ifferential Pressure Sensors: DLHR vs RSC Comparison III
13. Dez. 2018
In continuation of my efforts to evaluate the Honeywell RSC Trustability and AllSensors DLHR differential pressure sensors, I’m trying to also get some „dynamic“, actual airspeed data. An article by xDevs.com reported a scale error of ca 5% for the RSC sensor; the DLHR was found to be within specs. Unfortunately, I don’t have the means for reliable measurements. I did had the chance to use a simple wind generator with airspeed meter. It was clear that it won’t be very accurate, but I thought it might be worthwhile to use. I was wrong.
The setup and recorded data are shown below. The DLHR data I corrected by subtracting an offset of 4.85 Pa, and the RSC data by subtracting 0.83 Pa. There is some info in here: The DLHR zero-pressure offset reported some days ago (here) was ~5.4 Pa, which implies a „zero-offset stability“ of ~0.6 Pa. For the RSC the offset was ~0.6 Pa, and now is 0.83 Pa. With that correction, the data of the RSC and DLHR are pretty consistent – within experimental error – which is pretty low here as seen by the huge noise in the data with the wind turbine on. A further point to note is the quantization in the temperature data of ~0.25 K. The resolution of the temperature sensors themselves is much better than that. The 0.25 K comes from the airspeed UAVCAN message, which uses float16 and Kelvin as units; the offset of 273.14 K significantly cuts down the resolution which would not happen with Celsius. This is just another example of the general observation that the UAVCAN messages of the standard DSDL set are very poorly designed. I also tried to „calibrate“ the RSC/DLHR against the simple pitot tube. The reproducibility was some few m/s, but a clear mismatch has to be noted. For two wind speed settings the simple pitot tube was measuring 160-165 Pa and 80-85 Pa, and the RSC/DLHR sensors were reporting 140-145 Pa and 75-80 Pa. Clearly, this experiment wasn’t even close to accurate enough to draw any conclusions as regards the scale accuracy of the RSC and/or DLHR sensors. I need to find a way to do better. LOL.
