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]

I am returning to this as we have now more data on this issue.

We have been testing Bosch BME680 on normal office settings with following cycle:

1. Heat to 400 C for 1 second

2. Drop the temperature for 150 C for 30 seconds

We repeat this cycle continuously. It seems that BME680 will saturate after couple of days and lose its sensitivity totally. At first you get some changes in resistance when person stands close to the sensor but after a day or two the sensor will essentially break down. 

Is the cause for this the continuous heating? There is no mentioning of this in the spec sheet. According to it we assumed that the sensor could withstand prolonged heating at least on low temperature (150C). 

[o_o]

Hi Oseania,

As you know by now, the resistance decreases in presence of pollutants, and increases in clean air. 13007335 is the maximum resistance that can be measured by the sensor.

Heating/cooling cycle used has a big impact on the baseline of the gas resistance in the environment. I do not think that the sensor is really damaged by this cycle, but simply that extended heating duration makes the baseline exceed the limits of the ADC.

You can solve this be either:
1- Adjusting your heating cycle
2- Placing the sensor in air that contains more pollutants

I imagine that option 1) is more practical. Again I would give you the same advice as handytech and suggest that you consider using the BSEC library. Bosch Sensortec has characterized the sensor and developed 2 working modes for indoor air quality sensing using the BME680 (data rates 1/3 and 1/300 Hz). If you really want to develop your own working mode, I would suggest that you start with the heating cycle of BSEC closest to your desired application, and go from there.

o_o