METAL 

 DETECTOR 



Figure 6 

 Setup for testing the range of pulse-induced systems. 



From the results of these tests, it is clear (in air at least) that larger detection distances can be 

 expected with the Forster Ferex unit. 



Electronic Characteristics Analysis. The electronic characteristics of the pulse-induced 

 systems were analyzed in order to obtain a baseline comparison of common features. Several 

 of the characteristics examined include pulse width, response time, energy per pulse, and battery 

 life. Figure 8 shows a general block diagram for pulse-induced metal detecting systems. Table 

 2 summarizes the test results. In comparing these results with the results of the detection 

 threshold tests, the units with the larger signal output have the greater detection range. They also 

 have the shortest battery life. Also, the response time of the different units should be noted. 

 In comparison to the other units, the Fisher Pulse 8 has a very long resf)onse time. The long 

 response time is undesirable since the unit can easily miss a target unless the coil is moved very 

 slowly. 



Ocean Tests 



In January and February 1986, ocean tests of the four candidate metal detection systems 

 were conducted offshore of the West Jetty at the Naval Construction Battalion Center, Port 

 Hueneme, California. These tests were conducted to determine the detection capability of each 

 unit for buried chain (1-1/2 inch) and buried armored cable (3-1/2-inch diameter). No tests were 

 planned at this time for detection of an anchor (6,000 pounds) buried to 10 feet and armored 

 pipeline (5-inch diameter) buried to 2-1/2 feet. 



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