So what are the known issues with this sensor? Is it yet safe to fly with it?
There’s a mention of this in the Plane 3.8.5 release notes
liang-tang has found what looks to be a floating point precision problem (which will only really manifest itself at low speeds), and I’ve encountered what looks to be missing correction factors for a variety of atmospheric conditions (primarily pressure drop in the hose, which is being badly aggravated by a fairly high density altitude)
EDIT: For now until we’ve chased these things down I’d consider the driver experimental and recommend using caution for now. (I encountered conditions where the sensor was off by 50% for me, so that needs to be resolved before I can endorse it).
The thing with this sensor is that its not really a differential pressure sensor, because this sensor needs an airflow through it to be able to measure.
Basically the sensor measures the airflow trough it via the cooling of an heating element by the airflow. This is kind of the same as with an hot wire anemometer.
Here is an article from the manufacturer on how that works:
https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/14_Specialist_Articles/Sensirion_Specialist_Article_Gas_Flow_Bypass_EN.pdf
Most important:
The integrated calibration is implemented so that the flow can be
correctly measured over the entire temperature range. Consequently, no further temperature compensation is
required for the conversion of the differential pressure output signal to mass or volume flow.
Do we still compensate this sensor for altitude and temperature?
@palm369 You are correct about how the sensor works. But because we are not interested in a mass flow number, but a differential pressure number you do require an external barometer (which we of course have on the autopilot), but any errors with this will propagate to the airspeed driver. Further the sensor is designed to be used without tubing. When used with tubing you need to compensate for the pressure drop in the hose, which does scale with altitude (and temperature). https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/8_Differential_Pressure/Sensirion_Differential_Pressure_Sensors_SDP3x_Pressure_Drop_In_Hose.pdf
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The main advantage of the special measuring method of this sensor is the high sensitivity, reliability and validity at low airspeeds (less than 10-12 m/s). For our tiltrotor VTOL “Mozart” with stallspeed at about 9 m/s, the measurement accuracy in this area together with the unnecessary offset calibration is a huge advantage. This of course says nothing about advantages or disadvantages of the SDP33 at higher speeds, where the usual pressure difference sensors can exploit their advantages.
Rolf
Thanks for the link. Didn’t know that. Might be a real problem.
Is it at all possible to correct the measurement over the whole speeds and altitudes we fly at?
Maybe we can do the Airspeed calibration at two different speeds so we get the exponent of the correction function?
This is really complicated… 
As I have this speed sensor here I wonder if there is some progress on the issues ? As I am not experienced I will follow the recommendation not to use it untill it is safe.
Although I haven’t tested this in temperature/density altitude extremes, this sensor has done very well for me. I’ve flown it over 20 hours in calm to 15m/s wind gusts and it has worked very well for me. I can’t speak to its accuracy, but the safety bonus of not having to pre-flight calibrate is a HUGE bonus.
Wow, never saw a log like that. Normally even on the most calm day there is 2-3 m/s wind. But here the wind is almost ZERO 
And additional, we had 35 degrees celcius!
Do you know if/what version of quadplane supports this sensor and dual-airspeed sensors?
Thanks in advance.
You mean arduplane? Quadplane is a feature of that.
see here: https://github.com/ArduPilot/ardupilot/blob/plane3.9/ArduPlane/release-notes.txt
Thanks. I knew it was a feature of arduplane, but didn’t know if all the tweaks in a beta were effective for all features of that code chain. Looks like it is and looks like it became an official released version in April!
Thanks for the help - it’s much appreciated.
@WickedShell is there any plan to add tube length as a parameter to make this more accurate?
Like we discussed at interdrone you currently prefer the DLVR sensor? Where can I procure that? a google search isn’t giving me anything.
@jace26 It should be done, but I can’t say that it’s high on my list at all.
The sensor I’ve been using recently is the DLVR-L05D
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I’ll see if I can convince my guys to pick this up.
did y’all make your own board for this chip, or how do you have it wired up? Are you using it SPI or IC2? Most of the airspeed sensors we have laying around have a little board with some circuitry, but the data sheet for this seems to only require a pull up resistor for ic2.