Zephyr: A High Altitude Long Endurance Unmanned Air Vehicle ...

not accurate enough and when plotting a graph to examine average velocities, theerror may give distorted speeds.3.3.3 Built in ErrorsThe sensor has a maximum built in error of 3.0% which can contribute to theproblem. As the manufacturer states that the error could be between 1% and 3% itis hard to account for this error.3.3.4 OperationThe sensor has only been tested to a -25ºC operating temperature so it is not knownwhether it will withstand, and then correctly measure, the airspeed at high altitudeswhere it is colder. Evidence suggests that although it still manages to take a reading, itis not accurate and gives an airspeed value that is much faster than reality.3.3.5 Zener DiodeThe voltage supply to the sensor on the aircraft is 12V, and the maximum outputvoltage is 4.5V. The sensor is connected through a Zener diode into an analogue-todigitalconverter (ADC) on a printed circuit board (PCB), as seen in figure 8.38