BME680 changes its sensitivity

[Oseania]

Hi,

We are testing BME680 in mobile application, where the sensor is heated and measured periodically (every 5 minutes). The heating is done to 400C. The heating and measurement time is 30s and this is repeated three times. We have noticed that the sensor starts to move towards saturation limit ( around 13007335). This means that after a while we are not able to perform the measurements. Is the heating time too much and does this cause degradation? Is heating-cooling cycle too much for the sensor?

[Oseania]

Regarding the issue, we have found out that this is reproducible with several sensors. I was wondering if this is related to the long heating sequence (30 seconds) where the standard max by the software is 3s? Could this prolonged heating cause degradation in the metal-oxide layer of the gas sensor? 

[handytech]

Due to the extended heating duration at this high temperature, it is possible that you make the gas resistance values reach the range limit in the ASIC and therefore saturation.

Note that we strongly recommend using the BSEC library in either LP or ULP modes.

[Oseania]

We tested with two other sensors which are not housed in plastic housing. These are working fine with the given heating.

There is some adhesive in the enclosure and a very small venting hole which is basically plugged. I was starting to think following causes:

• our test set-up materials emit gases that somehow destroy the sensor (adhesives or plastics are containing forbidden chemicals)
• our test set-up runs out of gas (vacuum is formed) and thus making the ambient conditions impossible for the sensor to function properly

[handytech]

Thank-you for the update, both points are valid as test conditions are very important to understand this behavior. If saturation is only observed within a specific hardware or in specific test conditions, that would already help closing down on the root-cause. Please double check that you are following all the recommendations in BME680's HSMI. Lab/test chamber conditions also need to be carefully considered in order to (re)produce realistic/valid environmental conditions.