579 
A. Hole for alignment of brass plate with mold 
B. Rubber insulation surrounding tourmaline crystal 
C. Drilled hole to admit bolt for attaching brass plate to structure 
D. Clamp to secure gage in cavity of brass plate 
E. Wax-filled cable of copper tubing 
In use, the entire assembly is bolted to the facing plate of the structure being tested. 
PRECAUTIONS IN THE USE OF PIEZOELECTRIC GAGES 
Inasmuch as piezoelectric gages are high-impedance sources, certain 
precautions must be taken in their use. If the cable leading from the pickup 
to the amplifier input is too long, then it acts as a transmission line with 
attendant frequency distortion of the signal. This is due to the fact that 
the high impedance of the gage does not match the low surge impedance of the 
cable; the latter is generally less than 100 ohms. This will be discussed in 
greater detail in the section headed "Cables and Recording Channels," pages 
WZ He) iKts}- 
