A description of the use of this barograph is given in Part II, "Operations," of this report.
B. Temperature Measurement
To interpret some of the observed balloon behavior, a knowledge of the temperature of the gas and the outside air temperature was required. The evaluation of "superheat" effects was accomplished primarily by exposing a conventional radiosonde thermistor inside the balloon with a control thermistor measuring the free-air temperature. Similarly, a thermistor was sometimes installed inside the battery-pack housing to measure the temperature of the batteries.
While this system was in use it was general practice to use the standard government service thermistors ML 376/AM (brown) and ML 395/FMQ-1 (white). The white elements were needed when the external temperature was measured, since no adequate protection from the sun was available. Also, at floating level there is no ventilation to be had since the balloon is stationary with respect to the air.
The resistance of the thermistors was switched into the grid circuit of the blocking oscillator of the AM-1 transmitter, and by comparison with pre-flight calibrations the audio frequency transmitted could be interpreted in terms of temperature. To record the signal after it was received, a fast-speed Brush Co. Oscillograph Model BL212 is used. (Due to the frequency response of the Brush recording system, the circuit was arranged to give lower frequencies than a standard radiosonde for the same temperature range.) A sample calibration chart is shown in Figure 34.
Figure 34. Sample calibration chart for temperature measurements.