px4-firmware/Tools/models/sdp3x_pitot_model.py

"""
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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
# and tubing as provided by px4/drotek (1.5 mm diameter)



import numpy as np
import matplotlib.pyplot as plt

P_cal=96600. #Pa
P_amb=96600. #dummy-value, use absolute pressure sensor!!


## differential pressure, sensor values in Pascal
dp_SDP33_raw=np.linspace(0,80,100)




dp_SDP33=dp_SDP33_raw*P_cal/P_amb


## total length tube in mm = length dynamic port+ length static port; compensation only valid for inner diameter of 1.5mm
l_tube=450

## densitiy air in kg/m3
rho_air=1.29


## flow through sensor
flow_SDP33=(300.805 - 300.878/(0.00344205*dp_SDP33**0.68698 + 1))*1.29/rho_air



## additional dp through pitot tube
dp_Pitot=(0.0032*flow_SDP33**2 + 0.0123*flow_SDP33+1.)*1.29/rho_air

## pressure drop through tube
dp_Tube=(flow_SDP33*0.674)/450*l_tube*rho_air/1.29

## speed at pitot-tube tip due to flow through sensor
dv=0.125*flow_SDP33

## sum of all pressure drops
dp_tot=dp_SDP33+dp_Tube+dp_Pitot


## computed airspeed without correction for inflow-speed at tip of pitot-tube
airspeed_uncorrected=np.sqrt(2*dp_tot/rho_air)

## corrected airspeed
airspeed_corrected=airspeed_uncorrected+dv


## just to compare to value without compensation
airspeed_raw=np.sqrt(2*dp_SDP33/rho_air)


plt.figure()
plt.plot(dp_SDP33,airspeed_corrected)
plt.xlabel('differential pressure raw value [Pa]')
plt.ylabel('airspeed_corrected [m/s]')
plt.show()



##plt.figure()
##plt.plot(dp_SDP33,airspeed_corrected/airspeed_raw)
##plt.xlabel('differential pressure raw value [Pa]')
##plt.ylabel('correction factor [-]')
##plt.show()
##
##
##
##plt.figure()
##plt.plot(airspeed_corrected,(airspeed_corrected-airspeed_raw)/airspeed_corrected)
##plt.xlabel('airspeed [m/s]')
##plt.ylabel('relative error [-]')
##plt.show()