and transferred to the chart recording. These are later checked against the laboratory 

 scale. 



Surface readings are simultaneously collected from the Institute research vessel and 

 the Chesapeake Lightship. The laboratory scale is compared to these field readings and 

 adjusted if necessary. 



During analysis of data, a mean is marked along the pen trace and degree lines inked 

 in where necessary to show temperature fluctuations. i 



The above method of chart calibration is especially useful in the warmer months when 

 gradients are low and the total temperature rar^e small. 



INSTRUMENT PROBLEMS 



The Model IT-1 purchased by the Virginia Institute of Marine Science was initially 

 found to possess a significant reading error. A laboratory calibration indicated that the 

 error was linear with the greatest discrepancy in the low temperature range (IRT 3l' F - 

 reference thermometer 38'F) and only a small error at higher temperatures (94-l/2°F - 

 95°F). Moreover, the needle on the readout dial was extremely "nervous" and hunted over 

 a rai^e of more than eight degrees. Factory modifications dampened the needle to a hunt- 

 ing range of not more than 2°F. Subsequent laboratory tests following calibration disclosed 

 a small reading error of about two degrees at low temperatures still present but none in the 

 higher ranges. 



During calibration of the chart recorder, it was found that in order to get the desired 

 attenuation (maximum chart width per degree) over small temperature ranges a low milli- 

 volt setting on the recorder (25 mv or less) and a high millivolt output from the IRT were 

 necessary, but whenever the output was adjusted to give the proposed range, the recorder 

 pen went off scale. The problem was solved by connecting two potentiometers and a 1-1/2- 

 volt battery into the IRT-recorder cable. This gave the recorder a greatly extended zero 

 and permitted the pen to be brought back on scale. Using this circuitry, it has been possible 

 to develop a scale of one degree per inch on the 10 inch Sargent recorder, permitting ex- 

 tremely accurate reading of a trace. 



The convenient attenuator built into the Sargent recorder permits "fine-tuning" scale 

 adjustments in addition to the recorder adjust screw on the IRT console. By careful adjust- 

 ment a chart can be calibrated so that one division equals exactly one degree, four divisions 

 equal exactly one degree, etc. — greatly simplifying data reduction. 



During early surveys it was noted that the console needle was nervous in flight al- 

 though quiet during lab tests. The data from one entire flight, in fact, was useless because 

 of the wild needle swings and extremely inaccurate readings. The problem was traced to 

 slipstream currents disturbing the sensing head. The effect was particularly pronounced 

 in cold weather when the frigid air blast likely had a cooling effect on the reference cavity. 

 The sensing head was subsequently mounted two feet above the aircraft deck on an ar^le 

 iron "T" and no further trouble was encountered. 



-64- 



