## 3 Experimental Proceeding
### Calibrations  
In order to determinate the real uncertainty of measurement associated with each MEMS and to with automated flowmeter, calibrations were performed to each device separately. The calibrations were performed according to the Guide to the Expression of Uncertainty in Measurement--GUM [7]. A Ruska 7750i Air Data Test Set (ADTS) [16] was used, for absolute and differential pressure calibration and a thermal mass flowmeter for volumetric flow rate calibration. The model 7750i is indicated for avionics instrumentation and represented the latest generation ADTS, having unequalled precision and long term stability with the latest pressure control technology, provides high performance measurement and control of all air data parameters [16]. For the calibration of the absolute pressure sensor, the sensor was placed in a barometric chamber where standard pressures were forced by the vacuum pump of the ADTS (see Figure 4). Five different pressures were forced inside the chamber, which, according to the U.S. Standard Atmosphere [3], refer to the altitude of: sea level, 10, 20, 30, 40 and 50 feet. Table 4 represents the calibration sheet of this sensor. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Operating Characteristics** & \multicolumn{1}{c}{**Minimum**} & **Tipic** & **Maximum** & **Unit** \\ \multicolumn{1}{c}{**(\(V_{5}\)= 5.0 V)**} & & & & \\ \hline Pressure Range & 0 & - & 400 & mm H\({}_{2}\)O \\ Full Scale Span (\(V_{FSS}\)) & - & 3 & - & V \\ Accuracy & & \(-\)1.5 & - & +1.5 & \% \(V_{FSS}\) \\ [0, 100] mm H\({}_{2}\)O [10, 60] \({}^{\circ}\)C & & & & (with autozero) \\ Accuracy & & \(-\)2.5 & - & +2.5 & \% \(V_{FSS}\) \\ [100, 400] mm H\({}_{2}\)O [10, 60] \({}^{\circ}\)C & & & & (with autozero) \\ Accuracy & & \(-\)6.25 & - & +6.25 & \% \(V_{FSS}\) \\ [0, 400] mm H\({}_{2}\)O [10, 60] \({}^{\circ}\)C & & & & (without autozero) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: MPXV5004 DP technical data. \begin{table}
\begin{tabular}{c c} \hline \hline
**Features** & \\ \hline
**Work Voltage** & 5V \\
**Input Voltage (recommended)** & 7–12V \\
**Input Voltage (limit)** & 6–20V \\
**Digital I/O Pin** & 20 (7 PWM) \\
**Analogic Input pin** & 12 \\
**Intensity by pin** & 40 mA \\
**Intensity in pin 3.3 V** & 50 mA \\
**Flash Memory** & 32 KB (4 KB _bootloader_2) \\
**SRAM** & 25 KB \\
**EEPROM** & 1 KB \\
**Maximum Frequency** & 16 MHz at 4.5 V \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Atmega32u4 technical data. Considering the calibration of the differential pressure sensor the same ADTS was used, connected to the positive pressure tap. This calibration is expressed in Table 5.  
The calibration of the automated flowmeter was performed placing the two flowmeters in series (the thermal mass flowmeter and the automated flowmeter). The tests were performed with air at three different pressures: sea level, 30 kft and 50 kft. In Table 6 the calibration sheet at sea level is presented. At this pressure was obtained the maximum uncertainty of measurement. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference Pressure (mbar)** & **Sensor Reading (mbar)** & **k** & **Uncertainty (\(\pm\)mbar)** \\ \hline
1013.250 & 1013.18 & 2.02 & 0.16 \\
696.817 & 696.32 & 2.07 & 0.15 \\
465.633 & 464.49 & 2.03 & 0.1 \\
300.896 & 299.18 & 2.17 & 0.13 \\
187.539 & 185.43 & 2.52 & 0.13 \\
155.972 & 113.66 & 2.2 & 0.08 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Absolute pressure sensor calibration sheet. Figure 4: Calibration’ setup: (**a**) barometric chamber; (**b**) laptop computer; (**c**) Air Data Test Set (ADTS) and (**d**) vacuum pump. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference Pressure (in H\({}_{2}\)O)** & **Sensor Reading (in H\({}_{2}\)O)** & **k** & **Uncertainty (\(\pm\)in H\({}_{2}\)O)** \\ \hline
1 & 0.97 & 2.65 & 0.03 \\
5 & 4.94 & 2.2 & 0.04 \\
10 & 9.93 & 2.28 & 0.04 \\
14 & 13.91 & 2.65 & 0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Differential pressure sensor calibration sheet.