718 
IV. DETAILS OF INSTRUMENTATION 
7. Piezoelectric gauges and associated equipment 
Eight separate channels were uscd to transmit, amplify, and record the 
Signals from eight tourmaline gauges. The cight cables for the gauge sig- 
nals, plus cables for the pilot gauge signal (when still—film cameras were 
used) and the firing line cable, were all made up into a unit for convenience 
in paying out. The pilot gauge cable was interchangeable with those of the 
recording gauges, and under certain conditions could serve as a spare. 
Writing speeds for the oscillographs from over 3004 sec/ine with the elec 
tronic sweep and still-film camera dowm to less than 100 msec/in, with the 
rotating—drum cameras were available, Block diagrams showing the connec 
tions of the various components for both types of recording are given in 
Figs. 6 and 7. The individual components were so designed that one type of 
recording may be substituted for the other in less than 30 minutes by chang- 
ing patch-cord connections and camera backs, 
(a) Gauges. — (i) Crystal elements, The piezoclectric gauges used 
for RELIANCE work were constructed from tourmaline wafers of approximately 
1/8-in, thickness and 1/2~in, diameter (Fig. 8). Electrodes were attached 
to the faces of these elements by various means, the more successful of 
which have been the Brashear silver-electrolytic copper and the baked sil- 
ver spray process [2,3]. 
(ii) Assembly of crystal elements. The crystal elements with elec-— 
trodes attached were assembled inta doublet gauges (Type A) or quadruplet 
gauges (Type B) [2]. In the Type A assembly the positive faccs of the two 
erystals were sweated together and attached to the central conductor which 
was led off through a copper tube, while extensions of the copper tube were 
fastened to the two outside negative faces of the two crystals. In the 
Type B assombly (Fig. 8) two doublet clements similar to Type A were fastened 
on either side of a central stcel tab, The two outside faces and the two 
central facos of the crystals were negative and were connected clectrically 
to this tab which was then fastened rigidly to the copner tube. The two 
positive electrodes were connectcd to the central conductor which was led 
through the copper tube. Due to the use of mich thinner crystal elements 
in Type B it was possible tocmploy quadruplet gauges with an over-all thick- 
ness no greater than 1/8 in. 
(iii) Waterproofing the completed gauge. Various methods of water— 
proofing these gauges have been found to be satisfactory. Among the materials 
used were moulded rubber, rubber tape and Bostik cement, Tygon and Zophar 
wax G276. The last material mentioned was found to be the most satisfactory 
in warm weather, but rubber tape and Tygon were better in cold weather. 
Good coatings on guages must be mechanically strong, have satisfactory 
dielectric properties, be free of bubbles, be adhesive, be free of electrical 
Signal, be thin and easy to apply. 
Des 
