738 
V. DETAILS OF GEAR 
13. Gauge mounts 
The manner in which the mechanical gauges and the piczoelectric gauges 
were mounted was found to have an important bearing upon the results, both 
with respect to the absolute level and the reproducibility, The very early 
work was done with the gauges hanging on free suspension from various cables, 
This manner of mourfting was abandoned soon, however, because of the large 
scatter in results from shots fired under identical conditions, From then 
on the work was done with the gauges rigidly mounted in blocks. 
(a) large composite gauge blocks, -- The first gauge block successfully 
used and the one used most generally was the large composite gauge block 
holding two UERI-diaphragm gaugés, two NOL crusher gauges and two Modugno 
gauges (Fig. 3B,2)). It will be noted that the ball-crusher gauges were 
mounted with their faces flush with the face of the block, The lModugno 
gauges were screwed into the block so that the face of the gauge plate was 
roughly 1 in. in front of the face of the block. The diaphragm gauges were 
mounted in the lower half of the block so that their face plates were flush 
with the block. The overall dimensions of the block were 1): x 1) x ) in., 
and fastened to the bottom of the block was a piece of )-in, channel iron 
) £t long which attached to the spacer cable in such manner that the face 
of the gauge block was always perpendicular to the line of propagation of 
the shock wave. The block was suspended by a chain bridle from the back 
plate of the block so that it was fairly well balanced when hanging freely. 
The first blocks made weighed over 250 1b with all the gauges in place. 
Later on these were lightened so that they weighed from 195 to 200 1b with 
all gauges in place. No difference could be found in either absolute level 
or reproducibility of results as a result of this lightening of the blocks, 
Since the effective diameter of a baffle is the distance from the center of 
a gauge to the nearest edge, the UERI-diaphragm gauges were not baffled any 
more in these blocks than they were when suspended individually. However, 
the centers of the Modugno gauges were 3-1/2 in, from the edge of the block 
which gave them a greater baffle than they would ordinarily have hac. The 
exact effect of this baffle on the Modugno gauges was complicated by the 
fact that the gauge plates were 1 in. in front of the face of the block 
proper, so that the baffling was not effective until 30 to 35,.sec after 
the shock wave had struck the lModugno gauge plate, The distance from the 
center of the ball—crusher gauges to the nearest cdge of the block was 2 in. 
so that the effective baffle of these gauges had a 2-in,. radius. 
(i) Effect of baffling on ball~crusher gauges in the composite blocks. 
To study the effect of the baffling of the ball-crusher gauges in these com- 
posite blocks, a pair of ball-crusher gauges were mounted on l—in. brass 
rods in the Modugno-gauge hole in the block. The faces of the crusher gauges 
were 8—1/) in. in front of the face of the block itself, This prevented the 
wave reflected from the face of the block from striking the gauges until 
about 270y: see after the shock wave had struck the gauges. As the ball- 
crusher gauge action for large charges is completed in from 150 to 200, sec, 
these gauges were effectively unbaffled, After correcting for the difference 
E32 
