours. Note: No 

 audio output was generated during this period of battery use. 



6 



105.1 



Battery voltage low. 



7 



107.5 



New batteries installed. Battery life was 43.0 hours. Note: No 

 audio output was generated during this period of battery use. 



8 



107.5 



Reliability testing completed. 



This problem was corrected during the testing by changing a resistor value in the low battery 

 circuit. About 30 minutes of operation is available after the low battery indicator light comes 

 on. 



Operational Effectiveness 



To determine the operational effectiveness of the BP&CL, both laboratory and ocean tests 

 were conducted. The objective of the laboratory tests was to establish detection thresholds for 

 the BP&CL. The effects of sand on the detection distance of buried objects were also 



20 



