722 
ls) — 
the system by noting the rise of the step and its decay. Voltage steppers 
which have been employed at this laboratory have used as standard voltage 
sources both battery and regulated electronic power supplies [17]. Steppers 
using a battery as a source of standard potential have the inherent diffi- 
culty of being high-impedance devices. The electronic stepper which depends 
upon voltage regulator tubes as the source of standard potential has a low 
impedance output which is essential for use with the Q-step, The voltage 
stepper involved a time delay and a switching circuit. The time delay was 
so adjusted that the potential was switched from one level to another after 
the spot had progressed a certain distance: across the screen. Any one of 
several standard voltages was selected so that the step height corresponded 
roughly to the expected peak height of the pressure-time curve. The steppers 
were also provided with an exponentially decaying step which approximates 
the form of the shock wave. This proved to be very useful for determining 
the frequency response of the oscilloscope as well as checking focus and 
intensity settings. On the later model electronic steppers a voltage— 
standardization check was provided by checking the potential source from 
the VR tubes against the potential of a dry cell. Periodic checks of both 
the electronic and battery sections were necessary with a standard cell 
and potentiometers. A triggering pulse, emitted with the initiation of the 
time delay for the stepper, was used to start the single sweep for the still- 
film cameras, or to brighten the beam on rotating—drum cameras. 
(iv) Capacitance bridge. When the voltage calibration was used it was 
also necessary to determine the capacity of the gauge and cable system in 
order to calculate the gauge output. A capacitance bridge, included with 
the RELIANCE equipment for this purpose, was based on a substitution method 
in a bridged-T network [17]. The nominal driving frequency for the bridge 
was 10 ke/sec. This bridge was also used to aid in locating faults in 
cables as well as for measuring the standard condensers used in the Q-step. 
(v) Q-step calibration network. By applying a known voltage in 
series with a known capacitance across the cable used, it was possible to 
eliminate the necessity of independent voltage and capacitance determinations 
[4,17]. The principle of this is illustrated in Fig. 16. For recording 
signals the connection is as shovm in Fig. 16(a) and the output voltage Vt 
is 
where CoVo is the charge developed by the gauge and Co is much smaller than 
oye the cable capacity, For calibrating the cable and indicating instruments, 
the connection shown in Fig. 16(b) is used and a step voltage Vs is applied. 
The output voltage under these conditions is 
Gale 
