Indoor & Outdoor unit detection wide deviation

Hello community,
New to the forum but excited to start this journey with everyone.

I’m testing an outdoor and indoor new out of box unit physically next to eachother. Both unit have the latest firmware but am seeing a wide deviation in the readings for the same items measured between the indoor and outdoor units. Is this expected?

I’m considering to purchase more units but want to make sure the precision and accuracy of these devices are matched. Thanks!

The CO2 seems to be in the realm of the accuracy of the units, so I wouldn’t worry about that one. The PM2.5 values are a bit off and I have 2 indoor units sitting next to each other and the humidity is within 1.5%

Are both of these mounted in their proper orientation? The indoor unit sitting upright mounted to a wall or using the stands so air can get in the vents in the bottom?

Similar for the outdoor model, is it elevated so air can flow up into the protected vents?

We are considering use these AirGradient units measurement as triggers to activate servos. Just curious if some type of manual calibration/offset is needed out of the box (aside from CO2)?

Also the PM is within official spec.

Plantower PMS5003T (laser scattering principle).
Accuracy: ±10%@100~500μ g/m³, ±10μg/m³@0~100μ g/m³

The PM003Count is actually a non calibrated figure more for giving a finer granulation of the PM when very low so it should not be compared.

The RH is a bit wide but we use a compensation algorithm for it which we might need to fine tune at a later stage. Do you have a 3rd source for RH?

We have several RH within 6 feet as comparison.

  1. Ecobee 4 Thermostat: 46% RH
  2. Amazon Smart Air Quality Monitor: 43%

It is more inline with the indoor Airgradient. Here is another snapshot for comparison.

The compensation algorithm we developed for the open air assumes outdoor operation. I saw it being off indoors to a higher extent. I assume that (even small) wind makes a difference.

Could you place it outdoors (in complete shadow) and see how it compares there?

The outdoor unit will eventualy go to outdoor location, however, I do not have another outdoor RH monitor to compare the readings nor should we intentionally introduce uncessary dust to the new indoor monitor sensors. Would your team look into this deviation between the indoor and outdoor Airgradient?

We did exactly this a few months ago. Here is the presentation (focusing on the temperature correction but same was done for the relative humidity).

Good information. Thank you!

In my understanding the pm003 count is the number of particules in a volume of 0.1Liter (as the sensor spec tells) so if you multiple it by 10 000. It should give a good view of how many particules there are in 1 cubic meter.
You can compare this number with the ISO 14644-1 standard (Clean Room Classifications & ISO Standards | American Cleanrooms Systems)
I’m correct ?

In theory yes but I would be extremely cautious to trust these absolute numbers as it really is a very low cost PM module. The count numbers in my opinion should really be seen as a relative comparison over time axis.

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I agree, i remember the spec giving a 50% precision on this value.