The Forster Ferex 4.021 consists of two fluxgate magnetometers mounted in tlie opposite 

 ends of a probing bar. This unit is available in both land and underwater versions. The 

 underwater version, shown in Figure 5, is designed for use in bore-hole applications. The 

 system consists of a 24-inch-long submersible probe, extension cable, power supply, and a 

 control/signal strength indicator unit. The power and control units are not waterproof. Control 

 features include the following: 



1. Sensitivity Dial - The sensitivity of the unit is adjustable between 3 gammas and 

 10,000 gammas. 



2. Operating Mode Switch - The operating mode switch provides selection of one of 

 the following: 



a. Normal searching. 



b. Normal searching with some small ferrous metals damped out. 



c. Special searching for searching next to large ferrous metal objects such as 

 pipes. 



d. Compass to find north, south, east, and west. 



3. Sensitivity Test Switch - A momentary contact switch for checking proper 

 operation. 



4. Battery Check - Located at the first position of the sensitivity dial. 



5. Volume Control - Two momentary contact switches (up and down) for adjusting 

 the audio output of the probe. 



Laboratory Tests 



The objective of the laboratory tests was to provide initial performance data on the 

 candidate metal detecting systems. Three sets of laboratory tests were performed: (1) comparison 

 of physical characteristics, (2) sphere of detection tests, and (3) electronic characteristics analysis. 

 The results of these tests are summarized below. 



Comparison of Physical Characteristics. The physical characteristics of each unit were 

 examined for general construction, human factors engineering, and maintenance. Table 1 lists 

 test results of the items measured or evaluated. Appendix B contains a discussion of qualitative 

 results. 



