Temperature sensor oscillations

[ebroder (Evan Broder)]

I have a Purple Air Zen installed outdoors, and I’ve been using the local JSON endpoint to pull data into my Home Assistant install. However, I’m seeing some weird behavior where the temperature and humidity sensors seem to be showing significant oscillation from minute-to-minute:

I’m hitting the /json endpoint, so I would expect to be getting values that are 2-minute averaged (although maybe that’s just the particulate sensors?). And it only seems to affect the temperature/humidity sensors, not anything else.

My best guess is that this is the gas sensor in the BME688 turning a heater on/off, but I don’t think there’s any way to tell from what I can see externally. The oscillation gets as wide as 12-13° at times, and it doesn’t seem like I will get an accurate value by (e.g.) just taking a 5m average, so I’m not sure what cleanup I should be applying to this data.

Any suggestions for how to resolve this?

[ebroder (Evan Broder)]

Oh I should also say that I don’t think the BME688 heater is a complete explanation. If you look at this data from last night, it seems like sometimes the temperature reading oscillates “down” (i.e. between the true reading and some lower reading) and sometimes it oscillates “up”.

Temperature reading higher than reality would be consistent with the BME688 heater, but temperature reading lower than reality doesn’t really make any sense.

(As a note, these readings have the current adjustments for estimated temperature and humidity; I can’t tell if the humidity adjustment formula is wrong, or if it’s just a case of garbage-in-garbage-out)