18 
The following describes a typical operation, including ad- 
justments and calibrations, of the digital data recording system. 
The temperature bridges were balanced to give zero voltage out- 
put at 9°C, and thus the digital voltmeter read 0.000 volt at 9°C. 
The bridge span was adjusted to give approximately 20 millivolt 
output at 19°C, and the amplification then adjusted (approximately 
500) so as to produce 9.999 volts on the digital voltmeter. There- 
fore, the voltmeter readings had a sensitivity of 1 volt per 1°C, 
and the least count of the voltmeter corresponded to 0. 001°C. 
These adjustments are made by switching calibrate resistors 
corresponding to even degree temperatures into bridge number 28 
(fig. 5B). After calibration is completed, this channel monitors 
a resistance located on the strut. Bridges 27 and 29 also pro- 
vided calibration voltages once every scanning cycle. The resis- 
tor providing the bridge number 27 calibration value corresponded 
to 10°C while that of bridge number 29 corresponded to 18°C. The 
computer can then, while reading the tapes, determine from these 
two calibrate voltages the correct sensitivity to apply to readings 
in that particular scan cycle. In this manner any changes as a 
function of time in the power supply batteries, gain of the ampli- 
fier, etc. , can be compensated for continuously. 
The pressure bridge output (fed to channel number 30 of the 
input scanner) is amplified at the gain determined by the temper - 
ature circuits. The result is a maximum depth capability (digital 
voltmeter reading 9.999 volts) of approximately 400 feet, with a 
readout least count of 0.04 feet. 
The logging cycle rate is normally set at 10 seconds. Thus, 
every 10 seconds a cycle, consisting of a time, 26 temperature 
readings, 3 calibrate readings, 1 depth reading, and another time 
reading, is indicated. This means that the sampling speed is ap- 
proximately 3-4 readings per second. In this mode both the tape 
punch and printed tape recorder are used at all times in recording 
data. 
Several features of this digital data recording system pro- 
vide flexibility for future expanded uses. A considerable effort was 
spent in specifying the system so that a maximum number of oper- 
ating modes could be realized with a minimum number of changes. 
