m 



MEASUREMENT OF PRESSURES 



merits. Gauges of this type should, however, be very useful if sub- 

 jected only to low pressures or short durations of high pressure or if 

 short life is not important. 



D. Performance of piezoelectric gauges. Although the piezoelectric 

 gauges which have been developed and used for underwater explosion 

 pressure measurements are by no means foolproof or free of objection- 

 able errors and difficulties in use, they are perhaps the most versatile 

 single tool yet employed, and when properly used are capable of giving 



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CRYSTALS- 



SPLIT 



LUCITE 



HOLDER 



LEADS 



22SZ2222SZ 



w. 



h 



7^1 



w. 



J 



SIDE FACE 



Fig. 5.12 Construction of gauge with Rochelle salt or ADP crystals. 



very satisfactory quantitative results in a variety of applications. The 

 pressure levels which have been measured with at least apparent reli- 

 ability range from less than 100 to more than 30,000 Ib./in.^. Small 

 34 inch Type B gauges have withstood pressures of the order of 90,000 

 lb./in.2 (3 inches from the center of a 3^ pound charge), failure under 

 these conditions resulting from destruction of the copper tubing con- 

 necting cable rather than shattering of the crystal. Not all gauges will 

 last for a large number of explosions at high pressures, but shock wave 

 pressures up to at least 20,000 Ib./in.^ from several hundred pounds of 

 explosive can be practically measured as a routine matter. Tourmaline 

 gauges of various sizes have been used to investigate secondary or bubble 

 pulses of charges ranging from 3^ pound or less to 300 pounds in weight, 

 and a variety of gauges have been used for providing synchronizing sig- 

 nals and measuring time intervals in underwater sound ranging. The 

 tourmaline gauges used for shock wave measurements of service weapons 



