760 



ELECTRICAL METHODS 



[Chap. 10 



network is synchronized by the received transient itself. Fig. 10-86& 

 shows an arrangement developed by West/* in which the primary impulses 

 of 50-cycle frequenc}^ and rectangular wave form are supplied by a thy- 

 ratron relaxation oscillator controlled by a tuning fork. In the figure the 

 synchronization of a reference signal by this oscillator is indicated; the 

 reference lead may be dispensed with by synchronizing a local oscillator 

 with the transient of the potential circuit. 



In still another Eltran method, the technique is based on the assumption 

 that the ground circuit has capacitive reactance in addition to resistance. 

 The transient potential feeds two parallel circuits. One portion is ampli- 

 fied to actuate the sweep while the other is mixed in a double triode with 

 the reference signal, after it has passed through an adjustable network. 



tooo' 



wMk^.'^ ' *;j^vw^A'vsyw<k ' s^"VAVvvv-^/'/'>'< ' ^/^y^^ 



SOui 

 T/iyrafron 

 Relaxation 

 Oscillator 



woo' 



hJ- 



1000'- 



FiG. 10-866. Arrangement for comparison of transients with simulating 

 network (after West). 



From the mixer the signal goes through an amplifier and thence to the 

 vertical plates of a cathode-ray oscillograph. Time constants of transients 

 are then expressed in terms of the value of the variable element in the 

 compensating network required for balance (probably RC) and maps are 

 contoured in units of reciprocal time constants. Fig. 10-87 shows such 

 contours for the Sandy Point oil field in Brazoria County, Texas. The 

 productive area coincides with contours of high reciprocal time constants. 

 Recent developments in mixing, synchronizing and simulating circuits 

 have been discussed by Klipsch." In the mixing of the reference signal 

 with the received impulse, a bridge circuit has been found advantageous. 

 The potential transient and the reference signal produced by an oscillator 



•'^ S. S. West, Geophysics, 111(4), 306-314 (Oct., 1938). 

 " P. W. Klipsch, Geophysics, IV(4), 283-291 (Oct., 1939). 



