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2. Input and Screening of Data 



A preliminary scan of the voltage records is made to 

 calculate the mean and standard deviation of each. In each record, 

 sampled points that are greater or less than 3 standard deviations 

 from the mean are truncated to the average value of their two 

 neighboring points. The number and magnitude of high and low 

 truncations made in each record are reported at the terminal. If an 

 unusually large number of alterations are necessary for a record, the 

 operator may choose to disallow the particular record from further 

 spectral analysis. The mean of each record is recalculated and is 

 then subtracted from each of the transducer signals. 



3. Conversion from Voltage to Pressure Signals 



The differential signals are converted from volts to pounds 

 per square inch differential (PSID) which corresponds to 

 P (arm) -P (center) . These values are then divided by the distance 

 between the sensor positions for each arm to yield the pressure 

 differential per inch of length along an arm. To maintain a 

 consistent sign convention among the pressure differences across the 

 instrument, the signs of the dPl and dP2 signsals are reversed. The 

 four differential channels' signals are now in the form: 



dPl = (P (center) - P (arml) ) / Axl 



dP2 = (P (center) - P(arm2)) / ax2 



dP3 = (P(arm3) - P (center)) / ax3 



dP4 = (P(arm4) - P (center)) / ax4 



