Reference for VOC-calibration of BME680

[Vindski]

I still do not understand how the initial calibration of BSE680 for VOC, is done. Do you use a certain mix of gases (standardized mix), and measure the signal? Then double the concentration and check if the signal is doubled? Or is the calibratin done in accordance with some defined standard?

You have said that: "BME680 have no selection, so it is sensitive for almost all VOC component". But still i guess you need to calibrate it against something defined?

[Jet]

Hi SIr:

   Regarding BME680 calibration and verification description in our lab, please see the datasheet 1.2 Gas sensor specification.

  We use bvoc mixture to test sensor and besc algorithm and create baseline, but base line need be re-created with the environment change.

  So when the customers use a new BMP680, need to run under a good environment and a bad environment to re-create baseline until accuracy is 3.

The IAQ accuracy is reflects the current state of the background calibration process, such as:

1. IAQ Accuracy=0 could either mean:
   1. BSEC was just started, and the sensor is stabilizing (this lasts normally 5min in LP mode or 20min in ULP mode),
   2. there was a timing violation (i.e. BSEC was called too early or too late), which should be indicated by a warning/error flag by BSEC,
2. IAQ Accuracy=1 means the background history of BSEC is uncertain. This typically means the gas sensor data was too stable for BSEC to clearly define its references,
3. IAQ Accuracy=2 means BSEC found a new calibration data and is currently calibrating,
4. IAQ Accuracy=3 means BSEC calibrated successfully.

[Jet]

The IAQ accuracy is reflects the current state of the background calibration process, such as:

1. IAQ Accuracy=0 could either mean:
   1. BSEC was just started, and the sensor is stabilizing (this lasts normally 5min in LP mode or 20min in ULP mode),
   2. there was a timing violation (i.e. BSEC was called too early or too late), which should be indicated by a warning/error flag by BSEC,
2. IAQ Accuracy=1 means the background history of BSEC is uncertain. This typically means the gas sensor data was too stable for BSEC to clearly define its references,
3. IAQ Accuracy=2 means BSEC found a new calibration data and is currently calibrating,
4. IAQ Accuracy=3 means BSEC calibrated successfully.

[Vindski]

Thank you.

Although the sensor is tested with bVOC mixture, I suppose it still reacts to other VOCs? Reacts to all VOCs?

I plan to use this sensor for measuring air quality in a number of bedrooms, for a period of 2-3 weeks, and move sensor from bedroom to bedroom. 
I wonder if these measurements will be 100% relative (showing strictly internal changes in each different bedroom), or if I also will get some information about difference in TVOC between bedrooms?
I assume the first days in a new bedrooms will show more of how the concentration is different from the previous room, and after some days, when the local background calibration has worked, it is more precise on variation in the room, and less valid for caomparing with other rooms. Is this right?

[Jet]

Hi Sir:

   yes,  it still reacts to other VOCs and reacts to all VOCs.

  These measurements will be 100% relative and can't be compared between the different bedrooms, only reflect the air quality worse or better, which means the device is in more better air condition or more worse when move sensor from bedroom to bedroom and sensor will be re-calibrated to fit in new ambience. They only can be compared under the same condition after a long time.

[Vindski]

I understand this local background calibration is quicker if there is a good variatioin in concentration, but how long time more or less? Is it done as fast as in  a day or two in good conditions? Or does it usually take a whole week?