sensor data influenced by other sensor?

jojo

@Felix-Bayer Yes, I'm aware. On the other side, some days ago the timestamps of the last calibration were quite old, 4 values were from mid january, 1 from November, and only 2 from recent dates (mid/end of february).

I use the correction suggestion from sugo. These values seem much more accurate, when comparing them to the values delivered nativly by airq.

If I think that the Zero-line has shifted and thus a new calibration value is required, I put the airq for around 2 hours outside, and check the values of official measurements. Using them for calibration , it seems.accurate. (anybody without a official station nearby could use https://db.eurad.uni-koeln.de/de/vorhersage/eurad-im.php to get a rough impression for any european location).

Jojo

sugo

From
https://sensirion.com/media/documents/984E0DD5/61644B8B/Sensirion_Gas_Sensors_Datasheet_SGP30.pdf

"The SGP30 features an on-chip humidity compensation for the air quality signals (CO2eq and TVOC) and sensor raw signals
(H2 signal and Ethanol signal). To use the on-chip humidity compensation an absolute humidity value from an external humidity
sensor like the SHTxx is required. Using the “sgp30_set_absolute_humidity” command, a new humidity value can be written to
the SGP30 by sending 2 data bytes (MSB first) and 1 CRC byte."

I have the strong feeling this is not applied, can you please confirm?

Mario [air-Q]

@sugo sorry for the late answer. the mailing system of the forum was down - nobody noticed. I will check this.

sugo

@Mario-air-Q
Do you have some news?

I currently use this formula, for integrated correction would be for sure far better

platform: statistics
name: "min T"
entity_id: sensor.airq_temperature
state_characteristic: value_min
max_age:
minutes: 2000
sampling_size: 2000

state: "{{ states('sensor.airq_voc') | float * ( 2 / states('sensor.airq_absolute_humidity') | float ) ** 0.8 - 11 * ( states('sensor.airq_temperature') | float - states('sensor.min_t') | float ) }}"

Felix [air-Q]

@sugo
thank you for participating and sharing this informations. I linked this forum post and the one from home assistant to our Devs so they can look over it and decide if/how to integrate this in our code, i think we also need a decision wether this should be implemented on FW- oder App-Level.

Felix [air-Q]

@sugo
In general, there is also the fact that a volume concentration (%, ppm or ppb) does not change with temperature or pressure, but the mass concentration (µg/m3 or mg/m3) does. Therefore, the lower the temperature falls while the volume concentration remains constant, the higher the mass concentration per cubic meter becomes, since the air then becomes increasingly dense.