The Xiaomi Particle Counter Is So Inaccurate It Should Not Control the Purifier

ओह! यह पोस्ट हिन्दी में उपलब्ध नही हैं।अंग्रेजी संस्करण के हेतु यहाँ क्लिक करे l

Thomas Talhelm

Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.

20 thoughts on “The Xiaomi Particle Counter Is So Inaccurate It Should Not Control the Purifier

  1. I tested in my home two Xiaomi Air purifiers (2nd generation), and the stand-alone Xiaomi PM2.5 meter.

    The stand-alone meter is using laser technology, just like any other decent PM2.5 meter on the market. Yet, Xiaomi refuses to answer what technology lies behind the integrated sensor within the Air purifier (1st or 2nd generation). It is interesting to note, that on its 3rd generation of the air purifiers, Xiaomi ditched the old sensor technology, and switched to laser technology too (same technology as in the stand alone meter).

    From my experience, the stand-alone PM2.5 meter from Xiaomi seems to be accurate (when comparing to government PM2.5 meters in my area). Regarding the integrated meters inside the two Xiaomi air purifiers (2nd generation) that I’ve tested, one was constantly ~40 ppm higher than the stand alone meter, and the other seemed to be more in correlation with the stand alone.

    In any case, anyone who uses the Xiaomi air purifiers (2nd generation), simply purchase the stand alone meter if you want accurate control.

    1. Hi, I recently bought a Mi Air 2 purifier and was interested in buying the separate pm2.5 monitor, but so far I’ve found virtually no info on how much control and automation you can program the purifier via the data from the monitor. Can you tell me what is achievable with the two devices working together? I’ve already got a Laser Egg 2, but that has no way of controlling the speed of the Xiaomi purifier.

    1. Hi Max! I tested the Mi1, Mi2, and Mi2 Pro. Unfortunately I only have a record of the Mi1 and Mi2 data. The Mi2 Pro was at a friend’s apartment, where I had access for a limited period of time. The pattern of the data on the Pro versus the Dylos and the Laser Egg was the same as the Mi1 and Mi2–when air was bad, the Mi2 Pro was vastly undercounting. When air was very good, it was overcounting.

      Does Xiaomi claim that the Mi2 Pro has a better particle counter? I’ve searched their website and haven’t found any claim about the particle counter. If you find a specific claim, let me know. Also, if you have a particle counter and the Mi2 Pro, let’s set up another test!

      1. My story is similar to as MATIJA’s. Received Xiaomi Air Purifier 2s few days ago. It shows 001 almost all the time. However, when smoke is around or spraying something near it – it goes to 70-200-600. Then in few minutes goes back to 001. Looks like working, but don’t understand how my indoor air could be so clean, just don’t believe it.

        Any solutions or comments appreciated.

  2. I can confirm that the air purifier 2 never shows less than 9. As for the issue with the AP2 going back to auto after 3 hours it should be possible to circumvent this using the app’s automation options. E.g. set it to change modes at certain times. Not an ideal solution for sure, but should work. I just got the Xiaomi laser pm2.5 sensor and it generally shows far lower values than the AP2 built-in sensor. The sensor is linked to the AP2, but unfortunately the automation options that deal with pm2.5 concentration don’t seem to work very well. When I set a rule that the AP2 should turn on when PM2.5 levels exceeded 15, the rule wasn’t triggered when it reached eg 17. However when I set the limit to 35 and i sprayed some shoe impregnation spray near it or burned some paper it worked without issue. It seems it has problems with the smaller numbers or something.

  3. Xiaomi also offers a standard alone monitor. Will this essentially be the same tech as found within the air purifiers? If so I’m worried about wasting my money.

    I’m debating whether to buy the xiaomi air monitor or the laser egg. The reason I’d prefer the xiaomi is because I already have a fair amount of stuff in my house from them! It’ll all be the same smart system, rather than using yet another APP for the laser egg.

    Does anyone have any ideas?

    1. Good question Chris. We’re yet to actually test the standalone Xiaomi Air monitor (although it’s something we want to do soon!). Ultimately the sensors in these devices are all the same (they cost around $5-$10 per sensor) but what’s different between each monitor is the calibration and testing of the devices. I know this is something Laser Egg have worked on a lot (see the article we wrote about how humidity affects the Laser Egg), but I’d be less sure about the Xiaomi (since they’re a company that puts out 101 different devices). Having said that, I have no doubt it’ll be ‘reasonably’ accurate, but accurate enough to ensure your air is clean 100% of the time… that’s a difficult one to answer.

  4. Hello,
    just read the article out of curiosity, and well some points are somehow weird. I belive the sensor is quite accurate, if they build in what they claim to use. Purely from the technical PoV.
    But going by your data it is more likely, that the software used is wrongly programmed. They write to use shinyei sensors, which do not give an output in any unit but in an voltage equivalent between around 0.5 and 5V. So going by this, the Data you get is most likely the output Voltage of the sensor. Most likely the developer for the purifier took that output directly and fed it to the software as input.
    And herein lies the problem, going by your data he most likely used the wrong stepping for the adc in the control unit, which resultet in a voltage output in far too high steps.
    Well to say it in an easy way, the got a dounce to programm the software and set the electronics, and in the pro version they most likely simply used a sensor which gives digital output and therefore does not have that problem.

    1. Rolf, you’re right that the software-side of particle sensors is often the most important, since there are so many variables at play especially when you’re converting from a particle count (which the sensor gives) to a concentration or AQI (which is what we’re most often used to). In some of the more accurate air quality monitors we tested, they all use fine-tuned software to adjust for different variables.

      Having said that, there are other issues with the sensor in the Xiaomi, firstly that it’s located right next to the purifier. This means you’re only getting an indication of the air around the purifier, as opposed to on the other side of the room. This can be dangerous if you’re using the Xioami in auto-mode, where the sensor is reading clean air (near the machine) but the truth is the air on the other side of the room is not clean.

  5. Moin Moin,

    thank you very much Thomas for your interesting and well written articles. I share the same observations with my Mi2 purifiers but comparing the Mi2 Pro to my laser egg and Xioami particle counter, the results fit much better and also the MI Pro goes down to 1.

    A tip for all Mi purifier users: I only use my purifiers in manual mode! How does it work? You just have to program under automation: If the PM2.5 concentrations is below 500 (which means always), switch to manual mode. This is how you can prevent them to switch to auto mode after some hours automatically!

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