Table 3. Metal Detecting Systems Testing Summary 



Item 



SCUBA 

 Tank (Twin 



72) 



Laboratory 



Tests 



Ocean Tests 



SCUBA 



Tanks 



(Twin 



72) 



Chain 



(1-1/2 

 Inch) 



Armored 



Cable (3- 



1/2-Inch 



Diam) 



Anchor 

 (6,000 

 Pounds) 



Armored 



Pipeline 



(5-Inch- 



Diam) 



TEMP 

 Threshold 



None 



None 



6ft 



3ft 



10 ft 



2-1/2 ft 



Garrett 

 XL500 



5.1 ft 



4.0 ft 



<4ft 



1.5 ft 



Not 

 Tested 



Not 

 Tested 



Fisher 

 Pulse 8 



5.7 ft 



Not 

 Found 



Not Found 



Not Found 



Not 

 Tested 



Not 

 Tested 



White's 

 PI-1000 



3.3 ft 



<3 ft 



<4 ft 



Not 

 Detected 



Not 

 Tested 



Not 

 Tested 



Forster 

 Ferex 



Not Tested 



Not 

 Tested 



5ft 



3ft 



Not 

 Tested 



Not 

 Tested 



2. The Forster Ferex unit has the greatest detection range among the systems tested. 

 As shown in Table 3, the Ferex unit met the TEMP threshold for detection of armored cable and 

 was within 1 foot of meeting the TEMP threshold for detection of chain. These tests were con- 

 ducted with the unit set at a sensitivity of 300 gamma. While the unit does have a greater 

 sensitivity (and presumably a greater detection distance), it was difficult to use at a higher 

 sensitivity for the following reasons: 



a. The diver's gear became a significant magnetic target. To reduce this 

 effect will require either nonmagnetic equipment for the diver or a standoff device (about 5 to 

 7 feet) between the probe and the diver. 



b. Periodic adjustment (zeroing) is required and the diver does not have direct 

 access to the control instrumentation with the present configuration of the unit. Since the control 

 instrumentation is not waterproof, all tuning adjustments (such as selecting the operating mode 

 (mode 1, 2, or 3) and the sensitivity, as well as periodic compensation for background noise) 

 must be done at the surface by a remote operator rather than at the dive site by the diver. This 

 operating scenario can easily result in confusion (particularily at the higher sensitivity levels) 

 unless the diver and top-side operator know exactly what the other person is doing. 



c. Use of an earphone as the sole means to provide detection signals to the 

 diver is inadequate. Although the diver earphone provides a good general indication of target 

 strength, it does not adequately provide specific location information. This is because the tone 



14 



