2 BME280 sensors read different RH

[keoma_]

I have two BME280 sensors mounted on two PCBs. When I put these two boards side by side inside a humidity chamber, the RH readings are 15 to 20% apart. I tried to recondition the sensors by leaving them in the chamber, with humidity > 45%, for over a week but that did not change the difference between the sensors.Is this an issue where I need to use a different reconditioning method and which one would you recommend? this difference of RH seems to exist with other pairs of boards. When compared to other sensors, the "Pump" sensor seem to be a lot closer to the actual value. The data in the graph was taken over a 24 hour period after reconditioning. Any help would be appreciated.

[BSTRobin]

Hi keoma_,

Thanks for your inquiry.
Does your customized BME280 board comply with HSMI specifications? https://www.bosch-sensortec.com/media/boschsensortec/downloads/handling_soldering_mounting_instructi...
What are the units of the horizontal and vertical coordinates in the diagram?
Do you have a BME280 Shuttle Board 3.0 comparative test?

[keoma_]

The Y axis is RH and temperature multiplied by 100.

The X axis is the number of minutes from the start the test. 

The boards does meet the HSMI spec.

I do not have a BME280 shuttle board. Just comparing two custom boards we built.

[helen01]

Two BME280 sensors may be factory calibrated differently, resulting in inconsistent readings.

You could try the following steps to fix,

Calibrating the sensor:
Using a high-precision hygrometer as a reference, place both BME280 sensors and the reference hygrometer in the same environment, record the readings, and adjust the sensor readings to the reference values. Make offset adjustments in the software to ensure that the sensor readings are consistent with the reference values.

Properly reconditioning the sensor:
Recondition the sensor as per standard methods. Store the sensor in an environment at 70°C and 75%RH for 12 hours, then store it in an environment at 70°C and less than 5%RH for 12 hours, making sure to recondition it strictly according to the above steps.

Ensure a consistent environment:
Make sure that both sensors are at the same temperature, as temperature will affect the humidity readings. Also, make sure that the airflow environment is consistent for both sensors, without objects blocking it, to avoid local environmental differences affecting the readings.

Adjust the sensor position:
Make sure that both sensors are in the same position in the humidity chamber to avoid microenvironmental differences due to position differences affecting the readings. This can be verified by fixing the sensor position or testing it multiple times in the same position.

Check the firmware and software:
Update the firmware of the sensor, making sure to use the latest version to avoid reading differences due to firmware issues. Verify that the data processing and averaging methods for both sensors are consistent to ensure that no discrepancies are introduced at the software level.

[Lies]

If these options do yield positive results, it might be necessary to implement an application-level calibration, with a known accurate reference point, to correct the readings. For example, if you know the "Pump" sensor is providing a closer actual value, you can use it as a correction factor for the BME280 sensors.

As the BME280 provides high accuracy and precision for its price point, such discrepancies might hint more towards abnormalities in individual units rather than a widespread issue. If such large differences persist consistently across multiple pairs, it might be worth reaching out to the relevant customer support or considering an alternative sensor for your requirements.

Remember also that the accuracy of any individual BME280 at any point is within the stated accuracy tolerance of ±3%RH. If these discrepancies lie within the stated tolerance range, this might not be indicative of any issue.

If the problem is still not solved, I suggest you contact Bosch Sensortec.