698 
=i age 
Capacitative circuit, the charge being determined in terms of a voltage and 
fixed capacitance. If a step voltage is applied, the method also determines 
the transient response of the systems 
Consider the network of Fig. 27(a)e If the admittance of the gauge 
and coupling impedance in parallel is Y(iu), the voltage developed at the 
recorder is given by Vp = Q,/[%5 + Y(iw)/iu}, where Qy is the charge de- 
veloped by the piezoelectric gauge, If, to calibrate the system, a known 
(b) 
Figs 27. Connections for Q=step calibration, 
voltage V, is applied 1s shown in Fig. 27(b), the resultant voltage Vp at 
the recorder is given by 
Vo = CgV5/[Cy + ¥(iv) /ia). 
Eliminating the admittance Y(iw), we have for the charge Q: 
Qs Cg Vg (Vp/Vq), 
Hence the gauge output Q is determined in the terms of the fixed capacitance 
C,, the voltage Vs, and a ratio of voltages (or deflections) indicated by 
the recording system. Both the gauge circuit and recording system are cali- 
brated in the one operation and the procedure is valid for any frequency or 
time characteristic of the applied voltage as long as the gauge circuit can 
be regarded as a two-terminal network” In work at this laboratory, the 
voltage Vs is ordinarily applied by a step-function generator [see Sec. l(b)J, 
and the transient response of the cable and recording system is thereby de- 
termined. 
16/75 the gauge circuit includes a coupling cable, this restriction will 
not be satisfied for transients occurring in intervals of the order of the 
transit time for the length of cable, 
