We are considering "bme280" Digital humidity and pressure sensor for our application. Need some clarification related to "pressure sensor" performance.
1) In datasheet, relative accuracy stated as 12 Pa.
a. Is it a Part to Part variation?
b. What is the repeatability of this Sensor over time (say 24 hours) (measured drift / oscillations in pascal, if there is no change in environment)?
2) In end application (0 to 1000 Meter altitude), we need to measure the as close as 10 Pa Pressure difference (Difference from two sensors readout).
a. We have a flexibility of doing error cancellation (Read the two sensor values and the difference is marked as offset error which will be used to calibrate the reading). Will this bring the effective error less than 10Pa (peak to peak)?
b. If above solution gives 10 Pa (peak to Peak) accuracy, how frequent (24hours once / 48 hours once) we need to do a new error calculation?
Your clarification will help us to proceed the design. Looking forward to receive your response ASAP.
Let me try to comment on your questins as following:
1. the relative accuracy is not part to part deviation. it is consider to the same sensor deviated from different pressure environment.
2. the part to part deviation can be consider to use absolute accuracy. it is also can be consider as offset of each sensor and can be calibrated on the production line or any time with reference pressure sensor.
3. sensor long term stability performance is 100Pa over 1 year. So 24 hours can be considered as no drift since it is even less than the noise level (consider the pressure environment is stable).
4. If you wants to achieve 10Pa relative accuracy or at least able to tell you 10Pa difference when pressure environment changed, you need to consider to use BMP390(L) whose relative accuracy is 6Pa.
5. If sensor is in stationary position, the method of error (offset) cancellation is not helping too much. If sensor is moving, and you can always get high accurate reference sensor value, it might help and you can calibrate sensor per day or even more frequent.
Thank you for our detailed response.
We are going to use the sensors (2 Numbers) in stationary location, where the air velocity will differ. Our Objective is to measure the "Pressure Difference" (So to estimate the air velocity) and our requirement is "10pa difference should be measurable".
From your comments and datasheets we are sure that +-10pa relative change shall be measured by BME280.
1) Assume we have two BME280 sensors and they are calibrated (Offset corrected) once per day.
2) What is the "expected error in Pa" between two sensor reads over one full day (There is no change in Pressure and temperature). This data is not availble in the datasheet. I call this as a "Part to Part" variation. correct me if i am wrong.
We couldn't use BMP390L as we also want to measure Humidity.
Advance thanks and looking forward to hear from you
Suppose you have two BME280, and calibrated with same reference sensor.
So those two have same output just after calibration. Thus, all the offset including solder drift are compensated already. Part to part deviation has be compensated here also.
So the sensor read out difference is only includes noise and TCO. If the we also say the environment temperature is all the same for all case we considered.
Then only noise need to be added. if using highest accuracy mode, the noise will be 0.2 *2 = 0.4 Pa around (typical). the maxium noise need to be released via NDA. you can contact local FAE to get NDA then with the maxium noise figure ( 3 sigma based).
This is assume the pressure environment are same for those two sensors.
If consider one sensor environment changed for pressure, then you need to add relative accuracy also for difference of two sensor read out.
Here, the drift is ignored since 24 hours will not noticable drift on sensor side.