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michaelahern / homebridge-airthings

A Homebridge plugin for Airthings air quality monitors via the Airthings Consumer API.
ISC License
38 stars 6 forks source link

'VOC Density': characteristic was supplied illegal value #8

Closed benjholl closed 2 years ago

benjholl commented 2 years ago

on higher VOC levels i get a warning like the following:

[05/01/2022, 19:58:04] [homebridge-airthings] This plugin generated a warning from the characteristic 'VOC Density': characteristic was supplied illegal value: number 1705.4481447162475 exceeded maximum of 1000. See https://git.io/JtMGR for more info.
[05/01/2022, 19:58:03] [Wohnzimmer WavePlus] {"battery":100,"co2":642,"humidity":46,"pressure":952.9,"radonShortTermAvg":96,"rssi":-48,"temp":18.4,"time":1641409069,"voc":556,"relayDeviceType":"hub"}

by using this online converter on the given data with a molecular weight of 78, i would expect a value of about 1.8, not 1705 like in the error message.

image

could it be, that the units "ppm" (as used by airthings) and "ppb" (as used by many formulas) have been mixed?

michaelahern commented 2 years ago

The Airthings device tech specs and app show they are measuring VOC as ppb, not ppm. Have you seen any references to ppm in the Airthings ecosystem?

It seems that the HomeKit Accessory Protocol Spec has a max value of 1000 for VOC Density, which is what's causing that error message. Seems like that's a low max value if Airthings is measuring ranges >2000 ppb or a reasonable max if they're in fact measuring ppm..

benjholl commented 2 years ago

The Airthings device tech specs and app show they are measuring VOC as ppb, not ppm. Have you seen any references to ppm in the Airthings ecosystem?

i have to apologize: aparently i am the one who mixed up ppm and ppb. You are right, VOC is measured in the App/Dashboard and referenced in all of Airthings documents as ppb.

My bad, sorry.

Now i am wondering about the homekit max value of 1000, but that ist none of our business i guess... i think this issue can be closed.