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

Therefore max pressure: p = ½ x 1.225 x (9.52) 2p = 55.51 Pap = 0.56 mbarThis means a sensor should be found that has a range between 0 mbar and 0.56 mbar.Once I had calculated the pressure ranges I could find a sensor (All Sensors Inc,model DS0032, see Appendix 1) that had a corresponding range of 0 – 0.6 mbar [8].Its voltage output range is also 4.5V (when the pressure/airspeed is 0), and 0V (whenthe pressure/airspeed is at its maximum, i.e. 0.6mbar).The average airspeed that Zephyr flies at is 6ms -1 , which corresponds to a pressure of3.5mbar. The corresponding voltage at this pressure is less than 2V and therefore theZener diode should not draw any current, thus eliminating the error.As the range is much smaller than the previous sensor, and much closer to the speedsof Zephyr, the output voltage will always be towards 0V as the velocity will be at theupper end of the range towards 10ms -1 . The previous sensor had such a large rangethat even at Zephyr’s maximum speed it was still in the lower end of the range andthus the higher end of the voltage.41