{"id":479,"date":"2018-12-27T17:04:42","date_gmt":"2018-12-27T17:04:42","guid":{"rendered":"https:\/\/smartairfilters.com\/mn\/?p=479"},"modified":"2019-06-01T06:57:29","modified_gmt":"2019-06-01T06:57:29","slug":"xiaomi-particle-counter-inaccurate-not-control-purifier","status":"publish","type":"post","link":"https:\/\/smartairfilters.com\/mn\/en\/blog\/xiaomi-particle-counter-inaccurate-not-control-purifier\/","title":{"rendered":"The Xiaomi Particle Counter Is So Inaccurate It Should Not Control the Purifier"},"content":{"rendered":"

Tech companies love to talk about how automation, internet of things, and the connected house are going to make the machines we use every day more convenient. But does it work? Anyone who\u2019s used Apple\u2019s Siri or \u201ctalk to text\u201d feature know that the promises of technology sometimes fall short.<\/p>\n

 <\/p>\n

Here\u2019s the Xiaomi air purifier, the Mi2 to be precise.<\/p>\n

\"\"<\/p>\n

 <\/p>\n

And here\u2019s the air quality readout coming from a small particle on the side of the machine.<\/p>\n

\"\"<\/p>\n

<\/h3>\n

The Promise<\/strong><\/h3>\n

And here\u2019s what it promises to do\u2014detect how bad air is in your home, turn the purifier on when air is bad and turn it off when air is good. If it can do that, it means we can breathe clean air without the fan on high all the time. That\u2019s awesome because it means less noise and less wasted electricity.<\/p>\n

 <\/p>\n

The Test<\/strong><\/h3>\n

We previously\u00a0<\/span>tested how good the Mi2 purifier was at cleaning the air, and found shocking results: it left air unsafe 86% of the time<\/a>. This time around, we wanted to do a more methodical test of the particle counters inside the Mi purifiers.<\/p>\n

I tested the Mi1, Mi2, and the more expensive Mi2 Pro version against three particle counters. None of the Mi\u2019s were new, but the Mi2 was relatively new, used to do just a few weeks of testing.<\/p>\n

 <\/p>\n

I set up the two Laser Eggs and the Air Visual Node on a chair next to the built-in particle counter on the Mi2.<\/p>\n

 <\/p>\n

\"\"<\/p>\n

 <\/p>\n

I burned a cigarette in a closed 12m2 room and then turned on the purifier on high until the air got clean again (about 30 minutes from start to finish). That way we can test for accuracy from clean levels to truly toxic levels. I set my phone to take pictures of all the readings every 30 seconds.<\/p>\n

 <\/p>\n

How Accurate SHOULD It Be?<\/strong><\/h3>\n

But wait, before I get to the results, I want to set expectations. I\u00a0<\/span>don\u2019t<\/strong>\u00a0<\/span>expect the Xiaomi particle counter to be really accurate. It\u2019s a cheap particle counter inside a machine that costs less than some of the particle counters I\u2019m about to compare it to. We need to have realistic expectations.<\/p>\n

 <\/p>\n

So what are realistic expectations? I don\u2019t ask for it to be great. All I ask is that that it works well enough to do what it\u2019s designed to do\u2014run the auto mode.<\/p>\n

 <\/p>\n

Results<\/h3>\n

Even against modest expectations, the Xiaomi was off by a lot. When the air was bad, the Xiaomi was off by an astounding 218 micrograms.<\/p>\n

To give a sense of how large that discrepancy is, the\u00a0<\/span>WHO 24-hour limit<\/a>\u00a0<\/span>is 25 micrograms. The Xiaomi\u2019s error alone was over 8 times the WHO limit.<\/p>\n

 <\/p>\n

Here\u2019s what that looked like live.<\/p>\n

 <\/p>\n

\"\"<\/p>\n

 <\/p>\n

The Xiaomi seemed like it almost stopped counting past 50 micrograms. At that rate, the Xiaomi was saying the air inside was at orange or \u201cunhealthy for sensitive groups\u201d when it was really in the purple \u201cvery unhealthy\u201d range.<\/p>\n

