MH-Z19B Range

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stazo
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MH-Z19B Range

#1 Post by stazo » 25 Nov 2019, 21:58

Hello. I am using the MH-Z19B sensor with ESPeasy. I have a measuring range of 400-5000 PPM. Can I change the range to 400-2000 PPM in the ESPeasy interface? I connect via HW Serial0 GPIO-3 (D9) TX / GPIO-1 (D10) RX. Thanks

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Re: MH-Z19B Range

#2 Post by TD-er » 25 Nov 2019, 22:06

I have disabled the commands to do so, since there is a good chance you can destroy your sensor, or at the very least end up with a sensor without proper calibration.
If you like, you can enable the commands in the source code of the plugin and build it yourself.

stazo
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Re: MH-Z19B Range

#3 Post by stazo » 26 Nov 2019, 07:22

TD-er, what is the measuring range of your MH-Z19 ?? (sorry for my english using google translator)

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Re: MH-Z19B Range

#4 Post by TD-er » 26 Nov 2019, 08:48

I think it is 0 .. 2000.
That's a value we hardly every reach in our home.

What is your language? I can also read Dutch if you find it easier to write.

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Re: MH-Z19B Range

#5 Post by stazo » 26 Nov 2019, 09:02

My native language is Ukrainian. Your measurement range 0-2000 was set by default? How do you connect your sensor? PWM or Serial Port?

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Re: MH-Z19B Range

#6 Post by TD-er » 26 Nov 2019, 09:50

On the 2 (working) MH-Z19 sensors I have, I have not changed the range.
I do use the ESPEasy plugin via serial, not via PWM.

On the defective MH-Z19 I have, I did change it and it does seem to be changing the range.
However, the calibration may then be invalid if you change the range.

stazo
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Re: MH-Z19B Range

#7 Post by stazo » 26 Nov 2019, 11:21

I installed a sensor in the bedroom. I have a reading of 1700-2500 PPM. Is this the norm for the range 400-5000 ?? I read that the readings should be 600-1000, but this is probably for the range of 400-2000 PPM

Where did you install your sensors and what are their readings?

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Re: MH-Z19B Range

#8 Post by TD-er » 26 Nov 2019, 12:05

Whether it is a plausible reading does depend on where you place the sensor.
Things to keep in mind:
- Don't allow direct IR light to enter, so no sunlight, but also not place it directly above a heater.
- Don't place it near your head.
- Burning something will produce CO2 (cooking on gas, burning a candle, etc)

One is hanging on a wall in the living room and one is in my daughter's bedroom on the opposite wall as where she sleeps.

When you exhale, the CO2 concentration of the air leaving your mouth is about 40'000 ppm (!!!).
So this has to mix with the rest of the air in the room before you measure it or else you get useless readings. (well depending on what you want to measure ofcourse ;) )

If your lowest reading is 1700, then your base calibration is off by a huge factor.
Try enabling the ABC calibration in the plugin and leave the sensor for a few days in a well ventilated room, or at least in a room where no people or animals stay for long.

Typical lowest CO2 value should be around 400 ppm, but in some areas (e.g. a city or industrial area), the CO2 concentrations may be higher.
For example, when I drove through Germany, the CO2 values measured on the outside of my car were sometimes over 1000 ppm in the outside air.

Having a lot of plants also may have negative impact on CO2 levels at night, but during the day they should help to reduce the CO2 levels in the room.

stazo
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Re: MH-Z19B Range

#9 Post by stazo » 26 Nov 2019, 13:04

I put the sensor out the window, after 20 minutes it showed 400 PPM.
Autocalibration did not include. When I breathe on it for a long time, it shows 5000 PPM.
How do I know which readings are normal in this range and which are critical?
The instructions say that:
400-600 PPM - Clean Air
600-800 PPM - Good
800-1000 PPM - Normal
1000-1200 PPM - Not Good
1200-1500 PPM - Bad
1500-2000 PPM - Critical
Where can I find these values ​​for the 400-5000 PPM range?

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Re: MH-Z19B Range

#10 Post by TD-er » 26 Nov 2019, 16:57

stazo wrote:
26 Nov 2019, 13:04
[...]
Where can I find these values ​​for the 400-5000 PPM range?
That should be the same list.
The only thing changed between 2000ppm and 5000ppm range is the range and thus also the resolution.
But it seems like you may have a sensor that is re-programmed to be the wrong range maybe?
My daughter's room is about 3x3x2.5 meter and with closed door and 2 persons sleeping in there (parent + girl of 5 yrs old) the CO2 level rises 600 ppm in 2 hours.

What you should do is chart the values.
In a closed room, with a person in the room, the CO2 level will rise quite fast (+/- 200 - 300 ppm per hour), but still you should see a smooth curve if the sample interval is in minutes. (no jumps)
When you leave the room and shut the door immediately (CO2 can get out quite fast), you should see a slow decline.
If the decline doesn't show jumps, then the sensor is operating as it should.
The calibration uses >2 points, meaning that if one of them is totally off, you would see jumps in values.

As a rule of thumb, the 700 - 1000 ppm range is when you start to "smell" the need of fresh air.
But that's also rather subjective, since you can also have 700 ppm outside and still the feeling you get a lot of fresh air.

Our living room is rather large (3 rooms without doors) and is 3x3 + 5x5 + 4x3.
With 2 adults in there for the entire evening, the CO2 level does rise to 1200 ppm (more if we cook using gas)
It then takes almost the entire night to get back to 400 ppm.
If you see the charts clipping at the bottom, you know the 400 ppm value is set incorrect (can be set using ABC)

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Re: MH-Z19B Range

#11 Post by stazo » 28 Nov 2019, 07:04

Thank you for your responses.
I'll try to turn on auto-calibration and move the sensor out of the window for a couple of days.
I'll see what changes. Then I will unsubscribe

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Re: MH-Z19B Range

#12 Post by TD-er » 28 Nov 2019, 14:09

I don't think "hanging out the window" is helpful here.
A well ventilated room is best.
The thing is, temperature and humidity have influence on the CO2 measurement and also you really want to avoid direct sunlight on the sensor.
I do have the impression the MH-Z19 does keep track of the temperature for calibration (also for the base calibration), so if it has been run in 5 degree outside, there is no guarantee it will then run well at room temperature.

It is best just to have the ABC enabled in ESPeasy and then let it run for a few days, preferably in a room that's not used a lot.
Also do not power the sensor down for at least a few days, as it does track the "on time" to decide when 24h have passed to update the automatic base calibration (ABC)

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