Now i woud like to understand when i can consider accurate the iaq values. Can i consider correct the values when iaq accuracy is 2/3 and not accurate when iaq accuracy is 0/1? another question is about the Calibration, at first i tried the sensor for some hours and get always iaq accuracy=1, then i red in the forum that it needs some stimuli to get a correct calibration, so now i used a bit of paper wet of alchol. This time the iaq accuracy in few minutes reaches value=2 and then 3 but after few days it returned to 1. What caused this behaviour? And how can i avoid it to have always an accuracy=2/3 and a valid iaq value? Values obtain are in the range 0-250 and values higher than 250 seems to be clipped to that value, but from datasheet the possible range is 0-500, is it normal? am i doing something wrong? i would like to avoid the alchol thing every time i power on the sensor, could be possible with these functions?
The IAQ accuracy definition was indeed added to the Q&A section in this post. Hopefully that can help clarify the meaning of each possible value.
The alcohol trick can be used to validate that BSEC is running properly, but shouldn't be used as a method to calibrate the sensor and could explain some of the described behavior. Since BSEC's calibration process is self-calibrating based on its background history, the performance of the IAQ output will be influenced by such a calibration method.
Last thing i am not using the save/state load state functions because i am using the Lite Version, can that functionality solve some of these problems?
As BSEC seems to be running without any error, the described behavior doesn't seem to be linked to the usage of the Lite version. Note that using the Lite version does prevent you from loading any config string, and therefore from possibly increasing the history period considered for the background calibration.
Values of CO2eq and Bvocs are always clipped to 0, and i know for sure in that 70 hours CO2 increased a lot, maybe there is a enable parameter that i am not considering? I am using the C driver and the example from Bosch without differences in the code.
Based on your overall behavior, it seems most likely that these outputs were not enabled in your applications, and you should look in the direction pointed out in this reply. In the meantime, we have now enabled these two outputs by default in the sample code of the current (and upcoming) BSEC release(s).
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Below are some more details about the different outputs you listed, hopefully that will help you pick the best solution for your application:
The main difference between IAQ and static IAQ (sIAQ) relies in the scaling factor calculated based on the recent sensor history. The sIAQ output has been optimized for stationary applications (e.g. fixed indoor devices) whereas the IAQ output is ideal for mobile application (e.g. carry-on devices).
bVOC eq estimate:
The breath VOC equivalent output (bVOC eq ) estimates the total VOC concentration [ppm] in the environment. It is calculated based on the sIAQ output and derived from lab tests.
CO2 eq estimate:
Estimates a CO2-equivalent (CO2 eq ) concentration [ppm] in the environment. It is also calculated based on the sIAQ output and derived from VOC measurements and correlation from field studies.
Since bVOC eq and CO2 eq are based on the sIAQ output, they are expected to perform optimally in stationnary applications where the main source of VOCs in the environment comes from human activity (e.g. in a bedroom).
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How can we realize the following:
Calibrate a reference sensor in a reference sensor platform (base on an ESP 8266 or ESP-12f) and extract its calibration data.
Write this calibration data to multiple sensor plattforms.
Make all sensor plattforms work without further calibration (as we have a stored reference calibration).
It is not possible to calibrate multiple sensors against a single reference due to the working principle of this gas sensing technology. Therefore we decided to offer background calibration as part of the BSEC library.
So e.g. storing a calibration, powering down and moving the sensor to a complete new location with different IAQ, the resulting IAQ value is more or less close to the one before.
I don't believe I fully understood your statement here, or why would the IAQ value be more or less the same after all these changes to the sensor and its environment?
Addendum: If what was described above is not possible, a reduced use case would be: Holdong power on the BME680, but sending only the ESP 8266 (or whatsever computer is used) to sleep. At least this setup should somehow be able to hold / recover fast (= in seconds). Is this possible somehow?
To get the best performance, it is recommended to run the gas sensor measurements in the same operating mode. Having your MCU go to "sleep" mode in-between measurement should be possible, if the state file could be stored/restored in time between measurements, and if your system could successfully both maintain a precise sampling period and keep track of the real timestamps. Alternatively, it would also be possible to run your "edge" device in a "sensor only" mode, while running BSEC remotely (e.g. on a server, in the cloud, ...).
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Thank-you for providing the complete data-log including raw sensor signals. I have shared your data internally already, and hope that we will be able to further process it to provide extra feedback.
Based on quick overview of raw gas output, I could observe significant contrast between the longer phase of higher concentration, and shorted periods of low concentration. Therefore the overall trend observed in your graph seems consistent with the VOC concentrations observed by the sensor.
Unfortunately, it is difficult to comment on the scaling factor you observe outside. I personnaly do not have a lot of experience with outdoor data, and therefore I do not really know what a CO2 reference sensor would/should output. Also, the BME680 itself is a relative tVOC sensor and not a CO2 sensor. BSEC outputs were tuned using a bVOC mixture, and the CO2-equivalent/bVOC-equivalent outputs was later added on popular demand (based on lab tests and field studies). Therefore bVOC-eq and CO2-eq outputs are expected to perform optimally where the main source of VOCs in the environment comes from human activity (typically indoor).
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Working lifetime of a sensor is highly dependant on the use-case, environmental and stress conditions, etc. Therefore we cannot guarantee a standard lifetime because there are so many differents applications and respective mission profiles our sensors are used for.
We do not have extra calibration certificates for our sensors, as the expected performance is already as listed in the specifications of the datasheet.
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