799 
PIEZO-ELECTRIC GAUGES - DEVELOPMENT OF THE 
MINIATURE TYPE 
A. H. Bebb, D. R. J. Wallace and D. W. Taylor 
Naval Construction Research Establishment 
May 1947 
” * ¥ * * * * * 
SUMMARY 
The development and experimental tests carried out with miniature 
tourmaline piezo-electric gauges involving different modes of construction 
are described in this report. 
The effeot of different thicknesses of clectrodes, either cemented 
or sintered at high temperature to the crystal faces, of electrodes made 
from various materials, of many forms of insulation suoh as tcelcothenc, 
rubbor tape, paraffin wax-vaseline, rubberoid wax, oured natural latex and 
combinations of these insulators are described in some detail. Plates are 
included to illustrate the results obtained from the many constructional 
changes carricd out. 
To evolve a rcliable gauge, the shots fired at it in various stages 
of progress consisted mainly of standard 14 1b. T.N.T. blocks in standard 
canisters. Bare 14 1b. T.N.T. charges as well as sphcrical P.E. charges 
have also beon utilised. 
It is believed that the design of the gauge is now completely 
satisfactory for recording pressure-time pulses resulting from underwater 
explosions, and work to this end in open water is now proceeding. The 
effects of the presence of targets, water-backcd and air-backed, in the 
neighbourhood of the explosive oharges, will also be studied in the near 
future. It is intended to use the miniature gauge close to explosive 
charges. 
INTRODUOTION. 
Descriptions have previously been given of the three types of piezo- 
elcotric gauges developed at this Zstablishment for the mcasurenent of 
underwater explosion pressurcs, and also of a special wide-range amplifier 
for use with the gaugcs. At that time, no shots had been fired against 
the tvo small types of gauges, and whilst it had been proved that both were 
mechanically robust, it remained uncertain whether firing under controlled 
conditions would reveal certain improvements in design. Under static 
conditions of calibration, all three gauges had exhibited similar pressure- 
time rccords. In order to avoid a re-design of calibration pressure 
apparatus for the small gauges, the original was modified by fitting a solid 
brass cylinder up to the level of the non-return valve connecting the 
reinforced rubber hose from the pump to the pressure cylinder, and a new 
lid was constructed which enabled the gauge to be inserted into the steel 
cylinder without resort to the laborious method of threading the gauge and 
its long length of attached special Signal-free cable through a gland. 
The large type of gauge has been proved reliable in miscellancous 
trials and whilst it must be accepted that due to its large size it oan 
only enable the average pressure from an underwater explosion to be recorded, 
nevertheless for such tests as comparative efficiency of explosives, it 
Meets a definite requirement. 
TRS serieale 
