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<br />field study. The instrument cannot be run on the ground without approximately 40 m S.l <br />airflow over the element. Power to operate the instrument is enabled only by a "weight-on- <br />wheels" switch after aircraft take-off or by a manual override on the ground for testing. <br /> <br />4.12 Aircraft Data Acquisition System <br /> <br />The Science Engineering Associates (SEA) Model 200 data acquisition system is based on <br />the ffiM AT computer system architecture with a table-driven software package. Most features of <br />the system are controlled by user-modifiable text tables. These user tables control acquisition, <br />computation, display, and storage. The tables may be modified by most word-processing programs, <br />allowing the user to configure the system easily for each new research program. <br /> <br />Specifications <br />Computer: Intel 80386 CPU, 20 MHz, 80387 math co-processor. <br />Clock: Using the 8Mhz bus frequency as a base frequency. <br />Screen: Dual VGA monitors <br />Analog to Digital: 32 differential input channels, 16 bit AID acquisition rates, 0 to 6000 Hz <br />One dimensional probe interface: Acquisition rates 0-3000 Hz. <br />Two-dimensional probe interface: Asynchronous acquisition <br />Storage medium: Dual40-Megabyte small computer systems interface tape drive. <br /> <br />Calibration <br />The AID converter is audited annually against a National Institute of Standards and <br />Technology (NIST) traceable, calibrated millivolt standard. <br /> <br />5. DATA PROCESSING <br /> <br />Data were recorded inflight on 40-Mbyte tape cartridges. After flight, the data were <br />transferred to a PC for processing. A program, incorporating the equations in Table 2, was used to <br />process I-second averaged files in engineering units ( pre-program values were used initially, then <br />updated as field calibrations were performed). Headers defining the variable were added to each <br />column and the files were saved in ASCII format. <br /> <br />Table 2. Measurements and algorithms used for data reduction <br /> <br />. Measurement Algorithm <br /> <br />Time Read directly from onboard computer <br /> <br />True air speed (TAS)(m S-l) (2CpTJ((P+PJ/P)R/mcP-1])112 <br />where Cp = 1005 (J deg-1 kg-I) <br />Tf= Free air Temperature (deg) <br /> <br />16 <br />