602 » 
32 
amplifier have? The duration of the pressure from an ounce of tetryl is ap- 
proximately 35 microseconds. Thus 
T = 35 
Ro=0.97 = xX~ 
Then 
1 to 
x 4 1 10 va T 
ty = tr = 0.2 microsecond 
This imposes a severe requirement upon the amplifier, as can be 
seen from the following example. Suppose that the frequency response of an 
available amplifier falls off by 8 per cent at 300 kilocycles. It then has a 
time of rise equal to 3/4 microsecond, a time too large to give the desired 
accuracy for an explosion of an ounce of tetryl. 
It may be asked, what is the smallest charge for which the cited 
amplifier will record 97 per cent of the peak pressure? The duration of the 
pressure varies as the cube root of the mass of the charge. Therefore, the 
desired value of weight Wof the charge may be obtained if the required dura- 
tion is known. In this case 
RK, = 0.97 
ty = 0.75 
1 t 
ET o Ser 
Therefore 
T = 0.75 x 170 = 127 microseconds 
Comparing this time with the duration of an explosion of one ounce of tetryl, 
we have 
W. (*22)° = 47.8 ounces of tetryl 
Therefore the required charge is 3 pounds or more of tetryl. 
If valid measurements are to be made it is necessary to take such 
precautions as working with relatively large charges or using very high fi- 
delity amplifiers and cables which are not too long. 
THE TMB RECORDING CHANNEL 
The Taylor Model Basin recording channel consists of a series of 
units as indicated by the block diagram in Figure 20. The amplifier was de- 
signed by members of the staff and responds to frequencies up to 300 
