Strange multiple DS18B20 behaviour (same bus)

[defender52]

Hello everyone,

Have you ever met such a behavior - unstable readings from 2 ds18b20 connected to the same 1-wire bus (1 common pull-up resistor 4.7k). The third one works ok.
All the sensors are placed into concrete ("warm" floors) so in fact the temperature can't change so fast as graphs show:

graphs.JPG (52.75 KiB) Viewed 10156 times

sensors settings.JPG (67.05 KiB) Viewed 10156 times

Devise resolution settings are set the same for all 3 sensors (12 bit).
GIT version: mega-20190108
Any idea?

[grovkillen]

I'd say, update to latest version and test. If the units still display the same behavior I would look into how those units are wired, star or one wire, stubs or right to the stem wire etc.

[defender52]

Thanks, I'll try to update.
Connection scheme is a star.
I suppose that 2 sensors don't work at resolution 12 bit for some reason. It looks like 9 bit.

[grovkillen]

Yes the jumps look 9-bit:ish.

[TD-er]

The green line is indeed hopping between 0.5 degree values, so that looks like a resolution issue.
If you only have one connected, is its reading more stable?

And indeed, what GrovKillen suggests, try the latest build (yesterday's build is also fine), since that has some fixes in it for Dallas sensors.

[defender52]

Thanks for replies,

I've updated it to the last version - no use.
Tried just to disable 2 sensors - no effect.
I'll try to disable it physically, but later (it is war away from me).

I wonder, if different sensors addressing corresponds somehow with this issue?
Please look at the addresses:
The one working ok has XX-XX-XX-XX-XX-XX-X-XX
And the other 2 have XX-XX-X-XX-XX-X-X-XX

What do you think?

[TD-er]

Can you make an issue for this (suspect missing leading zero) on GitHub?
Then Uzi18 will very likely have a look at it.

[jimmys01]

The green line seems to be the problematic one. At 20:00 on the left of the screen you can see a couple of readings of about 13,25c . This coresponds to 10bit or moe resolution. In the right of the diagrams it jumps from 13 to 12,5 and 13,5 that coresponds to 9 bit resolution...

I would check that the sensors are not wet, are not counterfit (dont know how to check that).
What is your data acquisition Interval?
Do your sensor addresses start with 28-xx.....?