 <\/p>\n

OK, so the Xiaomi undercounts\u2014severely at times. It turns out that\u2019s not the only problem. If we zoom into the low range, the Xiaomi was overcounting.<\/p>\n

\"\"<\/p>\n

 <\/p>\n

I suppose a 9-microgram discrepancy might sound like not a big deal, but on the other hand, the Xiaomi was overestimating the real number by a factor of 10.<\/p>\n

 <\/p>\n

\"\"<\/p>\n

 <\/p>\n

The Xiaomi 1 Is Inaccurate Too<\/strong><\/h3>\n

Maybe the Mi2 I got was just broken. Maybe the shipping guy dropped the machine on the way to my home and damaged the particle counter.<\/p>\n

 <\/p>\n

To test that possibility, I tested an older Mi1 against the Dylos Pro (which\u00a0<\/span>also scored well<\/a>against the official PM2.5 numbers). The results showed the same pattern as the Mi2.<\/p>\n

 <\/p>\n

\"\"<\/p>\n

 <\/p>\n

I also tested the Mi2 Pro, and it showed the same pattern. Thus, this seems to be a consistent problem with Xiaomi purifiers.<\/p>\n

 <\/p>\n

How Do We Know Those Other Numbers Are Correct?<\/strong><\/h3>\n

Hang on, aren\u2019t we assuming the Laser Egg and the Node are the right numbers? How do we know that those are the right ones, and the Xiaomi is the wrong?<\/p>\n

 <\/p>\n

Smart Air ran comparison tests of the Node and Laser Egg with official PM2.5 numbers for six days. The Node and the Egg\u00a0<\/span>correlated with the official PM2.5<\/a>\u00a0<\/span>at a very respectable r = .98, with an average error of 4.8 micrograms for the Node and 6.5 micrograms for the Egg. That makes me confident their numbers are a good approximation of the true concentration.<\/p>\n

 <\/p>\n

Bottom Line<\/strong><\/h3>\n

The Xiaomi particle counter is extremely inaccurate\u2014so inaccurate that it should not be used to control your purifier. The problem is, Xiaomi doesn\u2019t give users a choice (which I explain below).<\/p>\n

 <\/p>\n

This Could Explain the Xiaomi Left Air at Dangerous Levels in Our Tests<\/strong><\/h3>\n

Smart Air\u00a0<\/span>tested the Xiaomi Mi2 air purifier in a real Beijing apartment<\/a>\u00a0<\/span>for 12 nights, and the results shocked me. I honestly thought it\u2019d do a fine job. After all, purifiers are just fans and filters. But the Xiaomi left the air at unhealthy levels for 86% of the time.<\/p>\n

\"\"<\/p>\n

 <\/p>\n

The fact that the Xiaomi so severely underestimates pollution levels could explain why it so often leaves the air at those unsafe levels. I found similarly atrocious results when I tested the Philips auto mode, which convinces me that the technology behind air purifier auto modes just isn\u2019t good enough yet. I would not use an auto mode in my home.<\/p>\n

<\/h3>\n

Why This Problem Is More Than Just an Accuracy Problem<\/strong><\/h3>\n

The Mi2 is fine purifier when it\u2019s on high. Our\u00a0<\/span>open-source tests<\/a>\u00a0<\/span>show that it does a great job on high (check out the first three hours in the test graph above). But the problem is the Mi2\u00a0<\/span>forces users to use auto mode<\/a>. No matter what you do to the machine, it will switch to auto mode after three hours. Sounds weird, right? We asked customer service three times just to be sure.<\/p>\n

 <\/p>\n

That means unless you wake up every three hours during the night and switch the machine back onto high, you have to use auto mode and the particle counter that controls it. I hope Xiaomi fixes this simple design flaw, but until they do, I would not use a Xiaomi in my home.<\/p>\n

 <\/p>\n

Read more for extra data and methods.\u00a0I also test the possibility that the particle counter is inaccurate because it\u2019s on the inside of the machine and so sampling air that is different from air outside the machine.<\/p>\n

 <\/p>\n

<\/h3>\n

Extra Data and Methods<\/strong><\/h3>\n

Mi1 Test Method<\/h4>\n

I tested the Mi2 in the Smart Air office and the Mi1 at my home, so the room and methods were slightly different. In the office, I burned a cigarette to make the particle counts go up. At home, I don\u2019t have any cigarettes, so I burned a piece of paper.<\/p>\n

