VOLTAGE REGULATOR — "Powerstat" variable transformer #20 

 Superior, 646306, Model 375 BU 



VOLTAGE INDICATOR - Simpson voltmeter (0-150 v) 



FREQUENCY INDICATOR - JBT frequency meter, Model 34-FHXX-Z 

 (100-130 v) 



RECORDER CAUBRATION 



No attempt has been made by the writer to match up actual temperatures to strip- 

 chart scales (40° equals 40 on a chart, 80° equals 80, etc.) as has been done by other 

 workers. Instead, absolute chart paper scales have been disregarded completely in an 

 effort to achieve the greatest possible chart width per degree of temperature. In order to 

 accomplish this, the first step was to estimate the maximum and minimum surface tem- 

 peratures expected on a given survey date. The recorder was then calibrated so that these 

 values fell near the edges of the chart — leaving enough scale width at each margin to 

 allow for a few degrees error in the original estimations. 



As an example let us assume that on a shelf flight in February the expected minimum 

 temperature would be near freezing along the shoreline and the maximum might be 70 de- 

 grees in the Gulf Stream Front near Cape Hatteras. The IRT and recorder would then be 

 set up in the laboratory prior to the flight and two water baths prepared, one at 75 degrees 

 and the second an ice mush. A proper millivolt setting is selected on the recorder and the 

 recorder adjust screw on the IRT console turned as the sensing head is alternately aimed 

 at the warm and cold baths until the recorder pen makes a full sweep of the chart. 



The laboratory accuracy check is accomplished by placing a magnetic stirrer and 

 reference thermometer in the ice mush. The water bath should be small enough so that 

 the water is well mixed by the stirrer, but not roiled. Thermometer bulb should not touch 

 the sides of the bath. When the ice has melted and the water begins to warm up, readings 

 are taken at frequent intervals on the reference thermometer and the temperatures written 

 on the chart paper opposite corresponding positions on the pen trace. 



The test can be accelerated by raising the temperature in steps (i.e., pouring 

 amounts of hot water into the bath, allowing mixing, marking temperature, adding more 

 hot water, etc.) Once the readings are completed, a small amount of chart should be torn 

 from the spool and the positions of the two extreme readings marked on it. As scale 

 accuracy tends to break down at very low temperatures, it is advisable to use a tempera- 

 ture near 40-45 degrees as the lower reference point. By use of dividers a scale is then 

 constioicted on the chart paper. Positions of the other readings taken during calibration 

 are then matched to the scale to verify accuracy. 



The calibration is rechecked periodically during flights by a water bath and reference 

 thermometer. As a final check during flights, console dial readings are taken at intervals 



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