BORE-HOLE INVESTIGATIONS 



1071 



The sonde is a system of electrodes, mounted on an insulating mandrel, which is 

 lowered into the hole on the end of the cable, to which it is connected by means of a 

 threaded sleeve. The cable passes over a sheave located at the surface above the bore 

 hole. In order to raise or lower the sonde in the hole, the cable is wound or unwound 

 on a reel, set permanently on the truck and driven by a power take-off from the engine 

 of the truck. The various electrodes of the sonde are connected by means of insulated 

 conductors in the cable, through a slip-ring collector on the reel, to the appropriate 

 terminals of the recording instruments. 



Fig. 667. — Control panels and recording camera for electrical 

 logging of oil wells. (Courtesy of Schlumberger Oil Well Survey- 

 ing Company.) 



In the recorder a photographic film is exposed by narrow beams of light, reflected 

 frotn each galvanometer mirror. The deflection of each beam of the film is propor- 

 tional to the potential difference being recorded by that galvanometer. The circuits 

 are adjusted so that suitable sensitivity scales for the S.P. and apparent resistivities 

 are obtained. Figure 667 is a view of the control panels and recording camera. 



The film in the recorder moves in synchronism with the movement of the sonde 

 along the hole, so that the effect of each light beam is to trace on the film a curve. 



