AliBottom #3: Comparison of three CO2 meters with AliExpress

Apparently, one of them does not have a CO2 sensor. But there is good news – a couple of years ago, the cheapest home CO2 monitoring device cost at least $ 80, and now a fairly high-quality model can be bought for half the price.

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What are they needed for

Excess levels of carbon dioxide adversely affect performance and well-being. GOST 30494-2011 says that indoor air with a CO2 content of 1000 to 1400 ppm is considered to be of low quality, while its normal level outside in the city is 450 ppm. In my personal experience, in all cases where the concentration exceeds 1500 ppm, ventilation is clearly required.

If you are wondering what levels of CO2 can be measured in different situations, check out this article of mine.

What did you buy

This time I bought two inexpensive devices – one for about 900 ***, and the second for 2100 ***.

A cheap one comes across on AliExpress under different brands, but more often as noname. On the case there is a mention of the model – M8.

The type of installed CO2 sensor is not specified, there is only a mention of the measurement range from 400 to 5000 ppm and the capacity of the built-in battery – 1200 mAh.

The second device was sold under the Winsen brand. Most likely this is his real manufacturer. The product card mentioned the model WS1308B, but there is no mention of the brand or model on the device itself and the box. On Ali, it can be found under a bunch of different brands and as an unnamed one.

The device has an adjustable screen brightness, and it looks very nice. The specifications indicate that an infrared CO2 sensor (NDIR) is installed inside, as well as a 1600 mAh battery. It is powered by a 5-volt charger, which is not included in the kit.

Examination

I compared the readings with the HT-501 model, which has a Swedish CO2 sensor from SensAir. Her review can be found here. This model was in the hands of many testers, where it was compared with professional devices, and there were no complaints about it.

The test tactic was as follows: I placed the devices in the same conditions, waited 20 minutes to exclude the unplanned influence of something (you can accidentally breathe on some while you are carrying it) and compare the readings.

So let’s go. First I will put a photo with testimony, then comments on it. I apologize in advance for the quality of some of the pictures, they were screenshotted by me from the video footage.

Morning in the bedroom, where the window was slightly ajar. HT-501 and WS1308B are in solidarity in the testimony, and the M8 does not “notice” anything bad.

Another room. The air here is also not very fresh. Here’s the story with the M8 – as soon as I took it in my hands to move it to a new place, its readings instantly jumped to 1500 ppm and after 20 minutes in peace and quiet dropped only to ~1400. One gets the impression that he simply reacted to the movement and then began to show something from the bulldozer.

On the balcony, the readings of the HT-501 and WS1308B began to diverge steadily by about 90 ppm. And the M8 behaved and was completely curious – he felt fresh air and immediately dropped the readings to the minimum 440 ppm (I didn’t see him less), but after 20 minutes he suddenly lifted them up to 1200.

And once again the room, where the air was slightly freshened with the ajar balcony. HT-501 and WS1308B kept their divergence. M8 somehow “guessed” that he was removed from the balcony, and gave another “guess”.

And a couple more pics:

I state that the HT-501 and WS1308B differ slightly in their testimony, but on the whole they follow the same pattern. But the M8 is constantly in guessing mode. It’s time to see what’s inside.

What is inside

To be honest, I could not carefully open the M8 case. I thought that it was on latches, but in fact it turned out to be on the screws that were under the glued plastic screen cover. And since the device did not fulfill its main function, only fooling me, I decided to make a small comic show out of its opening, which can be viewed in the video review starting at 8:36.

Of course, there were people who see war in everything, and they have already explained to me where to go and what to do. But, if you follow their logic, it is necessary to urgently close all shooting galleries in the country and remove half of children’s toys for boys from sale. In general, friends, let’s not see any hints in every joke or associate them with something that has nothing to do with the joke or the very intention of the author.

Now to the point. Inside the device, an unnamed sensor was found (it was slightly wrinkled during the “opening”).

Identification attempts turned into a little detective story. Based on appearance alone, I found an electrochemical CO2 sensor with model number MG-812. It is produced by the aforementioned company Winsen. I also found a pdf for it. In accordance with it, the sensor has a linear dependence of the output voltage on CO2, and the measurement range is not limited to a value of 10,000 ppm.

But here is the nuance – this sensor costs at least 520 ***, while the cost of the device with it starts from 800 ***. In addition to the sensor, the surf has a large LCD screen, a battery, and electronics. Is it really all together with the body costs 280 ***?

Further searches led to the MP503 universal air quality sensor in the same 8 mm housing and also without markings. Price tags for it start at 82 ***. Compare appearance:

Judging by the description, this sensor reacts anyhow and to anything. Sellers write that it allegedly detects ammonia, smoke, aromatic hydrocarbons, alcohols, benzene, etc. Apparently, the cunning Chinese decided to tie his readings to the level of CO2. The logic is that if the air is fresh, then the sensor should not register anything. And if the sensor reacts to something, then it has not been ventilated for a long time. In fact, if we discard the issue of accuracy of readings, in half of the cases M8 does not even approximately “guess” the state of the surrounding air and CO2 levels.

Despite all the coincidences, I will not unequivocally state that the MP503 is installed in the M8 instead of the MG-812, but it looks very similar.

Now a few words about Winsen WS1308B. There were also problems with opening it. Most likely, it is also on hidden screws, because I could not open the case slot in the corners even with a metal tool. I believe that the familiar MH-Z19B infrared sensor is installed inside, since the manufacturer mentions NDIR in the specifications.

Results

First the bad news, then the good. A cheap monitor with model number M8 turned out to be non-working. During the two weeks of observations, he only showed an adequate (not accurate) level of CO2 a few times. Everything else is more like trying to guess. At least a third of the time, he displayed generally incorrect data (he overestimated it at times, or underestimated it at times). Whether the sensor is real or not is an open question. If it’s genuine, then anything related to electrochemical MG-812 should be avoided. If not real, then only devices with a price tag below $ 20-25 should be avoided.

Another disadvantage of the device is a loud alarm about exceeding the level of 1600 ppm. Not disabled. After he squeaked angrily at the whole apartment three times in one minute at 4 o’clock in the morning, I no longer left him on.

The good news is that if a couple of years ago a working device with a CO2 sensor cost at least $ 80, now you can definitely buy it for $ 35. For example, the same Winsen WS1308B from this review.

And if you need a device with a PC connection and data accumulation, then I see the HT-501 as a very reasonable purchase.

Something like this.

PS Earlier in the same series, I had a post about trash chargers with Ali and cheap lamps. And if in general you are interested in the continuation of this topic, you can subscribe to my Telegram or Zen (links in the signature).

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