I picked up my Mi Air Purifier 3H today, unpacked it straight away and put it into operation. The display shows 002 or 001. The air should be very clean. However, when the sun is low in the sky, you can see the dust particles dancing in the air. It is very dusty in the room. Therefore the question: what exactly does the sensor measure? Does the sensor only react to the smallest particles (PM2.5) or should it also react to larger dust particles?

According to the pollen map from MeteoSwiss, the pollen concentration is very high today. I can hardly imagine that we have such clean air in the house. That's why I picked up some "dust" from the nearest hazel bush and "waved" it in front of the sensor - no reaction. I would have expected the fan to switch up 3 levels immediately.

Can anyone tell me how fast/slow the sensor reacts? What is the expected behaviour? Is the fan more active, for example, when one has ventilated? What concentrations are indicated indoors in the Winterthur area today (2.3.2021)?

Is my sensor possibly defective?

Question

I picked up my Mi Air Purifier 3H today, unpacked it straight away and put it into operation. The display shows 002 or 001. The air should be very clean. However, when the sun is low in the sky, you can see the dust particles dancing in the air. It is very dusty in the room. Therefore the question: what exactly does the sensor measure? Does the sensor only react to the smallest particles (PM2.5) or should it also react to larger dust particles?

According to the pollen map from MeteoSwiss, the pollen concentration is very high today. I can hardly imagine that we have such clean air in the house. That's why I picked up some "dust" from the nearest hazel bush and "waved" it in front of the sensor - no reaction. I would have expected the fan to switch up 3 levels immediately.

Can anyone tell me how fast/slow the sensor reacts? What is the expected behaviour? Is the fan more active, for example, when one has ventilated? What concentrations are indicated indoors in the Winterthur area today (2.3.2021)?

Is my sensor possibly defective?

Accepted Answer

I have also been using the 3H for a few months. I am not satisfied with the automatic control. I have already cleaned the sensor a few times (with a hoover). You can't clean it much. I then only operate it manually. When I ventilate the window, I turn the thing up to maximum, but the noise of the fan doesn't allow me to work next to it :-(
The circulation and cleaning at high level is very good. But I would also be happy if the thing had better control and you could influence how many particles it should turn up and how high.
In other forums I have read about similar problems with the measurement.

Answer

I have a supplement on the sensor quality: if you open the windows, the particle measurement values increase immediately and are comparable with the values on this website https://www.breezometer.com/air-quality-map/. So the sensor seems to be OK as far as the PM2.5 readings are concerned.
However, larger dust particles are definitely not detected and you have to use the Mi Air 3H in a time-controlled manner.

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