is there any need to use mhzabcdisable

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GravityRZ
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is there any need to use mhzabcdisable

#1 Post by GravityRZ » 05 Feb 2021, 21:16

the current P049 plugin for the MH-Z19 has a setting to disable ABC calibration.

does this disable setting stick with reboots and power off/on?

the reason i am asking is i see that there is an mhzabcdisable command but do not know if this should be used

All the info i read dates back to 2017 so it looks like the command is obsolete and replaced by the gui setting but i am not sure

thanks.

current readings from the MH-Z19 are very promising. nice sensor, only temperature does not seem accurate but doe not need that one

TD-er
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Re: is there any need to use mhzabcdisable

#2 Post by TD-er » 05 Feb 2021, 22:30

There are very good reasons why one may want to disable ABC on a MH-Z19 CO2 sensor.
No, the setting will not be written to persistent storage of the sensor, but the ESPEasy plugin will monitor the sensor and every time the sensor reboots (it may also crash on its own every now and then) it sets the ABC disable again.

Reason to have it ENABLED:
The sensor ages, which causes the sensor to become less sensitive over time.
This will result in a drop in reported CO2 concentration and since the firmware also limits the CO2 value to +/- 400 ppm (lower values will be truncated) and thus result in lots of charts showing a flat curve at around +/- 400 ppm for a long time.

Reason to have it DISABLED:
The MH-Z19 sensor uses 24h as ABC interval, which is really not usable in a lot of situations.
For example the next few days here in the Netherlands we will expect really cold wind from the east, so you can be sure the house will not be as much ventilated as it should be.
If the ABC would remain enabled, you would see lower and lower reported CO2 values every day as the lowest recorded CO2 value during 24h will be set as the new 400 ppm point.
So the air quality can get really bad and the sensor will report it to be just fine.

GravityRZ
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Re: is there any need to use mhzabcdisable

#3 Post by GravityRZ » 05 Feb 2021, 22:40

thanks. good info.

this evening i will a window open to see what the max amount of co2 will be.
indeed tomorrow there will be snow so opening windows then is not an option.

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Re: is there any need to use mhzabcdisable

#4 Post by TD-er » 05 Feb 2021, 22:45

Keep in mind that "outside CO2" is not always "400ppm" (or whatever level we're at now on a global scale)
Plants no longer take in CO2 when the sun is set. As a matter of fact they start to exhale CO2 during the night.
So when there is almost no wind, the CO2 sensor in my car parked outside can go as high as 700+ ppm during the night.

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