Hello!
I hope that this is known thing and someone suggest a solution. My airspeed sensor shows 5km/h without wind (in my room).
I spent decent time debugging this thing. Here is details.
Configuration
My setup has pixhawk 4 from Holybro with PX4 autopilot v1.12.3 and SDP33 airspeed sensor from Drotek.
Connectivity
The sensor is connected via i2c. It is discoverable using i2cdetect command. Therefore I assume that the issue is not related to connectivity.
Sensor health
I checked the sensor by connecting it to Arduino and read raw sensor values using Sensirion example.
Raw output:
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.55
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.55
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.53
DifferentialPressure[Pa]:0.15 Temperature[°C]:26.54
DifferentialPressure[Pa]:0.25 Temperature[°C]:26.57
DifferentialPressure[Pa]:0.10 Temperature[°C]:26.57
DifferentialPressure[Pa]:-0.05 Temperature[°C]:26.58
DifferentialPressure[Pa]:-0.10 Temperature[°C]:26.57
DifferentialPressure[Pa]:8.05 Temperature[°C]:26.56
DifferentialPressure[Pa]:36.30 Temperature[°C]:26.58
DifferentialPressure[Pa]:99.40 Temperature[°C]:26.58
DifferentialPressure[Pa]:115.85 Temperature[°C]:26.63
DifferentialPressure[Pa]:45.05 Temperature[°C]:26.57
DifferentialPressure[Pa]:41.90 Temperature[°C]:26.59
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.63
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.61
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.60
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.60
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.62
DifferentialPressure[Pa]:0.00 Temperature[°C]:26.62
It shows shows 0.00 for differential pressure when the sensor is still. And shows not zero when I blow to the pitot tube. Therefore I think that the sensor function well.
Calibration
I followed the manual AirSpeed Calibration | PX4 User Guide (v1.12) and calibrated the sensor several times to compare calibration result.
Sometimes after calibration QGroundControl shows -5km/h. in this case autopilot marks the sensor as not calibrated after restart.
Sometimes QGroundControl shows 5km/h. I expect to have 0km/h. I played with various parameters to find a way to negotiate this, but this was unsuccessful.
Probably I did something wrong. I appreciate any help. I have no idea how to resolve this situation.
Thank you,
Anton