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Update SDP3x Airspeed Correction (#8242)

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Update the model for the standard configuration based on the model from Sensirion and add also an option to do the tube pressure loss correction from Sensirion for other configurations.
This commit is contained in:
Florian Achermann
2017-11-23 04:03:26 +01:00
committed by Daniel Agar
parent 85a7a0a86a
commit a5cc4bcd08
8 changed files with 163 additions and 68 deletions
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49
Tools/models/sdp3x_pitot_model.py
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@@ -30,18 +30,29 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
# 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=np.linspace(0,800,100)
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=400
l_tube=450
## densitiy air in kg/m3
rho_air=1.29
@@ -50,19 +61,21 @@ 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=28557670. - 28557670./(1 + (flow_SDP33/5027611)**1.227924)
## 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*0.000746124*l_tube*rho_air
dp_Tube=(flow_SDP33*0.674)/450*l_tube*rho_air/1.29
## speed at pitot-tube tip due to flow through sensor
dv=0.0331582*flow_SDP33
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)
@@ -74,18 +87,24 @@ airspeed_corrected=airspeed_uncorrected+dv
airspeed_raw=np.sqrt(2*dp_SDP33/rho_air)
plt.figure()
plt.plot(dp_SDP33,airspeed_corrected/airspeed_raw)
plt.plot(dp_SDP33,airspeed_corrected)
plt.xlabel('differential pressure raw value [Pa]')
plt.ylabel('correction factor [-]')
plt.ylabel('airspeed_corrected [m/s]')
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()
##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()