593 
23 
Laboratory at Woods Hole, in connection 
Coble 
with the use of larger charges. These 
experiments differed from the earlier To 
Amplifier 
Charge 
ones mainly in two respects: charges 
of 250 grams of tetryl were exploded 
instead of detonators, and each of the 
cables tested was part of a complete 
piezoelectric gage assembly. The crys- Figure 11 - Positions of Cable and 
Crystal Relative to Charge 
tal signal was delayed so as to sepa- in the tuple 
rate it from the initial part of the 
cable signal. This was done by bending 
the eable into the shape of an isosceles triangle with the crystal at its ver- 
tex 30 inches from the base; see Figure 11. The charge was placed at the same 
distance on the other side of the base. Hence the pressure pulse struck the 
cable about half a millisecond before reaching the crystal. 
Cable signals obtained simultaneously from a Belden Series 84.00 
rubber-sheathed cable and from a TMB cable are shown in Figures 12 and 13. 
In these pictures the time sweep proceeds from left to right; thus the first 
disturbance at the left is that due to the cable. The steep signal which 
follows is produced by the crystal,* and the peculiar appearance of the sub- 
sequent portion of the curve was probably caused by the output of the crystal 
overloading the amplifier. Pairs of such records from ten explosions were 
obtained. These show a steady change in the condition of the rubber cable as 
Pressure Wave Strikes Cable 
Pressure Wave Strikes Cable 
21.6 millivolts f eee 
NEF ss Wave Strikes Crystal 
Figure 12 - Voltage Signal Produced Figure 13 - Voltage Signal Produced 
Nery 3 
‘2.1 millivolts : 
Pressure Wave Strikes Crystu! 
by a Rubber Cable Subjected to an by a TMB Cable Subjected to an 
Underwater Explosion of Underwater Explosion of 
250 Grams of Tetryl 250 Grams of Tetryl 
* The amplifier gain-required to produce a sizeable cable signal was much too high for the crystal signal. 
