MH-Z19 offset and scale differences!?

[batal131]

When you reboot, could you test with the latest source to see if the problems with the Generic HTTP Advanced are now fixed?

Ok, I'll try to update to latest version.

If you do the scatter plot, then you can see how well they correlate. And even 100 ppm off is not bad, as long as the average offset is close to 0. Some sensors may react slower, or faster to changes due to internal filtering.
But that also means they will show a shift in time on rise and fall of the curve. However the rise of CO2 concentration may still be more steep than the fall of the concentration.
For example when cooking on gas, the CO2 levels increase really fast, but they take more time to go back to lower levels, with people in the same room.

It is quite fascinating to look into these figures

Currently MH-Z19B without ABC is very good correlated with S8 (with factory calibraion).
And yes, we have gas oven, so sometimes I have >1500ppm (and that's good for testing!)

Both MH-Z19Bs are reporting raw values, not sure if I need to change theirs filters.

[TD-er]

[...]
Both MH-Z19Bs are reporting raw values, not sure if I need to change theirs filters.

The filters I created are only making it less responsive.
And the option "Use unstable readings" (or how it is called) does not have effect on the B version. Only on the A version.
It should make the A and B version behave the same. (based on what I think the B version does internal)

[batal131]

When you reboot, could you test with the latest source to see if the problems with the Generic HTTP Advanced are now fixed?

Updated all 3 boards to latest sources (manually compiled) - still has problems with one board (reboots every 10-15 minutes).

All boards identical (wemos mini 3.0.0). Bought together.

Currently (with HTTP Advanced) 2 of 3 boards works ok (no reboots). One reboots every 10 minutes

With Generic HTTP no problems.

Logs are empty (with level 4).

[batal131]

Implemented scatter

ppm reported every 1 minute. For graph grouped by 5 minutes. Data for last day (after 5 days of running)
And basic chart (same data)

average difference for MH-Z19B without ABC is only 41 ppm! For ABC version is 95 ppm (and its increasing each day, damn 1 day calibration)

[TD-er]

That looks quite nice, the scatter plot.
So if you're running for a while, the version with ABC should show some drift and thus a wider band?
Also interesting to "swap" the data by placing other sensors on the X-axis.

[batal131]

That looks quite nice, the scatter plot.
So if you're running for a while, the version with ABC should show some drift and thus a wider band?
Also interesting to "swap" the data by placing other sensors on the X-axis.

Yes, I'll create different graphs after few weeks of testing

BTW, have you checked latest datasheet for MH-Z19B? I've found only Chinese version
http://style.winsensor.com/pro_pdf/MH-Z19B.pdf

[batal131]

Small update.

Room wasn't ventilated properly for 26 hours (it was just before previous calibration). And now MH-Z19B (ABC) calibrated. From +100ppm (comparing to S8) to -100ppm...
Lowest ppm during last 24h was 600ppm. So MH-Z19B now thinks that this 600ppm is 400ppm... Terrible behavior.

[TD-er]

[...]
BTW, have you checked latest datasheet for MH-Z19B? I've found only Chinese version
http://style.winsensor.com/pro_pdf/MH-Z19B.pdf

This one is more readable http://www.winsen-sensor.com/d/files/in ... ver1_0.pdf

[batal131]

This one is more readable http://www.winsen-sensor.com/d/files/in ... ver1_0.pdf

Yep, but mine is newer (1.3 vs 1.0) But I could not find any reasonable difference. Need to translate it somehow.

[batal131]

I've finished with my tests (MH-Z19B vs SenseAir S8).

So, finally MH-Z19B is very good with ABC turned OFF (and properly calibrated, of course).
At the same time MH-Z19B very bad if you room not ventilated every day.

Here is graph of two MH-Z19B (both with ABC turned OFF!) and one S8. Average difference (comparing to S8) is 1ppm and 10ppm.