I wonder if the VOC sensor in 82000277 has failed or is near to failing?
In recent weeks, the only time it seems to give “clean-air” readings is when the weather is warm (10 degrees C) and dry.
I am pretty sure there are no persistent sources of VOC’s in this area.
The vendor’s web page says operating temperature should be OK down 0 degrees C.
I think the problem with this are some short, very high readings which blow up the vertical scale of the diagram too much.
Zoom in a time range without large peaks and you’ll see nice, plausible looking values.
It would be better to use logarithmic scaling for VOC and PM… @Radu?
You are missing the point. The reason the graph looks like that is because the unit is producing readings of 30Meg to 50Meg for short periods of time – perhaps only 1 or 2 samples. Historically, the “sensible readings” have been in the range of 300K. The ratio of 30M to 300K is 100:1. According the specs the Winsen MP503, the range from quite polluted to quite clean is on the order of 10:1. So such big readings cannot be coming from a healthy sensor.
This sensor gives lower readings with more VOC. These >10Meg “spikes” would therefor represent sudden spikes of amazingly clean air amongst a background of almost continuous high pollution. This is nonsensical.
These very big readings of >>10M have only appeared in recent months (coinciding with colder weather) that is why I suspect it is the start of a failure. I see that the device has a small built-in heater, perhaps that is what is failing. I suppose time will tell.