forked from Archive/PX4-Autopilot
110 lines
3.3 KiB
Python
110 lines
3.3 KiB
Python
"""
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Copyright (c) 2017, Sensirion AG
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright notice, this
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list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions and the following disclaimer in the documentation
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and/or other materials provided with the distribution.
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* Neither the name of Sensirion AG nor the names of its
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contributors may be used to endorse or promote products derived from
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this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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"""
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# formula for metal pitot tube with round tip as here: https://drotek.com/shop/2986-large_default/sdp3x-airspeed-sensor-kit-sdp31.jpg
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# and tubing as provided by px4/drotek (1.5 mm diameter)
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import numpy as np
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import matplotlib.pyplot as plt
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P_cal=96600. #Pa
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P_amb=96600. #dummy-value, use absolute pressure sensor!!
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## differential pressure, sensor values in Pascal
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dp_SDP33_raw=np.linspace(0,80,100)
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dp_SDP33=dp_SDP33_raw*P_cal/P_amb
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## total length tube in mm = length dynamic port+ length static port; compensation only valid for inner diameter of 1.5mm
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l_tube=450
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## densitiy air in kg/m3
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rho_air=1.29
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## flow through sensor
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flow_SDP33=(300.805 - 300.878/(0.00344205*dp_SDP33**0.68698 + 1))*1.29/rho_air
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## additional dp through pitot tube
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dp_Pitot=(0.0032*flow_SDP33**2 + 0.0123*flow_SDP33+1.)*1.29/rho_air
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## pressure drop through tube
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dp_Tube=(flow_SDP33*0.674)/450*l_tube*rho_air/1.29
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## speed at pitot-tube tip due to flow through sensor
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dv=0.125*flow_SDP33
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## sum of all pressure drops
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dp_tot=dp_SDP33+dp_Tube+dp_Pitot
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## computed airspeed without correction for inflow-speed at tip of pitot-tube
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airspeed_uncorrected=np.sqrt(2*dp_tot/rho_air)
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## corrected airspeed
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airspeed_corrected=airspeed_uncorrected+dv
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## just to compare to value without compensation
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airspeed_raw=np.sqrt(2*dp_SDP33/rho_air)
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plt.figure()
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plt.plot(dp_SDP33,airspeed_corrected)
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plt.xlabel('differential pressure raw value [Pa]')
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plt.ylabel('airspeed_corrected [m/s]')
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plt.show()
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##plt.figure()
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##plt.plot(dp_SDP33,airspeed_corrected/airspeed_raw)
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##plt.xlabel('differential pressure raw value [Pa]')
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##plt.ylabel('correction factor [-]')
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##plt.show()
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##
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##
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##
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##plt.figure()
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##plt.plot(airspeed_corrected,(airspeed_corrected-airspeed_raw)/airspeed_corrected)
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##plt.xlabel('airspeed [m/s]')
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##plt.ylabel('relative error [-]')
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##plt.show() |