My Mi air purifier 2 was constantly stuck on max in auto mode, and the pm2.5 reading was always 600. So I inspected the sensor and it seems like the little infrared light diode is dead. Whiile I was looking for the replacement part, I saw a laser sensor that claims to be better than the original Mi infrared sensor and it slots right into the Mi air purifier 2.
The thing is, I googled that company and there was an article from 2014 that claimed a product they put out was a scam, because the chip in one of their pm2.5 sensors was using a Sharp chip that wasn't capable of measuring particles as tiny as pm2.5. See below:
Measuring PM2.5 for 200rmb: the SamoAir Review - Chengdu Living
I tried digging for more info on their G7 sensor but I can't seem to find any information regarding which chip it uses, so right now I'm stuck because it's pretty much the only ready made option available.
This is what I'm interested in buying:
If you have any insight, please do let me know, it would be greatly appreciated! Thanks, mate.
The data sheet for that thing is contains no sensitivity specs and it's described as a "dust sensor for air conditioners" which doesn't inspire confidence If it's just to get the thing working again, who cares how accurate it is? It's not like the original sensor is a high precision piece of equipment.
So, is the problem that that the Mi is stuck on max all the time and is unusably loud because the sensor is busted? If that's the case, then why don't you go into the Mi Home app and force it to the Favourite setting, and manually set that (long press the Favourite icon) to a more bearable speed?
I manually set the speed of these things anyway, never use Auto. That's the sole function that makes this purifier anything other than a minimalist looking house decoration. In fact, I am surprised to even hear that Auto boosts the fan speed, it's never done that under normal operation for me.
It seems like the company has another name for the international market called Plantower. The Samoair G7 is Plantower pms7009, and there seems to be a bit more information on the internet. I'm digging through it right now, will report back if I can interpret the data at all.
Not sure how reputable this website is though.
The Plantower PMS5003 and PMS7003 Air Quality Sensor experiment
I went ahead and bought it on Taobao for 165, will report back when I receive it (it should be the end of the month because of Chinese New Year). Apparently it's the same sensor as the one in the Middle purifier 2s and Pro, so at least it's better than the original one.
According to a review, the mi air purifier 2 will only stay on max for 3 hours at a time before activating the auto mode. So it makes sense to get the sensor working. Xiaomi has also been accused of lowering the pm2.5 reading to give an impression that the air purifier is working. It will be fun to see if using a third party sensor will stop that behavior.
I'm convinced that Auto mode is useless, it runs at minimum speed which results in almost no filtration of the room. At lower speeds, the Xiaomi might also just create a smaller bubble of cleaner, recirculating air, around itself.
If you're concerned about air quality, the most useful measure is PM2.5, which is the particle size that causes long term health issues. Larger sizes might cause allergies or irritation, but are not linked to things like increased risk of cardiovascular disease . To measure PM2.5, you probably want a different sensor. I've looked at dual particle size counts on another meter (same on in the last link of yours), and they are only loosely correlated.
Consider one that's known to be capable of smaller particle sizes, and also able to be positioned further away from the purifier.
If it's RMB30, it's so cheap that you should just get one anyway, but I wouldn't rely on it any more than I rely on the existing Xiaomi meter. I'd definitely be interested to read your findings after you install it.
I have a pm2.5 external sensor (need to check the model/brand), and the Xiaomi on auto does decrease the levels of particles noticeably within 20-30mins. The Xiaomi stands in a corner of the room, and the sensor in the opposite, next to my computer desk. The measures on the Mi's sensor are not too far off from the external one (but they usually show as slightly lower than what the external sensor says).
So far I haven't had trouble...I'll run some more checks on a polluted day.
EDIT: The sensor is the PMS 5003 from Plantower.
Last edited by timonoj; 06-02-2018 at 09:31 AM.