Correlation between older and newer PM Sensors

[Kieran]

I’ll start with a graph, because a picture says a thousand words.

For context, ‘Lounge’ is an older sensor (purchased June this year) that is in front of a large 12x24" H14 HEPA filter (part of a project I’m working on) - and ‘High Kitchen’ (purchased September this year) is near the ceiling of the kitchen, pretty much above ‘Lounge’, and definitely nowhere near the HEPA filter.

AG Support tells me the PM0.3 numbers are not calibrated so can’t be compared between different batches of the PM sensor - fair enough. But PM2.5 is still considerably inaccurate - either one way or the other.

I’ve got two older sensors, and three newer sensors, and all three newer sensors report PM levels considerably below the older sensors when placed right together.

It would appear to me that either the older sensors are inaccurate, or the newer sensors are inaccurate, because they can’t both be inaccurate reporting numbers so wildly different?

[Achim_AirGradient]

We have identified this issue. It seems that a batch of Plantower PM sensors show lower than usual numbers and something was not properly calibrated in their factory.

The good news is that we believe we can actually adjust this very well with a compensation formula based on the PM count numbers that we are already having. Our scientists are currently working on this and we believe it will be available towards the weekend.

We are also currently writing a detailed blog post about this issue with a lot more background information. I will keep you updated in this thread.

[Martin_Moller_Larsen]

Is there a way to identify if you are affected by this issue? It looks pretty similar to mine: Airgradient vs Airthings View plus PM2.5 mesurements

[Achim_AirGradient]

There is a sticker with a production date and serial number on the PM sensor. Can you share your number?

We are also investigating if we can detect these units electronically.

[Martin_Moller_Larsen]

Yes. I think it’s this :