BME 280 humidity reading less than actual

[adityap708]

Hi,

I am working with BME280 sensors for over a year now. I currently have 10 BME280 sensors, all from Adafruit. 

8 sensors are showing humidity -8% and 2 sensors are showing +12% humidity. I am checking them against the UT333 sensor and handheld psychrometer. 

I have tried to recalibrate the sensors, by dry baking them in reflow oven at 120c for 2 hours and rehydrating them for 24 hours at 80%+ humidity. 

After recalibration attempt, 2 sensors that were showing +12% humidity are now showing correct readings. but the remaining 8 sensors which were showing -8% are still showing -8% humidity. 

How can I fix this? 

[Vincent]

The relative humidity output is within range of 0% - 100%.  there is no possibility to output negative humidity value. 

The -8% can be caused by compensation / calculation errors in SW.

Did you able to use the lasest BME280 API on Github?

https://github.com/BoschSensortec/BME280_driver

If possible,  you can provide all calibration parameters as well as the ADC value from register to us, we can cross check at our side about those parameters first. 

[adityap708]

Apologies for the confusion, I didn't mean value are showing negative. 

I was saying values are less than actual by 8%.

When The psychrometer is showing 77% humidity, all 8 BME sensors show 69%. 

Also, could you please let me know how to use the official API with Arduino? 

[Vincent]

Sorry, i don't have a working example under Arduino for BME280 right now. 

But the official API is based on C langurage,  it can be called by Arduino code directly if you just include the head file in your Arduino project. 

For the 6 sensors with 8% deviation compared to reference sensor output,  did you also compare the temperature output of those sensors? 

are they output the same temperature value?

Further more,  i want to double check with you that both sensors are put into same environment, right? 

[adityap708]

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@Vincent wrote:

For the 6 sensors with 8% deviation compared to reference sensor output,  did you also compare the temperature output of those sensors? 

are they output the same temperature value?

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Sensors with an 8% deviation are showing temperature 0.8 to 1.1 degrees less than the actual temperature.

I am cross-checking the temperature and humidity with a handheld psychrometer and HTC-206 hygrometer. And yes, all sensors are in the same environment.