I'm looking for barometer sensors for use in Arduino projects. One of the items I consider is the HP206C (at Reichelt, Germany). The vendor contradicts himself a little bit when he mentions 0.1 m and 0.01 m accuracy. Therefore I'm trying to look it up in the data sheet.
The original data sheet provided by Reichelt says:
Pressure Relative Accuracy +/- 0.6 mbar
Pressure Resolution of Output Data 0,01 mbar
Altimeter Resolution of Output Data 0,01 m
So, the datasheet contradicts itself, IMHO.
There's a newer data sheet by the Producer available as well. It says:
Pressure Relative Accuracy +/- 0.5 mbar
Pressure/Altitude Resolution in Pressure mode 0.01 mbar
Pressure/Altitude Resolution in Altimeter mode 0.1 m
That's ok so far.
The product is advertised with 0.1 m. Is that a realistic number? IMHO the output resolution is irrelevant, only the accuracy matters.
If my bank account has $1000.00, I can increase the output resolution to $1000.00000 but the values do not get better, right? The accuracy is still 1 cent, even if the output resolution is 1 millicent.
Is my understanding correct?
From the comments of @PlasmaHH, it seems I need to explain the application:
- I need relative pressure measurement only, not absolute values. That's why I ignore other values in the data sheet.
- I cannot wait "a few seconds" and take an average of the measured values. Reason is: I need to measure the height of a short flight, which lasts less than 2 seconds.
Best Answer
Accuracy is not resolution !
Accuracy means just that, how accurate is the reading. For this sensor:
Pressure Absolute Accuracy (0 C to 50 C): -1.5 to +1.5 mbar
That means if the actual pressure is say 1000 mbar, then the sensor is guaranteed to report a value between 998.5 mbar and 1001.5 mbar.
Resolution is different, it is about the number of digits you see so
1000 mbar vs 1000.01 mbar
On the 1000 mbar reading the resolution is 1 mbar, a difference of 1 mbar is needed to get to the next lower or higher reading.
On the 1000.01 mbar reading that step is only 0.01 mbar so it has a 100x higher resolution.
That 1000.01 mbar doesn't have to be more accurate.
For example, Sensor A showing a reading of 1000 mbar, it has a resolution of 1 mbar and an accuracy of +/-0.5 mbar
Sensor B showing a reading of 1000.01 mbar, it has a resolution of 0.01 mbar and an accuracy of +/-1 mbar
Obviously sensor A is more accurate, sensor B just suggests that it is more accurate (by showing more numbers) but it isn't.
You will however be able to see smaller changes with sensor B.