I have a BME280, embedded on an Enviro+ for Raspberry Pi from Pimoroni.
I have trouble getting good values for the humidity. The pressure is accurate, the sensor temperature a bit above environment temperature, as expected. However, the humidity values are too low. I tested this in an air tight container with NaCl saturated distilled water, with an expected humidity of ~75% at 20 degrees Celcius. After 24 hours, the measured humidity is around 16-17% too low. The BME280 reads around 58/59% instead of ~75%.
I use C code with the official Bosch driver from Github, used the raspberry pi example code as reference for my test application and followed the data sheet for "indoor measurements", set the chip in "normal" mode with its recommended oversampling, filtering and time interval settings. But also in "weather station" settings, setting the chip in "forced" mode (no oversampling, no filtering, reading every minute) gives the same result.
Is this normal behavior of the sensor? What can I do to improve accuracy?
From the information on the open source website, we can see that the software of BME280 has been integrated into Enviro+ for Raspberry Pi . Could you test this software and compare it with your test data?