SGP41 Air Quality Sensor - Replace TVOC for VOC

[rp2019433]

PROBLEM DESCRIPTION

SGP41 Air Quality Sensor measures VOC and NOx Index. Details regarding VOC and NOx index measurements are specified in chapter 3.3 of the Datasheet SGP41 Datasheet.

However, Tasmota currently labels SGP41 measurements as TVOC, while the correct term is VOC Index. The same applies for NOx. It would be better if NOx Index was used.

SENSOR = {"Time":"2025-02-14T03:12:12","SGP41":{"VOC_Raw":30105,"NOX_Raw":11857,"TVOC":94,"NOx":1}}

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[sfromis]

As those cheap corroded tin sensors are unable to actually get numbers for some specific VOC, but simply an inaccurate indication of the combination of many VOC types (and other things) in the air, the term "TVOC" (for Total VOC) seems more correct than using "VOC" alone. Also preferable to use a common term across different sensors doing the same thing with the resistance of blobs of corroded tin.

[rp2019433]

Hi sfromis.
I get your point, but there is difference between SGP30 ad SGP4x (40/41) sensor.

SGP30 provides TVOC in ppb SGP30 Datasheet
SGP40 provides VOC Index SGP40 Datasheet
SGP41 provides VOC Index and NOx Index SGP41 Datasheet

TVOC range is 0 ppb to 60000 ppb. VOC and NOx Index range is 1 to 500.

Since they provide different measurements, I don't think using the same term is correct. It can lead to confusion, especially when creating automations in Home Assistant because the "same" TVOC term from sensor SGP30 and SGP41 will bring different range values.

[sfromis]

What I mean is that "VOC" is just less descriptive, and a bit more misleading than "TVOC", which is the only thing you can, sort of, get out of those globs of corroded tin.

And none of them is useful to say what or how much is in the air without both calibration, and specific knowledge of what the deviation could be from, like in an industrial setting.

The resistance varies with other factors than just volatile organic compounds. All of the manufacturers are just "wrong" about giving a "precise" number based on size of their glob of corroded tin, and some arbitrary calculation.

The only useful info you can get from the numbers is that if the number deviates significantly from what you normally get, then you can ponder about a reason why. And don't even start comparing values from different brands of tin corrosion.

[Jason2866]

All this numbers are marketing creations. Don't tell anything in real world. Just there is maybe something in the air...
If there would be an SI definition for we could talk about wrong or not. So it is only a fantasy creation from different manufacturers.