809 
td Bes 
rise for all these records is 8 microseconds and the oscillations exhibit 
twice the frequency registered by the 1" gauges Bare and spherical charges 
again show smoother contours for the tails of the pressure time pulses than 
the standard charges in containers, 
(c) The two-ply 3" gauge. 
The construction of this gauge is described in Appendix 2. It 
consists of two crystals 1/16" thick, the central silver foil electrode 
being connected to the central cores of the cable and the outer silver 
sintered faces being connected to the cable braid. Apart from the 
special rubberoid wax at the base of the gauge to remove all possibilities 
of trapping air cavities, the only insulation is a film of cured natural 
latex surrounding the gauge and blended into the rubber covering of the 
cable itself. 
(a) Results with the two-ply 3" gauge. 
Three face-on pressure-time signatures are shown on Plate 13, 
Records 1, 2 and 3. These were obtained with the standard 14 1b. T.N.T. 
charge, the bare 1+ 1b. T.N.T. oharge and the 14. oz. P.E. spherical charge 
(without primer) respectively. 
In the case of the spherical charge, the smoothing effeot on the 
tail of the signature is particularly noticeable. The overshoot and sharp 
times of rise are again predominant features for the face-on records of all 
three charges. 
Further pressure-time pulses are shown on Plate 13, Reoords 4, 5 
and Records 6, 7. In the case of Records 4 and 5, the faces of the crystals 
were parallel to the water surface, the gauge being turned through 180° 
for the second record. Similarly for Records 6 and 7, the faces of the 
crystals were perpendicular to the water surface, the gauge in the latter 
case being also turned through 180°. In Records 4, 5, 6 and 7, the cable 
of course was led away from the onset direction of the pressure front, the 
charge in all of these four records being a ii 1b. T.N.T. bare charge. 
For these edge-on records, the time of rise is 8 microseconds, and the 
natural oscillation frequencies of the crystals are clearly discernible. 
DISCUSSION OF RESULTS AND CONCLUSIONS. 
The constructional details of the three types of plezo-electric 
gauges developod at this Establishment have been described elsewhere. One 
of the objects in producing the medium type was to adhere to the principle 
of using the seme type of construction and of gauge insulation (paraffin 
Wax-vaseline mixture) as that for the well-tried large type of gauge. In 
fact only one short series of shots was fired against the medium type of 
construction, and the gauge itself was simply the original two-ply miniature 
type 4" in diameter with thick steel outer electrodes 1/16" thick surrounded 
by a brass case and having wax-vaseline insulation. e pressure-time 
signaturesrecorded with the medium type of gauge were not satisfactory. 
This is partly duc to the clectrodes, as can be seen from this present 
report, partly due to oscillations set up by the brass case, and partly due 
to the type of insulation. 
This report deals with the constructional modifications made to the 
miniature gauge from that given(1) in Appendix 2; the finalised design 
evolved as a result of a large number of tests. 
The cable developed at this Establishment(1) has been used throughout 
these tests. The ratio cable signal/gauge signal has been proved to be a 
negligible quantity even in the case of the miniature gauge. 
The telcothene and rubber tape formerly used in insulating the gauge 
into a robust unit has been abandoned, and the final design has simply a 
coating of cured natural latex. 
The air eeeose 
