711 
-Se 
Gay) Recording of gauge signals. The signal from the master control 
panel was fed directly into the vertical amplifiers of the cathode-ray os-— 
cilloscope, The trace of this signal on the Y-axis of the cathode-ray tube 
was recorded cither by a rotating-drum camera or a still~film camera, In 
the former case no signal was uscd on the X-axis, while in the latter case 
a linear sweep was introduccd in the X-axis, For cach record a time cali- 
bration must calibrate the drum or sweep speed, and a voltage (V=step) or 
charge (Q-step) calibration must be put on the film to calibrate the elcc= 
trical and photographic amplification of the trace. If a voltage step is 
used for this, the capacitance of the cable and gauge system must be mea— 
sured separately on a capacitance bridge, while if a charge calibration is 
used independent determinations of the capacitance and voltage are unnec= 
essarye 
(iv) Interpretation of records. The photographic records so obtzined 
were analysed by transforming thein into absolute units of pressure and time 
from comparison with the V— or Q-step and the time calibration, This was 
formerly done by measuring the records on a movable=stage micrometer micro= 
scope, but more recently the pressure-time curves have been projected on 
photographic paper simultancously with a two-dimensional grid which has 
been adjusted for the X-axis to read in absolute time units and for the Y- 
axis to read absolute pressure units, according to the time and voltage 
calibrations (see Fig. 1). After the pressure-time curves have been trans— 
formed into their absolute units, the peak pressure may be read off directly 
and the impulse and energy factor may be integrated graphically. The energy 
factor obtained by this simple graphical integration does not include the 
after-flow energy, which is important for spherical shock waves. Other 
pertinent data which are apparent on the pressurc—time curves may also be 
noted at this time. 
(b) Mechanical=gauge instrumentation. — (i) The UERL diaphragm gauge 
The gauge that has proved itsclf to be the most reproducible for all routine 
measurements of explesive cffectiveness has been the UERL diaphragm gauge 
[5]. This gauge consists essentially of a stecl pot 3=1/2 in, in diameter 
on the face of which is mounted a thin diaphragm, The diaphragm materials 
and thicknesses vary, but for large-scale measurements lh-gauge (B and S) 
steel was generally uscd. lExplosives were compared by taking ratios of the 
maximum deflections of the diaphragms after being subjectcd to the explosive 
shock wave. For large charges these diaphragm gauges read a quantity that 
corresponds tc peak pressure, although the finite time of gauge action is 
longer than for the ball-crusher or Modugno gauges. The gauges were mounted 
in pairs, sometimes in a heavy gauge block and other times in a very light 
gauge block. 
(Gem) The Naval Ordnance Laboratory ball-crusher gauge. The Naval 
Ordnance Laboratory ball-crusher gauge [6] was uscd in vory large numbers 
because of its operational simplicity and small sizc. A 1/2~in. diameter 
piston rests directly on a copper sphere which is supported by an anvil. 
When the piston is struck by the explosive shock, the copper sphere is de= 
formed, the amount of deformation being a measure of the explosive effective- 
nesSe The spheres used for most work were 3/8 in. in diameter, although 
the gauge was so designed that 5/32—in, diameter spnores could also be uscde 