 <\/p>\n

The size of the office room was 12m2. My room at home was larger, probably closer to 15m2.<\/p>\n

 <\/p>\n

Is the Xiaomi inaccurate because the particle counter is inside the machine?<\/h4>\n

I wondered if the particle counter is inaccurate because it\u2019s on the inside of the machine and therefore not getting a good sample of air. One way to test this is to take the particle counter out of the machine, which isn\u2019t very hard. Even when I did that, the numbers still consistently undercounted when pollution was high and overcounted when pollution was low. Thus, I don\u2019t think the problem is the placement of the particle counter.<\/p>\n

 <\/p>\n

What are the Xiaomi numbers exactly?<\/h4>\n

One frustrating part of the Xiaomi is that it doesn\u2019t label the air quality numbers. Are they micrograms, China AQI, US AQI, or something else? I can\u2019t understand why they wouldn\u2019t label the numbers.<\/p>\n

 <\/p>\n

This isn\u2019t just a nerd concern. It could really affect the results because the\u00a0<\/span>relationship between micrograms and AQI isn\u2019t linear.<\/a><\/p>\n

 <\/p>\n

\"\"<\/p>\n

 <\/p>\n

If you dig around deeply enough through the Xiaomi, they do say that the numbers are micrograms. Thus, I compare micrograms to micrograms in the analysis.<\/p>\n

 <\/p>\n

Can the Xiaomi get below 10 micrograms?<\/h4>\n

The lowest number the Xiaomi registered was 9 micrograms, while the Node was registering 0.2 micrograms and the Eggs 1 microgram. That made me wonder, is it even possible for the Xiaomi to display numbers below 9? Is it programmed not to go below that number?<\/p>\n

 <\/p>\n

To get to the bottom of it, I turned on\u00a0<\/span>the DIY 1.1<\/a>\u00a0<\/span>and pointed it directly onto the Xiaomi particle counter. When I do the same\u00a0<\/span>test with the Dylos particle counter<\/a>, the numbers go down to zero. But with the Xiaomi, the numbers stayed around 10 micrograms. Therefore, I think the Xiaomi is either registering phantom particles or programmed not to go below 9.<\/p>\n

<\/h3>\n

Original Data<\/h3>\n

I\u2019m making the original data available as an Excel file download\u00a0<\/span>here<\/a>.<\/p>\n

<\/h3>\n

Node Numbers<\/h3>\n

Why Were the Node Numbers Low?<\/h4>\n

In the main graph in the article, you\u2019ll see that the Node numbers were lower than both of the Laser Eggs. The Node I used in the test was about a year old (although the Laser Eggs weren\u2019t new either). One problem with older particle counters is that dust accumulates inside the machine and restricts the air flow. The guy behind AQIcn.org\u00a0<\/span>tested an old Dylos<\/a>\u00a0<\/span>and found it was undercounting when concentrations were bad. Then he cleaned out the dust inside with compressed air and found it got up to higher numbers.<\/p>\n

 <\/p>\n

I suspect the same thing was happening with the Node in our tests. That can be a particular problem when the particle counter is subjected to really high levels of particulate, like in our cigarette tests.<\/p>","protected":false},"excerpt":{"rendered":"

Tech companies love to talk about how automation, internet of things, and the connected house are going to make the machines we use every day more convenient. But does it work? Anyone who\u2019s used Apple\u2019s Siri or \u201ctalk to text\u201d feature know that the promises of technology sometimes fall short. … Read more<\/a><\/p>\n","protected":false},"author":4580,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-479","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/posts\/479","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/users\/4580"}],"replies":[{"embeddable":true,"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/comments?post=479"}],"version-history":[{"count":1,"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/posts\/479\/revisions"}],"predecessor-version":[{"id":480,"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/posts\/479\/revisions\/480"}],"wp:attachment":[{"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/media?parent=479"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/categories?post=479"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/smartairfilters.com\/mn\/en\/wp-json\/wp\/v2\/tags?post=479"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}