BRIDGE 



Z9QT D K E7 > 



Figure 22-2. Block diagram of induction logging system. K 

 J = electrical conductivity. 



magnetic susceptibility. 



For high-detail observations, a special contact-type probe is used in which 

 the sensing coil is 3 inches long. The coil is kept in contact with the side of the 

 hole by a bow-spring arrangement. This tool is referred to as a "Minimag" 

 since it is a miniature magnetic tool. 



Susceptibility probes of this type have a resolution of approximately 

 1 x 10 ~ 6 centimeter-gram-per-second (cgs) unit. 



TOTAL FIELD LOGGING An adaptation of the flux-gate-type total-field 



airborne detectors has been made into a bore- 

 hole probe. The sensing element is a saturable core magnetometer. It must be 

 aligned in the direction of the total field by two aligning magnetometer elements 

 at right angles to one another and in a plane perpendicular to the measuring 

 element. The aligning elements operate a servo control to keep the measuring 

 element in the direction of the total field. A simplified block diagram of the 

 system is shown in Figure 22-3. The aligning coils are marked A and T, while 

 the measuring coil is H. The borehole probe contains only the sensing elements, 

 the servo drive motors, and the gimbal-supported table for the sensing elements. 

 The electronics required to operate the tool is located at the surface. This tool 

 has a resolution of approximately ± 1 gamma. 



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