2. Compensation Switch - The compensation switch is used to "zero" the instrument 

 in operating modes 1 and 2. This feature compensates for magnetic noise at a search site by 

 resetting the output to read zero. 



3. Test Switch - The test switch is used to check for prof)er operation of the system. 



4. Sensitivity Selector Switch - The sensitivity switch is used to select one of eight 

 sensitivity levels between 0.3 to 1,000 gammas. 



5. Volume Switch - The volume control switch regulates the output level of the 

 audible signal. 



Modifications to the existing system consisted of reconfiguring the tool for use in both 

 the dipped mode (from an inflatable boat) and a diver-held mode. The modifications included 

 new, waterproof housings for the control electronics and batteries, a telescoping standoff device 

 (to maintain distance between the diver's gear and the sensing probe), and a cable reel for using 

 the probe in the dipped mode. Figure 10 shows the EDM BP&CL. 



Reliability Tests 



Reliability is expressed as the probability that the BP&CL will perform its functions 

 without failure within performance characteristics for a 4-hour mission. The threshold reliability 

 specified for this tool by the TEMP is 90 percent. 



The mean time between failure (MTBF) is an estimate of the true system reliability based 

 on the mission time and threshold reliability. To assure that the test duration will verify the 

 system reliability, a confidence level multiplier is applied to the MTBF estimate. Table 5 

 summarizes the required test durations for confidence levels of 60, 80, and 90 percent. The 

 number of failures recorded within the test period determines the confidence level achieved at 

 90 percent reliability. Based on this information, a 98-hour test period with no failures is 

 required to demonstrate a 90 percent reliability with 90 percent confidence for a MTBF of 42 

 hours. 



Table 5. Reliability Test Time Required 



MTBF (hours) 



Confidence 

 Level (%) 



Test Time (hours) 



Failures 



1 Failure 



2 Failures 



42.4 

 42.4 

 42.4 



60 

 80 

 90 



38 

 70 



97 



85 

 130 

 160 



130 

 180 

 220 



18 



