Technical Guide to the UTAD-2 Wind Tunnel
8. Data Acquisition and Processing System
System is built on PC with "Celleron" 600 MHz processor and multifunctional extension board ICPDAS PCI-1802, which includes 32-channal multiplexor with 12-bit 125 kHz analog-to-digital converter, 32-channel digital input, and 32-channel digital output.
Software is written in C++ language. It includes programs for conducting tests of different types and common files with calibration coefficients and other necessary data used by the programs.
8.3 Real Time Data Processing
As a rule 256 samples of output signals are acquired at each angle-of-attack. Using measured signals physical values (loads, dynamic pressure, etc.) are calculated. Aerodynamic loadings are obtained by subtracting tare loadings from loadings in airstream. Using this, the aerodynamic coefficients are calculated. For a sample of 256 values of each aerodynamic coefficient digital denoising is performed, outliers are removed, and mean value and standard deviation are calculated. Support loadings are calculated and subtracted from coefficient mean values and angle-of-attack is corrected for upwash interference. Final values of aerodynamic coefficients together with angle-of-attack and velocity values are written into the output protocol file. On-line plotting includes current coefficients values vs. time plots and final values of aerodynamic coefficients vs. angle-of-attack plots.
8.4 System Calibration
Calibration is performed for the entire measuring path. To the input end of each path a known reference signal (e.g. loading, pressure, etc.) is applied, as described in section 5. The resultant output signals are then processed and written in the calibration protocol file. Calculated values of coefficients of calibration functions are written into the coefficient file to be read by an appropriate program and used to calculate physical values using measured voltage ones.