Appendix E
GROUND SURFACE ACCELERATION
MEASUREMENTS
-E.1] INTRODUCTION
_
During the past year the Explosion Kinetics Branch of BRL has
‘undertaken the problem of developing and proving the feasibility of a
"- self-contained, self-recording scratch type accelerometer.
.
After considering several methods of approach it was decided to
modify;the Engineering Research Associates (FRA) elements already on
hand. _Actually the only components of the ERA elements that were
retained: were the springs.
Essentially the prototype PRL accelerometers
were constructed somewhat like the original ERA elements, save the
modifications, heeded to convert the elements to a self-recording type.
E.2
TNSURUAENTATION
. E.2.l1
Elements
The new acedterometer elements have a mounting post, an FRA
spring, a mass at the gadpt the spring, a stylus spring with stylus
attached to the end of fhe ~nss and a damping plate.
Figure C,12
shows the complete ..:.
y or both the standard gage and the drum
gage elements.
The ':-+', ari:tcal members of the elements are the ERA
springs and the weights ‘of te masses.
A frictional damping between
the stylus and recording disc as used rather than a viscous fluid
damping.
vl
E.2.2 _vounting of Elements
The elements that were nounted-in the P_
gages were oriented in
a vertical and horizontal plane so ithat vertical and horizontal
acceleration could both be recorded on thé} same disc as the pressure
versus time record.
This mounting systen s shown in Figure C.18. The
drum gage had only one element which neagured vertical accelerations.
The gage and mounting post_are shown in Rigure|Cc.1
E.5
E.3.1
CALIBRATION OF ACCELEROMETER ELEMENTS
Static Calibration
The protctype accelerometer elements were calitb
ited at the Naval
Ordnance Laboratories (NOL) facility at White Oak, Maryland. A low
speed centrifuge was used to make static calibrations. “The centrifuge
is known as the "NOL Centrifuge (Low speed) XL-1A",
78
A mounting device