Chap. 9] 



SEISMIC METHODS 



597 



is not considered. Fig. 9-105 shows the response curve of various com- 

 mercial reluctance detectors and one inductive detector in terms of voltage 

 developed on the first amplifier grids for ground motions of l/x amplitude. 



100 millivolts 

 per micron 



-0- 



I 



Frt^uenct/ 



20 



40 



60 



80 



Fig. 9-105. Voltage at grid of first amplifier tube in millivolts per micron ground 

 motion (through impedance matching transformer) of some commercial reflection 

 detectors. R, reluctance detectors; h, inductive detector, oil damped; le inductive 

 detector, electromagnetically damped. 



The difference in the response curves N and S is due to the fact that S 

 is adjusted to a low and iV to a high natural frequency. 



2. Amplifier. A specific solution for the response of an ampHfier is 

 difl&cult to give because of the complexity and variety of the individual 

 circuits employed. As a rule, detector and galvanometer are coupled to 



